s.e. hosseini/future energy may 2022| volume 01 | issue 01 | pages 01-04 1 news & views the us hydrogen fuel industry today and future seyed ehsan hosseini in december 2021, the us department of energy (doe) unveiled the office of clean energy demonstrations with $21.5bn in federal funding to deploy the advanced green technologies. the most significant portion of the budget, $9.5bn, has been dedicated to renewable hydrogen to commercialize innovative technologies and establish four regional hubs and a recycling and manufacturing program. green hydrogen is already the focus of the doe's energy initiatives, which aims to mitigate the cost of renewable hydrogen production by 80% over the next decade. he us government has dedicated $9.5bn to develop green hydrogen as a part of the $1.2 trillion bipartisan infrastructure bill. the bill includes $8bn budget for the large-scale regional renewable hubs; at least one hub would employ fossil fuels, one would apply renewable energy, and one would use nuclear power. the doe offered $1bn of this funding for research and development (r&d) in green hydrogen electrolysis, and the remaining $500m was allocated to the manufacturing and recycling of hydrogen. the bill requests the federal government to deploy the first-ever national hydrogen roadmap and strategy for the us. it is expected that the bill will help doe to play a crucial role in the climate agenda by obtaining 100% carbon pollution-free electrical power generation by 2035 and net-zero carbon emissions by 2050 [1]. additional financial support for green hydrogen, including a $1.85 trillion budget, is being negotiated by the democratic-controlled us congress to enact the bill. the bill would include $3.5bn in grants for domestic manufacturing of hydrogen fuel cell and battery electric vehicles, along with $200m to support hydrogen fueling equipment. but the considerable part of the hydrogen budget would dedicate to the tax credit for hydrogen production technologies that are significantly cleaner than the traditional steam methane reforming (smr) method. analyses have indicated that tax credit could make renewable-based hydrogen production cost-competitive or cheaper than smrbased hydrogen production techniques in certain us markets [2]. the renewable hydrogen market has an incredible potential to grow substantially across the next two decades. the zero-carbon emission hydrogen utilization in transportation, maritime and heavy industry will speed up the decarbonization targets in the us. the total hydrogen production addressable market has the potential to pass $1 trillion by 2050 compared to around $125 billion today. nevertheless, today green hydrogen production is extremely more expensive than the grey hydrogen produced from unabated non-renewables, which account for 9599% of the world’s hydrogen demand. the cost of green hydrogen is $3-8/kg, while the grey hydrogen cost is $0.501.70/kg. currently, just 200 mw of electrolyzers are developed globally, and not all of them are using green energy. the world’s largest operating renewable hydrogen project today, in quebec, canada, is just 20mw. over the past 20 years, the feed-in tariffs and national tenders have dramatically mitigated the cost of wind and solar power generation, and it is believed that renewable hydrogen could trace a similar path. the consensus view is that the us government should subsidize green hydrogen in short to medium term to reduce its overall cost and make it affordable to achieve a sustainable market for green hydrogen [3]. in this context, oklahoma has formed a partnership with louisiana and arkansas to accelerate the hydrogen economy and create a regional hydrogen hub to consider tax credits for individuals and businesses producing and utilizing green hydrogen fuel. these states are situated to illustrate the entire value chain of hydrogen fuel and are situated to tackle the hard-to-decarbonize sectors such as transportation, industrial sectors and manufacturing. to develop hydrogen utilization in heavy-duty transportation, the us senate works on “hydrogen for trucks act” and “hydrogen for ports act” proposals to incentivize heavy-duty vehicle owners to buy hydrogenfuelled trucks and deploy the use of hydrogen-related technologies in shipping applications and ports. approximately 25% of all transportation greenhouse gases are emitted by heavy-duty vehicles while accounting for only a small portion of vehicles on the road. however, hydrogen fuel cell-powered vehicles release no tailpipe emissions, making cleaner transportation without sacrificing range or reliability. the “hydrogen for trucks act” program would enable fleet owners to switch to zero-emission hydrogen fuel cell vehicles, and the “hydrogen for ports act” program would develop hydrogen-fuelled equipment at ports and in shipping applications in a single location that can share hydrogen infrastructure [4]. references [1] home ns energy n.d. https://www.nsenergybusiness.c om/ (accessed march 17, 2022). [2] commodity & energy price benchmarks | argus media n.d. https://www.argusmedia.com/e n (accessed march 17, 2022). [3] recharge | latest renewable energy news n.d. https://www.rechargenews.com / (accessed march 18, 2022). [4] florida daily | news from around the state n.d. https://www.floridadaily.com/ (accessed march 18, 2022). open access journal https://doi.org/10.55670/fpll.fuen.1.1.7 may 2022| volume 01 | issue 01 | pages 01 seyed ehsan hosseini department of mechanical engineering, arkansas tech university, 1811 n boulder ave, russellville, ar, 72801, usa seyed.ehsan.hosseini@gmail.com future energy journal homepage: https://fupubco.com/fuen this article is an open-access article distributed under the terms and conditions of the creative commons attribution (cc by) license (https://creativecommons.org/licenses/by/4.0/). https://orcid.org/0000-0002-0907-9427 https://doi.org/10.55670/fpll.fuen.1.1.7 mailto:seyed.ehsan.hosseini@gmail.com https://fupubco.com/fuen m. safarishaal /future energy february 2024| volume 03 | issue 01| pages 13-17 13 article comparative analysis of power consumption time series in deprived and developed regions of iran masoud safarishaal* university of oklahoma norman, usa a r t i c l e i n f o article history: received 22 march 2023 received in revised form 20 april 2023 accepted 27 april 2023 keywords: time series, load forecasting, power distribution *corresponding author email address: masoud.safari@ou.edu doi: 10.55670/fpll.fuen.3.1.2 a b s t r a c t this paper presents a comparative analysis of power consumption time series at 12 o'clock every day between 2020 and 2022 for one distribution network in sistan and one in tehran. the aim of this study is to compare the development and climate differences between these regions, as well as the impact of social, industrial, and environmental factors. by comparing a deprived area with an area in the capital, we aim to identify potential disparities in power consumption and identify potential areas for improvement. we employed the crp tool software and toolkit for time series analysis and used various methods to compare and predict the predictability of each time series. our findings suggest significant differences in power consumption between the two regions, which could be attributed to socio-economic and environmental factors. overall, this study sheds light on the potential impact of regional differences on power consumption and highlights the need for further research in this area. 1. introduction time series analysis is a statistical technique that involves analyzing and modeling patterns in time-varying data [1,2]. it is used in many fields, including economics, finance, engineering, and the natural sciences [3-4]. one of the main goals of time series analysis is to understand the underlying processes that generate the data, which can then be used to make forecasts and predictions about future values [5]. for example, consider a company that wants to forecast its monthly sales for the next year. by analyzing historical sales data, they can identify trends and seasonal patterns, such as increased sales during the holiday season. using time series analysis techniques, they can build models that capture these patterns and use them to make accurate predictions about future sales. overall, time series analysis is a powerful tool for understanding and predicting patterns in timevarying data. by using appropriate techniques and models, analysts can make accurate forecasts and gain insights into the underlying processes that generate the data [6-10]. in this study, we compare and analyze two-time series related to power consumption at 12 o'clock every day in the period of 2012 to 2014 for two distribution networks in sistan and one in tehran. the goal of our analysis is to explore the differences in power consumption patterns between these two regions and to investigate the impact of various factors such as climate, industrial activity, and socio-economic conditions on power consumption. to prepare the data for analysis, we first normalized the time series to ensure that they conform to the assumptions of the time series model. we also de-trended the data to remove the effects of long-term trends and focus on the underlying patterns in the time series. our analysis reveals interesting differences between the power consumption patterns in sistan and tehran. for example, we observe that the upward trend in power consumption is more pronounced in tehran, possibly due to the faster rate of industrial development and population growth in the region. we also find that the impact of weather conditions on power consumption is more significant in sistan, where most of the power consumption is due to household appliances (figure 1 and figure 2). overall, our study sheds light on the complex interplay of various factors that influence power consumption patterns in different regions of iran. the insights gained from this study can inform policy and decision-making related to energy consumption and sustainable development in the country. 2. histogram diagram a comparison of the histogram diagrams in figures 3(a) and 3(b) reveals that the power consumption in the sistan network is higher than that of the region of tehran under future energy open access journal https://doi.org/10.55670/fpll.fuen.3.1.2 february 2024| volume 03 | issue 01 | pages 13-17 journal homepage: https://fupubco.com/fuen issn 2832-0328 mailto:masoud.safari@ou.edu https://doi.org/10.55670/fpll.fuen.3.1.2 https://fupubco.com/fuen m. safarishaal /future energy february 2024| volume 03 | issue 01| pages 13-17 14 consideration. however, when the de-trended data in figure 3(c) is compared, it becomes apparent that the load fluctuations are minimal throughout the year. this aspect is highly favorable for the operation of the system, and it makes the manufacturing sector more inclined to invest in such networks. figure 1. load of sistan and tehran figure 2. graph related to the de-trended time series of sistan power consumption and tehran power consumption 3. false nearest neighbor figure 4 displays the false nearest neighbor (fnn) plot for both time series. this plot is generated using the fnn (data) command in matlab software and is commonly used to estimate the optimal embedding dimension for a time series. the fnn plot reveals that the sistan time series has a dimension of 8, while the tehran time series has a dimension of 7. this suggests that the sistan time series exhibits less predictability and is more challenging to forecast accurately. 4. mutual information (mi) figure 5 displays the result of applying the mi (data) command, which utilizes the mutual information method to estimate the delay in the time series. the delay is found to be 6 for sistan and 5 for tehran, as determined by identifying the first minimum of the chart. additionally, the false nearest neighbor (fnn) graph in figure 4 shows that the sistan time series has a dimension of 8 while the tehran time series has a dimension of 7. these findings indicate that the sistan network is less predictable and more difficult to forecast than the tehran network. the fuzzy body diagram demonstrates that the behavior of both time series is chaotic, which suggests that they have limited predictability. (a) (b) (c) figure 3. hist diagram: (a) tehran (b) sistan (c) detrend tehran and sistan 5. cross recurrent plot figure 6 illustrates the cross-recurrence plot for both power consumption time series, revealing the chaotic nature of both systems. however, the plot for the tehran network shows a higher number of parallel lines. as confirmed by previous methods, this indicates that the tehran time series is more predictable than the sistan time series. notably, the large squares in the plot for the sistan time series reveal its seasonal behavior, which was previously observed in the time series diagram. 6. xcf diagram figure 7 displays the cross-correlation function (xcf) diagram for both time series. the xcf command is used to measure the correlation between the data sets. the diagram shows that the correlation between the data in tehran is very high, indicating that the data is closely related to each other. this high level of correlation makes it easier to predict the behavior of the data. m. safarishaal /future energy february 2024| volume 03 | issue 01| pages 13-17 15 figure 4. false nearest neighbor (fnn) (a) (b) figure 5. mi. (a) tehran (b) sistan 7. power spectrum density the power spectrum density diagrams in figure 8 were generated using the psd (data) command. these diagrams show the distribution of power across different frequencies in the time series data. specifically, the density spectral integral plots the average signal strength over a range of frequencies. this analysis can provide insights into the dominant frequencies present in the time series and can be useful in identifying periodic patterns or trends. (a) (b) figure 6. diagram of cross recurrent plot (a) tehran (b) sistan figure 9 shows the phase space diagram for both time series in a 3d display. a phase space diagram is a useful tool for visualizing the behavior of a dynamical system in three dimensions. it plots the system's state variables against each other, with each axis representing a different variable. the resulting pattern of points can reveal the underlying structure of the system, such as periodicity, chaos, or other types of dynamics. in this case, the phase space diagram shows that both time series exhibit chaotic behavior, as evidenced by the irregular and unpredictable pattern of points in the 3d space. this confirms the findings from the other methods used in this study, which also indicated that the time series are difficult to predict due to their chaotic nature. overall, the phase space diagram provides additional insight into the underlying dynamics of the power consumption time series and reinforces the need for sophisticated forecasting methods that can account for the complex and unpredictable behavior of these systems. m. safarishaal /future energy february 2024| volume 03 | issue 01| pages 13-17 16 (a) figure 7. xcf diagram: (a) tehran (b) sistan (a) (b) (b) figure 8. psd diagram of two time series figure 9. phase body diagram for a) sistan and b) tehran time series m. safarishaal /future energy february 2024| volume 03 | issue 01| pages 13-17 17 8. conclusion in this study, we analyzed and compared two-time series related to power consumption at 12 o'clock every day in 2020 and 2022 for two distribution networks in sistan and one in tehran. our analysis revealed that the seasonal power consumption in sistan is significantly impacted by weather conditions, as most power consumption in sistan is due to household appliances. in contrast, power consumption in tehran is less dependent on weather conditions and is driven more by the city's industrial nature, which makes it more predictable. we also found that the upward trend in power consumption in tehran is primarily due to the city's faster development and population growth, whereas sistan, being a deprived area, has not experienced many changes in power consumption during the two years. finally, we observed that the difference in power consumption between seasons is more pronounced in sistan compared to tehran. overall, our findings suggest that regional disparities in power consumption are closely linked to socio-economic and environmental factors, and further research in this area is needed to inform future policies and initiatives aimed at promoting sustainable development in different regions of iran. ethical issue the author is aware of and complies with best practices in publication ethics, specifically concerning authorship (avoidance of guest authorship), dual submission, manipulation of figures, competing interests, and compliance with policies on research ethics. the author adheres to publication requirements that the submitted work is original and has not been published elsewhere in any language. data availability statement datasets analyzed during the current study are available and can be given following a reasonable request from the corresponding author. conflict of interest the author declares no potential conflict of interest. references [1] bunde, a. & piersol, a.g. (2003). random data: analysis and measurement procedures (3rd ed.). john wiley & sons. doi:10.1002/9781118032428 [2] hyndman, r. j., & athanasopoulos, g. (2018). forecasting: principles and practice (2nd ed.). otexts. isbn: 978-0987507112 [3] brockwell, p. j., & davis, r. a. (2016). introduction to time series and forecasting. springer. [4] galit shmueli and kenneth c. lichtendahl jr “practical time series forecasting with r: a hands-on guide [2nd edition] (practical analytics)” jul 19, 2016 [5] rami krispin “hands-on time series analysis with r: perform time series analysis and forecasting using r” may 31, 2019 [6] shumway, r. h., & stoffer, d. s. (2017). time series analysis and its applications: with r examples (4th ed.). springer. [7] hossain, m. s., pota, h. r., & ali, m. a. (2019). "a review of electricity load forecasting techniques." renewable and sustainable energy reviews, 103, 29-43. [8] raza, s. a., siddiqui, s. a., & ahmed, s. (2020). "forecasting daily peak electricity demand using artificial neural networks: a case study of pakistan." energy reports, 6, 346-352. [9] zhang, g., patuwo, b. e., & hu, m. y. (1998). "forecasting with artificial neural networks: the state of the art." international journal of forecasting, 14(1), 35-62. [10] hong, t., & fan, s. (2016). "short-term load forecasting using a hybrid model of wavelet transform, arima and support vector regression." applied energy, 178, 188198. this article is an open-access article distributed under the terms and conditions of the creative commons attribution (cc by) license (https://creativecommons.org/licenses/by/4.0/). jacob geels/future energy may 2022| volume 01 | issue 01 | pages 12-15 12 perspective electrical power consumption reduction in the bitcoin mining process using phase change material jacob geels department of mechanical engineering, arkansas tech university, 1811 n boulder ave, russellville, ar, 72801, usa a r t i c l e i n f o article history: received 26 february 2022 received in revised form 01 april 2022 accepted 06 april 2022 keywords: phase change materials, cryptocurrency, bitcoin latent heat capacity, sensible heat capacity corresponding author email address: jacobgeels808@gmail.com doi: 10.55670/fpll.fuen.1.1.10 a b s t r a c t in this paper, the idea of applying phase change materials (pcms) as a method of energy use reduction in bitcoin mining will be investigated. the possible applications discussed include the implementation of pcms in the mining equipment itself, the integration of pcms into the mining warehouse envelope, and the use of pcms in air conditioning systems. these applications aim to decrease energy requirements for warehouse climate control systems by decreasing their cooling load, and by increasing the efficiency of the miners by keeping them at a cooler operating temperature. this reduction in energy usage will help reduce bitcoin’s carbon footprint produced by fossil fuels electricity production. 1. introduction cryptocurrencies have been around for a little more than a decade and have gained enormous popularity over the last few years due to their decentralized nature and increasing value. with the prices of the most notable cryptocurrency, bitcoin, being over $57,000 per unit as of the writing of this paper, it is no wonder so many individuals and companies have taken up bitcoin mining [1]. bitcoin “mining” is the process of validating a user-to-user transaction on the bitcoin network, also known as the blockchain. there is a need to check the validity of each coin being exchanged since bitcoin is a digital currency, making it easy to counterfeit. known as double-spending, it is one of the digital currency’s biggest issues and is a security threat to the coin's value [2]. the validation is done by using computational power provided by “miners” or network users to verify the history of the bitcoin being used in the transaction [3]. each transaction or block is checked to ensure all bitcoins involved have a history within the blockchain and are valid. if a person tried to use a counterfeit coin in a transaction, it would not be verified, and the transaction would not go through. the blockchain is known as a proof of work mechanism [4]. whichever user verifies the transaction is then rewarded with a set amount of bitcoin for their efforts. that is where the “mining” comes in. the more computational power you have, the more likely you are to solve a block and get rewarded. these computations are usually done either by cpu or gpu, which draw power. an estimate of bitcoin’s network wide power usage can be seen in the bitcoin energy consumption index and is estimated to be around 199.41 twh annually. if bitcoin were a country, it would rank 23rd in the world in power usage. this much power usage makes an estimated carbon footprint of 94.72 mt of co2 per year, comparable to the country of thailand [5]. due to the daunting nature of bitcoin’s co2 emissions and the risk, it poses to the environment, much research is going into developing technologies that reduce bitcoin’s energy usage and, thereby, carbon footprint. one such technology is the implementation of pcms into the mining equipment itself, as well as the mining warehouse envelope. this new idea has the potential to reduce the temperature of the electronics and the buildings they are housed in, reducing energy usage needed to keep them cool so that they run at peak efficiency. applications of pcm’s in this field were examined for their feasibility. 2. energy usage of bitcoin mining the major issue with bitcoin mining, or the mining of any cryptocurrency for that matter, is the enormous amounts of energy required to run their networks. this is because bitcoin and most other cryptocurrencies are proof of work systems. this means that the network of users each simultaneously future energy open access journal https://doi.org/10.55670/fpll.fuen.1.1.10 may 2022| volume 01 | issue 01 | pages 12-15 journal homepage: https://fupubco.com/fuen issn 2832-0328 mailto:jacobgeels808@gmail.com https://doi.org/10.55670/fpll.fuen.1.1.10 https://fupubco.com/fuen jacob geels/future energy may 2022| volume 01 | issue 01 | pages 12-15 13 tries to solve “blocks”, or puzzles given to the users by the network to verify transactions. the process of verifying transactions must start with a proof of ownership. since bitcoin is a digital currency, it could be easily counterfeited, flooding the market with fake coins leading to inflation and the devaluation of the coin. this is avoided by the proof of work system. all users on the network agree on a set of rules that determine who owns what coins. if someone were to make a duplicate coin and try to use it in a transaction, the network would not be able to verify ownership, and the transaction would not go through. whichever user solves the problem the fastest gets a reward of a few bitcoins for their efforts. this is how “mining” of bitcoin is done. the problem comes in with how this proof of work system operates. all users on a network must have the computational power to solve these puzzles. these devices are usually cpu or gpu, which both draw power. since all users on the network are trying to solve a single block at once, there are many computers running at once, only doing a single task. once the block is solved, all the computing devices move to the next block [4]. this is an incredibly inefficient system. bitcoin is estimated to use approximately 1994.26 kwh of electrical energy per transaction. this is enough to power the average household in the united states for 68.35 days [5]. the enormous energy consumption is not the only issue. per transaction, bitcoin also has an estimated carbon footprint of 947.27 kg co2. this is comparable to the carbon footprint of 2,099,484 visa transactions [5]. all this energy is being used, and carbon is being released for a single transaction. clearly, something must be done to mitigate this issue. one might think, why not just get rid of bitcoin? the issue is that it has value. with a price per coin of over $57,000 as per the writing of this paper, mining bitcoin is very lucrative [1]. companies that have invested millions of dollars into their mining operations will not simply stop due to its ever-increasing environmental impact. because of this, ways to lower bitcoin’s energy consumption and thereby its carbon footprint are the alternative. that is what this paper aims to investigate, and it is discussed below. 3. phase change materials a phase change material (pcm) is a material that absorbs and releases heat as it changes from one phase to another (solid-liquid, liquid-gas, etc.). known as latent heat capacity, this property of a material is how much heat energy it can absorb or release per unit mass before it transitions to another phase. as the material absorbs heat energy, it thaws at a constant temperature until the entire body moves to a higher energy phase. the opposite is also true. once the material is in a higher energy phase and heat energy is no longer being added, the pcm will steadily release heat energy until it freezes back into its solid state. this is also true for liquid-gas transformations, but most applications only use solid-liquid transformations due to the volumetric changes that occur in the latter case. different materials have their own well-defined melting, freezing, and evaporating temperatures. this means that pcms can be tailored to a specific application based on the operating temperature ranges for that application. the primary advantage of a pcm over a constant phase material is sensible heat capacity versus latent heat capacity. sensible heat capacity is a material's ability to absorb heat energy per unit mass per degree celsius when no phase changes occur. this is important because, for most substances, their latent heat capacity is much higher than their sensible heat capacity. take water as an example. its latent heat capacity is 334 kj/kg, where its sensible heat capacity is only 2.1 kj/kg/c [6]. this means that it takes approximately 159 times more energy to melt 1 kg of ice than it does to raise the temperature of 1 kg of ice by 1 degree c. because of this pcm’s make excellent insulation/thermal storage materials. also, due to being able to absorb such huge amounts of energy, they can also be used as passive heat sinks. if a system cannot get rid of enough heat at peak operating temperatures, pcms can be used to store that heat until it can later be removed once the system is no longer at peak conditions. these two premises are what will be investigated further later in this paper. as with the application of any technology, pcms are chosen based on a variety of selection criteria. the first criteria for a pcm are that it must be able to absorb vast amounts of heat energy when changing phase. this means it needs a high latent heat capacity (heat of fusion) and be very dense. next, the pcm must have a fixed/well-defined boiling and freezing point so that it can be used as a design criterion. the pcms must also be resistant to cycling fatigue. as they are frozen and thawed many times over their life, pcms that wear out or lose heat transfer capabilities with this fatigue is undesirable. pcms chosen have to be able to avoid supercooling. this is the ability of the substance to stay liquid well below its freezing point. materials that have this ability are undesirable for thermal storage applications since they do not change phase at the design temperature, not utilizing the energy storage benefits that occur at the phase transition. pcms must also be non-hazardous. they must not be poisonous or corrosive to typical construction materials. lastly, pcms must be practical economically. to be used commercially, pcms must be price competitive with current insulations [7]. there are two main types of pcms: organic and inorganic. there are also eutectic pcms, which are just various mixtures of organic or inorganic pcms. both organic and inorganic pcm’s have their benefits and disadvantages. organic pcm’s advantages are that they are chemically stable, freeze without supercooling, are compatible with conventional construction materials, and melt congruently. their initial cost is more than inorganics, but after installation costs, they are competitive. the drawbacks of organic pcms are that they are highly flammable, can produce toxic fumes when burned, and have low latent heat storage capacity. some examples of organic pcms are paraffin waxes and fatty acids. inorganic pcms consist primarily of salt hydrates. their main advantages are that they are non-flammable, low-cost, readily available, and have a high latent heat capacity. the disadvantages of using inorganic pcms are chemical instability, issues with supercooling, and corrosiveness [8]. 4. applications of pcms in electronics one way to implement pcms into a mining setup is to have them in the electronics themselves. this can be done at different levels in electronics. the first level pcms can be applied at is the chip level. at this level, pcms are most useful whenever the electronics operate transiently, they cycle jacob geels/future energy may 2022| volume 01 | issue 01 | pages 12-15 14 between on/off or to take care of peak heat levels. in both cases, the pcms would act as a heat reservoir, either to store excess heat until the off-cycle as in the first case or to store excess heat until peak heat load subsides and release it then as in the second case [9]. for bitcoin mining operations, however, the former is not useful since most mining operations run 24/7, meaning there is no off-cycle for the pcm to release its stored heat. however, it can be used if there is an allowable operating temperature range that contains the pcm in use’s freeze/melt point. this would allow the pcm to thaw and refreeze, keeping the electronics within the desired range while still utilizing the high heat capacity of the pcm when it changes phase. another method of pcm implementation in electronics would be at the circuit board level. like their application at the chip level, the implementation of pcms at the board level requires either transient operation or an established operational temperature range that contains the pcm's freeze/melting point. the pcms can be integrated into the board structure or help passively cool the electronics. they can also be added to more widely used heat sinks, such as cooling fins, to increase the sink’s thermal mass [9]. 5. applications of pcms in the bitcoin mining warehouse one of the most promising applications of pcms is their integration into buildings. there are multiple ways how this can be done, including active building systems, passive building systems, free cooling systems, and peak load shifting systems. the primary system of focus in this paper will be passive building systems, or the integration of pcms into building materials, effectively increasing heat storage capacity. in these systems, the entire building envelope acts as thermal storage. the pcm melts during the day, absorbing energy, and freezes at night, releasing that energy back into the building environment. this reduces both the energy needs for cooling the building during the day and heating it during the night. this type of system also has the benefit of not needing pumps or fans to cool the pcms like active systems do, further lowering energy needs. pcms can be integrated into many different construction materials. wall panels, roof panels, wall insulation, and concrete floors are some examples. walls panels for many buildings consist of plasterboard/drywall because of its cheap nature. these panels consist of a gypsum-water mixture put between two pieces of paper. pcms could be added to these panels by either direct integration or by encapsulation, depending on the design considerations for the desired pcm. it has been shown that the temperature of a room can be reduced by up to 4oc when using pcms impregnated gypsum board [10]. plasterboard/drywall is also commonly used as roof panels, so a similar process to that of the wall panels could be applied here as well. wall insulation’s thermal performance can also be increased when pcms are added. pu-enhanced foam has the potential to reduce the peak cooling load of a wall by up to 40%. in addition, standard cellulose insulation impregnated by microencapsulated pcms has also been shown to have a measurable impact on cooling load; however, the exact measured impact depends on the wall orientation [11]. floor thermal performance can also benefit from pcm impregnation. pcms can be added to concrete slabs by either direct immersion, some form of encapsulation, or by utilizing lightweight aggregates to absorb the pcm before adding to the concrete [12]. pcm panels can also be used as a floor substitute [13]. this addition gives the possibility of the most energy savings. this is because the floor is the only envelope surface that is in direct contact with another solid (the ground), its main mode of heat transfer is conduction, which is the most efficient form of heat transfer. this means that the heat flux of the floor of a building is typically much higher than the walls or roof, leading to a larger heat loss through this surface. the application of pcm in building materials is usually done in buildings where people work/live to help keep the building at a comfortable temperature without running an hvac system continually. in addition to implementation into mining warehouse envelopes, pcms can also be implemented into air conditioning systems to help shift the cooling load away from peak hours. these augmented systems are similar in configuration to traditional air conditioning systems as they still have a compressor, heat exchanger, evaporator, etc. however, they also include a cold storage device that uses pcms as its energy storage medium [14]. these cold storage devices charge themselves during the night when cooling loads and power demand are low and release it during the day to supplement the main cooling system. this cold energy is stored in the form of solidified pcms and is released as excess waste heat from the air conditioning system is inputted into the cold storage device, melting the pcm. this type of system helps to maintain the desired temperature band more easily within the building and lowers operational costs by not having to pay premium electric prices during peak hours [15]. the mentioned methods can similarly be applied to bitcoin mining setups as the electronics must be kept cool. while human comfort temperatures and optimal electronic temperatures are in different temperature ranges, the same premise of reducing cooling load can still be applied. the only difference would be the need to select a pcm whose phase change range is within the desired operating range for the mining equipment. 6. conclusions the enormous energy requirements of bitcoin mining and the ability of pcms to be used as excellent thermal storage materials were discussed. in addition, design requirements and considerations of pcms were reviewed. lastly, the possible applications of pcms in building envelopes in the form of impregnation of the wall, roof, and floor materials were evaluated. pcms have been shown to be able to reduce the cooling requirements of electronics and rooms. with this knowledge, bitcoin’s miners can reduce the energy use, and thereby carbon footprint, of their mining operations. more research needs to be done to make pcm-impregnated construction materials cheaper to manufacture, making them cheaper to implement. these materials must be competitive with traditional construction materials if they are to be used, as bitcoin mining is done to make turn profit. ethical issue the author is aware of and complies with best practices in publication ethics, specifically with regard to authorship (avoidance of guest authorship), dual submission, manipulation of figures, competing interests, and compliance jacob geels/future energy may 2022| volume 01 | issue 01 | pages 12-15 15 with policies on research ethics. the author adheres to publication requirements that the submitted work is original and has not been published elsewhere in any language. data availability statement data sharing is not applicable to this article as no datasets were generated or analyzed during the current study. conflict of interest the author declares no potential conflict of interest. references [1] “cryptocurrency prices, charts and market capitalizations.” coinmarketcap, https://coinmarketcap.com/. [2] pérez-solà, cristina, et al. “double-spending prevention for bitcoin zero-confirmation transactions international journal of information security.” springerlink, springer berlin heidelberg, 24 nov. 2018, https://link.springer.com/article/10.1007/s10207018-0422-4. [3] conti, mauro, e. sandeep kumar, chhagan lal, and sushmita ruj. "a survey on security and privacy issues of bitcoin." ieee communications surveys & tutorials 20, no. 4 (2018): 3416-3452. [4] stoll, christian, et al. “the carbon footprint of bitcoin.” joule, cell press, 12 june 2019, https://www.sciencedirect.com/science/article/pii/s 2542435119302557#bib1. [5] “bitcoin energy consumption index.” digiconomist, 6 nov. 2021, http://bitcoinenergyconsumption.com/. [6] “phase change materials.” energy technologies, https://www.crodaenergytechnologies.com/engb/functions/phase-change-materials. [7] www.sitewizard.co.uk. “types of phase change materials.” pcmproducts.net, https://www.pcmproducts.net/phase-changematerial-solutions.htm. [8] “phase changing materials.” http://www.madhavuniversity.edu.in/, https://madhavuniversity.edu.in/phase-changingmaterials.html. [9] marongiu, maurice. “thermal management of electronic equipment using phase change materials (pcms).” electronics cooling, 1 aug. 2019, https://www.electronicscooling.com/2019/03/thermal-management-ofelectronic-equipment-using-phase-change-materialsp. [10] zhou, d., et al. review on thermal energy storage with phase change uhra home. https://uhra.herts.ac.uk/bitstream/handle/2299/127 72/906724.pdf;sequence=2. [11] baetens, r., et al. phase change materials for building applications: a state-of-the-art review. 2010, https://sintef.brage.unit.no/sintefxmlui/bitstream/handle/11250/2473861/phase%20 change%20materials%20for%20building%20applicat ions.pdf?sequence=5. [12] bentz, dale p., and randy turnpin. potential applications of phase change materials in concrete technology. sciencedirect, 10 apr. 2007, https://citeseerx.ist.psu.edu/viewdoc/download?doi= 10.1.1.81.3315&rep=rep1&type=pdf. [13] frigione, mariaenrica, et al. “phase change materials for energy efficiency in buildings and their use in mortars.” materials (basel, switzerland), mdpi, 17 apr. 2019, https://www.ncbi.nlm.nih.gov/pmc/articles/pmc651 5401/. [14] li, shuang-fei, et al. “a comprehensive review on positive cold energy storage technologies and applications in air conditioning with phase change materials.” applied energy, vol. 255, 2019, p. 113667., https://doi.org/10.1016/j.apenergy.2019.113667. [15] omara, adil a.m., and abuelnour a. abuelnour. “improving the performance of air conditioning systems by using phase change materials: a review.” international journal of energy research, vol. 43, no. 10, 2019, pp. 5175–5198., https://doi.org/10.1002/er.4507. this article is an open-access article distributed under the terms and conditions of the creative commons attribution (cc by) license (https://creativecommons.org/licenses/by/4.0/). https://madhavuniversity.edu.in/phase-changing-materials.html https://madhavuniversity.edu.in/phase-changing-materials.html https://madhavuniversity.edu.in/phase-changing-materials.html lg soares et al. /future energy february 2023| volume 02 | issue 01 | pages 23-26 23 article photodecomposition of water\ethanol mixtures for the production of hydrogen using as catalysts tio2 fibers luana góes soares*1, maurício de oliveira vaz2, sérgio ribeiro teixeira2, annelise kopp alves1 1ceramic materials laboratory, federal university of rio grande do sul, rio grande do sul, brazil 2thin film and nanostructure laboratory, federal university of rio grande do sul, rio grande do sul, brazil a r t i c l e i n f o article history: received 02 august 2022 received in revised form 08 september 2022 accepted 14 september 2022 keywords: energy, ethanol, hydrogen, fibers, water-splitting *corresponding author email address: lugoes.soares@gmail.com doi: 10.55670/fpll.fuen.2.1.4 a b s t r a c t the consumption of hydrogen as an automotive fuel has been growing since the 1980s. it can be used both as a gasoline blend and as a pure fuel. all human activities involve the use of energy. some examples are: fuels for transport and heating, electricity for various purposes, among others. it is a basic element for the production and commercialization of any goods or services and represents one of the main expenses of families. thus, projected future trajectories for energy prices are of obvious interest to consumers and producers. the use of hydrogen generation and storage technology is an energy generation option to replace current fossil fuels, as it offers the opportunity to obtain energy with reduced environmental impacts and which does not pollute the environment. in this work, tio2 fibers were obtained by the electrospinning technique and used as catalysts in the photodecomposition of water-ethanol mixtures for the production of hydrogen. the x-ray diffraction technique (xrd) was used to characterize the synthesized catalysts, the bet method provided measurements of the specific area, and scanning electron microscopy (sem) analyzed the morphology of the samples. the results indicate that the fibers that contain the anatase phase in greater proportion have a high surface area and were the most effective in the production of hydrogen. 1. introduction the increase in energy demand is related to macroeconomic growth, which translates into more disposable income for families, allowing for greater consumption of fuel, electricity, and other energy uses. with this, it is necessary that companies demand more energy, aiming to facilitate a greater production of goods and services. the literature reports that the elasticity/income ratio of energy consumption is around 1, that is, under normal conditions, the percentage increase in an economy causes a corresponding increase in the demand for energy. countries such as the united states and countries that subsidize fuel, as well as oil-producing countries, which command the rise and taxation of fuel prices, interfere negatively in energy intensity. currently, energy sources are being sought that combine energy efficiency, energy security, and the reduction of polluting gas emissions into the atmosphere. the generation of energy through h2 creates substantial incentives not only for the adoption of efficiency measures and technologies to reduce consumption but also for the substitution of fossil energy sources. below we highlight some examples of sustainable energy: plug-in hybrid electric vehicles, ethanol, biodiesel, and hydrogen [1]. within this context, hydrogen (h2) has attracted the attention of researchers, due to some characteristics, such as the fact that it can be stored for later consumption, converted into electrical energy, serving as a link between various forms of energy because of its high energy value, among others [2]. several techniques have been applied for the separation of water, such as catalytic reform of organic compounds and biological processes, aiming at the production of h2. using these techniques, hydrogen is obtained by breaking the water molecule [3]. some ways to produce hydrogen include: primary energy sources (such as coal, natural gas, and oil); intermediate sources (chemicals such as refinery, ammonia, and ethanol), and alternative energy sources (such as biogas, waste gases, and biomass). obtaining hydrogen using photocatalytic processes is still low. the main disadvantage of using these processes is the possibility of recombination of the electron/hole pair, which future energy open access journal https://doi.org/10.55670/fpll.fuen.2.1.4 february 2023| volume 02 | issue 01 | pages 23-26 journal homepage: https://fupubco.com/fuen issn 2832-0328 mailto:lugoes.soares@gmail.com https://doi.org/10.55670/fpll.fuen.2.1.4 https://fupubco.com/fuen lg soares et al. /future energy february 2023| volume 02 | issue 01 | pages 23-26 24 is generated during the photocatalytic process. another factor that contributes to its low use is because tio2 has a wide band gap (~3.2 ev), which allows its activation only under uva light irradiation. therefore, this work shows the efficient production of hydrogen by water-splitting, using tio2 catalysts and ethanol as a sacrificial agent [4]. 2. experimental for the synthesis of fibers by electrospinning, the following reagents were used: titanium propoxide (sigmaaldrich), glacial acetic acid (sigma-aldrich), anhydrous ethyl alcohol (zeppelin), and a 10% solution by weight of polyvinylpyrrolidone (pvp – sigma-aldrich, 1.300,000 g/mol). 3. methodology 3.1 obtaining fibers by electrospinning the first step for the synthesis of fibers by electrospinning was to prepare the precursor solution that contained the mixture of: 2.5 ml of titanium propoxide (tip); 2 ml of glacial acetic acid and 5 ml of an alcoholic solution containing 10% by weight of polyvinylpyrrolidone (pvp). after completion of the first step, a 5 ml plastic syringe was connected to a 1 mm internal diameter stainless steel hypodermic needle and filled with the precursor solution. the needle was connected to the high voltage source. the distance between the needle tip and a rotating cylindrical collector covered with aluminum foil was 12 cm. a voltage of 13.5 kv was applied between the needle and the collector. an infusion pump (kd scientific) controlled the flow of the precursor solution (1.8 ml/h). fibers were collected every 30 minutes for a period of 4 hours daily. after obtaining the fibers by electrospinning, they were subjected to heat treatment in an electric oven (sanchis) at temperatures of 650 °c, 700 °c, 750 °c or 800 °c, with parameters of 1 hour and a heating rate of 1.4 °c/min in order to remove polymeric material and form crystalline phases. 3.1.1 characterization methods to identify the phases formed in the samples, a philips x'pert diffractometer was used, with cukα radiation, operating with a voltage of 40 kv and a current of 40 ma, a speed of 0.05°/min, and a step of 1 s in the range of 5° to 75°. the diffractograms obtained were compared with the jcpds database (joint committee on powder difraction standards) using the x'pert hightscore® software. the specific surface area was determined using the brunauer emmett teller (bet) method. the equipment used was an autosorb nova 1000e, quantachrome instruments. the morphology of the samples was observed through the technique of scanning electron microscopy (sem). band gap energy was determined by diffuse reflectance spectroscopy (drs). the equipment used was a dual-beam uv-vis-nir spectrophotometer cary agilent 5000, with an integrating sphere in diffuse light reflection mode. the photocatalysis process was carried out in a photocatalytic reactor made of pyrex glass, where the radiation was provided by 12 black light lamps of 8 w each (fluor blb t5, sadokin). after the start of the assay, 4 ml aliquots were withdrawn with a syringe at 15-minute intervals, filtered through a 0.2 µm filter, and transferred to polymethlmethacrylate (pmma) cuvettes. then, the aliquots were analyzed for their absorbance cary 5000, agilent, with uma accessory by scanning the wavelength of the radiation λ = 365 nm. the determination of photocatalytic activity was performed based on the c/co ratio, where c is the molar concentration of the aqueous dye solution with the catalyst at the time of analysis and co is the initial molar concentration of the aqueous dye solution without the presence of the catalyst. 3.2 hydrogen production hydrogen was produced using a quartz reactor consisting of double walls through which the water circulated, with a constant temperature of 25 0c. after this step, the catalysts, one at a time, were submerged in a solution of 7.5 ml of deionized water and 2.5 ml of ethanol. before starting irradiation, analytical argon was bubbled through to remove dissolved gases, and the system was deaerated through a vacuum line. to simulate sunlight, a 300 w xenon lamp illuminated the reactor. the gases produced were collected using a hamilton gas syringe at 30 min intervals for 4 h and quantified using a gc-agilent 6820 chromatograph. the total volume of samples injected into the chromatograph was 1.000 μl. 4. results and discussion figure 1 depicts the diffractogram of the fibers. the samples without heat treatment (wht) were amorphous. the tio2 catalysts formed anatase (jcpds 01-078-2486) up to 700 ◦ c. from 750 ºc, rutile (jcpds 01-077-0442) was also identified. the first characteristic peak of the anatase and rutile phase appears at approximately 2ө = 25.271º e 27.294°, respectively. figure 1. diffractogram of tio2 fibers figure 2 shows sem illustrations of the microstructure of tio2 fibers. analyzing these images, the tio2 fibers do not seem to have a preferential orientation, appearing to have an elongated and continuous microstructure. figure 2. sem illustrations of the microstructure of tio2 fibers lg soares et al. /future energy february 2023| volume 02 | issue 01 | pages 23-26 25 figure 3 demonstrates the surface area of the tio2 fibers. where it is possible to notice that there is a nonuniform distribution of fiber diameters obtained by electrospinning. this is an undesired characteristic of the fibers formed during the process. finding a way to control the uniformity of the diameter becomes difficult since the lack of uniformity, apparently, is caused by the inconstancy of the jet during the path to the collector and by the nonuniformity in the division of electrical charges within the fluid. figure 3. size distribution of tio2 fibers table 1 shows the band gap values of tio2 fibers synthesized by electrospinning and heat treated at 650 ºc, 700 ºc, 750 ºc, and 800 °c. it is noted that in relation to the tio2 p25 catalyst, the values obtained for the synthesized fibers were lower, which indicates that the synthesized materials have a great capacity to act as semiconductors. for all tio2 fibers synthesized by electrospinning were able to absorb light in the visible region (400-700 nm) of the electromagnetic spectrum. these differences in band gap values result from the different phases present in the synthesized fibers, from the presence of incomplete bonds on the surface of this material, which influence the reduction of the band gap, which favors the optical properties of the material and also the surface effects on the distribution of electronic levels [2]. by analyzing the results presented in figure 4, it is clear that the heat treatment temperature benefits the removal of the zone of maximum slope of the absorption curve for longer wavelengths. these changes in the bands correspond to the electron transfer that occurs when the electron passes from vb to cb, where the antibonding 2p orbitals of o2 (bv) are transferred to the empty 3d orbital of lower energy of ti4+ (bc). the interesting to observe, by comparing the percentages of anatase and rutile with the respective energy gap values described in table 1 respectively, that the lowest eg value occurs when the tio2 fibers are composed of 100% of the anatase and without the formation of the rutile phase, that is, this is an indication that the reduction in the proportion of anatase in the tio2 fibers influences the “gap” value of the tio2 band. band gaps in semiconductor materials are closely related to the absorbed wavelength range, where the gap decreases with increasing absorption wavelength, and which can be proven by the gap values presented for tio2 fibers treated thermally at 650 ºc and 700 ºc, which showed a gap of 2.66 ev and 2.90 ev, and absorbed λ= 471 nm and 427 nm, respectively. table 1. band gap and wavelength values corresponding to tio2 fibers and p25 standard figure 5 depicts the catalytic activity of tio2 fibers in the degradation of the methyl orange dye during 135 minutes of exposure to uv-a light (λ= 365 nm). the most photoactive tio2 samples were those treated at 650 °c and 700 °c, respectively. due to the majority presence of the anatase phase, proven to be the most photoactive phase of tio2 and for presenting the lowest band gap values, 2.66 ev and 2.90 ev, respectively. the presence of anatase in the mixture ensures greater absorption of light. the light absorption of the rutile phase is lower than that of the anatase form, and this lower light absorption results in lower photocatalytic activity. as the heat treatment temperature increases, the formation of the rutile phase occurs, which is the tio2 phase with the lowest photocatalytic activity, and its appearance and the increase in the band gap values, 2.94 ev and 2.95 ev, are responsible for the decrease in photocatalytic activity of tio2 fibers treated at temperatures of 750 ºc and 800 ºc, respectively. figure 4. the absorption spectrum of tio2 fibers and the p25 standard. figure 6 the evolution of h2 production by the tio2–p25 (reference) and tio2 fibers. all synthesized samples produced h2. the highest h2 production was achieved by the catalysts of tio2-650 ºc, with approximately (86.6%) h2 production capacity. these results confirmed that the heat treatment temperature associated with bandgap mitigation contributed to the formation of a larger number of oxygen vacancies. the conduction occurs through consecutive leaps of o2 vacancies within the tio2 crystal structure in almost all oxygen ion conductors. the joint action of these factors gave titanium structural phase stability. rising heat treatment temperatures allowed o2 vacancies to acquire the mobility required to move in a disordered state inside the anionic fibers samples band gap (ev) λ (nm) anatas e % rutile % tio2 p25 evonik 3.20 387.5 80 20 650o c 2.66 471.0 100 700o c 2.90 427.0 100 750o c 2.94 422.7 50 50 800o c 2.95 420.5 30 70 lg soares et al. /future energy february 2023| volume 02 | issue 01 | pages 23-26 26 subnet [5]. in an investigation using ethanol and pt-doped tio2 for h2 production, it was found that the solution ph impacts the gas production rate. it was indicated that either neutral or basic reaction media h2 production because oh is absorbed on the catalyst surface, which possibly increases the gas production rate. the oh groups on the catalyst surface might participate in two processes: (1) trapping the holes and (2) transferring charge between the semiconductor and the electrolyte solution. participation in these two processes mitigates the recombination rates between the electron-hole pairs. therefore, greater ph in the synthesis of samples could have contributed to enhanced oh groups on the catalyst surface [5]. figure 5. photocatalytic activity of the fibers and the p25 standard in the degradation of the mo dye figure 6. evolution of hydrogen production using tio2 fibers as catalysts and commercial tio2 (p25) was presented for comparison 5. conclusion with this study showed that the water-splitting technique is a promising route to synthesize tio2 catalysts since all synthesized samples demonstrated photocatalytic capacity for the production of h2, applying ethanol molecules as sacrificial reagents, which functioned as electron donors for h2 photogeneration in photocatalytic reactions. among all the synthesized samples, the tio2 catalysts heat-treated at 800 ºc had the lowest hydrogen production capacity, probably because tio2 in pure water has the highest rate of recombination of the electron/hole pair. the samples heat treated at 650 ºc were the most effective in hydrogen production, reaching 86.6% effectiveness in hydrogen generation. due to the reduction of sample bandgap, an increase in heat treatment temperature, which increased the concentration of o2 vacancies (point defects) that played a fundamental role in the movement of the tio2 crystal lattice. which caused a greater photocatalytic capacity and to absorb visible light, which trapped the electrons, thus preventing the recombination of electron/hole pairs. acknowledgment the authors are grateful for the financial support of the federal university of rio grande do sul (ufrgs), the coordination for the improvement of higher education personnel, and cnpq. ethical issue the authors are aware of and comply with best practices in publication ethics, specifically with regard to authorship (avoidance of guest authorship), dual submission, manipulation of figures, competing interests, and compliance with policies on research ethics. the authors adhere to publication requirements that the submitted work is original and has not been published elsewhere in any language. data availability statement data sharing is not applicable to this article as no datasets were generated or analyzed during the current study. conflict of interest the authors declare no potential conflict of interest. references [1] e. and y. terco, sustainable brazil, 2011. https://cuadrivio.net/publication/vwluassets/sustai nable_brazil_-_world_cup/_file/copa_2014.pdf [2] l. silva, correlação entre as propriedades fotocrômicas e atividade fotocatalítica dos óxidos de titânio e tungstênio, 2018. [3] l. soares, m. vaz, s. teixeira, a. alves, absorbance determination and photocatalytic production of hydrogen using tungsten and tio2 oxide nanostructures as catalyst, 2021. [4] c. rangel, r. silva, t. paiva, b. charrasse, produção de hidrogénio solar com simultânea mineralização de poluentes orgânicos, 2014. [5] a. garcia, w. guaglianoni, d. garcia, l. soares, m. vaz, s. teixeira, m. pereira, t. basegio, f. clemens, a. alves, fabiano s. rodembusch, c. bergmann, facile synthesis by peroxide method and microwave-assisted hydrothermal treatment of tio2 with high photocatalytic efficiency for dye degradation and hydrogen production, 2018. a.maka et al. /future energy february 2024| volume 03 | issue 01| pages 18-22 18 article simulation and modeling of the possibility of implementing solar high-concentrating photovoltaic in libya ali o. m. maka1*, mohamed alatrash2, tarik ghalut3 1the libyan centre for research and development of saharian communities, mourzq, libya 2harouge oil operation, tripoli, libya 3university of tripoli, tripoli, libya a r t i c l e i n f o article history: received 01 april 2023 received in revised form 29 april 2023 accepted 05 may 2023 keywords: concentrating photovoltaics, triple-junction cell modelling and simulation, solar energy *corresponding author email address: maca_4212@yahoo.co.uk doi: 10.55670/fpll.fuen.3.1.3 a b s t r a c t concentrating photovoltaics is a type of solar photovoltaic technology that relies on sunlight concentrating to produce electrical energy. in this regard, high-efficiency solar cells comprise many different materials cells, and energy band gaps are stacked respectively on top of each other. this technology, depending on a large portion of the solar spectrum component, which absorbed by the triple-junction solar cell; the consequence is a rise in the device’s conversion efficiency. the layers of semiconductor materials, including gainp/gainas/ge, are coupled in series to gain high efficiency. besides, an accurate assessment of the energy yield from a concentrating photovoltaic (cpv) device throughout its lifetime and the electrical performance characteristics in different operating environments is required. hence, an mscs-1d: v-2 solar cell simulator tool and a system advisor model (sam) are used to model and simulate performance behavior. in this paper, we modeled and simulated mini solar concentrating photovoltaics. based on that, solar cpv technology can be implemented in such regions to generate electricity and heat. moreover, the selected region has a great potential for direct normal irradiations (dni) annually. in addition, that encourages further study via applying large-scale in the form of cpv power plants. 1. introduction the need for energy has been growing recently, and supplies that depend primarily on fossil fuels are utilized to supply home and industrial demands. however, it’s also commonly known that fossil fuels are the main contributors to environmental pollution, which leads to global warming issues, and their availability is constrained. based on that, people worldwide look forward to developing renewable energy technology for environmental friends [1]. also, the development of solar energy technology can play a significant role in fulfilling sustainable development shortly [2]. over the years, scholars have become increasingly interested in solar energy or solar photovoltaic (pv) technologies. however, conventional pv cells have a large module area and limited conversion efficiency. the solar-concentrating photovoltaics have attracted attention from scholars and manufacturers over the past few decades to address the constraint. therefore, using specific concentrators and lenses or mirrors, the incident solar radiations are focused on smaller scales; this results in electrically more effective photovoltaic cells through cpv devices [3, 4]. the concentrating photovoltaic technology can be utilized to generate electricity in space and on earth. it is important to mention that about 46% of incident solar energy can be converted to electricity by cpv cells, with the remaining energy being lost as heat [5]. a different materials energy band gap is used in the technology of the third generation of photovoltaic solar cells, which are stacked on top of each other, and the yield is highly efficient solar cells. a concentrating pv module typically comprises a high-efficiency solar cell and a light concentrator, which can be manufactured from a mirror, a parabolic dish, or lenses [68]. the operating evaluation of cpv modules is essential for performance evaluation and rated power estimation, which may also result in design enhancements to the solar cell assembly, packaging of the optics concentrating, or the need for thermal management [9]. due to its high energy yield, the high-concentrating photovoltaics hcpv technique is widely utilized in electrical energy generation. however, in highconcentrating pv technology, as a consequence of optic concentration, the cell operating temperature rises to more future energy open access journal https://doi.org/10.55670/fpll.fuen.3.1.3 february 2024| volume 03 | issue 01 | pages 18-22 journal homepage: https://fupubco.com/fuen issn 2832-0328 mailto:maca_4212@yahoo.co.uk https://doi.org/10.55670/fpll.fuen.3.1.3 https://fupubco.com/fuen a.maka et al. /future energy february 2024| volume 03 | issue 01| pages 18-22 19 than 120oc. nevertheless, for higher operating performance, longevity, and reliability aspect, it is always advised to keep cell/module temperature equal to or less than 80oc [6, 10]. the energy band gap of the semiconductor materials restricts the theoretical efficiency of the single solar cell. based on that, the shockley queisser efficiency constraint, which caps the single cell’s efficiency at 31%, is an important loss factor to consider [11]. so, that leads to thinking about finding advanced ways to develop solar cell efficiency above those limited values. hence, different energy band gaps of semiconductor materials are utilized to decrease thermalization losses and boost conversion efficiency [12, 13]. it is worth mentioning that saudi arabia is one of the meddle-east countries with harsh environments and has implemented many applications of hcpv systems since the 1980s. the designed system operated at a concentration ratio of 1400 x; as reported in the system operating performance, it worked well and was harmonious with the environment [14]. therefore, this work modeling and simulates the performance behavior of a triple-junction solar cell/modules and mini cpv. this gives an idea of the cell’s behavior to improve the design and enhance performance. the consequences are drawn through performance analysis and prediction of energy yield. this work is a primary study towered large-scale, and in the future, we look forward to seeing that implementation on the ground. 2. modeling approach in this work, we set up one triple-junction solar cell using the so-called mscs-1d: v-2, solar cell simulator. it characterized electrical performance under a concentration ratio from 1 to 1000 x and estimated cell efficiency. based on that, in doing so, we set up a module/array of triple-junction using so-called the system advisor model (sam), owner of the international renewable energy laboratory (nrel). subsequently, it estimated annual module efficiency during the daytime. therefore, the environmental data of sebha city, located in southwest libya, is considered in the characterization of performance behavior analysis. that depends on the national solar radiation database (nsrdb), which includes the parameters of dni, wind speed, ambient temperature, and air mass. furthermore, the integration of overall power produced also predicts yearly energy yield. hence, the tools used in this study are due to their powerful tools, accuracy, and accessibility of software; for that reason, we used them for the simulation. moreover, the performance analysis of solar cells and module takes place by quantifying the conversion efficiency. figure 1 shows the proposed flowchart of the predicted modeling/simulation approach. the three layers of cell behavior under sunlight are described in detail. therefore, the ultraviolet and visible portions of the solar spectrum are absorbed by the gainp top one-layer cell. its response to wavelengths between 300 and 700 nm with an energy band gap eg = 1.8 ev. the infrared spectrum portions are absorbed by the gainas middle layer cell. it responds to wavelengths between roughly 700 and 900 nm with an energy band gap eg =1.4 ev. finally, the bottom layer cell ge responds to wavelengths between 900 and 1800 nm and absorbs lower energy photons in the infrared portion of the solar spectrum with an energy band gap eg = 0.7 ev. figure 1. flowchart of predicted modeling/simulation approaches. it’s important to give some theoretical equations utilized in the model of triple-junction solar cells. the key to the solar cell electrical performance parameters can be quantified using the equations (1-5) respectively [15]. 𝐽𝑠𝑐,𝑖 = 𝐶𝑅. ∫ 𝑆𝑅𝑖(𝜆). 𝜂𝑜𝑝𝑡(𝜆). 𝜆2 𝜆1 𝐺(𝜆). 𝑑𝜆 (1) 𝐽,𝑖 = 𝐽𝑜,𝑖 (𝑒𝑥𝑝 𝑞(𝑉+𝐽,𝑖.𝑅𝑠 𝑛.𝐾𝑏.𝑇𝑐 − 1) − 𝐽𝑠𝑐,𝑖 (2) 𝑉𝑜𝑐,𝑖 = 𝑛.𝐾𝑏 .𝑇𝑐 𝑞 𝑙𝑛 ( 𝐽𝑠𝑐,𝑖 𝐽0,𝑖 + 1) (3) 𝐹𝐹 = 𝑃𝑚𝑎𝑥 𝑉𝑂𝐶.𝐽𝑆𝐶 = 𝐽𝑚𝑎𝑥.𝑉𝑚𝑎𝑥 𝑉𝑂𝐶.𝐽𝑆𝐶 (4) 𝜂𝑒𝑙 = 𝑃𝑚𝑎𝑥 𝑃𝑖𝑛 = 𝐽𝑠𝑐.𝑉𝑜𝑐.𝐹𝐹 𝑝𝑖𝑛 (5) from the modeling/simulation results, the maximum module power was about 596 w, and the average conversion efficiency was approximately 30%. table 1 lists the key specification details of the simulation parameters of concentrating photovoltaic module. table 1. the characteristic of a high -concentring photovoltaic the concentration is used to evaluate an electrical performance perspective. since the concentration ratio rises, it will lead to more energy of photons absorbed by the cell, for example, via 500 or 1000 times, i.e., equal to 500 x or 1000 x; it depends on how much light is available. also, it is worth noting that the one sun or (x) is equal to 1000 w/m2. thus, the short-circuit current intensity (jsc) is increased proportionally to calculate the concentration ratio. so, the generated photo-current is directly proportional to the concentration rations due to the absorption of photon flux. parameters values number of cells 20 concentration ratio 1-1000 x area of module 2 m2 optical efficiency 90 % a.maka et al. /future energy february 2024| volume 03 | issue 01| pages 18-22 20 consequently, the following is the concentration ratio described in terms of the electric perspective. 𝐶𝑅 = 𝐽𝑠𝑐,𝑋 𝐽𝑠𝑐 (6) in multi-junction solar cells, the p-n junctions also facilitate a pv conversion. hence, these p-n junctions are electrically coupled in series in most devices. therefore, a tunnel junction is needed between two p-n junctions to guarantee low resistance to electricity between the two junctions' various energy band gaps due to doping in every junction. in the application of triple-junction solar cell assembly, due to the series connection, the combined three layers’ overall current density is limited by a lower current density, as given by the relationship (7). jtotal = min (j1,j2,j3 ) (7) 3. results and discussions 3.1 triple-junction solar cell the amount of incident sunlight energy converted to electrical energy is known as conversion efficiency. from the modeling results of (10 mm x 10 mm) dimensions, one cell of triple-junction solar cell assembly under variation of concentration ratio from (1 to 1000 x). the efficiency was logarithmic increases as the results of light rose. in order to comprehend the performance behavior of solar cells, a characterization of the cell takes place by determining the efficiency. the expense of solar energy can be indirectly reduced by attaining high efficiency. higher efficiency helps boost power production and lower the overall system cost, even though the cells are expensive; meanwhile, several cost elements of a power plant and photovoltaic system are associated. as shown in figure 2, the concentration ratio versus cell efficiency simulation results; also show a typical solar receiver assembly, including a solar cell example. figure 2. the efficiency of triple-junction solar cells versus various concentrating ratios it is important to be mentioned that in high efficiency, iiiv materials with certain band gap energies and approximately the same lattice constant must be taken into while developing the semiconductor materials of assembly. for the overall energy prediction of the solar hcpv systems or for enhancing module designs, the electrical characterization of solar hcpv modules is an important step. while the technology of multi-junction solar cells is used, and there are more components in the structure, the electrical characterization of ultra-high concentration photovoltaics (uhcpv) is different and more challenging than that of traditional solar pv in terms of heat removal devices and optical [16]. 3.2 triple-junction solar module many factors are to be considered to determine solar cell/module efficiency, e.g., the quantum efficiency, internal resistances, the maximum power point, the limitation of thermodynamic efficiency, the reflectance efficiency of the cell’s surface, and the type of solar cell [17]. the module assembly consists of several solar cells linked to gain a high energy yield. the annual module conversion efficiency was estimated from januarydecember. the average module efficiency is 30%, and the maximum module power is 596 w. the simulation results are based on the normal reference irradiance of 1000 w/m2; the environment temperature is 25oc, the wind speed is about 4 m/s, and the air mass of 1.5. figure 3 illustrates approximates of yearly module conversion efficiency during the daytime. figure 3. estimation of annual module conversion efficiency during daytime 4. prediction of annual energy yield predicting energy yield is an important task involving the determined characteristics of pv devices under various conditions and weather information from the investigation region. to build up a solar cpv power plant, direct normal irradiance (dni) is one important parameter to consider in designing. therefore, the area of study is very rich in the high potential of dni annually. the daily average of dni is approximately 3.99 kwh/m2 daily, and the wind speed is 3.4 m/s. hence, the typical meteorological year (tmy) data which contains a weather file, is used for a selected area of study. the sum accumulation of monthly energy depends on the hours of operation, so during the summer season is more time for daylight in contrast to other seasons. therefore, there are rarely scattering clouds reported in the region. also, consider the dusty windstorms in such a harsh environment, which leads to dust accumulation on the top module surface; a clean/washing strategy can highly alleviate this. figure 4 presents the direct normal irradiance of the selected area. a.maka et al. /future energy february 2024| volume 03 | issue 01| pages 18-22 21 figure 4. the monthly sum of accumulation of the solar radiation dni although other design elements have an impact, the behavior of an hcpv module is significantly reliant on the solar cells’ behavior. in the solar hcpv modules, the most significant environmental parameter is dni; also, the temperature of the solar cells and the spectrum of direct sunlight. the behavior of the multi-junction or triple-junction solar cells must be well designed, which is important to actually estimate how much energy high-concentrating photovoltaic hcpv modules will produce. the daily energy produced (ep) for each day is calculated via the integration of the output power per hour, which is given in equation (8). 𝐸𝑝 = ∫ 𝑃(𝑡). 𝑑𝑡 𝑡2 𝑡1 (8) where p(t) represents the mean power as a function of the time of the triple-junction module at every time step, and t1 and t2 are the times of sunrise and sunset, respectively. the energy production viewpoint showed that the typical solar modules produce more energy during the summer since there is a huge amount of dni available. the seasons of autumn, winter, and summer are different from one another because summer has the most sunshine while winter and autumn have the least. figure 5 represents the prediction of annual solar energy production. energy yield estimates and models energy production in a certain location over time to provide the full view of the amount of energy by (kwh). figure 5. prediction of annual solar energy production. the expense can be significantly reduced by maximizing yearly energy yield during the stage of designing and implementing a photovoltaic system. furthermore, since the modeling can predict how the solar modules and other assembly components of the system will perform in relation to energy production estimates, they also impact system cost by lowering overall expenses. 5. conclusion this work presented a simulation of a mini solar cpv application; this technology can benefit by generating electricity and heat. hence the heat might be used for other purposes, e.g., water heating, desalination, or heating systems. furthermore, the development of modeling techniques for the electrical characterization of these devices is improved through developments in our understanding of the behavior of high-concentrating photovoltaics hcpv modules. from simulation analysis, electrical characterization of cpv devices and module energy yield of the mini plant. furthermore, the solar cpv technology needs attachment equipment on the rear side for either active or passive cooling technology to keep the cell temperature working at an acceptable degree. in libya, the solar radiation intensity is almost similar across the country in terms of the dni and other environmental parameters, which encourages implementing cpv technology anywhere. it is important to mention that no scattering clouds obstacle is available in the region. further work we suggested includes a technoeconomics study and the prospect of implementing a largescale in form of a cpv power plant. acknowledgment many grateful thanks to the libyan authority for research science and technology, and many thanks to the staff in the libyan centre for research and development of sahrain communities. also, many thanks to the anonymous reviewers for their constructive comments in improving this paper. ethical issue the authors are aware of and comply with best practices in publication ethics, specifically concerning authorship (avoidance of guest authorship), dual submission, manipulation of figures, competing interests, and compliance with policies on research ethics. the authors adhere to publication requirements that the submitted work is original and has not been published elsewhere in any language. data availability statement datasets analyzed during the current study are available and can be given following a reasonable request from the corresponding author. conflict of interest the author declares no potential conflict of interest. references [1] t. chow, "performance analysis of photovoltaicthermal collector by explicit dynamic model," solar energy, vol. 75, no. 2, pp. 143-152, 2003. [2] a. o. maka and j. m. alabid, "solar energy technology and its roles in sustainable development," clean energy, vol. 6, no. 3, pp. 476-483, 2022. [3] a. valera, e. f. fernández, p. m. rodrigo, and f. almonacid, "feasibility of flat-plate heat-sinks using jan feb mar apr may jun jul aug sep oct nov dec 0 50000 100000 150000 200000 250000 300000 d ir e c t n o rm a l ir ra d ia n c e ( w /m 2 ) a.maka et al. /future energy february 2024| volume 03 | issue 01| pages 18-22 22 microscale solar cells up to 10,000 suns concentrations," solar energy, vol. 181, pp. 361-371, 2019. [4] a. dey, z. u. ahmed, and m. r. alam, "thermal and exergy analysis of pin-finned heatsinks for nanofluid cooled high concentrated photovoltaic thermal (hcpv/t) hybrid systems," energy conversion management: x,vol. 16, p. 100324, 2022. 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[9] m. theristis, e. f. fernández, g. e. georghiou, and t. s. o'donovan, "performance of a concentrating photovoltaic monomodule under real operating conditions: part i–outdoor characterisation," energy conversion management, vol. 154, pp. 311-321, 2017. [10] a. o. maka and t. s. o'donovan, "transient thermalelectrical performance modelling of solar concentrating photovoltaic (cpv) receiver," solar energy, vol. 211, pp. 897-907, 2020. [11] w. shockley and h. j. queisser, "detailed balance limit of efficiency of p‐n junction solar cells," journal of applied physics, vol. 32, no. 3, pp. 510-519, 1961. [12] a. o. maka and t. s. o'donovan, "analysis of thermal response and electrical characterisation of triplejunction solar cells based on variable solar spectral irradiance and air mass," thermal science engineering progress, vol. 10, pp. 269-279, 2019. [13] a. o. maka and t. s. o'donovan, "effect of thermal load on performance parameters of solar concentrating photovoltaic: high-efficiency solar cells," energy built environment, vol. 3, no. 2, pp. 201-209, 2022. [14] h. khonkar et al., "ultra-high cpv system development and deployment in saudi arabia," in aip conference proceedings, 2013, vol. 1556, no. 1, pp. 172-175: american institute of physics. [15] e. t. mohamed, a. o. maka, m. mehmood, a. m. direedar, and n. amin, "performance simulation of single and dual-junction gainp/gaas tandem solar cells using amps-1d," sustainable energy technologies assessments, vol. 44, p. 101067, 2021. [16] p. m. rodrigo, r. velázquez, e. f. fernández, f. m. almonacid, and a. lay-ekuakille, "a method for the outdoor thermal characterisation of high-concentrator photovoltaic modules alternative to the iec 62670-3 standard," energy, vol. 148, pp. 159-168, 2018. [17] c. j. chen, physics of solar energy. john wiley & sons, 2011. isbn: 978-0-470-64780-6. this article is an open-access article distributed under the terms and conditions of the creative commons attribution (cc by) license (https://creativecommons.org/licenses/by/4.0/). h asemi et al. /future energy february 2023| volume 02 | issue 01 | pages 09-14 9 article theoretical analysis of the performance and optimization of indirect flat evaporative coolers hamidreza asemi1, rahim zahedi2*, sareh daneshgar3 1faculty of engineering, science and research branch, islamic azad university, tehran, iran 2department of renewable energy and environmental engineering, university of tehran, tehran, iran 3faculty of electrical engineering, iran university of science and technology, tehran, iran a r t i c l e i n f o article history: received 13 july 2022 received in revised form 16 august 2022 accepted 22 august 2022 keywords: indirect evaporative cooling, exergy, optimization *corresponding author email address: rahimzahedi@ut.ac.ir doi: 10.55670/fpll.fuen.2.1.2 a b s t r a c t external-cooling indirect evaporative coolers with different configurations and working air sources are incomprehensively analyzed and compared so far. this paper investigates the mechanism and theory of operation of indirect flat-panel evaporative coolers based on x-analysis. then, based on the second law of thermodynamics analysis, the entropy production rate of the flat-plate heat exchanger of the cooler is calculated. as a result of this analysis, the optimal energy efficiency-evaporation efficiency and cooling capacity values are presented in terms of effective parameters in the design. 1. introduction one of the most common methods used to cool environments is the passage of hot air over wet surfaces at low temperatures, called "evaporative cooling." this method is considered compared to mechanical (compression) cooling systems due to its cheaper and non-use harmful refrigerant in the ozone layer [1]. an essential drawback of this type of cooling is the lack of proper control of ambient humidity. this form is produced by the indirect evaporative cooling method to a large extent, and cooling with the desired quality is prepared. mode of operation as shown in figure 1, indirect evaporative coolers have two primary and secondary airflows. the initial air has no contact with moisture and enters the desired environment after cooling. suppose the secondary air is in direct contact with the water film. in that case, this action causes the water film to evaporate and the transformer plates to cool down, eventually removing heat from the primary air. the mixture of these two breaths of air provides favorable conditions for the environment. rawabawale and sapali [2] analytically evaluated the influence of size variation of the cooling tower on exergy loss and found that the cooling tower with a larger length than height yields smaller exergy loss with higher thermal efficiency. kiyaninia et al. [3] experimentally and theoretically investigated the exergoeconomic performance of a solar photovoltaic-based direct evaporative air-cooling system. the results showed that for an inlet air with a temperature of 30oc and relative humidity of 30%, the maximum system exergy efficiency was obtained at about 20%. martineza et al. [4] and nada et al. [5] studied the energy and exergy performance of different wet pad materials of evaporative coolers through experiments and found that the exergy efficiency was between 70% and 94% under different pad thicknesses. this research comparatively analyzes the energy and exergy performance of indirect flat evaporative coolers on the basis of a verified numerical model and experimental correlation. 2. thermal analysis the control volume is considered for thermal analysis of the cooler according to figure 2. it is worth mentioning that the analysis of the mass heat transfer process of this type of air conditioner is complex. therefore, in the thermal study, it is necessary to consider hypotheses to do the calculations quickly. hypotheses are: • lewis number: 1 = le • mass heat transfer coefficients are assumed to be constant. future energy open access journal https://doi.org/10.55670/fpll.fuen.2.1.2 february 2023| volume 02 | issue 01 | pages 09-14 journal homepage: https://fupubco.com/fuen issn 2832-0328 mailto:rahimzahedi@ut.ac.ir https://doi.org/10.55670/fpll.fuen.2.1.2 https://fupubco.com/fuen h asemi et al. /future energy february 2023| volume 02 | issue 01 | pages 09-14 10 • the effect of mass heat transfer between secondary air droplets is considered to be negligible. • saturation enthalpy changes with humid secondary air temperature are linear. • the plates are considered completely wet. • heat transfer to the environment is negligible. figure 1. isometric view of indirect evaporation cooler figure 2. control volume of an indirect evaporative cooler 2.1 energy balance for primary air according to figure 2, the primary air loses its heat significantly, so: 𝑈0(𝑡 − 𝑡𝑤) = �̇�𝑃𝑐𝑃 ⅆ𝑡 (1) as a result, after integration, the number of primary air units using x-theory is as follows [6]. (𝑁𝑇𝑈)𝑝 = 𝑈0𝐴 𝑚𝑃𝑐𝑃 = −ln ( 𝑡2−𝑡1 𝑡1−𝑡𝑤 ) (2) the initial air impact factor will be as follows. 𝜀𝑃 = 1 − 𝑒𝑥𝑝(𝑁𝑇𝑈)𝜌 = 𝑡1−𝑡2 𝑡1−𝑡𝑤 (3) 2.2 energy balance for secondary air in figure 2, a differential element from the air contact surface shows a wet surface. thermal balance for the earth element from [7]: ℎ𝐷(ℎ𝑤 − ℎ) ⅆ𝐴 = �̇�𝑠 ⅆℎ (4) by integrating equation (5) (𝑁𝑇𝑈)𝑠 = ℎ𝐷𝐴 �̇�𝑠 = ℎ𝐷𝑐𝑃𝐴 �̇�𝑠𝑐𝑃 = −ln ( ℎ0−ℎ𝑤 ℎ0−ℎ𝑖 ) (5) after arranging the above equation, the coefficient of the effect of the secondary air is as follows: 𝜀𝑠 = 1 − 𝑒𝑥𝑝(−𝑁𝑇𝑈)𝑠 = ℎ𝑖−ℎ0 ℎ𝑖−ℎ𝑤 (6) according to the linear proportion of changes in the enthalpy of humid air with the ratio of temperatures [8]: 𝑐𝑤𝑏 = ℎ0−ℎ𝑖 𝑡𝑤0− 𝑡𝑤𝑖 (7) cwb is the specific saturation temperature of equation (7) as follows. 𝜀𝑠 = 1 − 𝑒𝑥𝑝(−𝑁𝑇𝑈)𝑠 = 𝑡𝑤0− 𝑡𝑤𝑖 𝑡𝑤𝑖− 𝑡𝑤 (8) assuming 1 = le (i.e., assuming that the rate of penetration of the rate of heat transfer and mass diffusion are the same at the contact surface of air-water): 𝐿𝑒2∕3 = ℎ𝐶 ℎ𝐷𝐶𝜌 → ℎ𝐶 = 𝐶𝜌ℎ𝐷 (9) with replacement (9) in (5): (𝑁𝑇𝑈)𝑠 = ℎ𝑐𝐴 �̇�𝑠𝑐𝑃 = −ln ( 𝑡𝑤0− 𝑡𝑤 𝑡𝑤𝑖− 𝑡𝑤 ) (10) 2.3. energy balance between the primary and secondary air by defining the coefficient of cooling effect in indirect evaporative coolers [9]: 𝜀𝑠 = 𝑡1−𝑡2 𝑡1− 𝑡𝑤𝑖 (11) the energy balance equation between the primary and secondary air will follow: �̇�𝑝𝑐𝑃(𝑡1 − 𝑡2) = �̇�𝑠 (ℎ𝑂 − ℎ𝑖) (12) incidentally, according to equation (7) 𝑡2 = 𝑡1 − 𝑐𝑚𝑎𝑥 𝑐𝑚𝑖𝑛 (𝑡𝑤0 − 𝑡𝑤𝑖) (13) while cmin and cmax are: 𝑐𝑚𝑖𝑛 = �̇�𝑝𝑐𝑃 (14) 𝑐𝑚𝑎𝑥 = �̇�𝑠𝑐𝑤𝑏 (15) by placing equation (13) in equation (2): h asemi et al. /future energy february 2023| volume 02 | issue 01 | pages 09-14 11 𝜀𝑃 = 𝑐𝑚𝑎𝑥 𝑐𝑚𝑖𝑛 ( 𝑡𝑤0− 𝑡𝑤𝑖 𝑡1− 𝑡𝑤 ) (16) by placing equation (6) in equation (5), water temperature 𝑡𝑤 = 𝜀𝑠( 𝑐𝑚𝑎𝑥 𝑐𝑚𝑖𝑛 )+𝜀𝑃+𝑡1 𝜀𝑠( 𝑐𝑚𝑎𝑥 𝑐𝑚𝑖𝑛 )+𝜀𝑃 (17) by placing equation (17) in equation (2), the coefficient of the cooling effect of the cooler is: 𝜀𝐶 = 1 1 𝜀𝑃 + 1 𝜀𝑆 ( �̇�𝑝𝑐𝑃 �̇�𝑠𝑐𝑤𝑏 ) (18) in addition, to calculate the heat transfer coefficients of the primary and secondary air passages and the sticky surface, respectively [10] are: 𝑁𝑢 = 0.023𝑅𝑒𝐷ℎ 4/5𝑃𝑟1/2 𝑅𝑒 > 2300 (19) 𝑁𝑢 = 7.54 𝑅𝑒 ≤ 2300 (20) where: 𝑅𝑒𝐷ℎ = 4�̇� 𝛱𝐷𝜇 , 𝐷ℎ = 2𝑏 2.4. calculate the drop in air flux by multiplying the capacity of the air conditioner the pressure drop of the whole system due to local friction drops is calculated according to the following equations [11]. 𝛥𝑃𝑓 = 𝑓 𝐿 𝐷ℎ 𝑣2𝜌 2 (21) 𝛥𝑃𝑙 = ∑ 𝐾 𝑣2𝜌 2 (22) 𝛥𝑃𝑡 = 𝛥𝑃𝑓 + 𝛥𝑃𝑙 (23) as a result, the required power of the device blower, assuming ηm =1, is [12]: 𝑤 = �̇�𝑃𝛥𝑃𝑃 𝜂𝑃 + �̇�𝑠𝛥𝑃𝑠 𝜂𝑠 (24) 2.5. calculating the energy efficiency ratio the energy efficiency ratio of eer is equal to 𝐸𝐸𝑅 = 𝑄𝑐 𝑤 (25) where qc is the cooling capacity of the indirect air conditioner can be calculated from the following equation. 𝑄𝑐 = �̇�𝑝𝑐𝑃(𝑡1 − 𝑡2) (26) 2.6. analysis of the second law for indirect plate evaporative coolers there are several evaluation criteria for the optimal operating conditions of thermal systems. one of the most reliable criteria is the second law analysis or exergy analysis. figure 2 shows that an indirect plate air conditioner is like a plate heat exchanger with the opposite flow for secondary airflow and cross-flow for primary air. in order to obtain a statement to calculate the initial airflow exergy rate, we assume that the surface temperature of the plates is constant throughout the length of the plate, which is a reasonable assumption for this type of cooler. the rate of production of primary exergies of such plates is as follows, which includes two parts: output and output [13, 14]. (𝑒𝑡,𝑝) 𝑖𝑛 = 𝑅𝑎𝑡1ln (1 + 1.6)𝜔𝑜 (27) (𝑒𝑡,𝑝) 𝑜𝑢𝑡 = 𝑐𝑃𝑡0 ( 𝑡2 𝑡0 − 1 − 𝑙𝑛 𝑡2 𝑡0 ) + 𝑅𝑎𝑡0 ln (1 − ∆𝑃 𝑃0 ) + 𝑅𝑎𝑡𝑜ln (1 + 1.6)𝜔𝑜 (28) moreover, entropy production for secondary air is in equations (29) and (30). in addition to heat transfer and friction, it also has the mass transfer term due to evaporation, which consists of input and output. (𝑒𝑡,𝑆) 𝑖𝑛 = (𝑐𝑃 + 𝜔𝑐𝑃𝑣)𝑡0 ( 𝑡𝑊𝑖 𝑡0 − 1 − 𝑙𝑛 𝑡𝑊𝑖 𝑡0 ) + (1 + 1.6𝜔𝑜)𝑅𝑎𝑡0 ln ( 𝑃 𝑃0 ) + 𝑅𝑎𝑡0[(1 + 1.6𝜔𝑜)𝑙𝑛 1+1.6𝜔𝑜 1+1.6𝜔 + 1.6𝜔𝑜 ln 𝜔 𝜔0 ] (29) (𝑒𝑡,𝑆) 𝑜𝑢𝑡 = (𝑐𝑃 + 𝜔𝑜𝑢𝑡𝑐𝑃,𝑣)𝑡0 ( 𝑡𝑊𝑜 𝑡0 − 1 − 𝑙𝑛 𝑡𝑊𝑜 𝑡0 ) +(1 + 1.6𝜔𝑜𝑢𝑡) 𝑅𝑎𝑡0 ln (1 − ∆𝑃 𝑃0 ) + 𝑅𝑎𝑡0[(1 + 1.6𝜔𝑜𝑢𝑡)𝑙𝑛 1+1.6𝜔𝑜 1+1.6𝜔𝑜𝑢𝑡 + 1.6𝜔𝑜𝑢𝑡 ln 𝜔𝑜𝑢𝑡 𝜔𝑜 ] (30) as a result, the total entropy production rate is calculated as follows: 𝑠𝑔𝑒𝑛 = 1 𝑇0 {[�̇�𝑃𝑒𝑡𝑝 + �̇�𝑠𝑒𝑡𝑠] 𝑖𝑛 −[�̇�𝑃𝑒𝑡𝑝 + �̇�𝑠𝑒𝑡𝑠] 𝑜𝑢𝑡 } (31) based on the entropy production equations (27 to 31), the design method of indirect coolers mentioned in the first part of the article, the functional relationship of the total entropy production rate is as follows: �̇�𝑔𝑒𝑛 = 𝑓(�̇�𝑝, �̇�𝑠, 𝐿, 𝑤) (32) 3. results and discussion a computer code has been prepared to calculate the design values such as the temperature of the air leaving the air conditioner, the energy efficiency ratio, and to observe the effect of effective parameters such as plate length and mass flow rate on the eer according to figure 3. figures 3 and 4 result from these calculations. as shown in figure 4, the initial outlet air temperature of the t2 model was compared with the experimental reference results [4]. the difference between the modeling results and the experimental results is about 3%, and this difference is due to ignoring the effects of environmental parameters in modeling. figure 5 compares the cooling effect of x with the experimental results [4]. after designing the system according to equations (27) to (32), the entropy produced by the system is investigated. it is evident that the system, based on the design conditions, is faced with limitations in selecting the values of w and l. due to these limitations, the mentioned values must be considered in a specific range. the variables are examined by keeping the other parameters constant on the entropy production rate of the system, and finally, the optimal values of the system design are obtained. it is worth noting that the optimization of design variables by the exergy method (the second law of thermodynamics) is not economically optimal for systems. therefore, in practice, in order to optimize the systems, both thermo economic studies should be done. h asemi et al. /future energy february 2023| volume 02 | issue 01 | pages 09-14 12 figure 6 shows the entropy production rate in terms of the secondary air flow rate changes at a constant value of the primary airflow rate. the design shows that the maximum and minimum point distance values are minimal. figure 7 shows the entropy production rate of initial airflow. as shown in this figure, the maximum and minimum entropy production points are not within the design range. this trend indicates the low sensitivity of the entropy production rate to the initial air flow rate. figure 4. comparison of the initial air outlet temperature of the model with experimental results figure 5. comparison of the cooling coefficient of the model air conditioner with the experimental results figures 8 and figure 9 show the entropy production rate in secondary air discharge in different primary discharges and the entropy production rate in secondary air discharge in different primary discharges, respectively. as can be seen, at a certa in amount of primary or secondary air flow rate, the minimum entropy production can be achieved by selecting another reasonable flow rate. figure 10 also shows the entropy production rate in terms of plate length. it is observed that the longer the plate lengths are selected in this type of short coolers, the more the entropy production rate figure 3. flowchart design of direct evaporative coolers h asemi et al. /future energy february 2023| volume 02 | issue 01 | pages 09-14 13 increases. as a result, the length of the pages should be selected by the primary and secondary discharges for maximum efficiency. figure 6. entropy production rate in terms of secondary air flow figure 7. entropy production rate in terms of initial air flow figure 8. entropy production rate in terms of primary air discharge in secondary discharges figure 9. entropy production rate in terms of secondary air flow in primary flows figure 10. entropy production rate in terms of plate length in secondary discharges 4. conclusions in this study, the energy and exergy performance of cooling indirect flat evaporative coolers and direct evaporative coolers are compared and analyzed on the basis of the developed mathematical model. the main conclusions are given as follows: 1) indirect evaporative coolers have better performance than direct evaporative coolers in dry areas. 2) exergy analysis is an excellent tool to optimize the parameters affecting the performance of indirect evaporators. the increased fresh air flowrate reduces the cooling efficiency and exergy efficiency of all evaporative coolers. ethical issue the authors are aware of and comply with best practices in publication ethics, specifically with regard to authorship (avoidance of guest authorship), dual submission, manipulation of figures, competing interests, and compliance with policies on research ethics. the authors adhere to publication requirements that the submitted work is original and has not been published elsewhere in any language. data availability statement data sharing is not applicable to this article as no datasets were generated or analyzed during the current study. conflict of interest the authors declare no potential conflict of interest. h asemi et al. /future energy february 2023| volume 02 | issue 01 | pages 09-14 14 abbreviations and greek symbols a effective heat transfer surface (m2) b the distance between the two cooler plates (m) cmax maximum heat transfer capacity(w/oc) cmin minimum heat transfer capacity(w/oc) cp specific heat capacity to air (kj/kg oc) cpv specific heat capacity of water vapor (kj/kg oc) dh hydraulic diameter (m) et,p primary air exergy (w/kgk) et,s secondary air exergy (w/kgk) hi enthalpy of secondary air inlet (kj/kg) ho enthalpy of secondary air outlet (kj/kg) hw enthalpy of air saturation at the common air and water level (kj/kg) k local drop coefficient l the length of the plates of indirect evaporators (m) le louis number �̇�𝑎 air mass flow (kg/s) �̇�𝑝 primary air flow (kg/s) �̇�𝑠 secondary air flow (kg/s) eer energy efficiency ratio f friction coefficient hc conduction heat transfer coefficient (w/m2oc) hd mass transfer coefficient (kg/m2s) nu nusselt number 𝛥𝑃𝑓 pressure drop due to friction (pa) 𝛥𝑃𝑙 local pressure drop (pa) 𝛥𝑃𝑝 initial pressure drop 𝛥𝑃𝑠 secondary pressure drop pr prandt number re reynolds number sgen production entropy t1 dry bubble temperature of the primary air inlet t2 dry bubble temperature of the primary air outlet twi wet bubble temperature of secondary air inlet two wet bubble temperature of secondary air outlet tw saturation temperature of the joint surface of air and water to ambient temperature ṁw mass flow of water ntup number of primary air transfer units ntus number of secondary air transmission units u0 the total heat transfer coefficient between the primary air and the common surface of the secondary air of water 𝜀𝐶 cooler effect coefficient 𝜀𝑝 primary air impact coefficient 𝜀𝑠 secondary air impact coefficient ρ air density 𝜂𝑝 fan efficiency of the first part 𝜂𝑠 secondary fan efficiency 𝜇 adhesion coefficient ω𝑜𝑢𝑡 humidity for secondary exhaust air ω0 humidity for the environment references [1] y. yang, g. cui, and c. q. lan, "developments in evaporative cooling and enhanced evaporative cooling-a review," renewable and sustainable energy reviews, vol. 113, p. 109230, 2019. [2] n. rawabawale, "exergy analysis ofthe cross current cooling tower," journal of thermal engineering, vol. 6, no. 4, pp. 499-510, 2020. [3] a. kiyaninia, h. karimi, and v. m. avargani, "exergoeconomic analysis of a solar photovoltaicbased direct evaporative air-cooling system," solar energy, vol. 193, pp. 253-266, 2019. [4] p. martínez, j. ruiz, p. martínez, a. kaiser, and m. lucas, "experimental study of the energy and exergy performance of a plastic mesh evaporative pad used in air conditioning applications," applied thermal engineering, vol. 138, pp. 675-685, 2018. [5] s. nada, a. fouda, m. mahmoud, and h. elattar, "experimental investigation of energy and exergy performance of a direct evaporative cooler using a new pad type," energy and buildings, vol. 203, p. 109449, 2019. [6] z. duan et al., "indirect evaporative cooling: past, present and future potentials," renewable and sustainable energy reviews, vol. 16, no. 9, pp. 68236850, 2012. [7] r. zahedi, s. daneshgar, m. a. n. seraji, and h. asemi, "modeling and interpretation of geomagnetic data related to geothermal sources, northwest of delijan," renewable energy, 2022. [8] c. guo, q. liu, b. zheng, y. you, and y. li, "development of model based on condensation area ratio and effect on heat transfer capacity of indirect evaporative cooling," applied thermal engineering, vol. 164, p. 114557, 2020. [9] r. zahedi, a. shaghaghi, m. t. tahooneh, and a. ahmadi, "numerical simulation of combustion of sulfide-biomass concentrate ingredients and contaminants in copper furnace smelting," future energy, vol. 2, no. 1, 2023. [10] h. yang, w. shi, y. chen, and y. min, "research development of indirect evaporative cooling technology: an updated review," renewable and sustainable energy reviews, vol. 145, p. 111082, 2021. [11] j. wu et al., "investigation of heat transfer and pressure drop of co2 two-phase flow in a horizontal minichannel," international journal of heat and mass transfer, vol. 54, no. 9-10, pp. 2154-2162, 2011. [12] s. suryawanshi, t. m. chordia, n. nenwani, h. bawaskar, and s. yambal, "efficient technique of airconditioning," in proceedings of the world congress on engineering, 2011, vol. 3, pp. 2036-2041. [13] u. sajjad et al., "a review of recent advances in indirect evaporative cooling technology," international communications in heat and mass transfer, vol. 122, p. 105140, 2021. [14] s. daneshgar and r. zahedi, "optimization of power and heat dual generation cycle of gas microturbines through economic, exergy and environmental analysis by bee algorithm," energy reports, vol. 8, pp. 13881396, 2022. this article is an open-access article distributed under the terms and conditions of the creative commons attribution (cc by) license (https://creativecommons.org/licenses/by/4.0/). s. sheykhbaglou/future energy february 2023| volume 02 | issue 01 | pages 27-37 27 article properties of turbulent non-premixed methane/air flames in a miniature-scale swirl burner under different coaxial airflow swirl numbers soroush sheykhbaglou*1 1school of mechanical, aerospace, and maritime engineering, amirkabir university of technology (tehran polytechnic), no. 350, hafez ave, tehran, iran a r t i c l e i n f o article history: received 24 august 2022 received in revised form 24 september 2022 accepted 30 september 2022 keywords: miniature swirl burner, flame lift-off, flame characteristics, intermittency distribution, otsu threshold, flame pulsating displacement *corresponding author email address: soroush.sheykh@aut.ac.ir doi: 10.55670/fpll.fuen.2.1.5 a b s t r a c t this study investigates the dynamics and properties of non-premixed methane/air flames under three swirl numbers by segmenting flame images using the otsu thresholding technique. under three operating conditions, the lean blow out (lbo) and flame length, lift-off height, maximum width, flame angle, and flame pulsing displacements in terms of flame center of gravity, length, and width are measured and compared. a high-speed camera is used to record video of flames, and the image processing of frames collected from a high-speed video was accomplished by using the intermittency distribution method to quantitatively compare flame attributes. the findings show that increasing the swirl number from 0.5 to 0.7 generally has an unfavorable effect on the lbo at given fuel flow rates, and the lbo of flames under 35° (0.6 swirl number) and 40° (0.7 swirl number) swirlers has decreased up to about 15% and 40%, respectively when compared with a 30° swirler (0.5 swirl number). additionally, observations indicate that the flame length (𝐿) and liftoff height (𝐿𝑂) drop as the swirl number rises, although the flame width (𝑊) and angle (𝛼) show an ascending tendency. besides, flame lift-off reveals an increasing-decreasing trend with an increment in the airflow, and flame length decreases as the airflow rate increases. it was also observed that flame pulsating displacements in terms of center of gravity (𝛿𝐶𝐺), length (𝛿𝐿), and width (𝛿𝑊) increases with an increase in the fuel flow rate, and as the swirl number is increased, 𝛿𝐶𝐺 and 𝛿𝐿 lessens, while 𝛿𝑊 increases. 1. introduction image segmentation is a key step that enables feature extraction and identification in the field of image analysis and processing. several techniques are used to perform the segmentation task: (1) threshold-based methods, (2) edgebased methods, (3) region-based methods, (4) clusteringbased methods, (5) partial differential equation-based methods, and (6) artificial neural network-based methods [1]. thresholding-based approaches are the most often used segmentation techniques among them because they are straightforward, simple to grasp, and easy to use [1, 2]. combustion device design must take into account aspects such as flame form and size [3]. threshold segmentation of pictures from photography and high-speed video recordings is a cheap and efficient way to obtain flame characteristics. several relevant studies to obtain flame characteristics from image processing can be found in [4-12], which are generally based on the intermittency distribution approach. the flame height and lift-off of propane turbulent jet diffusion flames attenuated by carbon dioxide at ambient temperature and pressure were studied by tao et al. [9]. they discovered that when 𝐶𝑂2 concentration increases, and the flame height drops. additionally, it was shown that when 𝐶𝑂2 concentration rises, the flame lift-off height also rises. future energy open access journal https://doi.org/10.55670/fpll.fuen.2.1.5 february 2023| volume 02 | issue 01 | pages 27-37 journal homepage: https://fupubco.com/fuen issn 2832-0328 mailto:soroush.sheykh@aut.ac.ir https://doi.org/10.55670/fpll.fuen.2.1.5 https://fupubco.com/fuen s. sheykhbaglou/future energy february 2023| volume 02 | issue 01 | pages 27-37 28 the flame length of buoyant turbulent slot flames was examined by gao et al. [13]. they created a rough prediction correlation for the length of the flame. they found that the flame length for the buoyancy-dominated and momentumdominated flames is proportional to (𝐹𝑟𝑚)1/3 and (𝐹𝑟𝑚)0(modified froude number that shows the relationship between initial speed and buoyancy), respectively. zhou et al. [10] analyzed the flame height and lift-off height of rectangular fuel jet source fires. the flame buoyancymomentum froude number varied between 0.38 and 3.06. it was noticed that as the aspect ratio rises at a certain heat release rate, the flame height decreases. zhang et al. [5] examined the features of curving flames in a tunnel model of a smaller size. they discovered that the recorded flame length under these conditions is almost comparable to that of flames in open space. in addition, they offered an empirical model for predicting the flame's tilt angle. ligang et al. [14] measured the height of the coal jet flame using image processing. image processing included the roi (region of interest), filtering, grayscale, binarizing, and edge detection processes. the height of the flame was seen to decrease when the oxidizer temperature and main air velocity increased. since swirl plays a significant role in flame stability, swirling flames are often used in practical combustion systems such as gas turbine engines and industrial burners [15, 16]. it is commonly acknowledged that swirl increases the local velocity fluctuations, hence increasing the turbulent burning velocity. moreover, the swirl-induced recirculation zone may function as a heat source, causing heated products to interact with fresh reactants upstream [17]. because of high energy density of hydrocarbon fuels, combustion-based micro-power devices are a more attractive option for portable power generation than rechargeable batteries [18-22]. in these systems, swirling flows are one method for flame stabilization [2330]. to the best of authors’ knowledge, there has never been research on the effects of swirl number on turbulent flame dynamics and characteristics by taking advantage of threshold-based image segmentation method. using the otsu threshold approach, this study compares the properties of turbulent swirling flames, including flame length, lift-off height, angle, maximum width, and pulsating displacements (in terms of flame center of gravity, length, and width), for three swirl numbers. 2. experimental setup figure 1(a) depicts the experimental setup and flow delivery system layout. air and fuel are supplied by an air compressor and a high-pressure cylinder, respectively, and their pressures are then regulated using pressure reduction valves. methane was used as fuel, and azbil mpc0020 and kobold dms-5 mass flow controllers with 1% full-scale accuracy regulate the flow of air and methane, respectively. images of flames were taken with a nikon v1 camera in its high-speed mode (400 fps) with a resolution of 640 × 240, a f-number of f/2.8, and a sensitivity of hi 1. the miniaturescale burner employed in this study is illustrated in figure 1(b). the core component of the burner is its axial flat vane swirlers which are made of polylactic acid (pla). the construction of these swirlers was met using additive manufacturing techniques, and their geometrical characteristics are presented in table 1. this burner's fuel nozzle consists of five 1 𝑚𝑚 holes that are encircled by coaxial air. 3d-printed flat vane axial swirler are used to swirl coaxial air. beer and chigier proposed the following equation to get the well-known dimensionless theoretical swirl number for a swirler with a constant vane angle [23]: 𝑆𝑛 = 2 3 1− ( 𝐷ℎ 𝐷𝑠𝑤 ) 3 1−( 𝐷ℎ 𝐷𝑠𝑤 ) 2 tan 𝜃 (1) where 𝐷ℎ is the swirler hub diameter, 𝐷𝑠𝑤 is the swirler diameter, and 𝜃 is the vane angle from the centerline. table 1. specifications of studied swirlers swirler no. vane angle, 𝜃, (°) swirl number, 𝑆𝑛 , (−) 1 30 0.5 2 35 0.6 3 40 0.7 no. of vanes: 10 vane thickness: 0.5 𝑚𝑚 hub diameter, 𝐷ℎ: 4.5 𝑚𝑚 tip diameter, 𝐷𝑠𝑤: 6.5 𝑚𝑚 swirl direction: counter-clockwise 3. results and discussion in this section, the flame lean blowout limits, flame characteristics, including flame length, lift-off height, maximum width, flame angle, and flame pulsing displacements in terms of flame center of gravity, length, and width are measured and compared under three coaxial airflow swirl numbers and three operating conditions (table 2). table 2. experimental conditions case airflow rate, (𝑠𝑙𝑝𝑚) methane flow rate, (𝑠𝑙𝑝𝑚) coaxial airflow swirl number, 𝑆𝑛, (−) 1 3.0 0.100 0.5 2 3.0 0.150 0.5 3 3.0 0.200 0.5 4 3.0 0.100 0.6 5 3.0 0.150 0.6 6 3.0 0.200 0.6 7 3.0 0.100 0.7 8 3.0 0.150 0.7 9 3.0 0.200 0.7 3.1 lean blowout (lbo) limits in the present study, flame lean blowout limits are determined according to [12, 24]: (1) initially, a sustained diffusion flame is produced at a predetermined fuel flow rate, while the airflow rate is maintained at its minimum; (2) second, the airflow rate is increased by 0.1 slpm while the fuel flow rate stays constant until the flame is extinguished; (3) the airflow rate at which the flame blows out (extingushes) is the lean blow out limit for the adjusted fuel flow rate; (4) this process is performed three times, and the average values are provided in this paper. s. sheykhbaglou/future energy february 2023| volume 02 | issue 01 | pages 27-37 29 (a) (b) figure 1. (a) experimental setup and flow delivery system, (b) miniature-scale swirl burner s. sheykhbaglou/future energy february 2023| volume 02 | issue 01 | pages 27-37 30 figure 2(a) compares lbo values for three swirl numbers of 0.5, 0.6, and 0.7 for methane flow rates ranging from 0.050 to 0.500 slpm with an increment of 0.050 slpm. it has been seen that the equivalence ratio at which the flame blows out rises as the fuel flow rate is increased. it has also been seen that increasing the swirl number from 0.5 to 0.7 generally has an unfavorable effect on the lbo at given fuel flow rates (the flame blows out at lower airflow rates or higher equivalence ratio). this can be attributed to the following factors: (a) interaction between flame base and fuel nozzle due to an increase in the recirculation zone; (b) entrainment of cold outside air due to the recirculation zone; and (c) flame cooling due to an increase in the rate of strain on the flame with increasing swirl strength. in order to properly examine the impacts of raising the coaxial airflow swirl number from 0.5 to 0.7 on lbo, the findings of figure 2(a) are compared to 30° swirler using the following equation: diff in φ = 𝛷35° 𝑜𝑟40° 𝑠𝑤𝑖𝑟𝑙𝑒𝑟 − 𝛷30° 𝑠𝑤𝑖𝑟𝑙𝑒𝑟 𝛷30° 𝑠𝑤𝑖𝑟𝑙𝑒𝑟 × 100% (2) (a) (b) figure 2. (a) lean blow out (lbo), (b) percentage difference in lbo compared with 30° swirler the percentage difference in the equivalence ratio at lbo under two swirl numbers is depicted in figure 2(b). negative and positive values indicate lower and higher equivalence ratios for lbo compared to 30° swirler, respectively. at two fuel flow rates of 0.050 and 0.100 slpm, a 35° swirler produces lower equivalence ratios for lbo. however, at fuel flow rates larger than 0.100 slpm, flames formed under swirl numbers of 0.6 and 0.7 blow out at higher equivalence ratios than flames formed under swirl number 0.5. for flames under 35° and 40°, the lbo has decreased up to about 15% and 40%, respectively. 3.2 flame characteristics in this section, the process for measuring is as follows: first, the fuel is introduced at predefined flow rates (0.100, 0.150, and 0.200), ignited, and a sustained diffusion flame is created for each swirler; second, the airflow rate is steadily raised until it achieves the desired value of 3; then, a nikon v1 is used to record a high-speed video of the formed flame at 400 fps for 5 seconds, resulting in 2000 frames. within the scope of this investigation, visual luminosity served as the indicator for flame contours. the objective was to more clearly depict form variations seen in flame photographs (not to get an accurate location of the reaction zone). thresholding-based approach, which is the most common segmentation method because of its simplicity, ease of understanding, and implementation, is used to extract flame contours of an image [1, 2]. the intermittency distribution approach is used to examine and compare flame length, liftoff height, maximum width, and angle. this methodology has also been used in other research too [4-6, 9-11, 25]. in this procedure, the probability of a flame's existence is determined using the following steps: (a) 2000 frames are converted to grayscale and then preprocessed; (b) the otsu thresholding algorithm, one of the most common methods in combustion, is applied to these grayscale images; (c) the thresholded images are binarized; (d) intermittency distribution is obtained by averaging the obtained images; (e) flame existence probability is obtained using a color bar (figure 3 and the first row of figure 5); (f) a threshold of 0.5 is applied to maintain the part with existence probability greater than 50%; (g) by converting the image coordinates to metric coordinates, flame length, lift-off height, maximum width, and angle are obtained (figure 3). in figure 4, quantitative comparisons of the flame's length (l), lift-off height (lo), maximum width (w), and angle (α) are shown for three different swirl numbers and operating conditions. in these figures, l, lo, and w are normalized to swirler diameter (d_sw). it is observed that the flame length and liftoff height drop as the swirl number rises, although the flame width and angle show an ascending tendency. additionally, it has been shown that raising the methane flow rates causes an increase in these variables except for the flame angle. the radial mixing of air and fuel is improved and accelerated by increasing the swirl number, which also accelerates chemical processes. by moving the reaction zone upstream, swirl may also extend the residence duration during which reactants and products can coexist. as the swirl number rises, fuel can also be efficiently entrained. all of these may shorten the visible flame length as well the flame lift-off height. in addition, when the swirl number is rising, the flame width and angle increase because radial mixing is improved and the fuel and air mixture is pushed outward. s. sheykhbaglou/future energy february 2023| volume 02 | issue 01 | pages 27-37 31 when the fuel flow rate is increased for swirling flames, the entrainment by swirling air diminishes owing to accelerated fuel velocity, resulting in more fuel burning in diffusion mode by the air from the surroundings. as a consequence, the flame lengthens, and its lift-off height increases with an increment in the fuel flow rate. on the other side, the fuel nozzle geometry may be responsible for the rise in flame width and angle with an increase in fuel flow rate. it is also observed that the flame lift-off height and angle exhibit the least sensitivity to an increase in fuel flow rate for a swirl number of 0.7. this is shown in table 3, which was generated using matlab's curve-fitting toolbox with 95% confidence bounds (linear curve-fitting). table 3. slopes of linear fitted curves for normalized flame lift-off and angle swirl number, 𝑆𝑛 , (−) 𝐿𝑂/𝐷𝑠𝑤 versus fuel flow rate 𝛼 versus fuel flow rate 0.5 1.662 −290.2 0.6 2.123 −273.3 0.7 0.7077 −189 figure 5 depicts the mean flame shape (mean of 2000 frames for each operating condition) and its normalized intensity map as a function of the swirl number at 0.200 and 3 slpm methane and airflow rates, respectively. it has been shown that the bottom section of the flame has the greatest normalized intensity value, and by raising the swirl number, this area expands radially, the flame's width grows, and its length reduces. the mean flame contour (boundary) is obtained after applying the otsu threshold to the grayscale mean flame and separating the foreground and background. the change of flame shape with airflow rate at a given fuel flow rate of 0.200 slpm for a 30° vane angle swirler (s_n=0.5) is shown in figure 6 (single frames from 2000 frames of each operating condition is presented only). the following observations can be made: flame lift-off reveals an increasing-decreasing trend with an increment in the airflow rate, and the decreasing section corresponds to improved mixing of fuel and air because swirl has shown its effect. flame length is affected by the airflow rate increase, and it decreases as the airflow rate increases. this is consistent with the findings in [26]. for swirling flames, this tendency is the consequence of an increase in turbulence intensity with an increase in airflow rate, which enhances fuel-air mixing and reduces flame length. at airflow rates, when flame lift-off has a declining trend, flame width reduces as airflow rate increases. this may be described as follows: when the swirl exerts its impact, a recirculation zone is created, which recirculates fuel and air, so decreasing the flame width. these findings are similar to other swirl numbers and operating conditions investigated in this research (table 2). in this investigation, the flame's center of gravity as well as its length and width, are used to examine flame fluctuations (pulsating displacements). the flame center is used to determine the position of the flame as a point utilizing the center of gravity concept (mass center in this case). each pixel serves as a local point for calculating the mass center, and the intensity of each pixel represents its mass [27]. to obtain flame fluctuations, the otsu threshold is used to generate binarized images of 2000 frames for each operating condition (boundaries of all 2000 frames are shown simultaneously in figure 7 for methane and airflow rates of 0.200 and 3 𝑠𝑙𝑝𝑚, respectively). the mean center of gravity (𝑥𝐶𝐺,𝑚𝑒𝑎𝑛 , 𝑦𝐶𝐺,𝑚𝑒𝑎𝑛), length (𝐿𝑚𝑒𝑎𝑛), and width (𝑊𝑚𝑒𝑎𝑛) are determined; then, the standard deviation is then used to calculate the flame's pulsating displacement in terms of the flame's center of gravity, length, and width [28]: 𝛿𝐶𝐺 = √ ∑ [(𝑥𝐶𝐺,𝑖−𝑥𝐶𝐺,𝑚𝑒𝑎𝑛) 2 +(𝑦𝐶𝐺,𝑖−𝑥𝐶𝐺,𝑚𝑒𝑎𝑛) 2 ]2000 𝑖= 1 2000 (3) figure 3. definitions of flame length, lift-off height, maximum width, and angle s. sheykhbaglou/future energy february 2023| volume 02 | issue 01 | pages 27-37 32 (a) (b) (c) (d) figure 4. normalized (a) flame length, (b) lift-off, (c) width, (d) angle as a function of swirl number 𝛿𝐿 = √ ∑ (𝐿𝑖−𝐿𝑚𝑒𝑎𝑛)22000 𝑖= 1 2000 (4) 𝛿𝑊 = √ ∑ (𝑊𝑖−𝑊𝑚𝑒𝑎𝑛)22000 𝑖= 1 2000 (5) where 𝐿𝑖 and 𝑊𝑖 stand for the length and maximum width of the 𝑖𝑡ℎ frame, respectively and 𝑥𝐶𝐺,𝑖 and 𝑦𝐶𝐺,𝑖 are the 𝑥 and 𝑦 coordinates of the 𝑖𝑡ℎ frame’s center of gravity. figure 5. flame existence probability, mean flame, its normalized intensity map, and its otsu threshold versus swirl number at fuel and airflow rates of 0.200 and 3 slpm, respectively figure 6. the change of flame shape with airflow rate at a given fuel flow rate of 0.200 slpm for a 30° vane angle swirler (sn = 0.5) s. sheykhbaglou/future energy february 2023| volume 02 | issue 01 | pages 27-37 33 figure 7. fluctuations of flame boundary for methane and airflow rates of 0.200 and 3 slpm under three swirl numbers (obtained from 2000 frames for each experimental condition) figure 1 in appendix i shows the flame length and width difference (𝐿𝑑𝑖𝑓𝑓 = |𝐿𝑖 − 𝐿𝑚𝑒𝑎𝑛|, 𝑊𝑑𝑖𝑓𝑓 = |𝑊𝑖 − 𝑊𝑚𝑒𝑎𝑛|) over time spanning from 0 to 5 𝑠. observations reveal that when the swirl number rises, the peak values for flame length and width differences shift to lower and higher values, respectively. on each figure, the mean values of these differences are also displayed (𝐿𝑑𝑖𝑓𝑓,𝑚𝑒𝑎𝑛 and 𝑊𝑑𝑖𝑓𝑓,𝑚𝑒𝑎𝑛). it is observed that as the swirl number is increased, 𝐿𝑑𝑖𝑓𝑓,𝑚𝑒𝑎𝑛 and 𝑊𝑑𝑖𝑓𝑓,𝑚𝑒𝑎𝑛 show a decreasing and increasing trend, respectively. this is presented quantitatively in figure 2 in appendix i. it is also noted from figure 2 in appendix i that these values (𝐿𝑑𝑖𝑓𝑓,𝑚𝑒𝑎𝑛 and 𝑊𝑑𝑖𝑓𝑓,𝑚𝑒𝑎𝑛) rise when the fuel flow rate increases. the changes of 𝛿𝐶𝐺 , 𝛿𝐿, and 𝛿𝑊 with the swirl number at three fuel flow rates are determined and depicted in figure 3 in appendix i based on the above-mentioned formulae for quantifying flame fluctuations. it is noticed that flame pulsating displacements in terms of center of gravity (𝛿𝐶𝐺), length (𝛿𝐿), and width (𝛿𝑊) increases with an increase in the fuel flow rate; although the increase in 𝛿𝐶𝐺 from 0.6 swirl number to 0.7 swirl number is negligible. additionally, it has been shown that as the swirl number is increased, 𝛿𝐶𝐺 and 𝛿𝐿 lessens, while 𝛿𝑊 increases. 4. conclusion the in this work, turbulent non-premixed methane/air flame dynamics, and properties in a miniature-scale swirl burner were investigated under three different swirl numbers using high-speed video recordings of swirling flames. for the measurement of flame length, lift-off height, maximum width, and angle, an intermittency distribution approach based on the otsu threshold method for image segmentation was used. furthermore, the flame's center of gravity as well as its length and width, are used to examine flame fluctuations (pulsating displacements). the following are the main conclusions: • increasing the swirl number from 0.5 to 0.7 has an unfavorable effect on the lean blowout (lbo) at a given fuel flow rate (the flame blows out at lower airflow rates or higher equivalence ratio). this can be attributed to the interaction between flame base and fuel nozzle due to an increase in the recirculation zone, entrainment of cold outside air due to the recirculation zone, and flame cooling due to an increase in the rate of strain on the flame with increasing swirl strength. additionally, for flames under 35° (0.6 swirl number) and 40° (0.7 swirl number) swirlers, the lbo has decreased up to about 15% and 40%, respectively, when compared with the 30° swirler (0.5 swirl number). • observations indicate that the flame length (l) and lift-off height (lo) drop as the swirl number rises, although the flame width (w) and angle (α) show an ascending tendency. additionally, it has been shown that raising the methane flow rates causes an increase in these variables except for the flame angle. additionally, flame lift-off reveals an increasing-decreasing trend with an increment in the airflow rate at a specified methane flow rate, and the decreasing section corresponds to improved mixing of fuel and air because swirl has shown its effect. besides, flame length is affected by the airflow rate increase, and it decreases as the airflow rate increases. for swirling flames, this tendency is the consequence of an increase in turbulence intensity with an increase in airflow rate, which enhances fuel-air mixing and reduces flame length. • flame pulsating displacements in terms of center of gravity (δ_cg), length (δ_l), and width (δ_w) increases with an increase in the fuel flow rate; although the increase in δ_cg from 0.6 swirl number to 0.7 swirl number is negligible. additionally, it has been shown that as the swirl number is increased, δ_cg and δ_l lessens, while δ_w increases. ethical issue the author is aware of and complies with best practices in publication ethics, specifically with regard to authorship (avoidance of guest authorship), dual submission, manipulation of figures, competing interests, and compliance with policies on research ethics. the author adheres to publication requirements that the submitted work is original and has not been published elsewhere in any language. data availability statement all data that support the findings of this study are included within the article (and any supplementary files). conflict of interest 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[24] alsulami r, windom b. liquid jet fuel property impacts on combustion performance. journal of propulsion and power. 2020;37. doi: 10.2514/1.b38209. [25] sheykhbaglou s, karami s. comparative study on threshold selection for measuring characteristics of turbulent swirling flames in a miniature-scale swirl burner. signal, image and video processing. 2022. doi: 10.1007/s11760-022-02344-7. [26] patel v, shah r. experimental investigation on flame appearance and emission characteristics of lpg inverse diffusion flame with swirl. applied thermal engineering. 2018;137:377-85. doi: https://doi.org/10.1016/j.applthermaleng.2018.03.10 5. [27] yoon j, kim m-k, hwang j, lee j, yoon y. effect of fuel– air mixture velocity on combustion instability of a model gas turbine combustor. applied thermal engineering. 2013;54(1):92-101. doi: https://doi.org/10.1016/j.applthermaleng.2013.01.03 2. [28] xiong c, liu y, fan h, huang x, nakamura y. fluctuation and extinction of laminar diffusion flame induced by external acoustic wave and source. scientific reports. 2021;11(1):14402. doi: https://doi.org/10.1038/s41598-021-93648-0. https://doi.org/10.1038/s41598-021-93648-0 s. sheykhbaglou/future energy february 2023| volume 02 | issue 01 | pages 27-37 35 appendix i (a) (b) (c) figure 1. fluctuations of flame length and width differences with time (2000 frames in 5 seconds) for methane and airflow rates of 0.200 and 3 slpm under three swirl numbers: (a) 30°; (b) 35°; (c) 40°. s. sheykhbaglou/future energy february 2023| volume 02 | issue 01 | pages 27-37 36 (a) (b) figure 2. (a) ldiff,mean and (b) wdiff,mean as a function of swirl number at three fuel flow rates of 0.100, 0.150, and 0.200 slpm at the airflow rate of 3 slpm s. sheykhbaglou/future energy february 2023| volume 02 | issue 01 | pages 27-37 37 (a) (b) (c) figure 3. flame pulsating displacements in terms of (a) center of gravity, (b) length, and (c) width as a function of swirl number at three fuel flow rates of 0.100, 0.150, and 0.200 slpm and at the airflow rate of 3 slpm m. rajabali pour and m. azimian /future energy may 2022| volume 01 | issue 01 | pages 16-23 16 article analysis of high voltage shunt capacitor bank over-voltage breakdown detection mohsen rajabali pour1, mohammad azimian2* 1malaysia-japan international institute of technology, universiti teknologi malaysia, jalan sultan yahya petra, 54100, kuala lumpur, malaysia 2engineering department, razak faculty of technology and informatics, universiti teknologi malaysia, jln sultan yahya petra, 54100, kuala lumpur, malaysia a r t i c l e i n f o article history: received 10 march 2022 received in revised form 11 april 2022 accepted 17 april 2022 keywords: shunt capacitor banks, component aging over-voltage breakdown, detection method mallet algorithm corresponding author email address: mazimian82@gmail.com doi: 10.55670/fpll.fuen.1.1.11 a b s t r a c t the traditional over-voltage breakdown detection method ignores the suppression of the inrush current of over-voltage breakdown, resulting in low over-voltage signal detection accuracy and a large detection deviation. as a result, a method is proposed for detecting and analyzing the ageing over-voltage breakdown of high voltage shunt capacitor banks. the breakdown model of aged components of the container group is built to determine the breakdown time of the container's overvoltage. based on this, the annual load of the capacitor bank's aged component material is evaluated, and data on overvoltage breakdown strength is collected. the mallet algorithm is used to decompose and convert strength data into electrical signals. the high voltage shunt capacitor's over-voltage breakdown inrush current suppressor is built by combining the second-order under damping circuit and the voltage divider. based on this, the parameters of hv shunt capacitor overvoltage breakdown are obtained, and the detection of hv shunt capacitor overvoltage breakdown of aged hv shunt capacitor banks is completed. the simulation results show that the proposed detection method's over-voltage breakdown output is in perfect agreement with the monitoring device's actual output and has ideal application performance. 1. introduction capacitor faults in substations occur frequently, which pose a great threat to the safe operation of the power grid and cause great economic losses to power enterprises. the failure of shunt capacitors is related to the manufacturing level, operating conditions, and the reliability of the control protection device. the correct analysis of capacitor faults and the reduction of faults, and the improvement of grid reliability is of great importance to the improvement of economic benefits of power enterprises and the society [1-2]. therefore, some good research results have been obtained for the breakdown detection of aged over-voltage of hv shunt capacitor banks in related fields. in literature [3], the overvoltage dynamic control method of circuit breaker was proposed to detect the over-voltage breakdown of aged capacitor banks. develop capacitor overvoltage breakdown strategy. the dynamic puncture characteristics of the contact gap of the shunt capacitor during the over-voltage phase are obtained by using the puncture characteristics measuring device. according to the dispersion of the over-voltage time between the capacitor and the shunt capacitor, the corresponding control strategy of the over-voltage breakdown of the capacitor is developed. this method is difficult to suppress the over-voltage inrush and easy to cause the damage to capacitor equipment in actual operation. literature [4] is analyzed the capacitor group of internal components in the process of running through a string, the second string, and the breakdown of discharge voltage of fault phase capacitor transient variation. the peak value of discharge current is estimated. in the emtp simulation software to establish the breakdown model of the capacitor, calculated and analyzed the breakdown of the element equivalent circuit parameters on the influence of the peak discharge current: the larger the resistance value is, the smaller the peak breakdown current will be. with the increase of resistance value, the decline of the peak breakdown current will slow down. future energy open access journal https://doi.org/10.55670/fpll.fuen.1.1.11 may 2022| volume 01 | issue 01 | pages 16-23 journal homepage: https://fupubco.com/fuen issn 2832-0328 mailto:mazimian82@gmail.com https://doi.org/10.55670/fpll.fuen.1.1.11 https://fupubco.com/fuen m. rajabali pour and m. azimian /future energy may 2022| volume 01 | issue 01 | pages 16-23 17 in this paper, a breakdown model of aged components in the container group is constructed for the breakdown fault of aged capacitors. the mallet algorithm is used to decompose the strength data and convert it into electrical signals. suppress overvoltage breakdown magnetizing inrush current and complete the detection of overvoltage breakdown of high voltage shunt capacitor banks. the result of the simulation experiment verifies that the detection deviation of the proposed method is very small compared with the actual monitoring result and the simulation result, which indicates that the proposed method has certain practical value in engineering. 2. over-voltage breakdown detection of aged hv shunt capacitor banks 2.1. the breakdown model of aging components in the container group was established when the aged element of the hv shunt capacitor bank operates under too high a voltage, the dielectric dissociation increases, and partial discharge may occur, which will increase the dielectric loss and lead to a dielectric breakdown in serious cases. the damage to the capacitor in operation is analyzed. the typical damage of capacitance aged element is the electric breakdown, and the fault feature is a short circuit. assume that the running capacitor has a breakdown failure of an internal capacitance aged element. it is usually the individual components inside the capacitor that break down first, and the faulty component that breaks down becomes short-circuited, causing the faulty capacitor to lose a capacitor string. suppose that the capacitance of a single capacitor is c. the total number of internal capacitance aging components in series is m series (4 strings in this paper). if the faulted capacitor has a series breakdown and the outer fuse is not fusing in time, the equivalent circuit of the faulted capacitor is shown in figure 1. 2.2. breakdown sequence of capacitor overvoltage the over-voltage of high voltage shunt capacitors in different periods is realized according to a certain time sequence. not in the same period, over-voltage said the timing of figure 2. at the initial stage, the hv shunt capacitor is powered on, and the digital signal processor performs the reset operation. at this point, it is necessary to disconnect the contacts of power relays 1k , 2k connected to the hv shunt capacitor, and complete the initialization of different modules. in the second stage, the shunt capacitor enters the standby state. during this period, the shunt capacitor continuously detects the dc voltage of the hv shunt capacitor. when the dc voltage of the hv shunt capacitor circuit is greater than the high limit or less than the low limit, the operation starts from the initial stage again. assuming that the dc voltage in the standby stage is always normal, the third stage will be entered. relay contacts and 2k are closed, the voltage and frequency of the hv shunt capacitor are detected, and the rms value of the shunt capacitor voltage is calculated. after the delay time st b, the effective value of capacitor output frequency and voltage is determined. assuming that both items are in the normal range at this time, then the contact m is closed, and the hv shunt capacitor enters the power generation state after the completion of overvoltage over the same period. assuming that the frequency and voltage of the network are abnormal, the hv shunt capacitor enters the initial stage. cf r1 break f r2 cron vrf i figure 1. fuse fusing capacitor inside not outside string element breakdown equivalent figure initial stage the third stagethe second stage check the output voltage and frequency of capacitor inrush suppressor access continuous detection of capacitor dc voltage 3k1 2k k、 are closed 1 2 3k k k、 、 are break off are break off figure 2. the over-voltage sequence of high voltage shunt capacitor in different periods 2.3. breakdown strength data collection prior to data acquisition, the annual load status of the capacitor bank material needs to be evaluated. unit vector iterative search for each subregion of aging element material, and the iterative search objective function is: 2 , , , 1 1 = + exp( ) t n m i i i t i i t i i i t t i e p p p     = =  + +  (1) where, i , i , i , i , and i are the material loss angle coefficients of conventional unit i capacitor bank elements; t for collecting time, divided into 24 hours a day, each time for one hour; ,i tp refers to the micronized impurities of a unit i in the t period. the material fuel cost and annual load condition compensation of the aged components in the region were taken as the total cost of the breakdown strength data [5]: 2 , , 1 1 ch , t d , 1 ( ) 1 1 + ( ) 2 t n c i i i t i i t t i t d dch t dch t t d f a b p c p p k t w p t  = = = = + +  +    (2) m. rajabali pour and m. azimian /future energy may 2022| volume 01 | issue 01 | pages 16-23 18 where, ia , ib and ic are the environmental cost coefficients of the conventional unit i ; d is the discharge efficiency of capacitor bank elements; ,dch tp is the discharging power of the elements of the capacitor bank at the time; tk is the electricity price at time t ; t is the discharge period; dw is the discharge loss coefficient of capacitor bank elements; chd is the discharge mechanical damage coefficient of capacitor bank components. taking the daily load variance as the safety index of capacitor bank component materials, the average load of 24 time periods in a day is obtained as follows: ,t , , , 1 1 ( ) t d ch t w t dch t t p p p p p t = = + − − (3) by obtaining the average load of aging component materials, the data signal acquisition function of the material breakdown strength of capacitor bank components is obtained: , 2 ,t 1 , ( ) t w t c v d t m dch t p f l p p e p= = − + (4) where, ,tdp is the current load demand of aging element materials at a time t ; ,w tp is the breaking elongation of capacitor bank elements at t a time; ,ch tp is the depolarizing power of the material of the capacitor bank element at t a time. through the capacitor set of components material breakdown strength data acquisition function, can be a variety of biological damage and pollution degree to detect index classification data such as data collection[6].on the basis of obtaining the breakdown strength data of capacitor bank components, the signal conversion of the breakdown strength data is conducted. 2.4. breakdown of strength data signal conversion on the basis of data collection of material breakdown strength of capacitor bank components, signal conversion is carried out on the collected data. mallet algorithm is used to decompose the data and reconstruct the decomposed data [6]. in order to eliminate the component material breakdown strength data of the capacitor bank will cause the deviation of the test result. the data on the material breakdown strength of capacitor bank components are processed. firstly, the data of material breakdown strength of capacitor bank components are decomposed by wavelet, and the data of breakdown strength is converted by signal, and the wavelet is selected. the decomposition level n is calculated, and the breakdown strength data of capacitor bank elements are decomposed into n layers. the wavelet function needs to select an orthogonal wavelet, and the signal conversion formula of the breakdown strength data is as follows: ( ) ( )j j n v n x e x n e l   − =− =  (5) where, ( )x n is the breakdown intensity data signal; ( )jx e  represents a complex number, and the negative number varies with the angular frequency, and the negative number is used to represent the frequency domain signal of the breakdown intensity data;  is distributed between ( , )− + [6-7]. secondly, the high-frequency coefficients in the breakdown strength data of capacitor bank components are detected to reduce the deviation: the breakdown strength data in the n layer are processed with a high-frequency coefficient [8-9]. finally, one-dimensional wavelet reconstruction is carried out for the breakdown strength data: the lowfrequency coefficients in the n layer breakdown strength data and the processed high-frequency coefficients are taken as the basis. the breakdown strength data is reconstructed by a one-dimensional wavelet transform [9]. 1 , , , 1 ( )j t t c ch t dch t trip t d s s p t p t s x e   −= +  −  −  (6) ,trip ts s l=   (7) min maxts s s  (8) where, c is the material detection efficiency of aging components, and ts is the mechanical damage coefficient in the period t ; ,trip ts is the material detection deviation of capacitor bank elements in the period t ; s is the average mechanical damage coefficient per unit distance; l is the breakdown strength; mins and maxs are the upper and lower limits of detection indexes respectively. through the above operation, the parts of the material breakdown strength data of the capacitor bank elements that will cause the deviation of the test results are eliminated [10]. the online test result of material breakdown strength of capacitor bank components is more accurate. 2.5. overvoltageltage breakdown inrush current suppression the over-voltage breakdown inrush current suppressor of high voltage shunt capacitor is constructed by combining the second-order under damping circuit and the voltage divider. it is connected to the third winding of the capacitor to ensure that the voltage amplitude on different windings of the capacitor is different, but the phase is the same in order to eliminate the inrush current that occurs in different overvoltage stages of the hv shunt capacitor. the specific process is described as follows: in the third winding of high voltage parallel capacitor and power connection between the inrush current limiter. disconnect the main winding of the shunt capacitor on the low-voltage side of the transformer and energize the third winding of the capacitor with an inrush current suppressor. steady-state alternating flux is generated in the transformer core in parallel with the capacitor: 2 cos( )m t  = − + (9) where,  is over-voltage angle, m is excitation inductance,  is capacitor reactance, and t is capacitor running time. m. rajabali pour and m. azimian /future energy may 2022| volume 01 | issue 01 | pages 16-23 19 on the basis of the formula (1), implementation of capacitor main winding over-voltage electricity. without considering the active power loss of the hv shunt capacitor, the relationship between excitation voltage u and core flux  in the equivalent circuit of the capacitor is as follows:  2 sin( ) /mu u t d dt  = + = (10) where, u represents the capacitor's power supply side voltage, mu represents the electrified signal of the gate coil of the hv shunt capacitor, d represents the iron core loss in the instant of the capacitor's over-voltage breakdown, dt represents the primary side leakage inductance, and the iron core flux chain  can be expressed as follows: cos( )m t c  = − + + (11) where, c represents the capacitance value. the flux linkage in the iron core of the hv shunt capacitor at different over-voltage periods is conserved, then: 0 cos( ) cos( )m t tt c t   =− + + = + (12) where, 0t t= represents the initial running time of the capacitor, then the magnetic bias in the iron core of the hv shunt capacitor at the moment of over-voltage breakdown is: 0r c = = (13) the transient process of the hv shunt capacitor can be avoided by the above process. the third winding is disconnected at any time after the overvoltage breakdown of the hv shunt capacitor. at this point, there is no effect on the main magnetic circuit of the shunt capacitor, and the steadystate operation can be entered. the inrush current suppressor is realized by a second-order under a damped system. the main reason for using this system is that the characteristic roots of the transfer function of the secondorder under a damped system are a pair of conjugate complex roots. only the damping ratio of the second-order under a damped system needs to be set effectively. it can track the input voltage frequency and phase of each circuit of the hv shunt capacitor. the purpose of restraining the inrush current in each loop is realized. the input voltage source of the hv shunt capacitor is set as follows: 2 sin( )i mu u t = + (14) the corresponding expected output voltage of the second-order under a damped system can be expressed by the following formula: 0 2 [1 exp( / )]sin( )mu u t t t = − − + (15) where, t is the time constant. the input signals ( )iu s and output signals 0 ( )u s of each circuit of the hv parallel capacitor are laplace transform [11]. there are: 2 2 0 2 2 2 2 ( ) 2 2 1 ( ) 2 ( ) ( 1/ ) i m m u s u s u s u s s t      = +   = −  + + + (16) where, s stands for sinusoidal current. the transfer function of the second-order under a damped system can be obtained from the above equation: 0( ) ( ) / ( )ih s u s u s= (17) by combining formula (8) and formula (9), it can be known that the transmission function of the second-order under a damped system is a function of  andt , and the variation interval of  is given by using the following formula: min max min max 0 2          =  = (18) where, min and max respectively represent the maximum and minimum over-voltage angles. based on the above considerations, the value t should be appropriately increased: (1) when the value is large, the influence  can be minimized; when the value is small, the above second-order under a damped system can be regarded as an equivalent second-order system, and the equivalent second-order system has a lower design cost. (2) by increasing the value t , the steady rise of voltage amplitude on the third winding of the hv shunt capacitor can be guaranteed. the constant variation of the voltage amplitude at the output end of the capacitor leads to the change in the magnetic flux of the iron core, which reduces the possibility of causing the inrush current of the capacitor. the transfer function given in formula (9) is simplified, then: 2 2 2 2 ( ) 1 ( ) s h s s a   +  = − + + (19) according to the design scheme of capacitor in surge suppressor described in the above formula, appropriate hv shunt capacitors, inductors and resistors are selected by the following formula to control the control characteristics required by different over-voltage of hv shunt capacitors. 22 3 1 2 2 2 2 1 1 ( ) n n ur l t u r r l t lc t   =   + =   = +  (20) where, 2nu and 3nu respectively represent the corresponding rated capacitance values of the capacitor twom. rajabali pour and m. azimian /future energy may 2022| volume 01 | issue 01 | pages 16-23 20 phase winding and three-phase winding, l representing the inductance and 1 2r r r= = represents the resistance. 2.6. parameter condition and detection of the overvoltage breakdown of high voltage shunt capacitor suppose that tu the effective value of the primary voltage of the isolation transformer during the gridconnected power generation stage of the high-voltage parallel capacitor li is the effective value of the current when the grid-connected power generation is at the maximum power and m is the capacitor circuit regulation. the vector triangle relationship of the high-voltage shunt capacitor is given by the following formula [12]: 2 2 1 2[ ( ) ]d t f m m lmau u l l i= + + (21) where, f is the speed, 1ml and 2ml are the inductance values of the shunt capacitor circuit, and 2 tu is the open-circuit voltage of the shunt capacitor 2 2 1 22 [ ( ) ]t f m m l d u l l i u ma + + = (22) it can be seen from the above formula that when the high-voltage shunt capacitor outputs the equivalent maximum power, the smaller the m value is, the higher the corresponding open-circuit voltage of the capacitor is, and the higher the voltage borne by the high-voltage shunt capacitor. it is assumed that the dc voltage of the high voltage shunt capacitor is low at the current stage, and m reaches the maximum, and has no output power. at this time, the voltage can only maintain the operation of the shunt capacitor itself. at this time, formula (22) can be converted into [13]: min 2d tmu u= (23) mindu is used to describe the minimum open-circuit voltage of the shunt capacitor. according to relevant certification standards [14], the normal operation output frequency range of a high-voltage shunt capacitor is 48.5-50.5hz, and the range of single ac voltage is 186-240v. these two factors can constitute the ac side parameter conditions of the over-voltage breakdown of a high-voltage shunt capacitor. the shadow area given in fig. 3 is used to characterize the over-voltage breakdown area of the shunt capacitor. when the relay contacts 1k and 2k are closed, the high-voltage shunt capacitor should detect the effective value and frequency of the grid voltage in different periods. when the voltage frequency and effective value of different periods are in the shaded area in fig. 3, it indicates that the power grid is in normal operation at this time, and the shunt capacitor is allowed to close the power relay contact 3k , and the high-voltage shunt capacitor will turn into the power output state after full over-voltage, otherwise, the contact will be disconnected point 1k , 2k capacitor into standby mode[15]. the output voltage of the high-voltage capacitor is detected after closing contacts 1k and 2k . in order to make the output voltage stable enough time, dt is required to be long enough. after many times of debugging, 80dt ms= is selected. after dt a period, the average output voltage and whether the power grid is normal are determined. if the current period is normal, 3k is closed, and contacts 1k and 2k are disconnected. voltage/v frequency/hz figure 3. over-voltage breakdown area of high voltage shunt capacitor 2.7 construction of online detection platform according to the data processing results, an online detection platform for the breakdown strength of capacitor bank components is constructed. the platform is mainly composed of a signal processing unit, signal receiving unit, and signal transmitting unit. the narrow pulse signal is transmitted from the signal transmitting unit to the capacitor bank component material. in the capacitor bank component material, the narrow pulse signal will continuously propagate and be affected by the breakdown strength of the capacitor bank component material, thus generating the reflection pulse corresponding to the breakdown strength. the signal receiving unit is set at the other end of the capacitor to receive the data and transmit the signal. the reflected pulse and transmitted pulse emitted by the unit are stored in the buffer of fpga, and the data is transmitted to the upper computer by the serial port of fpga. the reflected pulse is analyzed by the detection algorithm in the upper computer, and the breakdown strength of the capacitor bank component material corresponding to the reflected pulse is obtained, so as to realize the online detection of the breakdown strength of the capacitor bank component material. the specific detection process is shown in figure 4. cable status signal processing unit signal transmitting unit data signal collection state judgment trend analysis on line detection of breakdown strength data figure 4. specific detection process m. rajabali pour and m. azimian /future energy may 2022| volume 01 | issue 01 | pages 16-23 21 among them, the hardware of the signal processing unit mainly includes a controller, analogue-to-digital conversion chip, and upper computer. the model of the controller is hdl verilog, and the controller can work with various simulation tools; the specific model of analogue-to-digital conversion chip is ad7810, which is a low-power a/d conversion acquisition chip, which is powered by a single power supply, has the highest sampling frequency of 100khz and serial data interface, and can be connected with the upper computer to realize the hardware function of the signal processing unit. the software of the signal processing unit is the breakdown strength detection unit, which mainly uses the detection algorithm to analyze the reflected pulse so as to realize the detection of the breakdown strength of capacitor bank components. the signal receiving unit mainly includes a step delay chip and a programmable digital delay pulse receiver. the specific model of step delay chip is ad9501, which can support both cmos level and ttl level and can achieve the minimum delay time of 10ps and the maximum trigger frequency of 50mhz; the programmable digital delay pulse receiver is mainly responsible for the reflection pulse corresponding to the breakdown strength receive. the signal transmitting unit mainly includes a delay pulse trigger circuit and programmable digital delay pulse transmitter. the delay pulse trigger circuit mainly uses an a/d conversion chip to trigger the delay pulse, which is mainly composed of a voltage comparator, step wave generator, and oblique wave generator; the programmable digital delay pulse transmitter is mainly responsible for transmitting narrow pulse signal. through the signal processing unit, the signal receiving unit, and the signal transmitting unit, the online detection of the breakdown strength of the capacitor bank components is realized. 3. experimental results and analysis 3.1 output results of aging over-voltage breakdown detection of high voltage shunt capacitor bank components simulation calculation of capacitor breakdown in a series of time, the solid dielectric inside the capacitor is only a few tens of microns film, the breakdown of capacitor aging components belongs to voltage breakdown. the breakdown of a c-phase capacitor is simulated by the simulation model. the breakdown of capacitor aging components occurs at the time when the c-phase bears the peak voltage. the phase of the sinusoidal current on the capacitor is 90° ahead of the voltage phase at both ends of the capacitor. the current breakdown phase is approximately 0. in the simulation calculation. when the c phase is set at 9.8ms, the voltage at both ends of the capacitor is close to the peak value of phase voltage. the breakdown process is simulated as the control switch is closed. the breakdown point of a series of components of the capacitor is equivalent to the series branch of small resistance and small inductance. the main observed quantities are the current of the branch where the capacitor is broken down and the voltage and current of the threephase capacitor circuit. figure 5 shows the current waveform on the breakdown capacitor branch during the breakdown process. figure 6 shows the voltage waveform on the threephase capacitor. the positive peak voltage waveforms in the figure are b, c, and a-phase capacitors respectively. the voltage on the c-phase capacitor drops rapidly and the voltage drop is 392v. the breakdown current waveform and voltage waveform of the three-phase capacitor in the process of overvoltage breakdown are shown in fig. 5 and fig. 6. 9 9.5 10 11.51110.5 12 200 400 600 800 1000 1200 1400 t/ms i/ a (a) breakdown current waveform 9 9.5 10 11.51110.5 t/ms 200 400 600 800 1000 1200 1400 i/ a (b) breakdown current enlargement figure 5. the current waveform on the breakdown capacitor branch 0 5 10 15 20 25 30 -10 -5 0 5 10 t/ms u /k v figure 6. the voltage waveform of the three-phase capacitor during the breakdown 3.2 comparative analysis of simulation results and fault data recorded by a monitoring device in order to verify the effectiveness of the proposed method, the proposed method is used to detect the overvoltage breakdown process of aging components of a real shunt capacitor bank, and the results are compared with the real monitoring results of the monitor. in order to monitor the failure process of capacitor bank, a power supply bureau in guangdong province. a high voltage shunt capacitor online monitoring device is installed on several capacitor banks with frequent faults. it can record a variety of fault data of the capacitor bank in time, including current and phase voltage data of each capacitor branch. the data sampling frequency of the monitoring device is 10 khz. it can record various waveforms of the breakdown process quickly. two breakdowns occurred in the capacitor. the effective value of capacitor c8 current increased from 55.2a to 83.4a. the online monitoring device of the shunt capacitor shows its fault and gives an alarm. the current of other capacitors has no obvious change. the effective value of the c8 current of the capacitor bank increased to 134.4a again after the capacitor bank was maintained in this working state for about 75 min. the current of other capacitors is basically unchanged. after the capacitor bank is in this state for about 200 ms, the capacitor bank is removed from the system. after the failure of the capacitor bank, it is detected. faulty capacitor c. the variation of capacitance is 53.6 μf. according to the fault current records and post fault detection results of each m. rajabali pour and m. azimian /future energy may 2022| volume 01 | issue 01 | pages 16-23 22 capacitor branch, it can be inferred that the first increase of c8 current is the performance of a series of capacitor aging components in its internal four strings, and the second current increase is the performance of a series of capacitor aging components in the remaining three strings. at this time, an unbalanced current is detected by neutral line unbalance protection. after 220 ms of protection setting value. the relay protection of capacitor bank acts. make the vacuum circuit breaker of the capacitor bank open the capacitor bank at 740ms. fig. 7 is the fault recording of the breakdown of the internal capacitance aging element of a capacitor in phase c recorded by the monitoring device and the detection results of the method proposed in fig. 8. 96 100 104 108 112 116 120 124 128 -400 0 400 800 1200 t/ms i/ a figure 7. waveform recording of monitoring device 100 104 108 112 116 120 124 128 t/ms -400 0 400 800 1200 i/ a figure 8. test results of the proposed method it can be seen from the fault waveform in figure 8. when a series of capacitor aging components are broken down, the current of the capacitor branch is about 0 before the breakdown, and then there is a high-frequency discharge oscillation for about 2 ms. the discharge front is very steep, and the first peak value is about 1050a. in terms of breakdown current peak value, oscillation frequency, and transition time, the above theoretical and simulation analysis are in good agreement with fault waveform records. 4. conclusions as the main reactive power compensation device of the substation, the shunt capacitor bank is in a high temperature and high voltage environment for a long time. due to insulation aging and other reasons, the dielectric strength of the capacitor will gradually decrease. in addition, due to the instantaneous over-voltage between the electrodes of the capacitor, the weak components inside the capacitor may break down, resulting in capacitor damage. this paper presents an analysis method of the aging over-voltage breakdown of high voltage shunt capacitor banks. the simulation results show that the detection results of the proposed method are identical to the actual detection results, and the application performance is good. ethical issue the authors are aware of and comply with best practices in publication ethics, specifically with regard to authorship (avoidance of guest authorship), dual submission, manipulation of figures, competing interests, and compliance with policies on research ethics. the authors adhere to publication requirements that the submitted work is original and has not been published elsewhere in any language. data availability statement data sharing is not applicable to this article as no datasets were generated or analyzed during the current study. conflict of interest the authors declare no potential conflict of interest. references [1] ghossein n. e., sari a., venet p., effects of the hybrid composition of commercial lithium-ion capacitors on their floating aging, ieee transactions on power electronics, 2019, 25(3), 115-126. 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[15] yamazaki h., kurui y., saito t., et al., cmos-embedded high-power handling rf-mems tunable capacitor using quadruple series capacitor and slit with dielectric bridges structure, jpn. j. appl. phys, 2018, 57(10), 1002-1013. this article is an open-access article distributed under the terms and conditions of the creative commons attribution (cc by) license (https://creativecommons.org/licenses/by/4.0/). https://xueshu.baidu.com/s?wd=author:(haolun%20yu)%20&tn=se_baiduxueshu_c1gjeupa&ie=utf-8&sc_f_para=sc_hilight=person https://xueshu.baidu.com/s?wd=author:(yi%20wang)%20&tn=se_baiduxueshu_c1gjeupa&ie=utf-8&sc_f_para=sc_hilight=person https://xueshu.baidu.com/s?wd=author:(blaabjerg%20frede)%20&tn=se_baiduxueshu_c1gjeupa&ie=utf-8&sc_f_para=sc_hilight=person https://xueshu.baidu.com/s?wd=author:(fed%c3%a1k%20viliam)%20&tn=se_baiduxueshu_c1gjeupa&ie=utf-8&sc_f_para=sc_hilight=person https://xueshu.baidu.com/s?wd=author:(kim,%20chang-hwan)%20&tn=se_baiduxueshu_c1gjeupa&ie=utf-8&sc_f_para=sc_hilight=person https://xueshu.baidu.com/s?wd=author:(rhee,%20sang-bong)%20&tn=se_baiduxueshu_c1gjeupa&ie=utf-8&sc_f_para=sc_hilight=person https://xueshu.baidu.com/s?wd=author:(rhee,%20sang-bong)%20&tn=se_baiduxueshu_c1gjeupa&ie=utf-8&sc_f_para=sc_hilight=person fh. almotairy & af. almarshoud /future energy august 2024| volume 03 | issue 03| pages 14-23 14 article achieving zero-bill for the grid-connected pv systems in saudi arabia governmental schools: a techno-economic analysis f. h. almotairy1, a. f. almarshoud2* 1national grid company, buraydah, saudi arabia 2department of ee, college of engineering, qassim university, saudi arabia a r t i c l e i n f o article history: received 01 february 2024 received in revised form 03 march 2024 accepted 11 march 2024 keywords: solar energy, pv grid-connected, photovoltaic system, techno-economic analysis, lcoe *corresponding author email address: dr_almarshoud@qec.edu.sa ab.almarshoud@qu.edu.sa doi: 10.55670/fpll.fuen.3.3.2 a b s t r a c t governmental schools are characterized as ideal places for installing gridconnected pv systems due to the availability of large spaces on their roofs. schools are also characterized by their good annual load profile, in which most of the loads occur during the day, and there are no loads on nights or weekends or during summer and vacations. moreover, in the winter, the loads drop dramatically due to the lack of air conditioning. this special annual load profile provides a relative property to government schools with regard to exporting the energy generated during off days to the general electricity grid. the main objective of this research is to attempt to design a grid-connected pv system that can balance imported and exported energy to the grid to achieve an annual zero bill based on the energy exchange tariff in saudi arabia. three different schools in buraidah city were selected for investigation. the annual energy consumption was estimated from energy bills for 3 years and compared with actual installed loads. the performance analysis was done by applying three widely used indicators: yield factor, capacity factor, and performance ratio. also, the economic analysis was done using the life cycle analysis methodology based on the local market prices to find the levelized cost of energy (lcoe) and the payback time. the results of economic and performance analysis revealed the professionality of installing grid-connected pv systems in government schools. 1. introduction the constant increase in the population of the world has resulted in a high demand for water, food, and energy sectors [1]. the process of generating energy is facing significant challenges, such as fluctuations in market price, security, cost, and sustainability [2, 3]. moreover, the rise in awareness of environmental issues has directed the scientific circle to develop sustainable and alternative energy sources [4-6]. with the help of these implications, the energy system transformation has also received much attention from people who are more focused on solar cells and biofuels [7, 8]. sustainable and hybrid energy systems like biomass, geothermal, wind, and solar are viewed as crucial technologies in the renewable innovation phase [9, 10]. between these energy resources, solar energy is a pollutionfree generation of electricity without the emission of greenhouse gases (ghg) to the environment [11, 12]. the radiation of solar contains a high amount of energy in one minute that can be utilized as an excellent opportunity for pollution-free harvesting of energy [13]. apart from being able to decrease the damage to the environment, the utilization of solar panels can save the cost of electrical energy constantly. utilizing solar panels does not need regular maintenance, thus resulting in a more efficient method to save costs [14, 15]. pv grid-connected systems are one of the remarkable types of solar energy systems utilized widely because of the backup generators of solar panels. lately, electricity prices have increased in saudi arabia due to the tariff consumption of electricity service providers in 2018. hence, in 2018, the electricity and cogeneration regulatory authority accepted the utilization of a pv grid-connected system for houses and assisted in giving an advantage to lessen the bills of electricity loads faced in summer without any interruption. the government schools were affected after the notable increase in the electricity bills; most were charged higher than the houses since the tariffs were charged on them. hence, public schools are classified as one of the finest places for installing pv systems because of the large spaces available future energy open access journal https://doi.org/10.55670/fpll.fuen.3.3.2 august 2024| volume 03 | issue 03 | pages 14-23 journal homepage: https://fupubco.com/fuen issn 2832-0328 mailto:dr_almarshoud@qec.edu.sa https://doi.org/10.55670/fpll.fuen.3.3.2 https://fupubco.com/fuen fh. almotairy & af. almarshoud /future energy august 2024| volume 03 | issue 03| pages 14-23 15 on their roof that can be utilized to install these systems. the majority of the load is applied in the daytime due to the presence of staff and students; however, at night, there is no presence of load. therefore, the surplus can be given to the electrical network during vacations or weekends. in addition, during winters, there is a dramatic drop in energy demand as a result of less air conditioning use. the main aim of this research study is to reduce the electricity bill of selected public schools annually to zero after employing a pv gridconnected system on the roof of the schools. 2. literature review in recent years, a growing body of research has explored innovative approaches to enhance energy efficiency and sustainability, particularly in regions with high energy demands such as saudi arabia. almasoud and gandayh [16] review the utilization of pv systems to produce electricity in saudi arabia. the outcomes revealed that during peak hours, peak saving can be achieved by employing pv systems compared to traditional power generation systems. they also indicate that after estimating the total amount of health and environmental impacts compared to fossils. another study examines the pv system's economic feasibility of installation on the consumer side. the study utilized a package of ret screens to simulate various installation of pv cases in saudi arabia among 5 cities (dammam, najran, jeddah, buraydah, and tabuk) by including the latest price of components of pv systems, demand of energy, and every city meteorological property. the evaluation was performed based on the newly exchange tariff of energy and regulations, and the outcomes of the study revealed that if the pv system is developed to generate yearly energy demand for houses, the payback time will be less than ten years, and the lcoe will be less than 0.1 sar/kwh. the research demonstrates that expanding pv system capacity higher than demanded annually will be economically infeasible due to the low rate of exported energy to the grid [17]. rashwan et al. [18] conducted an environmental feasibility and cost-effective analysis of changing the power supply from electrical to solar pv modules. a 12 kw pv system was calculated utilizing the worldwide pv project model. they determined that placing pv systems in areas that have high rates of electricity was feasible after examining 3 different scenarios. the off-grid pv system showed great results regarding issues related to the environment and reducing the emission of carbon dioxide. a study was conducted on installing pv systems on the roofs of mosques and stated that this system would save a lot of money. they concluded that installing pv systems on mosques and residences in saudi arabia would be highly effective even without the assistance of the government. it was notable that when the net metering system was examined, the initial outcomes of the model recommended that about 250 kilowatts be installed to decrease the net present cost (npc). specifically, it was noted that the energy installation bill was zero practically, showing the exported and imported energy was equal virtually [19]. flood et al. [20] examined pv systems on 130 houses that were environmentfriendly in those areas where the building was insulated to take benefits of solar power. it has the power to produce a yearly income of about 4 to 8 thousand euros, which shows support for using solar power and the advantages of subsidies. moreover, in 2014, it was noted that schools saved about 5 thousand dollars on electricity bills from the main grid as high power was exported between holidays and weekends [21]. the research was performed in meknes, where two connected grid pv systems were examined. a difference between the results was made in the measurement and simulation of the systems, as they were technology-wise different and capacity-wise similar. the comparison based on measurement reported that a smaller number of differences was found due to similarities in the database and solar irradiance [22]. johnson & ogunseye [23] constructed and developed a pv grid-connected system in nigeria on the government's building's roof. the research utilized pv*sol 2016 software to examine the amount of electricity generated every day of the year. the outcomes showed that the continual pv system output was greater than the everyday energy consumption. a pv system in a school in izmir, turkey, was connected to the roof to examine for cooling, heating, and other electrical loads. the study proposed two cases; in the first case, 180 solar panels were placed, whereas in the second case, 265 solar panels were placed. in the second case, it covered schools at a rate of consumption which was 162 percent higher than in the first case. moreover, extra profit was obtained in the second case for the school [24]. 3. method 3.1 study design in the current study, three schools in the city of buraydah were selected i.e., buraidah secondary school, prince abdulelah secondary school, and anas bin malik primary school. all three schools contain the same climate conditions but they are different in regards to the requirement of energy and the area of the school's roof. 3.2 ethical approval ethical approval was obtained from the education department in buraydah city. 3.3 study procedure 3.3.1 meteorological data saudi arabia receives abundant sunlight all year, so it was suggested that the pv system would work effectively at any site in the country. per day, an average of 6.08 kwh/m2 global horizontal irradiance (ghi) was found in the city. the meteorological data was collected with the help of k.a.care's renewable resource monitoring and mapping (rrmm) program. the collected data is shown in table 1, which includes the recorded metrological data in addition to the sun irradiance calculated at both horizontal and tilted planes. 3.3.2 measurement of load profile the rate of consumption of energy at any time is measured. to evaluate the profile load, a bill of energy consumption was collected from the electrical energy providers between 2017 and 2019. figure 1 illustrates the average consumption of electricity bills for the selected schools. table 2 shows the difference between the annual consumption noted by monthly energy bills and the calculated consumption based on installed loads. fh. almotairy & af. almarshoud /future energy august 2024| volume 03 | issue 03| pages 14-23 16 figure 1. monthly average consumed energy of schools under study there was no big difference; therefore, the energy consumption annually extracted from monthly bills was utilized for calculation. 3.3.3 selection of pv module a pv module (hiku6 mono perc, cs6 w-550ms) from the canadian solar company was selected for evaluation in the current study for various reasons, such as availability in the local market, warranty, and performance. table 3 shows the specification of the module for which it was selected in the study. table 2. annual energy consumption (recorded and estimated) table 3. specification of selected pv module at stc recorded by bills (kwh) estimated using installed loads (kwh) anas ibn malek school 87100 84401.6 buraidah high school 286730 277258.5 prince abdulelah school 172600 164602.6 cell type mono-crystalline nominal max. power (pmax) 550 w operating voltage (vmp) 41.7 v operating current (imp) 13.2 a open circuit voltage (voc) 49.6 v degradation factor (%) 1st year 2%subsequent annual 0.55% short circuit current (isc) 14 a module efficiency (%) 21.5% noct 42±3c° temperature coefficient (%/c°) 0.34% dimensions (mm) 2261*1134*35 mm table 1. meteorological data of buraidah city month ambient temperat ure c global horizontal irradiance ghi kwh/m2/d relative humidity % global radiation (tilted) gti* kwh/m2/d atm. pressure mpa daily diffuse radiation horizontal kwh/m2/d wind speed m/s january 13.17 4.24 42.18 5.31 942 1.57 3.7 february 17.95 5.34 30.33 6.04 940 1.8 3.79 march 21.7 5.7 32.2 6.25 937 2.79 4.15 april 26.11 6.25 22.58 6.17 936 3.18 4.18 may 31.08 7.1 15.05 6.29 934 3.47 3.84 june 34.28 8.15 10.26 6.84 931 2.82 3.72 july 34.91 8.13 10.04 6.97 929 2.28 3.41 august 36.57 7.54 10.56 6.95 930 2.26 3.55 september 33.57 6.68 12.04 6.92 933 2.35 3.53 october 26.33 5.61 18.56 6.51 937 2.03 3.78 november 20.77 4.37 39.82 5.06 940 1.7 3.82 december 16.77 3.83 46.9 4.85 943 1.52 3.67 average 26.10 6.08 24.21 6.18 936 2.31 3.76 *the tilt angle equals the latitude of the corresponding location-buraidah city fh. almotairy & af. almarshoud /future energy august 2024| volume 03 | issue 03| pages 14-23 17 throughout the school's visit to fields, the building's area of the rooftop was estimated, and it was found that there were no walls or barriers that could lead to shading on the panels. hence, the areas of rooftops of all 3 schools under evaluation were determined to be unrestricted. the selected modules of the pv system's maximum number were examined based on the roof area availability of selected schools. with this reference, 2 significant factors are generally reviewed to increase the installation of solar system efficiency. they are as shown: • orientation: it is not affected whether the installation is a portrait or landscape. • row spacing: it is also called the shading distance, which is the shortest distance between rows without the shading possibility. table 4 depicts the maximum number of pv modules that can be installed on the roof for each school utilizing the selected module. table 4. the maximum number of modules that can be installed the name of the school number of pv modules anas ibn malek 351 buraidah 782 prince abdulelah 290 3.3.4 sizing and optimization of the pv system the array of pv systems will be sized utilizing the selected module of pv system to satisfy the demand for energy annually, taking into consideration the location's climatic characteristics. hence, the impact of the change in the temperature of the pv cell on the efficiency of the pv array must be examined. utilizing equations (1) and (2), the efficiency of the pv system module can be estimated depending on the solar radiation and average ambient temperature at the site all over the year. therefore, the pv array is differentiated by its new average efficiency (ηe), which is estimated by the average module cell temperature, tc [25, 26]: 𝜂𝑒 = 𝜂𝑅[1 − 𝛽(𝑇𝐶 − 𝑇𝑅)] (1) 𝑇𝐶 − 𝑇𝑎 = 𝑁𝑂𝐶𝑇−20 800 ∗ 𝐺𝑡 (2) where ηr is the efficiency of the pv module at the reference temperature (tr), and the temperature coefficient for the efficiency of the module (β) needs to be collected from the datasheet of the pv module to investigate the array average efficiency (ηe). as shown in the equation, tc is the mean ambient temperature (ta) function, and noct, which is the temperature of the nominal operating cell, the gt constitutes the solar irradiance on the tilted surface denoted in w/m2 [27]. the energy output of the pv array can be measured utilizing equation (3) as shown: 𝐸𝐴 = 𝜂𝑒(𝑁𝑜. 𝑜𝑓 𝑚𝑜𝑑𝑢𝑙𝑒𝑠 ∗ 𝐴 )𝐺𝑡(1 − 𝐿𝑃𝑉)(1 − 𝐿𝐶) (3) where ea is the delivered energy by the pv array, a is the area of the pv module, gt shows the irradiance of solar on the tilted plane denoted in (wh/m2/d), and lc is power conditioning losses and lm is miscellaneous pv array losses. to calculate the amount of energy fed into the grid, equation (4) illustrates that the injected energy into the grid is equal to the produced energy by the pv array lowered by losses of the inverter: 𝐸𝑔𝑟𝑖𝑑 = 𝐸𝐴 ∗ 𝜂𝑖𝑛𝑣 (4) utilizing equations (3) and (4), pv array size can be obtained. 3.4 performance indicators to calculate the performance indicators iec 61836 (international electrotechnical commission) and iec 61724 (international electrotechnical commission), three effective performance indicators were employed in the current study: the performance ratio, capacity factor, and yield factor. the results of these indicators allow us to find the long-term variance in the performance of the pv system. 3.4.1 yield factor the yield factor calculates the pv array productivity under specific conditions of weather is shown as follows [28]: 𝑌𝐹 = 𝐸𝑔𝑟𝑖𝑑( 𝐾𝑊𝐻 𝑦𝑒𝑎𝑟 ) 𝑃𝑎𝑟𝑟𝑎𝑦(𝐾𝑊𝑝𝑒𝑎𝑘) (5) 3.4.2 capacity factor the capacity factor specifies the usability percentage and is defined as the fraction of the annual energy production ratio to the energy amount of the pv array [28]: 𝐶𝐹 = 𝑌𝐹 8760 (6) 3.4.3 performance ratio it is the pv energy quantity given to the grid for a specific period divided by the theoretically calculated amount depending on the data of the stc module. it is not impacted by size or location and gives the losses effect on the nominal power array caused by the inefficiency of the inverter, mismatch of wiring, and a few other losses when changing from dc to ac power, such as the temperature of pv module, irradiance insufficient utilization and component failures of components. the pr indicator is estimated as follows: 𝑃𝑅 = 𝑌𝐹∗𝐺𝑆𝑇𝐶 ∑ 𝐺𝑡 (7) where σgt is the accumulative irradiance, and gstc is the amount of irradiance at stc. 3.5 economic analysis economic indicators are essential for the feasibility of pv systems. the present study utilizes several parameters, such as the lcoe and payback time. the specifications and pricing of the pv system components were recorded from the local market. 3.5.1 levelized cost of energy (lcoe) the lcoe is a generally utilized statistic that shows the present net value of the electricity unit cost throughout the lifetime of a specific technology related to the production of electricity. it can be utilized to guide renewable energy goalsetting and other policies that motivate the adoption of renewable energy. moreover, these findings can facilitate producers of renewable energy in locating suitable places for validations and measurement resources. calculating the lcoe, which represents the present net value of the electricity unit cost for the lifetime of a definite production system of electricity in $/mwh is the first crucial step in fh. almotairy & af. almarshoud /future energy august 2024| volume 03 | issue 03| pages 14-23 18 examining the economic potential of a region shown as follows: 𝐿𝐶𝑂𝐸 = 𝐿𝐶𝐶 ∑ 𝐸𝑝𝑣𝑁 𝑛=1 (8) 3.5.2 payback time the payback time is the time necessary for yearly solar savings to become positive and cumulative solar savings to reach zero. this time can be obtained with and without discounting the savings, as shown in equations 9 and 10, respectively [29], as shown: 𝑛𝑝𝑎𝑦𝑏𝑎𝑐𝑘 = 𝑙𝑛 ( 𝐶𝑖𝑛𝑖𝑡𝑖𝑎𝑙∗𝑖 𝐹𝐿𝐶 +1) 𝑙𝑛(1+𝑖) (9) 𝑛𝑝𝑎𝑦𝑏𝑎𝑐𝑘 = 𝑙𝑛 ( 𝐶𝑖𝑛𝑖𝑡𝑖𝑎𝑙∗(𝑖−𝑑) 𝐹𝐿𝐶 +1) 𝑙𝑛( 1+𝑖 1+𝑑 ) (10) where f is the fraction of solar, l is the annual load (kwh/year), and c is the electricity cost (sar or $ per kwh) from the utility grid. 4. results and discussion table 5 demonstrates the maximum number of modules of the pv system and the pv array size allowed for selected schools based on the roof area availability. depending on the pv array size, the output of energy throughout the year was estimated utilizing equations 3 and 4 and compared with the energy measured, which is the consumed energy by the three schools, as depicted in table 6. the energy produced by the array of pv systems annually mostly equals the measured energy annually, which means that the annual energy balance is satisfied (exported energy = imported energy). table 5. pv array size for the selected schools table 6. generated energy and energy demand comparison school name generated energy (calculated) consumed energy (measured) anas ibn malek 88526.73 87100 buraidah 287172 286730 prince abdulelah 172735 172600 however, the annual energy balance does not satisfy the annual zero bill, which was the main objective of this study. this is due to the large difference in the energy exchange tariff, which is 0.05 sar/kwh for exported energy and 0.32 sar/kwh for imported energy. therefore, to satisfy the annual zero bill, the amount of exported energy should increase until the price of exported energy equals the price of imported energy. to achieve this condition, the size of the pv array should increase gradually until satisfying this objective, taking into account the following two constraints: • the size of the pv array should not exceed the maximum number of pv modules allowed for each school. • the annual zero bill should be satisfied until the last year of the project lifecycle, which is due to normal degradation in the output power of pv modules as a result of pv module aging. for the three schools, the size of the pv array increased, considering the previous constraints. anas school satisfied the need for an annual zero bill at 132 modules, buraydah school satisfied the need for a yearly zero bill at 516 modules, and the abdulelah school reached the maximum allowed number of modules (290) but did not satisfy the need for an annual zero bill. figures 2, figure 3, and figure 4 show comparisons of the annual generated energy (calculated) and annual energy demand (measured) for the three schools under study after increasing the size of the pv array. figure 2. comparison of generated energy and energy demand of anas school figure 3. comparison of generated energy and energy demand of buraydah school in figures 2-4, the produced energy covers the energy requirement majority of the year, which reveals that the energy surplus will be exported to the grid except from september to november. based on this, the yearly net bill and exchange rate of energy were estimated for the entire lifecycle of the project as shown in table 7. due to the exported energy is sold at 0.05 sar/kwh, while the tariff for imported energy from the service provider is 0.32 sar/kwh, school name size of pv array max. no. of modules anas ibn malek 82 351 buraidah 266 782 prince abdulelah 160 290 fh. almotairy & af. almarshoud /future energy august 2024| volume 03 | issue 03| pages 14-23 19 the cash gain flows remain low. the difference values with a negative sign represent the amount of money to be paid to the service provider. as demonstrated in figure 5, figure 6, and figure 7, the influence of the degradation coefficient on the output energy over the life of the pv system affects the amount of profit and loss and the difference between them. furthermore, the findings have demonstrated that anas bin malik school and buraidah school could achieve an annual zero bill because the difference between profit and loss was found to be equal in the last year of the system's life, whereas prince abdulelah school did not achieve an annual zero bill because its losses began to increase in 8th year of the system's life as a result of high loads and the lack of sufficient roof space to install solar panels. figure 4. comparison of generated energy and energy demand of abdulelah school table 7. yearly net bill over the lifecycle for the selected schools (sar) year anas ibn malek primary school buraidah high school prince abdulelah high school 1 2026.38 7229.73 799.11 2 1966.27 6909.46 666.79 3 1906.49 6590.96 535.21 4 1847.04 6274.20 404.34 5 1787.92 5959.19 274.20 6 1729.12 5645.91 144.77 7 1670.65 5334.36 16.06 8 1606.39 5024.52 -111.95 9 1531.98 4716.38 -239.25 10 1457.97 4409.94 -365.85 11 1384.37 4105.18 -492.18 12 1311.18 3802.10 -662.51 13 1238.39 3500.69 -831.91 14 1166.00 3200.93 -1000.38 15 1094.01 2902.82 -1167.92 16 1022.41 2606.35 -1334.54 17 934.65 2311.52 -1500.24 18 843.47 2018.30 -1665.03 19 752.79 1726.70 -1828.92 20 662.61 1436.70 -1991.90 21 572.92 1148.29 -2153.99 22 483.73 861.47 -2315.19 23 395.03 576.23 -2475.50 24 306.81 292.56 -2634.93 25 219.08 10.45 -2793.48 figure 5. variation of the annual net bill and the generated energy over the project lifecycle for anas bin malik school fh. almotairy & af. almarshoud /future energy august 2024| volume 03 | issue 03| pages 14-23 20 figure 6. variation of the annual net bill and the generated energy over the project lifecycle for buraydah high school figure 7. variation of the annual net bill and the generated energy over the project lifecycle for prince abdulelah school fh. almotairy & af. almarshoud /future energy august 2024| volume 03 | issue 03| pages 14-23 21 concerning the performance indicators of the solar system month-wise of selected schools, the yield factors are associated with the generation of energy by the capacity of the system and pv system. as shown in figure 8, figure 9, and figure 10. the yield factors of all schools were between 137.45 and 180 kwh/kw over the whole year. meanwhile, the capacity factor was between 18.62 percent and 24.25 percent. the outcomes of the performance ratio for the three systems were between 83 percent to 92 percent. in general, these indicators are reasonable and encourage the use of these three pv systems. the similarity in performance indicators between the three schools under study is because all the schools use the same pv module and have the same meteorological data; additionally, they differ in energy demand, which affects the size of the pv system but does not affect any of the performance indicators. figure 8. variation of monthly yf for the schools under study figure 9. variation of monthly cf for the schools under study figure 10. variation of monthly pr for the schools under study 4.1 economic analysis table 8 shows the total amounts utilized in these schools. there was a small difference among the schools considering the values of lcoe. these differences are a result of the pv system size in every school, which shows the system's lifecycle cost and the generation of energy during the lifecycle of the system. hence, the lcoe is directly linked with the pv system's cost of lifecycle, and it is not directly linked with the pv system's overall efficiency. the payback time generally depends on investments that were made initially and savings annually because of the avoided bills of electricity of the provider of the services after employing the pv system. table 8. economic indicators (all costs in sar) based on the preceding findings, we conclude that a gridconnected pv system is especially beneficial for government schools; in general, the use of such a system prevents excessive consumption during peak hours, helping to reduce the peak demand of the service provider and supply surplus energy to the grid. this thesis achieved a zero bill for the anas and buraydah schools for the lifespan of the grid-connected solar energy system. however, prince abdulelah school did not reach the study target owing to excessive consumption and a lack of suitable space for the addition of solar panels. the consumption of buildings is rationalized by disseminating and developing knowledge of the significance of rationalizing consumption in an affordable manner and replacing electrical equipment with energy-efficient equipment, particularly air conditioning, which is highly effective. if these strategies are used, they will provide considerable and positive savings in terms of lowering consumption bills and the possibility of reducing the size of the solar energy system, thus lowering the cost bills of the components. 5. conclusion the study examines the utilization of the grid-connected pv system for public schools in buraidah city to achieve an annual zero-bill. the research revealed that rooftops of indicator anas ibn malek primary school buraidah high school prince abdulelah high school total initial cost 258902.49 1012073.37 568800.93 periodic costs for maintenance/operation 18907.18 18907.18 18907.18 periodic costs for inverter (once time) 12879.36 50346.58 28295.56 salvage value (30% of initial cost) after 25 years 14002.22 54735.96 30762.46 lifecycle cost (lcc) 276686.80 976592.74 582980.81 levelized cost of energy (lcoe) sar/kwh 0.0846 0.0763 0.0811 payback time (undiscounted) year 8.40 9.78 9.21 payback time (discounted) year 13.47 17.46 15.68 fh. almotairy & af. almarshoud /future energy august 2024| volume 03 | issue 03| pages 14-23 22 schools are large and have sufficient space; hence, installing grid-connected pv systems will not just lower the bills of electricity and costs of government but also reduce the need for utilization of fossil fuel to power technologies. with the help of mathematical calculation, economic and performance indicators, which include yield factor, capacity factor, and performance ratio, were obtained. based on the findings, the current study concluded that the pv system is significantly beneficial for public schools. the utilization of these systems avoids high energy consumption during peak hours, facilitating the reduction of the need for electrical energy from the service providers. the study achieved zero bills for buraydah and anas school for pv system lifespan. however, prince abdulelah school does not achieve the target of the study due to the lack of space for installing more solar panels. deploying grid-connected pv systems in governmental schools in a wide range across the country will result in many benefits: • reducing the bill paid annually for energy as a result for the big reduction in energy demand of school, which will be reflected on the annual budget of education ministry. • deploying grid connected pv systems in schools may be considered as small distributed generation units which will provide some benefits to the utility grid, including: reduction in the power losses due to the energy is generated near the place of consumption, increasing the power supply security due to the variety of energy sources, enhancing the grid resilience. • also, it can potentially shave off the peaks in the energy demand, especially in the summer period due to air conditioning loads; this will remove the need to build a new peaker power plant. • from a financial point of view, deploying grid-connected pv systems in schools will result in delaying major investment in building new power plants, upgrading a substation, or building new transmission lines. • from an environmental point of view, deploying grid connected pv systems in schools will leads to significant reduction of greenhouse gas emissions especially carbone dioxide due to burning fossil fuels. the results of economic and 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[online]. available: http://store.elsevier.com/ https://creativecommons.org/licenses/by/4.0/ g.a. urdaneta et al. /future energy august 2022| volume 01 | issue 02 | pages 09-16 9 review solar power satellites: technical challenges and economic feasibility gerardo antonio urdaneta*, christopher meyers, lauren rogalski department of mechanical engineering, arkansas tech university, 1811 n boulder ave, russellville, ar, 72801, usa a r t i c l e i n f o article history: received 24 march 2022 received in revised form 25 april 2022 accepted 30 april 2022 keywords: solar power, microwave transmission, specific impulse, low earth orbit (leo) *corresponding author email address: gerar4406@gmail.com doi: 10.55670/fpll.fuen.1.2.3 a b s t r a c t world energy consumption is constantly rising; therefore, it is essential to investigate different possibilities to produce power in the medium and long term. the sun is a clean source of power that is virtually inexhaustible. photovoltaic (pv) power stations are used to harness this energy, but they are not completely reliable since they depend on weather patterns. to overcome this problem, large satellites with extensive solar panel surfaces can be placed in orbit. these satellites, known as solar power satellites (sps), would be positioned in geostationary orbit (geo) thus constantly providing energy while avoiding meteorological conditions and erosive factors. these benefits make solar power station an appealing option for the energy of the future. therefore, in this paper, the possibility and challenges of using solar-powered satellites are explored. the mechanisms regarding microwave transmission, photovoltaic collection, radiation impact, and propulsion are discussed. the advantages and disadvantages of solar-powered satellites are discussed regarding cost and practicality, and the current race between different countries to achieve this technology was examined. it was found that power could be collected with an efficiency of over 30% using gallium-arsenide photovoltaic cells. to minimize radiation effects, the use of a 100-micron transparent pilkington borosilicate glass (commercially known as cmg cover glass) could be employed. for spacecraft propulsion, hall thrusters provide the optimal combination between efficiency and thrust. finally, the cost analysis indicates that to make the sps viable, launch costs to geo must be decreased by a factor of 10, solar panel efficiency must be increased to 40%, panel density must be minimized, and international cooperation must be achieved. 1. introduction solar power satellites (sps) are being looked at not only as sources of energy on earth but also as an incentive to reduce the size and launch costs of satellites [1]. today’s world is currently suffering from increased consumption of its resources. with such increasing demand, it is necessary to begin exploring other energy sources. there are three main reasons for this drive for new and more reliable resources, such as the fluctuation of the petroleum industry peaking, the fuel-derived greenhouse gas effect, and in general, growing global demand for energy. sps collect the solar radiation in space and transmit it using a microwave energy beam to a receiving antenna on earth which transforms it into electricity [2]. when it comes to solar-powered satellites, there are many benefits over other traditional forms of power supply. sps is not affected by the weather or the earth’s atmosphere. this allows sps systems to be set in the most optimal path for solar and energy absorption. on the earth’s surface, the average solar power per unit area is 250 w/m2 whereas in space is 1366 w/m2 [3]. unlike terrestrial solar power, solar power in space does not need to be stored anywhere in case of drastic weather. furthermore, the space vacuum superconductor property for electromagnetic energy transmission is an important benefit over transmission systems on earth. energy is constantly lost in transmission grids due to electric resistance, whereas it is completely conserved in space. using sps’ is not directly harmful to the environment, given that there are no carbon dioxide emissions produced, so it is a clean and safe energy source [4]. sps could be potentially better than ground-based photovoltaic (pv) solar power because of the space's virtually unlimited power availability and lower transmission losses [5]. solar radiation can be more easily accumulated in space than on earth, and it is constantly available [6]. the japan aerospace exploration agency (jaxa) has made recent progress toward the solar space station, which developed a future energy open access journal https://doi.org/10.55670/fpll.fuen.1.2.3 august 2022| volume 01 | issue 02 | pages 09-16 journal homepage: https://fupubco.com/fuen issn 2832-0328 mailto:gerar4406@gmail.com https://doi.org/10.55670/fpll.fuen.1.2.3 https://fupubco.com/fuen g.a. urdaneta et al. /future energy august 2022| volume 01 | issue 02 | pages 09-16 10 technological map that shows a 1 gw commercial system by 2030 [5]. other efforts are located in the ongoing conferences about sps and wireless power transmission (wpt) and an evaluation by the international academy of astronautics (iaa) [7]. if accidents happened in space, they would not be as harmful on earth. it must be noted that the cost of this type of power generation is high, and there is a concern about environmental issues as they relate to the power transmission and launch emissions. the benefits of sps are a 6-fold increase in available power, longer useful life compared to terrestrial pv systems, and no necessity for energy storage which in conventional systems causes losses up to 40% [8–10]. space-based solar power consists of two types of technologies: how beams are transmitted to earth and the design of the satellite and receiver module [11]. the first technology is further divided into three categories: the method of collecting solar power in space, transmitting the power to earth, and receiving the power on earth. on the other hand, concerns about sps are regulations, adverse health effects, terrorism, and profit. the fear of terrorism is a problem because of the high-power microwave source and the high gain antenna, which produces an extreme surge of energy that could be used as a weapon. the main worry about the sps is that of profit since they can cost as much as hundreds of millions of dollars over time [5]. this, however, could be understood for a future of clean energy in an economy of growing demand. regarding the future of the technology, over time more deliveries of the crew, fuel, and other cargo will be needed for the international space station (iss). this information proves that there is a need for the development of more efficient launch technologies. by considering all these factors, the objective of this study is to determine the present possibility and future use of sps systems. 2. solar power collection there are various proposed ideas for collecting solar power. photovoltaic cells that exchange the solar energy for direct current (dc) electricity can be used. even though this idea seems a desirable choice, silicon cells are susceptible to radiation. this indicates that the accumulator would have to be made of gallium-arsenide (gaas) cells, which have an increased resistance to radiation. although these cells are radiation resistant and have efficiencies over 30%, their costs are two orders of magnitude higher than regular silicon solar cells [12]. another option within photovoltaic systems is thinfilm cells. these thin-film cells help to keep costs down, being that they are the cheapest type of pv cells. this arrangement of a system can output efficiency of 6% to 25% that produces an overall electric power flux production of 150 w/m2. one of the other concepts observed is the space electric power production approach of solar dynamic systems that use heat to run a thermal cycle connected to a generator. this method has a higher efficiency than the pv array/battery systems reaching 20-30% and can distribute continuous power in leo without batteries [13]. the last possible method for solar collection is to use space solar energy by orbital mirrors of ample size, made of reflective thin film plastics, to converge and provide energy. additionally, power storage may be required to keep a constant supply of power in the sps. smaller satellite systems use on-board storage devices such as lithium polymer or lithium-ion batteries with specific energies between 150-250 wh/kg [14]. for the sps case, the pv gaas solar cell choice can be employed due to its reliability and wide literature available. likewise, a group of li-ion batteries can be used to provide the sps with additional power as a redundant measure to ensure its systems are online at any given time. 3. microwave transmission since the wired transmission is extremely unfeasible due to the long distances, a low radio frequency in the microwave spectrum (2.4 ghz) or higher within the infrared range is needed. the most popular models for sps rely on microwave transmission systems to convey the power they collect to earth [15–17]. microwaves are a form of low-energy electromagnetic radiation that exhibit wavelengths of 1 mm to 30 cm and are well suited for carrying energy through space [15]. these systems convert dc electrical power into radiofrequency (rf) power, which is transmitted through free space and eventually converted from rf power back to dc electrical power [16,18]. for its implementation on sps, frequencies of 2.4 ghz to 3.3 ghz (13 cm~10 cm) are generally selected because these wavelengths provide for maximum efficiencies over long distances when attenuation over time and losses due to atmospheric effects are considered [15–18]. for a plant of 5 gw total power transmission, the transmitting antenna would need to be on the scale of 1 km in diameter and the rectenna on the scale of 7 km in diameter. these dramatic antenna sizes are needed to create an energy distribution at the rectenna that is nondestructive to the environment, safe for people, and thermally manageable [15,16]. the connection and concentrated delivery of microwaves from the transmitting antenna to the rectenna would be coordinated and maintained via a guiding laser. the uplink between the satellite and the rectenna located on the surface of the earth could be online over 99% of the year due to the geometries of its orbit [15,18]. this entails nearly 24 hours of solar power generation. this technology is desirable because it offers relatively highefficiency conversion and energy delivery in the range of 50%-75% dc to dc efficiency [19]. in addition to the more extended collection periods and efficient power delivery allowed by microwave transmission, the photovoltaic cells could maintain an ideal relationship with the position of the sun, further maximizing their efficiency. in terms of possible challenges, the likelihood of a malfunction occurring in the systems controlling the uplink between the antenna and rectenna poses a potential hazard in the form of a straying microwave beam. if power concentrations are above allowable levels, this potential malfunction could pose a threat to the health of humans and other organisms. for this and for legal reasons, power concentrations reaching the ground would need to be ensured below allowable levels as regulated by the environmental protection agency (epa) in the united states or the equivalent regulating body in each given country utilizing this technology. this raises another issue: the lack of international precedence for such a utility. an sps system utilizing microwave power transmission in the gigawatt range would involve every political territory surrounding the equator that it passes over, necessitating new international guidelines and agreements to regulate and allow for such systems. for obvious reasons, this could prove to be a particularly reluctant concern. furthermore, due to the power intensity of such a signal, fears about this technology being weaponized may arise. transmitting a microwave beam in the gigawatt range of power through the air will completely erase any wireless communications attempting to cross its path and heavily distort communications even at considerable distances from the rectenna. this impasse is the primary issue limiting the broader usage and development of wireless power transmission historically [16]. g.a. urdaneta et al. /future energy august 2022| volume 01 | issue 02 | pages 09-16 11 land usage and availability remain a problem regarding the microwave power transmission, as they have for other conventional energy production methods, due to the dramatic scale the rectifying antenna requires [15]. this necessity highlights land as the primary limiting factor involved in the implementation of a viable sps utilizing microwave power transmission and diminishes the perceived potential for the scalability of such systems. although low energy microwaves on a scale of up to a few millimeters are generally believed to not affect humans or animals, there exist no definitive studies which demonstrate the impact or lack thereof of prolonged human exposure to moderate concentrations of waves in the infrared spectrum. this system's unprecedented and dramatic nature may produce unforeseen ecological and human risks. 4. effects of radiation on solar cells and electrical components radiation is a significant factor in orbit. to account for this, both spacecraft and equipment require extensive shielding against it, thus making them heavier, which is not optimal for space missions [20]. satellite semiconductor materials are especially susceptible to collected radiation doses. in harsh space conditions, highly charged particles and electromagnetic rays constantly bombard electrical components and solar cells, causing continuous performance degradation. charged particles consist of electrons with energies of up to 10 mev and protons that can carry hundreds of megaelectron volts of energy. cosmic rays also constitute a problem due to their high ionization capabilities, ability to carry gigaelectron volts of energy [21]. when these particles impact the semiconductor material, the energy carried by the particle is transferred to the atoms, displacing them from their initial positions. the shifted atoms will be incapable of efficiently conducting current in the electric components, reducing the materials’ conductivity. in the case of solar cells, the displacement damages caused by the shifted atoms will decrease the carrier’s diffusion length, subsequently producing diminished performance [22,23]. to efficiently shield electronic devices and solar units in the sps from radiation, it is necessary to know how vulnerable these elements are, the yearly dose presented at geostationary orbit (geo), and the lightest materials that will provide the maximum shielding. bhat et al. [24] determined the yearly radiation dose at geo using radiation-sensitive field-effect transistors (radfets). different aluminum spherical covers with variable thickness were used to shield the system components. the results showed that for an aluminum shield thickness of 11 mm the yearly radiation amount was four orders of magnitude lower than those elements that did not present protection. from figure 1, it is possible to observe that the optimal aluminum thickness for electric component shielding is located between 7 mm and 11 mm, since thinner walls would dramatically increase the radiation impact, and thicker walls would only be able to produce marginal decreases in the radiation effects [24]. although it is essential to keep in mind that the added weight caused by the implementation of shielding would increase launching costs, therefore, thinner walls (< 7 mm) for system protection would be preferable. even if a wall thickness of 11 mm is chosen, the amount of radiation the electric systems are bombarded with is still 700 times higher than on earth. therefore, lighter materials that can be more effective against radiation are needed, such as bismuth oxide doped glasses [25]. moreover, solar cells in the sps would also be drastically affected by ionizing radiation, therefore, it is essential to understand the failure mechanisms presented in them. irradiation environments cause ionization and shift damage (non-ionizing) failure processes in solar cell units [26]. the latter is the leading cause of degradation in extraterrestrial solar panels. figure 2 and figure 3 show the relative damage coefficient for dual gaas/ge junction solar cells as functions of proton and electron energy, respectively. figure 1. ionizing radiation dose as a function of aluminum dome thickness [24] figure 2. gaas/ge solar cell relative damage as a function of proton energy for different cover glass thickness [27] it is possible to observe that to maximize useful solar cell life, it is necessary to have at least a 6 cm cover glass plate on the panels. the employment of such a plate would keep proton damage at a minimum, but it would not be effective against high-energy electron impacts (over 10 mev ). contrarily, these high-energy particles are comparatively uncommon (below 1% of all given protons and electron impacts have energy over 300 kev, see figure 4) thus, the employment of a 3 cm thick cover glass or thinner is also viable to eliminate damaging radiation [28]. another option is g.a. urdaneta et al. /future energy august 2022| volume 01 | issue 02 | pages 09-16 12 the implementation of nanowire array solar cells that may reduce the need for shielding, particularly protons with energies between 100-350 kev and 1 mev electron [20]. figure 3. gaas/ge solar cell relative damage as a function of electron energy for different cover glass thickness [27] figure 4. probability distribution of particle occurrence in geosynchronous orbit as a function of their temperature (energy) [28] since weight is such a critical factor for the sps design, it is necessary to determine the estimated mass addition for a 5 gw sps with a solar panel surface area of 14 km2 at 368.82 w/m2. the borosilicate type cmg cover glass is a typical material used to cover gaas solar cells due to its superior optical, radiation, solar absorbance, and emissivity properties [29,30]. at a density of 2554 kg/m3, if 1 cm cmg cover glass thick is chosen the total shielding mass would be 3.5756 *108 kg making the project infeasible. therefore, the protective thickness must be reduced at the expense of radiation protection. if 100 microns of cmg shields are used, the total mass is significantly decreased to 3.5756 *106 kg. figure 5 shows the total sps mass for different shielding thicknesses. this is still incredibly heavy, but it would make the sps possible while simultaneously obtaining radiation protection. in conclusion, radiation shielding can be achieved with a thickness of 100 microns of cmg cover glass at the expense of extra cost and weight. figure 5. sps total mass for cmg cover glass thickness of 0.01, 0.001, and 0.0001 m 5. propulsion system in terms of the desired orbit, nasa stated that the best place for a solar space station is in geo. by placing the system in geo, it would be possible to maintain a fixed connection between the transmitting and receiving antenna by keeping the sps fixed relative to the surface of the earth. this would enable the energy supply to large population zones around the planet [31]. for the sps to stay in orbit, avoid collisions, and adjust the effects of solar pressure (which is going to produce substantial deviations due to the sps’s ~14 km2 surface area) it will need a propulsion system capable of quickly changing its trajectory. the fuel mass must be kept to a minimum to prevent increases in launch cost while simultaneously having enough to complete the spacecraft mission time. to accomplish this objective, the thrusters must be as efficient as possible (high specific impulse) while at the same time being able to provide enough thrust for quick reaction maneuvers. electric thrusters are a promising option due to their increased efficiencies, although most are incapable of producing enough thrust. even though the thrust produced by electrostatic acceleration systems is around two orders of magnitude lower than their chemical counterparts, they can achieve higher specific impulses. a desirable propulsion system for the sps could be that of the hall thruster. they can achieve specific impulse values of ~1500 seconds, which is almost ten times higher than those from chemical combustion engines. it is also worth mentioning that hall propulsor efficiency increases as the power supplied rises. hall engines work by creating a radial magnetic field in their circular ionization chamber capable of accelerating electrons. then a neutral gas, generally xenon, is released into the chamber to be ionized; this ionized gas is later expelled from the chamber at elevated velocities along with a stream of electrons to maintain the spacecraft’s electrical neutrality [32]. the sps can employ hall engines because they can provide enough thrust (0.01 n-0.25 n) to perform fast changes in the trajectory; they also have the capability of increasing their produced thrust from their known limits since no technical limitations have been found when supplying more than 100 kw of power [33,34]. 6. comparison with terrestrial solar power generation (tsps) it is crucial to evaluate the efficiency of space solar stations to conventional solar power plants. the average solar power per unit area on the surface of the earth is 250 w/m2 compared to ~1360 w/m2 in space near earth [35]. the maximum efficiency of conventional photovoltaic cells is around 20%, while multi-junction photovoltaic cells designed g.a. urdaneta et al. /future energy august 2022| volume 01 | issue 02 | pages 09-16 13 for satellites can maintain efficiencies of around 30% and 35% [22,36]. this results in an overall power production of 50 w/m2 on earth and 409.8 w/m2 on the sps system. when considering the efficiency of microwave power transmission of 90% the power delivered to earth by the sps will be 368.82 w/m2 of pv surface [15]. however, over the course of a day, this loss is compensated for by the fact that solar exposure is continuous in the sps, meaning that the average power production will be maintained at 368.82 w/m2 compared to the terrestrial panel, which will average only 14.6 w/m2 over the course of the day. this means that in terms of actual power generation, conversion and transmission of solar power is over twenty-five times as efficient on sps systems when compared to terrestrial ones, with a percent difference of 184.8%. however, this efficiency neglects one critical factor, which is the land area required for the rectenna. therefore, the true power generated in terms of power flux (w/m2) from sps systems will be limited by the power flux density allowable, which is generally dictated by safety guidelines established by government organizations. as this is the case, the true efficiency in w/m2 of power generation using a sps transmitting 5 gw at 3.3 ghz at 90% efficiency, in terms of land area needed on earth, is 100 w/m2 [15]. even though this is a critical issue, the sps is still over six times more efficient (in terms of surface coverage) than conventional pv systems. 7. cost analysis: current and predicted budget the main problem with the current sps stance is its immense size: a 1 km transmitting antenna, 7 km receiving antenna, and ~14 km2 of solar panels are needed to produce the desired 5 gw of power at the power density of 368.82 w/m2. therefore, the sps will be extremely heavy which causes a dramatic increment in the station’s initial price due to expensive launch costs to geo. if an area density of 1.76 kg/m2 (3 mm thick) for solar panels is considered, the solar panels would weigh an estimated 23859 metric tons. to put this size into perspective, the sps panels without the transmitting antenna would be around 47 times heavier than the international space station (iss). although launch costs to low earth orbit (leo) have been reduced by a factor of 20 over the past two decades, the current cheapest cost per kilogram to leo has been achieved by spacex’s falcon heavy with a value of 1400 $/kg [37]. the cost to take a kilogram of payload to geo orbit is generally six times greater than that of leo. these factors result in an expense of around $200 billion just for the launching phase of the station panels. if the shielding weight is factored in, that would be an additional $30 billion in launching costs. the manufacturing costs of silicon solar cells would also have to be included; considering a solar panel price of 100 $/m2 the total expenditure would amount to $5 billion. it is necessary to consider that the actual solar cells needed are made of gallium-arsenide, which is significantly more expensive when compared to silicon cells which would further drive costs up. additionally, the development of both transmitting and receiving antenna would also have to be considered, the former further increasing launch costs since it is going to be located alongside the solar units in space. an estimate for the development and manufacture of both receiving and transmitting antennas would be around $20 billion. this estimation was performed by comparing the total surface area of both transmitting and receiving antenna with the fast telescope area, then that ratio was multiplied by the fast construction cost of $100 million [38]. these considerations would make the initial project cost $255 billion, rendering the project presently impractical. from figure 6 it is possible to observe the cost distribution for the sps at the current 2022 us dollars (usd). figure 6. current sps total cost distribution in 2022 billion usd therefore, to make the project economically viable, launch costs to geo must be decreased by a factor of 10 when compared to the current prices to leo performed by the falcon heavy rocket (~140 $/kg), solar cell efficiency must be increased to 40%, and solar cell density should be reduced from 1.76 kg/m2 to 1 kg/m2 on 3 mm thick units while improving their radiation resistance. making an estimation by including the different assumptions stated above, a cost of $48 billion can be obtained. figure 7 shows the cost distribution after these predictions in 2022 usd. although the new costs for the solar power station could be dramatically reduced, this final overall price is still incredibly expensive for just one private company to assume; therefore, international support and private consortiums are essential to improve the feasibility of the task. figure 7. predicted sps total cost distribution in 2022 billion usd 8. international competition and recent progress as previously mentioned, launch costs to leo have been reduced by a factor of 20 over the past two decades, which has enabled space accessibility for a broader range of organizations. these extraordinary launch cost reductions along with continuous breakthroughs in photovoltaic technology, wpt, and radiation shielding methods, have reignited the interest of international organizations, private companies, and governments in space solar energy [39]. in the us, through sponsored research by northrop grumman, a group of scientists at the california institute of technology asserts to have developed an sps model capable of emitting solar energy from space [40]. the us government has also shown some interest in the idea over the years; in 2007 the national security space office (nsso), through its report “space-based solar power as an opportunity for strategic g.a. urdaneta et al. /future energy august 2022| volume 01 | issue 02 | pages 09-16 14 security” concluded that this technology could advance the united states’ geopolitical stance in the contemporary space race [41]. in this regard, the us military leads the most important effort in the country by allocating $178 million towards solar space power research and development [40]. in this new space race, private companies are now capable of contributing towards space solar technology. firms such as solaren, powersat corporation, and space energy are tackling different challenges under this project. companies are unifying efforts to achieve this, as it is the case with solaren who partnered with pacific gas & electric to deliver power from space. on the other hand, powersat corporation has focused on the technological challenges of the project. this eager participation from the private sector shows how this technology has a promising future in relation to humanity’s net-zero emissions goal [41]. the european space agency (esa) is also interested in this technology. the agency has started an initiative to demonstrate the sps potential for providing energy by selecting 13 ideas for funding. since solar power from space is an interdisciplinary problem, these research topics deal with distinct challenges such as sunlight collection or wireless transmission safety [42]. in 2021, the esa hosted a workshop about solar power satellites with the goal of investigating the sps impact on fighting climate change. in addition, the space agency also performed a cost analysis to determine the feasibility of the sps business as a source of clean energy [42]. china is also trying to obtain an advantage in this possible new market. the country is preparing to launch a demonstrative sps around the 2030 and a commercial station by 2050 [39]. to achieve this deadline, the chinese state has funded the bishan project, which is focused on creating a floating platform that will rise 300 meters above the ground and attempt to transfer the solar energy captured to the surface. if successful it will be relocated at 22 km above earth surface to continue testing [43]. they also expect to complete their high voltage transmission line and wireless energy transfer tests by the end of the decade, which will allow the rapid scaling of wpt technology for the sps [40]. another country that has also started to commercialize solar space technology by 2050 is japan. in 2017, the japan aerospace exploration agency (jaxa) announced that it would have an sps online by the first half of this century. the japanese agency has partnered with mitsubishi to develop a demonstration system capable of supplying megawatts of energy and has redirected many of its resources into wpt and robotic assembly technology research [44,45]. considering these aspects, sps technology has the potential to change the world. in 2021, the energy consumed in the us was about 4 trillion kilowatt-hours [46]. if only one 5-gw solar power station is considered, it would be able to provide 1% of all the energy us citizens consume in a year, assuming it would be online on a daily basis. it is also important to note that this power would not be constrained by weather patterns, as it is the case for solar and wind, and price fluctuations due to geopolitical conflicts, unlike oil and natural gas. however, and most importantly, this technology gives humanity the chance to achieve a future with zero net emissions. therefore, it is possible to conclude that more international cooperation is needed to accomplish this goal. 9. conclusion the feasibility of solar satellite space stations was explored through the lenses of current technology. present innovations were proposed for the development of the system while simultaneously discussing the challenges it would face. it was determined that the most beneficial orbit to locate the system was at geo because it would allow the station to be on a fixed-point relative to earth. galliumarsenide pv cells can be a viable option for power collection due to their high efficiencies and radiation resistance properties. regarding the power transmission from the station to the receiving antenna, the desired frequencies are from 2.4 ghz to 6 ghz, being these the magnitudes that present the least atmospheric attenuation and thus being the most efficient to transmit power. using these frequencies, a total of 5 gw of power can be achieved at 90% efficiency. when it comes to ionizing radiation, a cmg cover of 100 microns can be used to reduce solar cell damage. moreover, it was determined that hall thrusters would be the optimal propulsion system for the station since they can provide the most advantageous combination between fuel efficiency and thrust. in terms of present viability, it was determined that the sps is not economically possible mainly because of launch mission costs to geo. technical challenges such as reduction of solar unit density, increase in cell efficiency, and radiation shielding are some of the most important factors to make the sps a viable option. in addition, a project of this magnitude would require the cooperation of several entities to make it a reality requiring international and private support. in conclusion, more research must be done regarding the reduction of payload costs to leo and the development of radiation-resistant and efficient solar units to provide a future where satellite power energy is possible. ethical issue the authors are aware of and comply with best practices in publication ethics, specifically with regard to authorship (avoidance of guest authorship), dual submission, manipulation of figures, competing interests, and compliance with policies on research ethics. the author adheres to publication requirements that the submitted work is original and has not been published elsewhere in any language. data availability statement data sharing is not applicable to this article as no datasets were generated or analyzed during the current study. conflict of interest the authors declare no potential conflict of interest. references [1] j.c. mankins, n. kaya, m. 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[46] use of electricity u.s. energy information administration (eia), (n.d.). https://www.eia.gov/energyexplained/electricity/use -of-electricity.php (accessed april 25, 2022). this article is an open-access article distributed under the terms and conditions of the creative commons attribution (cc by) license (https://creativecommons.org/licenses/by/4.0/). a. shaghaghi et al. /future energy may 2024| volume 03 | issue 02| pages 31-36 31 article energy consumption reduction in a building by free cooling using phase change material (pcm) aidin shaghaghi1, reza eskandarpanah2, siavash gitifar3, rahim zahedi4, hossein pourrahmani5, mansour keshavarzzade6, abolfazl ahmadi1* 1department of energy systems engineering, iran university of science and technology, tehran, iran 2department of energy, islamic azad university science and research branch, tehran, iran 3faculty of mechanical and energy engineering, shahid beheshti university, tehran, iran 4department of renewable energy and environmental engineering, university of tehran, tehran, iran 5group of energy materials (gem), école polytechnique fédérale de lausanne (epfl), 1951 sion, switzerland 6department of mechanical engineering science, university of johannesburg, johannesburg, south africa a r t i c l e i n f o article history: received 04 july 2023 received in revised form 06 august 2023 accepted 14 august 2023 keywords: latent heat thermal energy storage, phase change material, free cooling, numerical analysis *corresponding author email address: a_ahmadi@iust.ac.ir doi: 10.55670/fpll.fuen.3.2.4 a b s t r a c t it is significantly important to implement energy storage systems nowadays. latent heat thermal energy storage (lhtes) systems contain numerous advantages as a result of their small temperature variation and higher energy storage densities during storage. the present paper deals with the cooling load of a room in zanjan, iran using carrier software. then, a free cooling system using commercial paraffin rt25 was numerically analyzed as phase change material (pcm) while investigating the effects of the flow rate of the storage tank and inlet air temperature overcharging and discharging procedures. based on cold energy storage simulation, by airflow with the temperature of 20°c at night, the paraffin is solidified in 4 h. stored cold energy of 1.4 kw in pcm releases energy through a free cooling system within 2.1 h of july afternoon in the room. 1. introduction the domestic and commercial sectors consume about 40% of the world's total energy and produce a third of the greenhouse gases, a significant portion of which is spent on heating, cooling, and air conditioning. one of the effective ways to improve the use and protection of energy resources is the development of energy storage systems. latent thermal energy storage using phase change materials has high efficiency and reliability and also, due to high energy storage capacity, has received much attention [1]. the basis for using phase change materials for free ventilation of buildings has two stages: first, at night, when the ambient temperature is lower than room temperature, the flow of cool ambient air passes through the energy storage unit, and the heat of the phase change material in the liquid state and the material begins to freeze at a constant temperature. then, when the room temperature rises above the desired level during the day, the cool air stored in the phase change material is evacuated. as the hot air passes through the energy storage unit, the phase change material receives this heat and melts at a constant temperature, and finally, the desired cooled air enters the room. the efficiency of an open-air conditioning system largely depends on the climatic conditions of the environment. the properties of the phase change material, especially its melting temperature, are very important, and this temperature should be in the range of daily temperature changes. airflow is very important for the successful operation of an open-air conditioning system, and if this flow is adequate, then heat transfer will be successful [2]. according to ashrae standard 55, thermal comfort is a mental condition that expresses the sense of human satisfaction with environmental conditions. this standard has presented a proposed list of temperatures and airflows for different environmental conditions and buildings, which generally provides room comfort temperature in summer at 23.5°c to 25.5°c therefore, in free ventilation applications for buildings, phase change materials are preferred with a phase change temperature of 18°c to 30°c [3]. one of the most important studies on the free ventilation system was carried out by chinnasamy et al. [4], which aimed to reduce the air conditioning load in buildings. na2so4.10h2o hydrated salt with a melting temperature of 21°c was used as a phase changer. the prototype of this system was installed and tested in an ordinary office, so results show that 270wh of future energy open access journal https://doi.org/10.55670/fpll.fuen.3.2.4 may 2024| volume 03 | issue 02 | pages 31-36 journal homepage: https://fupubco.com/fuen issn 2832-0328 mailto:a_ahmadi@iust.ac.ir https://doi.org/10.55670/fpll.fuen.3.2.4 https://fupubco.com/fuen a. shaghaghi et al. /future energy may 2024| volume 03 | issue 02| pages 31-36 32 thermal energy was stored during 8 hours of office work. if the pilot system replaces conventional cooling units in the uk, co2 emissions will decrease by 430 tons per year. takeda et al. [5] studied the storage system with a platform of phase change materials for air conditioning of the building in japanese weather conditions. room temperature for ventilation was stabilized at 26°c, and the experimental model consisted of a rectangular air conditioning duct with a granule phase change material (the phase change temperature was 22.5°c to 25°c). using computer simulation, the potential of this system in reducing air conditioning load during summer was investigated for eight japanese cities, and kyoto having the highest efficiency with a reduction of the air conditioning load of about 62.8%. yamaha and misaki [6] considered an air distribution system with phase change materials inside the air duct, which was designed to cool the air and reduce the cost of electricity consumption in japan. the phase change material was a combination of fatty acid and paraffin, which initially measured and recorded the properties of the compound. the charging process of the phase change material (cold storage) was done from 5 to 8 a.m., and the discharge process was from 13 to 16 pm. for a typical office building in nagoya city, 5.4 kg/m2 of the phase change material was able to keep the room temperature constant and desirable, and the suitable melting temperature of the material for successful system performance was 20°c. streeti and butala [7] considered a latent heat storage unit for free ventilation, which contained 3.6 kg of commercial rt20 paraffin with a melting point of 22°c and a heat storage capacity of 172 kj / kg. the results of numerical simulation and experimental work are very close to each other. the results showed that when the inlet air temperature is 26°c and the inlet air velocity is 1 m/s, the stored cold can keep the air below 24°c for 2.1 hours. in the present article, first, the cooling load of one of the rooms in zanjan, with a cold and dry climate, was calculated in the hottest month of summer (july). then, a numerical simulation of the free ventilation system with latent heat storage using rt25 phase change material of commercial paraffin type made by the german company robiterm, was performed to investigate the potential of free ventilation to cool the room. 2. physical model in this paper, a flat plate heat exchanger [8] with layers containing phase change materials is used. the reason for choosing this type of heat exchanger is flexibility in adjusting the surface area, controlling the flow rate of passing air, and easy construction. the volume of the selected control for numerical simulation is shown in figure 1, and this geometry was created using gambit software; the dimensions can be seen in figure 2. due to the temperature gradient, a smaller mesh should be used in the area adjacent to the air with the phase change material. for this research, the number of cells was calculated at 15 thousand. 3. numerical modeling fluent software uses the enthalpy-porosity method to model the melting and freezing process [9]. in this method, the location of the joint surface separating the two phases is not explicitly specified; instead, there is a value called the liquid fraction, which represents a fraction of the cell volume that is liquid, and this value is calculated in each repetition based on the enthalpy equilibrium [10]. the mushy zone is the part where the liquid fraction varies between zero and one, and this region is modeled like a quasi-porous medium in which the amount of porosity changes from one to zero as the material freezes. when the material inside the cell is completely frozen, the porosity is zero. figure 1. selected control volume for numerical analysis figure 2. the geometry of problem (mm) 3.1 the governing equations the conservation equations of mass and momentum are derived from relationships (1) and (2) [11]: 𝜕𝜌 𝜕𝑡 + ∇. (ρv) = 0 (1) 𝜕 𝜕𝑡 (𝜌𝑣) + ∇. (𝜌𝑣𝑣) = ∇. [𝜇(∇𝑣 + ∇𝑣𝑇)] − ∇𝑃 + 𝜌𝑔 + 𝑆 (2) s is a momentum source that contains parts of the sensitive area porosity, surface tension at the joint surface of the two phases, and other external forces entering the surface. this value is calculated using eq (3) below [12]: 𝑆 = 𝐶(1−𝛽)2 𝛽3 𝑣 (3) table 1 shows the properties of rt25. according to eq (4), the enthalpy is written as the sum of the tangible enthalpy (h) and the latent heat (h), where the tangible enthalpy (h) is obtained from eq (5). 𝐻 = ℎ + ∆𝐻 (4) ℎ = ℎ𝑟𝑒𝑓 + ∫ 𝐶𝑝. 𝑑𝑇 𝑇 𝑇𝑟𝑒𝑓 (5) liquid fraction (β) is defined as eq (6): 𝛽 = { 0 1 𝑇−𝑇𝑠 𝑇𝑙−𝑇𝑠 𝑇 ≤ 𝑇𝑠 𝑇 ≥ 𝑇𝑠 𝑇𝑠 ≤ 𝑇 ≤ 𝑇𝑙 (6) the amount of latent heat h can be written in eq (7): ∆𝐻 = 𝛽𝐿 (7) finally, the energy equation is written as an eq (8): 𝜕 𝜕𝑡 (𝜌𝜌𝐻) + ∇. (𝜌𝑣𝐻) = ∇. (𝐾∇𝑇) + 𝑆𝑛 (8) a. shaghaghi et al. /future energy may 2024| volume 03 | issue 02| pages 31-36 33 table 1. properties of rt25 [13] property value melting and freezing temperatures 24 (c) latent heat 155 (kj/kg) heat capacity 2000 (j/kg.k) density 770 (kg/m3) thermal conductivity 0.2 (w/m.k) 3.2 boundary conditions in this paper, the boundary conditions are such that the inlet air enters the system at a certain speed and temperature, so the inlet is selected as the velocity inlet type. in the part where the air comes out, the boundary condition of the outflow is selected, and the boundary condition of the layers between the air and the phase change material is wall type. due to the symmetry in the problem and according to the selected control volume, the upper and lower walls are considered symmetrical. 3.3 initial conditions the velocity and temperature of the air entering the tank are two important variables to evaluate the performance of the thermal energy storage system in the melting and freezing processes. to consider different states for temperature and speed, it is best to make these variables dimensionless. reynolds number is used to de-dimensionalize the velocity, which is calculated for the flow through the channel using eq (9). for reynolds numbers less than 2,300, the flow is calm, and for reynolds numbers larger than 2,300, the flow is turbulent. in order to de-dimensionalize inlet air temperature in the melting process, it is better to use the stephen number, which is defined by eq (10) [14]. 𝑅𝑒 = 𝜌.𝑉.𝐷ℎ 𝜇 (9) where ρ is density, v is the velocity of the input air, dh is the hydraulic diameter of the channel, and µ is the dynamic viscosity of the air. 𝑆𝑡𝑒 = 𝐶𝑝(𝑇𝑖𝑛−𝑇𝑚) 𝐿 (10) where cp is the specific heat capacity, tin is the temperature of the input air, tm is the melting temperature of matter, and l is the latent heat of matter. the initial conditions during the melting and freezing process are briefly listed in table 2. during the charging process, given that the rt25 phase change temperature is about 24°c, it is assumed that the initial temperature of the material in the tank is 3 degrees above the freezing temperature of 27°c. table 2. initial conditions process velocity (m/s) reynolds number temperature (c) stephen number charge 7 10811 20 charge 9.3 14446 20 discharge 3 4660 30 0.075 discharge 4 6213 31 0.088 according to figure 3, the dry temperature of zanjan is 20°c during the night to the morning. also, due to low airflow, using a ventilation fan the air speed entering the tank increases. from 4 p.m. onwards, when the ambient temperature is the highest, the common ventilation of the building has been extinguished, and free ventilation is used for cooling. the air temperature entering the tank is 30°c and 31°c in the melting process with an average temperature. also, using a ventilation fan, the air velocity entering the tank reaches 3 m/s and 4 m/s. figure 3. the temperature of zanjan city on the hottest day of july 3.4 solution conditions fluent software has two different solution methods, one based on pressure and the other one based on density in the simulation of the melting and freezing process; only a pressure-based solver can be used. the flow is transient, and the standard k-e method is used to model the turbulence. piezo algorithm is selected for the pressure-velocity relationship, and also presto method is selected for pressure discretization, and the second-order upstream design method is used for energy discretization. the under-relaxation factors for pressure, density, momentum, liquid fraction, and energy are 0.7, 1, 0.3, 0.9, and 1, respectively. convergence criteria were selected values of 10-4 for mass and momentum conservation and 10-8 for energy conservation. 4. calculation of room cooling load basically, the correct estimation of the cooling load depends on the detailed examination of the load components in the ventilated environment, like complete plans of the building and the general design of the space. in this article, the building shown in figure 4 is a residential unit with an area of 120 square meters as a south ground floor. figure 4. plan of the building a. shaghaghi et al. /future energy may 2024| volume 03 | issue 02| pages 31-36 34 the area of the building is asphalt, the average reflection coefficient of the ground surface is 0.2, and also the thermal conductivity of the soil in the area is 1.35 w/m.k. first, in order to check the amount of cooling load required to design the ventilation system, the cooling load of one of the rooms selected here, bedroom a, is calculated. the door of the room is made of wood with dimensions of 0.9*2.5 m2, the window is made of aluminum with dimensions of 1.8 *1.2 m2, and the lighting equipment consists of a fluorescent lamp and an incandescent lamp. also, the number of people using a room is considered. by using the carrier software for july, the amount of cooling load during one day and night is calculated and shown in figure 5. also, the amount of aeration required for the room is about 420 m3/h. figure 5. the cooling load of sleeping room a 5. results and discussion 5.1 validation of numerical simulation to validate numerical simulation, the results are first compared with the experimental work done in reference [8] and shown in (figure 6). the average error rate between numerical and experimental results is about 4%, which is valid numerical results. 5.2 cooling storage process figure 7 shows the change in temperature of the phase change material and the output air of the system over time. with the entry of cool air into the system due to heat absorption from the material, first, the temperature of the material decreases to freezing temperature, then phase change begins, and the temperature decreases with a gentle slope. finally, after complete freezing of the material, the temperature decreases again with a steep slope. at a constant temperature, the higher the velocity of the air entering the system, the faster the material freezes. when the air arrives at 20°c and the tank speed of 7m/s, the complete freezing of the material lasts for 4 hours. by increasing the inlet speed to 9.3m/s, the total freezing time of the material reaches 3.5 hours. 5.3 the process of discharging cooling energy according to the profile of ambient air temperature during the day for zanjan, the cooling energy discharge process has been studied in the following four different conditions. in the first and second cases, the reynolds number is 6213, and the stephen number changes from 0.075 to 0.088. in the third and fourth cases, the reynolds number is 4660, and the stephen number changes from 0.075 to 0.088. figure 6. validation of numerical analysis during charging process figure 7. the temperature of the pcm and outlet air during the charging process figure 8 shows the temperature change of the phase change material over time. when hot air enters the tank, the frozen phase change material absorbs heat from the hot air and reaches its melting temperature after 0.5 hours. then the phase change begins, and the temperature rises with a gentle slope, and finally, after the material has completely melted, the temperature rises again with a steep slope. the liquid fraction during the melting process is shown in figure 9. in a constant reynolds number with a 17% increase in stephen's number, the melting time decreased by 0.5 hours, and in a constant stephen number with a 25% reduction, the melting time increased by 1 hour. one of the most important results of the paper is the temperature of the output air for ventilation of the room, which is shown in figure 10. as time goes on and the material melts more and more, the outlet air temperature increases. tamaskani and esfahankalateh [15] have conducted a study with the aim of determining the range of thermal comfort for the city of zanjan. the results show that the comfort temperature inside the room for july is about 23°c to 28.5°c. according to the calculations, the output air temperature of the storage tank for ventilation of the room up to 26.5°c is considered the permissible temperature. the results are summarized in table 3, so in the lowest reynolds number and a. shaghaghi et al. /future energy may 2024| volume 03 | issue 02| pages 31-36 35 the lowest stephen number, the best situation occurs, and there is comfortable air ventilation for 2.1 hours. figure 8. temperature variation of the pcm during the discharging process figure 9. variation of liquid fraction during the discharging process figure 10. temperature variation of the outlet air during the discharging process another important result is the amount of cooling air created by free ventilation. during the melting process, the cooling load is constantly decreasing, and the higher the reynolds number or stephen number, the higher the cooling load. in figure 11, a comparison is made between the amount of cooling air required by the room and the cooling air created by the free ventilation from 16:00 onwards. according to this diagram, free ventilation has provided the required cooling air for up to 2.1 hours, an average of 1.4 kw of cooling air has been injected into the room. table 3. result of discharging process condition outlet air temperature (c) aeration (m3/h) duration of ventilation (h) melting rate (%) first 25.5 – 26.5 570 1.5 56 second 25.9 – 26.5 570 1 45 third 25.1 – 26.5 420 2.1 74 fourth 25.4 – 26.5 420 1.5 55 figure 11. comparison of cooling load during the discharging process 6. conclusion in this paper, the effects of temperature and velocity of the air entering the free ventilation system with cold storage were investigated by a numerical simulation, and the following results were obtained: • in the charging process, the complete freezing of the phase change material takes 4 h to complete when the air enters the heat exchanger with a temperature of 20 ° c and a speed of 7 m/s. • in the discharge process, in a constant reynolds number with a 17% increase in stephen's number, the melting time decreased by 0.5 hours, and in a constant stephen number with a 25% reduction, the melting time increased by one hour. • in the discharge process, in the lowest reynolds number, which is 4660, and the lowest stephen number, which is 0.075, the best ventilation occurs. in this case, the melting process takes 5 hours, and 2.1 hours of optimal air is available for room ventilation. the amount of aeration, in this case, is 420 m3/h, which is sufficient. also, during this period, an average of 1.4 kw of cooling air was injected into the room. a. shaghaghi et al. /future energy may 2024| volume 03 | issue 02| pages 31-36 36 ethical issue the authors are aware of and comply with best practices in publication ethics, specifically concerning authorship (avoidance of guest authorship), dual submission, manipulation of figures, competing interests, and compliance with policies on research ethics. the authors adhere to publication requirements that the submitted work is original and has not been published elsewhere in any language. data availability statement datasets analyzed during the current study are available and can be given following a reasonable request from the corresponding author. conflict of interest the authors declare no potential conflict of interest. references [1] a. ghodrati, r. zahedi, and a. ahmadi, "analysis of cold thermal energy storage using phase change materials in freezers," journal of energy storage, vol. 51, p. 104433, 2022. [2] r. zahedi, m. a. n. seraji, d. borzuei, s. f. moosavian, and a. ahmadi, "feasibility study for designing and building a zero-energy house in new cities," solar energy, vol. 240, pp. 168-175, 2022. [3] r. american society of heating and a.-c. engineers, thermal environmental conditions for human occupancy: ansi/ashrae standard 55-2017 (supersedes ansi/ashrae standard 55-2013) includes ansi/ashrae addenda listed in appendix n. ashrae, 2017. [4] v. chinnasamy and s. appukuttan, "a real‐time experimental investigation of building integrated thermal energy storage with air‐conditioning system for indoor temperature regulation," energy storage, vol. 1, no. 3, p. e43, 2019. [5] s. takeda, k. nagano, t. mochida, and k. shimakura, "development of a ventilation system utilizing thermal energy storage for granules containing phase change material," solar energy, vol. 77, no. 3, pp. 329-338, 2004. [6] m. yamaha and s. misaki, "the evaluation of peak shaving by a thermal storage system using phasechange materials in air distribution systems," hvac&r research, vol. 12, no. s3, pp. 861-869, 2006. [7] u. stritih and v. butala, "energy savings in building with a pcm free cooling system," strojniški vestnikjournal of mechanical engineering, vol. 57, no. 2, pp. 125-134, 2011. [8] m. rajagopal and r. velraj, "experimental investigation on the phase change material-based modular heat exchanger for thermal management of a building," international journal of green energy, vol. 13, no. 11, pp. 1109-1119, 2016. [9] f. estelaji, a. naseri, and r. zahedi, "evaluation of the performance of vital services in urban crisis management," advances in environmental and engineering research, vol. 3, no. 4, pp. 1-19, 2022. [10] m. a. alzoubi, a. nie-rouquette, and a. p. sasmito, "conjugate heat transfer in artificial ground freezing using enthalpy-porosity method: experiments and model validation," international journal of heat and mass transfer, vol. 126, pp. 740-752, 2018. [11] p. reggiani, m. sivapalan, s. m. hassanizadeh, and w. g. gray, "coupled equations for mass and momentum balance in a stream network: theoretical derivation and computational experiments," proceedings of the royal society of london. series a: mathematical, physical and engineering sciences, vol. 457, no. 2005, pp. 157-189, 2001. [12] h. asemi, r. zahedi, and s. daneshgar, "theoretical analysis of the performance and optimization of indirect flat evaporative coolers," future energy, vol. 2, no. 1, pp. 9-14, 2023. [13] s. kamkarhaghighi, "a review of experimental study about thermal behavior of pv panel incorporating metallic tubes filled with pcm," energy, vol. 2, no. 1, 2021. [14] q. mao and y. zhang, "thermal energy storage performance of a three-pcm cascade tank in a hightemperature packed bed system," renewable energy, vol. 152, pp. 110-119, 2020. [15] a. tamaskani esfahankalateh, m. farrokhzad, o. saberi, and a. ghaffarianhoseini, "achieving wind comfort through window design in residential buildings in cold climates, a case study in tabriz city," international journal of low-carbon technologies, vol. 16, no. 2, pp. 502-517, 2021. this article is an open-access article distributed under the terms and conditions of the creative commons attribution (cc by) license (https://creativecommons.org/licenses/by/4.0/). r hajimineh and a moghani /future energy may 2023| volume 02 | issue 02| pages 29-38 29 article the important factors of saudi arabian policymaking in renewable energy resources rahmat hajimineh1*, amir mohammad moghani2 1department of communication and social science, east tehran branch, islamic azad university, tehran, iran 2eco faculty, allameh tabataba'i university, tehran, iran a r t i c l e i n f o article history: received 16 october 2022 received in revised form 17 november 2022 accepted 28 november 2022 keywords: saudi arabia, renewable energy resources, energy security, energy consumption *corresponding author email address: r.hajimineh@gmail.com doi: 10.55670/fpll.fuen.2.2.4 a b s t r a c t there is no doubt that saudi arabia exports the most oil. the country has considered notable investments in renewable energy to diversify its economy and decrease dependence on oil export. the research aims to analyze the key factors that have influenced saudi arabia's renewable energy policy. the main question of our article is: what are the influential factors in saudi arabia's energy policy on renewable energy sources? in response, the research hypothesizes that the growing energy consumption of saudi arabia and its favorable geographical location for renewable energy production caused the country to invest in renewable energy for its energy mix, economy, and carbon emission reductions. to investigate the research hypothesis, we have used the theoretical framework of energy security by benjamin sovacool. the findings show that saudi arabia’s capital investments in renewable energy provide opportunities for the government to create a modern industry that creates jobs and revenue with the support of the private sector. furthermore, industries and residences use renewable energy for electricity. therefore, renewable energy has decreased fossil fuel dependence and diversification of the country's energy mix consumption. data are collected through the library method. the analysis method is descriptive. 1. introduction renewable energy resources in the middle east region, like east asia and europe, have not developed enough for several reasons. first, the existence of enormous natural resources (oil and gas), and second, the lack of sufficient knowledge and investments in the research sector and development of renewable energy. according to the bp statistical review of world energy 2022, middle eastern countries collectively hold 31.3% of the world’s oil production and 29.3% of the world’s gas production. but the question arises, why should countries in the persian gulf council see the future differently? saudi arabia's economy is the largest in the arab region. for decades, saudi arabia has relied heavily on the oil industry to build and maintain its prominent position in world politics. a significant amount of co2 is released into the atmosphere by saudi arabia’s reliance on crude oil for electricity production. furthermore, the production of electricity from renewable energy is at a low level. the country has a high energy consumption due to its growing industries and population and will be unable to produce energy for domestic consumption in the future. thus, saudi arabian government has invested in renewable energy sources. the country aims to achieve 50% of its electricity consumption from renewable sources. there have been a lot of studies discussing renewable energy resources and policy in saudi arabia. salam & khan [1] have completed their analysis of saudi arabia would be able to export more natural gas and oil if it reduced its domestic use of fossil fuels. solar energy can also be used as an alternative to fossil fuels in saudi arabia. furthermore, this process will contribute to the stability and security of the persian gulf region. waheed [2] analyzed the theoretical and empirical effects of non-oil exports and tourism on the economic growth of saudi arabia. he concluded an efficient strategy for sustainable economic growth in saudi arabia is increasing non-oil export, such as renewable energy technologies, which can be an alternative to oil production. al-saidi [3] analyzed the indicators, goals, and processes of the saudi arabian energy transition toward renewable energy. he concluded that saudi arabia's energy transition is primarily driven by economic pressures. mosly & makki [4] analyzed the saudi government's benefits from developing renewable energy. they concluded that renewable energy resources help to decrease fossil fuel consumption for electricity generation and exports of fossil fuels. the residents, however, benefit from the lower energy bills and government subsidies. future energy open access journal https://doi.org/10.55670/fpll.fuen.2.2.4 may 2023| volume 02 | issue 01 | pages 29-38 journal homepage: https://fupubco.com/fuen issn 2832-0328 mailto:r.hajimineh@gmail.com https://doi.org/10.55670/fpll.fuen.2.2.4 https://fupubco.com/fuen r hajimineh and a moghani /future energy may 2023| volume 02 | issue 02| pages 29-38 30 abubakar & dano [5] analyzed saudi arabia’s climate change. therefore, they concluded climate change is a threat to saudi arabia because of its sensitive ecosystems, limited freshwater reserves, and substantial coastal development. in this regard, al-douri et al. [6] in their studies concluded that green energy helped saudi arabia to overcome air temperature, humidity, and pollution. amran et al. [7] analyzed the current status, growth, potential, resources, sustainability performance, and future prospects of renewable energy technologies in saudi arabia. they concluded utilizing and developing renewable energy technologies could play a significant role in ksa's future. in this regard, tlili’s research [8] concluded that solar and wind energy technologies contributed to reducing energy demand and creating efficient forms of energy. barhoumi et al. [9] analyzed the energy resources in saudi arabia and their exploitation capabilities in terms of human resources. they concluded that a qualified workforce would be prepared using appropriate equipment and training. research, development, and industrial production will be essential components of the energy production chain, as well as for the development of renewable technologies. scholars emphasized the construction of universities and the training of specialized human resources. in addition, the different articles assume that renewable energy resources could be alternative choices to fossil fuels. the research aims to investigate the factors influencing saudi policymaking regarding renewable energy. in this regard, the authors use the energy security theory by benjamin sovacool. 2. theoretical framework energy is essential for sustainable economic growth. industrialization and economic growth have increased energy consumption since the turn of the century. the scope of energy security assessments has expanded in recent years, now covering electricity reliability, oil and gas security, pipelines, lng terminals, and the entire energy supply chain infrastructure [10]. energy security within a consumer country means being able to provide energy services at reasonable prices without interruption. in contrast, major oil and gas producers aim to access new reserves and ensure the demand for their products. saudi arabia's energy security analysis is classified as energy producing country. benjamin sovacool defined energy security: "energy security should include the interconnected dimensions of availability, affordability, efficiency, and stewardship” [11]. in the following, “energy security” dimensions will be discussed. 2.1 availability energy availability refers to the ability to secure “sufficient and uninterrupted supply” and the minimization of the dependence on imported fuels. therefore, availability relates to ensuring relative independence and diversification of energy fuels and services [12]. 2.2 affordability the affordability of energy is a reflection of the economic feasibility of supplying it. affordability is defined as providing adequate and uninterrupted supply at a reasonable price. energy affordability is also affected by the personal ability to pay [13]. therefore, energy exporting and importing countries are sensitive to energy price volatility. 2.3 efficiency the concept of energy efficiency encompasses not just engineering but also management and policy [14]. to ensure energy security, it is often necessary to increase energy efficiency, manage demand, substitute fuels, change consumer behavior and reduce energy consumption levels through effective technology. the development of energy technology improves the quality of energy services by reducing the costs and externalities associated with energy delivery [15]. 2.4 stewardship the concept of stewardship goes beyond protecting the environment; it also involves the governance of the energy system. furthermore, the governance of energy has important in stewardship. as a measure of what countries have accomplished in reducing pollution, acid rain, greenhouse gas, and carbon dioxide emissions can reflect responsible environmental stewardship [16]. the following metrics can be used to measure the energy security dimension: the availability of oil and natural gas is measured by import dependence. affordability is measured by energy prices such as electricity, oil, etc. energy efficiency is measured by electricity use per capita and the average fuel economy of passenger vehicles. environmental stewardship is measured by carbon dioxide (co2) emissions [17]. 3. geography features of saudi arabia 3.1 saudi arabia on the sun belt most of arabia is occupied by the kingdom of saudi arabia. as shown in figure 1, saudi arabia has access to the persian gulf and the red sea. furthermore, the rub al-khali, or the empty quarter of saudi arabia is the largest continuous sand desert in the world. its oil region is also in the eastern province along the persian gulf. saudi arabia's latitude is equal to 24° 16' 0.86" n, indicating that the country lies on the equator. saudi arabia's longitude is equal to 45° 06' 28.26" e, showing that the country lies in the eastern hemisphere of the world [19]. solar resources are abundant in sunbelt countries at 40 degrees from the equator. furthermore, five sun belt regions receive the majority of long-term direct solar radiation. sunbelt regions include the mediterranean and northern africa, south africa, china and india, latin america, and australia [20]. figure 2 shows saudi arabia's sunbelt located in the west and southwest of the country. saudi arabia’s average insolation in ranges from a maximum of 7.004 kwh/m2 in bisha and a minimum of 4.479 kwh/m2 in tabuk. the southern regions of the country, including bisha, nejran, and sulayyil, experience higher levels of insolation [22]. 3.2 saudi arabia's wind energy resource wind power by using turbines generates electricity. wind power can be an exciting alternative energy generating for saudi arabia. figure 3 shows that saudi arabia has two regions for wind energy that include the coastal regions of the persian gulf and the red sea. wind speeds are higher within the northeast, in the center, and near the mountains in the west. the average wind speed of the east is equal to 7.5-8 m/s and on the west coast is equal to 7-7.5 m/s. r hajimineh and a moghani /future energy may 2023| volume 02 | issue 02| pages 29-38 31 figure2. saudi arabia solar irradiation [21] figure 1. geographical location map of saudi arabia [18] r hajimineh and a moghani /future energy may 2023| volume 02 | issue 02| pages 29-38 32 furthermore, the average wind speed of the central region is equal to 5-6.5 m / s [23]. “king abdullah city for atomic and renewable energy (kacare) has established ten metering stations: in sharurah, hafar al batin, two sites in yanbu, and two sites in aljof, traif, jeddah, and riyadh [24]. 3.3 geothermal energy of saudi arabia geothermal energy is heat within the earth. the geothermal word origin includes two greek words geo (earth) and thermal (heat). due to the continued production of heat within the earth, geothermal kind of a renewable source. governments use geothermal energy for industry, to heat buildings, and to generate electricity [26]. the most significant use of geothermal energy is electricity generation. the kingdom is rich in geothermal energy, mainly distributed in the west and south. saudi arabia is one of the most active geothermal countries in the middle east. geothermal resources of saudi arabia can be divided into three levels: low, medium, and high enthalpy resources. sources of medium enthalpy on the western and southwestern coasts (especially in the areas of al lith and jazan) and shallow surface waters are represented by hot springs. in the geothermal region of saudi arabia, the temperature varies from 150 to 300 degrees celsius [27]. based on figure 4, highenthalpy sources, it is located in the red sea, west of saudi arabia. 4. results and discussion 4.1 energy availability security supply in saudi arabia is not monitored as it is in energy-importing countries. the country isn't worried about supplying energy to run its economy, at least for now. the government instead is concerned about how to protect its domestic oil assets against security threats and ensure that future generations will be able to use them successfully. saudi arabia owns 17% of the world's proven oil reserves [29]. therefore, a large share of saudi arabia’s fiscal revenue is derived from oil, which is an important part of its economy. in 2010, oil revenues accounted for 75 percent of budget revenues, with high volatility, peaking at 93 percent in 2011 and failing to 53 percent in 2020, as the covid-19 crisis reduced global oil demand. therefore, government budget balances have also fluctuated with oil prices, with large surpluses during boom times and deficits when oil prices are depressed [30]. aside from oil, saudi arabia also has natural gas, iron ore, gold, and copper. the country’s manufacturing sector has also grown at an average annual rate of 75% until 2018 [31]. the country ranks as the largest energy consumer in its fuel production [32]. by 2038, saudi arabia will become a net oil importer if it does not reduce oil consumption in the energy sector [33]. the role of energy in human lives and economic activity cannot be overstated, both as a scale of development and as a primary need of humanity [34]. therefore, energy consumption per capita is the measure of economic progress in a country. for sustainable economic growth, saudi arabia must search for alternative fuels for its industry. economic growth and industrial development are closely tied to electricity consumption and production. according to british petroleum statistics, saudi arabia has grown by 4.7% in its electricity production in the last decade. furthermore, in 2021, a total of 356.6 terawatt hours of electricity was generated, which was a significant portion of the energy used to generate electricity from oil and gas. figure 3. saudi arabia’s wind speed [25] r hajimineh and a moghani /future energy may 2023| volume 02 | issue 02| pages 29-38 33 figure 5 illustrates that saudi arabia has less diversity in its electricity production than iran and the united arab emirates. saudi arabia generates half of its electricity from oil, which is higher than its two neighbors. diversification of its electricity production is also important for the country's economy and industry. 4.2 energy affordability population growth and industrialization have increased the energy demand, putting additional pressure on saudi arabia’s economic and environmental sectors. despite its vast oil reserves, saudi arabia faces different structural problems due to its fixed rate of oil production per citizen, which is aggravated by rapid population growth and high unemployment. the population of saudi arabia in 2000 was 20,600,000 people, to reach 35,700,000 people in 2022 [36]. domestic energy prices have been set by the saudi government below international market prices for a long time. subsidies on energy help low-income households and keep prices stable. energy subsidies, however, can lead to high energy demand and wasteful consumption while limiting incentives to invest in energy efficiency [37]. government energy subsidies help make energy affordable for domestic and industrial use, but cheap energy causes energy waste. 4.3 energy efficiency a rapidly growing population is a significant reason for the increasing energy consumption growth. energy subsidies and policies to attract investment for energy sectors such as aluminum and petrochemicals are also factors contributing to saudi arabia’s increasing energy consumption per capita. furthermore, due to the lack of fresh water, the country uses much energy for desalination to meet its basic water needs [38]. it is estimated that saudi arabia’s transportation sector consumes a million barrels of oil each day, which accounts for 21% of the country’s total energy consumption [39]. figure 6 shows that saudi arabia's electricity consumption has increased over the years. therefore, from 2010 to 2021, household and industrial consumption have grown significantly compared to other consumption. for efficient energy consumption in industries it is possible to contribute to efficient energy consumption by investing in technology and advanced industrial machines. in addition, improving households' energy consumption methods leads to greater efficiency. 4.4 stewardship an enormous amount of energy is required to boost economic growth and income. furthermore, economic growth leads to an increase in infrastructure and transportation activities, both require power to operate, and direct air pollution is expected. due to saudi arabia’s heavy reliance on fossil fuels for energy production, rising energy consumption could result in significant co2 emissions [41]. figure 7 depicts the co2 emissions of saudi arabia. therefore, the country's emission is equal to 588.8 million tons. furthermore, the co2 emissions of saudi arabia increased from 47.02.2 million tons in 1971 to 588.8 million tons in 2020. the co2 emissions of saudi arabia have increased by 5.28% on average per year [42]. aramco, the national oil company of saudi arabia, emits around 18 tons of co2 per person, making it one of the biggest co2 emitters in the world. figure 4. saudi arabia’s geothermal map [28] r hajimineh and a moghani /future energy may 2023| volume 02 | issue 02| pages 29-38 34 oil gas renewable energy coal nuclear power hydropower saudi arabia 139.9 215.9 0.8 0 0 0 iran 48.7 288.3 1.8 0.7 3.5 14.9 uae 0.05 123.7 5.2 0 10.5 0 0 50 100 150 200 250 300 350 te ra w at t h o u saudi arabia iran uae 0 50,000,000 100,000,000 150,000,000 200,000,000 250,000,000 300,000,000 350,000,000 2010 2011 2012 2013 2014 2015 2016 2017 2018 2019 2020 2021 m ax im u m e le ct ri ci ty c o n su m o ti o n ( m gh ) residential consumption government consumption commercial consumption industrial consumption other consumption figure 5. comparison of electricity production in saudi arabia, iran and the uae in 2021 [35] figure 6. electricity consumption in saudi arabia from 2010 to 2021 (in different sectors) [40] r hajimineh and a moghani /future energy may 2023| volume 02 | issue 02| pages 29-38 35 saudi aramco is the world’s largest carbon dioxide emitter, producing over 60 billion tons since the 1960s. 5. national renewable energy program of saudi arabia as a part of vision 2030, saudi arabia aims to diversify beyond oil production. a long-term strategic initiative led by saudi arabia's ministry of energy industry and mineral resources (meim); the national renewable energy program (nrep) directly supports the kingdom's 2030 vision. by implementing nrep, saudi arabia will reduce its oil reliance and reduce greenhouse gas emissions as a result of the paris agreement. also, new jobs will be created, stimulating economic development throughout the kingdom, thereby ensuring long-term prosperity consistent with vision 2030 [44]. the nrep is funded by public investment fund (pif). acwa power has plans to build 11.8 gw by 2025, fulfilling the government's aims to generate 50% of electricity from renewable sources by 2030 and the rest from natural gas [45]. one of the most successful projects of renewable energy resources is the sakaka project. the sakaka project is a 300mw photovoltaic (pv) solar. in april 2021, the sakaka project was commissioned by its developers, acwa power (70%) and algihaz renewable energy company (30%) [46]. another project is the wind farm. the dumat al jandal wind farm is the first wind power plant in saudi arabia and the largest plant in the middle east. the wind farm capacity is equal to 400mw. the plant is being developed by a consortium led by edf renewables (51%) and masdar (49%) [47]. the construction of the wind farm started in 2019, and the first wind turbines were installed in 2020. dumat al-jandal’s first stage of wind electricity generation began in august 2021 [48]. furthermore, the saudi ministry of energy is advancing renewable energy projects with a total capacity of 7.1 gigawatts (gws), which are in different stages of development. under nrep a further 15 gws are expected to be installed in 2022 and 2023, bringing the current capacity of renewable energy projects in the kingdom to 700 mw [49]. 6. the line city mohammed bin salman, crown prince, chairman of the neom company’s board, unveiled the idea of a linear city. neom company distributes announcements stating that line city will be a revolution in urban living, a $500 billion crossborder city in saudi arabia’s tabuk province. the linear city project is 100 miles long and located in the west of the country [50]. the line will be a smart city in the country. it is expected that neom will become a hub for the generation of renewable energy derived from wind, solar and green hydrogen, as well as a development ground for advanced technologies as part of a shift to a low-carbon economy. the line city is a future city powered by renewable energy. the use of artificial intelligence (ai) technology can provide all the energy it needs from geothermal, wind energy, solar pv, and batteries. furthermore, ai technologies can improve energy efficiency and renewable energy integration in a smart city and create cost-effective and environmentally friendly solutions for the city. upon completion, the city will create thousands of jobs for saudi arabia’s residents and diversify the country’s economy [51]. 1970 1980 1990 2000 2010 2015 2020 co2 emissions 47.02 187.55 173.48 265.15 487.93 611.59 588.81 0 100 200 300 400 500 600 700 to n s figure 7. saudi arabia's carbon dioxide emissions from 1970 to 2020 [43] r hajimineh and a moghani /future energy may 2023| volume 02 | issue 02| pages 29-38 36 7. challenges for widespread renewable energy development in saudi arabia renewable energy investment has faced many challenges worldwide, including financial, technical, and small market challenges. the cost of renewable energy technology, maintenance, and training still outweighs that of conventional energy sources. in general, wind turbines and solar pv are more costly to invest in but are less expensive to operate and maintain [52]. the saudi arabian shift to renewable energy is costly and challenging compared to fossil fuel technology. furthermore, pv and concentrated solar power (csp) technologies are ineffective in saudi arabia due to high temperatures and significant dust levels. high temperatures reduce pv efficiency, while dust reduces csp output, especially on reflectors. in order to solve these problems, pv systems need cooling and washing systems, which increase their maintenance costs [53]. since the country’s economy depends heavily on fossil fuels, nonrenewable energy dominates current energy markets. renewable energy must compete with fossil fuels. there is massive government support for fossil fuels, even though the government offers rebates and incentives for solar energy [54]. oil and gas operations in saudi arabia are controlled by aramco, the country's national oil company. it is the secondlargest producer of oil in the world. saudi arabia’s investments in natural gas and nuclear power indicate that these sources can be integrated into its future energy mix consumption and affect its investment in renewable energy. as long-term electricity sources, natural gas and nuclear power offer low fuel costs and high-capacity factors. the mix of energy sources should be taken into consideration by decision-makers and government entities in light of these facts [55]. therefore, the competition for renewable energy with the second-largest oil company is challenging. due to the cheapness of fossil fuels and their market dominance, the renewable energy market remains small and underdeveloped. 8. conclusion energy is the main factor in economic and industrial growth. the countries try a lot for the security of supply at an affordable price. with an annual economic growth of 7.5 percent, saudi arabia needs enormous energy. furthermore, population and industry growth caused energy consumption to increase, especially oil and electricity for domestic use. the industrial sector in saudi arabia is regarded as a promising area for business growth that could provide more privatesector jobs for citizens in the coming decades. saudi arabia has also discovered that its abundant crude oil inputs and cheap foreign labor aren't enough to generate wealth for its growing population. saudi arabia, therefore, is investing in renewable energy to diversify its economy and reduce its dependence on crude oil. the country’s location in the sunbelt and between the persian gulf and the red sea has made it a significant advantage in geothermal, solar, and wind energy production. further, saudi arabia is seeking to attract capital to the renewable energy sector. through private sector investments and public-private partnerships, saudi arabia can develop a new industry for renewable energy technology. thus, the country is encouraging private investments in renewable energy. as a result of saudi arabia's investment in renewable energy, domestic oil consumption and pollution can be reduced. furthermore, saudi arabia's commitment to the paris climate agreement has caused the country to turn to new energies to reduce carbon dioxide emissions. the infrastructures of saudi arabia are very energy-intensive, and a lot of energy spend on their use. therefore, saudi arabia has taken different steps to reform its energy prices to prevent energy wastage. the country must also encourage collaboration between science, technology, and innovation to accomplish its renewable energy goals. several challenges are facing renewable energy development, such as technological issues, high initial costs, low efficiency, funding shortages, and small market share. the government can solve these problems by establishing renewable energy projects with long-term power purchase contracts, which will provide stable revenues for investors. furthermore, the power purchase contracts could also protect buyers from future volatility in electricity. ethical issue the authors are aware of and comply with best practices in publication ethics, specifically with regard to authorship (avoidance of guest authorship), dual submission, manipulation of figures, competing interests, and compliance with policies on research ethics. the authors adhere to publication requirements that the submitted work is original and has not been published elsewhere in any language. data availability statement datasets analyzed during the current study are available and can be given following a reasonable request from the corresponding author. conflict of interest the authors declare no potential conflict of interest. references [1] salam, m. a., & khan, s. a. 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(2021, june 4). what are the problems faced by renewable energy? regen power. retrieved september 16, 2022, from https://regenpower.com/articles/what-are-theproblems-faced-by-renewable-energy/ [55] salim, a. m., & alsyouf, i. (2020, april 4). development of renewable energy in the gcc region: status and challenges. international journal of energy sector management, 14(6), 1049–1071. https://doi.org/10.1108/ijesm-07-2019-0012 this article is an open-access article distributed under the terms and conditions of the creative commons attribution (cc by) license (https://creativecommons.org/licenses/by/4.0/). https://ksa-climate.com/making-a-difference/nrep/ m. aliehyaei et al. /future energy may 2024| volume 03 | issue 02| pages 16-23 16 article development a policy for the production of bitcoins with renewable energy sources mehdi aliehyaei1, ali tofighi2, marc a. rosen3, hamed afshari4*, solmaz gheisari5, amir safari6 1department of mechanical engineering, pardis branch, islamic azad university, pardis new city, iran 2department of electrical engineering, pardis branch, islamic azad university, pardis new city, iran 3faculty of engineering and applied science, university of ontario institute of technology, 2000 simcoe street north, oshawa, ontario, l1g 0c5, canada 4food science & engineering department, faculty of civil & earth resources engineering, islamic azad university central tehran branch, tehran, iran 5department of computer engineering, pardis branch, islamic azad university, pardis, iran 6department of science and industry systems, university of south-eastern norway (usn), kongsberg, norway a r t i c l e i n f o article history: received 02 june 2023 received in revised form 04 july 2023 accepted 16 july 2023 keywords: bitcoin, energy, policy, social cost of air pollution *corresponding author email address: afshari1@gmail.com doi: 10.55670/fpll.fuen.3.2.2 a b s t r a c t bitcoin, the first decentralized digital currency introduced by an anonymous person or group since 2008, has attracted worldwide attention. a significant number of economists have introduced bitcoin as a new phenomenon in the 21st century that could reduce global inflation. given the tens of thousands of digital currencies that have emerged since the advent of bitcoin and its price growth trend over more than a decade, which are signs of the growth of this business. in addition to being money, bitcoin has always been considered a tool for investing and storing value, which is why it is called digital gold. one of the most important problems in the production or extraction of bitcoins is the highpower consumption by miners. if the energy sources of electricity generation are supplied by non-renewable energy sources, in addition to emitting air pollutant gases, it will increase greenhouse gases and consequently contribute to climate change. in this research, based on the idea of the authors, which is that the economic support of bitcoin is energy, a strategy for producing bitcoin from renewable energy sources is considered. first, the amount of electrical energy consumption by bitcoin production is calculated based on statistical data, and then based on the price of electricity in different countries of the world and its global average, the base price of bitcoin is calculated. in the following, four scenarios are proposed for the production of bitcoin by electricity supplied from non-renewable energy sources. these scenarios include coal-fired steam power plants, natural gas-fired power plants, natural gas/oil gas-fired power plants, and dual-cycle (steam and gas cycles) natural gas-fired power plants. based on the amount of electricity required to produce one bitcoin, the amount of pollutants emitted to produce bitcoin and its social costs are calculated. these costs should be added to the base cost of bitcoin production if nonrenewable energy sources are used to produce bitcoin. then, renewable energy sources for bitcoin production based on the price of electricity generated by renewable energy sources are examined. based on the analyses, how to choose the best renewable energy source to produce bitcoin is presented as a scenario. this article briefly answers two key questions: 1. at what price of bitcoin is it cost-effective for governments to produce it? 2. what is the best renewable energy source to produce it? these two questions can be useful in creating a roadmap and strategy for economists and governments. future energy open access journal https://doi.org/10.55670/fpll.fuen.3.2.2 may 2024| volume 03 | issue 02 | pages 16-23 journal homepage: https://fupubco.com/fuen issn 2832-0328 mailto:afshari1@gmail.com https://doi.org/10.55670/fpll.fuen.3.2.2 https://fupubco.com/fuen m. aliehyaei et al. /future energy may 2024| volume 03 | issue 02| pages 16-23 17 1. introduction blockchain is a system for recording information on a network of computer systems in a way that the information is secure, verifiable, and irrevocable. information is recorded in a series of "blocks", each containing transactions and other key data. each time a transaction is made, a new block containing the transaction is added. the entire stored and expanding information is called blockchain [1]. blockchain is designed to be difficult to hack, as any change must be verified against other versions in the blockchain system. bitcoin is the most well-known example of blockchain technology. in the bitcoin network, validation is done by mining rigs that compete with each other to solve a general algorithm and receive financial rewards for validating correctly. copies of the updated blockchain are then stored in distributed storage. each new set of transactions adds to the length of the blockchain [2]. bitcoin is a decentralized digital currency. this currency is single management and is transferred from one user to another without the need for an intermediary [3]. transactions in a network are encrypted. in the bitcoin mining process, the bitcoin miner is rewarded. this mining involves consuming a lot of electricity [4, 5]. bitcoin was invented by satoshi nakamoto in 2008 as a digital form of money, but no one knows who satoshi nakamoto is [6, 7]. it took more than a year for the first economic deal to be made. the global value of bitcoin at that time was 4 bitcoins per us cent. the first bitcoin transaction took place in 2010 when a man from florida paid 25 us$ to deliver two pizzas worth 25 us$ on may 22, 2010; at today's price, the same deal is worth 120 million dollars. in honor of this important moment, fans and supporters of digital currencies call 22 may pizza day [8, 9]. bitcoin has attracted investors and the world from its simple beginnings in 2008 to its peak in 2020. for more than a decade, its price has fluctuated a lot. bitcoin can be used to buy other currencies, products, and services. in the early days, the first bitcoin transactions on online forums were exchanged with people who traded goods and services for bitcoin. the value of bitcoin was initially determined by the individual [5]. after that, bitcoin's value grows by 200% annually. in november 2021, the price of bitcoin reached about 68,000 us$, and its market value reached about 1.2 trillion us$. of course, after that, it experienced many fluctuations [10]. over the years, the bitcoin mining process has become more complex. in 2011, a simple desktop computer could easily extract bitcoins, but now it takes 13 years for this device to be able to extract a bitcoin [6, 7]. it is clear that with the increasing complexity of mining, more energy is consumed to produce bitcoins. bitcoin energy consumption is somewhat straightforward to calculate: the amount of energy consumption is calculated based on the hash rate (total combined calculations to generate bitcoin transactions) and the hardware energy required (miners). it is estimated that bitcoin consumes 73.1 to 78.3 twh of electricity per year. this amount of energy is more than the total annual electricity consumption of countries like hongkong, ireland, austria, malaysia, and norway. it is estimated that bitcoin consumes 707 kilowatt-hours (kilowatt-hours) of electricity per transaction [11]. the energy consumption of a bitcoin transaction is approximately equal to the electricity consumption of a british family in two months [4, 12, 13]. the university of cambridge has added a new indicator called the cambridge bitcoin power consumption index (cbeci) to calculate daily power consumption by the bitcoin network. this is an alternative to the existing bitcoin energy consumption index (beci) [11, 12]. research on the relationship between bitcoin and its energy consumption can be divided into three general categories: energy consumption for bitcoin production, its environmental effects, and the use of renewable energy sources. but the number of studies about using renewable energy resources for bitcoin production is very limited in the third category of research. rehman et al. [14] examined the time-frequency relationship between the price of bitcoin and bitcoin mining during the period from january 2013 to october 2018. three sources of energy were considered: oil, coal, and gas. they showed that the production time of bitcoins for oil and gas from mid-2014 to 2016 was about 64 to 128 days. das and dutta [15] examined the relationship between bitcoin energy consumption and miner revenue. in their view, the relationship between the two is contradictory. they concluded that, due to the increase in costs and energy consumption for bitcoin production along with the downward trend of the market, bitcoin mining will not reach the endpoint that exits the market. as a result, cost-effective bitcoin mining depends on low-cost energy sources and efficient hardware. li et al. [16] statistically analyzed data on the monero currency code. they estimate that, in 2018, monero mining could consume 645.62 gwh of electricity worldwide. the mine also consumes about 30.34 gwh of electricity in china and emitted 19.12 to 19.42 thousand tons of carbon from april to december 2018. similar observations have been reported in the literature, which shows that mining bitcoin consumes a high amount of energy [11, 17-20]. sarkodie and owusu [21] have studied the effects of pollution produced on bitcoin production. the study was based on 4158 statistical data points acquired during the period july 7, 2010, to december 4, 2021. the 12 variables of the study include the maximum and minimum and the annual carbon footprint trend from three non-renewable sources (oil, gas, and coal). the annual carbon footprint trend in this study is measured and calculated based on the carbon dioxide produced and based on the method provided by the international energy agency [21]. stroll et al. [22] proposed a method for estimating the energy consumption of bitcoin production. based on the localization of ip addresses, the annual power consumption of bitcoin production up to november 2018 was equal to 45.8 twh, with annual carbon emissions between 22.0 and 22.9 mt. this annual amount of carbon dioxide production is equal to the annual production of carbon dioxide by jordan and sri lanka. krause and tolaymat [23] provided a way to calculate the minimum energy requirements of several digital currencies and their dollar value. the review period was from january 1, 2016, to june 30, 2018. calculations showed that bitcoin, atrium, light coin, and monroe mining consumed about 17, 7, 7, and 14 mj of energy, respectively, to produce one usd. in comparison, the extraction of aluminum, copper, gold, platinum, and rare earth oxides, respectively, consumed 122, 4, 5, 7, and 9 mj of energy to produce one us dollar, respectively. this comparison shows that, except for aluminum, cryptocurrency extraction consumes more energy than the extraction of minerals. the data also show that the network calculations for the four digital cryptocurrencies are constantly increasing. it is also estimated that the production of four currency codes emits 3 to 15 million tons of carbon dioxide. similar studies have concluded that, due to high energy consumption, digital currency markets can be an important source of carbon dioxide production [23, 24]. vries and stoll [25] examined the increase in e-waste through the increase in hardware for bitcoin production. according to the method presented, about 30.7 tons of toxic chemical waste m. aliehyaei et al. /future energy may 2024| volume 03 | issue 02| pages 16-23 18 and heavy metals are buried in the soil annually, which is equivalent to the annual e-waste in the netherlands. vries [26] concluded that renewable energy is not the answer to bitcoin sustainability. he suggested other alternatives to bitcoin mining, including a proof-of-stake mechanism. in this mechanism, the participating machines do not have to use their computing power. malfuzi et al. [27] studied the thermodynamics and economics of a bitcoin mining system that is powered by a solid oxide fuel cell. the fuel source of this system was natural gas or biogas. in that study, different scenarios related to bitcoin price and extraction difficulty were proposed. the system was studied based on the economic conditions of different countries. the results showed that iran, russia, and china are the best countries to extract bitcoin using grid electricity. iran, canada, and russia are also the best countries to extract bitcoins from the solid oxide fuel cell (sofc) system with natural gas. in general, in the mentioned countries, the profitability of sofc mining is less than that of grid mining. but the sofc has better sustainability and lower environmental costs. lei et al. [28] reviewed and analyzed the energy consumption of blockchain technologies and proposed policies in this regard. due to the expansion of the digital currency market and its growing popularity, and the high level of energy consumption and environmental issues, the production of bitcoins by nonrenewable energy sources is impacting the environment and energy security. therefore, the use of renewable energy sources can be considered an alternative. in this article, the amount of electricity consumed by miners to produce a bitcoin is calculated based on statistical data. based on the amount of electricity consumed and the price of electricity in different regions, and its global average, a model is proposed to calculate the base price of bitcoin. various scenarios for the production of bitcoins with renewable and non-renewable energy sources from an energy, economic, and environmental perspective are presented. finally, a conceptual policy for bitcoin production is proposed. the main objectives of this article are as follows: • provision of the theory that bitcoin value is supported by energy. • calculation of the base price of bitcoin based on the price of electricity in different countries and regions and based on the theory presented in this article (above objective). • calculation the amount of air pollutants to extract bitcoin if the energy source of power plants is non-renewable energy. • calculation of the social costs of air pollutants based on the amount of electricity used to produce bitcoin and the associated pollutants for which the cost should be added to the base price of bitcoin. • development of a strategy to produce bitcoin from renewable energy resources based on the price of electricity from systems that use renewable energy resources. 2. calculation of electricity consumption for bitcoin production an application-specific integrated circuit (asic) is an integrated circuit chip designed and built for a specific purpose. miner asic refers to the hardware used to extract a particular type of digital currency. therefore, an asic bitcoin miner is only for bitcoin mining. the extraction process means solving a complex mathematical problem using hash functions associated with blocks containing transaction data. the first miner to solve the puzzle can authorize the transaction or add bitcoins to the block. each winner of bitcoin mining receives a prize (a certain amount of bitcoin). this bonus includes all transaction fees. to calculate the amount of electricity required to produce bitcoin, the entire network must be considered. it should be noted that the amount of energy required for electricity depends on the miner model, its efficiency, and the difficulty of extracting bitcoins [5, 23, 29-31]. according to data published in the reference [32], a bitcoin is currently produced at 122,000 terra hash per second for 24 hours. note that hash rate or hash power is a measure of the performance of a miner device. in other words, a hash rate indicates the rate at which a miner succeeds in solving a hash to receive a reward. in the bitcoin extraction process, blocks containing approved transactions must be hashed before being added to the blockchain. the process of hashing blocks is also called hashing [32]. the number of asics required can be written as follows: 𝑁𝐴𝑆𝐼𝐶 = 122000 𝑁𝐻𝑅 (1) here, n denotes the number, and subscript hr means hash rate. the electrical energy required for one bitcoin production is calculated by [9, 33]: 𝐸 = 24 × 𝑁𝐴𝑆𝐼𝐶 × �̇�𝐴𝑆𝐼𝐶 (2) where �̇�𝐴𝑆𝐼𝐶 denotes electrical power consumption by one asic (kw). as an example, considering equations 1 and 2, the s19 pro 110 miner needs 86,509 kwh of electricity to generate a bitcoin [5, 23, 29-31]. the whole market does not use the above model. for this purpose, market share and different types of miner models are considered. this model was presented for the first time in reference [23]. so, the top bitcoin miner models that have the largest market share are considered [34]. table 1 shows the specifications of those miners. because the market share of those miners is almost in the same range, equal market share is considered for them. table 1. top bitcoin miner models [34] according to equations 1 and 2 and the data in table 1, the amount of electrical energy required to produce a bitcoin is equal to 120,360.2 kwh. 3. developing a methodology for calculating the base price of bitcoin the support of the currencies of countries is a certain amount of gold or other precious metals and foreign exchange reserves. according to the authors of this article, bitcoin is financially supported by energy. miner model nhr (th/s) ẇasic (kw) antminer s19 pro 110 3.25 antminer t19 84 3.15 avalonminer a1166 pro 81 3.4 whatsminer m30s++ 112 3.472 avalonminer 1246 90 3.42 whatsminer m32-62t 62 3.536 ebang ebit e11++ 44 1.98 ebit 12+ 50 2.44 https://www.softwaretestinghelp.com/bitcoin-mining-hardware/#1_antminer_s19_pro https://www.softwaretestinghelp.com/bitcoin-mining-hardware/#2_antminer_t9 https://www.softwaretestinghelp.com/bitcoin-mining-hardware/#4_avalonminer_a1166_pro https://www.softwaretestinghelp.com/bitcoin-mining-hardware/#5_whatsminer_m30s https://www.softwaretestinghelp.com/bitcoin-mining-hardware/#6_avalonminer_1246 https://www.softwaretestinghelp.com/bitcoin-mining-hardware/#7_whatsminer_m32-62t https://www.softwaretestinghelp.com/bitcoin-mining-hardware/#8_ebang_ebit_e11 https://www.softwaretestinghelp.com/bitcoin-mining-hardware/#10_dragonmint_t1 m. aliehyaei et al. /future energy may 2024| volume 03 | issue 02| pages 16-23 19 figure 1 shows the production or extraction cycle of bitcoins. in this process, electricity is generated by power plants that use renewable or non-renewable energy sources. if nonrenewable sources are used to generate electricity, the initial cost of equipment, installation, commissioning, and maintenance of the power plant along with the price of fuel is taken into account to calculate the price of electricity. but, if renewable energy sources are used, the cost of fuel is eliminated, but other costs still exist. in both cases, the generated electricity has a value and price that is consumed by the miners to produce bitcoins. thus, the value and price of bitcoin are inherently supported by the price of energy consumed to produce and extract it. so, the base price of bitcoin can be considered based on the price of electricity consumed to produce it. of course, at certain times, due to economic issues, the price of bitcoin can be more or less than its base, which is due to economic issues such as buyers' or sellers' power, injecting money into the market, expansionary or contractionary economic policies of governments, etc. then, the value and price of bitcoin can be evaluated from an economic point of view in two ways: technical and fundamental. but bitcoin's digital currency still has an intrinsic value that stems from the amount of electricity consumed to generate or extract it. except for specific periods, this value has been on the rise for more than two decades due to the increasing complexity of its extraction and production and the increase in the number of hash rates for its production or extraction. table 2 shows the electricity cost and base price of bitcoin in 2022 in different countries and its average global price. the electricity cost is taken from ref. [35]. based on the consumption of 120,360.2 kwh of electricity to produce a bitcoin, as described earlier in this article, the base price of a bitcoin is determined based on the price of this amount of electricity. figure 1. production or extraction process for bitcoins table 2. electricity cost and base price of bitcoin in 2022 in different countries and its average global price no. countries electricity cost (us$/kwh) [35] bitcoin basic cost (us$) 1 belgium 0.32 38515.4 2 chile 0.17 20461.3 3 china 0.09 10832.4 4 denmark 0.36 43329.8 5 france 0.2 24072.1 6 germany 0.35 42126.2 7 india 0.08 9628.8 8 italy 0.23 27682.9 9 japan 0.24 28886.5 10 kenya 0.22 26479.3 11 mexico 0.09 10832.4 12 new zealand 0.21 25275.7 13 qatar 0.03 3610.8 14 russia 0.06 7221.6 15 saudi arabia 0.05 6018.0 16 singapore 0.18 21664.9 17 turkey 0.06 7221.6 18 united kingdom 0.28 33700.9 19 united states 0.16 19257.7 20 world 0.135 16248.7 m. aliehyaei et al. /future energy may 2024| volume 03 | issue 02| pages 16-23 20 the base price of bitcoin shows the real value of bitcoin in a country or its global average. the change in the price of bitcoin higher or lower than its base price is due to market influences and is related to influential economic parameters. in connection with the subject of this article, if the price of bitcoin in the economic market grows above the base price, the production of bitcoin in that country is cost-effective. otherwise, it is not cost-effective. of course, special attention should be paid to whether the price of electricity in a country is its real value or whether the government subsidizes it. from table 2 and according to the price of electricity, the highest base price of bitcoin is for denmark and germany and the lowest is for qatar and saudi arabia. for example, the base price of bitcoin in qatar is 3610.8 us$, while in denmark it is 43,329.5 us$, which is about 14 times more. it can also be seen in table 2 that the highest electricity prices and consequently the base prices of bitcoin are related to continental europe and the cheapest are related to the middle east region due to abundant sources of fossil fuels. also, the average global electricity price is 0.135 us$ and the base bitcoin price is 16248.7 us$. 4. analysis of the production of bitcoin by nonrenewable energy sources to generate bitcoin from non-renewable energy sources, the following four scenarios are considered: • scenario 1: electricity is generated by a coal-fired steam power plant. • scenario 2: electricity is generated by a gas power plant that is fueled by natural gas. • scenario 3: electricity is generated by a gas power plant whose fuel is gas with gas oil. • scenario 4: electricity is generated by a combined cycle power plant that includes a gas power plant, steam turbine, and heat recovery steam generation (hrsg), and is fueled by natural gas. table 3 shows the unit amount of selected pollutants for the four scenarios [35]. in table 3, the pollutants considered are co2, nox, and so2. note that power plants emit other air pollutants, as well as wastes that enter the soil and water. in this article, only selected air pollutants during operation are considered. table 3. amount of pollutants produced for four scenarios for generating bitcoin from non-renewable energy sources figures 2 to 4 show the production of co2, nox, and so2 for four scenarios, for the production of one bitcoin. the highest amount of pollutants are related to scenario 1 due to burning coal in the steam power plant and the lowest is related to scenario 4, due to the recovery of gas turbine exhaust hot gas in hrsg for efficiency and to the use of natural gas as the fuel. to create a link between the economy and the environment, the social costs of environmental pollutants are considered. the social costs of environmental pollutants are considered here to be the costs that are indirectly imposed on people in the community due to environmental degradation. figure 2. quantities of co2 generated per bitcoin produced, for four scenarios figure 3. quantities of nox generated per bitcoin produced, for four scenarios figure 4. quantities of so2 generated per bitcoin produced, for four scenarios these costs include reduced productivity, illness, and death in the community. these costs depend on the living conditions of the community, the local location, and the type of environmental degradation. table 4 shows the social costs of co2, nox, and so2 pollutants [36, 37]. according to the data in tables 3 and 4 and figures 2 to 4, the social costs of air pollutants for the production of a bitcoin are 13384 us$, 6696 us$, 4050 us$, and 3368 us$, respectively, for scenarios 1 to 4. therefore, if any of scenarios 1 to 4 are used to generate electricity and, subsequently, bitcoin, the costs mentioned should be added to the base price of bitcoin (table 2). scenario co2 (g/kwh) nox (g/kwh) so2 (g/kwh) 1 930 2.1 8.8 2 800 1.6 1.4 3 610 1.1 0 4 510 0.9 0 m. aliehyaei et al. /future energy may 2024| volume 03 | issue 02| pages 16-23 21 table 4. social costs of co2, nox, and so2 pollutants [36, 37] 5. investigation of the production of bitcoin by renewable energy sources the main types of renewable energy sources considered here are geothermal, solar, biogas, wind, and hydro. the maximum, mean, and minimum levelized cost of electricity (lcoe) for various renewable energy resources are shown in table 5 [38-40]. the variation of lcoe from maximum to minimum depends on the potential of that country or region for that renewable energy source, import and export taxes, and other factors. table 5. maximum, mean, and minimum lcoe for various renewable energy resources 5.1 case study a detailed case study is now considered. the price of electricity and the base price of bitcoin in denmark are 0.36 us$/kwh and 43,329.8 us$, respectively. considering the high potential of wind energy in that country, the shore-wind turbine is selected to produce electricity. considering the data in table 5, the average cost of electricity is 0.05 us$/kwh. according to the price of electricity in denmark (table 2: 0.366 us$/kwh), the profit per kilowatt hour of electricity is 0.31 us$/kwh. according to the calculations in this article, 120360.2 kwh of electricity is required per bitcoin produced. now, if this amount of electricity is sold to the electricity grid instead of producing bitcoins, the profit will be equal to 37,311,662 us$. if we consider that bitcoin is generated by this system, and according to the price of electricity generated by this system (0.05 us$/kwh), the cost of producing a bitcoin is equal to 6018 us$. considering the current price of bitcoin (2 june 2022: 31,700 us$), the profit is 25,682 us$. to reach the tipping point, the profit from the sale of electricity is 37311.6 us$ should be added to the base price of bitcoin by non-renewable energy sources (6018 us$), which is 43329.7 us$, which is the same as the base price of bitcoin shown in table 2. note that if the electricity used to produce bitcoin is replaced by power plants that use fossil fuels, the social costs of environmental pollutants (part 4 of the article) should be added to the base price. also, in the case of bitcoin production by renewable energy sources, miners can be placed next to the power generator, thus the cost of electrical power transmission and distribution is eliminated. due to the new digital currency market, price changes for digital currencies are very sharp. in 2021, for example, the price of digital currencies fluctuated from about 34,000 to 61,000 us$. so the question is, if it is cost-effective to produce bitcoin in one period and not in another, is there an alternative way to use the electricity allocated to produce bitcoin? the answer to this question depends on various factors such as the needs of a region or country, the number of its natural resources, the level of the social and economic welfare of society, etc. there are several ways to consume electricity generated at a time when it is not cost-effective to produce bitcoins. for example, in a cold or hot region or country, heating and cooling loads for residential, commercial, and office buildings can be provided. in regions and countries that have a shortage of drinking water resources and in the vicinity of the sea or ocean, drinking water can be produced by reverse osmosis system, or in countries that have a shortage of fuel and have sufficient water resources, electricity can be used to split water via electrolysis to produce hydrogen as a clean fuel. along with all these solutions, we can continue to produce bitcoin and look at it as a long-term investment. 6. proposing a strategy to produce bitcoin by renewable energy resource in this part of the article, the following strategy is proposed for the production of bitcoin by renewable energy sources: • step 1: the potential of renewable energy sources in that region or country is examined and, according to the potential of these resources, and their availability and usability, the priorities of these resources are selected. • step 2: the price of electricity produced by power generation systems with renewable energy sources selected in the first step is calculated. to calculate the price of electricity generated, two modes are considered: with and without considering the transmission and distribution electrical network. • step 3: power generators in the country or region considered are examined. if the energy sources of power generation systems are non-renewable sources, the social costs of environmental pollutants (similar to scenarios 1 to 4 of part 4 of the article are added to the base price of electricity (table 2 of the article). • step 4: if the price of generated electricity by renewable energy resource system (considering the costs of electricity transmission and distribution) is less than the price of electricity without government subsidies and the price of bitcoin is less than the base price of bitcoin (table 2), electricity generation is neglected by the selected system in steps 1 and 2. • step 5: if the price of bitcoin is lower than the bitcoin base price shown in table 2 and the price of electricity generated by the proposed system of electricity generation with renewable energy sources is lower (taking into account the costs of transmission and distribution of electricity) than the price of electricity in that area or country, the generated electricity is sold to the electricity grid. air pollution values (us$/kg) co2 0.042 nox 7.3 so2 7.4 type of renewable energy resource sub-division lcoe (us$/kwh) max ave min wind on-shore 0.14 0.05 0.029 off-shore 0.2 0.088 0.049 solar pv utility-scale 0.172 0.056 0.034 commercial 0.14 0.094 0.074 residential 0.223 0.126 0.108 solar thermal 0.13 0.121 0.112 hydro reservoir (≥ 5 mw) 0.142 0.072 0.039 hydro run of river ((≥ 5 mw) 0.104 0.068 0.046 geothermal 0.12 0.099 0.078 biomass 0.182 0.118 0.053 m. aliehyaei et al. /future energy may 2024| volume 03 | issue 02| pages 16-23 22 • step 6: if the price of bitcoin is higher than the base price of bitcoin shown in table 2, the production of bitcoin by the system is recommended. in this case, bitcoin production miners can be placed next to the power generation system, which eliminates the cost of electricity transmission and distribution. 7. conclusion and policy implications bitcoin, the first decentralized digital currency introduced by an anonymous person or group since 2008, has attracted worldwide attention. a significant number of economists have introduced bitcoin as a new phenomenon in the 21st century that could reduce global inflation. given the tens of thousands of digital currencies that have emerged since the advent of bitcoin and its price growth trend over more than a decade, which are signs of the growth of this business. in addition to being money, bitcoin has always been considered a tool for investing and storing value, which is why it is called digital gold. one of the most important problems in the production or extraction of bitcoins is the high-power consumption by miners. if the energy sources of electricity generation are supplied by non-renewable energy sources, in addition to emitting air pollutant gases, it will increase greenhouse gases and consequently contribute to climate change. in the following, four scenarios are proposed for the production of bitcoin by electricity supplied from nonrenewable energy sources. these scenarios include coal-fired steam power plants, natural gas-fired power plants, natural gas/oil gas-fired power plants, and dual-cycle (steam and gas cycles) natural gas-fired power plants. based on the amount of electricity required to produce one bitcoin, the amount of pollutants emitted to produce bitcoin and its social costs are calculated. these costs should be added to the base cost of bitcoin production if non-renewable energy sources are used to produce bitcoin. if renewable energy sources are used to produce electricity that reaches the consumption of bitcoin production, in addition to solving the problems mentioned above, it can be an income-generating factor for countries, especially developing countries where the price of electricity is low. in this article, based on the price of electricity in different countries and regions, the base price of bitcoin is calculated, and a strategy is presented based on which price of bitcoin is cost-effective to produce for that country, considering the price of electricity. nomenclature hr: hash rate n: number �̇�: electrical power consumption subscripts asic: application-specific integrated circuit ethical issue the authors are aware of and comply with best practices in publication ethics, specifically concerning authorship (avoidance of guest authorship), dual submission, manipulation of figures, competing interests, and compliance with policies on research ethics. the authors adhere 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[40] renewable power generation costs in 2020 see: https://www.irena.org/publications/2021/jun/rene wable-power-costs-in-2020 [accessed 17 may 2022]. available from: https://www.irena.org/publications/2021/jun/rene wable-power-costs-in-2020 [access 2022]. this article is an open-access article distributed under the terms and conditions of the creative commons attribution (cc by) license (https://creativecommons.org/licenses/by/4.0/). as. umar and a. usman/future energy november 2023| volume 02 | issue 04| pages 01-09 1 article seasonal variation of surface energy balance over mubi northeastern nigeria during 2000-2020 abubakar saidu umar1*, adam usman2 1department of pure and applied physics, adamawa state university, mubi, nigeria 2department of physics, faculty of physical science, modibbo adama university, yola, nigeria a r t i c l e i n f o article history: received 01 january 2023 received in revised form 29 january 2023 accepted 01 february 2023 keywords: energy, temperature, heat, surface, mubi *corresponding author email address: abuumarsaidu@gmail.com doi: 10.55670/fpll.fuen.2.4.1 a b s t r a c t several studies have been undertaken on surface energy balance (seb) at various places in the world, but none have been undertaken for mubi, northeastern nigeria. in the effort of consideration, this study aims to evaluate the seasonal variation of seb in mubi, with emphasis on the observational data from 2000 to 2020. evaluation of seasonal variations was executed using time series analysis to find out the impact of precipitation, evapotranspiration, soil, and air temperature changes on seb components. it was found that the seb components variations of sensible heat (h) had a maximum value of 1035.13 wm−2 in the dry season, in the month of december, while a minimum value of 104.13 wm−2 during the rainy season, in the month of july; latent heat (lh), had a peak value of 5243.46 wm-2 in the dry season in the month of april, while in the rainy season, the lower value was found to be 2460.6 wm-2, in the month of august; soil heat (g) had minimum and maximum values of 886.43 wm-2 in march and 275.25 wm-2 in august respectively; and net radiative (rn) varies roughly between the highest month in march with 2809.35 wm−2 (rainy season months) and lowest month in august with 6879.69 wm−2 (dry season months). it was also found that precipitation, evapotranspiration, soil, and air temperature follow the same trend with some seb results, affirming their dependency on each other. therefore, it is expected that this study will help to understand the amount of energy received or emitted in the mubi region. along with the main work, some recommendations were made by researchers on some applications of seb to the community. 1. introduction it is highly essential to understand the interaction between the earth and the atmosphere, which mainly links to the principle of energy conservation, called surface energy balance. seb has been widely used to evaluate and compare the strength of the various factors affecting earth's surface. seb principle conditions that the amount of energy arriving at the earth's surface must equal the energy leaving the earth's surface over a period of time. otherwise, the energy is imbalanced. solar radiation is the only significant energy source on the earth that is transformed into various energy fluxes after entering into the atmosphere and earth’s surface [1]. most of these energies come in the form of heat absorbed by the earth's surface. in such processes, the resulting energy goes toward heating the earth's surface by warming up subsurfaces, earth's atmosphere, and water bodies, which are later emitted back to the atmosphere. seb establishes the state of the earth’s environment and responds to changes in the various energy transformation processes to account for all energy at the surface. surface energy balance models are based on balancing net radiation with ground heat flux, sensible heat flux, and latent heat flux assuming that heat advection is negligible [2, 3] expressed as: 𝑅𝑛 = 𝐺 + 𝐻 + 𝐿𝐻 (1) where rn is the net radiation flux (wm−2), g is the soil heat flux (wm-2), h is the sensible heat flux (wm-2), and lh is the latent heat flux (wm-2). the equation states that the net radiation flux received at the earth’s surface must either warm or cool the air above the earth's surface (sensible heat flux), evaporate water bodies (latent heat flux), or warm or cool the soil (soil heat flux). as previously mentioned in equation (1), incoming net radiative flux (rn) equals the combination of sensible heat (h), latent heat (lh), and soil heat (g) fluxes; the following are details explanations of individual’s flux. 1.1 net radiation flux (rn) the net radiation is the amount of heat energy delivered to do work at the surface of the earth. solar radiation (short future energy open access journal https://doi.org/10.55670/fpll.fuen.2.4.1 november 2023| volume 02 | issue 04 | pages 01-09 journal homepage: https://fupubco.com/fuen issn 2832-0328 mailto:abuumarsaidu@gmail.com https://doi.org/10.55670/fpll.fuen.2.4.1 https://fupubco.com/fuen as. umar and a. usman/future energy november 2023| volume 02 | issue 04| pages 01-09 2 and longwave radiation) are input energies to the surface energy balance. these energies, directly or indirectly, are the results of nuclear interactions occurring on the solar surface and is equal to the total available energy for the occurrence of the earth’s surface and atmospheric processes [4, 5]. basically, solar radiation has two acting parts: one is incoming (downward rs↓) radiation on earth’s surface that depends on the atmospheric transitivity, solar constant, solar altitude, and incidence angle, and another part are outgoing (upward rs↑) that is reflected back to space due to the combined effect of surface, clouds, aerosol, gases, etc [1]. therefore, surface net radiation (rn) in the one-source surface energy balance model is estimated from the sum of the difference between the incoming and the reflected outgoing shortwave solar radiations (0.15–5 µm) and the difference between the downwelling atmospheric and the surface emitted and reflected longwave radiations (3–100 µm) [6]: 𝑅𝑛 = (1 − 𝛼)𝑅𝑔𝑙𝑜𝑏𝑎𝑙 + 𝜀𝑠𝜀𝑎𝜎𝑇𝑎 4 − 𝜀𝑠𝜎𝑇𝑠 4 (2) where α is the surface albedo. surface albedo is a critical parameter that controls surface energy balance [7]. albedo is the fraction of incoming radiation attenuated by reflection processes in the atmosphere, with values ranging from 0 to 1 for the lowest and highest reflection, respectively. most of the estimated global solar radiations are often corrected by albedo, which contributes greatly to estimating the global average amount of incoming solar radiation onto a particular place on the earth's surface. this can affect surface albedo and radiation fluxes, leading to a local temperature change and, eventually, a vegetation response [8]. this implies that the global solar radiation received on the earth’s surface was more than the reflected radiation lost into space [9]. although the global annual mean land albedo varies from 0.18–0.26 [10,11], climate, biogeochemical, hydrological, and weather forecast models require regional surface albedo with an absolute accuracy of 0.02–0.05 for snow-free and snowcovered land [11]. for this study, a typical constant value of 0.03 is taken based on bastiaanssen [12], the value also corresponds to a value obtained by [7]. rglobal is the global solar radiation in w m–2, εs is the surface emissivity, εa is the atmospheric emissivity estimated as a function of vapor pressure, and σ is the stefan–boltzmann constant. surface emissivity is computed using an empirical equation by tasumi [13], based on soil and vegetative thermal spectral emissivities housed in the modis ucsb emissivity library [14]. 𝜀𝑎 = 0.95 + 0.01 lai for lai 3 ≤ 1 (3) 𝜀𝑎=0.98 when lai>3, where lai (m2 m−2) leaf area index; the ratio of the total leaf area for the surface one side of leaves per unit of ground area. lai is an indicator of biomass and canopy resistance to vapor flux and is computed using an empirical equation stemming from bastiaanssen [14, 15]. lai = −ln[(0.69 − saviid/0.59)/0.91 (4) where, for landsat images, savi 6 is based on the top of atmosphere reflectance of bands 3 and 4. several different methods have been proposed to estimate atmospheric emissivity, but according to brutsaert [16], atmospheric emissivity is given as: 𝜀𝑎 = 9.2 × 10−6𝑇𝑎 2 (4) 1.2 soil heat flux (g) soil heat flux (g) is the amount of heat transfer in vegetation and soil through molecular conduction. it is determined by the soil thermal conductivity and heat capacity which both depend on properties such as soil texture, i.e. fractions of sand, loam, and clay particles, and soil water content [17]. it also affects soil physical processes such as soil evaporation and aeration, chemical reactions in the soil, and biological processes such as seed germination, seedling emergence and growth, root development, and microbial activity [18]. soil heat flux (g), which is determined by the thermal conductivity of the soil and the temperature gradient of the topsoil, can be derived using the method developed by kustas and daughtry [19] and bastiaanssen [15], which is a function of surface albedo, surface temperature, and normalized difference vegetation index (ndvi) written as [20]: 𝐺 = 𝑅𝑛𝑇𝑠(0.0038 + 0.0074𝛼)(1 − 0.98(𝑁𝐷𝑉𝐼)4) (5) where the normalized difference vegetation index, ndvi. vegetation cover is one of the most important biophysical factors in determining seb through ndvi. ndvi is defined as a ratio of the difference in reflectivity of the near-infrared and red bands to their sum: 𝑁𝐷𝑉𝐼 = 𝑟𝑁𝐼𝑅−𝑟𝑅𝐸𝐷 𝑟𝑁𝐼𝑅+𝑟𝑅𝐸𝐷 (6) ndvi is a widely used technique to detect land use land cover change, especially changes in vegetation area and its pattern [21]. ndvi values range from 1 to -1. sparse vegetation (e.g. shrubs, meadows, and pastures) are expressed by values of 0.2 – 0.5 [22]. also, 0.2< ndvi<0.5, assumed to be a mix of bare soil and vegetation [23], 0.2-0.3 ndvi value represents shrub and grassland, 0.3-0.4 indicates sparse and unhealthy forest whereas >0.4 ndvi value represents healthy and dense vegetation [21]. high values (from 0.6 to 0.9) correspond to areas with dense vegetation, such as forest or agricultural vegetation, in the productive phase [24]. in this paper, the best features for the mubi region were described to vary from 0.1 to 0.5 due to the fractional land cover vegetation prevailing almost 80% cropland. the ndvi classification is indicated in table 1. table 1. the ndvi classification [25] 1.3 sensible heat flux (h) the sensible heat flux is the exchange of energy between the surface and the atmosphere obtained from the class/feature ndvi range water -1 ≤ 0.014 build-up 0.015 0.09 barren land 0.10-0.20 shrub and grassland 0.21-0.30 sparse vegetation 0.31-0.40 dense vegetation 0.41 ≤ 1 as. umar and a. usman/future energy november 2023| volume 02 | issue 04| pages 01-09 3 temperature difference between the surface and the atmosphere. calculation of the sensible heat flux of the surface is done using an aerodynamic function: 𝐻 = 𝜌𝑎𝑖𝑟𝐶𝑝 𝑑𝑇 𝑟𝑎ℎ (7) where, 𝜌𝑎𝑖𝑟 is the air density in kg/m3, cp is the specific heat of air at constant pressure, which is equal to 1000 (j/kgk), dt is the indicator of temperature difference in kelvin between two elevations near surfaces of z1 and z2, and 𝑟𝑎ℎ is the aerodynamic resistance (m/s) available for the heat transfer between z1 and z2, which are considered 0.1 and 2 meters [4, 26, 27]. aerodynamic resistance is affected by the surface roughness and is determined by vegetation height and structure, wind speed, and atmospheric stability [6]. here, aerodynamic resistance is taken to be 2 s/m due to the roughness of the study area. based on equation (7), the higher the temperature difference and the aerodynamic resistance, the larger the sensible heat flux. also, sensible heat flux is zero if the temperature difference or aerodynamic resistance is zero. 1.4 latent heat flux (lh) latent heat flux is the flux of energy associated with the evaporation or transpiration of water from the earth's surface to the atmosphere and vice versa [28], sometimes called evapotranspiration (et). the primary controls on et are energy inputs such as incoming solar radiation and the capacity of the air to hold more water vapor both from local water vapor (humidity) and from mixing with drier air controlled by wind speed [2]. this process cools the earth’s surface and moistens the atmosphere near the surface, which is why the estimation of et is crucial for developing climatic, hydrological, bio-geophysical, and ecological models to predict the weather and climate or climate change [1]. the latent heat flux (lh) can be expressed as: 𝐿𝐻 = 𝑅𝑛 − 𝐺 − 𝐻 (8) the above said components of earth’s seb are responsible for the heating or cooling of the land/soil (solar and thermal radiation), the heating and cooling of the air (sensible heat flux), and the evaporation of water from soil and vegetation (latent heat flux) [1]. from equation (1), when the amount of energy coming to the surface (rn) equals the amount of energy leaving earth's surface (g + h + lh), the surface is said to be in energy balance (zero), and the temperature remains constant. also, if the sum of the energies in equation (1) is not equal to zero, then the resulting energy and temperature are said to be an imbalance. moreover, if the incoming is more than the outgoing energy to the surface, then the energy is said to be positive imbalance and negative if the outgoing is more than the incoming energy. it is a negative imbalance because it contributes to global warming, while positive contributes to global cooling. such processes have an essential role in regional weather, climate, and hydrosphere cycles, as well as in regulating urban heat redistribution [20]. also, the exchange processes occurring at the land surface are of paramount importance for the re-distribution of moisture and heat in soil and atmosphere [29]. for the past decade, seb has become a standard tool to study the exchange of energy between the earth’s surface and atmosphere. the research of seb is often carried out in different places such as jakarta and neighboring regions by ilhamsyah [30], metropolitan cities of india during the 2000–2018 winter seasons by sultana and satyanarayana [28], greenland ice sheet by liu [31], naqu region of qinghai-tibet plateau during 2005-2016 by wang and ma [32], lake huron by petchprayoon [33], tilled and nontilled bare soils by akuoko [34], tropical river basin by kumar et al. [35], semiarid environments by small and kurc [36], storglacia¨ren, sweden by hock and holmgren [37], urban park and its surroundings by bäckström [38], two sahelian surfaces by verhoef et al. [39]. these studies motivated us to carry out such research in mubi, northeastern nigeria, to benefit from the resources that seb is disclosing. the application of energy balance to a wide mixture of agricultural crops and other vegetation is complex enough that there are still some areas of considerable empiricism and, therefore, the potential for local refinement [14]. at the same time, all physical, chemical, and biological processes respond to changes in conditions produced by changes in the seb. in recent times of agricultural and settlement expansion, increase in human population, over-exploitation of natural resources, and intense flux of earth's surface energy cause a serious threat to human beings, agriculture, and settlement. this is specifically true in mubi. hence, adequate information about seb status is relatively scarce in nigeria, particularly mubi. understanding and utilizing metamorphic trends, water vapor loss, precipitation, plant growth, drought monitoring, revegetating a barren area, irrigation scheduling, drainage practices, erosion, desertification, and global climate changes, among others, depends on seb, and has yet to be fully exploited in mubi. in an effort to fill this gap, this study aims to evaluate the seasonal variation of seb in mubi, with emphasis on the observational data from 2000 to 2020. along with the main work, some recommendations were made by researchers on some applications of seb to the community. 2. method and materials 2.1 study area mubi, northeastern nigeria, is within the foothills zone of mandara mountains terrains (characterized by hill landforms and flat plain land), at longitude 13.125 and latitude of 10.333 with an average altitude of about 650 m above sea level. due to its topography and climate, which is dominated by crops, mubi serves as one of the major agricultural regions in nigeria and is one of the most important economic activities in the region, with about 65% of the total working population being engaged directly. the seasonal variations of mubi were dry (in the months of november, december, january, february, march, and april) and rainy (in the months of may, june, july, august, september, and october) season. the estimated average temperature and precipitation in mubi are respectively 28.83°c and 1,154.75 mm over the last 20 years. the highest and lowest temperatures, respectively, occur in april and august, while precipitation almost occurs in the rainy season. 2.2 types and sources of data several parameters were acquired for this study. some of them are literature based, while others were obtained from meteoblue, as shown in table 2. mean daily global solar radiation, soil temperature (at 0-10cm depths), and air as. umar and a. usman/future energy november 2023| volume 02 | issue 04| pages 01-09 4 temperature (at 10m height) historical weather simulation data used in this research, with a spatial resolution between 4 and 30 km for the mubi location, were obtained from meteoblue product for the period of 20 years (2000-2020). although soil temperature may increase, decrease, or vary monotonically with depth, depending on the season and the time of the day [40, 41]. for this study, daily soil temperature data taken at the soil surface (0-10 cm) was adopted from the available data. these parameters are assumed to be homogeneous throughout the mubi station and offer an opportunity to evaluate seb and help understand the variability over time. table 2. data used for the analysis type of parameters values source of data global solar radiation (rglobal) varies over time (wm-2) meteoblue soil temperature (ts) varies over time (°c) meteoblue air temperature (ta) varies over time (°c) meteoblue albedo (𝛼) 0.03 dintwe, [7] soil emissivity (𝜀𝑠) 0.85 estimated by study air emissivity (𝜀𝑎) varies over time (unit less) evaluated air density (𝜌𝑎𝑖𝑟) 1.225 kg m-3 constant specific heat capacity of air (𝐶𝑝) 1000 j/kgk constant aerodynamic resistance (rah) 2 s/m tang et al. [6] ndvi 0.3 bid [21] stefan–boltzmann constant (σ) 5.67 × 10-8w m-2k4 constant evapotranspiration varies over time (mm) meteoblue precipitation varies over time (mm) meteoblue 2.3 method of data analysis and presentation as shown in table 2, the data acquired from literature and meteoblue weather station for mubi are all known constants, dependents, and independent variables that are accordingly derived, evaluated, or directly computed into equations 1 to 8 of seb fluxes. the data obtained went through pre-processes by averaging daily data to monthly and annual time intervals before calculations were taken. these methods of calculating seb components are purely empirical and were carried out basically to establish time series to capture the trends associated with changes. to present the result obtained from calculations, we selected dry and rainy seasons for typical weather conditions to analyze the variation of each component under seb for the analysis, and to test whether the variability is in line with the evaluation. application of time series analysis for annual and seasonal evidence of 2000 to 2020 periodicity was carryout using mathematica software for the presentation of results. 3. result and discussions it is very important to note that the monthly potential combination of net radiative heat (rn), sensible heat (h), latent heat (lh), and ground heat (g) fluxes equated monthly seb. therefore, the results of each of these parameters are discussed for better understanding. 3.1 variations of air and soil temperatures on the seb soil temperature is a measure of soil internal energy or heat content and changes in the heat gained or lost by the soil [42]. soil temperature is one of the most important factors that affect soil heat storage, soil heat flux, soil water flux, seed emergence, nutrient transformation, transport, uptake, and plant growth [43] plays a major role in ensuring crop productivity, sustainability and control of biological and biochemical processes which invariably affects soil organic matter formation, fertilizer efficiency, seed germination, plant development, the ability of the plant to survive during the dry season, nutrient uptake and decomposition, and disease and insect occurrence [44-48]. furthermore, increased soil temperatures will have a direct impact on water demand and crop yield [49], shift spring temperature threshold, indicating potentially longer vegetative period and earlier yield and subsequent secondary crop yield [50], and major changes in the morphology of the plant was evident [51]. plants stop growing when the soil temperature becomes too cool, and some stop growing when the soil temperature is too hot. the optimum range of soil temperature for plant growth is between 20 and 30°c, and the rate of plant growth declines drastically when the temperature is less than 20°c (suboptimal) and above 35°c (supra-optimal) [48]. based on this, it is observed that the soil temperature values of mubi were considerably stable, as expected for crops (figure 1). being able to determine temperature differences in mubi is important in the discussion of seb. figure 1. time series of monthly variations of air and soil temperature for mubi during 2000-2020 as shown (figure 1), the air and soil temperature trend is almost the same, but the difference has obvious seasonal as. umar and a. usman/future energy november 2023| volume 02 | issue 04| pages 01-09 5 changes. both air and soil temperature in november has a higher trend, which gradually decreases before reaching a peak in april. the soil temperature from october to april is higher than the air temperature (dry season), and the air temperature is higher than the soil temperature from may to september (rainy season). the trend values of temperature difference during dry and rainy seasons period of the year revealed interesting spatial variability patterns. as a result, groundwater loss is greater as drier and warmer conditions in mubi increase evaporative losses in the rainy season. the losses were less prominent in the dry season (that is from october to april than in the months in the dry season. the differences indicate why temperature highlights the importance of seb. in both cases, the month of april had the highest temperatures (33.34 °c), whereas the lowest was in the month of august (24.63°c). results also demonstrated that during the dry (november to may), both soil and air temperatures were warmer than the rainy (may to october) seasons temperatures. the air temperature showed an opposite trend, with soil temperature being warmer than the air temperature in the dry season. monthly, from january to april, the temperature increases higher and decreases from april to august, which then increases to the month of november, then decreases to january. january to december of each year indicates the temperature path reversal, creating seasonal and annual variations. in this situation, dry-season soils had a significantly higher temperature than rainy-season soils temperature. accordingly, continual air and soil temperature variations depend on response to changes in earth and atmospheric conditions of solar radiation, an increase of soil moisture content, air temperature, wind speed, rainfall, and others weather conditions. this phenomenon was due to the effects of weather conditions, which allow solar radiation to warm the earth's surface. therefore, the lower temperature of the surface of the earth generally gains cold at a higher rate of rainfall than the earth's surface in the dry season. 3.2 variations of precipitation and evapotranspiration on the seb as shown in figure 2, mubi experiences average precipitation and evapotranspiration of 1,154.75 and 479.33 mm annually. the highest and the lowest monthly precipitation value of 276.31 mm is found in the month of august and 0 mm in the months of december, january, and february, respectively. at the same time, the highest and the lowest monthly evapotranspiration value of 85.89 mm are found in the month of september and 9.63 mm in the month of january, respectively. during the dry season, both precipitation and evapotranspiration in mubi experience fewer magnitude variations than the associated rainy season values. a similar trend of precipitation and evapotranspiration variations was observed during this period of 20 years (figure 2). these similarities are attributable to the changes in various climatic variables such as air and soil temperature, heat from solar radiation, rainfall infiltrated into the soil, crop residue covering the soil surface, snow cover, freezing, and thawing. another reason could be the presence of a cloud, which may allow only a small part of solar radiation to reach the ground surface due to its ability to reflect a good part of the solar radiation [40, 41]. in the rainy season, this is not because of the input precipitation but due to the influence of the harmattan wind, which significantly reduces the amount of potential evapotranspiration [52]. figure 2. time series of monthly variations of precipitation and evapotranspiration for mubi during 2000-2020 the evapotranspiration (et) increases with precipitation and contributes to the highest water loss or gain in seb. the differences between them are wide in the rainy season, where et is relatively small and thus contributes to a larger fraction in lowering rn and lh (figure 3). higher values of et occurred during the corresponding months of higher precipitation in mubi. here, et is a collective term that includes evaporation from vegetation or any other moisturecontaining living surface (transpiration) and evaporation from the water bodies and soil and is used to describe the loss of water from the earth’s surface to the atmosphere by the combined processes of evaporation and transpiration [53]. a thorough understanding of the factors controlling the energy balance of cropped soil enables making accurate estimates or predictions of evapotranspiration and irrigation water requirements [54]. while contributing to the surface energy balance, et quantifies the water requirement for efficient water management [55-57], especially in sub-humid and humid climates [54]. according to the energy budget concept, when the surface is wet or heavily vegetated, net energy is mainly consumed by the evaporation and evapotranspiration of water in soil and vegetation [20]. in essence, if there is adequate water in the soil, the incoming solar radiation will be used for convective activities [52]. moreover, an increase in soil moisture gives rise to increased evaporation from the soil surface, and a substantial part of net radiation goes into evaporation, which also gives rise to the observed low temperature [41], and increasing evapotranspiration can decrease the surface temperature of tree canopy [57, 58]. atmospheric temperature is projected to increase with climate change, and it provides more energy to cause more evaporation [57]. salman et al. [59] used simple waterbalance equations and identified that when the temperature increases, it contributes to an increment in evapotranspiration, which leads to a large increase in crop water demand and a decrease in climatic water availability. with this, it is affirmed that evapotranspiration and precipitation are both important for balancing the effects of seb in mubi. here, seasonal variation of precipitation and evapotranspiration often represents the amount of water as. umar and a. usman/future energy november 2023| volume 02 | issue 04| pages 01-09 6 consumed from agriculture. thereby significantly helping farmers in mubi by projecting water management in farms. figure: 3. time series of monthly variations of sensible heat (h), latent heat (lh), soil heat (g), and net radiative fluxes during 2000-2020 3.3 surface energy balance results for each seb component of equations (2 to 8) are explained in this section. it is noted that each component of net radiative heat (rn), sensible heat (h), latent heat (lh), and ground heat (g) fluxes are discussed separately as follows: 3.3.1 net radiative flux net radiation flux (rn) is the component of seb defined by equation 2. as shown in figure 3, rn over the entire 20 years appeared to be a very wide trend, varying roughly between the highest month in march with 2809.35 wm−2 (rainy season months) and the lowest month in august with 6879.69 wm−2 (dry season months). here, rn controlled most of the variations in seb due to the large values of incoming global solar radiation energy onto the earth's surface. as the short wave radiation balance is lower due to high albedo (equation. 1), air and soil temperatures tend to be low. its trend follows the same pattern with temperature variations (figure 1). implying that higher rn defines higher temperature at the same time. principally, the differences of rn play major role in seb than others components. explaining that rn is higher than any other energy in seb. as shown, both the rn and lh in dry and rainy seasons have the same diurnal variation trend as that of air and soil temperatures (figure1). this revealed to us that they depend on each other. meanwhile, during the dry season, a large amount of rn reaches the earth's surface from the atmosphere leading to the temperature differences between the earth and the atmosphere. therefore, the high amount of rn found in the mubi region during the dry season and low in the rainy season may have a great impact on balancing energy between the earth's surface and atmosphere. 3.3.2 soil heat flux (g) as shown in figure 3, the minimum and maximum values g are respectively 886.43 wm-2 in the months of march and 275.25 wm-2 in august. at the same time, rn, lh, and g follow the same trend but at different values. the reason for this phenomenon is that solar radiation inhibits heat exchange between the atmosphere and the underlying earth's surface, which strongly impacts evapotranspiration and precipitation (figure 2). comparatively, the contribution of the g to seb is lower than that of rn and lh throughout these 20 years. 3.3.3 sensible heat flux (h) as shown in figure 3, during the dry season, in the month of december, h had maximum value of 1035.13 wm−2, while the minimum value during the rainy season, in the month of july is -104.13 wm−2. h values are the highest positive values during the months of october, november, december, january, february, march, april, and august mostly occur in the rainy season. while negative values were observed in the rainy season in the months of may, june, july, and september. it is positive because the incoming energy is absorbed by the soil and negative when emitted to the atmosphere. sensible heat flux is caused by an interaction between the earth's surface and the atmosphere, whose values are mainly determined in terms of thermal differences and wind speed. 3.3.4 latent heat flux (lh) as shown in figure 3, in the dry season, the peak value of lh is 5243.46 wm-2, observed in the month of april, while in the rainy season, a lower value was found to be 2460.6 wm2, in the month of august. the lh is usually characterized by the soil water contents on the earth's surface. as shown (figure 3), lh is in the opposite trend with precipitation and evapotranspiration (figure 2). therefore, the lower the value of lh, the higher the water contents on earth's surface (precipitation). lh has a great impact on determining and detecting seasonal variation in mubi. 3.4 surfaces energy imbalance surface energy imbalance is the method of evaluating whether the energy that is coming onto the earth's surface is the same as that is going out to the atmosphere. it is obtained by subtracting all outgoing energy fluxes from all incoming energy fluxes. that is rn lh+g+h. surface energy imbalance requires that the g+h+lh be equivalent to rn. when both sides are the same (subtracted to be zero), the interaction between the earth's surface and the atmosphere is balanced, called seb. as shown in figure 4, the energy exchange between the atmosphere and the earth's surface is minimal. the result shows close agreement with seb of +/2×10-12 to 4×10-12. therefore, the result is in agreement with seb (equation 1). figure 4. time series of annual surface energy imbalance for mubi during 2000-2020 as. umar and a. usman/future energy november 2023| volume 02 | issue 04| pages 01-09 7 4. conclusion it was concluded that the results based on the seb components are in agreement with its stated equations, thereby revealing the amount of incoming and outgoing energy in the mubi earth surface in inferences to long-term trends. it was also found that the seasonal variation results obtained is highly influenced by local precipitation, evapotranspiration, soil and air temperature, which might be affected by incoming solar radiation, rainfall, or other relatedmeteorological conditions such as albedo, soil moisture, wind speed, soil temperature. the information provided in this study would help in planning, decision-making, and assessing the changes in seb, which can comprehensively explore the recent seasonal changes and weather conditions over mubi. acknowledgments the authors are extremely grateful to the meteoblue ag, basel, switzerland, for providing us with the necessary data to carry out the present work. ethical issue the authors are aware of and comply with best practices in publication ethics, specifically concerning authorship (avoidance of guest authorship), dual submission, manipulation of figures, competing interests, and compliance with policies on research ethics. the authors adhere to publication requirements that the submitted work is original and has not been published elsewhere in any language. data availability statement data sharing does not apply to this article as no datasets were generated or analyzed during the current study. conflict of interest the authors declare no potential conflict of interest. references [1] 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[59] s. a. salman, s. shahid, h. a. afan, s. m. shiru, n. alansari, and z. m. yaseen, “changes in climatic water availability and crop water demand for iraq region,” sustainability, 12, 3437, 2020. this article is an open-access article distributed under the terms and conditions of the creative commons attribution (cc by) license (https://creativecommons.org/licenses/by/4.0/). https://doi.org/10.5772/20081 x.o durin et al. /future energy november 2022| volume 01 | issue 03 | pages 01-10 1 review a comprehensive review of the environmental impacts of hydropower projects in sarawak, malaysia xavier o’neal durin1, brendon moi xuen ming1, prashanth prashobh karunakaran1, lucas leong wun sin1, hadi nabipour afrouzi1*, kamyar mehranzamir2 1faculty of engineering, computing, and science, swinburne university of technology sarawak, 93350 kuching, malaysia 2department of electrical and electronic engineering, faculty of science and engineering, university of nottingham malaysia, jalan broga, 43500 semenyih, selangor, malaysia a r t i c l e i n f o article history: received 06 april 2022 received in revised form 10 may 2022 accepted 18 may 2022 keywords: environmental, social, impact, greenhouse gases, hydropower, sarawak *corresponding author email address: hafrouzi@swinburne.edu.my doi: 10.55670/fpll.fuen.1.3.1 a b s t r a c t sarawak is a state in malaysia that has many potential sites for hydropower dams as sarawak houses many hilly areas which are yet to be developed. as a result, many hydropower dams were proposed in sarawak. this paper reviews the environmental and social impacts of hydropower projects in sarawak. the murky river waters of sarawak contributed to a high level of sedimentation in the hydroelectric plant reservoirs which increases the emission of greenhouse gases through mineralization and indirectly affects the lifespan of a hydroelectric plant. the ecosystem is adversely affected by the loss of trees, destruction of habitat for flora and fauna, and the narrowing of rivers due to sedimentation. the construction of hydropower plants forces nearby indigenous communities to relocate, which are given compensation by the sarawak government. the issues behind the relocation process are explored in this paper with further details. the communities that are affected by the construction of the hydropower dams will have to be displaced from their original lands; thus, the approach by the government to compensate the affected locals in sarawak is explored in this paper. 1. introduction hydropower is widely utilized all over the world as it provides multiple benefits to various countries. for example, nigeria utilizes hydropower as a decentralized power source to solve the country’s limited power supply [1]. on the other hand, china has built more than 47000 dams all over the country [2, 3], including the biggest dam in the world namely the three gorges dam which can produce up to 84.7 billion kilowatt-hours per year of electricity, equivalent to the amount of energy that could be produced by burning 50 million tons of coal [4]. another country that also utilizes hydropower would be malaysia. malaysia has multiple dams throughout the nation, with sarawak generating most of the hydropower energy [5, 6]. sarawak is a state in malaysia situated on the island of borneo that is blessed with a vast number of rainforests. the bornean rainforests hold biodiversity of flora and fauna, boasting an estimated 4% of the world’s plant species and 5% of the world’s birds and mammals, consisting of 222 species of mammals, 420 species of birds, 3000 tree species, and 15000 flowering plant species [7]. over the past few decades, there has been a surge in the development of lands in sarawak, which is the largest state in malaysia out of the thirteen [8]. this has led to an increase in power demand in sarawak. initially, fossil fuels such as diesel, coal, and natural gas were used for the power plants in sarawak, meeting the power demand of 1250 mw based on the year 2015 [9]. however, due to diesel, coal, and natural gas being nonrenewable resources, sustainable approaches to generating renewable energy were introduced. one of them is hydropower generation. it is estimated that 12 hydroelectric power plants and two coal power plants will be built in sarawak by 2030 with a total capacity of 9380 mw to cater to the increasing power demand in the future [9]. although hydropower generation is praised for being a sustainable renewable source of electricity generation in sarawak, the construction of heps will inevitably affect the environment in terms of environmental degradation and water quality deterioration [10-19]. future energy open access journal https://doi.org/10.55670/fpll.fuen.1.3.1 november 2022| volume 01 | issue 03 | pages 01-10 journal homepage: https://fupubco.com/fuen issn 2832-0328 mailto:hafrouzi@swinburne.edu.my https://doi.org/10.55670/fpll.fuen.1.3.1 https://fupubco.com/fuen x.o durin et al. /future energy november 2022| volume 01 | issue 03 | pages 01-10 2 1.1 power generation in sarawak sarawak is a powerhouse when it comes it hydropower generation in malaysia. with the geographical advantage of sarawak in favor of hydropower, there are many potential sites for hydropower plants, as shown in figure 1. as of 2021, there are three major hydropower plants operating in sarawak, which are the bakun, murum, and batang ai hep. figure 2 shows the state of the bakun dam in 2010. baleh hydropower plant is also another major hydropower plant currently under construction which is expected to be operational in 2026. aside from these major hydropower plants, sarawak has coal-fired, gas, and diesel major power plants. the summary of which can be found in the table below. according to table 1, the majority of sarawak’s power generation is from the renewable source of energy with hydropower as the source of generation, totaling about 57.1%, excluding ongoing projects, after the commissioning of the tanjung kidurong extension project [21]. after the completion of baleh hep, hydropower will be contributing 64.6% of the total power generation of major plants. figure 2. bakun dam in sarawak, malaysia [22] 1.2 sarawak corridor of renewable energy (score) the malaysian federal government created five economic development corridors to stimulate global and domestic industrial investments, and score is one of them. the objectives of score are to secure a total of rm334 billion of private and public investments by 2030 for the development of sarawak [23]. the corridor spans a length of 320 km [24]. these industrial zones will then be supplied with an inexpensive and renewable source of energy harnessed from hydropower plants. under score projects, there are a total of twelve mega-dams proposed in sarawak to sustain the developments under score, two of which are already completed with the third one under construction. the first dam to emerge from this project, the bakun dam, has an impoundment area of 720 km2, which is roughly about the size of singapore [22]. followed by bakun dam is murum dam with a reservoir size of 245km2 and lastly, baleh dam will have a reservoir size of 588 km2 [25]. 2. environmental impacts of hydropower given that hydroelectric power is a type of renewable energy, it releases a very small amount of carbon into the air [5]. according to [20], the carbon intensity of the electricity supply in sarawak has decreased by 72% as depicted in figure 3. the water supply can also be used as drinking water and irrigation for agricultural usage. hydropower also helps in storing water which protects aquifers from depletion. this will reduce the frequency of floods and droughts. however, the water supply and irrigation can reduce the water available for power generation and therefore reduce the power generation output [26]. being a type of renewable energy, hydropower plants do not produce any waste, unlike coal or fossil fuel power plants. not to mention that it can prevent excess ghg (greenhouse gases) emissions. thus, air pollution is reduced along with the frequency of acid rain and smog occurring in the state. figure 1: hydropower plants in sarawak in 2017 [20] x.o durin et al. /future energy november 2022| volume 01 | issue 03 | pages 01-10 3 2.1 sedimentation and ghg emissions most rivers have a balanced inflow and outflow of sedimentations which controls the accumulation of sediments in the river [27]. when the river is impounded, the imbalance will accumulate sediments [28]. sedimentation in the impoundment area of the hydro dams contributes to ghg emissions through the mineralization process where it decomposes to produce co2 (carbon dioxide) and ch4 (methane). reservoirs with higher sediments raise aquatic weeds such as algae, and other plants, which increases the emission of carbon dioxide up to 0.03 pounds [29]. additionally, the formation of large dam reservoirs increases the emission of greenhouse gases through the decaying of biomass from the vegetation in the large, flooded areas [26]. although hydropower is considered a clean source of energy since it produces significantly fewer emissions compared to coal, hydropower has a ‘stored’ potential of ghg emissions that lies dormant within the sedimentation in its reservoirs [30]. table 1. list of major power plants in sarawak according to sarawak energy berhad [21] uncontrolled release of the sediments during the decommissioning of hydro dam affects both upstream and downstream rivers which may potentially impact the aqua life and riffle-pool habitats, deposition downstream, destabilization of stream banks, and a large amount of ghg emissions [31, 32]. figure 3. carbon intensity for electricity supply in sarawak since major hydro development [20] the study conducted by pacca analyzed the co2 emissions during the decommissioning of glen canyon dam, and he found that if all sedimentations are mineralized during decommissioning, the co2 emissions amounted to 33,000,000 metric tons. to put this into a better perspective, the construction of the dam emitted 800,000 metric tons, while the emissions associated with biomass decay in the reservoir during its operation was 3,500,000 metric tons [32]. the estimated yearly ch4 emission of major hydropower dams in malaysia is 387,340,000 kg, with sarawak contributing the majority of it at a total of 60.9% from bakun, murum, and batang ai dams, of which, bakun dam contributed the most at 41.26%, followed by murum dam at 14.54% of the total emission in malaysia [25]. sedimentation issue is especially serious in sarawak due to the vast rainforest region that is prone to rainfall. the study in reference [33] revealed that logging activities impacted the water quality of the streams after rainfall in terms of the increase of suspended solids from 8.3mg/l to 104.1mg/l. upstream logging, unsustainable agricultural methods, and erosion contributed to high levels of sedimentation, with bakun dam reservoir recording more than 500mg/l of sediments or an annual inflow of 9,000,000 tons [22,24]. sedimentation, if not controlled, can indirectly affect the lifespan of a hydropower plant by reducing the water storage capacity, increasing wear on machinery, and negatively impacting downstream rivers as the decommissioning of dams are motivated by maintenance cost, environmental or regulatory requirements [31, 34]. concrete dams that are built according to standards can easily reach a lifespan of 100 years, while the hydromechanical components such as the gates and motors are up to 30 to 50 years [35]. 2.2 geological and ecological impacts the construction of hydropower dams will include some degree of deforestation and land loss due to submersion. figure 4 and figure 5 show the forest geography before and after the construction of bakun and murum dam. it is evident that a huge amount of deforestation took place for the establishment of both dams, and a huge amount of land was submerged underwater. this will result in the destruction of wildlife and cause some wildlife population loss. the construction of the murum dam had threatened the population of 300 rare and endangered species [6]. in 2018 itself, the remaining intact forest was at an estimated 7.72 million hectares, which was around 62% of sarawak state, while the 13 hydroelectric dam projects plant type power gener ation (mw) status batang ai hydroelectric plant hydro (concrete face rockfill dam) 108 commissioned murum hydroelectric plant hydro (concrete face gravity dam) 944 commissioned bakun hydroelectric plant hydro (concrete face rockfill dam) 2400 commissioned baleh hydroelectric plant hydro (concrete face rockfill dam) 1285 ongoing (2026) bintulu kidurong power station gas combined cycle – 317mw open cycle – 165mw 482 commissioned bintulu tanjung kidurong extension – combined cycle gas turbine gas 421 x2 commissioning (2021) miri power station gas 102 commissioned mukah power station coal 135 x2 commissioned sejingkat power station coal 210 commissioned balingian power station coal 312 x2 commissioned (2019) kuching power station diesel 64 commissioned x.o durin et al. /future energy november 2022| volume 01 | issue 03 | pages 01-10 4 will collectively impact 1.7 million hectares of forests in sarawak [36]. figure 4. location of bakun and murum dam in 1995 before the construction figure 5. location of bakun and murum dam in 2016 after construction methods of rapid conversion where the areas deforested is replanted within a five-year period after clearance [37], cannot be applied here as the dams will drown out the once forested areas. as the hydropower plants in sarawak are situated in rural areas, the transmission of the generated power would require the cutting of tall trees in the forests to cater to the right of way as shown in figure 6 of the transmission lines [26]. the transmission lines proposed for baleh hep are rated at 500kv and will require an easement of 50 m. this transmission line has a span of 176 km in length and would total up to an area of about 880 hectares or 8,800,000 m2 [38]. other than that, the construction will bring destruction to the habitats of aquatic life and inhibit the migration of fish [5]. for example, the bakun dam has a catchment area of 1.5 million hectares, and a reservoir area of 70,000 hectares will destroy six rare and endangered species of fish. plus, the construction of the dam will change the hydrological regime of the area affected, and this will cause changes in water level, timing, and temperature [40]. this will severely affect the surrounding aquatic ecosystem. this also applies to all the protected flora and fauna, including the silvered leaf monkeys and bornean gibbons. plus, some hydroelectric dams will be located near certain protected areas, such as the mulu national park, which is home to one of the world’s largest caves and a unesco world heritage site. figure 7 shows the location of hydropower dams that will intrude on some protected areas in sarawak if the dams are to be constructed in the future with no changes to their location. 2.3 displacement of communities the construction of hydroelectric power plants in sarawak affects the livelihood of communities downstream when large communities are forced to relocate [41]. these indigenous groups rely on the forest and river integrity for their daily lives. not only will the construction of the dam force these people to relocate, but the act itself is also considered an ethnocide as it destroys the lifestyle that these communities have. prior to relocation, the residents of sungai asap relied mostly on the forest for their sustenance. after their relocation, they can no longer rely on the forest but are tied to the cash economy, with wages that are not compatible with the living costs. the relocation of large communities living at the hydropower project site to new sites may involve deforestation as lands will be cleared to make way for new settlements [26]. figure 8 shows the relocation of indigenous communities at the bakun dam site to the resettlement area at sungai asap, which is situated about 30 km from the bakun dam site [42]. based on the statistics released by sungai asap district office, the population affected by the bakun dam in 1998 was 9428 people [42]. that population accounts for 26.75% of the people in the belaga district in sarawak. 2.4 soil erosion a study was conducted by the united nations development program, and it was found that fully developed dams in sarawak could ruin the water quality and water levels [43]. this may lead to floods in the future. aside from that, the construction of ongoing and planned hydropower dams will increase the number of landslides occurring in the region. given that sarawak has a tropical climate, rainfall frequently occurs throughout the state. deforestation will remove the trees that are supposed to control the water levels through absorption. the rise in water-level, increased geological pressure, disturbances and deforestation will create favorable conditions for frequent landslides [36]. figure 9 shows the areas in sarawak that may be vulnerable to landslides if the planned hydroelectric dams were to be constructed as it is. figure 6. an example of right of way for ehv transmission lines [39] x.o durin et al. /future energy november 2022| volume 01 | issue 03 | pages 01-10 5 figure 7. the pan-borneo highway and hydroelectric dams in sarawak penetrating protected areas and key habitats of threatened species in borneo [36] figure 8. map location for the sungai asap resettlement area [42] figure 9. pan-borneo highway and hydroelectric dams in sarawak and imminent frontiers of landslides. the highway and hydroelectric dams with highly vulnerable landslide locations (circled) [36] 3. mitigation actions there are different ways to mitigate the environmental impact caused by hydropower dams and such methods include a full-cost benefit appraisal of the development of the hydropower plants by the relevant authority [36]. the appraisal covers the overall cost of the project, maintenance, and support services for the relocated communities. a commonly used appraisal is the environmental impact assessment or eia, which considers other implications on communities, culture, and economy aside from ecological impacts. [29]. however, past evidence indicated the implementation of eia in sarawak does not protect native customary land rights since it is not easily accessible and that the natives are disregarded from the whole assessment process [44]. thus, stricter enforcement is needed to ensure that all responsible parties are involved in the hydropower project. one of the mitigation actions suggested was the construction of small-scale hydropower plants or even the installation of mini-hydro systems instead of large-scale ones to save space and minimize the environmental effects [5, 45]. there have been several projects covering the installation of mini-hydro systems in sarawak, namely in bakelalan, located at the foothills of sarawak’s highest mountain, gunung murud [46]. previously, locals at bakelalan depended on diesel-powered generators for power [47]. however, being located so inland, the access roads were difficult to come by, which lead to high costs of diesel that only kept escalating and only to be worse during the wet seasons when the access roads are rendered useless, leading to a drop in diesel supply. this motivated the construction of a mini-hydro project; the public works department (pwds) worked in good faith and cooperation with the local communities. the bakelalan community constructed the dam, penstock, and turbine house and laid the pipeline and after completion, pwds distributed and managed the power network. the project ended up providing 30kw of energy that was distributed to 400 people of the buduk nur community 24 hours a day at the cost of rm600,000, which was a huge step up from the diesel power the community depended on that was at best run 4-6 hours daily [46]. these dams could be constructed at rivers near remote rural areas as a decentralized unit. aside from this, the flow of water from the reservoir can be regulated to minimize the impact on aquatic life. minimum flow release would allow some flow below the power plant, which helps maintain the current water ecological conditions [40]. on the other hand, sedimentation can be tackled through dredging [48] or through the construction of small-scale weirs [49] that can trap sand and particles for removal. apart from that, turbine technology could be investigated with the view of being fish-friendly to reduce the impact on the population of aquatic life. in the development of fish-friendly turbine technologies, the focus is on the mortality rates of the fish passing through the turbines. the voith minimum gap runner (mgr) was based on the kaplan turbine, which is the conventional turbine used in the hydropower dams. the mgr has smaller gaps between the runners and the turbine walls, which helps to prevent the fish passing through from being crushed by the runners. the injury rate of fish passing through the mgr is 1.5% as compared to 2.5% for the kaplan turbine [50]. figure 10 shows an improved version of the mgr, the alden turbine which enables no gap between the blades’ tips and the turbine walls. other suggestions include a resettlement policy for the communities to be relocated. the government should compensate these communities with provisions such as land, money, and an alternate source of livelihood. mussa et al covered-on dam removals as a mitigation method, given that it is the more frequently used management option around the world [40]. this focuses on old dams to be x.o durin et al. /future energy november 2022| volume 01 | issue 03 | pages 01-10 6 renovated or small dams that are no longer used. lastly, fish nurseries can be set up to conserve aquatic wildlife. the fertilization, hatching, growth, and release can be artificially managed to sustain the population of the aquatic life. figure 10. physical model of an alden turbine runner [51] 4. discussion 4.1 flora and fauna according to our review, hydropower will pose a threat to the environment as it is especially to flora and fauna surrounding the construction area. the state already has three large dams currently operating, which are murum, batang ai, and bakun. there are more dams on the way, with one of them being the baleh dam which was estimated to be in commission by 2025. in section 2.2, figures 4 and 5 showed how much of the forest was left after the deforestation for the construction of the bakun and murum dam. as the deforestation process is necessary for the construction of the dam, an environmental impact assessment or eia would be the alternative option to mitigate the environmental impact caused by the hydropower project. amidst the development of the state’s power generation, there are ways that can indirectly mitigate the environmental impact of hydropower. the equipment of the dams in commission can be improved such as the efficiency of power generation by the turbine. if the efficiency of the turbine can be improved, this would reduce the area needed for the construction of hydropower dams. other ways include minimizing the transmission loss along the power lines or increasing the efficiency of energy utilization on the receiving end of the line. this would be a cost-effective method to meet the state’s energy demand without expending any additional cost on constructing new hydropower plants. additionally, hybrid floating photovoltaicshydropower technology can be implemented in the hydropower dams in sarawak to reduce the number of hydropower dams to be constructed in the future. as shown in figure 11, the hybrid fpv-hydropower system maximizes the land used for a hydropower dam [52]. the hybrid fpvhydropower system can generate more power than a conventional hydropower system. this would, in turn, reduce the need to construct more hydropower plants in sarawak in the future. furthermore, the floating solar photovoltaics used in the hybrid fpv-hydropower system is also a clean, renewable energy source and has low carbon emissions, like hydropower. hence, the balance of the ecosystem in sarawak in the future can be maintained. 4.2 relocation following the decades upon decades of the continuous construction of hydropower dams in low and middle-income countries, there has yet to be any comprehensive remedy to cope with the severe impacts on the local people, even with the multiple frameworks developed such as the dams and development: a new framework for decision making made by the world commission on dams (wcd), or even sustainability guidelines launched by the international hydropower association (iha) and even with the rising rate of social impact assessment techniques [53]. if any future hydropower project affects an indigenous community, the relocation process can be improved. while the dam itself may displace their home, the community may not need to abandon the river on which their livelihood depends. it may be possible for them to move downstream along the river, given that the state of the river does not deteriorate upon the introduction of the dam. also, the government must oversee the process of relocation to ensure that an agreement can be reached between the indigenous community and the organization responsible for the construction. according to sarawak ordinance, whenever necessary, the power to enter on land for purposes of construction as written was to enable the works in relation to the installation of any system of distribution of energy under that ordinance, a licensee may do works on any land other than state land. it is also stated that compensation to all persons interested for any disturbance, damage, or disability that may be caused by it would be given. before entering any land, the licensee was required to give notice to the owner or occupier of the land stating the works that were to be done on the land; this notice was to be deemed to be properly given and sent by registered post or left at the usual or last known place of abode of the person-related. however, if the person cannot be found, the notice will be fixed conspicuously on some part of the land, the owner who received the notice was given 14 days upon placement of the notice to lodge an objection. the objection lodged shall allow an inquiry to be held by the director of lands and surveys to hear out all parties before deciding either to unconditionally or subject to terms, conditions and stipulations, as he thinks, is fit and authorize or prohibit any acts mentioned in the notice. if an objection is not lodged within the time limit of 14 days, the licensee may immediately enter the land and do all the acts specified in that notice [54]. figure 11. a hybrid fpv-hydropower system could be implemented in existing hydropower dams in sarawak [52] in sarawak, we can draw the case of the bakun dam, where around 50% of the impounded land was lands claimed under customary rights and the cost of resettlement x.o durin et al. /future energy november 2022| volume 01 | issue 03 | pages 01-10 7 was funded by the federal government while the actual implementation of the resettlement would be undertaken by the state government. in terms of farm compensation, it would be given according to the number of fruit trees. it was discovered that the rate changes that were initially promised were around rm50-52 per tree, however, the final compensation was around rm5-9 or rm 30, according to different villagers interviewed. there was also individual compensation for people born in 1998 where they were given rm13,000 per person, and compensation for burial grounds where those who wanted to move the grave were given a compensation of rm4000 and rm 1500/2000 to not move the grave [55]. despite that, these payments have been criticized for not being a more sustainable method of compensation for the people that were removed from their lands [56]. the compensation that was received by the locals was perceived as too little, which was mainly due to the land compensation because now, each family was only provided with three acres of land in the resettlement sites as compensation for the lost land that was used as the reservoir area which had been voiced out [56, 57]. thus, it would be wise for the government to have plans in place to give out proper compensation to be given to smoothen the relocation process while reducing the social impact to as little as possible. a system that reconstructs the tendering methods needs to be adapted to entice participation from local communities since, with a different approach, one can minimize the potential of corruption related to the management of high volumes of the public participation in energy supply [58]. at the same time, from a social policy perspective, we can see the positive effects of the relocation of the locals that were located in the reservoir area since they were now given access to better welfare services. at the resettlement site, people are given easier access to roads, clinics, and schools where the people previously had to travel by boat for an entire day just to reach the hospital. 4.3 sedimentation and greenhouse gases the sedimentation levels in sarawak are especially high due to deforestation, which causes erosion of soil, causing the river waters to be murky. the amount of ghg released from the sediments found within hydropower dams was reviewed under section 2.1, and it was found that the ghg emission in sarawak is the largest compared to peninsular malaysia at 60.9%. majority of which is contributed by bakun dam due to its large surface area of 695km2. thus, the contribution of ghg emission due to hep from the upcoming baleh dam is expected to be high as well since the projected surface area is 588km2. additionally, more major heps are planned for sarawak under score projects as well. however, the ghg emissions due to heps are still significantly lower than thermal power plants at 11g of co2 per kwh generation compared to 943g of co2 per kwh generation of coal-fired power plants [59]. as discussed under section 2.1, sedimentation also indirectly affects the lifespan of the hydropower dams. since the sedimentation levels are high in sarawak rivers, as evident from the annual inflow of 9,000,000 tons of sediments settling into the reservoir of bakun dam, the lifespan of bakun dam is estimated to be only 50 years [60]. while sarawak has yet to decommission any of its dams, the environmental impacts of dam decommissioning should be taken into consideration as the batang ai dam, which was commissioned in 1985, is nearing its end-of-life expectancy, accounting for the 50-year lifespan of bakun dam. hydroelectric dams can be repurposed after they are decommissioned as a water supply for irrigation and commercial uses, as well as recreation sites for tourism. these would require the lowering of the decommissioned hydroelectric dams. some decommissioned hydroelectric dams which are demolished would require the restoration of rivers. since sedimentation contributes the most to greenhouse gas emissions of heps, the issue can be solved in multiple ways. one of the ways to remove sediments is through periodic mechanical dredging. this method utilizes dredgers, which are machines that are specialized in removing sediments that lie in water bodies. this should help in reducing the accumulation of sediments in the long run. to assist in catching the sediments, small-scale weirs can be constructed to trap them for removal in the future. another method that can be implemented is the installation of a dedicated channel or canal in the dam to flush sediments periodically. this should help regulate the sediment buildup and ensure that ghg gas emissions are controlled. to tackle the emission of greenhouse gases from the sediments after demolishing the hydroelectric dams, the dig and dewater approach can be implemented where the decommissioned hydroelectric dam is drained, and the dried sediments are removed from the location. 5. conclusion to summarize, hydropower plants pose a threat to sarawak’s forests, rivers, and the communities living nearby the dams. the felling of trees and impoundment of the dam leads to soil erosion and major loss, which will inevitably negatively impact the ecosystem of sarawak, leading to the extinction of some flora and fauna species that are endemic to sarawak. as sarawak is bound for the construction of more major hydropower dams, this would mean a lot of forests would be submerged in the future. sarawak would then require proper management such as the eia to ensure that their ecosystem is preserved in the future. aside from the forest ecosystem, indigenous communities living by the rivers are also affected and must be relocated to allow the project to progress. oftentimes, these communities are not properly compensated upon relocation, and the people that were relocated before were unable to obtain proper compensation. these people had to reach out for legal methods through the court to obtain somewhat fair compensation for their relocation from their original lands. it is imperative for the government to give proper compensation that is planned well to satisfy these communities and ensure that they are conforming to the norms of a functioning society in future relocations that may occur when constructing a dam. it is also vital for the government to ensure the organization in charge of the hydropower project obtains a consensus from the indigenous communities who are to be relocated. this would ensure that both sides can negotiate the terms and conditions of the relocation process and compensation and that the communities are not left out throughout the entire process of the project. although hydropower is portrayed as a clean source of renewable energy, there are still ghg emissions associated with it through sedimentation, albeit at a much smaller scale compared to coal-fired power plants. the impoundment of the dam slows the flowing river current, which disrupts the natural sedimentation inflow and outflow, creating an imbalance that causes it to accumulate in the reservoir. sedimentation indirectly affects the lifespan of heps by decreasing the dam capacity and x.o durin et al. /future energy november 2022| volume 01 | issue 03 | pages 01-10 8 increased wear on the machinery. a large amount of sedimentation discharged during decommissioning will potentially threaten the ecosystem downstream from the heps and cause some rivers to become shallow and eventually dry out. hence, sediment management is a must in heps to ensure the lifetime of the dam as well as to keep the environment safe. the heps in sarawak must be monitored and maintained regularly in the future as the dams are so big that any cracks in the dams may cause the entire state to be flooded if the dams were to experience total failure. in the distant future, sarawak may need to prepare other renewable energy alternatives to hydropower, such as solar power plants or wind farms, as the estimated lifespan of hydropower plants in sarawak is about 50 to 70 years. the oldest hep in sarawak, which is the batang ai dam, is nearly three-quarters of its estimated lifespan. additionally, sarawak can look into the potential of hybrid fpv-hydropower systems to be integrated into the existing heps to reduce the reliance on hydropower. currently, there are many hydro projects being planned in sarawak, and these planning must be taken seriously in sarawak to keep sarawak’s rivers and forests safe in the future. these mitigation methods have to be further studied to enable the government to have more control over the construction of these hydroelectric dams, which ultimately, as a renewable source of energy, has more to be desired. especially in a developing nation like malaysia, a breakthrough would likely enable a sustainable future in terms of power generation in the long run. ethical issue the authors are aware of and comply with best practices in publication ethics, specifically with regard to authorship (avoidance of guest authorship), dual submission, manipulation of figures, 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[60] c. y. keong, “energy demand, economic growth, and energy efficiency – the bakun dam-induced sustainable energy policy revisited”, energy policy, vol. 33, no.5, pp. 679–689, 2005. this article is an open-access article distributed under the terms and conditions of the creative commons attribution (cc by) license (https://creativecommons.org/licenses/by/4.0/). r. khalid et al. /future energy august 2023| volume 02 | issue 03| pages 38-48 38 review the feasibility and analysis of electric taxi vehicles in singapore: a review rehan khalid, vishtreet conjobeeharry, abdullah saif sanai, chelward t. h. brown, hadi nabipour afrouzi*, ateeb hassan faculty of engineering, computing and science, swinburne university of technology sarawak, 93350 kuching, malaysia a r t i c l e i n f o article history: received 02 december 2023 received in revised form 12 january 2023 accepted 18 january 2023 keywords: electric taxis, transportation, feasibility, analysis, singapore *corresponding author email address: hafrouzi@swinburne.edu.my doi: 10.55670/fpll.fuen.2.3.5 a b s t r a c t taxi is one of the essential ways of transportation, which contributes to the depletion of non-renewable resources, congestion, emissions of harmful gases, energy consumption, and noise pollution. one way to reduce the environmental pollution caused by the road transportation system is to replace conventional and hybrid vehicles with pure electric-driven powertrains. in fact, evs were announced as the key element in the sustainable transport strategy in urban areas, but the company operating transport services using vehicle fleets should increase the demand for electric vehicles to spread awareness. this paper reviews the feasibility of ev taxis in singapore by analyzing the available infrastructure and energy prices. to introduce the electric vehicle in singapore as an electric taxi, the construction along with the location of charging infrastructure need to be properly planned. initiatives taken by different countries and the large-scale transition have also been reviewed. despite the drawbacks of battery electric vehicles (bevs), such as charging inconvenience and limited range, promising potential for ev taxis has been presented by the technological progress this paper also compared different aspects of the currently used taxis with ev taxis in singapore. for the augmentation of this transition, improvement of the business model, dissemination of charging infrastructure, and policy support can play a vital role. 1. introduction singapore contributes about 0.14% to global carbon emissions, but considering its relatively small population size, its average yearly emissions per capita is about 8 tons. in 2016, an average of 7,214,000 people used public transport in singapore daily. of that, 954,000 people commuted by taxis. the mrt, which is the most frequently used form of public transport, is already powered by electricity. to continue to reduce the emissions of co2, the team believes in electric taxis because electric cars have a smaller carbon footprint than ice cars. in singapore, currently, transport contributes to 14% of co2 emissions, which amounts to about 7 million tons of co2 [1]. the dependency of road transport on oil can deplete these non-renewable resources, and the pollution from these conventional vehicles causes different kinds of health problems. this is the reason why there should be an alternate way of lowering carbon emissions and dependency on oil. the usage of biofuel, electric powertrains, and improved versions of current vehicles are the three solutions that can be considered to tackle this issue. as the number of people is increasing, zero carbon emissions and dependency on oil seem like a long-term effort. for this situation, ev is the solution that satisfies the conditions. only an electric motor powered by a battery and charged when not in use is the simple principle of operation for evs. they are quite efficient, have a high acceleration, and can be charged at low-cost overnight [2]. these vehicles are operated with the help of batteries that can store high energy and, at the same time, need a large amount for the charging requirements with the use of a grid or renewable resources. during peak hours, it’s not recommended to charge the batteries, which in the end, impacts the life of the transformers [1]. as the industry and the government greatly boosted the development of evs, these vehicles are thought to be prevalent soon. the notion of replacing general petroleum cars with evs includes the following reasons: 1) evs make zero emissions of carbon dioxide, which fits the green trend in saving the environment, 2) the energy efficiency of evs is high, 3) lower running and maintenance costs. different sectors have shared the effort, and 95% of the emission is expected to reduce by the road transport sector. with these rising numbers, it is imperative that sustainable alternatives to transport need to be explored. the first company to launch electric taxis in singapore is hdt singapore holdings. in 2016, land transport authority (lta) future energy open access journal https://doi.org/10.55670/fpll.fuen.2.3.5 august 2023| volume 02 | issue 03 | pages 38-48 journal homepage: https://fupubco.com/fuen issn 2832-0328 mailto:hafrouzi@swinburne.edu.my https://doi.org/10.55670/fpll.fuen.2.3.5 https://fupubco.com/fuen r. khalid et al. /future energy august 2023| volume 02 | issue 03| pages 38-48 39 awarded the taxi service operator license for ten years. in early 2017, they launched their first hundred taxi cars on the road. their fleet is composed of byd e6 cars only, which is a fully electric cars. hdt taxi was on a trial basis for eight years. this pilot project is part of singapore’s ev phase 2 testbed, which is in collaboration with the lta and the economic development board (edb). this trial is performed to study the viability of the electric taxi in the singaporean land transport network. they needed to increase their fleet up to eight hundred cars, as required by the authorities. the company fulfilled this requirement by adding two hundred vehicles every year for the next four years after their establishment. by july 2022, it is expected to have this requirement fulfilled. hdt partnered with grab company and provided thirty cars that were to be used for e-hailing services. further research is still in-process in singapore, by the research & development center and in collaboration with local research institutes [3]. the second taxi company to launch electric taxis is comfortdelgro. in july 2018, two hyundai ioniq electric was released for trial by the company. then, in january 2019, they introduced two units of the newer hyundai kona electric for trial. the hyundai kona electric has a 64-kwh lithium polymer battery and offers a longer range than that of the ioniq electric. the trial will evaluate the roadworthiness of the vehicle, like the electricity cost, maintenance, mileage, and battery durability. the purpose of this article is to review the feasibility of ev taxis in singapore and evaluate whether the transition from taxis to ev taxis is economically, environmentally, socially, and ethically feasible. the current situation, types of public transport, energy prices, and measures that should be taken to supplant conventional taxis (ic and hybrid) with ev taxis will be reviewed. previously, many researches have been done on the technical aspects of evs, but the feasibility and commercialization are hardly addressed. therefore, the review of the feasibility of ev taxis is substantial. 2. feasibility of electric taxi vehicles in different countries 2.1 feasibility of ev taxis in malaysia the current conditions in malaysia are not favorable for an electric taxi fleet. electric taxis require many charging points to be viable in a city. in malaysian cities, there are not many places where electric vehicles can be charged. there are only 257 charging points in the whole country. most of these charging points are found in the states of kuala lumpur and selangor. each charging point would serve an average of 74 km2 in selangor and 5 km2 in kuala lumpur. this is a decent number. the situation is far worse in other states like sabah, with zero charging points, and sarawak, with only 4 charging points for an area of 120 000 km2. finally, there is not much support from the malaysian government like tax breaks. so, to drive an electric vehicle it would cost as much (or more) as any internal combustion engine. moreover, the buying cost of a conventional car is very affordable to the crowd; for example, the cheapest petrol car in malaysia, a perodua axia, manufactured in malaysia itself, costs only rm 24,000, whereas a nissan leaf, currently imported from japan and sold in malaysia at rm 188,888, will not appeal and be feasible to the taxi owners or companies, due to their income or salary, and the high initial buying cost [3]. economy-wise, malaysia does not have a huge hand in generating electricity from renewable sources of energy, and electricity is mostly generated by burning coal, and coal is imported from foreign countries, so shifting to electric taxis will have a huge impact on the economy when it comes down to the decision of buying more coal. another point to note is that conventional cars are locally manufactured, so the cost of import, shipping, excise duty, and others are rather inexistent or very less, as compared to the electric cars, which are all imported to be used as electric taxis. to make the shift happens, electric cars should be locally manufactured to make them more accessible to the taxi population. 2.2 feasibility of ev taxis in south korea unprecedented efforts have been made by south korea in the transition of commercialization of conventional vehicles to ev taxi services. on 6th september 2013, a pilot test of electric vehicle taxis was inaugurated in daejeon city. this was the first test of its kind that was performed for the analysis of the feasibility of ev taxis before introducing it to the commercial level. the vehicles adopted to perform the test were three sm3 ze’s (renaultsamsung motors). in 2014, as a result of this test, about 500 ic taxis were replaced by electric taxis [4]. according to the results of a study performed by baek, kim & chang 2016 on the feasibility of ev taxis, there is a possibility of real mileage higher than the calculated for ev taxis. this is because in the pilot test, the vehicles that were considered were not sharing charging infrastructure and were operated independently by the companies. the feasibility of ev taxis would be even higher if the selected cars were provided access to localized charging stations. moreover, the average value of the benefit to cost analysis (b/c) enhanced to 0.7 and consequently making the ev taxis feasible. following is the formula that was used to calculate the b/c ratio for ev taxis: 𝐵 𝐶 = 𝛴𝑡=0 𝑛 𝐵𝑡 (1 + 𝑟)𝑡 𝛴𝑡=0 𝑛 𝐶𝑡 (1 + 𝑟)𝑡 (1) where 𝐵𝑡 is the benefit in the year t, 𝐶𝑡 is the cost in the year t, 𝑟 is the discount ratio, and 𝑛 is the project duration. 2.3 feasibility of ev taxis in canada another study was performed by darcovich [5] using real-time driving data and running battery life simulations on the appraisal of the feasibility of ev taxis. performance targets for the ev simulations were obtained from the driving patterns of single and double-shift gasoline taxis. the data obtained from this study depicted that driving distance is set to 151 km/day for single shift and 298km/day for a double shift to get the results. as per the simulation results, 89% of the reference driving was met by a single-shift taxi in a 6-year period. whereas there was a need of mid-shift charging in double shift. the only drawback is the loss of revenue by a small percentage of distance, but it can easily be compensated by decreasing the operational costs. moreover, it was observed that degradation of battery is excited by the annual driving distances as compared to charging speed. in r. khalid et al. /future energy august 2023| volume 02 | issue 03| pages 38-48 40 conclusion of this study, ev taxis for both single and double shifts were economically and operationally feasible [5]. 2.4 feasibility of ev taxis in china beijing, the capital of china, has the largest fleet of evs with registration of around 46000 taxis. in 2011, the authorities in beijing decided to reduce carbon and other harmful emissions by introducing electric taxis. a program was introduced by the authorities to increase the purchase and usage of electric cars around the city by co-financing approximately 370 euros per month on the purchase. with this, nearly 10% of the city’s parking is being selected only for electric vehicles by the beijing anti-pollution drive. the same process is followed in another city shenzhen, where in 2010 only 40 taxis were used, then increased to 800 in 2013 [6]. in 2010, tokyo did an experiment with switchable batteries in ev out for three months before implementing it. for this test, three nissan rogue were converted to electric vehicles to examine how long it travels on a full battery and how long it takes to swap the battery with a fully charged one. after successfully completing the experiment, it was applied in tokyo’s electric taxi company, which saves time for charging, as the typical mileage of one taxi is around 300 km daily. 2.5 feasibility of ev taxis in europe the great number of charging stations in oslo is the main reason for having a high number of electric vehicles. these visible stations reduced the anxiety of people getting worried about the lack of charging facilities. in 2014, 1000 more charging stations were built of which 700 for public and 300 for private usage. then in 2015, the expansion of this project was carried out by adding 400 more stations for public use of the climate and environment funds. moreover, the people were given the exemption of vat of (25%) on any new vehicles, no fee for first-time registration, allowed to drive in any lanes, including the one reserved for taxis and buses, free from toll roads, can park their vehicles for free at any spot in public parking. development of a strategy for sustainable transport, the environmentally friendly solution provided, was implemented by the poznan city authorities, which increased the number of vehicles still 6000 around the polish roads [7]. in 2008, a company known as a better place in europe proposed the development of electric vehicles, by providing the services and network necessary for it and to eliminate the barriers which stop the development of evs on a national scale. however, in 2013, because of this action taken by better place, the range of services and infrastructures offered was wide. installation of a network of charging stations was carried along with embedded energy monitoring, route planning system, and support, which calculates the vehicle range and guides the driver to the available spot for charging. then finally, the network software was designed that monitor the battery and its need in order to anticipate energy demand, have real-time communication with the grid operators, and implementation of intelligent charging to avoid peak time and offset the intermittency of renewable energy sources. car clubs were introduced to mainly urban drivers, where they can borrow the evs on display if needed and pay for that time. this facilitated the urban driver without paying insurance and maintenance of the car, but to use irregularly. this technique was adopted from a car show known as yélomobile in la rochelle, france, which was carried in 1999 for a monthly subscription or €7/h for bevs. along with this, the second option was also introduced of renting a car for appropriate range, and during the trip their vehicle can be swapped with bev. local policies came into action, which have a crucial weight in the expansion of bev, after the car show developed at a city scale. the buyers were granted 25% of the vehicle’s cost or a max of 5000 pounds from the government. other positive steps taken by the local policies provided the evs a great advantage, like the road tax reduction which is based on the amount of carbon emissions produced. increase in diesel and petrol tax, which brought the people towards evs. parking fee reduction according to the driver’s habits is beneficial for some users. some preferential parking spots having charging points is implemented. around 30,000 charge points have been installed in 11000 different locations around uk. alone in london, 5000 rapid charging stations are there, which allow fleet operators, taxi drivers, and freight to quickly charge. nevertheless, planning is done for an additional 2700 charging stations near the residential area in london to facilitate drivers who cannot charge at their homes. now, after providing people with benefits, the growth of evs went from 3586 in 2013 all the way to 37092 in 2016. the strategy for norway was different, as approximately 73% of the population lives in row houses, detached or semidetached houses, and family house, charging opportunity is available for them, and thus from the data, it was not considered important to build infrastructure for charging station, but planning is done to provide a high-speed charging facility which is more relevant, but not important from selling point of view. a one-year membership is awarded in the ev association, mostly to those who are among the ev purchasers. norway has placed some tools and policies in hand to speed up the growth and make space in taxi companies for electric vehicles. these were the seven different roles, excluding the infrastructure of charging stations, which motivated the people to buy evs; exemption from vat, exemption from purchase tax, exemption from road tolling, free ferry tickets, bus lane access, reduction in the fee of vehicle’s license and free parking. around 11,500 electric vehicles were registered in norway during the first three months of 2019, which is added to the previous count of 200,000. although charging points were not needed, more than 10000 charging points were built to provide people with an additional benefit. from these charging points, 400 are rapid and semi-fast charging points [8]. a study was performed by bischoff & maciejewski on a transition of berlin taxis to bev’s fleet. according this study, it will take substantial effort to make this transition using the infrastructure that is currently available and requires executive and fiscal support. as per this study, there is a need for the installation of one 50-kw level 3 or 4 chargers for ten taxis. it was also concluded that peak energy consumption and usage of the charger would occur in winter term operations. as per the driver’s viewpoint, this state of the art technology can only be efficient if concessions are given for the battery life by reducing the energy costs expressively, and finally by subsidizing the service [9]. r. khalid et al. /future energy august 2023| volume 02 | issue 03| pages 38-48 41 3. feasibility analysis in singapore 3.1 public transport in singapore singapore is a city-country, which is situated below malaysia, and houses 5.3 million inhabitants [10]. it has among the best public transport in the world. they offer a wide array of public transportation, from buses, taxis, lrt to mrt. buses are the most convenient option for public transport, as they can cover every part of the island, compared to the transit services, which operate on rails that run in high traffic and certain neighborhoods only. mrt is also widely used as a mode of public transportation since it can transport a large crowd at one time and avoid road traffic congestion. it is also faster than buses and taxis because they do not run on roads; they have their own rail tracks built underground or overhead, and they only stop at their stations, and they have a higher traveling speed than buses. the downside of mrt is that its network is not extensively spread across the island and is only available in popular and frequented areas. figure 1 shows the average passenger trips per day by the different modes of public transportation for 2016. in 2013, the singaporean land transport authority (lta) focused in the public transportation sector, and according to their study, 63 % of all peak-hour trips were made by public transport [10]. figure 1. average daily transport ridership [11] however, same as every country got its own taxi network to serve as public transportation, singapore has also its taxi service. taxis are very popular across the globe because it provides transport service to the population with greater speed, comfort, privacy, ease, and convenience. its advantage over bus is that it does not run on a fixed route, so it can pick and drop the customers at any requested location or at their doorstep. they operate 24 hours and overnight. taxi drivers are very professional and experienced drivers, as they have a different driving test compared to a normal driver, and they are familiar in the region. they know the roads and the traffic conditions on the tip of their fingers. some taxi companies offer different types of vehicles, from standard passenger cars to luxurious cars and limousines, and disability, wheelchairaccessible and pet-friendly vehicles [12]. according to statista (2020), there are 18,542 taxi vehicles registered and circulating around singapore for 2019 [13]. taxis represent 3 % of the vehicle population in singapore and are responsible for about 15 % of the overall mileage driven. the need for electric taxis is to reduce carbon dioxide emissions and go towards an environment-friendly form of public transportation [10]. nowadays, there is an increased in popularity in ride-hailing services, like grab and gojek. this type of transport makes use of an online platform, like a website or a smartphone application to connect the passenger and the driver in the vicinity. unlike taxi services, where they use taxi registered, licensed, and regulated vehicles and drivers, this service operates by local drivers using their own personal vehicles. this cuts the costs of registration, license and insurance occurred with a registered taxi vehicle, and it is convenient to both drivers and passengers. it provides a cheaper fare compared to traditional taxi service. even with the introduction of ridesharing/hailing or e-hailing services, taxis still play an important role in modern society. taxis are the go-to transport for elderly and disabled persons, especially for those who are not exposed to smartphones and the internet. some tourists still prefer taxis as they can negotiate with the taxi drivers for tours and visits around the island and ask for recommended hotels and eating places. in that sense, it is more convenient for tourists who want this kind of traveling experience. some data for the densities of taxis per person and the flag-down and mileage fees for the first kilometer in the different cities are shown in figure2. figure 2. taxi density and flag-down fares for different cities [10] from the above chart, singapore has the highest taxi density and the lowest flag-down and first 1 km fares among the other cities listed. this is because the land transport authority required 65 – 70 % of the taxi fleet to be on the road back in 2013. in 2014, they changed the law. they required 70 % of the taxi fleet to drive 250 km per day, which required around 8 to 9 hours per day, six days per week. 3.2 taxi networks and companies in singapore eight taxi companies operate taxis in singapore: comfort transportation, citycab, yellow top taxi, smrt taxis, transcab services, smart automobile, premier taxis, and prime taxi [14]. figure 3 shows the taxi stops (stands) spread across the whole island. there were 270 taxi stands/stops in the whole island for the year 2013, according to data.gov.sg [15]. taxi operates by the shift systems. the one-shift taxi has one driver and drives around 347 km in a day. the two-shift taxi has two drivers who cover 260 km each per shift, which totals to 520 km in a day. the two-shift taxis are always on the road and only stopped when needed, that is for refueling, washing, r. khalid et al. /future energy august 2023| volume 02 | issue 03| pages 38-48 42 or changing driver. table 1 shows the taxi population of different companies up to december 2017 [16]. figure 3. land transport authority (lta) taxi stops islandwide [17] table 1. monthly taxi population by company [16] 3.3 energy prices in singapore in singapore, oil and gas prices have been high for many years ago. this is because singapore needs to import crude oil from overseas. the amount imported is more than it produces in its own country. also, if the petrol is coming from outside, transportation is required to bring oil to singapore, which costs money. singapore has imposed a fuel excise tax on top of the high price of fuel. singapore’s government strategy is to discourage people from owning a car because of their highly dense population packed in a small area, to avoid traffic congestion and parking problems, and high air pollution in the long run. the oil prices provided by the different companies are listed in table 2 [18]. table 2. singapore fuel price comparison per liter, dated 21st may 2020 [18] types of fuel caltex esso shell spc sinopec 92-octane s$1.98 s$1.98 s$1.95 95-octane s$2.02 s$2.02 s$2.02 s$1.99 s$2.02 98-octane s$2.52 s$2.39 s$2.41 s$2.33 s$2.39 others (e.g. vpower) s$2.65 s$2.55 diesel s$1.70 s$1.70 s$1.72 s$1.64 s$1.70 as it can be seen from the table below, diesel prices are lower than petrol prices, which explains the popularity of diesel cars used as taxis on the island, as the running or mileage costs of a diesel car will be lesser than that of an ice car. the price for the different ev charging points provided by the different companies in singapore are listed in table 3. every company has a different pricing strategy for its customers [19]. it can also be seen from the table below that the different companies are expanding their charging facilities by increasing the number of charging stations throughout the island. this is a positive approach to push both taxi and private car owners to switch to electric cars. the charging stations will be located in popular and frequented residential and commercial areas, with special thought to the “taxi uncles” who can charge their electric cars while having a drink at the nearest coffee shop and getting some rest. table 3. comparison of different ev charging points in singapore, dated 29th april 2020 [19] ev charging points number of stations price bluesg over 200 available island-wide; expected to hit 2000 in 2020 a yearly membership fee of s$20 to be paid to become a bluesg member. for ev charging, s$1 per hour for the first 3 hours, and s$2 an hour after that. shell recharge 10 (including fast charging stations) s$0.55 per kwh sp group 24; expected to hit 1000 with 250 being fast chargers in 2020 prices are calculated by kwh and are adjusted periodically on prevailing electricity costs. greenslots 50 from s$1.50 an hour 3.4 transition from conventional to ev taxis in singapore to differentiate from each other, companies used different cars adapted for different uses and for different choices of customers. taxis in singapore used to be petrol and diesel cars before, but diesel cars were in larger numbers. taxi drivers used to prefer diesel cars because of their efficiency and durability over petrol cars, due to the high amount of driving daily. also, diesel engines produce more torque, which makes it more drivable in the city. diesel cars must do lower maintenance, as compared to petrol cars, as diesel engines are tougher. diesel prices are usually lesser than petrol. diesel engines produce less carbon dioxide but in the cost of more carcinogenic gases. the trade-off for diesel cars is that they are more expensive to buy than petrol cars. also, there is a special tax on diesel vehicles in singapore. although the maintenance frequency is lesser in diesel cars, its costs are much higher than a gasoline car. the most common diesel cars used as taxis in singapore were the hyundai sonata and the toyota crown. with the advent of petrol-electric hybrid cars in the market, taxis, together with the public, got one more type of car to choose from, apart from conventional petrol and diesel, that was dated from years ago. in 2008, there was not a single unit of a hybrid taxi. in november 2017, it was reported to have 4000 hybrid taxis on singaporean roads, which accounts for approximately 17 % of the taxi car population [20]. the increase in hybrids in singapore was due to the new rules and regulations set by the land transport authority of singapore. the new emissionsbased taxation scheme provides a rebate of up to s$45,000 for hybrid taxis. hybrid cars contribute to a cleaner air. with the month company no. of taxis 2017-12 comfort 9,825 2017-12 citycab 3,419 2017-12 transcab 3,686 2017-12 smrt 3,380 2017-12 premier 2,055 2017-12 prime 691 2017-12 individual yellow – top 84 r. khalid et al. /future energy august 2023| volume 02 | issue 03| pages 38-48 43 advent of technology, the petrol-electric hybrid has improved significantly, since its introduction in 1997, with the launch of the toyota prius in japan. in 2009, prime taxi was the first company to launch hybrid taxis in singapore. they have experimented with hybrids and concluded that the diesel hyundai sonata and the new toyota prius hybrid average the same fuel cost per kilometer, which is 8 cents per kilometer. also, for replacing the batteries, prime taxi imports its batteries from its joint company, which costs s$2,200 each, instead of buying them from the authorized dealer toyota dealer, borneo motors, which costs s$5,200 each. hybrid taxis do not need to pay the annual diesel tax [20]. singapore reviewed its system of vehicle emissions in january 2018. the new vehicular emissions scheme (ves) is stricter and will be applied to all vehicles registered from 1st january 2018 to 31st december 2020 [21]. with the introduction of this new system, diesel cars have become lesser and lesser in singapore day by day because of higher running taxes. considering all these factors, hybrids are the better and the most cost-effective choice for taxis, as compared to the most used diesel and conventional petrol cars. to promote the use of environmentally friendly cars, taxi owners are given 40 % discount on their additional registration fee (arf). prime taxis, being the first one to launch hybrid taxis in singapore, has most of its fleet converted to hybrid cars today. then, other companies have followed the pace. almost, all taxi companies have already switched to hybrid vehicles for their standard or basic service. the most common car for the taxi is the toyota prius hybrid (both 3rd and 4th generation variants) on singaporean roads. the new hybrid car from hyundai, the ioniq hybrid is also present in a few numbers on singaporean roads and is being tested by the taxi company comfortdelgro. with all the positives received from the hybrid taxis in singapore, most of the taxi companies have already switched to hybrid vehicles due to the high oil prices and lower running costs paid to singapore authorities. the government has done its part to promote a greener and more sustainable approach by pushing taxis to convert to hybrid taxis, and it has been a successful operation. diesel cars have been decreasing day by day since the rise of hybrid taxis. in early 2020, the last hyundai sonata (diesel) retired. but contradictory, for the “taxi limo”, a short form for limousine service, they still use mercedes-benz e220 cdi and bluetec (diesel and petrol respectively), mercedes-benz viano and v220d (diesel) and toyota alphard (hybrid) [14]. but it is noted that for the “limo” service, customers are charged at a higher fare than that of the standard or regular taxi service. with the new stricter rules on the island, hybrid taxis do not make any sense since the year 2018, since their running costs have increased significantly, and they have become quite saturated on singaporean roads. during that period, electric cars also picked up and gained some popularity on the island. since june 2020, singapore has been occupied by 11 different electric vehicles of various brands, from which renault and bmw cars cannot be used as they fall in the coupe or supermini category, which are not suitable for taxi use. the price of the porsche, tesla, jaguar, and audi cars vary between a range of s$300k to s$550k, which makes it inappropriate for a taxi fleet due to their high price. in table 4, the electric vehicles that are being used as taxis in singapore are listed. the comparison can be made using the table, by which it is clear that using a hyundai kona electric for the taxi fleet is more suitable than any other electric vehicle, due to its maximum range; so it can cover 482 km just by consuming 13 kwh/100km, whereas the byd e6 can cover only km on a single charge by consuming 19.5 kwh/100km, which means it consumes more electrical power while delivering a lesser range than the hyundai kona electric. although the charging time is a bit higher than byd, the range and power consumption of the kona electric still have a decent value. two taxi companies are currently testing these electric cars to be used as taxis in singapore [23]. 3.5 charging infrastructure to cater for ev taxis in singapore these electric cars need to be charged to obtain their power source. hdt placed 75 charging points in 10 areas across singapore in 2016, for their launch on the island. the charging type is the type 2 charging standard, and it supports semi-fast charging, together with the normal charging of evs. the number of charging points is expected to rise in the coming years [24]. apart from charging from hdt charging stations, drivers of grab and hdt can access sp agreements between the companies. sp group offers two types of charging: dc charging, which is rated at 50 kw, and ac charging, which is rated at 43 kw. the dc charger charges the ev faster than the ac charger. in total, they have 38 charging points island-wide, half ac and the other half dc chargers (figure 4) [25]. their target is to build 1000 charging points by 2020, of which one-quarter of them will be fast dc charging [26]. their charging power ranges from 22 kw from the older chargers to 350 kw from the new extra highpowered chargers to charge bigger electric vehicles with higher battery capacity and greater driving range. other companies have set up ev charging stations for the public to use: byd charging station, shell recharge charging points powered by greenlots available at 10 shell filling stations throughout the island, greenlots charging stations, blue sg charging stations, and grab charging stations [27]. one shopping mall, city square mall, is equipped with its own charging stations in its two parking lots. few condominiums have installed ev charging points in their parking lots for their residence. in march 2020, it was noted that singapore counted 1600 chargers, which are accessed by the public. comfortdelgro has its own charging facility to cater to its research vehicles, which is the terra 54 cg charging station. their own subsidiary company, comfortdelgro engineering, partnered with greenlots to provide the dc fast charging that will be able to charge the evs in around 30 minutes. they have only two slots for the fast charger so far at this station, and it is open to the public at the cost of s$40 cents per kwh. taxi drivers can also opt to charge at the headquarters of the company at braddell and at komoco motors in alexandra, where fast-charging facilities are also available for the taxis of comfortdelgro. 4. comparisons 4.1 economical aspect electric vehicle battery is the most expensive component of ev taxis that increases open market value (omv) and consequently leads to increased taxes, for instance, additional registration fees (arf) [28]. r. khalid et al. /future energy august 2023| volume 02 | issue 03| pages 38-48 44 figure 4. sp group high-speed charging network [25] due to the increase in these taxes, acquisition costs are also subjected to increase, thereby reducing the economic competitiveness of ev taxis. on the other hand, conventional taxi vehicles do not have such expensive components and acquire a relatively cheaper petrol or diesel tank. therefore, to accelerate the adoption of ev taxis, encouraging policies should be devised by the government, such as the cost of traction battery should be excluded from the arf and only applies to the omv of the vehicle. so far, this exemption was only presented for the byd e6 in 2016, and the omv reduced significantly from 47,000 sgd to 17,237 sgd [28]. the overall basis for the feasibility of ev taxis supplanting conventional taxis is the total cost of ownership (tco). the tco of conventional and ev taxi for the span of 4 years from 2016 to 2020 was analyzed by robert [29], and the results depicted that battery electric vehicles incur a rise in maintenance cost as compared to hybrid electric vehicles. it was also found that conventional and ev taxis fell in the same range in 2016, whereas due to incessant decreases in the battery price, ev taxis were primarily cheaper by 2020. daily rental fee is another impediment to the feasibility of ev taxis. the survey of taxi drivers in singapore conducted by kochhan [30] confirms that higher daily rental fee is considered a detriment. this is because it is a fixed cost payable by the driver irrespective of how much he or she is earing in the respective day. nevertheless, an inconsequential positive correlation was also observed for the approval of high daily rental fee by those drivers that are expected to make two-shift taxis or use relief drivers and cover a higher total daily mileage. 4.2 environmental aspect for fossil fuel vehicles, the upstream greenhouse gases (ghg) emissions per energy content are comparatively lower than that for electricity, as shown in figure 5(a). higher upstream efficiencies of diesel, petrol and natural gas production are more responsible for this than the efficiency of electricity generation and distribution. the calculation of total ghg emissions per final energy well-to-wheels (wtw) analysis is based on the specified upstream well-to-tank (wtt) emissions and the specific direct emissions in the vehicle. while the cng emissions are low, the total emissions from diesel and petrol are on the same level at about 0.3 kg co2-eq./kwh. in singapore, the ghg emissions per energy are maximum for electricity, comprising only upstream emissions. the lower co2 emissions of the phev and bev versus the other vehicles are a direct outcome of the higher efficiency of these electrified vehicle concepts and the higher share of non-fossil electricity sources when compared to purely fossil-based gasoline and diesel. though the high upstream emissions factor remains, the lowest ghg emissions per/km have been obtained compared to diesel, petrol, and cng cars in bev taxis. as the final energy demand of the vehicle is relatively lower because of the high efficiency of the electric motor than the conventional engines, it leads to this outcome for bev taxis. the bev is clearly the best concept from a co2 wtw perspective in 2010 and will maintain this position through 2030. all vehicle concepts reduce their wtw co2 emissions from 2010 to 2020 very significantly, which is clearly shown in figure 5(b) and figure 5(c). during manufacturing, it has been observed that the amount of emissions caused are lower for petrol vehicle than for diesel vehicle. the similarity between a cng car and a gasoline car is the engine, as the same engine with smaller adjustments can be used. the differences include the additional natural gas tank and the extra ducting that results in an elevated amount of emissions. during the production of an electric vehicle, the high emissions caused are strongly dependent on the size of the battery or sometimes the use of special lightweight materials, like in the case of an electric vehicle approved (eva) [31]. 4.3 sustainability with the increased in evs in the roads, extra power needs to be generated from the traditional power generation plants, which in turn will lead to a similar ecological impact as using diesel or petrol in conventional vehicles [32]. manufacturers model type fast charging time (min) selling price (s$) power consumption (kwh/100km) maximum range (km) taxi company byd e6 suv 40 109,888 19.5 400 hdt taxi hyundai kona electric suv 54 140,999 13 482 comfortdelgro ioniq electric sedan 57 148,999 11.7 311 table 4. electric taxi cars currently in use by different taxi companies in singapore [22] r. khalid et al. /future energy august 2023| volume 02 | issue 03| pages 38-48 45 (a) (b) (c) figure 5. (a) ghg emissions per kwh final energy (b) wtt co2 comparison for 2010 (c) wtw co2 comparison for 2020 and 2030 [31] to address this issue, charging evs with green energy needs to be adopted. singapore has its electricity production by using natural gas reported to 95 %. natural gas is also burnt to produce electricity, but it is cleaner than fossil fuels but is not totally renewable or sustainable. singapore is going towards grid-connected solar energy to address the issues of natural gas electricity production. evs have battery packs to store their electrical energy. the issues related to the batteries in the sustainability of evs are the energy required to manufacture these batteries, and together with its emissions and consequences. 3430 kwh and 7176 kwh of energy is required to make a 25 kwh of lead-acid and nimh battery, respectively. also, the batteries of evs cannot be readily recycled. a large amount of energy is needed to recycle the batteries, or the defective batteries need to be disposed. 4.4 ethical and social aspects in general, ethical aspects ensure the community's safety, education, and empowerment for a process. there are certain factors that are well thought-out by the buyer or a user of ev taxis that are as follows: • perceived usefulness • service and system quality • perceived trust • perceived risk when it comes to the transition from conventional taxis and preferment of the ev taxi system, the above-described factors play a vital role in forming users’ psychological perceptions. it has been found that perceived cost is a negative variable on the other hand, perceived usefulness is a positive variable. therefore, to promote ev taxis, these factors should be considered as substantial variables, and singaporean government should devise strategies and policies for subsidizing taxi drivers’ expenses like purchasing, maintaining, repairing, and others. scientists and researchers should focus on problems that enhance ev taxis' reliability and find solutions for charging infrastructure to increase process efficiency [31]. regulatory measures like service and warranty procedures are sort of a problem for both ev and ice taxi drivers in singapore. moreover, the charging stations for ev taxis and petrol stations for hybrids & ice taxis are not alike. for instance, in a normal taxi fuelling station, drivers can easily stop and have a lunch or coffee break, unlike charging stations for ev taxis that are sometimes located at eccentric places having fewer facilities in the stations’ vicinity. on the plus side, electric cars take longer to charge, which allows the drivers to have longer resting hours, which is beneficial for drivers after a few hours of driving. they can comfortably have their meals and rest. in shenzhen, china, the facilities for charging electric taxis are well developed, and this city has the largest charging facility for electric taxis in the whole world, which counts 637 fast chargers [33]. with the coming of this facility, there has been a development in terms of socioeconomical aspects as well. businesses like shopping malls have been bult in its vicinity to promote economic development as well as social development. a large community engagement had happened in this locality. the problem that is happening with electric cars is they are getting updated so quickly, as compared to a conventional car, which gets updated in 4 to 8 years. when the new model of the electric car is released, the value of the older model drops constantly, which makes consumers perceive that they have lost their money. to afford the new electric cars with the newer technology and better range efficiency, consumers must pay a way higher price for them. also, the mindset of most of the population is not in favour of new technology. people usually do not want to take risks and pay such a high amount for a new unknown technology introduced which has not been proven and tested over the years. 5. discussions after reviewing different aspects of the electric taxi fleet that have been summarized in the above sections, it can be observed that ev taxis are viable. the driving pattern and the available charging infrastructure are the main constituents of the feasibility of ev taxis. the use of these taxis should be facilitated by short trips blended with good coverage of charging infrastructure. r. khalid et al. /future energy august 2023| volume 02 | issue 03| pages 38-48 46 the peak hours must be assisted with supporting mechanisms for the prevention of revenue loss due to charging required at productive hours, and this can be done by fusing charging time with breaks or low-demand hours of the day. singapore offers the most suitable condition for ev taxis since often braking, low speed, and less range is expected in the city. singapore’s economy is one of the best in the world and it attracts the vast majority of tourists every year. therefore, these people are more convivial with this type of transition than any other country. since it is very unlikely for a tourist to own a car, the taxi business is booming there, and foreigners like to explore new options and innovations and have the luxury to afford it. hence singapore is ethically an ideal place for this large-scale transition. table 5 summarizes the feasibility of ev taxis in singapore as compared to the current taxi system. the conventional taxi system is cost-effective today, but the difference is not very substantial and can be retrenched by encouraging government policies like withdrawing arf and other taxes etc. the chart clearly shows that ev taxis are a better choice environmentally because the dwindling sources of fossil fuels and growing environmental consciousness drives researchers and developers toward green energy. moreover, conventional taxis are ethically preferred because of the already established market, abundant fuel stations, and ample perceived trust. however, ev taxis in singapore still entail consideration to increase reliability which can be done in numerous ways, as reviewed in section 4.4 and lastly, ev taxis are also feasible as compared to conventional taxis on the basis of sustainability. however, there are some principled adjustments that are required. the imposed challenges can be tackled by taking the concerned authorities and already existing energy bodies on board and spreading energy literacy and the significance of ret’s (renewable energy targets) among the businessman community and industrialists. overall, this large-scale transition from a traditional taxi fleet to an ev taxi fleet is totally feasible in singapore. however, efforts should be made to provide a stable and cost-efficient system for the user. policies should be formulated by the taxi companies to enhance the user’s attitude towards the ev taxi system by endorsing the positive societal factors. 6. conclusion in this research paper, the feasibility of ev taxis has been reviewed. the main goal of this research was to review the feasibility of a large-scale transition to electric taxis in singapore that has been achieved by reviewing the current situation and development in singapore and then looking into the different aspects conferred to prove why and how electric taxis are the way-forward to replace currently used gasoline and conventional hybrids? the large-scale transition to electric taxis has been feasible in different countries like berlin, china, south korea, etc, as reviewed in earlier sections, and so will be feasible in singapore; however, this transition cannot happen overnight. it will take time to gradually make the switch by increasing the charging facilities, providing incentives and grants to motivate drivers, and slowly phasing out the diesel taxi cars and the rest of the gasoline and hybrid taxi cars. the noteworthy aspects that are deterring the transition to ev taxis in singapore are economical and ethical. however, this can be vanquished by taking the coveted means described in this paper. the decommissioning process has already been started, and it is expected that diesel and gasoline-powered taxi cars will phase out by the end of 2024 and 2030, respectively, and consequently be supplanted with ev taxis. ethical issue the authors are aware of and comply with best practices in publication ethics, specifically concerning authorship (avoidance of guest authorship), dual submission, manipulation of figures, competing interests, and compliance with policies on research ethics. the authors adhere to publication requirements that the submitted work is original and has not been published elsewhere in any language. data availability statement data sharing does not apply to this article as no datasets were generated or analyzed during the current study. conflict of interest the authors declare no potential conflict of interest. references [1] a. m. andwari, a. pesiridis, a. k. kontakiotis, and v. esfahanian, “hybrid electric vehicle performance with 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[31] a. kamil, “sp group rolls out first wave of electric vehicle charging points todayonline,” today singapore, 2019. https://www.todayonline.com/singapore/sp-grouprolls-out-first-wave-electric-vehicle-charging-points (accessed may 30, 2020). [32] g. teo, “sp group to double electric vehicle charging points to 1,000 by 2020 cna,” cna, 2019. r. khalid et al. /future energy august 2023| volume 02 | issue 03| pages 38-48 48 https://www.channelnewsasia.com/news/singapore/ sp-group-electric-vehicle-charging-points-1000-by2020-10863134 (accessed may 30, 2020). [33] s. c. kuttan, “commentary: why singapore is ripe for an electric vehicle revolution cna.” 2019, accessed: jun. 01, 2020. [online]. available: https://www.channelnewsasia.com/news/commentar y/singapore-electric-vehicle-car-sale-models-howmuch-price-12051780. this article is an open-access article distributed under the terms and conditions of the creative commons attribution (cc by) license (https://creativecommons.org/licenses/by/4.0/). ma ehyaei et al. /future energy february 2024| volume 03 | issue 01| pages 34-49 34 review a review of the integration of the copperchlorine cycle with other systems for hydrogen production mehdi ali ehyaei1, moein shamoushaki2, hamed afshari3*, mamdouh el haj assad4 1department of mechanical engineering, pardis branch, islamic azad university, parids city, iran 2department of industrial engineering, university of florence, florence, italy 3food science & engineering department, faculty of civil & earth resources engineering, islamic azad university central tehran branch, tehran, iran 4department of sustainable and renewable energy engineering, university of sharjah, sharjah, united arab emirates a r t i c l e i n f o article history: received 02 may 2023 received in revised form 05 june 2023 accepted 23 june 2023 keywords: hydrogen, copper-chlorine, exergy, heat, electricity, economic *corresponding author email address: afshari1@gmail.com doi: 10.55670/fpll.fuen.3.1.5 a b s t r a c t there are different methods for hydrogen production, among which thermochemical cycles are particularly important. one of the most common thermochemical cycles is the copper-chlorine cycle. in this cycle, the water electrolysis process takes place during a thermo-chemical reaction, and copper chlorine is used as a thermochemical reaction intermediate. this cycle requires two factors to produce hydrogen: a heat source with a temperature of about 520 oc and electricity. for this reason, it is possible to use the hot waste gases of industries or parabolic through collector and heliostat field to provide its heat. to supply electricity for this cycle, various alternatives from the power grid and wind turbine to heat recovery in cycles that use low-temperature energy sources are considered. in this article, the integration of the copperchlorine cycle with power generation systems has been discussed and investigated from the perspective of energy, exergy, and economics. this review is divided into two general parts using renewable and non-renewable resources. at the beginning of this article, various methods of hydrogen production focusing on the copper-chlorine cycle have been briefly discussed. in the following, the way this cycle works is explained along with energy, exergy, and economic equations, and the research done in this direction is explained. finally, a strategy for how to integrate the copper-chlorine cycle with other systems is described. studying this article, in addition to giving a better attitude in the field of integrating this cycle with other plants, is similar to a guideline for using the cycle along with other systems for better productivity. the conducted investigations showed that the recovery of hot industrial exhaust gas as a source of heat for the cu-cl cycle has a high potential for saving energy consumption and reducing environmental pollutants. to produce the required electricity, it is recommended to use cycles that work with a lowtemperature energy source, such as the organic rankine cycle and kalina cycles. also, if renewable energy sources are used, it is recommended to use parabolic through collectors and heliostats to produce the required heat. as in the case of non-renewable energy sources, cycles with low-temperature energy sources can be used. 1. introduction various factors, such as limited fossil resources, negative environmental impacts, utilization of hydrocarbon resources, and rising prices of fossil fuels, are among the reasons that many energy and environment experts have encouraged to create of a new structure based on energy security, environmental protection, and the improvement of system energy efficiency (ene) [1, 2]. accordingly, hydrogen is one of the best options to play the role of energy carrier in this new energy supply system [3]. hydrogen gas can produce high energy by burning in the presence of oxygen and producing only water. future energy open access journal https://doi.org/10.55670/fpll.fuen.3.1.5 february 2024| volume 03 | issue 01 | pages 34-49 journal homepage: https://fupubco.com/fuen issn 2832-0328 mailto:afshari1@gmail.com https://doi.org/10.55670/fpll.fuen.3.1.5 https://fupubco.com/fuen ma ehyaei et al. /future energy february 2024| volume 03 | issue 01| pages 34-49 35 this energy can be used as fuel to move vehicles as well as spacecraft and rockets. hydrogen as a renewable fuel can be considered an alternative to fossil fuels [4]. today, hydrogen is mainly used in the production of methanol, ammonia, and oil refining. hydrogen is also used in nasa's space program as fuel for spacecraft and in fuel cells that generate heat, electricity, and drinking water for astronauts [5]. among the features that distinguish hydrogen from other fuels, alternatives are its abundance, almost very low emissions, reduction of greenhouse gases, and production cycle reversibility [6, 7]. hydrogen production methods are divided into two general categories of use of renewable and non-renewable sources, which are as follows [8]: hydrogen production from renewable sources: • photoelectrochemical [9] • biologically [10] • biochemical [11] • thermochemical [12, 13] • radiolysis of water [12, 13] • water electrolysis [14, 15] hydrogen production from non-renewable sources: • steam reformer [16] • auto-thermal [17] • pyrolysis [18] due to the need for lower temperatures than the thermal processes of hydrogen production, electrochemical cycles of hydrogen production have received special attention. these cycles typically produce hydrogen using heat sources and a series of chemical processes. the chemicals used in this cycle are reused to create a closed cycle. the input of this cycle is water, and its output is hydrogen and oxygen. the general types of these cycles have the following three steps [13, 19]: • hydrogen production • oxygen production • chemical material recovery according to the research literature, there are more than 200 types of thermochemical cycles. but few types have become widespread and have been put to practical use. the most important types of these electrochemical cycles are as follows [20-23]: • copper-sulfate (cu-so4) symbols: a, b, c, …, h constants of shomate equations n number of years c specific cost (us$/kw) n annual duration of operation (hrs) ċ cost rate associated with a stream (us$) n project lifetime (equal to 25 years) c0 total investment cost (us$) npv net present value (us$) crf capital recovery factor p pressure (kpa) cu-cl copper-chlorine pp payback period (years) ex specific exergy (kj/kg) q̇ heat transfer rate (kw) ė exergy rate (kw) r discount factor (%) ėx exergy rate (kw) r universal gas constant, r=8.314 (kj/kmol.k) fk exergoeconomic factor s specific entropy (kj/kg.k) g gravitational acceleration (m/s2) spp simple payback period (years) h specific enthalpy (kj/kg) t temperature (k) i inflation rate (%) v velocity (m/s) irr internal rate of return ẇ power (kw) k specific cost of products (us$/kwh) x mass fraction k investment and installation cost of component (us$) y mole fraction lhv lower heating value (kj/kg) �̇� capital investment (us$) ṁ mass flow rate (kg/s) z height (m) abbreviations edr exergy destruction rate psa pressure swing adsorption ees equation engineering solver ptc parabolic through collector ene energy efficiency ro reverse osmosis exe exergy efficiency sam system advisor model hrsg heat recovery steam generator smoa static multi-objective optimization approach hsr heliostat solar receiver src steam rankine cycle med multi effect distillation system teg thermoelectric generator orc organic rankine cycle tes thermal energy storage pcm phase change material greek symbols 𝛈 efficiency φ maintenance factor subscripts 0 reference state condition (101.3 kpa, 25 ℃ ) i component number ch chemical in input cu-cl copper-chlorine cycle k component k chi chemical exergy out output d destruction w water f fuel ma ehyaei et al. /future energy february 2024| volume 03 | issue 01| pages 34-49 36 • copper–chlorine (cu–cl) • iron–chlorine (fe–cl) • cerium–chlorine (ce–cl) • vanadium–chlorine (v–cl) • hybrid chlorine • magnesium–iodine (mg–i) • cerium–chlorine (ce–cl) among the types of mentioned cycles, the cu – cl cycle has the following priorities [20, 24]: • low operating temperature • less setup and repair costs • consume less electricity • common chemical reactions require an adverse reaction given the importance of the cu-cl cycle and its superiority over other types of electrochemical cycles in the research literature, research is needed to examine this cycle in terms of energy, exergy, and economics. in this article, first, the processes performed in this cycle and its energy, exergy, and economic analyzes are presented. also, the energy sources used to launch this cycle are examined, and their limitations and benefits are presented. finally, a strategy for using this cycle to produce hydrogen is presented. 2. process description the cu-cl cycle is a four-step thermochemical cycle using copper chlorine intermediate to produce hydrogen. this cycle is a hybrid process that has both electrolysis and thermochemical steps. the maximum required temperature is about 530 oc. the thermochemical reactions performed, and the temperature range is shown in table 1 [22]. table 1. the cu-cl reactions performed the temperature range and the feed of each reaction no. chemical steps temperature range (oc) 1 2cucl(aq) + 2hcl (aq) +thermal energy+electrical energy→ 2cucl2 (aq)+ h2 (g) <100 2 cucl2 (aq)+ thermal energy → cucl2 (s) <100 3 2cucl2 (s) + h2o (g)+ thermal energy → + 2hcl (g)+cuo×cucl2 (s) 400 4 cuo and cucl2(s)+ thermal energy → 2cucl (l) + 1/2o2 (g) 500 the cu-cl cycle has three different types that have several different steps. the number of steps of this cycle is 3, 4, and 5 steps. in the 5-step cycle, copper production is electrolytic. then, it is transferred to a heat-generating hydrogen reactor and reacted to produce hydrogen with molten hcl and cucl gas. the 4-step cycle combines these steps to eliminate the intermediate step of solid copper production and displacement from cucl / hcl electrolysis. in the removed phase, electrolyte hydrogen and copper chlorine are produced. the aqueous product is then dried to produce copper chlorine particles. in a 3-step cycle, these steps are produced by supplying aqueous copper chloride directly to the hydrolysis chamber of the same copper oxychloride product. the 3-step cycle requires the least electrical energy and the 5-step cu-cl cycle requires the least heat energy. if an efficiency of 40% is assumed to convert heat energy into electricity in power plants, the best option in terms of energy consumption is the 5-step cu-cl cycle [25]. 3. theoretical modeling 3.1 mass and energy balance relations in general, mass and energy balance relations can be written as follows [26]: ∑ �̇�𝑖𝑛 = ∑ �̇�𝑜𝑢𝑡 (1) where �̇� means mass flow rate. �̇� + ∑ �̇�𝑖𝑛 (ℎ + 𝑉2 2 + 𝑔𝑍) = ∑ �̇�𝑜𝑢𝑡 (ℎ + 𝑉2 2 + 𝑔𝑍) + �̇� (2) for the cu-cl cycle, the mass-energy balance equations can be written as follows: ṁ𝑊 + ṁ𝐶𝑢𝐶𝑙2 = ṁ𝐻2 + ṁ𝑂2 + ṁ𝐶𝑢𝐶𝑙2 (3) ṁ𝑊ℎ𝑊 + ṁ𝐶𝑢𝐶𝑙2ℎ𝐶𝑢𝐶𝑙2 + �̇�𝐶𝑢𝐶𝑙 + �̇�𝐶𝑢𝐶𝑙 = ṁ𝐻2ℎ𝐻2 + ṁ𝑂2ℎ𝑂2 + ṁ𝐶𝑢𝐶𝑙2ℎ𝐶𝑢𝐶𝑙2 (4) subscript w means water. the molar base enthalpy in the cu-cl cycle is calculated according to the following equation [27, 28]: ℎ̅ − ℎ̅0 = 𝐴 𝑇 + 𝐵 𝑇2 2 + 𝐶 𝑇3 3 + 𝐷 𝑇4 4 − 𝐸 1 𝑇 + 𝐹 − 𝐻 (5) in equation no .8, t is one-thousandth of the temperature (k). the values of the coefficients a to h are shown in references [27, 28]. the ene for the cu-cl cycle is written as follows: ηenergy cu−cl = ṁ𝐻2lhvh2 �̇�𝐶𝑢𝐶𝑙+�̇�𝐶𝑢𝐶𝑙 (6) the cu-cl overall efficiency is much higher than that of water electrolysis, which is powered by thermal power plants. because in the cu-cl cycle, heat is directly used for hydrogen production. whereas in a water electrolysis system, electricity must be generated by power generation systems, and the electricity generated is used for hydrogen production. considering the efficiency of power plants, the efficiency of hydrogen production by water electrolysis device is about 30%, while in the cu-cl cycle, this value reaches 54%. if the heat loss of the systems is utilized for hydrogen production in the cu-cl cycle, the ene will be higher [25]. 3.2 exergy balance relation exergy maximum reversible useful work, from the initial state specified during a reversible process when it reaches environment equilibrium. exergy is a compound property that depends on the conditions of the system in an additional environment. in the science of thermodynamics, exergy is divided into kinetic, potential, physical, and chemical types. exergy per unit mass is called specific exergy, the equation of which is shown below [29, 30]: 𝑒𝑥 = ∑ 𝑥𝑖 𝑒𝑥𝑐ℎ𝑖 + 𝑉2 2 + 𝑔𝑍 + (ℎ − ℎ0) − 𝑇0(𝑠 − 𝑠0) + 𝑇0 ∑ 𝑥𝑖 𝑅𝑖 𝑙𝑛𝑦𝑖 (7) the cu-cl materials standard chemical exergy in the dead state condition is presented in references [28, 31]. ma ehyaei et al. /future energy february 2024| volume 03 | issue 01| pages 34-49 37 the molar base entropy in the cu-cl cycle is calculated as follows [27, 28]: �̅� = 𝐴 × 𝑙𝑛(𝑇) + 𝐵 × 𝑇 + 𝐶 × 𝑇2 2 + 𝐷 × 𝑇3 3 − 𝐸 × 1 2𝑇2 + 𝐺 (8) the exergy efficiency (exe) for the cu-cl cycle is written as follows: ηexergy cu−cl = ṁ𝐻2exh2 �̇�𝐶𝑢𝐶𝑙+�̇�𝐶𝑢𝐶𝑙(1− 𝑇𝑂 𝑇𝐶𝑢𝐶𝑙 )+ṁ𝐻2𝑂exh2o (9) the exergy destruction rate (edr) of the cu-cl cycle can be evaluated as follows: �̇�𝐷 = �̇�𝐶𝑢𝐶𝑙 + �̇�𝐶𝑢𝐶𝑙 (1 − 𝑇𝑂 𝑇𝐶𝑢𝐶𝑙 ) + ṁ𝐻2𝑂exh2o − ṁ𝐻2exh2 − ṁ𝑂2exo2 (10) 3.3 economic evaluation the payback period is one of the standard methods of evaluating economic plans, which is used by most financial analysts because it is easy to calculate. in this method, the criterion for evaluating the length time of investment return. shorter payback plans are more attractive than longer payback plans. this method is especially useful when comparing two or more designs with each other. in reality, the payback period it takes for the net cumulative cash flows of the project to be zero. in other words, it takes time for the initial investment in the project to equal its returns. simply put, it is the length of time that project costs are returned to investors. the payback period (pp) can be calculated by [32, 33]: 𝑃𝑃 = 𝑙𝑛( 𝐶𝐹 𝐶𝐹−𝑟.𝐶𝑛 ) 𝑙𝑛(1+𝑟) (11) internal rate of return (irr) means how much the company earns annually and on average by doing a project or an investment. the higher this coefficient, the more valuable the investment will be. this coefficient can be calculated by [3234]: 𝐼𝑅𝑅 = 𝐶𝐹 𝐶𝑛 [1 − 1 (1+𝐼𝑅𝑅)𝑁 ] (12) net present value (npv) in an investment is the difference between the cost to start investing and the present value of all the income streams from which the investment is made. the npv answers the question of whether it is possible to make a relatively large return on investment. npv can be calculated by the following relation [32-34]: 𝑁𝑃𝑉 = 𝐶𝐹 (1+𝑟)𝑁−1 𝑟(1+𝑟)𝑁 − 𝐶𝑛 (13) 3.4 exergoeconomic analysis exeroeconomic analysis is a combination of exergy and economic analysis to obtain more information about the exergy flow and product cost rates, and their relationship to investment costs. in this way, we can better understand the behavior of the system. the general equation of this analysis is as follows [35, 36]: ∑ �̇�𝑖𝑛.𝑙 𝑚 𝑖𝑛=1 + �̇�𝑄.𝑙 + �̇�𝑙 = ∑ �̇�𝑜𝑢𝑡.𝑙 𝑚 𝑜𝑢𝑡=1 + �̇�𝑊.𝑙 (14) the stream l cost rate is written as follows [35, 37]: �̇�𝑙 = 𝑐𝑙𝐸�̇�𝑙 (15) eẋl and cl represent exergy and specified cost. the capital investment rate can be written as [35, 37]: żl = φzlcrf 3600n (16) in equation 16, crf can be calculated by [35, 37]: crf = j(1+j)m j(1+j)m−1 (17) j and m denote the interest rate and project lifetime. the exergy destruction cost is calculated by [35, 37]: ċd.l = cf.leẋd.l (18) the exergoeconomic factor for component l can be calculated by [35, 37]: fl = żl ċd.l+żl (19) therefore, the more the exergy component is degraded, the lower the economic exergy coefficient. for component l, high and low values of fl indicate high investment and inefficient system performance, respectively. 4. the previous research 4.1 renewable energy resource siddiqui et al. [38] have studied a triple production system with a new arrangement whose energy sources are solar and geothermal. its subsystems include a flash steam geothermal power plant, an absorption chiller, a 4-step cu-cl electrochemical cycle, and a heliostat solar receiver (hsr). hsr provides the heat required for the cu-cl electrochemical cycle. the cu-cl electrochemical cycle waste energy is also used as the heat source of the absorption chiller generator. the products of this system are electricity (3398 kw), cooling (603.9 kw), and hydrogen (32.1 mole/s). figure 1 depicts the layout of this system under study. the operating fluids for the geothermal power plant, hsr, and absorption chiller are water, molten salt, and water/ammonia solution, respectively. in this research, aspen plus software has been used to model the cu-cl electrochemical cycle, and engineering equation solver (ees) software has been used for other components. the equations for ene and exefor this cycle are shown below [38]: ηenergy = �̇�𝑒𝑙,𝐺+�̇�𝐴𝐵𝑆+ṁ𝐻2lhvh2 �̇�𝑔𝑒𝑜𝑡ℎ𝑒𝑟𝑚𝑎𝑙+�̇�𝑠𝑜𝑙𝑎𝑟 (20) ηe𝑥ergy = �̇�𝑒𝑙,𝐺+�̇�𝐴𝐵𝑆,𝐸𝑉( 𝑇𝑂 𝑇𝐸𝑉 −1)+ṁ𝐻2exh2 �̇�𝑔𝑒𝑜𝑡ℎ𝑒𝑟𝑚𝑎𝑙+�̇�𝑠𝑜𝑙𝑎𝑟(1− 𝑇𝑂 𝑇𝑠𝑢𝑛 ) (21) subscripts abs, and el, g denotes the cooling and net electrical production by the system. the sun’s temperature is considered 5777 k. in the above energy equation, the output of the system, which includes the rate of hydrogen energy produced, cooling, and electricity, is divided by the sum of the system inputs, which include the rate of geothermal energy and solar radiation. while in the exergy equation, these values are calculated in terms of exergy flow. the ene and exe of this system are 19.6% and 19.1%, respectively, while the ene and exe of the cu-cl cycle are 35.3% and 35.9%, respectively. the cop and the exe of the absorption chiller are 0.54 and 0.32, respectively. the highest rate of edr is in steam turbines and the lowest in condensers. the efficiency of the above system depends to a large extent on the amount of solar radiation. for example, with increasing direct solar radiation ma ehyaei et al. /future energy february 2024| volume 03 | issue 01| pages 34-49 38 from 100 to 2300 (w/m2), ene and exe increase from 15.2% and 14.9% to 21.7% and 21.2%, respectively. the reason for this increase is the increase in the hydrogen production rate in the cu-cl cycle. according to previous studies, the ene range of the flash steam geothermal power plant is between 10% and 17% [39], while the studied cycle [38] with the hybrid energy sources of solar and geothermal reached an energy efficiency of 19.6%, which is 2.6% higher than the highest efficiency range of the flash steam cycle geothermal power plant. also, product diversity is another strength of this cycle. one of the problems of the system proposed in the ref [38] is the system control, how can two sources of solar energy that are not always available be controlled with a geothermal source to gain a stable production rate. sadeghi et al. [40] studied a multi-generation system to produce electricity, steam, and hydrogen. the subsystems of this multigeneration system are src, gas turbine, hsr, thermal energy storage (tes) with phase change material (pcm), cucl cycle, and heat recovery. they used energy, exergy, and exergy-economic analyses to evaluate the system, as well as, system optimization via a non-dominated sorting genetic algorithm-ii (nsga-ii) algorithm. the layout of the proposed multigeneration system is depicted in figure 2. the proposed system of ref [40] generates 370.8 kg/h hydrogen, 50.5 mw of electrical power, and 50.15 ton/h steam. the cu-cl cycle consumes 5.18 mw of electrical power for 0.103 kg of hydrogen production. also, the cu-cl purchase cost rate cycle accounts for 4.5% of the total system cost rate. the system ene and exe can be calculated as follows [40]: ηenergy = �̇�𝑛𝑒𝑡+�̇�𝑆𝑡𝑒𝑎𝑚+ṁ𝐻2lhvh2 �̇�𝑠𝑜𝑙𝑎𝑟 (22) ηexergy = 1 − �̇�𝑑 �̇�𝑠𝑜𝑙𝑎𝑟(1− 4 3 𝑇𝑂 𝑇𝑠𝑢𝑛 + 1 3 ( 𝑇𝑂 𝑇𝑠𝑢𝑛 )4) (23) in ref [40], another method is used to calculate the system exe. that is, instead of dividing the useful output exergy rate by the input exergy rate, the unit value is deducted from the ratio of the edr to the input exergy rate. in both methods, the same value is calculated for the exe of the system. the system ene and exe, and total edr are 48.2%, 45%, and 111 mw, respectively. the levelized cost of hydrogen and exergy are 10.9 us$/gj, and 1.6 us$/kg, respectively. al-zareer et al. [41] have evaluated a hydrogen production system utilizing solar energy. in this system, solar energy is converted to superheated steam by a one-megawatt hsr. part of the steam in the five-step cu-cl cycle is used to generate hydrogen and remains in the src to generate electricity. the hydrogen produced is compressed up to about 700 bar in a series of compressors. cu-cl and src components were modeled by aspen plus software. ees software was used for hsr simulation. this system produces 322 kw of electricity and 25.1 kg/h of hydrogen. figure 1. the schematic diagram of research done by siddiqui et al. [38] ma ehyaei et al. /future energy february 2024| volume 03 | issue 01| pages 34-49 39 the ene and exe of this system can be calculated from the following equations [41]: ηenergy = �̇�𝑛𝑒𝑡+ṁ𝐻2lhvh2+ṁ𝐻2hh2 �̇�𝑠𝑜𝑙𝑎𝑟 (24) ηexergy = �̇�𝑛𝑒𝑡+ṁ𝐻2exh2 �̇�𝑠𝑜𝑙𝑎𝑟(1− 4 3 𝑇𝑂 𝑇𝑠𝑢𝑛 + 1 3 ( 𝑇𝑂 𝑇𝑠𝑢𝑛 )4) (25) by comparing equations 22 and 24, it can be seen that equation 24 has an extra term in the nominator of the system ene equation. this is due to the compression of hydrogen up to a pressure of 700 bar by the proposed system related to this equation. the system ene and exe are reported to be 20.6% and 12.1%, respectively. the highest and lowest ene is related to the hsr and hydrogen gas compression. in terms of exe, the maximum and minimum values are related to the cu-cl cycle and hydrogen gas compression. the highest and lowest edr is related to the hsr and the four-step cu-cl cycle, respectively. from the mentioned results, it can be inferred that this integration is not suitable from the point of view of exergy. because it does not improve the system ene and exe compared to the four-step cu-cl cycle. dincer and temiz [42] proposed a system including a parabolic concentrated solar power plant, steam rankin cycle, fuel cell, and polymer electrolysis, two-face photovoltaic power plant, lithium bromide absorption chiller, and 4-step cu-cl cycle for electricity, cooling, and hydrogen generation. energy and exergy analyses have been performed for this system. the energy demand of this system is supplied by solar. generally, for solar systems and due to their unavailability at night, storage systems are used, for which a molten salt storage system has been used. the function of this system is that the solar energy of parabolic through collector (ptc) and photovoltaic cells are converted into heat and electricity. the heat obtained is used in the cu-cl cycle to produce hydrogen and the rest is converted into electricity in steam turbines. the power consumption of the cu-cl cycle is supplied by the electricity generated by solar cells and steam turbines, and the rest goes to the consumer. also, the heat dissipated by the steam turbine in the absorption chiller is converted into cooling. the proposed system configuration is shown in figure 3. similar to previous research, the aspen hysis is employed for cu-cl energy modeling. the ene and exe of this system are calculated from the following equations [42]: ηenergy = ṁh2lhvh2+ẇnet+q̇cooling �̇�𝑠𝑜𝑙𝑎𝑟 (26) ηexergy = ṁh2exh2+ẇnet+�̇�𝑐𝑜𝑜𝑙𝑖𝑛𝑔 �̇�𝑠𝑜𝑙𝑎𝑟(1− 4 3 𝑇𝑂 𝑇𝑠𝑢𝑛 (1−cos 𝛿) 1 4+ 1 3 ( 𝑇𝑂 𝑇𝑠𝑢𝑛 )4) (27) in which, δ means deflection angle. figure 2. the layout of the system presented in ref [40] ma ehyaei et al. /future energy february 2024| volume 03 | issue 01| pages 34-49 40 this system produces 315.9 kg/h of hydrogen, 22.7 mw of electricity, and 1.7 mw of cooling. the system ene and exe are reported at 36% and 31.2%, respectively. zhang et al. [43] have analyzed the energy, exergy, and economics of a solar system dual generating electricity and hydrogen. the optimization of this dual production system is done by the non-dominated sorting genetic algorithm ii. the system's subsystems include a four-step cu-cl cycle, hsr, and molten salt heat storage, a brayton cycle with an hrsg coupled by an organic rankine cycle (orc). to model this system, aspen-plus software, and fortran programming language have been used. this cogeneration system produces 7.3 mw of electricity and 1.91 kg/h of hydrogen. the system ene and exe are calculated by the following equations [43]: ηenergy = ṁh2lhvh2+ẇnet �̇�𝑠𝑜𝑙𝑎𝑟 (28) ηexergy = ṁh2exh2+ẇnet+�̇�𝑐𝑜𝑜𝑙𝑖𝑛𝑔 �̇�𝑠𝑜𝑙𝑎𝑟(1− 4 3 𝑇𝑂 𝑇𝑠𝑢𝑛 + 1 3 ( 𝑇𝑂 𝑇𝑠𝑢𝑛 )4) (29) the ene and exe, as well as the edr of this dual system, is reported to be 28.9% and 46.2%, and 165.3 mw respectively. the price of hydrogen produced by this system is estimated at 2.84 us$/kg. the payback period of this system with an initial investment of 60.85 million us$ equals 2.5 years. using the optimization algorithm, the system exergy efficiency increases to 50.9%, and the price of hydrogen produced decreases by 1.28 us$/kg. quagued et al. [44] have studied the potential of using ptc with the solar tracking system to supply the required heat for the four-step cu-cl cycle in the climatic conditions of algerian cities in algeria. in this plan, the electricity needed for the cycle is provided by external sources. the working fluid in the ptc is syltherm 800, which has stable conditions at high temperatures. in this article, information about the software used to analyze this system has not been given. the ene and exe of this system are as follows: ηenergy = ṁh2lhv𝐻2 �̇�𝑠𝑜𝑙𝑎𝑟+ẇin (30) ηexergy = ṁh2exh2 �̇�𝑠𝑜𝑙𝑎𝑟+ẇin (31) the hydrogen produced by this system is reported as 0.0125 kg/m2/h. the cu-cl ene without considering the ptc is equal to 40.4% and the exe of this system is equal to 92.2%. these values of ene and exe are within the range of references [45, 46]. temiz and dincer [47] have investigated the multiple production systems of electricity, heating, hydrogen, and freshwater, the energy required of which is supplied by geothermal and solar sources. the subsystems of this integrated system include a 4-step cu-cl electrochemical cycle, geothermal power plant, multi-effect distillation systems (med), ptcs, molten salt storage system, solar heat pump, and three-step src whose operating fluid is ammonia. the products of this integrated system are fresh water, heating, electricity, and hydrogen. figure 3. the proposed system configuration of ref [42] ma ehyaei et al. /future energy february 2024| volume 03 | issue 01| pages 34-49 41 the electricity production of this system is 1.65 kw with a price of 0.03 us$/kwh. also, the hydrogen production rate of the mentioned system is 0.01 kg/s with a price of 2.84 us$/kg. the production rate of heat and potable water in this system is equal to 15.7 kw with a price of 0.005 us$/kwh and the production rate of water is equal to 0.005 kg/s and its price is equal to 0.007 us$/liter. in this analysis, a hypothetical city near the geyser region of california is considered. this city has the largest sources of geothermal energy. for energy, exergy, and economic simulation the system advisor model (sam), hysys, and ees software are employed. the overall ene and exe of this integrated system are as follows [47]: ηenergy = ṁh2lhvh2+ẇnet+ṁpwhpw+�̇�ℎ𝑒𝑎𝑡𝑖𝑛𝑔 �̇�𝑠𝑜𝑙𝑎𝑟+�̇�𝑔𝑒𝑜𝑡ℎ𝑒𝑟𝑚𝑎𝑙 (32) ηexergy = ṁh2exh2+ẇnet+�̇�ℎ𝑒𝑎𝑡𝑖𝑛𝑔+ṁpwexpw �̇�𝑠𝑜𝑙𝑎𝑟+�̇�𝑔𝑒𝑜𝑡ℎ𝑒𝑟𝑚𝑎𝑙 (33) the ene and exe of this integrated system are equal to 27.4% and 13.7%, respectively. in the continuation of this research, sohani et al. [48] have optimized this system using nsga-ii and topsis algorithms. then, they compared the optimization results with the results of the static multi-objective optimization approach (smoa) algorithm. this method was a comparison between static and dynamic optimization algorithms. optimization variables include geothermal mass flow rate and hydrogen storage pressure. the objective functions are the amount of production of electricity, fresh water, hydrogen, heat, ene, and exe of the system and pp. by using the mentioned methods, the annual production of electricity, hydrogen, heat, and freshwater increased by 14.4, 13.5, 16.1, and 14.3%, respectively. also, the annual efficiency of energy and exergy increased by 3 and 5.2%, respectively. sadeghi and ghandehariun [49] analyzed the energy and exergy of a tripleproduction solar system of electricity, steam, and hydrogen. they have also optimized the desired system with a genetic algorithm. this integrated system includes a solar power tower, a four-step cu-cl cycle, a eutectic fluoride salt pcm storage system, hrsg, and src. the solar energy tower is used to provide heat for the cu-cl cycle and the waste heat of this cycle is used to provide heat for the steam cycle. the layout of this system is presented in figure 4. figure 4. the layout of the system presented in reference [49] ma ehyaei et al. /future energy february 2024| volume 03 | issue 01| pages 34-49 42 the air is first compressed and it enters the solar receiver to be heated. the air is used to charge the pcm when there is enough solar radiation, and it is heated by the pcm when there is not enough solar radiation. then the heated and compressed air is used to rotate the gas turbine and then it is returned to the pcm storage tank for a second time to be heated enough. after that, it is used as a heat source for the cu-cl cycle, heat exchangers, and src. in basic mode, this integrated triple-production system produces 41.7 mw of electricity, 343 kg/h of hydrogen, and 41 ton/h of steam. the ene and exe of this system can be written as follows: ηenergy = ṁh2lhvh2+ẇnet+�̇�𝑠𝑡𝑒𝑎𝑚 �̇�𝑠𝑜𝑙𝑎𝑟 (34) ηexergy = ṁh2exh2+ẇnet+�̇�𝑠𝑡𝑒𝑎𝑚 �̇�𝑠𝑜𝑙𝑎𝑟 (35) the ene and exe of this system are 45.1% and 49.0%, respectively. the highest share of the edr is related to the solar system and the lowest amount is related to the cu-cl cycle and src. by optimizing this system, the amount of hydrogen produced increases by about 43%. ishaq et al. [50] have studied the thermodynamic analysis of a triple production system of electricity, heat, and hydrogen, whose sources are solar and wind. the subsystems of this plant are a 4-step cu-cl electrochemical cycle, wind turbine, hsr, and hydrogen compression system. three compressors are used in this system, whose pressure ratios are equal to 5, 10, and 15, respectively. the working fluid of the hsr is molten salt. the wind turbine's electrical production is equal to 17505 kw, of which 5605 kw is consumed by the compressors used to compress the hydrogen gas, and the power output of this system is equal to 11900 kw. the hydrogen production rate of this system is equal to 455.1 kg/h. the system ene and exe are as follows [50]: ηenergy = ṁh2lhvh2+ẇnet �̇�𝑠𝑜𝑙𝑎𝑟+ẇr (36) ηexergy = ṁh2exh2+ẇnet �̇�𝑠𝑜𝑙𝑎𝑟+ẇr (37) the subscript r shows the rated power of the wind turbine. the ene and exe of this dual production system are 48% and 49%, respectively. 4.2 non-renewable energy resource ishaq et al. [51] have investigated the energy and exergy of a system that has produced electricity, hydrogen, and drinkable water using the wasted energy of the glass factory. the subsystems of this new arrangement include src, a fourstep cu-cl cycle, orc, med, and a hydrogen compression system by series compressors. the arrangement of this cycle is shown in figure 5. the way this system works is that a part of the waste heat of the glass factory is utilized as a heat source for the 4-step cucl cycle and a part is used to produce steam in the src. some of the waste heat of the src condenser is used as the heat source of the orc cycle, whose operating fluid is iso-butane. the remaining amount is used for the med system to produce potable water. using three series compressors, the hydrogen produced in this system is compressed to a 750 bar pressure. ees and aspen plus software have been used to simulate this system. if the hot gas exiting the glass factory has a temperature and flow rate equal to 1127 oc and 2500 kg/h, the electricity produced by the src steam turbine and the first and second orc turbines is 725, 727, and 697 kw, respectively. the ene and exe of this system are calculated from the following equations [51]: ηenergy = ṁh2lhvh2+ṁpwhpw+ẇnet �̇�𝑖𝑛 (38) ηexergy = ṁh2exh2+ṁpwexpw+ẇnet �̇�𝑖𝑛 (39) the ene and exe of this integrated system are equal to 36.5% and 38.1%, respectively. ishaq and dincer [52] have investigated the energy and exergy of a system with a new arrangement to recover the heat of the 805 oc hot gas from the exhaust of a factory (the type of factory is not specified). the mentioned system has hrsg, a thermoelectric generator (teg), reverse osmosis (ro), pressure swing adsorption (psa), orc, an ammonia production reactor, and a four-step cu-cl cycle. the products of this system include electricity, hydrogen, fresh water, and ammonia that the above system produces 43.2 kg⁄h of hydrogen and 160.0 kg⁄h of ammonia. the way this system works is that the hot gas from the factory turns the ro water into steam. this steam is converted into hydrogen in the cu-cl cycle. hydrogen produced together with nitrogen produced by the psa system is converted into ammonia in the ammonia production reactor. the heat of oxygen produced by the cu-cl cycle is recovered in the orc and teg subsystems to generate electricity. the produced electricity meets the electrical energy needs of other subsystems. the ene and exe of this system are calculated from the following equations [52]: ηenergy = ṁh2lhvh2+ṁnh3lhvnh3+ṁfwhfw �̇�𝑖𝑛+ẇnet (40) ηexergy = ṁh2exh2+ṁfwexfw+ṁnh3exnh3 �̇�𝑖𝑛+ẇnet (41) the system ene and exe are reported as 28.7% and 40.8%, respectively. fan et al. [12] have studied and analyzed the tri-generation system of electricity, cooling, and hydrogen by energy, exergy, and economic methods. this tri-generation system includes a gas turbine, a 4-step cu-cl electrochemical cycle, an absorption chiller, a heat recovery steam generator (hrsg), and an auxiliary boiler. the energy source of this system is natural gas a non-renewable energy source. the arrangement of this tri-generation system is shown in figure 6. the ees software is used to model this system. the trigeneration system produces 9.3 mw of electricity, 50.65 mw of cooling, and 84.9 kg/h of hydrogen. in this system, 66.2 mw of electricity is generated by a gas turbine, which due to the power consumption in the cu-cl cycle of 56.2 mw and 0.7 mw by 50 absorption chiller units, the net electrical power is reduced to 9.3 mw. the ene and exe equations of this triple production system are written as follows [12]: ηenergy = ṁh2lhvh2+ẇnet+q̇cooling ṁnglhvng (42) ηexergy = ṁh2exh2+ẇnet+�̇�𝑐𝑜𝑜𝑙𝑖𝑛𝑔 ṁngexng (43) ma ehyaei et al. /future energy february 2024| volume 03 | issue 01| pages 34-49 43 the heat of exhaust hot gas from the gas turbine for cooling and hydrogen production has a positive effect on system ene so that by adding a 4-step cu-cl cycle, and an absorption chiller, system ene increases from 19% to 29%, 43%, respectively. in the case of exe, this increase is greater. exe increases from 15% to 43.5%, and 44%, respectively. by comparing ene and exe, it can be concluded that adding an absorption chiller to the system has less effect on the system exe compared to ene. the highest rate of edr is related to a gas turbine and 50 units of an absorption chiller and the lowest amount is related to the auxiliary boiler and cu-cl cycle. this tri-generation system arrangement has an economic justification. incorporating the cu-cl cycle and subsequent absorption chillers reduces the payback time from 8.2 to 3.3 and 2.5 years, respectively. ishaq and dincer [53] have done the energy and exergy analyses of a new system that uses the heat of cement furnace slag (temperature around 1200 to 1600 oc) in the cu-cl cycle. with this method, hydrogen is produced and finally, it is converted into ammonia in the system. in this research, two furnaces have been considered. in addition to the cu-cl cycle, the sub-systems used include an hrsg, src, ammonia generator reactor, and cryogenic air separator. they used aspen plus software for this evaluation. the electricity required in the cu-cl electrochemical cycle is provided by the src. the final products of this system include electricity, ammonia, oxygen, hot water, and heat. the ene and exe of the system are calculated by the following relations [53]: ηenergy = ṁnh3lhvnh3+ẇnet+ṁo2ho2+�̇�ℎ𝑒𝑎𝑡𝑖𝑛𝑔+�̇�𝐻𝑊 �̇�𝑖𝑛 (44) ηexergy = ṁnh3exnh3+ẇnet+�̇�ℎ𝑒𝑎𝑡𝑖𝑛𝑔+�̇�𝐻𝑊+ṁo2exo2 �̇�𝑖𝑛 (45) hw denotes hot water. the electricity produced is equal to 3433 kw, and the hydrogen and ammonia produced are equal to 140.4 and 795 kg/h, respectively. the ene and exe of this system are equal to 36.1% and 30.1%, respectively. sayyadi [54] has investigated the integrated system of gas brayton cycle with hrsg, and cu-cl thermochemical cycle via energy, exergy, and economic point of view. in this system, electricity is generated in the gas cycle and the hot exhaust gas is utilized to convert water into superheated steam. superheated steam is used as the heat source of the cu-cl cycle. also, a part of the electricity produced in the gas cycle is consumed in the cu-cl cycle. matlab software was used for the simulation of this proposed system. he examined 39 gas turbine models and finally found that the mitsubishi hi 501 f model has the best performance for the arrangement of the proposed system. figure 5. the arrangement of the cycle presented in ref [51] ma ehyaei et al. /future energy february 2024| volume 03 | issue 01| pages 34-49 44 this proposed system produces 5867.5 kg/h of hydrogen with 735 mw of electricity. the ene and exe equations of this triple production system are written as follows [54]: ηenergy = ṁh2lhvh2+ẇnet ṁnglhvng (46) ηexergy = ṁh2exh2+ẇnet ṁngexng (47) after the mentioned analysis, the proposed system is optimized based on a genetic algorithm. five scenarios have been considered to optimize this system. in the first to third scenarios, ene, exe, and hydrogen-produced price are considered objective functions. in the fourth and fifth scenarios, energy efficiency and price of produced hydrogen and exe and price of hydrogen are considered objective functions. in the base state, the ene and exe and the price of produced hydrogen are equal to 46.8%, 44.8%, and 4.11 us$/kg, and using the fifth optimization scenario, these values are equal to 51.7%, 48.2%, and 3.97 us$/kg. 5. development policy 5.1 non-renewable energy resource for hydrogen production in the cu-cl cycle, a heat source with a temperature of about 500 oc and electricity and water are needed. therefore, the exhaust gases of all kinds of factories that have a temperature higher than 580oc can be a good source for hydrogen production by this cycle. these industries include cement, glass, copper, iron, petrochemicals, etc. the flare exhaust gas of petrochemicals is one of the important sources of energy to achieve this goal. the following options are suggested to supply the consumed electricity for this cycle: figure 6. the proposed system configuration of ref [12] ma ehyaei et al. /future energy february 2024| volume 03 | issue 01| pages 34-49 45 1. using network electricity if there is an electricity network near the cu-cl cycle. 2. some of the steam produced by the waste hot gases of the industries will be converted into electricity in the steam turbine. 3. if electricity is produced in the factory, the excess consumption of the factory components should be given to the cu-cl cycle. 4. if there are renewable energy sources, a power plant should be built to generate electricity from these sources. the produced electricity can be consumed in the cu-cl cycle. 5. the oxygen produced by the cu-cl cycle can be used as a heat source in cycles that do not require a hightemperature source to produce electricity. these cycles include orc, goswami cycle, and kalina cycle. 6. the remaining energy of the hot gas after supplying the required energy of the cu-cl cycle is used in the orc, kalina, and goswami cycles to supply the electricity required for the cu-cl cycle. by comparing the above methods, the best method can be chosen from the point of view of energy, exergy, and economics. figure 7 shows the schematic of this strategy. it is also reminded that a combination of the above strategies can also be used. 5.2 renewable energy resource as mentioned, three factors heat, electricity, and water are needed to produce hydrogen by the cu-cl cycle. naturally, wind, geothermal and water current sources cannot be used to provide the required heat for this cycle, the only renewable energy source that is capable of providing this heat is solar energy. that is if firstly, that region or region has a high potential for solar radiation, and secondly, a heliostat field or ptc should be used to convert this energy into heat. other types of solar collectors such as flat plates are not suitable for this task due to the limitations of the output fluid temperature. but to provide the electricity required for this cycle, the designer has more options and all types of renewable energy sources can be used provided they have a high potential in that area or region. figure 8 shows the schematic of this strategy. so, the following options can be considered to produce the electricity required for this cycle: 1. using network electricity if there is an electricity network near the cu-cl cycle. 2. if that area, in addition to the high potential of solar energy, is in the vicinity of geothermal sources, it is possible to convert the energy of the geothermal source into electrical energy in one of the different cycles..., kalina, orc, flash, and from this electricity used in the cu-cl cycle. 3. if that area, in addition to the high potential of solar energy, has a suitable wind speed, it is possible to use a wind turbine to produce electricity to provide electricity for the cu-cl cycle. 4. the output oxygen of the cu-cl cycle can be used in cycles that produce electricity with low-temperature sources (goswami, kalina, orc,….) 5. some of the steam produced by the ptc and heliostat field will be converted into electricity in a steam turbine figure 7. the schematic of the strategy developed for integration of the cu-cl cycle with systems powered by nonrenewable energy resources (options 1 to 6) ma ehyaei et al. /future energy february 2024| volume 03 | issue 01| pages 34-49 46 figure 8. the schematic of the strategy developed for integration of the cu-cl cycle with systems powered by renewable energy resources (options 1 to 5) 6. conclusion one of the challenges of the current century is the increase in energy demand, the reduction of fossil fuel resources, and environmental problems. fossil fuels are running out, and due to the destruction of the ozone layer, which has irreparable environmental effects, it is necessary to use suitable alternative fuels such as hydrogen. in addition to having characteristics such as reversibility, storage, and environmental friendliness, hydrogen has a higher calorific value than conventional fossil fuels. there are different methods for hydrogen production, among the thermochemical methods, the cu-cl cycle has been expanded and used more due to its relative advantages. according to the heat requirement of this cycle, it is possible to supply the heat needed for this cycle from the waste hot gases of various industries. therefore, the integration of this cycle with the systems of different industries has economic justification. in general, the requirement of this cycle to produce hydrogen is a heat source with a temperature of 520°c and electricity. to supply electricity to this system, there are different choices of cycles with low source temperature, grid electricity, and power plants with renewable energy sources. also, to provide heat, the heat needed for this cycle can be used by ptc or hsr, and there are many studies in this field in the research literature, the most important of which are described in this article. the most important results obtained from this research are as follows: 1. it is recommended to use the waste of hot industrial gases for hydrogen production by the cu-cl cycle, which can achieve a yield of over 50% due to the efficiency of this cycle and the regenerator heat exchanger. 2. according to the conditions of the system, its size... the pp of the cu-cl cycle is about 3 to 4 years if the hot gas heat is recycled, and about 6 to 8 years if the heat is supplied by hsr and ptc. 3. the hot gas discharged after recycling in the cu-cl cycle and reducing 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[54] h. sayyaadi, "a conceptual design of a dual hydrogenpower generation plant based on the integration of the gas-turbine cycle and copper chlorine thermochemical plant," international journal of hydrogen energy, vol. 42, pp. 28690-28709, 2017/11/30/ 2017. battisti, l., et al., experimental benchmark data for hshaped and troposkien vawt architectures. renewable energy, 2018. 125: p. 425-444. this article is an open-access article distributed under the terms and conditions of the creative commons attribution (cc by) license (https://creativecommons.org/licenses/by/4.0/). h. yousefi et al. /future energy may 2024| volume 03 | issue 02| pages 24-30 24 article co2 emission from the electricity sector in iran; calculation, prediction and reduction policies hossein yousefi, shiva ansaripour, aminabbas golshanfard, mohammad hasan ghodusinejad* energy modelling and sustainable energy system (metsap) research lab., faculty of new sciences and technologies, university of tehran, tehran, iran a r t i c l e i n f o article history: received 01 july 2023 received in revised form 02 august 2023 accepted 08 august 2023 keywords: co2 emission, renewable energy, gpr, fuel consumption forecast, reformation strategy *corresponding author email address: mh.ghodusi@ut.ac.ir doi: 10.55670/fpll.fuen.3.2.3 a b s t r a c t fossil fuel power plants produce a significant amount of co2 emissions, and this pollutant causes global warming, respiratory and heart diseases, and other significant issues. electricity interprets as a primary and rising demand in each energy system; thus, in this paper, carbon dioxide (co2) emission reduction was selected as the objective value for 2025. power plant fuel consumption was surveyed to calculate the co2 emission caused by each fuel. also, esfahan province (an industrial province in iran) was investigated as the study case. forecasting the fuel consumption for 2025 was run by two parameters: population and gross domestic production (gdp), which were forecasted by the report of the iran statics center and the gaussian process regression (gpr) method, respectively. the co2 emission of power plants was obtained using the coefficients of each fuel. based on iran's commitment to the paris agreement, a 4% reduction of co2 emissions is the main objective. thus, this study aims to reach this goal by implementing four scenarios: a) adding renewable energies, b) adding renewable energies and improving the generation efficiency, c) adding renewable energies and decreasing the grid losses, and d) combining the three scenarios mentioned above. according to these scenarios, reformation strategies compensated 10.5% of the required power, which was satisfied by renewable energies, and finally, this province can gradually satisfy a 4% reduction until 2025. 1. introduction the intergovernmental panel on climate change (ipcc) report, which is related to an increase of 1.5 ˚c the earth's temperature after the industrial revolution, expresses the combustion impacts of fossil fuels in greenhouse gases emission [1, 2]. today, climate-changing problems, global warming, rising numbers of respiratory and heart diseases, etc., have raised concerns in the countries. the paris agreement was signed in 2015 to balance the number of pollutants from human activities and ensure sustainable development in the second half of this century and limit the temperature increase up to 2˚c [3, 4]. due to the increase in population, the limitations of energy sources, and the environmental effects of fossil fuels, societies are moving towards alternative energies [5]. the pollutants emission generally is derived from five sectors: transportation, power plant, industrial, commercial-residential, and agricultural. as shown in figure 1, the power plant sector produces a significant amount of emissions. this sector contains three parts: generation, transmission, and distribution, which major contribution to pollution emissions such as co2, methane (ch4), nitrogen oxide (nox), sulfur oxide (sox), etc. are related to generation [6]. several theories mentioned a relationship between environmental pollution and economic growth [5-7]. on the other hand, the quality of the environmental parameter is affected by renewable energy development. thus, more than ever, societies are moving to use renewable energy resources to satisfy ecological indicators. finally, a u-shaped relationship between renewable energy resources and economic growth, or in other words, gdp per capita, will be derived [8, 9]. as a result of the new technologies development and increasing the number of consumers, electricity demand has been rising. lack of fossil fuel sources, fuel price, and combustion's harmful environmental effects are potential challenges during power generation. a solution to this problem is distributed energy planning (dep) [10]. according to the iea report, five factors can affect deps, which are: distributed generation (dg) technology, limitations on new transmission lines, increase in the electricity consumers with high reliability, privatization, competition in the electricity market, and climate change concerns [11]. iea forecasted a reduction of 1.4 to 13 gt in the co2 emission caused by power generation, which means about 90%, until the year 2050 [12]. iran is one of the most important oil and natural gas exporting countries. statistics show that more than 98% of iran's energy consumption is provided through these sources, which has led to severe problems such as air pollution, and the effects of future energy open access journal https://doi.org/10.55670/fpll.fuen.3.2.3 may 2024| volume 03 | issue 02 | pages 24-30 journal homepage: https://fupubco.com/fuen issn 2832-0328 mailto:mh.ghodusi@ut.ac.ir https://doi.org/10.55670/fpll.fuen.3.2.3 https://fupubco.com/fuen h. yousefi et al. /future energy may 2024| volume 03 | issue 02| pages 24-30 25 this pollution are more visible in metropolitan areas [13-14]. along with this, statics showed a share of 1.97% in global co2 emission in the year 2018, which made this developing country the seventh co2 producer country around the world [15]. furthermore, iran's energy balance sheet (2016) reports that annual co2 emissions released in the electricity sector are higher than any other pollutant [16]. figure 1. the contribution of each energy sector in the pollutant emissions most of the co2 emissions in 2016 for iran are related to natural gas, diesel, gasoline, mazut, and coal, respectively . figure 2 illustrates the importance of co2 and the share of other pollutants, as well. as can be seen, following co2, nox has a larger share in air pollutants [17]. in order to achieve sustainable development goals and control pollutants, consumption management and utilization of renewable energy sources are required. the high potential of renewable sources, like solar and wind, can help apply sustainable programs and strategies [14]. investment in renewable energy sources has been conducted so that solar power plants' installation had a growth rate equal to 50 between 2007 and 2017 [12]. about 195 countries signed the paris agreement, including iran, and each country made its commitments. based on the bill expressed in the iranian parliament, this country would decrease at least 4 percent of its emission by 2030 [18]. hence, this paper is focused on the 4 percent reduction of co2 emission. figure 2. the contribution of each pollutant 2. literature review the amount of fuel consumption due to the fuel type is determined by achieving the number of pollutants caused by the power plants. according to references [19] and [20], the most influencing parameters on fuel consumption in power plants are gdp and population. two main study areas focused on this research are demand forecasting and co2 emission reduction strategies. a comprehensive study of 50 countries worldwide, including iran, has investigated the impact of gdp, population growth, and renewables installation on air pollution [21]. it has concluded that the two first criteria have a positive effect on co2 emission. according to [22], a novel self-adapting intelligent grey model is a better approach than competing natural gas forecasting methods. the logistic model has been applied in [23] for long-term natural gas consumption forecasting in china. for getting the parameters of the logistic model levenberg-marquardt algorithm is adopted. in [24], the autoregressive–moving-average model with exogenous inputs (armax) model has been developed for residential and commercial energy demand forecasting in iran. alcaraz and villalvazo [25] presented the natural gas estimation shortage with econometric analysis based on panel data and analyzed the natural gas interconnection shortage and gdp. in 2017, scarpa and bianco [26] investigated long-term natural gas consumption, considering heating degree days, natural gas prices, and gdp per capita. to obtain this goal, they used the regression algorithm and the kalman filter method. the relationship between price and income with natural gas consumption has been shown by liu et al. [27]. the generalized least square method was used in this study. wang et al. [28] studied the natural gas consumption model with high accuracy by a mape value of 2.32% with a hybrid model based on the particle swarm optimization-wavelet neural network (pso-wnn). in [29], artificial neural networks (ann), multiple linear regression (mlr), and support vector regression (svr) was presented for forecasting natural gas consumption in istanbul with these criteria: seasonal index, temperature, price of natural gas, population and 12 years history of natural gas consumption. in [30,31], electricity consumption forecasting in a building is done by using the gpr method. sharifzadeh et al. [32] did a comparative study of ann, svr, and gpr for forecasting residential electricity demand. further, the gaussian process quantile regression is used in [33] to predict power load probability density. in some cases, the gpr method is preferred in forecasting wind forecasting because it is flexible to provide uncertainty representations [34, 35]. researchers have proposed some methods to decrease co2 emissions [36, 37]. dominkovic et al. [38] studied southeast europe to make a 100% renewable energy system for 2050 to achieve a zero-carbon energy community. for getting this object, biomass, and other renewable energies have been used. also, improving energy efficiency is considered a reformation strategy for decreasing co2. davíarderius et al. [39] expounded on the impact of electricity losses on co2 decrement. construction of dgs near the consumers and covering different generations with renewable energy are the two essential policies suggested in this research. technical progress, energy structure, and economic level are the variables considered in [40] to analyze their impact on co2 emission in china. also, it is concluded that technological advances have about a 1% effect on china's co2 emission. also, 14 years (2000-2014) of research in china indicated that technological developments had a remarkable impact on co2 emission [41]. the south asian association for regional cooperation (saarc) countries has been weighted and ranked based on the co2 emission issue by grey relational analysis (gra) [42]. the results have shown substantial pollution problems in india with the first rank; hence, renewable energy installation and adoption of iso14001 certification were introduced to solve this problem. toward reduction of carbon emission, reference [43] offered three assortments that contain adding a clean energy supply, h. yousefi et al. /future energy may 2024| volume 03 | issue 02| pages 24-30 26 development in energy conservation, and negative emission strategies like using ccs technology. 3. methodology: gpr gpr is a non-parametric probabilistic kernel method that can model arbitrary complex systems [32]. this method combines arbitrary variables with a number describing the joint gaussian distribution [33]. gpr models a probability distribution by functions and can be parameterized with statistical functions like mean m(x), which is the expected value of f(x), and covariance к(x-x') that defines the similarity between data points. it can be shown as: 𝑦 = 𝑓(𝑥) ∼ 𝐺𝑃(𝑚(𝑥), 𝜅(𝑥 − 𝑥 ′)) (1) where x and y are the input and output in the training dataset, respectively, and f(x) is called the latent variable. for simplification, mostly m(x) is considered to be 0. a variety of covariance functions can be used. some of the most common ones are squared exponential (se) (eq2), matern (ma) (eq3), and rational quadratic (rq) (eq4). 𝜅𝑆𝐸(𝑥 − 𝑥 ′) = 𝜃𝑓 2𝑒𝑥𝑝( ‖𝑥−𝑥′‖ 2 𝜃𝑙 2 ) (2) 𝜅𝑀𝑎(𝑥 − 𝑥 ′) = 𝜎2 21−𝑣 𝛤(𝑣) (√2𝑣 𝑥−𝑥′ 𝑙 )𝑣𝜅𝑣(√2𝑣 𝑥−𝑥′ 𝑙 ) ,𝑣, 𝑙 > 0 (3) 𝜅𝑅𝑄(𝑥 − 𝑥 ′) = 𝜎2(1 + 𝑥−𝑥′ 2𝛼𝑙2 )−𝛼 ,𝛼, 𝑙 > 0 (4) the se function is infinitely differentiable, so the gpr is so smooth using it, and it is too strict for physical action [34]. θf and θl are parameters that control the length scale. kv in matern covariance was modified bessel function. the function becomes simple when v is half floating-point v=p+1/2, where p is an integer. v is mostly considered to be v=5/2 and v=3/2. along with this, two effective methods were proposed to evaluate machine learning algorithms' performance; holdout-test, which mostly applies to large datasets, and cross-validation (cv), which is called k-fold validation. this approach divides the dataset into parts and estimates each fold's accuracy to prevent overfitting the output. also, by increasing the number of folds, more reputable outputs can be derived. figure 3. the electricity system of isfahan province 4. fuel consumption forecasting the energy system of isfahan province for 2016 is shown in figure 3, illustrating its high dependency on fossil fuels. furthermore, the importance of conversion and grid losses are apparent in this figure. as mentioned before, gdp and population are the essential parameters for estimating energy consumption. gdp was achieved using the gpr method, and the population was obtained by the combined method from the report of iran's statics center [44]. in this research, the estimation of gdp is based on historical data from 2006 to 2016. as a result, future data up to 2025 was achieved by applying the gpr algorithm to the current data. 4.1 population forecast population forecasting is conducted by the combined method, which utilizes inner population structure (i.e., mortality, age-sex composition, and fertility pattern) and outer impacting factor population structure (i.e., immigration) to forecast population. this method is the most common approach in population modeling and forecasting [44]. figure 4 illustrates the population curve for 19 years. 4.2 gdp forecast real data on provincial gdp from 2006 to 2016 is derived from the energy balance sheet [17]. the gpr method was used by applying a 10-fold validation method for the years 2016 to 2025. the results obtained from the gpr are presented in figure 5. 4.3 natural gas and diesel consumption forecast natural gas and diesel fuel consumption are shown in figure 6 and figure 7, respectively. as shown in table 1, most of isfahan's power plants are non-renewable and consume four fuel types, including diesel, coal, natural gas, and mazut. the consumption of mazut has gradually been discarded in recent years due to its high combustion pollutants. therefore, in the present study, its value for the future was considered to be zero. besides, coal usage for power generation is decreasing with a high slope and is used under particular conditions [45]. therefore, the coal consumption for future power plants is considered to be zero too. natural gas and diesel consumption are forecasted by applying the gpr approach with the three mentioned covariance functions and calculating r-squared for each one. h. yousefi et al. /future energy may 2024| volume 03 | issue 02| pages 24-30 27 the best-fitted covariance function is selected by comparing r-squared, matern with r-squared equal to 0.96 and 0.88. figure 4. the population of isfahan province (blue: historical data; orange: forecast data) figure 5. gdp of isfahan province (blue: historical data; orange: forecast data) figure 6. natural gas consumption forecast of powerplants (blue: historical data; orange: forecast data) figure 7. diesel consumption forecast of powerplants (blue: historical data; orange: forecast data) table 1. list of power plants in isfahan province 5. co2 emission calculation the difference in the heating value of the fuels and the efficiency of machines' burning fuels affect each fuel's emission per equal amount. in order to calculate the coefficient of co2 for the electricity sector caused by natural gas, the total volume of co2 produced by the natural gas electricity sector is divided into the total consumption of natural gas [46]. the accrued coefficient is 0.0022 tons per 1000 liters. using the same approach, the coal and diesel emission coefficient is calculated as 0.0011 and 2.905 tons per 1000 liters, respectively. finally, according to the data presented in the energy balance sheet and estimated values, the co2 emission of three more essential fuels in the electricity generation sector has been calculated, shown in figure 8. figure 8. co2 emission trend 6. emission reduction scenarios as represented in previous sections, co2 is becoming a critical problem in societies; therefore, co2 emission was considered an objective function. this research aimed to achieve a 4% reduction in co2 by the implementation of four scenarios as follows: s1. adding the photovoltaic s2. adding the photovoltaic and reforming the generation sector s3. adding the photovoltaic and reforming the grid s4. adding the photovoltaic and reforming the generation sector and the grid efficiency (%) capacity (mw) type name 26.4 249 steam zob ahan 26 gas zob ahan 27..9 210 steam fulad 31 108 gas fulad 38.3 1616 steam shahid montazeri 37.1 835 steam islam abad 28 87.6 gas hessa 31.7 324 gas kashan 32 954 gas chehel sotun 50.4 484 combinedcycle zavareh 39.7 126.7 gas distributed generation h. yousefi et al. /future energy may 2024| volume 03 | issue 02| pages 24-30 28 in the first step, total co2 production caused by power plants until the year 2025 was calculated, then 4% of this amount was considered as the criteria of reduction for these scenarios equals 860890 tons. in the second step, fuel consumption for the power plants (natural gas & diesel) was calculated using the coefficients of co2 emission. finally, according to fuel consumption and total energy production, one coefficient is obtained using eq5, which satisfies the reduction of co2 emission. 𝐺𝑒𝑛𝑒𝑟𝑎𝑡𝑖𝑜𝑛 𝑐𝑜𝑒𝑓𝑓𝑖𝑐𝑒𝑛𝑡 = 𝑇𝐸𝑃(𝑡) 𝑃𝐸𝐶(𝑡) (5) tep(t) and pec(t) represent the total energy production and primary energy consumption, respectively in tth year. for this amount of electrical energy, the following scenarios are explained: in scenario (1), renewable power plants would be replaced with fossil fuel to generate the calculated electrical power replacement. based on solar radiation and ambient temperature, isfahan has a high potential for pv energy generation [47]. according to the iran renewable energy and energy efficiency organization announcement, the estimated capacity of photovoltaic for isfahan province is 3220 mw [48]. so, these potentials can cover the rest power with less co2 emission. in scenario (2), an improvement in the efficiency of the fossil fuel plants was considered; thus, a ratio of needed power would be satisfied during generation. pv would be replaced with the rest of the required electricity. enhancements in efficiency include converting the gas turbine powerplant to a combined cycle powerplant or improving the powerplant components and equipment types. transmission and distribution losses play an essential role in grid optimization, and these can help the grid reach the optimum point. therefore, in scenario (3), with activities like reforming the distribution grid, installation of the low-loss transformers, changing the defective counter, etc., the grid losses would reach a minimum amount, and this will cause a decrease in fuel consumption of powerplants or on the other point of view, with constant fuel consumption, the grid has extra power for feeding the demands. eventually, in the last scenario, three scenarios were combined and expressed the amount of renewable power to improve efficiency and decrease the grid's losses. 7. results and discussion referring to figure 8, the total co2 emission in 2025 will be 21,522,259 tons for isfahan province, and it is aimed to reduce 4% of co2 emission, which means 860,890 tons of reduction. based on eq5, the generation coefficient in 2016 is 2852.3 and 1.30 for natural gas and diesel, respectively. this coefficient is variable for each year due to power plant efficiency and fuel alternation. powerplant efficiency trend analysis of 2005 compared to 2016 showed 2.73% growth in the bau scenario. reducing 4% of co2 emission by just decreasing fuel usage requires 1,086,303 mwh energy generation descending, as expressed in eq 5. in other words, 124.01 mw must be supplied using the appropriate sources. the scenarios mentioned above compensate for it by providing energy with different strategies. the capacity factor is the annual generation of a power plant divided by the product of the capacity and the number of hours over a given period (eq6). the photovoltaic capacity factor is an average of 20% for isfahan province. therefore, the equated power that should be provided by renewable energies can be calculated using the capacity factor formula. 𝐶𝑎𝑝𝑎𝑐𝑖𝑡𝑦 𝑓𝑎𝑐𝑡𝑜𝑟 = 𝑃𝑟𝑒𝑎𝑙 𝑃𝑛 × 100 (6) where preal and pn are the real output power and nominal power, respectively. table 2 shows a summary of the results of the calculations for different scenarios. this research aims to clarify the importance of power plant efficiency and grid losses in the contribution of co2 emission reduction. these two factors can help renewable energies, as shown in figure 9, to provide an environmental-friendly energy system. 8. conclusion in this paper, isfahan province power plants' co2 emission up to 2025 was estimated by considering the most affecting factors on consumers' electricity consumption (gdp and population). gp regression with a different covariance function was applied to the consumption trend from 2005 to 2016. the comparison was based on the best r-squared validation. finally, considering the air pollution reduction program, which aimed to reduce 4% of co2 emissions, four scenarios were discussed. the scenarios were based on altering renewable energies to recent infrastructures with a constant rate of technological improvements and alternative rate that impacts the promotion of efficiency and transfer losses. the main conclusions that can be drawn from this study are as follows: • matern covariance function can produce more satisfactory results for the fuel consumption trend. • diesel consumption has decreased with a high slope in recent years, and it will be reduced more within the upcoming years. • the primary fuel of power plants is natural gas in isfahan province. by descending other fuels like coal and diesel in power plants, natural gas compensates for it, and its consumption will be increased. table 2. the results and summary grid losses (%) efficiency growth (%) powerl ** (mw) powere * (mw) pv capacity (mw) generation coefficient diesel ngas 14.5 1 0 0 620.05 1.3 2852.3 s1 14.5 2.7 0 3.4 603.05 1.34 2931.02 s2 7.1 1 9.2 0 574.05 1.3 2852.3 s3 7.1 2.7 9.2 3.4 557.05 1.34 2931.02 s4 h. yousefi et al. /future energy may 2024| volume 03 | issue 02| pages 24-30 29 • by applying reformatory developments on existing instruments that include power plants, transport, and distribution networks, pollution will decrease, and the share of demand for renewable plant installation will be reduced. • the impact of reforming strategies is undeniable, especially for renewable installation issues like investment, land limitation, and low potential. further research can mostly focus on econometric aspects of renewable power plant installation and technological development costs. figure 9. comparison of scenarios ethical issue the authors are aware of and comply with best practices in publication ethics, specifically concerning authorship (avoidance of guest authorship), dual submission, manipulation of figures, competing interests, and compliance with policies on research ethics. the authors adhere to publication requirements that the submitted work is original and has not been published elsewhere in any language. data availability statement datasets analyzed during the current study are available and can be given following a reasonable request from the corresponding author. conflict of interest the authors declare no potential conflict of interest. references [1] adopted, i. p. c. c. 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[48] report on identifying potential sites and evaluating the renewable energy sources of iran., renewable energy and energy efficiency organization, ministry of energy, 2019. this article is an open-access article distributed under the terms and conditions of the creative commons attribution (cc by) license (https://creativecommons.org/licenses/by/4.0/). s. das et al. /future energy february 2025| volume 04 | issue 01| pages 01-07 1 article experimental investigation of cycling characteristics of anatase tio2 nanotubes as negative electrode of lithium-ion batteries simul das1, md. arafat rahman*1, md. saiful islam2, konok chandra bhowmik1 1department of mechanical engineering, chittagong university of engineering & technology, chittagong-4349, bangladesh 2department of nanomaterials and ceramic engineering, bangladesh university of engineering and technology, dhaka1000, bangladesh a r t i c l e i n f o article history: received 28 september 2024 received in revised form 01 november 2024 accepted 14 november 2024 keywords: anatase, tio2, nanotube, anode, lithium-ion battery *corresponding author email address: arafat@cuet.ac.bd doi: 10.55670/fpll.fuen.4.1.1 a b s t r a c t anatase tio2 nanotubes (nt-tio2) is synthesized via electrochemical anodization of 99.9% pure titanium foils in a fluorine containing ethylene glycol (eg) electrolyte and used as the anode of lithium-ion batteries (libs). in the first cycle, the charge-discharge capacities are 550 mahg-1 and 400 mahg-1, respectively, with columbic efficiency of 75.75%. at 40th cycle, charge-discharge capacities are found to be 375 mahg-1 and 325 mahg-1, respectively, with improved columbic efficiency of 86%. the superior electrochemical performances of this type of battery originated from its high specific surface area and highly nanotubes structure. these advanced features of the nanotubes provide higher contact between electrodes and electrolytes, shorten the diffusion pathways for conductive ions. 1. introduction lithium-ion batteries (libs) have emerged as a gamechanging technology in the search for effective and sustainable energy storage solutions. they have revolutionized modern portable electronics and made it possible to electrify several industries, including grid energy storage and transportation [1]. libs have replaced traditional energy storage systems because of their superior features, including high energy density, extended cycle life, and lightweight design for greater portability. the field of libs has observed continuous advancements in response to the increasing demand for energy storage systems with better performance metrics, such as higher energy density, quicker charging times, improved safety, and longer lifespans. in addition, the field of batteries for energy has witnessed considerable interest in the domain of nanofabrication. a multitude of materials for anodes have been identified, therefore instigating continuous investigations aimed at ascertaining feasible alternatives. the utilization of tio2, a transition oxide of metals, as a material for anodes in batteries powered by lithium ions offers a potentially advantageous substitute for traditional graphite [2, 3]. the investigation into the use of tio2 substances for anode applications may be traced back to the identification of the capability of lithium titanites to conduct lithium insertion activities. recently, there has been a growing interest in exploring the potential li-insertion properties of titanite spinels. this has led to a heightened focus on investigating different nanostructures of tio2 polymorphs, specifically for their applicability in li-ion battery systems. rutile, which is considered the most thermally stable polymorph of tio2, demonstrates a restricted ability to incorporate lithium ions, with a capacity of fewer than 0.1 lithium ions per unit of tio2 at room temperature [4]. li-reactivity was higher at a temperature of 120c when using a polymeric electrolyte instead of a liquid electrolyte. in these conditions, the first discharge reversible capacities were reported to be 0.5 li [2] and 1 li [5] per formula unit of tio2. it is noted that the diffusion of li in rutile exhibits a significant degree of anisotropy, characterized by rapid diffusion primarily along the channels aligned with the c-axis [6-10]. the utilization of a well-aligned and selforganized tio2 nanostructure array presents a promising opportunity for its application as a potential anode material in libs. it is noted that difficulties observed in the utilization future energy open access journal https://doi.org/10.55670/fpll.fuen.4.1.1 february 2025| volume 04 | issue 01 | pages 01-07 journal homepage: https://fupubco.com/fuen issn 2832-0328 mailto:arafat@cuet.ac.bd https://doi.org/10.55670/fpll.fuen.4.1.1 https://fupubco.com/fuen s. das et al. /future energy february 2025| volume 04 | issue 01| pages 01-07 2 of traditional graphite as a material for anodes in libs, such as the formation of sei layers, dendritic effects, exfoliation over cycling, toxicity, and structural collapse [11, 12]. the primary impetus behind this research stems from the need to address these limitations and explore alternative anode materials that possess desirable properties, with the goal of proposing a potential replacement for conventional graphite anodes. anatase tio2 has a theoretical capacity of tio2 is slightly lower (330mahg-1) compared to graphite's capacity of 372mahg-1; the focus of research has primarily been on the structural stability of tio2. this work highlights the usage of anatase tio2 nanotubes as the anode of libs. these nanotubes are created by anodizing pure ti foils in a neutral fluoride solution, followed by calcination. nanotube anatase structures with a significantly high specific area were created by carefully regulating the anodization and calcination processes. the primary cause of an interfacial process whereby lithium was stored on the surface of anatase particles was this sizable, exposed electrode area. the high specific surface area of anatase tio2 nanotubes electrodes exhibits the first cycle charge-discharge capacities are 550 mahg-1 and 400 mahg-1, respectively, with columbic efficiency of 75.75%. however, this electrode exhibited improved electrochemical performances of 375 mahg-1 and 325 mahg-1, respectively, with improved columbic efficiency of 86% after 40th charge-discharge cycle. 2. experimental 2.1 fabrication of anatase tio2 nanotubes using a pt plate as the cathode, 99.9% pure ti foil was oxidized to create tio2 nanotubes by the anodization process. the samples, particularly the ti foils, were cleaned for 30 minutes using distilled water and detergent water prior to anodization. after that, the samples were cleaned for ten minutes in a pure ethanol solution. following that, a final 20minute acetone immersion rinse was performed. after that, the samples were dried for 24 hours at 105 oc. two groups of all the ti samples that needed to be anodized were created. one set of samples was cleaned with distilled water after being scraped with 0-grade emery paper. both sets of ti foils underwent anodization in a water-based solution that contained 0.5 wt.% nh4f + 1m (nh4)2so4 + 10% of ethylene glycol (eg). anodization took place in a 100 ml solution, indicating that the electrolyte comprised 100 ml of distilled water, 0.5g nh4f (supplied by suen studio, china), and 13.2g 1m (nh4)2so4 (supplied by suen studio, china). the anode and cathode were connected to the positive and negative terminals of the dc power supply, respectively. the dc power supply's positive and negative terminals were linked to the anode and cathode, respectively. a dc power supply (dazheng brand, model ps-3050, china) provided a steady 32 v dc voltage for one hour and two hours, respectively, while maintaining a zero-current flow. figure 1. visual representation of fabrication steps of anatase tio2 nanotubes s. das et al. /future energy february 2025| volume 04 | issue 01| pages 01-07 3 a magnetic stirrer hotplate ('78-1 magnetic stirrer hotplate,' yaeccc brand, china) at an average speed of 400 rpm during the anodization process verified that the solutes in solution were mixed uniformly and that the ions were moving properly. following anodization, the anodized section of ti foils changed from having a grey appearance to a bluish one. after being cleansed with distilled water, all samples were put in a furnace and calcined for two hours at 550oc. the full process is depicted in figure 1. 2.2 characterization the nt-tio2 samples were analyzed using x-ray powder diffraction (xrd) to obtain crystallographic information. to account for various scattering and random orientations, scans were conducted at different 2θ angles. our analysis covered a 2θ range from 10 o to 90 o with a step size of 0.05o, utilizing cu kα radiation (empyrean, panalytical-netherlands) with a wavelength of ƛ = 1.5406å. the morphological and compositional characterization of anatase tio2 nanotubes was carried out using scanning electron microscopy and energy dispersive x-ray spectroscopy (sem-edx). for our experiment, sem-edx images were captured with a jsm 7600f from jeol (japan) at 5.0 kv and various magnifications. 2.3 electrochemical performance test coin cell battery case sets cr2032 (provided by lith co. china) were utilized for assembly purposes. anode samples measuring 18 mm in diameter and 0.1 mm in thickness (approximately 2 cm²) of nt-tio2, along with licoo2 coated aluminum sheet cathodes and a 20 mm battery grade pvc separator, fit perfectly into the cases. both sides of the separator were saturated with a few drops of 1m lipf6 (from ximen tmax battery equipment ltd., china) electrolyte, which was mixed in ethylene carbonate (ec) and diethylene carbonate (dec) at a ratio of 3:7. finally, crimping was performed at a pressure of about 100 psi using a battery crimping machine (metrology lab, cuet). 3. results & discussion 3.1 xrd analysis as illustrated in figure 2, the x-ray diffraction (xrd) technique is used to analyze the phase purity and crystallinity of ti and anatase tio2 nanotubes. tio2 has a tetragonal bodycentered crystal structure from space group i41/amd, and the lattice parameters for samples and ti foil are a = 3.79 å, c = 9.51 å. the anatase phase of tio2 is confirmed by these data. furthermore, the values match standard data (jcpds card no. 21-1272) exactly. at diffraction 2θ angles of 39.910 (101 plane), 52.770 (012 plane), and 70.4190 (013 plane), however, more noticeable anatase peaks are seen. the lack of any impurity phases within the detection range of the diffractometer indicates the purity of ti. it is observed that no additional diffraction peaks related to the oxide phase were observed. utilizing scherrer's formula, d=0.9λ/b cos(θ), with λ representing the x-ray wavelength in nanometers, b representing the full width at half maximum (fwhm) of peaks at 2θ, and θ representing the angle between the incident and diffracted beams in degrees, these diffraction data are entered. table 1 displays the crystal sizes of ti foil and the synthesized anatase nt-tio2 at various 2θ angles. 3.2 sem & edx analysis the plan‐view sem images and edx spectra of anatase nt‐tio2 is shown in figure 3. non‐uniform anatase nt‐tio2 arrays is grown by anodization, which is observed clearly underneath the ti substrates as shown in figure 3(a). the nanotubes are compact in this area. for the elemental characterization of the obtained nanotube layers, energy dispersive x-ray analysis is conducted. the edx spectrum indicates the presence of the tika peak at 4.508 kev and o peaks at 0.525 kev as well as c peak at 0.277 kev in the anodized sample as shown in figure 3(b). the obtained mass percentages of ti and o is observed to be 55.30% and 42.44%, respectively, and the atom percentage of ti, o, and c is 28.93%, 66.81%, and 4.26%, respectively. it is noted that peak of carbon is found at 0.277 kev with the percentage of c is 2.04%. figure 2. xrd patterns of different anatase nt-tio2 along with pure ti s. das et al. /future energy february 2025| volume 04 | issue 01| pages 01-07 4 table 1. crystal sizes ti foil and as synthesized anatase nt-tio2 sample no. crystallographic data for pure ti average crystal size (nm) a 2ѳ 35.90 38.14 39.92 47.30 52.77 62.78 70.42 38.27 b 0.22 0.32 0.23 0.20 0.26 0.22 0.33 d 40.42 28.01 38.76 46.31 36.18 46.02 32.16 crystallographic data of nt-tio2 b 2ѳ 22.87 25.37 27.51 36.21 38.47 40.23 47.61 53.06 63.07 70.71 65.66 b 2.07 0.36 0.44 0.16 0.16 0.10 0.10 0.09 0.13 0.09 d 4.21 24.39 20.09 56.26 58.35 89.19 92.14 111.45 80.33 120.18 figure 3. high magnification sem image and edx spectra of anatase nt-tio2 s. das et al. /future energy february 2025| volume 04 | issue 01| pages 01-07 5 3.3 electrochemical performance of anatase nt-tio2 as anode of libs the galvanostatic charge-discharge cycle is carried out to measure the electrochemical performance of the as-prepared anatase nt-tio2 anode. figures 4(a & b) show the changes in current and voltage with respect to charge-discharge time. the cut-off voltage ranges are 4v-3.8v. it is noted that the voltages remain 2.5v at the beginning of the cycling, as shown in figure 4(a). however, the voltage increases as the cycling moves forward, and after the 20th cycle, the voltage decreases. in contrast, the voltage and current both increase at the end of the 40th cycle of the charge-discharge process, where the voltage is found to be 4.2v, as shown in figure 4(b). figure 4(c) shows a variation in the rate of change in charge with a change in voltage (dq/dv) till 40 charge-discharge cycles for incremental capacity analysis, which identifies and quantifies changes in the electrochemical properties of the cell based on voltage measurements under constant current charge or discharge. it is observed that the phase transitions in the active electrode material anatase nt-tio2 caused by the intercalation and deintercalation of lithium at about 2.5v correlate with the incremental capacity peaks. it is worth mentioning that dq/dv analysis indicates the electrochemical performances of cell degradation over charge-discharge cycling, as shown in figure 4(c), due to an increase in internal resistance [13]. figure 5 shows the charge-discharge capacity and columbic efficiency of lib till 40 cycles. first cycle charge-discharge capacities are 550 mahg-1 and 400 mahg-1, respectively, with columbic efficiency of 75.75%, as shown in figure 5(a). higher initial capacities are ascribed to gel-like sei layer formation by electrolyte decomposition [14]. in addition, the low columbic efficiency is attributed to unstable sei formation, low reversible capacity, and electrolyte decomposition. however, in the subsequent 2nd cycle, the chargedischarge capacity comparably reduced to 500 mahg-1 and 360 mahg-1, respectively, due to the amorphous li2o formation, which required a huge amount of lithium and caused the loss of lithium [2]. the increased columbic efficiency of 75.4% in the 2nd cycle is attributed to stable sei layer formation. it is noted that the cell shows instability with fluctuating columbic efficiency, which is attributed to the larger volume expansion and pulverization effect of the anode. in addition, at the 27th cycle, the columbic efficiency is as high as 120%, as shown in figure 5(b). this phenomenon is typical for transition metal oxides due to the pseudo capacitance [15-17]. at the 40th cycle, charge-discharge capacities are found to be 375 mahg-1 and 325 mahg-1, respectively, and the columbic efficiency is observed to be 80%, which is comparable to the theoretical capacity of tio2 334 mahg-1. table 2 shows the comparison of charge and discharge capacities of this present work and previous work. it is noted that the charge-discharge capacities of this present work at 1st is observed to be 550 mahg-1 and 400 mahg-1, respectively, which is higher compared to 290 mahg-1 and 239 mahg-1, respectively. however, the observed columbic efficiency is slightly lower, 75%, compared to the previous work of 82%. this deficiency could be ascribed to the impurities in the electrolytes, and/or our cell is assembled in ambient without using a glovebox [18]. however, the electrochemical performances and columbic efficiency increased after the 40th charge-discharge cycle compared to the previous work. here, we are anticipating that the columbic efficiency will be improved over a large number of cycling of our synthesized material since columbic efficiency rises and irreversible capacity falls after the irreversible li insertion sites are filled and trace water has been used up in the first cycles [14]. figure 4. change of (a) current (b) voltage with respect to time from 1-20 charge-discharge cycles, c) change of dq/dv with respect to voltage from 1-40 cycles s. das et al. /future energy february 2025| volume 04 | issue 01| pages 01-07 6 4. conclusion anatase tio2 nanotube has been considered as one of the most attractive anode materials for lithium-ion batteries (libs) due to comparable energy density and life cycle compared to graphite. the nanotube features of nanostructure provide higher contact between binder-less electrode tio2 and electrolytes, shorten the diffusion pathways for conductive ions and electrons that ensure faster kinetics. the work represents a facile fabrication of anatase nt-tio2 via electrochemical anodization of ti foils. anatase nt-tio2 is used as anode libs. nanotubes provide a high surface area that allows for a higher electrode/electrolyte interface. hence, lithium storage capacity is greatly enhanced compared to bulk amorphous tio2. the cut-off voltage ranges are 4v-3.8v. it is noted that at the beginning of the cycling, the voltages remain at 2.5v. however, as the cycling moves forward, the voltage increases, and at the end of the 40th cycle of the charge-discharge process, the voltage is found to be 4.2v. the battery exhibits excellent 1st cycle charge-discharge capacity of 550 mahg-1 and 400 mahg-1, respectively, with 75.75% columbic efficiency. at the 27th cycle, the columbic efficiency is as high as 120%. this phenomenon is typical for transition metal oxide due to the pseudo-capacitance. at the 40th cycle, charge-discharge capacities are found to be 375 mahg-1 and 325 mahg-1, respectively, and the columbic efficiency is found to be 86%. the findings showed that anatase tio2 nanotubes' large surface area, short diffusion path, and quick kinetics make them promising electrode materials for lib applications. acknowledgments this work is financially supported by chittagong university of engineering & technology (cuet), bangladesh, through research grant no.: cuet/chsr-43-43.8.6. ethical issue the authors are aware of and comply with best practices in publication ethics, specifically concerning authorship (avoidance of guest authorship), dual submission, manipulation of figures, competing interests, and compliance with policies on research ethics. the authors adhere to publication requirements that the submitted work is original and has not been published elsewhere in any language. data availability statement the manuscript contains all the data. however, more data will be available upon request from the corresponding author. conflict of interest the authors declare no potential conflict of interest. references [1] chy, m.n.u., et al., mxene as promising anode material for high-performance lithium-ion batteries: a comprehensive review. 2024. 14(7): p. 616. [2] rahman, m.a., et al., improvement on electrochemical performances of nanoporous titania as anode of lithium-ion batteries through annealing of pure titanium foils. 2018. 27(1): p. 250-263. [3] rahman, m.a., x. wang, and c.j.j.o.e.c. wen, enhanced electrochemical performance of li-ion batteries with figure 5. change of specific capacity and columbic efficiency during (a) 1-20 and (b) 21-40 charge-discharge cycles at 1c current rating table 2. comparison of our work with previous work compare cycle no. unit our work previous work reference charge capacity 1st mahg-1 550 290 [19, 20] discharge capacity mahg-1 400 239 columbic efficiency % 75 82 charge capacity 40th /last mahg-1 375 238 discharge capacity mahg-1 325 198 columbic efficiency % 86 83 s. das et al. /future energy february 2025| volume 04 | issue 01| pages 01-07 7 nanoporous titania as negative electrodes. 2015. 24(2): p. 157-170. [4] kavan, l., m.j.e. graetzel, and s.-s. letters, facile synthesis of nanocrystalline li4ti5 o 12 (spinel) exhibiting fast li insertion. 2001. 5(2): p. a39. [5] kavan, l., d. fattakhova, and p.j.j.o.t.e.s. krtil, lithium insertion into mesoscopic and single‐crystal tio2 (rutile) electrodes. 1999. 146(4): p. 1375. [6] zachau-christiansen, b., et al., lithium insertion in different tio2 modifications. 1988. 28: p. 1176-1182. [7] macklin, w. and r.j.s.s.i. neat, performance of titanium dioxide-based cathodes in a lithium polymer electrolyte cell. 1992. 53: p. 694-700. [8] koudriachova, m.v., n.m. harrison, and s.w.j.s.s.i. de leeuw, diffusion of li-ions in rutile. an ab initio study. 2003. 157(1-4): p. 35-38. [9] johnson, o.j.p.r., one-dimensional diffusion of li in rutile. 1964. 136(1a): p. a284. [10] koudriachova, m.v., n.m. harrison, and s.w.j.p.r.l. de leeuw, effect of diffusion on lithium intercalation in titanium dioxide. 2001. 86(7): p. 1275. [11] ruan, c., et al., fabrication of highly ordered tio2 nanotube arrays using an organic electrolyte. 2005. 109(33): p. 15754-15759. [12] moradi, b. and g.g.j.j.o.a.e. botte, recycling of graphite anodes for the next generation of lithium ion batteries. 2016. 46: p. 123-148. [13] wang, r., et al., degradation analysis of lithium-ion batteries under ultrahigh-rate discharge profile. 2024. 376: p. 124241. [14] munonde, t.s. and m.c.j.j.o.e.s. raphulu, review on titanium dioxide nanostructured electrode materials for high-performance lithium batteries. 2024. 78: p. 110064. [15] paul, s., et al., tio2 as an anode of high-performance lithium-ion batteries: a comprehensive review towards practical application. 2022. 12(12): p. 2034. [16] zhang, y., et al., nanostructured tio2‐based anode materials for high‐performance rechargeable lithium‐ ion batteries. 2016. 2(8): p. 764-775. [17] paul, s., et al., nanostructured anatase tio2 as anode of high‐performance lithium‐ion batteries. 2022. 1(4): p. 20220018. [18] wang, l., s. riedel, and z.j.a.e.m. zhao‐karger, challenges and progress in anode‐electrolyte interfaces for rechargeable divalent metal batteries. 2024: p. 2402157. [19] xu, j., et al., electrochemical properties of anatase tio2 nanotubes as an anode material for lithium-ion batteries. 2007. 52(28): p. 8044-8047. [20] jiang, y., et al., fabrication strategies for high-rate tio2 nanotube anodes for li ion energy storage. 2020. 463: p. 228205. this article is an open-access article distributed under the terms and conditions of the creative commons attribution (cc by) license (https://creativecommons.org/licenses/by/4.0/). https://creativecommons.org/licenses/by/4.0/ b.w.z.cheng et al. /future energy august 2022| volume 01 | issue 02 | pages 28-45 28 article feasibility analysis and economic viability of standalone hybrid systems for marudi electrification in sarawak, malaysia brendan wong zhi cheng1, kamyar mehranzamir1, hadi nabipour afrouzi2*, ateeb hassan2 1department of electrical and electronic engineering, faculty of science and engineering, university of nottingham malaysia, jalan broga, 43500 semenyih, selangor, malaysia 2faculty of engineering, computing, and science, swinburne university of technology sarawak, 93350 kuching, malaysia a r t i c l e i n f o article history: received 01 april 2022 received in revised form 02 may 2022 accepted 07 may 2022 keywords: hybrid renewable energy system, off-grid, mini-grid, techno-economic optimization, rural electrification, feasibility analysis corresponding author email address: hafrouzi@swinburne.edu.my doi: 10.55670/fpll.fuen.1.2.5 a b s t r a c t a hybrid renewable energy system is a feasible solution for off-grid electrification where grid electricity is not available due to economic or technical limitations. in this study, rural electrification is performed on a small longhouse settlement, long moh, in sarawak, malaysia, with a population of 308 from 70 households. initially, a hybrid pv/hydro/dg/battery system is proposed due to the abundance of solar and hydro resources in the village. there have been a lot of studies based on pv/dg/battery systems in malaysia but less with the inclusion of hydropower. through simulation and optimization process, the most optimal system in terms of net present cost (npc) is found to be a hybrid hydro/dg/battery system which provides a total npc of $213,694.90, cost of electricity of $0.08/kwh, and operating cost of $9,495.56/year. the most environmentally friendly system is the proposed pv/hydro/dg/battery system due to less fuel consumption (12,863.63 l/year) and its high renewable penetration. the standalone diesel generator (dg) system was the least economic and most polluting system. the best system overall for rural electrification at the case study location is a hybrid hydro/dg/battery system due to its relatively low npc and emissions output compared to a standalone dg system. 1. introduction as of 2019, there has been a record of high global energy consumption of 162,189 twh, an increase of 20.9% compared to the energy consumption a decade ago in 2009, which was 134,116 twh. the world’s primary energy source is fossil fuels, such as natural gas, oil, and coal, which influence greenhouse gas emissions and adversely affect the environment [1]. burning fossil fuel produces large quantities of carbon dioxide, and it is the leading cause of man-made global warming. employing renewable energy systems (ress) such as hydro, wind, and solar has been gaining attention due to global warming and fossil fuel depletion concerns. in 2009, renewable energy consumption accounted for 8.1% of the global energy consumption, while in 2019, this figure increased to 11.4% [1]. however, as of 2018, 10.4% of the global population hasn’t had access to electricity [2]. in the state of sarawak in malaysia, there are a small but significant number of communities living in areas that are difficult to access and far from the national grid. due to technical issues, grid extension to those communities is too costly and not economically feasible. many of these communities are in areas only accessible by boat travel. the state government is aiming toward 100% electrification across the state by 2025, and as a result, various projects have been initiated by the government to increase electricity coverage in rural areas, such as sarawak alternative rural electrification scheme (sares) and the rural power supply scheme (rpss) [3]. despite considerable progress made by these schemes, as of 2018, 9% of the rural population still does not have an electricity supply which translates to an estimated number of 20,000 households [4]. access to electricity is essential for the socio-economic development of the state. it will give access to the construction of more social infrastructures, such as clinics and schools, which will improve the overall quality of life (qol) [5]. therefore, installing off-grid ress will be very beneficial to such communities. due to malaysia’s location in the equatorial zone, it receives an future energy open access journal https://doi.org/10.55670/fpll.fuen.1.2.5 august 2022| volume 01 | issue 02 | pages 28-45 journal homepage: https://fupubco.com/fuen issn 2832-0328 mailto:hafrouzi@swinburne.edu.my https://doi.org/10.55670/fpll.fuen.1.2.5 https://fupubco.com/fuen b.w.z.cheng et al. /future energy august 2022| volume 01 | issue 02 | pages 28-45 29 abundance of sunlight all year round. malaysia receives an average global horizontal irradiation of 4.5 𝑘𝑊ℎ/𝑚2/𝑑𝑎𝑦 [6]. sarawak’s geography is also characterized by having many rivers which have the potential of being used for hydroelectric power, such as micro hydropower turbines. as an example, the rajang river currently houses malaysia’s largest and tallest hydroelectric project, the bakun hydroelectric dam project (2400mw). thus, the combination of ress such as photovoltaic (pv) and hydro is a suitable choice for the electrification of rural areas in sarawak. the purpose of considering hydropower in the hybrid system as opposed to a pure pv-based system is to expectantly supply the offgrid network in cases where solar energy is not available, for example, during sundown and night-time. however, one downside of having a standalone res is that renewable sources are very dependent on environmental conditions, which directly affects the energy production levels of such systems. pv power levels depend on the average sun hours, while hydro systems such as micro hydropower turbines depend on the average rainfall levels and flow rate of rivers. reliance on a single technology also leads to system over-sizing, increasing the initial set-up cost of the system [7]. one solution to this problem is to integrate the usage of ress with conventional energy systems (cess) such as diesel generators to produce a hybrid renewable energy system (hres). this way, the energy system can be more reliable and consistent, which is a must for powering rural households to avoid supply interruptions. energy storage systems (esss) can also be integrated with hress to further harness renewable sources when there is an oversupply; for example, when the load demand during a sunny day is low, the extrasolar energy can be used to charge batteries in esss instead of going to waste. esss can then be discharged when there is a drop in ress power levels. a drawback to using res is that the initial investment required might be very high. however, due to policies for encouraging renewable energy growth, solar power is at its cheapest point historically. for example, the european union (eu) has set a goal to supply 32% of its energy from ress by 2030 [8]. for utility-scale solar power, the average cost of electricity generation is around usd45 per mwh, while a decade ago, it was usd300 per mwh, showing an 85% reduction in price [9]. it is also reported that the cost of building coal plants is higher than installing solar farms, with the average cost of coal plants being around usd100 per mwh. there have been a lot of studies discussing the usage of hybrid pv/diesel and pv/diesel/battery systems in malaysia, but very few researches have discussed the techno-economic feasibility of pv/hydro/diesel/battery systems, while hydropower is one of the most abundant renewable resources in malaysia. lau et al. [10] analyzed the usage of a hybrid pv/diesel system in malaysia for a 40house rural residential area with a 2 kw peak load per house. their analysis of the pv/diesel system was done in comparison to the standalone diesel system and pv/diesel/battery. standalone diesel systems had the lowest operation cost but had the most pollutant emissions. hybrid pv/diesel/battery had a lower operating cost than excluding batteries in their system. excess pv power was used to charge the batteries, significantly optimizing the hybrid system instead of being considered a loss. it was noted that the initial set-up cost of the pv system was very high, as high as usd5600 per kw. however, their study [10] was conducted in 2010, and pv technology prices have significantly reduced since that time. a study by rohit and subhes [11] is referred to justify the inclusion of hydropower in a hybrid system. their study was done in an indian rural village where the load requirements were approximately 500 kwh per day. the optimal hybrid system configuration is analyzed to be a hybrid pv/hydro/biodiesel with an ess (battery). the system architecture compromised a 20 kw pv array, 30 kw small hydropower station, 10 kw biodiesel generator, and 40 batteries rated at 6.94 kwh each. hydropower has been seen to supply 76% of the total energy consumed, while 14% was supplied by pv and the remaining 10% by biodiesel. hydropower could supply a large portion of the energy required as it could be online 24 hours a day, while pv depended on the sun hours of the day. the difference between a system with one renewable source and multiple renewable sources has also been analyzed in ref [11]. the overall flow for the planning and design process of an hres was then determined. firstly, an analysis of studies that implemented hybrid pv/diesel/battery systems was performed. this hres combination was the most common due to its relative simplicity of the low number of components and only one renewable energy generation source. chong et al. [12] have studied the techno-economic viability of a hybrid pv/diesel/battery system for a housing estate in harbin, china. load profiles were set up for the 4 seasons with different loads at varying hours of the day, and a peak power draw of 500 kw was present during winter and summer. different combinations of the three hress were simulated, and it was concluded that the full combination of a hybrid pv/diesel/battery system with a load-following dispatch strategy was the most cost-optimal option. the standalone diesel generator system was the most expensive due to the high operating cost and the large amount of fuel consumed by running the generators 24 hours daily. their study also considered different aspects such as sensitivity analysis and dispatch strategy and has detailed analysis for the calculations of input parameters for pv array and diesel generator. halabi et al. [13] have analyzed the performance of hybrid pv/diesel/battery systems in sabah, malaysia. two different locations have been chosen as the case studies, including an island and a rural area where existing hybrid pv/diesel/battery systems have been implemented. their study compared the existing system to a standalone diesel system and a 100% pv/battery renewables-only system. the final proposed system by halabi et al. [13] was a pv/diesel/battery system that had a low capital and replacement cost and lower renewables penetration. the initial investment for the new system was lower than the existing system in ref [13]. a conclusion was made that a standalone diesel system had the least economic benefit and highest negative environmental impact while it was viceversa for a fully renewable pv/battery system. including batteries in a res is noted to be essential to store excess energy and reduce power loss. a system with 100% renewables penetration is economically impractical due to high pv and battery capital and replacement cost; however, these prices are expected to decrease over the years with the introduction of more environment-conscious policies around the world. the techno-economic feasibility of different combinations of hybrid pv/diesel/battery systems for replacing existing fossil fuel generators in the outlying islands of taiwan was investigated by tsai et al. [14]. it was reported that pv/diesel system with 15% renewables b.w.z.cheng et al. /future energy august 2022| volume 01 | issue 02 | pages 28-45 30 penetration resulted in excess electricity of up to 2.6% a year being wasted, which was a significant amount [14]. but by employing ess, the excess electricity was reduced to 0.5%, showing the importance of ess such as batteries in the hres. a system with 40% renewables penetration was the optimal choice considering the net present cost (npc) and the cost of energy (coe). higher renewables penetration would lead to higher npc and coe, but those would result in reducing the fuel consumption and lower 𝐶𝑂2 emissions. their study also considered the region’s interest and inflation rates. these factors were commonly overlooked when performing economic analysis. another similar study has been done by rehman and al-hadhrami [15] to replace existing fossil fuel generators with a pv/diesel/battery system for a rural area in saudi arabia. the same outcome was observed where an increasing renewables fraction leads to lower diesel fuel consumption but higher coe and npc. their study concluded that a renewable penetration of 20% was the most optimum configuration. ashraf et al. [16] have completed their analysis of pv/diesel/battery combinations using an analysis method known as the elephant herding optimisation (eho) algorithm. they compared the results with those obtained by another proprietary derivative-free algorithm from a microgrid simulation software. their system had implemented objective functions such as low annualized cost, unmet load probability, and 𝐶𝑂2 emissions. eho algorithm successfully optimised a system that has the lowest 𝐶𝑂2 emissions and lowest capital cost. however, it had some limitations such as poor battery system optimisation which led to a large portion of wasted energy. thus, the proprietary algorithm was a simple and effective way of performing hres analysis. another study by salameh et al. [17] has analyzed different tracking systems for pv arrays in a hybrid pv/diesel/battery system. their systems contained several scenarios, including fixed structures, a continuous horizontal axis (elevation), a continuous vertical axis (azimuth), and dual-axis solar trackers. their objectives were to obtain a system with the lowest coe and highest renewable fraction. dual-axis solar tracker is noted to produce the best results with zero unmet load and a reasonable excess power percentage. the power output of the dual-axis solar tracker was 15.5% higher than that of the system with a fixed structure, showing the importance of the tracking systems when designing a pv system. furthermore, by installing the dual-axis trackers, a reduction of 69.7% of 𝐶𝑂2 emissions was recorded as more solar energy was harnessed. odou et al. [18] analyzed the effectiveness of a hybrid pv/hydro/diesel/battery system to power a remote area in africa. the area of interest compromised of 50 households and several social and commercial infrastructures such as schools, clinics, and water pumping systems. load profile was splinted into three categories, including household, community, and commercial load, each having its own hourly load demands. their hybrid pv/diesel/battery system was reported to be more economically feasible compared to a grid extension project considered over the project’s lifetime. the hybrid system also had a shorter payback period and up to 97% less 𝐶𝑂2 emissions compared to a standalone diesel system making it the best choice for rural electrification. hydropower potential at their location was good; however, the hydro site was too far from the village, incurring additional costs from grid extension and making it less economically feasible. thus, the effectiveness of certain renewable sources not only depends on their availability but also their distance to the required load. hoseinzadeh et al. [19] have analyzed the implementation of pv arrays, wind turbines, and batteries to supply an existing run-of-river plant due to the region of interest being water-scarce during hot seasons. the average power consumption modeled in the region was 665 kwh/day. during hot seasons, with just a standalone hydro plant, the power deficit could reach up to 125 kwh/day, which was 18.9% of the total required power. power deficit would result in households not having electricity or facing frequent blackouts. their study noted that for available hydropower of 61 kw, 20 kw of pv arrays and a 7.5 kw wind turbine should be added. batteries were also employed to store the excess solar energy produced during the day and to be discharged during high loads or at night. wind and hydro were both complementary to pv as those renewable sources were available at night. however, their study implemented a system with a renewable penetration of 100%, which was not recommended as renewable power is very source dependent. the effectiveness of a hybrid pv/wind/battery system for an energy-poor rural village in india was studied by krishan and suhag [20]. in their system, a maximum power point tracker (mppt) was implemented for the pv arrays and wind turbines. mppt helped to maximize power extraction of sources with variable power such as pv and wind. similarly, it was observed that the hybrid pv/wind/battery system performed the best compared to pv/battery and wind/battery showing the importance of having complementary renewable sources. however, the npc of the system was quite high ($228,353), considering the system was only powering a community of 54 people consuming an average of 168.23 kwh/day with a peak of 36.5 kw. oladigbolu et al. [21] have proposed a hybrid pv/hydro/wind/diesel/battery system to power a remote village located in nigeria. the remote village was gridconnected, albeit only having 4 hours of electricity daily. the village had a total of 250 households and 20 healthcare centers. load profile was divided into the two respective categories, including residential and healthcare, with varying hourly load demands. their study made comparisons to a hybrid pv/wind/diesel/battery system and noted that the amount of disseminated 𝐶𝑂2 by this system was four times of a pv/hydro/wind/diesel/battery system [21]. the res without hydro also had a higher operating cost, while most of the cost was spent on diesel fuel. however, the proposed system had generated 9.4% excess electricity, which should be minimized to allow for more efficient usage of the power system. the study noted that the proposed system had a high investment cost of $250,000, which was not economically suitable for implementation in a rural village. thus, the system should be downsized to reduce costs. a large-scale analysis was performed by baseer et al. [22] on an industrial city with an average load of 11,160 kwh/day while the peak load was 685 kw. they compared pv/diesel/battery, pv/wind/diesel/battery, pv/wind/battery, and wind/diesel/battery systems to identify the system with the lowest coe and npc. pv/wind/diesel/battery was the most suitable system, followed by the wind/diesel/battery system. the inclusion of diesel generators helped to reduce the coe and npc of the system. the capital cost of a 100% renewable energy-based system (pv/wind/battery) was 30% higher than non-renewable energy-based configurations in their study. similar to several studies [14, b.w.z.cheng et al. /future energy august 2022| volume 01 | issue 02 | pages 28-45 31 15, 20], a more environmentally friendly system can be obtained at the expense of higher initial investment, npc, and coe. their finding was also supported by another study done by aziz et al. [23], which analyzed pv/hydro/diesel/battery systems. they concluded that the full hybrid pv/hydro/diesel/battery system was the best performing system. pv/battery and pv/hydro/battery systems would have a lower emission production but higher npc and coe. in a much smaller scale study, haratian et al. [24] proposed a hybrid pv/wind/battery system to power a renewable energy laboratory in iran. the average load requirement was noted to be around 4kwh/day. however, due to the region’s low average wind speed of 3-4 m/s, installing the wind turbines in the system served to increase the coe and npc by 20% and 10 %, respectively. the region’s solar irradiation is around 5 𝑘𝑊ℎ/𝑚2/𝑑𝑎𝑦 which closely resembles the one in sarawak. the most economical solution was modeled to be a pv/battery system with 1.2 kw pv arrays and 6 units of 3 kwh batteries. even without the installation of wind turbines, there was no electricity shortage and the power generation could be done at a lower cost. this showed the importance of selecting the correct renewable sources according to region-specific characteristics such as wind speed and solar irradiation. elkadeem et al. [25] have provided a framework to ensure the optimal planning and design of hress and implemented said procedures to determine the feasibility of a hybrid pv/wind/diesel/battery system in sudan. the introduced framework was divided into five categories. firstly, the motivations such as environmental policies and financial incentives behind choosing hres as a power system were determined. next, a preliminary study was conducted to find which combination of renewable sources was suitable for that case study. different factors such as load demand, meteorological data, and existing systems were considered, and the most appropriate configuration of hres was found. after that, microgrid simulation software was utilized to provide a techno-economic and optimization analysis of the proposed hres. different variables, including the sizing of each renewable power component to obtain an optimal solution in terms of npc and coe, could be investigated at this stage. after having an optimized system, technical, economic, and environmental assessment was done to evaluate the benefits of the proposed system. lastly, a sensitivity analysis was performed to investigate the sensitivity of the proposed system against uncertain parameters such as variation in fuel price and interest rate. using this framework, the authors in ref. [25] successfully found a combination of hres appropriate for the load scenario, providing excess energy of 9.65% and reducing harmful emissions by 95% compared to standalone diesel generator operation. other authors such as chauhan and saini [26] also did the same study, including load and resource assessment, modeling of systems, problem formulation, demand management, and optimization in a case study in india. a summary of the related studies is tabulated in table 1 (appendix). the purpose of this study is to design the best configuration of pv/hydro/diesel/battery components for a small rural town located in the marudi division of sarawak called long moh. several objectives have been set to be achieved in this study. firstly, the average load profile of the rural community in sarawak is determined by the investigation. the available conventional and nonconventional sources of energy, such as solar irradiation, river flow, and diesel fuel cost, are obtained from national sources and meteorological references. having that information, a suitable size for the proposed pv array, hydroelectric station, diesel generator, and battery bank is then determined. the best possible combination of these sources in terms of environmental effects, economic, and technical performance are analyzed. the aim is to find a combination of hress that provides an acceptable capital cost, replacement cost, and cost of operation and maintenance. 2. site description 2.1 study area the case study location is a rural longhouse settlement named ‘long moh’ in the marudi district of the state of sarawak, malaysia. it is located at coordinates 3.0576° n, 115.0766° e, and approximately 550 km east-northeast of the state’s capital city kuching. the main source of income comes from agriculture, such as fruits, vegetables, and meat, where the goods are taken to bigger villages nearby to sell. the exact population data of long moh is unavailable as it is a rural area; however, a longhouse settlement can be estimated to have 70 households [27]. according to a census conducted by the department of statistics malaysia, the average household size in sarawak is 4.4; thus, it can be estimated that long moh has a population of 308 people [28]. the location can be seen in the map of sarawak given in figure 1 [29]. figure 1. long moh area in sarawak state long moh is currently not completely connected to the national grid; however, the government has plans in the future to do so. for now, the residents get power sparingly from portable diesel generators. the village is located next to the baram river, which is the proposed river for a 1200 mw hydropower station. however, strong protests from locals were made because flooding of the dam would have resulted in the displacement of over 20000 locals. thus, the project has since been halted indefinitely [30]. a micro-hydro station is one of the suitable renewable energy sources for long moh due to the strong hydropower potential of the baram river. b.w.z.cheng et al. /future energy august 2022| volume 01 | issue 02 | pages 28-45 32 2.2 solar data and temperature the average solar radiation data and clearness index for the year 2019 is obtained from nasa’s power data access viewer [31]. temperature data for long moh is illustrated in figure 2. the recorded temperature had an annual high of 23.06℃, a low of 21.9℃, and an average of 22.4℃. solar radiation data is the average amount of solar radiation that is incident on a horizontal surface on earth and has a unit of 𝑘𝑊ℎ/𝑚2/𝑑𝑎𝑦. the clearness index is a dimensionless measure of the clearness of the atmosphere, i.e., the amount of solar radiation that passes through the atmosphere to reach the surface of the earth. solar radiation ranges from 4.43 to 6.02 𝑘𝑊ℎ/𝑚2/𝑑𝑎𝑦 with a yearly average of 5.12 𝑘𝑊ℎ/𝑚2/𝑑𝑎𝑦. the clearness index ranges from 0.47 to 0.58 with a yearly average of 0.51. solar radiation data was also obtained from nasa as presented in figure 3. figure 2. temperature data for long moh in the year 2019 figure 3. solar radiation data for long moh in the year 2019 2.3 hydrological data a research team, in collaboration with a sabah-based non-governmental organization (ngo), leap (land, empowerment, animals, people), provided an analysis of the streamflow for long san, which is a village downstream of long moh [32]. the streamflow in long moh is assumed to be the same as in long san as the two villages are located not too far from each other along the same river. streamflow data is shown in figure 4. the flow rate has a monthly average of as high as 98 l/s and as low as 31 l/s, with an annual average of 65 l/s. 2.4 diesel fuel price in 2020, diesel fuel price was 1.74 malaysian ringgit (rm) per liter which equals $0.42. the fuel price in rural areas was the same as in the cities due to programs launched by the ministry of domestic trade and consumer affairs to bring down retail prices of essential goods, including diesel fuel, in the rural regions in sarawak [33]. figure 4. baram river stream flow data 2.5 load demand assessment as estimated earlier, the village of long moh contained a population of 308 with 70 households. the village also has other infrastructures such as a primary school, community church, and village store. thus, the four main contributors to load demand will be households, schools, churches, and store loads. a breakdown of the individual load demand is listed in table 2 (appendix) and figure 5. a normal weekday is assumed for the load profile, where they're in a power spike (21.48 kw) at 6 am. at 7 am, parents work, and children attend school until the afternoon, resulting in a low household load during that period. household load then picks up in the evening when the family is home, and another spike (36.45 kw) occurs at 8 pm. the household load then settles at 17.06 kw. the community church only has gatherings on sunday for 3 hours, while the village store is open 12 hours a day. this load is expected to be accurate for the whole year as malaysia does not have a winter season where the heating will cause the power draw to increase. a day-to-day variability and timestep variability of 2% is added to the load profile in the simulation software to make the load profile more realistic. the day-to-day variability shifts the load profile upwards or downwards randomly while maintaining its shape, while timestep variability changes the shape of the load profile while keeping the size constant. figure 5. load demand assessment for long moh b.w.z.cheng et al. /future energy august 2022| volume 01 | issue 02 | pages 28-45 33 3. methodology the following framework was established to successfully evaluate the appropriate hress configuration. firstly, a suitable location for hres implementation was determined. the required data such as solar radiation, temperature, and river flow were obtained from meteorological sources. these data have been fed into microgrid simulation tools to analyze the generated power by pv arrays and hydropower turbines. next, an hourly load profile was assessed based on the site’s population and estimated load demand. available infrastructures at the site also must be taken into consideration when the load profile is generated. a flowchart presents the implemented optimization procedure in this study (figure 6) [29]. figure 6. flowchart showing optimization procedure as seen from the ‘input data’ section, the technical specification and cost of each renewable generation component in the proposed hres is input into a simulation software together with the load profile and meteorological data of the case study. economic data referred to parameters such as project lifetime and expected inflation rate. simulation and optimization are performed by running iterations through a search space where the minimum and maximum number and size of system components are specified. after obtaining an optimized system, a sensitivity analysis is performed to gauge how variations in input variables such as diesel fuel cost, stream flow rate, and interest rate affect the overall performance of the system. this step is important if there is uncertainty in any of the input variables. for example, diesel fuel price is not a constant variable and will fluctuate according to global demand. thus, a sensitivity analysis of diesel fuel prices for a range of values helps the designer to analyze the effect of fuel price fluctuations on the economic performance of the system. 4. modeling of the hybrid res 4.1 system components there are four main components in this hybrid system, namely, pv modules, micro-hydropower turbines, batteries, and diesel generators (dg). a bi-directional converter is also required to convert the dc power provided by pv modules/batteries to ac power for loads and ac power from diesel generators/hydropower to dc power for battery charging. a simple schematic of the overall system components connection is given in figure 7. figure 7. schematic of the system 4.2 dispatch strategy a control strategy which is called the dispatch strategy is applied to diesel generators and battery bank operation when enough renewable energy is not available to power the load. three types of dispatch strategies, including cycle charging (cc), load following (lf), and combined dispatch (cd), are used. in cc strategy, whenever a diesel generator is required to be online to serve a load, it runs at full capacity, and the excess power generated would be used to charge the batteries. in the lf strategy, when a generator is required, it only runs to produce enough power to supply the required load. cd strategy intelligently moves between cc and lf strategies depending on the current netload. for low net loads, cc is used, while for high net loads, lf is used. 4.3 pv modules longi solar hi-mo4m monofacial modules (lr472hph-440m) were selected for this study. the specifications of this pv module under standard testing conditions of 1000 𝑊/𝑚2 irradiance and cell temperature of 25℃ are as follows: maximum power (0.44𝑘𝑊𝑝) is 440 w, open circuit voltage is 48.9 v, short circuit current is 11.46 a, maximum power voltage is 41.1 v, maximum power current is 10.71 a, and module efficiency is 20.2%. this pv module comes with a 25year linear output power warranty; thus, 25 years is selected as the lifetime of the modules, and no replacement is needed throughout the project’s lifetime. the 440 𝑊𝑝 the module has a market price of $230-$250; thus, the cost of the pv system is estimated to be $530/k𝑊𝑝 [34]. a tracking system is also required to ensure the modules are always facing the sun. tracking systems can be obtained for $100/k𝑊𝑝, while other b.w.z.cheng et al. /future energy august 2022| volume 01 | issue 02 | pages 28-45 34 soft costs including installation fee, shipping, import duties, and sales tax are estimated to account for 50% of the final cost [35], giving a total capital cost of $1260/k𝑊𝑝. derating factor is set to 99.45%/year which is obtained from the manufacturer’s datasheet which states the module will degrade < 2% in the first year and 0.55% from years 2-25. dust accumulations on the panels might contribute to the derating factor, however, the residents should perform periodic cleaning of the modules to prevent dust accumulation. periodic cleaning contributes to the annual o&m costs which is set to $10/k𝑊𝑝/year. the power output of pv modules is calculated using eq. 1 [36]: 𝑃𝑃𝑉 = 𝑌𝑃𝑉𝑓𝑃𝑉 ( �̅�𝑇 �̅�𝑇,𝑆𝑇𝐶 ) [1 + 𝛼𝑃(𝑇𝑐 − 𝑇𝑐,𝑆𝑇𝐶)] (1) where 𝑌𝑃𝑉 is the pv module’s output power under standard test conditions (stc) (kw), 𝑓𝑃𝑉 is the pv derating factor (%), �̅�𝑇 is the solar radiation incident on the pv array in the current time step (𝑘𝑊/𝑚2), �̅�𝑇,𝑆𝑇𝐶 is the incident radiation at stc (1 𝑘𝑊/𝑚2), 𝛼𝑃 is the temperature coefficient of power (%/℃), 𝑇𝑐 is the pv cell temperature in the current time step (℃) and 𝑇𝑐,𝑆𝑇𝐶 is the pv cell temperature under stc (25℃). pv cell temperature and ambient temperature are different. during the day, cell temperature can exceed the ambient temperature by 30℃ or more, while during the night, the cell temperature is the same as ambient temperature. thus, the temperature can be calculated as follows [36]: 𝑇𝑐 = 𝑇𝑎 + (𝑇𝑐,𝑁𝑂𝐶𝑇 − 𝑇𝑎,𝑁𝑂𝐶𝑇) ( 𝐺𝑇 𝐺𝑇,𝑁𝑂𝐶𝑇 ) (1 − 𝜂𝑚𝑝 𝜏𝛼 ) (2) where 𝑇𝑎 is the ambient temperature (℃), 𝑇𝑐,𝑁𝑂𝐶𝑇 is the nominal operating cell temperature (℃), 𝐺𝑇 is the solar radiation incident on the pv module (𝑘𝑊/𝑚2), 𝐺𝑇,𝑁𝑂𝐶𝑇 is the solar radiation at which nominal operating cell temperature is defined (0.8 𝑘𝑊/𝑚2), 𝜂𝑚𝑝 is the pv module’s efficiency at its maximum power point (%), 𝜏 is the solar transmittance of any covering over the pv module, and 𝛼 is the solar absorption factor of the pv module (%). 4.4 hydropower the micro hydropower turbine under consideration has the following specifications [32]: the design flow rate is 60 l/s, minimum flow ratio is 25%, maximum flow ratio is 150%, pipe head loss is set at zero percent, and turbine efficiency is 60%. in addition, the available net head is assumed to be 25 m, which is the net head available at a dam in long san, another village downstream of long moh. the cost of micro-hydropower is $1300/kw, which is obtained from previous microhydropower projects conducted by ngos such as create borneo. the lifetime is 30 years, while replacement costs are $1300/kw. o&m costs are negligible and assumed to be zero. power generated from the micro-hydro turbine can be calculated using [36]: 𝑃ℎ𝑦𝑑 = 𝜂ℎ𝑦𝑑⋅𝜌𝑤𝑎𝑡𝑒𝑟⋅𝑔⋅ℎ𝑛𝑒𝑡⋅�̇�𝑡𝑢𝑟𝑏𝑖𝑛𝑒 1000𝑊/𝑘𝑊 (3) where 𝜂ℎ𝑦𝑑 is the hydro turbine efficiency (%), 𝜌𝑤𝑎𝑡𝑒𝑟 is the density of water (1000 𝑘𝑔/𝑚3), g is the gravitational acceleration (9.81 𝑚/𝑠2), ℎ𝑛𝑒𝑡 is the effective head (m) and �̇�𝑡𝑢𝑟𝑏𝑖𝑛𝑒 is the water flow rate through the hydro turbine. for the hydro turbine flow rate, it must be more than the minimum flow rate specified; otherwise, it will be zero. likewise, the flow rate cannot exceed the specified maximum flow rate, and if it does, it will be capped at that value. nominal hydropower represents the size of the hydro system given streamflow equal to the design flow rate specified. the nominal hydropower for this turbine is 8.83 kw. 4.5 diesel generator diesel generators of a few sizes are considered, namely 12 kw, 33 kw, and 50 kw. the selected diesel generators are from the 50 hz, 230v premium generator series. diesel fuel consumption of the generators is 2.4 l/h for the 12-kw model, 6.18 l/h for the 33-kw model, and 12.7 l/h for the 50kw model. the three generators cost $6000, $8700, and $12500, respectively, including transportation costs. it has an estimated lifetime of 15000 hours and a replacement cost of 50% of the capital costs. replacement cost is lower than capital cost as only parts of the diesel generator need overhauling, and the generator is not swapped with a new unit. the o&m cost is set at 3% of the capital cost, and the minimum load ratio is set at 30%. other important parameters of diesel fuel for emissions calculation are carbon monoxide (6.5 g/l of fuel,) proportion of fuel sulfur converted to pm 2.2%, unburned hydrocarbons (0.72 g/l of fuel), particulate matter (0.49 g/l of fuel), and nitrogen oxides (58 g/l of fuel) [12]. 4.6 batteries a lead-acid battery of surrette s480 brand (6 v, 375ah (20-hour)) is chosen for this study. the minimum state of charge is set at 40% and the efficiency at 80%. four of these batteries are connected in series to form a dc bus voltage of 24 v. each battery unit has a capital and replacement cost of $390, while the o&m cost of $50/year is assumed [12]. battery quantities of 0-20 batteries with 4 battery intervals are considered. 4.7 converter a bidirectional converter is needed to convert ac to dc and vice versa. the converter is assumed to have the specifications as follows [14]: rectifier and inverter efficiency of 95%, capital and replacement cost of $900/kw, o&m cost of $1/kw/year, and a lifetime of 10 years. converter sizes of 0-10kw with 1kw intervals are considered. a summary of the component’s techno-economic parameters is given in table 3 (appendix). 4.8 economic modelling for each plan in the search space, the aim is to minimize npc required while being susceptible to constraints such as whether the system can satisfy the load demand. npc is defined as the cost incurred by a system over its project lifetime, minus its revenue. cost includes capital cost, fuel cost, operation and maintenance (o&m) cost, and replacement cost, while revenue is the salvage value which is simply the value remaining in a component at the end of the project lifetime. the salvage value is calculated as follows [36]: 𝑆 = 𝐶𝑟𝑒𝑝 ⋅ 𝑅𝑐𝑜𝑚𝑝−[𝑅𝑝𝑟𝑜𝑗−(𝑅𝑐𝑜𝑚𝑝⋅𝐼𝑁𝑇( 𝑅𝑝𝑟𝑜𝑗 𝑅𝑐𝑜𝑚𝑝 ))] 𝑅𝑐𝑜𝑚𝑝 (4) where 𝐶𝑟𝑒𝑝 is the replacement cost ($), 𝑅𝑐𝑜𝑚𝑝 is the component lifetime (years), 𝑅𝑝𝑟𝑜𝑗 is the project lifetime (years), and int() is a function that rounds down a real number to the nearest integer. real interest rate is used in the b.w.z.cheng et al. /future energy august 2022| volume 01 | issue 02 | pages 28-45 35 calculation between one-time costs and annualized costs and is given by the formula [36]: 𝑖 = 𝑖′−𝑓 1+𝑓 (5) where 𝑖′ is the nominal interest rate (%) (the rate at which borrowing occurs), and f is the expected inflation rate over the project lifetime (%). by implementing a real interest rate, inflation can effectively be factored out from the economic analysis. another important parameter is the coe, which is defined as the average cost per kwh of useful electrical energy produced by the system. it is calculated by dividing the annualized cost of electricity production by the total electric load supplied. in this study, a nominal interest rate of 6% and an inflation rate of 2% is set [37]. 5. results and discussion 5.1 overview in this section, the optimized system, together with its techno-economic, environmental, and sensitivity analyses, are presented below. an overview of the most optimized systems in their respective categories is tabulated in table 4 (appendix). the systems are sorted according to their npc in ascending order. out of 3,492 computer simulations, only 1,836 were feasible, and the best five systems of each configuration are analyzed. the configurations are hydro/dg/battery, pv/hydro/dg/battery, hydro/dg, pv/hydro/dg, and standalone dg. the most optimal system is the hydro/dg/battery system with a 33 kw dg, 4 batteries, 2 kw converter, and lf dispatch strategy. it has an npc of $213,694.90 and a coe of $0.08/kwh. it has the second-lowest operating cost (oc) of $9,495.56/year and the third lowest initial investment required (ic) of $23,537.70. this system has a renewable fraction (rf) of 45.72% with a diesel fuel consumption (fc) of 14,642.17l/year. excess electricity of 11.67% is produced with a 0% unmet load. compared to the third-best performing system, which is a hydro/dg system, adding the battery helps to bring down all the recorded parameters significantly at the expense of a slightly higher ic. this shows the importance of an ess in a renewable energy system. by choosing the hydro/dg/battery system instead of the hydro/dg system, a simple payback of 4.1 years can be achieved with a return on investment (roi) of 25.1%, which is the yearly cost savings relative to the initial investment. the worst performing system is the standalone dg system with a 50 kw dg implementing a cc dispatch strategy. it has an npc of $346,222.60, coe of $0.12/kwh, and oc of $16,664.54, which are 62%, 62.1%, and 75.5% larger than the hydro/dg/battery system. however, it has the lowest ic required at $12,500, which is the cost of the 50-kw diesel generator. fc is also the highest at 30,743.16 l of fuel consumed a year, contributing to 75% of the oc annually. figure 8 shows a comparison between the standalone dg system and the best performing hydro/dg/battery system. for the first year, the standalone dg system will have a lower cost overall; however, after 1.4 years, the cumulative cost for the hydro/dg/battery system becomes lower than that of the standalone dg system. an roi of 62.1% is also reported. the initially proposed system of pv/hydro/dg/battery has the lowest oc ($9,149.15/year), which is $346.41 less than the hydro/dg/battery system. however, it has a $10,822.90 higher npc ($224,517.80) and a $13,510 higher ic ($37,037.70). the oc is not low enough to justify switching to the proposed system, as shown in figure 9. throughout the project lifetime simulation of 40 years, simple payback is not possible, and consequently, an roi of 0% is recorded. thus, economically, the proposed system is not the most optimal configuration in this scenario. however, this system has the highest rf of 52.8% and thus the lowest diesel fc of 12,863.63 l/year, making it the most environmentally friendly system. 5.2 hybrid hydro/dg/battery system analysis the best performing system has the following specifications: 8.83 kw of hydropower, 33 kw of dg, 4 units of batteries, a 2-kw converter and using lf dispatch strategy. a breakdown of the costs involved in this system is given in figure 10. figure 8. hydro/dg/batt vs dg b.w.z.cheng et al. /future energy august 2022| volume 01 | issue 02 | pages 28-45 36 figure 9. hydro/dg/batt vs pv/hydro/dg/batt figure 10. cost summary for hydro/dg/battery system (cost type: net present) figure 11. electrical analysis for hydro/dg/battery system b.w.z.cheng et al. /future energy august 2022| volume 01 | issue 02 | pages 28-45 37 diesel power has the highest contribution to the npc of the system at 87.4% of the total npc, and 65.9% of diesel power’s total npc is used by diesel fuel costs. hydropower has the highest capital cost, but it has minimal o&m replacement cost due to the turbine having a lifetime of 30 years. battery and converter costs are minimal due to their low quantities and sizes. from figure 11, the fraction of energy generated by hydro is proportional to the streamflow, which is the highest in december and the lowest in october. consequently, the energy generated by dg is inversely proportional to streamflow as dg compensates for the remaining load that hydropower is unable to supply. overall, this system produced the lowest excess electricity of 11.7%, with a 0% unmet load. some excess electricity is required as an operating reserve, which is set as 10% load in the current time step. power draw is not constant and will fluctuate unpredictably. without an operating reserve, the power draw will exceed the capacity of the power system leading to an increase in unmet electric load. capacity shortage differs from the unmet load as capacity shortage considers both unmet load and unmet operating reserve. figure 12 shows the power sources plot, which plots the total electrical load, dg power output, hydropower output, and battery input power daily for the whole year. dg is the main source of energy for this system which explains its 87.4% contribution to the npc. in the months of july and october, when streamflow is the lowest, the dg operates continuously and does not switch off. input power to the battery is approximately zero during these two months as the dg is operating at full capacity to supply the electrical load. 5.3 environmental analysis dgs generate power from the combustion of diesel fuel, which releases pollutants such as carbon dioxide (co2), carbon monoxide (co), unburned hydrocarbons (uhc), particulate matter (pm), and sulfur dioxide (so2) and nitrogen oxides (nox). pollutant emissions for the top 5 performing systems are presented in table 5 (appendix). emissions are proportional to the amount of diesel fuel consumed by the system annually in g/l. the system with the least amount of pollutants is the proposed pv/hydro/dg/battery system having the least emissions of co2 (33,874 kg/year), co (83.6 kg/year), uhc (9.26 kg/year), pm (6.3 kg/year), so2 (82.5 kg/year), and nox (746 kg/year) due to its high renewables penetration. in comparison to the worst environmentally friendly system (dg), emissions savings of 58.2% are recorded for all pollutants. the optimal hydro/dg/battery system has an emission saving of 52.4% compared to the standalone dg system. emissions can be reduced further by switching to a more efficient dg that uses a higher grade of diesel fuel, such as euro5 diesel. 5.4 sensitivity analysis in this study, sensitivity variables selected are diesel fuel prices, annual average streamflow, annual average solar radiation, and interest rate. these variables have the most uncertainty and are expected to change throughout the projects’ lifetime. the variables are modified to ±50% of their original values with 25% of increments, as shown in table 6 (appendix). the result of the sensitivity analysis of the optimal system (dg/hydro/batt) is presented in figure 13. even with considering a 50% increase in diesel fuel price from $0.42 to $0.63, hydro/dg/battery is still the most optimal choice in terms of npc. annual average solar radiation is increased to give pv modules a higher energy generation potential, but the constant power flow from hydro is still the winner in this analysis. npc increases with diesel fuel price changes as expected which varies from a minimum of $152,118.10 to a maximum of $274,592.20 with ±50% fluctuations in the diesel fuel price. the system configuration remains the same as before when the diesel fuel price reaches $0.525/l and above, and the power converter is increased from 2 kw to 3 kw. next, the sensitivity variables are diesel fuel price and annual average streamflow. the results obtained are illustrated in figure 14. figure 12. power sources plot for hydro/dg/battery system b.w.z.cheng et al. /future energy august 2022| volume 01 | issue 02 | pages 28-45 38 figure 14. sensitivity analysis of diesel fuel price vs annual average streamflow with superimposed total npc figure 15. graph of npc and coe against interest rate figure 13. sensitivity analysis of diesel fuel price vs annual average solar radiation with superimposed total npc b.w.z.cheng et al. /future energy august 2022| volume 01 | issue 02 | pages 28-45 39 the system with the lowest npc is a dg/hydro system with 33 kw dg, 8.83 kw hydro, diesel fuel price of $0.21, and annual average streamflow of 97.9 l/s. the most optimal system varies between dg/hydro, dg/hydro/battery, and dg/pv/hydro/battery. the proposed dg/pv/hydro/battery system with 10 kw pv, 33 kw dg, 8.83 kw hydro, 8-12 batteries, and a 7-8 kw converter is the best choice when the scaled average of hydropower drops below 48.9 l/s. a minimum npc of $131,882.20 is recorded with the highest streamflow and lowest diesel fuel price, while a maximum npc of $363,726.70 is recorded with the highest diesel fuel price and lowest streamflow. the relation between the nominal discount rate, that is, the interest rate, the total npc, and coe, are plotted in figure 15. the nominal discount rates are set from 3% to 9% to realize the effect of changes in nominal discount rates on coe and npc. total npc decreases with an increase in the nominal discount rate. this is because total npc is the present value of all cash flows in the system. with an increase in interest rate, the present value of future cash flow decreases. on the other hand, coe increases slightly with an increase in interest rate. an increase in interest rate decreases the salvage value of components which results in a higher coe. the intersection between npc and coe occurs at ~5.75% representing the point at which the system is most economical. 6. conclusion this study presented an environmental and technoeconomic analysis of an off-grid hres for the electrification of a rural village in marudi, sarawak, malaysia. the initially proposed system was a hybrid pv/hydro/dg/battery system; however, the most economical system based on the computer simulation is a hybrid hydro/dg/battery system. the final hydro/dg/battery system consists of an 8.83 kw hydro generator, 33 kw dg, 1 string of 4 units of 6v batteries, 2 kw converter with an lf dispatch strategy. this system has an npc of $168,831.30, coe of $0.08/kwh, oc of $9223.59/year, ic of $23,537.70, and rf of 45.72%. excess electricity of 11.7% is recorded, which is acceptable to meet the 10% operating reserve. environmentally, this system produces 52.4% fewer emissions compared to the standalone dg system, which greatly helps in maintaining the green environment of the rural village. the emissions will affect the residents’ health and produce unwanted environmental impacts such as smog. economically, the hybrid hydro/dg/battery system has a simple payback of 1.4 years and an roi of 62% when compared to the standalone dg system. however, the proposed pv/hydro/dg/battery system is the most environmentally friendly system with the lowest diesel fuel consumption of 12,863.63 l/year and the lowest pollutant emission production. it also has the lowest oc at $9,149.15, but the npc is significantly higher than the optimal system (hydro/dg/battery) at $224,517.80, such that a simple payback is not possible when comparing the two systems. sensitivity analysis was performed to see whether the optimal configuration changes with ±50% changes in diesel fuel price, annual average streamflow, and annual average solar radiation. the hydro/dg/battery system is the most optimal choice in the sensitivity analysis of diesel fuel price and average solar radiation. for the analysis of diesel fuel price and average streamflow, dg/hydro/battery system is only optimal when the average streamflow is more than 58.73 l/s. average streamflow lower than 58.73 l/s would result in pv/dg/hydro/battery is the most optimal choice. npc and coe values increase with an increase in diesel fuel price and a decrease in annual average streamflow. the interest rate is also varied to determine its economic impact on the system. it was observed that an increase in interest rate leads to an increase in npc and a decrease in coe. according to the results above, a hybrid hydro/dg/battery system is the most optimal option with justifiable trade-offs for a slightly higher environmental impact. the initial investment required of $23,537.70 was reasonable considering that the village has a population of 308. rural electrification is a priority; given the impact it brings on the socio-economic development of the country. ethical issue the authors are aware of and comply with best practices in publication ethics, specifically with regard to authorship (avoidance of guest authorship), dual submission, manipulation of figures, competing interests, and compliance with policies on research ethics. the authors adhere to publication requirements that the submitted work is original and has not been published elsewhere in any language. data availability statement data sharing is not applicable to this article as no datasets were generated or analyzed during the current study. conflict of interest the authors declare no potential conflict of 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[36] homer pro 3.14. homer energy by ul 2020. this article is an open-access article distributed under the terms and conditions of the creative commons attribution (cc by) license (https://creativecommons.org/licenses/by/4.0/). b.w.z.cheng et al. /future energy august 2022| volume 01 | issue 02 | pages 28-45 41 appendix table 1. summary of the techno-economic studies conducted for hress main hres location daily electrical load (kwh/day) system components npc ($) ref. pv/dg/battery harbin, china 2300 500kw pv, 1250kw dg, 600 surette s460 batteries 8,162,822 [12] pv/dg/battery pulau banggi, sabah, malaysia 6632.86 800kw pv, 630kw dg, 2880 kwh batteries 9,345,510 [13] pv/dg/battery benin, africa 679.77 150kw pv, 50kw dg, 98 h3250 batteries 555,492 [18] pv/hydro/wind/dg/battery imo, nigeria 3853 50kw pv, 94.1kw hydro, 1kw wind, 150kw dg, 111kwh batteries 1,007,995 [21] pv/wind /dg/battery compound 1, al-jubail, saudi arabia 11,160 580kw pv, 550kw wind, 1800kw dg, 880 surette 4ks25p batteries 9,620,000 [22] pv/hydro/dg/battery sakran, iraq 23.29 13kw pv, 14.7kw hydro, 5kw dg, 8 surette 6cs25p batteries 113.201 [23] b.w.z.cheng et al. /future energy august 2022| volume 01 | issue 02 | pages 28-45 42 table 2. load demand assessment for long moh load categories components power draw (w) units hours active (hours/day) daily power consumption (kwh/day) time household ceiling fan 75 1 6 0.45 4pm-10pm 2 bed 1 bath standing fan 50 2 9 0.9 10pm-7am fluorescent lamp 32 4 5.75 0.736 3 units, 6am-7am, 7pm-10pm, 1 unit 7pm-6am led tv + set-top box 110 1 4 0.44 5pm-9pm washing machine 320 1 0.3 0.096 1 hour every 3 days water pump (0.5hp) 370 1 2 0.74 2 hours a day fridge 80 1 24 1.92 24 hours household total 5.282 70 households total 369.74 primary school ceiling fan 75 6 8 3.6 7am-3pm 100 students, 4 classrooms fluorescent lamp 32 12 8.5 3.264 10 units 7am-3pm, 2 units 7pm-6am office, canteen water pump (1hp) 750 1 4 3 2 hours a day school total 9.864 community church ceiling fan 75 4 0.43 0.129 3 hours a week fluorescent lamp 32 8 0.43 0.11008 3 hours a week church total 0.23908 village store standing fan 50 2 12 1.2 8am-8pm fluorescent lamp 32 5 5 0.8 8am-10am, 5pm8pm water pump (0.5hp) 370 1 1 0.37 1 hour a day store total 2.37 village total 382.21308 b.w.z.cheng et al. /future energy august 2022| volume 01 | issue 02 | pages 28-45 43 table 3. summary of proposed components' specifications component parameter specification component parameter specification pv power sizing 0-40kw, 10kw intervals diesel generator power sizing 12,33,50kw derating factor 99.45% minimum load ratio 30% temperature coefficient -0.35%/℃ lifetime 15000 hours nominal operating cell temperature 45℃ capital cost $6000,8700,12500 efficiency 20.20% replacement cost 50% of capital cost lifetime 25 years o&m cost 3% of capital cost capital cost $1260/kw replacement cost $1260/kw o&m cost $10/kw/year hydropower design flow rate 60l/s batteries nominal voltage 6v minimum flow ratio 25% capacity 375ah/20hour maximum flow ratio 150% lifetime 12 years pipe head loss 0% capital cost $390 turbine efficiency 60% replacement cost $390 net head 25m o&m cost $50/year lifetime 30 years batteries per string 4 capital cost $1300/kw string size 0-5, 1 string intervals replacement cost $1300/kw o&m cost $0/kw/year converter power sizing 0-10kw, 1kw intervals diesel fuel cost $0.42 efficiency 95% carbon monoxide 6.5g/l lifetime 10 years unburned hydrocarbons 0.72g/l capital cost $900/kw particulate matter 0.49g/l replacement cost $900/kw proportion of fuel sulphur converted to pm 2.20% o&m cost $1/kw/year nitrogen oxides 58g/l b.w.z.cheng et al. /future energy august 2022| volume 01 | issue 02 | pages 28-45 44 table 4. results from computer analysis s y st e m c o n fi g u ra ti o n p v ( k w ) h y d ro ( k w ) d g ( k w ) b a tt ( u n it ) c o n v ( k w ) n p c ( $ ) c o e ( $ /k w h ) o c ( $ / y r) ic ( $ ) r f ( % ) f c ( l / y r) e x ce ss ( % ) u n m e t (% ) h y d ro / d g /b a tt 8.83 33.00 4.00 2.00 213,694.90 0.08 9,495.56 23,537.70 45.72 14,642.17 11.67 0 p v / h y d ro / d g / b a tt 10.00 8.83 33.00 4.00 3.00 224,517.80 0.08 9,149.15 37,037.70 52.79 12,863.63 16.24 0 h y d ro / d g 8.83 33.00 229,164.90 0.08 10,435.84 20,177.70 37.64 16,622.58 17.64 0.002 p v / h y d ro / d g 10.00 8.83 33.00 2.00 239,287.90 0.09 10,222.27 34,577.70 41.42 15,652.74 23.70 0.002 d g 50.00 346,222.60 0.12 16,664.54 12,500.00 30,743.16 12.84 0 b.w.z.cheng et al. /future energy august 2022| volume 01 | issue 02 | pages 28-45 45 table 5. pollutant emissions from top 5 best performing systems system configuration co2 (kg/yr) co (kg/yr) uhc (kg/yr) pm (kg/yr) so2 (kg/yr) nox (kg/yr) hydro/dg/batt 38,558.00 95.20 10.50 7.17 93.90 849.00 pv/hydro/dg/batt 33,874.00 83.60 9.260 6.30 82.50 746.00 hydro/dg 43,773.00 108.00 12.00 8.15 107.00 964.00 pv/hydro/dg 41,219.00 102.00 11.30 7.67 100.00 908.00 dg 80,957.00 200.00 22.10 15.10 197.00 1,783.00 table 6. sensitivity variables and their respective values sensitivity variables values diesel fuel price ($) 0.21, 0.315, 0.42, 0.525, 0.63 annual average stream flow (l/s) 32.63, 48.94, 65.25, 81.56, 97.88 annual average solar radiation (kwh/m2/day) 2.562, 3.843, 5.124, 6.405, 7.686 interest rate (%) 3, 4.5, 6, 7.5, 9 s. mishra et al. /future energy november 2024| volume 03 | issue 04| pages 47-55 47 review deep-learning-based multi-timescale load forecasting in buildings: opportunities and challenges from research to deployment sakshi mishra*, stephen m. frank, anya petersen, robert buechler, michelle slovensky intelligent campus program, national renewable energy laboratory, golden, colorado, united states a r t i c l e i n f o article history: received 12 july 2024 received in revised form 18 august 2024 accepted 26 august 2024 keywords: deep learning, recurrent neural networks, long short-term memory, building load forecasting, grid-interactive efficient buildings, smart grid *corresponding author email address: sakshi.m@outlook.com doi: 10.55670/fpll.fuen.3.4.3 a b s t r a c t electricity load forecasting for buildings and campuses is becoming increasingly important as the penetration of distributed energy resources (ders) grows. efficient operation and dispatch of ders require reasonably accurate predictions of future energy consumption in order to conduct nearreal-time optimized dispatch of on-site generation and storage assets. electric utilities have traditionally performed load forecasting for load pockets spanning large geographic areas, and therefore, forecasting has not been a common practice by buildings and campus operators. given the growing trends of research and prototyping in the grid-interactive efficient buildings domain, characteristics beyond simple algorithm forecast accuracy are important in determining the algorithm’s true utility for smart buildings. other characteristics include the overall design of the deployed architecture and the operational efficiency of the forecasting system. in this work, we present a deep-learning-based load forecasting system that predicts the building load at 1-hour intervals for 18 hours in the future. we also discuss challenges associated with the real-time deployment of such systems as well as the research opportunities presented by a fully functional forecasting system that has been developed within the national renewable energy laboratory’s intelligent campus program. 1. introduction the commercial buildings sector in the united states consumed 1,671.61 trillion btu of energy in january 2020 alone (immediately prior to the onset of the covid-19 pandemic) and a total of 18,177.95 trillion btu in 2019 [1]. overall, buildings account for nearly 40% of the total energy consumption in the united states [2], and building energy consumption is projected to expand by an annual 1.5% globally [3]. even with many commercial facilities operating at reduced occupancy during the covid-19 pandemic, preliminary industry reports indicate that commercial building energy is again increasing as operators increase ventilation rates [4]. because buildings are among the largest consumers of energy globally, research to increase the design and operational energy efficiencies of the commercial sector (i.e., commercial buildings) will play a significant role in meeting energy and greenhouse gas emissions reduction targets. the penetration of behind-the-meter distributed energy resources (ders) is also increasing, owing to the decreasing cost of renewable energy technologies [5]. smart building operations can simultaneously reduce energy consumption (and, by extension, greenhouse gas emissions) and optimize behind-the-meter der dis-patch to save money for building owners/operators via additional value streams such as demand management (peak shaving), energy arbitrage, user-initiated demand-response, and optimal electric vehicle charging. properly deployed, these capabilities also benefit the utility grid by enhancing grid reliability and resilience, deferring or reducing capital expenditures required to upgrade the distribution grid, and helping balance the supply of renewable energy as its penetration increases. the u.s. department of energy’s gridinteractive efficient buildings initiative [6] describes the multi-faceted benefits of these smart building capabilities. smart building controls are also an integral component of autonomous energy grids [7], where they provide opportunities for granular device-level controls. proportional–integral–derivative (pid) controllers are still widely used in building controls for heating, ventilating, and air-conditioning (hvac) systems, largely because of their simplicity and fast solution times, as they employ numerical methods to determine the controlling parameters [8]. future energy open access journal https://doi.org/10.55670/fpll.fuen.3.4.3 november 2024| volume 03 | issue 04 | pages 47-55 journal homepage: https://fupubco.com/fuen issn 2832-0328 mailto:sakshi.m@outlook.com https://doi.org/10.55670/fpll.fuen.3.4.3 https://fupubco.com/fuen s. mishra et al. /future energy november 2024| volume 03 | issue 04| pages 47-55 48 however, the time-varying system dynamics characteristics of hvac control systems result in the inconsistent performance of traditional controllers, often leading to lesseconomic performance. moreover, the objectives of building control systems have shifted from being solely occupantcomfort and economic operations to being grid-interactive prosumers. as prosumers, building energy management systems have goals such as (i) maximizing the use of on-site distributed energy resources, (ii) managing consumption profiles based on time-of-use energy rates, and (iii) using onsite energy storage to reduce the peak demand for cost savings. such a complex set of objectives requires the use of advanced control techniques like model-predictive control [9]. implementation of intelligent dispatch and modelpredictive control algorithms that help achieve the abovestated goals to reduce overall energy consumption and operational costs of the building nearly always requires a forecast of the energy consumption of the building. these algorithms use these building load predictions to schedule the dispatch of flexible loads, on-site clean energy resources, and/or energy storage systems to optimize a desired metric, such as utility cost. forecast accuracy is a key driver of modelpredictive control algorithm effectiveness [8-10]. prediction of building energy consumption patterns is also important for detecting faults or operational anomalies in energy systems. therefore, building load forecasting systems are an essential component of smart buildings. building load forecasting is not a new research question; much research work in the literature has addressed this problem space [11-13]. commercial load forecasting tools for building energy predictions are also available [14,15]. the journey of successful research outcome to industry deployment, however, inevitably passes through the research-prototyping phase, and advanced building load forecasting systems are no exception. this is especially relevant for data-driven modeling projects where the type, quality, and pre-processing of data largely dictate the performance of the forecasting system. the work presented in this article sheds light on the end-to-end pipeline of building load forecasting systemsin a campus-wide prototyping setupusing advanced data-driven methods (recurrent neural networks). the following paragraphs delineate the types of modeling algorithms used in the literature for the building energy forecasting problem and specifically discuss works that have utilized data-driven modeling methods. as building systems become more advanced through next-generation sensors, controls, connectivity, and communications, they produce a large volume of empirical data available to building operators for decision-making. this data, along with meteorological parameters, can be harnessed to predict building and campus energy consumption. there are two main approaches available for this prediction task: (i) physics-based (or “white box”) modeling and (ii) data-driven (or “black box”) modeling. (physics-based models are termed “white box” because the inner workings of the model are typically open to the modeler, whereas data-driven models are termed “black box” because their prediction logic is often opaque.) a third category, “grey box” models [16], represents a combination of the physics-based and data-driven approaches. they combine a partial theoretical structure with data, offering relatively simpler model architectures. grey box models are generally trained or fit like data-driven models. physics-based building models such as energyplus® [17,18] model the physical relationships between the building characteristics (construction details, operation schedules, shading information) and environmental parameters (sky conditions) to calculate building energy consumption [19]. data-driven models, on the other hand, make predictions by learning the pattern empirically from historical data. datadriven models have two major subcategories: (i) statistical models and (ii) machine learning models. deep learning models are a subset of machine learning models that are capable of learning complex nonlinear relationships between the inputs and the predicted variable(s). recurrent neural networks (rnns) are an advanced variant of deep neural networks that are capable of incorporating temporal dependencies between the input and output variables. long short-term memory networks (lstm) are a variant of rnns that are effective at capturing longer-term temporal dependencies in the data sets. there are numerous advanced applications of predictive analytics in the renewable energy field [20]spanning the energy system from generation (solar and wind forecasting) to consumption (smart buildings energy forecasting to fault predictions). because the focus of this article is smart buildings’ predictive analytics application, herein, we discuss literary works focused on data-driven building load forecasting. recent research has established the utility of neural networks for forecasting the energy consumption of both individual buildings and groups of buildings. for example, a machine-learning-based forecasting model is presented in [21], whereas [22] covers a review of the intelligent system for power load forecasting. a polish power system study with a deep learning approach is presented in [23], and [24] takes a deeper look at a hybrid system based on lstm for short-term power load forecasting; similarly, reference [25] presents an rnn-based robust short-term load forecasting framework. an online adaptive rnn-based load forecasting algorithm with smart meter data is presented in [26]. short-term load forecasting for urban loads using an artificial neural network is tackled in reference [27]. an lstm-based method is improved for short-term load forecasting [28]. on the research end of the building load forecasting spectrum, the existing literature has extensively focused on assessing the effectiveness of machine learning (specifically deep learning) models for the building load prediction problem. the commercial end of building load forecasting spectrum, on the other hand, focuses on using proven and tested traditional methods in prepackaged software products. both these extreme ends of the building load forecasting problem space do not address the “research prototyping” step for incrementally adopting cutting-edge prediction methodologies. that is to say, none of these works have covered a holistic picture of the deep-learning-based prediction system deployment process—in a research setup—which starts with the data collection and curation process and continues to critically assess the challenges and opportunities with its end-to-end deployment and continued use. the work presented in this paper contributes a perspective on how to move data-driven algorithms from research to practical deployment by presenting a case study s. mishra et al. /future energy november 2024| volume 03 | issue 04| pages 47-55 49 of designing, building, and deploying a research prototype of a deep-learning-based building load forecasting system. the current section lays out the introduction and background behind the presented work, and the rest of the paper is organized as follows: section ii provides a brief introduction of the real-time testbed (intelligent campus) utilized for deploying the deep learning models. section iii discusses the algorithm employed in modeling, methodology, and benchmarking. section iv presents the challenges faced, lessons learned, and opportunities that a fully functional and deployed load forecasting system presents for modern buildings. section v concludes the paper with a discussion of outlook. this paper is an extended version of our preprint [29]. 2. intelligent campus the intelligent campus platform at the national renewable energy laboratory (nrel) was established to collect historical and real-time building performance data to support analytics that enhance operational awareness and decision-making with respect to energy use. the platform was developed using open standards and protocols (figure 1) with the intent to provide an architecture that is readily transferable to other campuses [30]. since its inception, the intelligent campus platform has evolved into a program providing an ecosystem for the use of the nrel campus as a living laboratory. the intelligent campus program offers nascent energy analytics technologies and algorithms a pathway to mature toward commercialization. the intelligent campus program includes an interdisciplinary portfolio of projects aimed at prototyping the future of smart, sustainable, resilient, and self-healing buildings. by providing an environment for technology demonstration in real facilities, the intelligent campus program is bridging the gap between theoretical research into building efficiency technologies (which are often published but rarely deployed) and practical application. intelligent campus pilot projects include detailed monitoring and analysis in order to identify and improve technology shortcomings. figure 1. end-to-end data collection architecture (from [29]) 2.1 data: measurement, collection, and curation advanced analytics and model-predictive control algorithms for smart buildings require reliable, internally consistent building performance data. nrel collects a variety of performance data at its south table mountain campus. the campus has a single common utility electric meter for all facilities, including the campus’s central heating and chilled water plant. eighteen campus buildings have whole-building electrical meters; several other small buildings do not have dedicated electrical meters. several newer buildings have submetering by end-use, per the requirements of ashrae 90.1 [31]. facilities that consume heating and chilled water from the central plant have thermal meters for heating and chilled water consumption. nrel captures the electric and thermal meter interval data using a central energy management information system (emis). the emis also collects interval data from the campus building automation system and syncs data from several cloud data sources via web application programming interfaces, including utility data from the campus main electricity meter and nrel’s onsite research weather station [32]. to maximize accessibility for operations and research, intelligent campus organizes collected interval data per the project haystack standard [30,33]. these interval data are available to serve as inputs for predictive load models. 2.2 predictive analytics intelligent campus’s predictive analytics project applies recent machine learning and deep learning advances to develop and continuously improve load forecasting capability for nrel’s south table mountain campus. intelligent campus executes research, prototyping, and enhancement in a cycle so that practical deployment lessons can be folded back into early-stage research, increasing the ultimate effectiveness and eventual impact of the work. intelligent campus’s building load forecasting work builds from prior nrel research that predicts expected building performance based on exogenous inputs [34]. s. mishra et al. /future energy november 2024| volume 03 | issue 04| pages 47-55 50 as an academic discipline, load forecasting approaches can be studied using static postprocessed data sets. transferal of these results to a real-world setting requires, at a minimum, some underlying sensor infrastructure, a mapping of sensor data streams to model inputs, and quality control on the measured data being fed to the model. therefore, the focus of the current effort is twofold: (i) to automate, replicate, and scale the predictive algorithms and (ii) to improve accuracy by leveraging state-of-the-art neural networks. 3. load forecasting using deep learning 3.1 deep learning: long short-term memory network artificial neural networks are universal function approximators. they are capable of representing complex nonlinear relationships in high-dimensional data sets such as the one being employed for building load forecasting in this work. deep learning algorithms, which employ multiple hidden layers, have powerful generalizing capabilities. that is, they are able to make reasonably accurate predictions for previously unseen scenarios because of their ability to learn the intricate structures in large data sets. feedforward neural networks, sometimes referred to as “vanilla” deep neural networks, have the fundamental drawback of independence among the time-series samples/data points, which makes them an ineffective choice of algorithm for time-series-based prediction problems. this is because the entire state of the feedforward neural network is cleared after processing each time-series sample, which means that the network starts mapping the inputs and output for the next time step from scratch, thereby failing to account for the impact of the previous time step’s input variables. recurrent neural networks (rnn) are advanced types of deep neural networks that overcome feed-forward neural networks’ limitations. they are different from feedforward neural networks because of the presence of additional directed edges that introduce temporal memory components, enabling them to capture complex nonlinear relationships between the temporally related inputs and outputs across multiple time steps. this makes them effective at modeling time-series forecasting problems. a long short-term memory (lstm) network [35], shown in figure 2, is an rnn variant that is able to learn long-term dependencies between the input features and the predicted variable [36]. figure 2. lstm memory cell diagram (from [29,36]) figure 2 displays a typical memory cell for an lstm network. in the figure, 𝐶 denotes the cell states at different points in time 𝑡; 𝑓𝑡 , 𝑖𝑡, and 𝑜𝑡 denote the forward, input, and output gates, respectively; ℎ(𝑡) is the hidden state at time 𝑡; and 𝑊𝑓 , 𝑊𝑖 , 𝑊𝑐 , 𝑊𝑜 are the weights. further explanation can be found in [36]. 3.2 performance measure the evaluation metric used to measure the performance of the forecasting algorithm is the mean squared error (mse). the difference between the ground truth (i.e., the actual future time-step value of the measurement being predicted) and forecasting values (i.e., output of the deep learning model) is calculated using mse: mse = 1 𝑛 ∑ (av𝑗 (𝑡) − ov𝑗 (𝑡)̂ ) 2 𝑛 𝑗 = 1 (1) where 𝐴𝑉𝑗 (𝑡) is a vector of actual (ground truth) values and 𝑂𝑉𝑗 (𝑡)̂ is a vector of forecasted (output) values. 3.3 case study: building load forecasting on a research campus in this case study, the energy consumption at the main electricity meter for the café building on the nrel south table mountain campus is predicted at an hourly resolution. there are six input features used for training the model: relative humidity, barometric pressure, dry bulb temperature, global horizontal irradiance, total cloud cover, and wind speed. these data are from nrel’s solar radiation research laboratory data set [32]; however, they also represent measurements commonly available from highquality weather stations worldwide. the model is run for 200 epochs with the data spanning a year’s interval: 10and 2months train/test split, respectively. we use a single-layered network with 35 neurons. the following mse plot (figure 3) shows the train and test losses over several thousand iterations. despite the difference between final train and test losses, no overfitting was observed in the experiment. figure 3. mean squared error (mse) error plot for train and test data (from [29]) s. mishra et al. /future energy november 2024| volume 03 | issue 04| pages 47-55 51 the model can produce load forecasts at multiple future time steps, as shown in figure 4 for the café building's main power. the models use the most recent 12 hours of weather data to capture the transient effect of weather on energy consumption and use the time of day and day of the week to capture time-based energy consumption patterns, such as those related to building occupancy. because neural networks can learn non-linear relationships, the trained models are able to infer complex behaviors, such as the pre-occupancy energy spike in the café due to early morning food preparation. each model outputs a prediction of building load from the current time step to 18 hours in the future in 1-hour increments. this input-output structure applies to all buildings that were studied on the nrel campus. model performance was not seen to change significantly as the length of the forecast window increased/decreased, but the training time was significantly impacted by the length of the training window (number of hours of historical data used as input to the model). 4. operational load forecasting system deployment a primary research objective of the case study was to establish deployment and continuous improvement pathways for the developed algorithms. that is, developed algorithms should be able to be rapidly deployed for testing within the intelligent campus platform and iteratively improved with minimal retooling. the intelligent campus team intends to expand the algorithm to forecast other quantities (such as building electricity meters, thermal meters, and photovoltaic system generation) and to support additional exogenous variables. therefore, from a software development point of view, the system’s input-output architecture must be flexible, replicable, and scalable. due to the nature of the deep learning algorithms used, ongoing access to data is an integral part of the continued operation of the system. periodic retraining of the models as more data gets collected has the potential to increase model accuracy. figure 4. multi-time horizon forecast (from [29]) the following two subsections describe the challenges and opportunities that open up for smart buildings’ research and prototyping once those challenges are addressed. understanding the deployment aspect of a deep-learningbased forecasting system, therefore, completes the re-searchprototyping loop. 4.1 challenges 4.1.1 data availability and quality control “garbage in, garbage out”––a common phrase used in the machine learning community––captures the importance of this step of data collection and curation. assembling a machine learning training data set begins with proper commissioning and maintenance of meters, sensors, and other data inputs. data should have proper units and scaling. (although in some circumstances, a machine learning model could be successfully trained from improperly scaled or otherwise corrupted input data, if those data stream errors were corrected in the future, the model would need to be retrained). automated accumulation of new training data (without extensive human review) presents data quality challenges. nrel’s intelligent campus team has implemented quality check mechanisms for the measurements coming from the sensors in real time before they are fed to the model. one example is removing the outliers identified by the values lying outside of three standard deviations. another is operating basic fault detection rules that check for stuck sensors (constant value for long periods of time), logically out-ofrange data (such as significant solar radiation recorded at night), and similar anomalies. these checks not only improve machine learning model quality but also provide an opportunity to detect and correct errors in the measurement systems and equipment. s. mishra et al. /future energy november 2024| volume 03 | issue 04| pages 47-55 52 4.1.2 integration with emis and scalability the practical implementation of a forecasting system requires reliable interfaces for transferring data to the model and for transferring model outputs to an analytics system that consumes them. the forecasting system developed for this case study communicates with the nrel emis via an application programming interface defined by the project haystack standard [33]. the emis provides forecast inputs, and the forecast system, in turn, writes forecasts back to the emis. adherence to a metadata standard and an open application programming interface allows the forecasting system to be rapidly retrained and redeployed for new sites. any database that adheres to the project haystack standard and correctly tags the required input points can be connected to a new instance of the deep learning algorithm, and a new model can be trained with minimal effort. when the forecasting system runs in integration with emis, it is also important to be able to redeploy the model (with either architectural or training updates) without service interruption. because forecasts cover a span of time but are frequently updated, managing caching is a key challenge. in addition, the forecast read/write system must be flexible enough to handle arbitrary forecast inputs and outputs. additionally, given the computationally intensive nature of deep learning models, scalability in terms of available computing power for retraining the models is another interesting challenge. 4.1.3 online vs. offline training training is an important consideration for deeplearning-based forecasting systems because deep-learning models’ accuracies have been shown to keep rising with more training. offline training is a relatively simpler way of implementation in which the machine learning models are retrained by a manual process where an engineer copies the old model to a local machine, trains it further with the new data, and transfers it back to the servers where the systems are deployed. offline training, therefore, requires more human hours over the course of the system’s operation because human intervention is needed to train the models further at regular intervals. the online training approach, on the other hand, is an automated process. at its simplest, an online training system trains models on a schedule (for example, every 1 to 2 months) without any manual intervention [37]. though setting up the automated training pipeline initially requires additional planning and coding, this online training eliminates the maintenance dependency on human intervention to move the models offline, retrain them, and upload them back into the forecasting system pipeline regularly. thus, online training can increase operational efficiency and reduce opportunities for human error to impact the forecasting system. moreover, because a robust metering platform has already been established as the first step in the process of our prototype of intelligent campus, high-quality data are constantly accumulating and can be used to increase the accuracy rates of our models. for our final implementation, we have chosen the online training option. 4.1.4 continuous improvement as described above, deep learning models are capable of increasing accuracy as more data is made available for training. also, in the initial stages, when the accuracy of the model is not satisfactory, given the shortage of data points to train it, large changes in predictive behavior can be offputting to end users. therefore, along with iterative training, we conduct model enhancement with hyperparameter tuning as the operational circumstances change over time. this is an infrequent yet desirable step. 4.1.5 generalizability another typical challenge in deploying deep learning models for multiple prediction points (i.e., building-wise energy consumption forecasts) is generalizability. because each prediction point has its own model, the deployment architecture must address the need for automated model generation. to address the challenge of generalizability, the forecasting system’s data preprocessing and postprocessing modules are designed with the capability to take in a generic variable named “point-id” that is used as a reference to fetch the respective machine learning model and input data streams. 4.2 opportunities an automated end-to-end pipeline for load forecasting deployed on-site, with an online training mechanism in place, enables many opportunities to harness the predicted data for furthering the smart buildings’ research. in the following subsections, we describe three potential applications. 4.2.1 demand management motivations for electricity demand management (peak shaving), including utility demand charge reductions and reduced carbon footprint. (when the peak of multiple buildings and campuses coincides with the utility peak, lower-efficiency “peaking” power plants fired by gas or diesel are used to support the grid, which translates to proportionally higher greenhouse gas emissions.) reducing peak demand requires the ability to predict the timing and magnitude of peak demand, then preemptively shift load or dispatch energy storage assets to avoid the peak. 4.2.2 energy arbitrage energy arbitrage is another cost-saving opportunity available for grid-interactive buildings in cases where on-site energy storage is available. energy arbitrage is performed by participating in the energy markets by charging energy storage (for example, batteries) when electricity prices are low and discharging storage to sell power back to the grid when prices spike. even in utility markets where bidirectional electricity exchange is not possible, a form of energy arbitrage is possible by buying energy when prices are low, storing the energy locally, and dispatching the energy locally to meet load when energy prices are high. energy arbitrage can be accomplished by employing near-real-time or real-time optimization algorithms. however, the real-time optimized storage dispatch requires reasonable foresight into future onsite energy consumption, thereby making building load forecasts an important component of the system. 4.2.3 load flexibility a third opportunity to save energy costs for building operations is shifting the load based on the time-of-use energy rates. building load can be classified as critical, which consists of loads that cannot be deferred, and flexible, which s. mishra et al. /future energy november 2024| volume 03 | issue 04| pages 47-55 53 consists of loads whose consumption can be scheduled within a given time window. examples of critical loads include lights, fans, microwaves, computing systems, etc.; these loads must be available for use when needed. examples of flexible loads include dishwashers, laundry, and even heating and cooling (buildings can be precooled/preheated). with adequate foresight, flexible loads can be shifted to minimize energy costs. this also requires predicting the building’s future energy consumption. 5. conclusion the paradigm of grid-interactive efficient buildings, i.e., dynamically operating buildings that constantly exchange information and energy with the utility grid, is increasingly gaining traction in both the research community and in industry. such smart buildings will operate in harmony with the grid to make electricity more affordable and integrate a larger share of ders while meeting the comfort and productivity needs of the buildings’ occupants. nrel’s intelligent campus is a living laboratory that is dedicated to accelerating the research and deployment of various pieces of the smart buildings puzzle, serving as a vital testbed for the innovative solutions that push the frontier of smart building operations. in this article, we describe and critically discuss a deep learning building load forecasting system that is an important module of smart buildings’ overall controls. through the critical discussion, we highlight that the characteristics beyond simple algorithm forecast accuracy are important in determining the algorithm’s true utility for smart buildings. we demonstrate that metering, collection, and curation of data is a crucial part of the prototyping process of such an advanced forecasting system. using lstms, the deep learning model can predict the building and campus load for an 18-hour’ time horizon. the architecture is flexible with the time resolution; sub-hourly predictions can be enabled with minimal modifications to the code. using intelligent campus as the platform for testing the research findings in real-time settings, we shed light on the deployment aspect of such advanced forecasting systems. we conclude that a well-architected design of the forecasting system is key to its effectiveness. to take a forecasting algorithm from the research phase to deployment for practical use, building engineers will need to focus on the endto-end pipeline, which requires considerations for multiple submodules such as access to data, data handling, seamless integration with the existing building data platform, model training, and update mechanism, periodic performance checks, and model enhancement with hyperparameter tuning as operational circumstances change. the end-to-end forecasting system presented in this work forms a robust platform for furthering research in the building energy predictive analytics problem space. we plan to expand this work in the following directions: 5.1 probabilistic forecasting rather than generating a point forecast for every time step, a range can be outputted with the estimated minimum and maximum values serving as the upper and lower bounds for a prediction band within which the actual consumption in the future time step will fall. having a range instead of point forecasting is especially helpful in the fault detection application where consistent outliers (outside of the band points) indicate a potential issue that can be further investigated by the building’s operations team. moreover, probabilistic forecasting using deep neural networks is an active inquiry front on the research end of the forecasting technology’s spectrum. 5.2 predictive maintenance current practice in the building industry is to perform “schedule-based” maintenance for fault prevention, which is not effective in terms of flagging the equipment vulnerable to a fault beforehand. the next generation of the faultprevention mechanism is “condition-based” or “preventive” maintenance. this involves using statistical analysis to assess the health of the patients and estimate the probability of failure in order to inform the operators. the presented forecasting system can be further developed for predictivemaintenance applications where the occurrence of a specific fault on the system, which may occur due to unusual wearand-tear on equipment, can be predicted well in advance, thereby preventing equipment failure from triggering faults. author contributions conceptualization, sakshi mishra, stephen m. frank, and anya petersen; method-ology, sakshi mishra and stephen m. frank; software, anya petersen and sakshi mishra; validation, stephen m. frank and robert buechler; formal analysis, sakshi mishra; resources, stephen m. frank and michelle slovensky; data curation, stephen m. frank; writing—original draft preparation, sakshi mishra, stephen m. frank, and anya petersen; writing—review and editing, robert buechler and michelle slovensky; visualization, sakshi mishra, robert buechler, and marj schott; supervision, michelle slovensky; project administration, anya petersen; funding acquisition, michelle slovensky. all authors have read and agreed to the published version of the manuscript. ethical issue the authors are aware of and comply with best practices in publication ethics, specifically concerning authorship (avoidance of guest authorship), dual submission, manipulation of figures, competing interests, and compliance with policies on research ethics. the authors adhere to publication requirements that the submitted work is original and has not been published elsewhere in any language. funding this research was funded by the u.s. department of energy office of energy efficiency and renewable energy building technologies office. acknowledgments this work was authored by nrel, operated by alliance for sustainable energy, llc, for the u.s. department of energy (doe) under contract no. de-ac36-08go28308. funding provided by the u.s. department of energy office of energy efficiency and renewable energy building technologies office. the views expressed in the article do not necessarily represent the views of the doe or the u.s. government. the authors wish to acknowledge the national renewable energy laboratory’s continued support in enhancing the research and prototyping capabilities of the intelligent campus program. the authors would like to thank marj schott (nrel) for contributing figure 1 to the article. s. mishra et al. /future energy november 2024| volume 03 | issue 04| pages 47-55 54 data availability statement data sharing does not apply to this article as no datasets were generated or analyzed during the current study. conflict of interest the authors declare no potential conflict of interest. references [1] total energy monthly energy review, u.s. energy information administration,, 02 05 2020. 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[28] j. cui, q. gao and d. li, "improved long short-term memory network based short term load forecasting," hangzhou, china, 2020. [29] s. mishra, s. m. frank, a. petersen, r. buechler and m. slovensky, "deep-learning-based, multi-timescale load forecasting in buildings: opportunities and challenges from research to deployment (preprint)," vol. 1, no. 1, pp. 1 13, 2020. [30] d. cutler, s. frank, m. slovensky, m. sheppy and a. petersen, "creating an energy intelligent campus: data https://data.openei.org/submissions/144 s. mishra et al. /future energy november 2024| volume 03 | issue 04| pages 47-55 55 integration challenges and solutions at a large research campus," in aceee summer study on energy efficiency in buildings, pacific grove, ca, 2016. [31] ashrae, "energy standard for buildings except lowrise residential buildings, standard 90.1-2019," 2019. [32] t. stoffel and a. andreas, "nrel solar radiation research laboratory (srrl): baseline measurement system (bms)," national renewable energy laboratory, golden, colorado (data), 1981. [33] "project haystack," 2020. [online]. available: https://project-haystack.org/. [34] g. p. henze, s. pless, a. petersen, n. long and a. t. scambos, "control limits for building energy end use based on frequency analysis and quantile regression," energy efficiency, vol. 8, p. 1077–1092, 2015. [35] s. hochreiter and j. schmihuber, "long short-term memory," neural computation, vol. 9, no. 8, pp. 17351780, 1997. [36] s. mishra and p. palanisamy, "an integrated multitime-scale modeling for solar irradiance forecasting using deep learning," arxiv.org, 2019. [37] cloud-architecture-center, google, "mlops: continuous delivery and automation pipelines in machine learning," 2021. this article is an open-access article distributed under the terms and conditions of the creative commons attribution (cc by) license (https://creativecommons.org/licenses/by/4.0/). https://creativecommons.org/licenses/by/4.0/ m. salmanian and a. bayat /future energy november 2023| volume 02 | issue 04| pages 10-23 10 review urban heat island: a primary guide for urban designers mohammadhassan salmanian1*, akram bayat2 1faculty of design and architecture, universiti putra malaysia,43400 serdang, malaysia 2faculty of architecture and urbanism, iran university of science and technology, iran a r t i c l e i n f o article history: received 16 december 2022 received in revised form 23 january 2023 accepted 01 february 2023 keywords: urban design, urban heat islands, thermal comfort *corresponding author email address: gs57464@student.upm.edu.my doi: 10.55670/fpll.fuen.2.4.2 a b s t r a c t today, the most severe issue in metropolitan areas is rising surface temperature due to poor urban design. given the significance of the urban thermal island, numerous studies have been done to discover the mechanisms influencing its growth and decline. thermal comfort is relatively simpler to accomplish inside a building, whereas it is considerably more challenging to achieve in open spaces, and hence far less work has been done on it. the construction of urban thermal islands has emerged as one of the most serious concerns of our day, and it has captured the scientific community's attention. attention to this subject has expanded dramatically in scholarly articles and research, particularly in the recent decade. because of the subject's relevance, this study aims to undertake a systematic evaluation and thematic analysis of papers and scientific research in this field. according to studies, the urban heat island is influenced by climatic elements and city-building factors. all climate influences are sunlight, wind speed and direction, cloud cover, soil and air humidity, precipitation, latitude, seasonal change, topography, and proximity to rivers and the sea. although these elements are almost uncontrolled in existing cities, they are essential in finding new cities or deciding the direction of city development. the second element category is controllable and primarily connected to city planning and building. recognizing the significance of these factors can demonstrate the relevance and value of urban planning and design in lowering urban heat islands. we review the nature and aspects of this phenomenon in this article by exploring the theoretical foundations of this topic. 1. introduction for many, the supply of basics like fresh water, food security, and electricity is anticipated to be impacted by a climate warming system. concurrently, efforts to mitigate and adapt to climate change will equally inform and influence the global development agenda. it is crucial to understand how climate change and sustainable development are related. the least equipped to withstand the projected shocks to their social, economic, and environmental systems will be the most negatively impacted by these shocks. these poor and emerging countries-primarily the least developedwill be the majority [1]. in comparison, this increase is outweighed by an increase in the number of families, implying that the overall number of people per family drops. as a result, our cities will continue to grow, putting further strain on the existing urban area. current urbanization patterns significantly impact how we plan, build, and live in our cities. the transition from rural to urban settings includes a variety of human-caused consequences, such as a loss of biodiversity or a lack of water supplies [2]. it also affects the shape and energy budgets of the urban environment, leading to higher temperatures than in the undeveloped environment [3-5]. the urban heat island (uhi) phenomenon is centered on this. luke howard, a british meteorologist, was the first to study the phenomenon; in 1818, he found a sizable rise in the center of london [6]. for a long time, neither science nor politics supported the uhi. this changed in 1971 when the club of rome issued its limits to development report. the study was the first to explore the consequences of population development on uhi, making it one of the most visible repercussions of humancaused environmental change. in general, the study sparked a fundamental debate regarding the reality of climate change and a search for factual data to demonstrate human proficiency in it. in the case of uhi, the formation and consequences were examined and analyzed until it became clear that an increasing proportion of our population was subjected to urban atmospheric conditions. the dilemma of climate change and uhi has seen substantial adjustments in future energy open access journal https://doi.org/10.55670/fpll.fuen.2.4.2 november 2023| volume 02 | issue 04 | pages 10-23 journal homepage: https://fupubco.com/fuen issn 2832-0328 mailto:gs57464@student.upm.edu.my https://doi.org/10.55670/fpll.fuen.2.4.2 https://fupubco.com/fuen m. salmanian and a. bayat /future energy november 2023| volume 02 | issue 04| pages 10-23 11 the recent two decades as politicians and cultures have begun to pay greater attention to the issue. the worldwide debate was dominated by effect evaluation and how to deal with them, leading to significant new knowledge on preventative and adaptation activities. however, because politicians and society have called for a comprehensive solution to the effects of climate change and uhi, the efforts taken thus far have not been practicable. the emphasis shifted from natural science to a multidisciplinary approach, emphasizing information development and collaboration among scientists, planners, and decision-makers. to develop sustainable locations, urban planners and designers must handle the repercussions of this argument, such as higher knowledge volumes, demand for diverse, sustainable settings, and improved political and social wealth [6]. however, in the recent debate, other consequences, such as increasing sea levels or global warming, have overshadowed the uhi hypothesis. this is not surprising given the calamities in bangladesh and new orleans, but the uhi should not be neglected. for example, recent heat waves in europe have sparked a significant national discussion, with thousands of direct causes of death and sickness. furthermore, there are significant effects on municipal water and energy supplies. rising energy demand strains city climates and water supplies [7]. thus, the uhi is one of several climate change-related outcomes that put space planners under pressure; planners must use vast amounts of new knowledge to create well-planned and secure areas. environmental experiments have created several theories regarding limiting adverse impacts in the case of the science-based uhi. the main thing today is to understand how to apply all of the current knowledge and how to deal with the influence of politics and culture in creating wellplanned and thriving areas, and therefore how to implement the steps successfully. more research must be conducted to clarify how to build a clear uhi strategy for a region and apply all broad initiatives in local planning practice. in this approach, the adverse effects of uhi will be reduced, assuring long-term growth in our cities. 2. urban heat island: concept there are several points of view when it comes to challenging uhis. few people will immediately begin dreaming about global warming, while others will speculate about the pacific ocean's tiny islands, but the primary number has never been heard. the position of uhi is always relatively limited or nonexistent in today's discourse on climate change, environmental development, and eco-engineering. this lack of exposure can be interpreted in various ways, all of which must be addressed in this study. still, one of them is the phenomenon's vague and dubious existence. this section will explain the exact phenomenon, beginning with the fundamentals of uhi [8]. there are substantial differences in the notion of uhi and its outcomes. the influence of urban surfaces, wind patterns, and global warming is widely debated. however, there is a consistent interpretation of the underlying concept of uhi, which can be defined as the variation in temperature between urban and rural areas (figure 1) [2]. in literature, uhi is an improvement in urban temperature. the question here is, what is the exact growth and how it is made. measurements and forecasts vary worldwide due to current variations in geographic climate conditions [9]. an examination of a wide range of environmental and planning literature indicates the issue of the uhi's thermal effect notion. as a result, it is critical to research on a local scale to explain the case of the urban environment, considering the particular climatological and morphological circumstances. to better understand the specific causes of uhi and its relevance to urban planning, we shall first review the theoretical foundation of this section. figure 1. the definition of an urban heat island [5] 2.1 theoretical basis for urban heat islands, the lowest atmospheric level affects state and local climates. at the same time, other experts believe that uhi's effects on global temperatures have yet to be fully realized. the uhi-world climate change relationship will be discussed further in this section. 2.1.1 urban climatology while people have historically adapted to their surroundings, climate change poses new and unprecedented hazards to lives and livelihoods. given increasing uncertainties and ambiguity about climate adaptation, interest has grown in the previous two decades. even though it was initially used in the 1990s, the ipcc definition gained traction. the fourth of these evaluations is "the most recent change in natural or human systems in response to current or expected climatic stimuli or their repercussions, which mitigates harm or capitalizes on positive opportunities" [10]. additionally, the united nations framework convention on climate change (unfccc) conference of the parties (cop) meetings have added to this growing knowledge. cop 21 highlighted the importance of setting a global goal for adaptation "develop adaptation capability, enhance resistance, and reduce climate change vulnerability" [11]. in addition to natural disasters, metropolitan areas are at risk from unexpected climatic hazards (e.g., urban heat islands, impervious surfaces exacerbating flooding, coastal development threatened by sea-level rise, etc.) [12]. additionally, most people on earth live in metropolitan regions [13]. many assets are at risk from climate change because they are hubs of the global economy [14]. m. salmanian and a. bayat /future energy november 2023| volume 02 | issue 04| pages 10-23 12 additionally, urban locations provide distinct options for adaptability. first, judgments for adaptation frequently call for locally specialized activities, which are best suited by local-level decision-making [15]. secondly, urban settings foster inventiveness and efficient energy usage. numerous charity foundations, in particular, encourage local adaptation by funding initiatives like the kresge foundation's examination of urban populations' climatic resiliency and susceptibility to urban adaptation. the initiative will assist in meeting urgent demands for climate action and guide decisions regarding housing, land use, water supply management, transportation, and other issues relating to policies and finances, including motivating local communities to act and advising them on what to do to improve their health and resilience to climate change. fourth, given the significance of cities in addressing climate change, cities have lately become more competitive, as seen by growing interest in c40, 100 resilient cities, etc. [16]. this results from numerous cities' adaptation efforts and expanding research on urban adaptation [17]. additionally, the adaptation clearinghouse of the georgetown climate center [18] tracks some state-level adaptation proposals, and researchers have examined the data. the demands and progress of urban adaptation are examined in recent study literature [19]. additionally, a sizable examination of national adaptability has been conducted, which includes monitoring national risk, addressing climate change threats, and enhancing overall national adaptability [20]. 2.1.2 urban climate the urban climate closely interacts with energy demand, outdoor comfort, and energy systems. the geometric complexity, heterogeneity, and link of cities to meteorological events confound urban microclimate modeling [21]. the city and climates are two artificial and natural systems that are inextricably linked in constructing various city places such as buildings, green rooms, urban networks, etc. aside from practical, visual, and aesthetic aspects, it is also vital to consider the city's climate and climatic design standards. the four primary climatic factors in the architectural structure of urban areas are "solar radiation," "wind flow," "relative humidity," and "temperature." controlling the two indicators of sun radiation and wind flow allows for precise relative temperature and humidity control. as a result, the first stage in climatic design is to understand the influence of changes in these climatic factors on environmental comfort. 2.1.2.1 solar radiation the sun is the source of the energy that determines our climate. radiation from the sun reaches earth as electromagnetic energy. all things emit electromagnetic radiation, which may be thought of as waves with peak-topeak lengths that vary with the surface temperature of the item. the electromagnetic radiation from the sun that penetrates earth's atmosphere has a peak within the visible human range of wavelengths, around 400-700 nanometers, and the temperature at the sun's surface is approximately 6000°k, four (nm). we refer to the whole range of the solar spectrum, which extends from 280 nanometers (nm) to around 3000 nm (or 0.28 micrometers, abbreviated m, to 3 m), as short waves or solar radiation [22]. understanding solar efficiency is crucial for urban planners and architects when designing urban structures. as the most logical approach to gathering solar energy, it is crucial to incorporate solar electricity into buildings with rooftops and façades. it has a significant impact on architecture. mature solar technologies are more likely to produce preferable solutions during the early design phase. early integration can be eased when architects know where the most significant energy may be produced. real estate developers may also find solar power a crucial asset because they can see the energy produced in the envelope [23]. furthermore, energy conservation and emission reduction have been elevated to a crucial strategic position in the people's republic of china's 13th five-year plan on energy strategy. solar energy is excellent for sustainable energy with no restrictions and can be utilized everywhere. solar energy usage offers enormous development potential and is reliable and effective. solar energy generation and use in urban areas will limit the excessive use of traditional fossil fuels, prevent the deterioration of urban ecosystems, and ensure that urban areas have a healthy natural ecosystem [24]. the first area is where emergencies with energy usage may be addressed and finally resolved in the city. the lack of solar potential included in the conventional urban planning process, which is a deciding element to attain smart energy cities made up of zero energy structures, gave rise to the discussion of solar urban planning. the modern city that le corbusier envisioned was not realized. however, considering urban planning as the first sector to apply solar design logic was a creative idea. energy experts and urban planners have long considered solar radiation and associated difficulties as active elements in urban development. the urban heat islands (uhi) and outdoor thermal comfort have been recognized as prosperous urban design areas among the numerous solar energy instances researched. uhi will quickly discuss these two areas of urban design below [25]. 2.1.2.2 urban heat island in the 1810s, luke howards made the first reference to urban heat. in contrast to the city's rural surroundings, he saw "an artificial excess of heat" in london. mitchell (1953) began his studies in the united states in the 1950s. recently, there has been much global study on the urban heat island effect [26]. in metropolitan settings, a microclimatic phenomenon is referred to as a "heat island." it entails an appropriate air temperature rise in metropolitan regions, which is often warmer than the nearby rural neighborhoods (figure 2). when breezes are light, the temperature differential is often more suitable at night than during the day. in terms of the seasons, the urban heat island effect primarily affects those who live in cities in the summer and winter. addressing the uhi hazard to human health in urban areas is essential. the intensely scorching summer temperatures substantially impact the quality of life in cities. they may be summed up as a severe decline in public health, a warmer biosphere, and increased energy use [27]. the uhi phenomenon has an impact on urban areas for several reasons. the primary factor is the physical properties of the materials that make up urban surfaces, which absorb solar energy rather than reflect it. longwave radiation is emitted depending on the surface's excess warmth, especially at night. a constant energy balance is also maintained by the tiny m. salmanian and a. bayat /future energy november 2023| volume 02 | issue 04| pages 10-23 13 amounts of natural surfaces often present in metropolitan settings. the waste heat produced by energy usage is another aspect of the temperature rise [27]. figure 2. diagram of an urban heat island phenomenon [27] the negative consequences of climate change are made worse by the rising urban development rate. specifically, energy demand has increased by 14% over the past ten years because of its fast urbanization. by 2030, at least 61% of the world's population will live in cities. nearly four billion people, or 80% of the world's urban population, will live in the cities of industrialized nations, accounting for 95% of the population growth. however, this development may present a chance for ecologically responsible urban renewal or rebuilding [28]. the following are some significant factors that have fueled the expansion of uhi in metropolitan areas: surface: the critical element impacting uhi is the soil surface content. solar power is collected in the city and emitted during the day and night. therefore the disparity between the thermal entry of urban areas and their rural counterparts would also increase the heat island's size. urban heat islands would be constrained by the increased emissivity from the sky and wind [29], demonstrating the most significant differences between urban and rural temperatures [30]. urban surfaces use materials that absorb short-wave radiation to boost their thermal capacity, which increases their ability to absorb solar energy [31]. lack of plants: there is a wealth of data on how plants and greenery affect air temperature. according to reports, large parks are typically 1-2°c colder than populated areas, although this temperature difference can reach up to 5°c [29]. lack of vegetation in urban areas reduces the evapotranspiration, shade, and cooling benefits of plants that promote uhi and warm the city [30]. high buildings: high-rise building situations need special consideration. because continuous slab buildings have varied surfaces that reflect and absorb sunlight, keeping urban areas warmer, they can obstruct fresh air and wind flow [28]. human activity: environment-harming human actions include using air conditioning, driving, and building factories [32]. both directly and indirectly, heat is affecting the climate. these processes pollute the environment, affect the input and exhaust radiation, and release heat and humidity [33]. this increased temperature could lead to detrimental health and environmental and economic consequences on the local environment [34]. experts claim that excess heat exposure in the united states kills more people every year than deaths from other combined cases [28]. these high-heat occurrences disproportionately harm the city's young, old, and sick residents, and it appears that there is insufficient economic assistance to mitigate the adverse health effects of excessive heat [35]. the cost of living would go up if uhi were improved since it would require more energy for cooling and refrigeration in urban areas. additionally, it is predicted that energy consumption will rise by 2 to 4% for every one-degree celsius increase in the intensity of the uhi [30]. compared to this, due to fast urbanization, energy demand has increased by 14% over the past ten years [36]. because energy is essential to human life, this will soon become a worldwide concern due to the risk that energy may become scarce [37]. in a hot and dry climate, uhi is more likely to result in high temperatures and decreased air moisture, decreasing comfort and heat stress in metropolitan areas (figure 3) [29]. figure 3. the consequence of adaptation possibility: thermal stress is much less likely to occur as there are more chances for environmental management [40]. all of these conditions are made worse by the uhi, including heat and cold stress, excessive sun exposure, bug infestations, water, and air pollution, waste, noise, adverse effects on energy consumption, and fires. heat exhaustion, heat syncope, heart attacks, and heat cramps are symptoms of uhi, which also refer to heat and heart failure [38]. the possible effects of uhi include the unfavorable social and economic effects of hot weather. only necessary confinements will be made to the unpleasant environment, i.e., by limiting outside social activities and going shopping and working [39]. an essential aspect of this is the expanding usage of air conditioning, which drives up energy costs and consumption, leading to frequent power outages and air pollution [30]. local heat waves may impact the welfare and health of residents in addition to temperature factors. over 800 people perished in chicago's 1995 heat wave [41]. in 2003, heat-related diseases in paris led to 15,000 fatalities across europe [42]. air pollution will rise as a result of urban heat islands. according to studies by sarrat et al. [43], urban heat islands in paris affect the levels of ozone and nitrogen oxide (nox) . the energy needed for cooling also rises due to the urban heat islands. in turn, additional heat is released into the city, aggravating the urban heat island effect [44]. the unexpected effects of human activity on the climate, or accidental climate change, are most evident in urban settings. cities influence climate and atmospheric composition changes at local, regional, and even planetary dimensions. as m. salmanian and a. bayat /future energy november 2023| volume 02 | issue 04| pages 10-23 14 cities struggle to deal with catastrophic occurrences like storms, floods, and droughts, the atmosphere also influences their infrastructure, citizens' health, and public safety. in order to intelligently limit undesirable effects and increase advantageous ones, proper knowledge, description, and modeling of these interactions are required. in the end, this offers the scientific information required to plan, oversee, and run communities that are healthier, more sustainable, and more resilient [45]. by examining the historical and environmental effects of global urbanization, this part establishes the framework for the urban climate. outdoor thermal comfort: there are several reasons to improve the outside environment in urban areas. making cities more appealing and accessible is now more crucial because of the positive social, cultural, and economic effects. if the outside environment is thermally comfortable, utilization of the metropolitan region is more likely to rise. additionally crucial to human well-being is thermal comfort. this is particularly crucial in warm nations since rising temperatures raise the risk of heat-related illnesses. furthermore, in friendly nations where suitable outdoor areas enhance outdoor liveability, outdoor activities are available for most of the year. the interior climate will also benefit from a thermally suitable external environment, resulting in less energy used for space cooling [46]. recent ecosystem changes have impacted the viability of outdoor constructed settings [47]. effective urban planning, which attempts to produce successful and useable outdoor spaces, is tested by the cumulative consequences of these changes in urban outdoor spaces. the thermal environment is given great significance as one factor affecting the outdoor environment's quality. therefore, urban planners and designers investigate how people perceive and engage with outside weather situations. while accommodating their daily needs, the thermally comfortable urban environment may let individuals interact with their surroundings. on the other hand, unfavorable temperatures may make people less likely to engage in outside activities and use more energy for inside cooling [48]. one thermal comfort index is computed and used to indicate the combined impact of the study's environmental variables (such as air temperature, relative humidity, wind speed, and radiant temperature) and two individual components (such as garment insulation and metabolic activity level). to evaluate and forecast comfort in thermal settings, more than one hundred thermal comfort indices have been employed; the majority of these were created to identify interior conditions [49]. among others, the top three thermal comfort indicesphysiological equivalent temperature (pet) [50], universal thermal climate index (utci) [49], and outdoor standard effective temperature (out set) [51] were created especially for outdoor conditions and are frequently used in thermal comfort studies conducted outside. other standard outdoor thermal comfort indices include pet utci, out set, thermal discomfort index (tdi), effective temperature (et), operative temperature (top), and perceived temperature. these indices are in addition to pet utci and out set (pt). the projected mean vote (pmv) or adaptive predicted mean vote was employed in several research (apmv). however, the steady-state assumption of pmv may render it unreliable in the face of changing external circumstances. in early research, de freitas [52] employed the caloundra beachgoers as case studies to determine thermal sensation threshold values using the skin temperature energy balance index (stebidex) and heat budget index (hebidex). the effective standard temperature (set) thermal comfort index was expanded by pickup and de dearso that it could be used in outdoor situations. this thermal index has been employed in several comfort studies and continues to serve as the foundation for two-node models [46]. the most common outdoor thermal comfort indices utilized in recent investigations were pet or utci. please also de freitas and grigorieva [53] and coccolo et al. [54] for a thorough analysis of thermal comfort indices. let us think about thermal comfort in the outdoors, with the complexity of the high spatial and temporal variability of environmental variables. the interplay between the physical environment, physiological, and psychological factors is even more difficult. outdoor thermal comfort has been a hot topic due to discussions about sustainable urban settings, often unwelcoming developments in city centers, and the growing significance of open spaces under climate change [48]. a consistent deep core temperature of about 37oc must be maintained for the human body to operate appropriately, balancing heat gains and losses from the environment and basal metabolic rate. according to the physiological reactions of the human body, this fundamental heat balance equation reflecting the heat exchange between the body and the atmosphere has served as the foundation for current thermal regulations [55]. the main environmental factors influencing the thermal environment and comfort include air and mean radiant temperature, air movement, and humidity. additional characteristics that define system changes that affect the body's heat generation and dissipate to the environment include behavioral acts like clothing and metabolic activity, along with the corresponding energy production. solar radiation is an extra climatic factor in interior settings that have been used to describe the physiology of thermal comfort in the outside context. in order to assess the thermal load that individuals are subjected to, over 100 thermal comfort and stress indices have been created experimentally or based on advanced energy budget models. these indices have been used as indications for alert systems, urban planning, ergonomic guidance, and public weather services [48]. the original wind chill index was one of the earliest and most popular indexes to consider wind's influence on refrigeration [56]. this indicator has been frequently applied and modified in public weather forecasts [57], especially in nations with extremely cold climates. a workshop conducted online in 2000 due to decades of systematic windchilla use served as the foundation for creating the windchill program. on the opposite end of the spectrum, thom's discomfort index (di), also known as a temperature-humidity index (thi), is a wellliked empirical assessment for warm, humid conditions [58]. in the interim, urban designers developed an interest in thermal comfort to enhance space design. in what was known as the "bioclimatic chart," olgyay [59] incorporated the impacts of many climatic components, including solar radiation data, which were to be employed for outdoor circumstances (figure 4). the heat balance model of the human body used inside to determine thermal comfort levels was also updated by penwarden [60] to include a term for m. salmanian and a. bayat /future energy november 2023| volume 02 | issue 04| pages 10-23 15 solar radiation. different garment insulation values were incorporated in the olgyay chart [59], an improvement over earlier models. two different comfort charts are provided for wandering in the sun and the shade. there are categories for merely sweating, comfortable, and slightly shivering, and the combined effects of sun and shade with air temperature, wind, and different garment levels may be investigated. later, arens and bosselmann [61] offered further recommendations for comfort criterion. they put forth much effort to improve downtown san francisco and toronto. figure 4. the olgyay bioclimatic chart [59] the physiological equivalent temperature (pet), based on an energy balance model of human physiology, was one of the most widely used indices created for the outdoor setting [50]. since pet utilizes oc as its unit, it is easier for experts other than biometeorologists to understand and is thus more commonly utilized. since its creation, it has been widely used as a universal thermal index to evaluate thermal settings [62]. it has been utilized in modeling studies to assess how geometry and other design-related factors affect the comfort of outdoor spaces [46]. in contrast, rayman and other software models for assessing outdoor thermal comfort conditions have included it as an index [63] and the threedimensional envi-met [64]. the fact that all thermal indices, including pet, are based on steady-state energy balance models of the human body is an essential limitation of most thermal indices. thermal equilibrium is an uncommon occurrence for humans outside, nevertheless. because of this, the steady-state method is inadequate [65]. in response, cost action 730 created and released the utci, or universal thermal comfort index, in the summer of 2009 [49]. the dynamic 340-node model developed by fiala [66] is the foundation of the utci, which enables estimations of the thermal status of various body sections. with numerous technologies that simulate the human body's anatomical, thermal, and physiological characteristics, we can now evaluate outdoor thermal comfort to differing degrees of sophistication. nevertheless, we have removed people from their natural environment [48]. we are facing a similar, if not wider, divergence in the outdoor context, much like how studies in climate chambers alienated people from entire buildings, leading to the debate between conventional and adaptive thermal comfort conditions [67] and ultimately to adaptive comfort standards [55]. such a discussion might be crucial when creating public places for sustainable urban settings with wider consequences for climate change [48]. in order to better comprehend the gap between actual and simulated data, we need to go beyond thermal physiology without minimizing the thermoregulatory system's role in obtaining thermal comfort in an outdoor setting. the living person is not a "closed system," as cabanac [68] emphasizes, and behavioral, and other cognitive variables may improve our comprehension of the subject. 2.1.3 surface uhi surface temperatures influence air temperatures indirectly but significantly in the long run. a part of the urban canopy layer influences temperatures at the micro-level. at temperatures ranging from 27 to 50°c (50 to 90°f), surfaces exposed to sunlight, such as concrete or asphalt, can become hotter than the surrounding air, whilst shaded areas maintain similar air temperatures. these warmer floors mainly contribute to night-time urban heating, creating heat and preventing the town from cooling. this type of uhi is present in the weather, particularly solar radiation, and it varies around the planet [69]. additionally, because they cause sun exposure, the micro-scale location and street geometry elements have a significant impact. using a remote sensing approach, the surface uhi data are frequently shown as thermal pictures [70]. 2.1.4 atmospheric uhi another phenomenon is a uhi in the atmosphere, which elevates air temperatures. even slight variation exists between the atmospheric island's intensity and surface temperatures. the average difference in temperature between urban and rural areas is between 1.2 and 4.4 degrees (2 and 8 degrees fahrenheit) [71]. it is the main reason urban regions produce warmer air than rural areas due to the spatial effect of uhi, which is a theoretical notion of uhis. as a result, the uhi phenomenon is primarily determined by its atmospheric presence and is only influenced by surface temperatures [69]. the canopy and borders, components of the planetary limits, make up the two levels of any atmospheric uhi. islands in the canopy layer, where humans reside, may be found in the lowest layer of the atmosphere from the earth to its boundaries [69]. locally, they boost the air's temperature in the streets or small areas. the street canyón, a deep, narrow city street that commonly experiences uhi, is a typical canopy layer occurrence [72]. the leading causes of this form of uhi include evapotranspiration, albedo change, construction materials, and urban planning [2]. islands of constrained strata emerge at the mesoscale and impact whole cities or nearby metropolitan regions. the layer that stretches from the end of the canopy layer to where urban landscapes impact the atmosphere is known as the boundary layer [72]. the actual location is 2 kilometers above the horizon of the majority of nations. essential aspects of uhis include city layout, spatial geometry, wind and weather patterns, and urban energy budgets [2]. 2.2 urban heat island formation to explain processes and ramifications at the national and local levels, we must first understand the urban climate. according to landsberg [4], the urban climate is connected to global climatic changes rather than being a distinct phase. geological circumstances, the troposphere, and the lower layers of the atmosphere all impact it. the synoptic or largem. salmanian and a. bayat /future energy november 2023| volume 02 | issue 04| pages 10-23 16 scale atmosphere regularly interacts with the urban setting and produces a variety of complicated and sluggish weather phenomena. an essential and significant process that regulates emission concentrations is the effect of temperature on wind cycles [73]. climates in rural and urban areas change due to geography and terrain structure. urban terrain is a heavily built, packed, and impermeable surface, whereas rural or agricultural lands are typically differentiated by vegetation, loose soil, and open space. based on this distinction, surface heat islands (shis), the first type of uhis, are created. atmospheric heat islands, the second group of uhis, may be distinguished from shis (ahis) [4]. 2.2.1 urban heat island; urbanization in 1973, oke [74] established the first connection between urbanisation, city size, and uhis. he found a significant association between the population density (p) of 10 north american cities and the difference in urban-rural temperatures (t) using data and models from earlier studies. urbanization and city size to uhi's is found using equation (1) [74]. ∆𝑇𝑢−𝑟(max) = 2.96𝑙𝑜𝑔𝑃 − 6.41 (1) although this model is solely centered on the ideal situation of uhi, the topic of urbanization and uhis was exceptionally helpful. it started a series of studies on the connection between temperature and the metropolis. nearly fifty years later, the causes of uhi training in cities were examined and reported. three critical aspects result from urbanization processes, albeit there is no consensus on their exact causes and actions: 2.2.1.1 the built environment the move from rural to urban has various implications. with this in mind, there are two immediate effects. second, when settlements expand their borders, the natural terrain is transformed into new built-up regions. one of the crucial regulators in surface ecosystems, evapotranspiration processes, is reduced by vegetation and natural soil deterioration [73]. the warmth of the surface of the trees and the plants fell, as did the shade [75]. the contemporary urban surface or materials, which collect heat rather than reflect it, serve as enhanced heat reservoirs. the material's thermal emittance, heat capacity, and albedo cause this. the most important is "albedo, a diminutive of the latin word albus (white). after reflecting off a surface, the amount of radiation or light is transmitted into the atmosphere. the oil's thermal absorption, heat, and albedo bring this on. it is the quantity of radiation or light that the earth emits into space. the latin word albus is where the word "albedos" comes from "(white) and are harsher [9]. 2.2.1.2 the human activity more residents are now affecting the urban landscape as cities become more considerable. an example is excess heat generated on a warm day by average air conditioning. besides, people have waste heat in themselves, which results in higher air temperatures. these causes are called anthropogenic heating [5]. 2.2.1.3 urban geometry urban geometry is another aspect affecting the uhi. the density of the area, measured by the houses' scale and distance, influences the overall temperature, particularly during the night [76]. urban geometry has three influences on the city's climate, according to voogt [77]. first, concentrating solar radiation in areas of the building leads to more excellent absorption of solar radiation. secondly, the sky view factor and radiation depletion are influenced by closely spaced houses. third, population density impacts air-to-surface traffic, which decreases convective heat loss. three aspects are part of urban energy, including the built environment and human interaction. there are specific criteria by which urban geometry interacts with uhi in particular: albedo changes [a]: albedo refers to the overall percentage of solar energy a particular surface reflects [78]. the average reflectiveness time, angle, and spectrum on a specific surface or surface combined is what the word means, which can be interpreted in various ways. in other words, albedo is the capacity of a surface to reflect solar radiation, which makes it an essential component in urban climates. to better comprehend different albedos, table 1 provides some common albedos for various surfaces. we may assume that human surfaces that are dark have lower albedos than surfaces that are bright because dark surfaces receive less sunlight and generate more heat [73]. connor is researching exactly how albedo and urban surface temperatures are related. on the dark-colored surface, he saw that outlying neighborhoods had a higher average temperature. in conclusion, significantly darker materials and surfaces impacted by people result in decreased albedo and heat gain [79]. table 1. examples of albedo's for different surface types [79] solar radiation/ sky view factor: urban geometry frequently influences urban temperatures through solar radiation and the albedo. based on albedo and urban geometry, the sun's energy typically reflects, dissipates, and is absorbed in urban areas [70]. the difference between the two factors is how solar radiation contributes to the impact. brief or visible light, which humans perceive as light, alters albedos. on the other hand, the consequences of urban geometry are susceptible to longwave or infrared radiation. urban topography is essential, but the total solar radiation balance of absorbed heat through albedo adjustment prevails [80]. longwave radiation, usually rereleased at night into the atmosphere, may be contained in urban environments and materials during the day. improving urban texture and the urban response contributes to stronger solar radiation absorption. also, the radiative heat emission at night is disrupted because of the small open space. the urban canyon, a little street flanking significant buildings, is a well-known phenomenon of this dilemma. although the high facilities asphalt 0.05-0.10 concrete 0.10-0.30 forest 0.15 bare soil 0.20-0.30 brick 0.20-0.40 green gra 0.25 white cement 0.78 snow 0.85 m. salmanian and a. bayat /future energy november 2023| volume 02 | issue 04| pages 10-23 17 produce shadows throughout the day, the radiation touching the soil is mirrored and retained in the materials several times. the heat is trapped, and these streets do not cool off at night because of the restricted entry into the open air [81]. the sky view factor frequently reflects the link between urban layout and thermal impacts (svf). the svf is an index representing the sky's visible surface [70]. a low svf, for example, results in street heat capture and the formation of a street canyon. giridharan explored the link between urban temperatures and the svf after demonstrating significant relationships between night-time uhi and viewing variables in hong kong. thus, the svf index is important in uhi because it measures the influence of urban geometry and solar radiation on urban temperatures [82]. anthropogenic heat [qf]: the preceding section defined the heat created by human energy use, primarily by cars and energy use in buildings. this extra heat is thus the outcome of greater human mobility or production behavior. oke [5] expresses the exact idea of anthropic heat as the following formula: 𝑄𝐹 = 𝑄𝐹𝑉 + 𝑄𝐹𝐻 +𝑄𝐹𝑀 (2) the heat produced by automobiles, stationary sources (air conditioning), and metabolism are referred to as qfv, qfh, and qfm. metabolism is the utilization of resources and the cost of the humans in formulation 3. thus, elevated human behaviors lead to higher urban air temperatures in three distinct ways [80]. sensible heat [h]: sensible heat is the heat we experience due to surface-air differences [70]. convection circles form when metropolitan areas heat the air above, removing the further temperature increase. however, population density also reduces convective heat loss. mills [83] and bottema [84] investigated the relationship between a surface-air exchange (or ventilation) and urban density. figure 5 depicts how urban spatial patterns influence surface-air exchanges as a function of urban and raw material density (the standardized area percentage) and z0/h longitude. it teaches us that as a city's built-in density grows, so does its roughness, resulting in less airflow and lower convective heat loss (figure 5). this is accomplished in the urban canopy layer, and the proportion of built-up regions is modified. evapotranspiration [λe]: the movement of moisture from the soil, plants, or trees to the atmosphere is known as evapotranspiration. it includes perspiration from plants and trees and water and solar evaporation. areas are impacted by cooling [70] and assess power to deeper soil layers [85]. moving from rural to urban settings has lessened this opportunity to cool down places. according to bastiaanssen, who has researched evapotranspiration, it is a component of the surface's energy balance and is determined by other factors like soil or responsive heat [h]. this suggests that the system is overly intricate [86]. thermal storage [g]: the usage of ground heat has not received as much research as other factors. in general, decreased solar reflectance in metropolitan locations improves soil heat storage. recent research, however, has indicated that urban layout and certain building materials impact heat storage. in summary, thermal stocking and higher urban temperatures are the only effects attributed to the decreased reflection of urban materials [70]. figure 5. convective heat loss mills [84] 3. urban heat islands impact the most well-acknowledged advantages of uhi mostly pertain to well-being. to maintain and safeguard the environment. national discussions on uhis and their impact have resulted from recent heat waves that killed thousands of people. however, the effects on the water and energy market have recently received increasing attention. although many us communities have dealt with these issues for years, the uhi has introduced new, challenging issues that require sufficient attention. this section will first go through the impacts of uhi on cities and the areas around them, starting with an increase in energy usage. 3.1 energy to keep you comfortable when temperatures rise, more cooling is needed. as a result, suburban neighborhoods and large office buildings use more power and switch to air conditioning and other sources of cold air. a significant factor affecting uhis is the increase in energy use, which also affects a range of other occurrences. energy shortages are generally caused by rising energy usage in the following sectors: 1. energy production and potential shortages. this puts pressure on the electricity generated and provided during the heat wave. in order to maintain good energy sources for the coming decades, power output could thus be improved during warmer periods. emerging technologies will also be introduced, and delivery and distribution will also increase. nevertheless, the energy economy is another approach to this problem. that is one of the most significant issues with air pollution in cities nowadays due to global warming [87]. 2. increased power production, consumption, and carbon emissions from new fossil fuel combustion. the impact on public health and air quality will be discussed in the next section. 3. the increased use of water. metropolitan primary energy sources continue to compress the thermodynamic cycle using much water [2]. 4. humans cause more heat pollution. increase in human activity results in increased heat, known as anthropogenic heat. more anthropogenic heat is produced as a result of primary air cooling. this is a continuous circle since it is one of the causes of uhi. without interference, this influence would merely enhance the overall impact of uhis [8]. 3.2 heat stress the european towns and people's uneasiness during the 2003 heat wave was made evident. the effects were m. salmanian and a. bayat /future energy november 2023| volume 02 | issue 04| pages 10-23 18 considered in france, with minimal adaptation and public awareness. in the summer, 15,000 hospital admissions and fatalities were recorded [89]. the heatwave claimed the lives of over 35,000 people in europe, which sparked several discussions regarding heatwaves, uhis, and their effects at the national and international levels. klinenberg offers a different illustration of how heat waves and uhis might have an impact [90]. heat waves and uhis in cities have severe and significant health effects. urban officials and politicians usually lack awareness of their predicament, which results in inadequate education and an underestimation of the thermal danger. medically speaking, a person is in danger if they have heat stress, a condition in which their core body temperature rises significantly. some symptoms are heat cramps, redness, and health hazards such as heat stroke [91]. as a result, heat waves and exhaustion threaten urban public health. additionally, social and other variables raise the risk of heat stress. for instance, old and socially isolated persons are more vulnerable to heat waves than others. the united states centre for control and prevention of diseases (cdc) has published preventive guidance for personal health and safety on its website on these additional factors. according to the us centers for disease control and prevention (2009), the following are some of the hazards and susceptible groups: 1. elderly people and kids who are not watched by or under control. 2. individuals who are unobserved or uncontrolled and are socially or physically isolated. 3. a lack of preparedness and knowledge. 4. insufficient hydration consumption, irrespective of the amount of activity. 5. increasing heat quickly in cars or other vehicles. 6. outdoor activities that are not regulated or watched as a result, some groups of people and circumstances also exacerbate the hazards associated with metropolitan heat. residents must be informed of the dangers of heat waves to shield themselves from the repercussions. based on the knowledge a person may have access to, this is essentially a responsibility of the individual concerning heat stress [91]. 3.3 air quality uhi has negative impacts on urban air quality, even though they are caused mainly by intense stress on public health. higher temperatures increase energy requirements in urban settings, as this section addresses. increased demand immediately correlates to increased oil output, which has the impact of raising fossil fuel carbon [70]. smog is moreover frequently brought on by high temperatures. according to heat island research group studies, every degree of fahrenheit beyond 70°f. accidents involving smog have increased by 3%. smog and previous pollutants harm the human body, causing low discomfort, severe breathing conditions, and even lung cancer [92]. 3.4 water resources uhi's role in this situation is significant for four reasons: first, a general temperature increase impacts water resources in the area, increasing drought and reducing availability for the metropolis [2]. this deficiency impacts many areas, including public health, industry, climate efficiency, marine habitats, etc. second, heat emission happens when precipitation strikes urban surfaces like buildings and floors. after that, the water temperature is automatically increased. the gross rise may reach 7 degrees fahrenheit when it reaches the sewer. following transit and deposition in the lakes, rivers, and streams, the elevated temperature will impact the existence and habitats of aquatic ecosystems [93]. thirdly, a lack of clean water significantly impacts agricultural productivity, typically consuming 75% of a region's total water supply. with less water available, crops and yield suffer, and agricultural commodities' quality and output decrease. the waterplan should end this and provide plenty of water for both urban and rural areas [94]. fourth, in addition to the biological impacts of water quality, elevated temperatures directly impact the biosphere. especially when natural settings undergo fast changes, natural species and ecosystems cannot adapt, which results in decreased exosomes and a loss of biological diversity. uhis are hazardous to whole ecosystems and animals because they cause a considerable temperature spike over a certain period [89]. 3.5 economics anything used to be expensive. calculating the dynamic evolution and composition of the uhi and its outcomes is more expensive. however, higher carbon dioxide and ozone levels are linked to more illnesses and higher hospital and healthcare costs. furthermore, during periods of harsh weather, production and human activity decrease. for instance, outdoor work is affected by high temperatures and slows down during heat waves, especially building and maintenance. taking corrective and mitigating action is also advantageous for the city [8]. 4. discussion: urban heat islands design strategies adding such theoretical backgrounds gives the basis for uhi adaptation/mitigation. this section aims to conceptualize all potential urban planning and architecture policy initiatives in line with the study design. an outline of proposed potential approaches focused on scientific articles has been made here to accomplish this conceptualization. 4.1 urban forestry the loss of vegetation restricts the process of evapotranspiration and the release of latent heat. as largescale urban expansion patterns develop, this is one of the primary causes of the uhi effect. therefore, conserving present biomass while planting new trees and plants is a clear action. urban forestry increases the amount of evapotranspiration, the number of shadows it casts, and the amount of sunlight that may enter the canopy. kurn et al. [95] and the us environmental protection agency [70] estimated that woods could be up to 5°c [9°f]. suburban neighborhoods containing plants and trees are 2-3°c [4-6°f] cooler than comparable non-green neighborhoods. colder than open regions. other research has also shown how vegetation lowers the urban temperature, including yoshida [96] and nabeshima [97]. 4.2 cool roofs the roof is one of the two main factors influencing the urban albedo. as was covered in the albedo section, it affects the balance between solar energy absorption and reflection. by absorbing sunlight, darker surfaces may heat up to 82 °c (182 °f), which impacts air temperatures. on any given day, m. salmanian and a. bayat /future energy november 2023| volume 02 | issue 04| pages 10-23 19 conventional roofs can be between 55 and 85°f [31-47°c] cooler than the air, according to considerable research on the efficiency of cool roofs by konopacki et al., whereas cold roofs appear to settle at a temperature between 10 and 20°f (611°c) [98]. there are three main categories of cooling-down roofs: single-ply membranes, cool roof coatings, and biomass. the first and second types of cool roofs thus employ unique materials that change the solar radiation budget. the third type of roofing, called "green roofing," combines cool roofing with more unusual urban flora. especially in large building projects and residential neighborhoods, cool and green roofs are extensively employed in the us. 4.3 cool pavement like cool roofs, heated flooring raises temperatures throughout the urban energy budget. figure 6 illustrates a roadway with typical pavement and heating effects. the temperature of the surface is in the range of 140 to 150 °f. the temperature of the road (is 60-65oc). traditional flooring keeps the heating fuel in place, raising the air and surface. permeable floors are only one example of cutting-edge, cooler flooring developed through various research methods. when moisture is present, this flooring enables air, water, and water to move through the floor to avoid cooling [70]. further research on cooling pavements is done by haselbach [99] and mallick [100], concentrating on the various options to reflect solar light as effectively as feasible. figure 6. the temperature of pavements [100] 4.4 green buildings the term "green building" is somewhat ambiguous since it refers to various laws, regulations, standards, and building materials emphasizing long-lasting constructions. as a result, not all of these treatments were specifically designed to adjust to uhis; other events impacted some. however, all green building activities were supervised by the us green building council (usgbc), a nonprofit organization that promotes green buildings globally. the primary endeavor of this organization is the leed, a world certification system. green building solutions may be used in the design, construction, operations, and maintenance with the help of this accreditation [101]. 5. conclusion although there are several recommendations and standards for reducing the urban heat island, each city's circumstance is unique. in order to lessen the severity of the uhi, political decision-makers, legislators, or urban planners must implement several methods addressed in this research. however, the city's well-planned tree-planting initiative is its main tactic for reducing the severity of the uhi. the four rest tactics are impacted by increasing the awareness strategy. without sufficient knowledge of the effects of the outdoor living environment on the enclosed environment and the extent to which it might jeopardise human comfort and health, appropriate levels of comprehension of land management and plant cover, roof cover and new materials, buildings and traffic activity strategies will not be attained. political decision-makers, planners, and architects must put more effort and support into decreasing the uhi and lessening its impacts on the city. the general people must exert fresh and increased pressure on political decisionmakers so that they are forced to accept the necessity of important new national and regional initiatives on urban sustainability without reservation. planning and designing for the uhi of the city requires developing several techniques and rules that guarantee the cities stay vibrant and aesthetically built as planned. the city's sustainable, liveable, beautiful, and prosperous vision may be achieved using climate-responsive design principles. ethical issue the authors are aware of and comply with best practices in publication ethics, specifically concerning authorship (avoidance of guest authorship), dual submission, manipulation of figures, competing interests, and compliance with policies on research ethics. the authors adhere to publication requirements that the submitted work is original and has not been published elsewhere in any language. data availability statement data sharing does not apply to this article as no datasets were generated or analyzed during the current study. conflict of interest the authors declare no potential conflict of interest. references [1] united nations. 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(2011). green building impacts and results. url: https://www.usgbc.org/articles/benefits-greenbuilding. this article is an open-access article distributed under the terms and conditions of the creative commons attribution (cc by) license (https://creativecommons.org/licenses/by/4.0/). n.barua et al. /future energy may 2024| volume 03 | issue 02| pages 01-15 1 article comparative analysis of electrochemical behaviors of lithium-ion batteries using the dual potential msmd battery models: case studies on various thermal conditions nirjhor barua, md. arafat rahman*, md. mamunur roshid department of mechanical engineering, chittagong university of engineering and technology, chittagong-4349, bangladesh a r t i c l e i n f o article history: received 12 may 2023 received in revised form 25 june 2023 accepted 15 july 2023 keywords: electrochemical, simulation, lithium-ion battery, multi-scale-multi-domain model, thermal conditions *corresponding author email address: arafat@cuet.ac.bd doi: 10.55670/fpll.fuen.3.2.1 a b s t r a c t the high energy density and long cycle life of lithium-ion batteries make them a preferred option for electric vehicles. the efficiency and life span of lithiumion batteries are particularly sensitive to temperature; thus, it becomes essential to maintain an ideal temperature range. in this context, we concentrated on two widely used electro-chemistry (equivalent circuit model and ntgk) models of a single cell of a dual potential msmd lithium-ion battery while taking into account two significant methods of heat transfer under varying c-rates (0.25c, 1c, 2c, and 5c). we investigated the highest temperatures that two e-chemistry models could reach in varying ambient temperatures (typical summer, winter, and room temperature). the maximum temperature-raising tendency in the ecm due to natural convection is greater than the maximum temperature-raising tendency due to radiation regardless of the environmental temperatures and various c rates (0.25c, 1c, and 2c). however, the trend line of the maximum temperature rise is different in the ntgk model, where the maximum temperature rise due to radiation is greater than the maximum temperature rise due to convection for 0.25c, 1c, and 2c rates in -5°c and 40°c environmental temperatures. in the ntgk model, at 0.25c, 1c, and 2c rates for winter and summer temperatures, the maximum temperature rise owing to radiation is larger than that due to convection. the ntgk model, however, produced somewhat superior findings for the radiation mode of heat transfer at ambient temperature. therefore, it can be said that convection is a better thermal condition than natural convection in the ntgk model. 1. introduction consumers are familiar with lithium-ion batteries after a great deal of research and use. it is commonly used in electrical items and electric cars. in recent years, a potential market for electric urban vehicles has formed, with competitive series among mobile device manufacturers. a special focus is being paid to developments in highperformance lithium-ion batteries (such as a high level of energy density, high open circuit voltage, and minimal selfdischarge). despite the widespread use of lithium-ion batteries in portable and small electronic devices, there are still some important issues that need to be resolved before practical applications of electrical vehicles (evs), hybrid electrical vehicles (hevs), and microgrids with significant energy storage capacity can be taken into account. heat control and management are the most critical concerns in lithium-ion batteries, as excessive temperatures reduce charge/discharge efficiency and battery life and can potentially pose a safety risk. the significant temperature increase that occurs during the charging and discharging of hevs and evs is the main cause for worry in the heat regulation of lithium-ion batteries (libs) since it may result in thermal runaway. understanding lithium-ion battery discharge behavior is crucial for the thermal management of libs in hybrid electric vehicles and electric vehicles [1]. although a lot of research work has been conducted in recent years to enhance the thermal management of li-ion batteries; however, relatively few have been devoted to the future energy open access journal https://doi.org/10.55670/fpll.fuen.3.2.1 may 2024| volume 03 | issue 02 | pages 01-15 journal homepage: https://fupubco.com/fuen issn 2832-0328 mailto:arafat@cuet.ac.bd https://doi.org/10.55670/fpll.fuen.3.2.1 https://fupubco.com/fuen n.barua et al. /future energy may 2024| volume 03 | issue 02| pages 01-15 2 investigation of the discharge behavior of lithium-ion batteries using ansys fluent. in common parlance, there is a relationship between battery temperature variation and electric efficiency. however, to make battery modeling simpler, it is frequently done by using a one-dimensional mass transfer model, which may work at least for cells with parallel plate electrodes. chen and evans suggested that due to the anisotropic thermal characteristics of a stack of many cells, a two -or three-dimensional model (of heat transmission) is required for battery thermal modeling and established a mathematical model to analyze the thermophysical properties of libs and lpbs (lithium polymer batteries) [2]. the purpose of thermal management was to analyze how factors in battery design and working conditions affect the temperature rise and profile and to assess the risk of thermal lag. the modeling results showed that under typical battery operation, battery temperatures were unlikely to reach the temperature that triggers thermal runaway, while during high-rate discharge (for example, during the relatively brief period of intense power extraction from a battery), heat may not be transferred out of a large cell stack. localized heating may raise battery temperature to the thermal runaway onset temperature within one minute, according to research on heat transfer in the presence of extremely focused heat sources caused by battery abuse (such as short circuits). a battery modeling at a constant environmental temperature of 25°c only, which was based on the localized heat production approach, considering a manganese oxide spinel/carbon cell using a 2d-coupled thermal-electrochemical technique, has been reported [3, 4]. the matrix and solution phases of the model include reversible, irreversible, and ohmic heat. most of the research works focused only on the convection mode of heat transfer for a better thermal management system of a lithium-ion battery [5-7]. van et al. [8] analyzed the effects of forced convection in the thermal management system. however, very few studies were carried out concerning radiation as the primary thermal condition. hatchard et al. suggested that radiation may be responsible for up to 50% of the heat that a li-ion cell releases into the environment at oven exposure conditions. the label is usually the outermost surface of the cell, and its emissivity determines how well heat is transferred by radiation [9]. in this present study, we focused on two commonly used electro-chemistry (ecm and ntgk ) models of a single cell of a dual potential msmd lithium-ion battery considering two dominant methods of heat transfer under various c-rates. we compared the maximum temperatures achieved by two e-chemistry models under different environmental temperatures (winter, room temperature, and summer). we compared the simulation results to explore which e-chemistry model performs better in thermal management systems under various environmental temperatures. 2. model development in this study, ansys fluent (version 2023 ansys-r1) software was used to perform the computational fluid dynamic (cfd) analysis, which makes use of the finite-volume approach to separate the physics equations by figuring out the mathematical equations of the fluids. the combined heat transmission nodal points, which include two dominant heat transfer methods, including convection and radiation, are modeled using mathematical formulas. ansys commonly uses the following models to predict the behavior of chemical, thermal, and electrical processes in a battery: • empirical battery model with single potential • multi-scale multi-domain dual-potential battery model (msmd) 2.1 single-potential empirical battery model this model is based on investigations that have been performed by [10] and [11]. the integral form of the electric potential equation is as follows: ∫ ∇. (σ∇ϕ) v dv = ∫ jda a (1) the term "a" stands for apparent current density, "j" for local interface area, and "ϭ" for electrical conductivity. for the single potential empirical battery model (spebm) the mathematical equations are used according to [10] and [11]: j = y(ϕc ϕα u) (2) here, (ϕc − ϕα) is the difference between the cathode and anode side electric potentials at the separator interface, and y and u are gu’s parameters. the single-potential empirical battery model (spebm) is limited in its capacity to study a wide range of electrochemical events in battery systems, especially those with complex geometries. 2.2 multi-scale multi-domain (msmd) dual-potential battery model by effectively linking the physics of batteries, battery discharge, safety, and thermal management, the multi-scale multi-domain (msmd) battery model, sometimes referred to as the "multi-scale multi-domain" battery model, is used to study the discharge of lithium-ion batteries. the ansys fluent dual potential multiscale multi-dimensional battery model (msmd) addresses various physics in many solution domains by using a homogenous model related to a multiscale multidimensional method to resolve these constraints. it is important to note that the msmd method uses three different electrochemical submodels, which are as follows: • the newman, tiedemann, gu, and kim (ntgk) model. • equivalent circuit model (ecm). • newman's pseudo-2d (newman's p2d) model. in this study, equivalent circuit model (ecm) and the newman, tiedemann, gu, and kim (ntgk) models are discussed considering various c-rates, states of charge, and depth of charge. the ecm model, which works with batteries of all types, not only li-ion batteries, is both affordable and highly adaptable. using a 2d table that plots each parameter against the temperature and soc. notably, this is the only form where the impact of temperature is taken into account explicitly. in charge/discharge cycles when the electric load doesn't exhibit any sudden fluctuations, the ntgk model is satisfactory. additionally, some models, such as the ecm, will be more accurate if the electric load changes quickly since they neglect the inertial variations. however, the pseudo-2d model, created by newman's team utilizing a porous electrode and concentrated solution theory, is a physicsbased model that accurately simulates the transit of lithium ions in a battery [12]. although newman's pseudo-2d model is the most popular electrochemistry model, it is computationally more expensive than the other two en.barua et al. /future energy may 2024| volume 03 | issue 02| pages 01-15 3 chemistry models [12]. so, for computational simplicity, only ecm and ntgk models are discussed in this study. the multiscale multidomain (msmd) technique is useful for assessing various physical parameters in several solution domains. based on the conservation of charge during discharge, the poisson equations are as follows: ∇.(σ+∇ϕ+)ǀ ω+ = -j (3) ∇.(σ-∇ϕ-)ǀω= +j (4) here, the effective electrical conductivities of the positive and negative electrodes are σ+ and σ–, the phase potentials of the positive and negative electrodes are ϕ+ and ϕ –, the transfer rate of the volumetric current, calculated using an electrochemical submodel, is j (a/m3), and the domains of the positive and negative electrodes are ω+ and ω–, respectively. the functional form is determined by the electrode polarisation curve. h. gu and huo et al. found that j varies linearly with cell voltage [11] and [13]. the ntgk model was suggested by kwon et al. [14]: j = αy[u (ϕ+ ϕ-)] (5) where, α is the specific area m2 /m3 of the electrode sandwich sheet in the battery cell, while u and y are the empirical fitting parameters. the following u and y functions were proposed by huo et al. [13]. 𝑈 = ao + a1(dod) + a2(dod)2 + a3(dod)3 + a4(dod)4 + a5(dod)5 (6) 𝑌 = bo + b1(dod) + b2(dod)2 + b3(dod)3 + b4(dod)4 + b5(dod)5 (7) where, the coefficients ai and bi (i = 0, . . . 5) are constants to be calculated experimentally. the fitting parameters used to determine the potential and current density distributions on the electrodes during discharge are shown in table 1. table 1. the fitting parameters were used in the ntgk model parameter constant value a0 4.3104 a1 -1.9184 u a2 2.8835 a3 -6.8305 a4 -9.7601 a5 -4.8786 b0 879.2 b1 -4606.2 y b2 -23,007.5 b3 -86,540.6 b4 101,993.2 b5 -44,914.4 according to van-thanh et al. [8], the nominal capacity multiplied by the c rate equaled the discharging current, and the discharge rate dictated how long a battery could operate. the lower the discharge rate, the longer the battery could operate. the maximum temperature was outside the manufacturer's working range at discharge conditions greater than 3c. yi et al. [15] discovered that the ambient temperature is extremely sensitive during this sort of experiment. because of the electron transfer during electrochemical processes, a substantial amount of heat is created in the li-ion battery at a high discharge rate. the liion battery's heat generation q (w) is separated into three parts: reaction heat qr (w) polarisation heat qp (w), and joule heat qj (w) [13]. the volumetric heat source in the battery cell can be expressed as irreversible heat from the internal resistance of the cell j[voc (ϕ+ ϕ-)] and reversible heat from the electrochemical reaction inside the cell –jt 𝑑𝑉oc 𝑑𝑇 . moreover, the heat produced by the resistance of the current collecting tab and the electrical contact between it and the lead wire is included, however, the heat produced by the resistance of the electrical contact between it and the lead wire is excluded. the entire amount of heat generated can be expressed as the equation given by van-thanh et al. [8]: q = j[ voc(ϕ+ ϕ-) -t dvoc dt ] + σ + v2 ϕ + σ -v2 ϕ – (8) where, voc is the open-circuit potential of the cell (v), and t is the working temperature of the battery. we have considered two different dominant thermal conditions (convection and radiation) to study the cases of different discharge rates. according to newton's law of cooling, the quantity of heat dissipated owing to the movement of a fluid (air) can be calculated using the following equation. qa= ha(tb-ta) (9) where tb is the battery temperature, ta is the ambient temperature and ha is the coefficient of air convective heat transfer coefficient of air, which is 5 w/𝑚2𝑘 in this present study. in this study, we illustrated the effect of radiation heat transfer in the thermal management system for both electrochemistry models (ntgk and ecm). hence, we have considered the radiation emissivity of the battery cell to the maximum possible (ε = 1). the heat dissipation of a single cell of a lithium-ion battery can be calculated by the equations used by hatchard et al. [9]. pr(t) = aσε(t4-tw 4) (10) where pr(t) is radiation power in j/s as a function of temperature, a is the surface area, tw is the temperature of the surrounding (assumed to be a black body), and ε is the emissivity of the surface. emissivity (ε) is a dimensionless quantity between 0 and 1. it represents the fraction of blackbody radiation that the surface in question emits (a black body by definition has ε = 1), σ is the stefan-boltzmann constant (5.669 x 10-12 w/(cm2 k)). for values of t near tw, eq (10) can be expanded in a taylor series: 𝑃(𝑇) = 4𝐴𝜎𝜀𝑇𝑊 3 ∆𝑇 + 6𝐴𝜎𝜀𝑇𝑊 2 ∆𝑇2 + 4𝐴𝜎𝜀𝑇𝑊∆𝑇3 + 𝐴𝜎𝜀∆ (11) here, ∆t is the temperature difference between the surface and the surroundings and if ∆t= tw-t, rearranging eq (11) gives 𝑃(𝑇) 𝐴∆𝑇 = 4𝜎𝜀𝑇𝑤 3 + 6𝜎𝜀𝑇𝑤 2∆𝑇 + 4𝜎𝜀𝑇𝑤∆𝑇2 + 𝜎𝜀∆𝑇3 (12) eliakim and karmeli put out an accurate, acceptable, and comprehensive electrical battery model [16]. figure 1 shows the electrical battery model that was used in the equivalent n.barua et al. /future energy may 2024| volume 03 | issue 02| pages 01-15 4 circuit model. the six-parameter ecm model has been adopted by ansys [1]. figure 1. the electrical battery model is used in the ecm model [1] where, rseries=rs, rtransient_ s=ri, rtransient_ l=r2. the voltage-current relationship can be obtained by solving the following mathematical formulas of electrical circuits used by madani et al. [1] and m. chen et al. [16]: 𝑉(𝑡) = vocv(soc) + v1 + v2 + r2(soc)i(t) (13) dv1 dt = − 1 r1(soc)c1(soc) v1 − 1 c1(soc) i(t) (14) dv2 dt = − 1 r2(soc)c2(soc) v2 − 1 c2(soc) i(t) (15) d(soc) dt = − i(t) 3600qah (16) the open-circuit voltage, resistor resistances, and capacitor capacitances are dependent on the state of charge of the battery for a specific battery (soc). these two dependents can be illustrated in various procedures in ansys as the following set of equations used by [1] and [16]: rs = ao + a1(soc) + a2(soc)2 + a3(soc)3 + a4(soc)4 + a5(soc)5 (17) r1 = bo + b1(soc) + b2(soc)2 + b3(soc)3 + b4(soc)4 + b5(soc)5 (18) c1 = co + c1(soc) + c2(soc)2 + c3(soc)3 + c4(soc)4 + c5(soc)5 (19) r2 = do + d1(soc) + d2(soc)2 + d3(soc)3 + d4(soc)4 + d5(soc)5 (20) c2 = eo + e1(soc) + e2(soc)2 + e3(soc)3 + e4(soc)4 + e5(soc)5 (21) vocs = fo + f1(soc) + f2(soc)2 + f3(soc)3 + f4(soc)4 + f5(soc)5 (22) chen's function is represented by the following set of equations [16] : rs = a0exp[a1(soc)] + a2 (23) r1 = b0exp[b1(soc)] + b2 (24) c1 = c0exp[c1(soc)] + c2 (25) r2 = d0exp[d1(soc)] + d2 (26) c2 = e0exp[e1(soc)] + e2 (27) vocv = f0exp[f1(soc)] + f2 (28) the source terms for the aforementioned equations are calculated as the following [1] : jech = i/vol (29) 𝑞𝐸𝐶ℎ̇ = i vol [vocv − (ϕ+ − ϕ−) − t du dt ] (30) where, vol=the battery volume, i= current, vocv= the open circuit voltage, and ϕ+& ϕ−are phase potentials. 2.2.1 physical modeling a single lithium-ion battery cell has been modeled using ansys design moduler. a three-dimensional rectangular-shaped battery cell is designed. figure 2. dimensions of a single-cell li-ion battery in figure 2, the geometry and dimensions of the single cell of the msmd dual potential lithium-ion battery are illustrated. all the units are taken as millimeters. the thickness of the cell is taken as 2mm. the geometry properties of the simulation are given in table 2. table 2. geometrical properties of the experiment 2.2.2 mesh generation to assure the accuracy of transient simulations, grid number is crucial. mesh details of the experiment are given in table 3. 2.2.3 material selection there are mainly two types of material defined in the msmd battery model. they are fluid and solid materials. the fluid material is defined as ‘air’ and the solid material is defined with three different materials. the active cell zone is details of body body fff/solid volume 5.568e-05 m3 surface area 0.057028 m2 faces 6 edges 12 verticles 8 fluid/solid solid shared topology method automatic geometry type workbench n.barua et al. /future energy may 2024| volume 03 | issue 02| pages 01-15 5 defined as lithium hexafluorophosphate. the positive electrode is defined as aluminum and the negative electrode is defined as copper. the material properties are provided in tables 4-7. table 3. details of the mesh of the experiment element order linear element size 1.e-003m growth rate default by ansys (1.2) average surface area 3.6582e-003 m3 maximum layers 5 inflation algorithm pre-executive mesh metric skewness nodes 97230 elements 63780 table 4. active cell zone material properties (lithium hexafluorophosphate) material name lithium hexafluorophosphate density 1500 kg/m3 specific heat coefficient 871 j/(kg k) electrical conductivity 1e+07 s/m table 5. positive electrode material properties (aluminium) material name aluminium density 2092 kg/m3 specific heat coefficient 871 j/(kg k) electrical conductivity 3.541e+07 s/m table 6. negative electrode material properties (copper) material name copper density 8978 kg/m3 specific heat coefficient 381 j/(kg k) electrical conductivity 1e+07 s/m table 7. surrounding fluid properties (air) material name air density 1.225 kg/m3 specific heat coefficient 1006.43 j/(kg k) electrical conductivity defined per uds s/m viscosity 1.7894e-05 3. results and discussion to analyze the results two dominant thermal conditions (convection, and radiation) have been considered, and the two most common electrochemical models ( ecm and ntgk) are used. we have varied the c rates(0.25c, 1c, 2c, and 5c ) to analyze the thermal conditions of a single cell of the msmd dual potential lithium-ion battery. in the case of convection, certain boundary conditions are also taken into account. the temperature of the free stream temperature (-5°c, 27°c, and 40°c) is varied considering different temperature conditions according to the average temperature of the winter and summer seasons of bangladesh. the heat transfer coefficient is taken as 5 w/𝑚2𝑘 for each case of the free stream temperature. the initial heat generation rate is considered to be 0 w/m3. for radiation, we have considered the same temperatures for external radiation (-5°c, 27°c, and 40°c). we have considered the entire outer surface of the single cell of the lithium-ion battery as a black body and therefore took the maximum emissivity of the surface (ε=1). the same thermal conditions are implemented in both ecm and ntgk models, and then we carried out our simulations for 1000 iterations and 1500 seconds flow time. the lowest stop voltage and the highest stop voltage are considered as 3v and 4.3v respectively, and the nominal capacity of the battery cell is considered as 14.6 ah. 3.1 equivalent circuit model 3.1.1 thermal condition: convection typically, heat generation within the libs occurs at normal temperatures as a result of charge transfer and chemical processes during charging and discharging [17, 18]. the total heat generation of battery discharge consists mainly of electrochemical reaction heat, ohmic heat, and active polarization heat. during the battery's discharge, these temperatures are generated in the positive electrode, electrolyte, and negative electrode. the three types of heatgenerating sources mentioned above vary in cell space. lithium extraction and intercalation occur during the discharge electrochemical process at the anode/electrolyte and cathode/electrolyte interfaces, respectively. lithium extraction heat and lithium intercalation heat are two different components of the electrochemical process heat. similarly to this, the terms for lithium extraction and intercalation make up the active polarization heat. the anode and cathode electron-conduction resistance as well as the ionconduction resistance contribute to the ohmic heat [17]. to understand the thermal behavior and overall heat generation resulting from the aforementioned sources, we explored the ecm e-chemistry model based on different boundary conditions (convection and radiation) considering different environmental temperatures. contours of total static temperatures in the whole cell of the dual potential msmd liion battery are shown in figure 3, figure 4, and figure 5 considering the boundary conditions as convection for various environmental temperatures of 268k, 300k, and 313k respectively. the nominal capacity multiplied by the c rate gave the discharging current its value. the discharge rate of a battery determines its working time, so the greater the discharge rate, the longer the battery's operating period will be. n.barua et al. /future energy may 2024| volume 03 | issue 02| pages 01-15 6 in figure 3, temperature variations are shown in a single cell of dual potential msmd li-ion battery with various crates (0.25c, 1c, 2c, and 5c ) with equivalent circuit model. natural convection is considered in the boundary condition. the free stream temperature is taken as 268k (typical winter temperature in asia). in figure 3(a), for the 0.25 c rate, the minimum temperature is 268.6371 k, and the maximum temperature is 268.6637 k, which shows a very slight increase from the environmental temperature (268k). in figures 3(b), 3(c), and 3(d), the c-rate was varied from 1 c, 2 c, and 5 c, and the maximum temperature was obtained 275.0931 k, 295.6211 k, and 402.9109 k respectively. as we can see for increased c-rates, the maximum temperatures are increased rapidly. for 1 c, the maximum temperature increased by only 2.64%, while for the 2 c rate the battery cell showed a significant temperature rise of 10.30% from the figure 3. temperature variation in a single cell of dual potential msmd li-ion battery with various c-rates with equivalent circuit model considering free stream temperature of 268k: a) for 0.25c-rate, b) for 1c-rate, c) for 2c-rate, and d) for 5rate figure 4. temperature variation in a single cell of a dual-potential msmd li-ion battery with various c rates with an equivalent circuit model considering free stream temperature of 300k: a) for 0.25c-rate, b) for the 1c rate, c) for the 2c rate and d) for the 5rate n.barua et al. /future energy may 2024| volume 03 | issue 02| pages 01-15 7 ambient temperature, and for the 5 c rate, the temperature rose drastically by 50.339% from the ambient temperature. the simulation ended after 570s for 5 c-rate because the maximum temperature at the 5 c rate was above the designated operating range. in figure 4, temperature variations are shown in a single cell of dual potential msmd li-ion battery with various crates(0.25c, 1c, 2c, and 5c ) with equivalent circuit model considering natural convection as the boundary condition, and the free stream temperature is taken as 300k (room temperature in asia). just like in figure 3, the temperature variations show a similar pattern in figure 4. in figures 4(a), 4(b), 4(c), and 4(d), the maximum temperatures for 0.25c, 1c, 2c, and 5c rates are 300.4373 k, 306.8669 k, 327.3949 k, and 430.1342 k respectively. for 0.25 c, the maximum temperature is slightly increased, while for 1c, 2c, and 5c rates the maximum temperature rose to 2.28%, 9.13%, and 43.37% from the ambient temperature. in figure 5, temperature variations are shown in a single cell of dual potential msmd li-ion battery with various c-rates(0.25c, 1c, 2c, and 5c ) with equivalent circuit model considering natural convection as the boundary condition, and the free stream temperature is taken as 313k (typical summer temperature in asia). just like in figure 3 and figure 4, the temperature variations show a similar pattern in figure 5. in figures 5(a), 5(b), 5(c), and 5(d), the maximum temperatures for the 0.25c, 1c, 2c, and 5c rates are 313.3455k, 319.775k, 340.303k, 441.1937 k, respectively. for 0.25 c, the maximum temperature is just slightly increased from the environmental temperature, while for 1c, 2c, and 5c rates the maximum temperature rose 2.258%, 8.723%, and 40.96% respectively from the ambient temperature. in figures (3-5), it is seen that for higher environmental temperatures the maximum temperature increase rate is lowered in each c-rates for convective boundary conditions. this is because the ambient temperature has significant effects on the electrolyte property in the li-ion battery [19]. however, the maximum temperatures for each c rate tend to rise higher with an increase in environmental temperatures. in each case, the maximum temperature is obtained in the active cell zone regardless of the c-rates and environmental temperature. 3.1.2 thermal condition: radiation the configuration of the cell's surface has a significant impact on how much heat is released by radiation. the label is usually the cell's exterior surface, and its emissivity determines how well heat is transferred via radiation. li-ion battery cells with the largest thermal endurance will result from choosing labels with the highest possible emissivity (ε = 1) [9]. therefore, in this study, we have considered the maximum possible external thermal emissivity (ε = 1) for each case. we have considered the initial heat generation rate to be 0 w/m3. contours of total static temperatures in the whole cell of the dual potential msmd li-ion battery are shown in figure 3, figure 4, and figure 5 considering the boundary conditions as radiation for various external radiation temperatures of 268k, 300k, and 313k, respectively. in figure 6, temperature variations are shown in a single cell of dual potential msmd li-ion battery with various c-rates (0.25c, 1c, 2c, and 5c ) with equivalent circuit model. radiation is considered in the boundary condition. figure 5. temperature variation in a single cell of dual potential msmd li-ion battery with various c-rates with equivalent circuit model considering free stream temperature of 313k: a) for 0.25c-rate, b) for 1c-rate, c) for 2c-rate and d) for 5rate n.barua et al. /future energy may 2024| volume 03 | issue 02| pages 01-15 8 the external radiation temperature is taken as 268 k (typical winter temperature in asia). in figure 6(a), for 0.25 c rate and maximum temperature is 268.8422k. which shows a very slight increase from the environmental temperature(268k). in figures 6(b), 6(c), and 6(d), the c-rate was varied from 1 c, 2 c, and 5 c, and the maximum temperature was obtained 275.7793k, 295.33k, and 371.8228k respectively. for the 1c rate, then the maximum temperature of the single li-ion battery cell increased up to 2.90% from the environmental temperature. the maximum temperature considerably rose with greater c rates. for the 2 c rate, the maximum temperature rose by 10.19% and for the 5c rate, the maximum temperature increased rapidly to 38.73% from the ambient temperature. while taking the heat transfer mode as radiation, the maximum temperature exceeded the designated working range for 5 c, and the simulation stop conditions arrived after 570s just like the previously discussed convective boundary conditions. in figure 7, temperature variations are shown in a single cell of a dual potential msmd li-ion battery with various c rates (0.25c, 1c, 2c, and 5c ) with the equivalent circuit model considering radiation as the heat transfer mode. the external radiation temperature is taken as 300 k (room temperature in typical asia). figure 7(a) shows that the maximum temperature obtained for the 0.25 c rate is 300.3606 k, which is almost the same as the environmental temperature. from figures 7(b), 7(c), and 7(d) we can see that for higher c-rates higher temperatures are obtained. for 1c, 2c, and 5c the maximum temperatures are found as 305.5259k, 320.6266k, and 386.0818k respectively. at 1c rate, the maximum temperature increased by only 1.84%. for higher c rates, the maximum temperature rose rapidly. for 2c and 5c rates, the maximum temperature increased up to 6.87% and 28.69% from the ambient temperature, respectively. in figure 8, temperature variations are shown in a single cell of a dual-potential msmd li-ion battery with various c-rates (0.25c, 1c, 2c, and 5c) with an equivalent circuit model considering radiation as heat transfer mode. the external radiation temperature is taken as 313 k (typical summer temperature in asia). figure 8(a) shows that the maximum temperature obtained for the 0.25 c rate is 313.0591k, which is almost the same as the environmental temperature. from figures 8(b), 8(c), and 8(d) we can see that, for 1c, 2c, and 3c the maximum temperature is 314.2582k, 317.8055k, and 419.8545k. it indicates that for 1c, 2c, and 5c the maximum temperature increased by up to 0.40%, 1.535%, and 34.13% from the ambient temperature, respectively. in the aforementioned figures 6-8, increasing the environmental temperatures, the maximum temperature increase rate is decreased in each c-rates for radiative boundary conditions, which shows a similar trend discussed in figures 3-5. however, the maximum temperatures for each c rate tend to rise higher with an increase in environmental temperatures. in each case, the maximum temperature is obtained in the active cell zone regardless of the c-rates and environmental temperatures. 3.2 ntgk model 3.2.1 thermal condition: convection to comprehend the physics underlying the complicated nature of lithium-ion batteries, electrothermal models are crucial. in this study, we focus on two commonly used electronic chemistry models to analyze the results comparatively. in figures 9, 10, and 11, we discussed the maximum temperatures obtained by the single cell of an msmd dual potential li-ion battery considering the boundary conditions as natural convection. we varied the environmental temperature (free stream temperature) to explore the thermal behavior of li-ion batteries in different situations. figure 6. temperature variation in a single cell of dual potential msmd li-ion battery with various c-rates with equivalent circuit model considering external radiation temperature of temperature of 268k: a) for 0.25c-rate, b) for 1c-rate, c) for 2c-rate and d) for 5rate n.barua et al. /future energy may 2024| volume 03 | issue 02| pages 01-15 9 contours of total static temperatures in the whole cell of the dual potential msmd li-ion battery are shown in figure 9, figure 10, and figure 11 considering the boundary conditions as convection for various environmental temperatures of 268k, 300k, and 313k, respectively. the nominal capacity multiplied by the c rate gave the discharging current its value, just as same as in the previously discussed ecm e-chemistry model. the discharge rate of a battery determines its working time, so the greater the discharge rate, the longer the battery's operating period will be [6]. in figure 9, temperature variation in a single cell of a dual potential msmd li-ion battery is shown with the ntgk electrochemistry model for various c rates while the boundary conditions are taken as natural convection. the environmental temperature is considered 268 k (typical winter temperature in asia). figures 9(a), 9(b), 9(c) and 9(d) represent the temperature variations in the battery cell for 0.25c, 1c, 2c, and 5c rates, respectively. it is seen that for the 0.25c rate, the maximum temperature increased to 268.4804k, which is slightly higher than the ambient figure 7. variation of temperature in a single cell of a dual-potential msmd li-ion battery with various c rates with an equivalent circuit model considering an external radiation temperature of 300 k: a) for 0.25c-rate, b) for the 1c rate, c) for the 2c rate and d) for the 5rate figure 8. variation in temperature in a single cell of dual potential msmd li-ion battery with various c-rates with equivalent circuit model considering the external radiation temperature of 313 k: a) for 0.25c-rate, b) for the 1c rate, c) for the 2c rate and d) for the 5rate n.barua et al. /future energy may 2024| volume 03 | issue 02| pages 01-15 10 temperature. for 1c, 2c, and 5c rates, the maximum temperatures were 272.3053 k, 281.8218 k, and 439.7356 k, respectively. for 1c, the maximum temperature increased only 1.60% from the environmental temperature, while for higher c rates, it increased rapidly. for 2c and 5c rates, the maximum temperatures increased up to 5.15% and 64.08% respectively. it shows that, in the ntgk model, the maximum temperature increase rate rapidly increases with higher c rates. for the 5 c rate, the battery simulation stop condition arrived after 570 s. in figure 10, temperature variations are shown in a single cell of the dual-potential msmd li-ion battery with various crates(0.25c, 1c, 2c, and 5c ) with the ntgk model considering natural convection as the boundary condition and the temperature of the free stream is taken as 300k (room temperature in asia). in figure 10(a), it is shown that the maximum temperature increased by 300.1283k, which is almost the same as the environmental temperature. figure 9. variation in temperature in a single cell of a dual potential msmd li-ion battery with various c rates with the ntgk model considering the free flow temperature of 268 k: a) for 0.25c-rate, b) for the 1c rate, c) for the 2c rate, and d) for the 5rate figure 10. variation of temperature in a single cell of a dual-potential msmd li-ion battery with various c rates with the ntgk model considering the free stream temperature of 300 k: a) for 0.25c-rate, b) for the 1c rate, c) for the 2c rate, and d) for the 5-rate n.barua et al. /future energy may 2024| volume 03 | issue 02| pages 01-15 11 from figures 10 (b), 10 (c), and 10(d) we see that the maximum temperatures obtained for 1c, 2c, and 5c were 302.19k, 308.111k, and 431.601k respectively. for 1c, 2c, and 5c rates the maximum temperatures increased up to 0.73%, 2.70%, and 43.86% respectively from the environmental temperatures. in figure 11, temperature variations are shown in a single cell of dual potential msmd li-ion battery with various c-rates (0.25c, 1c, 2c, and 5c ) with ntgk model considering natural convection as the boundary condition, and the free stream temperature is taken as 313k (typical summer temperature in asia). the temperature variations show a similar pattern in figure 11 just like in figures 9 and 10. in figures 11(a), 11(b), 11(c), and 11(d), the maximum temperatures for 0.25c, 1c, 2c, and 5c rates are 313.0101 k, 314.6604 k, 319.5787 k, and 429.6515 k respectively. for 0.25 c, the maximum temperature is just slightly increased from the environmental temperature, while for 1c, 2c, and 5c rates the maximum temperature rose 0.53%, 2.101%, and 37.26% respectively from the ambient temperature. figure 11 also showed a similar trend to the previous analysis where the maximum temperature increase rate decreased with the increase of the environmental temperatures. however, the maximum temperature always increased with the increase of c rates. 3.2.2 thermal condition: radiation we considered the maximum possible external thermal emissivity (ε = 1) for each case in the ntgk model, just like the model of the equivalent circuit previously discussed. we considered the initial heat generation rate to be 0 w/m3. figures 12, 13, and 14 depict contours of total static temperatures across the dual potential msmd li-ion battery's whole cell where boundary conditions are regarded as radiation for varying external radiation temperatures of 268k, 300k, and 313k, respectively. in figure 12, temperature variations are shown in a single cell of dual potential msmd li-ion battery with various c-rates (0.25c, 1c, 2c, and 5c ) with ntgk model. radiation is considered in the boundary condition. the external radiation temperature is taken as 268 k (typical winter temperature in asia). in figure 12(a), the 0.25 c rate and the maximum temperature are 268.8422k which shows a very slight increase from the environmental temperature (268k). in figures 12 (b), 12 (c), and 12(d), the c-rate was varied from 1 c, 2 c, and 5 c, and the maximum temperature was obtained 275.7793 k, 295.33 k, and 371.8228 k, respectively. for the 1c rate, the maximum temperature of the single li-ion battery cell increased up to 2.90% from the environmental temperature. for higher c rates, the maximum temperature increased significantly. for the 2 c rate, the maximum temperature rose by 10.19% and for the 5c rate, the maximum temperature increased rapidly to 38.73% from the ambient temperature. while taking the heat transfer mode as radiation, at 5 c rate the maximum temperature was outside the specified operating range, and the simulation stop conditions arrived after 570s just like the previously discussed convective boundary conditions. in figure 13, the external radiation temperature is taken as 300k (room temperature in typical asia), and temperature variations in a single cell of msmd dual potential li-ion battery are shown. in figure 13(a), the maximum temperature for the 0.25c rate is 300.1069k, which is only slightly higher than the environmental temperature. the maximum temperature increased rapidly with higher c rates. in the aforementioned figures 13(b), 13(c), and 13(d) for 1c, 2c, and 5c the maximum temperature obtained was 301.8011k, 306.5999k, and 421.5734 k, respectively. for 1c, 2c, and 5c the maximum temperature increased to 0.60%, 2.199%, and 40.52% respectively. figure 11. variation in temperature in a single cell of dual potential msmd li-ion battery with various c-rates with the ntgk model considering the free-flow temperature of 313k: a) for 0.25c-rate, b) for 1c rate, c) for 2c rate and d) for 5rate n.barua et al. /future energy may 2024| volume 03 | issue 02| pages 01-15 12 for the 5c rate at room temperature, the temperature in the battery cell increased drastically which indicates the battery conditions were outside the specified operating range. as the battery geometry was quite low and comparatively a large amount of current discharging conditions was provided, the battery simulation stop condition arrived and indicated a thermal runaway. in figure 14, the external radiation temperature is taken as 313k (typical summer temperature in asia), and temperature variations in a single cell of msmd dual potential li-ion battery are shown. in the aforementioned figure 14 (a), the maximum temperature for the 0.25c rate is 313.3035k, which is only slightly higher than the environmental temperature. for higher c rates, the maximum temperature increased rapidly. in the aforementioned figures 14 (b), 14 (c), and 14(d) for 1c, 2c, and 5c the maximum temperature obtained was 317.8952k, 331.4985 k, and 392.7853k respectively. for 1c, 2c, and 5c the maximum temperature increased by up to 1.56%, 5.9%, and 25.49% respectively. figure 12. variation in temperature in a single cell of dual potential msmd li-ion battery with various c-rates with the ntgk model considering an external radiation temperature of 268 k: a) for 0.25c-rate, b) for 1c rate, c) for 2c rate and d) for 5rate figure 13. variation of temperature in a single cell of a dual-potential msmd li-ion battery with various c rates with the ntgk model considering an external radiation temperature of 300 k: a) for 0.25c-rate, b) for the 1c rate, c) for the 2c rate, and d) for the 5-rate n.barua et al. /future energy may 2024| volume 03 | issue 02| pages 01-15 13 figure 14. variation of temperature in a single cell of a dual-potential msmd li-ion battery with various c rates with the ntgk model considering an external radiation temperature of 313 k: a) for 0.25c-rate, b) for the 1c rate, c) for the 2c rate, and d) for the 5-rate figure 15. maximum temperature vs. discharge rate for the ecm and ntgk models with different thermal conditions n.barua et al. /future energy may 2024| volume 03 | issue 02| pages 01-15 14 from figures 12, 13, and 14, it is observed that, for higher environmental temperatures, the increase rate of the maximum temperature from the environmental temperature is comparatively lower in the ntgk model than in the ecm model, while the boundary conditions are considered as radiation. just like the previously discussed convective boundary conditions for the ntgk e-chemistry model in figures (6-8), figure 12, figure 13, and figure 14 also showed a similar trend where the maximum temperature increased with increasing environmental temperature. the maximum temperature was always obtained in the active material (electrolyte ) zone. in figure 15, the maximum temperature vs. discharge rate is shown for both ecm and ntgk e-chemistry models considering convective and radiative boundary conditions. in each case, it is observed that for higher discharge rates the maximum temperatures increased rapidly. up to 2 c rate, the battery was inside the specified operating conditions and the temperature increased stably. however, at a high c rate (5 c), in each case, the battery was beyond operational condition. due to the specified maximum and minimum stop voltages of the battery, the materials property of the battery cell, and the geometry of the battery cell, a sharp increase was observed in each environmental condition at 5c, regardless of the boundary conditions. the environmental temperature had a significant effect on the increase rate of the maximum temperatures. it was because the environmental temperature played a crucial role in the activation energy inside the li-ion battery cell. 4. conclusion we have seen for each of the electrochemical models, the temperature rises drastically after the 2c rate and the maximum stop condition of the simulation arrived just after 570s. for the ecm model while taking the thermal condition as natural convection and the free stream temperature as 268k, 300k, and 313k respectively, the highest temperature of the msmd dual potential lithium-ion battery the single cell raised to 402.9109k, 430.1342k, and 441.1937k respectively for 5c discharge rate. for the ecm model, in the natural convection mode of heat transfer, the battery cell temperature increased by up to 9.48% while the environmental temperature changed from winter (-5°c) to summer (40°c) temperature. for radiation, the battery cell temperature is increased to 371.8288 k, 386.0818 k, and 419.8545 k for 5c rate with the corresponding environmental radiation temperature 268 k, 300 k, 313 k, which means the temperature increase rate of the cell raised to 12.91% but the maximum temperatures are lower than the ecm model’s highest temperatures for convection in each case. from figure 13 it is also clearly visible that for various discharge rates (0.25c, 1c, and 2c ), the maximum temperature-raising tendency in the ecm due to natural convection is greater than the maximum temperature-raising tendency due to radiation regardless of the environmental temperature (-5°c, 27°c, and 40°c). therefore, radiation is found to be a better thermal condition than natural convection in the ecm model. however, the trend line of the maximum temperature rise is opposite in the ntgk model, where the maximum temperature rise due to radiation is greater than the maximum temperature rise due to convection for 0.25c, 1c, and 2c rates at -5°c and 40°c environmental temperatures. for 5c in the ntgk model, the magnitude of maximum temperatures showed a variation from the temperatureraising trend line in figure.13 which was due to the arrival of the maximum stop condition of the simulation, where the simulation stopped just after 570 s of flow time. in the ntgk model, the maximum temperature rise due to radiation is greater than that due to convection for 0.25c, 1c, and 2c rates for winter and summer temperatures. however, at room temperature, the radiation mode of heat transfer showed a bit better result in the ntgk model. so, it can be said that in the ntgk model, convection is a better thermal condition than natural convection. after analyzing the simulation results of the highest temperatures reached by implementing two different electrochemical models in a single cell of a dual potential msmd lithium-ion battery, we can conclude that the radiative thermal condition of the e-chemistry of the equivalent circuit model is just a little better than the convective thermal condition of the ntgk model at elevated summer temperature (40°c). however, the convective thermal condition of the ntgk model shows a significantly better thermal management system and less heat generation in winter (-5°c) and at room temperature(27°c) compared to the radiative thermal condition of the ecm model. acknowledgment this work is supported by the university grants commission of bangladesh-grant no. 37.01. 0000.73.06.065.22.1607. the corresponding author is responsible for ensuring that the descriptions are accurate and agreed upon by all authors. ethical issue the authors are aware of and comply with best practices in publication ethics, specifically concerning authorship (avoidance of guest authorship), dual submission, manipulation of figures, competing interests, and compliance with policies on research ethics. the authors adhere to publication requirements that the submitted work is original and has not been published elsewhere in any language. data availability statement data sharing does not apply to this article as no datasets were generated or analyzed during the current study. conflict of interest the authors declare no potential conflict of interest. references [1] s. s. madani, m. j. swierczynski, and s. k. kaer, “the discharge behavior of lithium-ion batteries using the dual-potential multi-scale multi-dimensional 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[19] s. ma et al., “temperature effect and thermal impact in lithium-ion batteries: a review,” prog. nat. sci. mater. int., vol. 28, no. 6, pp. 653–666, 2018, doi: 10.1016/j.pnsc.2018.11.002. this article is an open-access article distributed under the terms and conditions of the creative commons attribution (cc by) license (https://creativecommons.org/licenses/by/4.0/). j. moradi et al. /future energy february 2025| volume 04 | issue 01| pages 43-49 43 perspective advanced thermal management strategies for electric vehicles: enhancing efficiency, reliability, and performance jamshid moradi1, amin mahmoudzadeh andwari1*, ayat gharehghani2, juho könnö1 1machine and vehicle design (mvd), materials and mechanical engineering, university of oulu, p.o. box 4200, fi90014 oulu, finland 2school of mechanical engineering, iran university of science and technology, tehran, iran a r t i c l e i n f o article history: received 20 december 2024 received in revised form 26 january 2025 accepted 09 february 2025 keywords: thermal management, electric vehicles (evs), power electronic components (pecs), battery thermal management system (btms), cooling technologies, heat dissipation *corresponding author email address: amin.m.andwari@oulu.fi doi: 10.55670/fpll.fuen.4.1.5 a b s t r a c t thermal management plays a crucial role in enhancing electric vehicles' performance, reliability, and lifespan (evs) by effectively dissipating heat from key components, including electric traction motors, power electronic components (pecs), and batteries. this paper explores various thermal management strategies tailored for these systems, highlighting their advantages, limitations, and technological advancements. in electric traction motors, heat dissipation is primarily addressed through active and passive cooling techniques such as forced convection, heat pipes, and phase change materials (pcms), with recent advancements like direct slot cooling (dsc) improving efficiency. similarly, pecs and electronic chips face thermal challenges due to electrical resistance, requiring innovative solid-state, air, liquid, and two-phase cooling methods to prevent performance degradation and component failure. battery thermal management systems (btms) are equally critical, as temperature variations directly impact efficiency, safety, and cycle life. active, passive, and hybrid btms technologies—including liquid cooling, thermoelectric systems, pcms, and heat pipes—are evaluated based on their effectiveness in maintaining optimal operating temperatures. this paper comprehensively analyzes emerging cooling solutions, addressing key tradeoffs between efficiency, cost, and design complexity. by integrating advanced thermal management techniques, the ev industry can achieve improved energy efficiency, enhanced safety, and prolonged component durability, paving the way for more reliable and sustainable electric mobility. 1. introduction the global transition to electric vehicles (evs) and hybrid electric vehicles (hevs) is accelerating due to increasing environmental concerns and the demand for sustainable transportation solutions. however, one of the most critical challenges in ev and hev development is thermal management, which directly impacts efficiency, reliability, and safety. key components such as electric traction motors, power electronic components (pecs), and batteries generate significant heat during operation, which, if not managed effectively, can lead to performance degradation, energy loss, and potential safety hazards such as thermal runaway. efficient thermal management is essential to dissipate excess heat, maintain optimal operating conditions, and extend the lifespan of these components [1,2]. electric traction motors, which convert electrical energy into mechanical motion, experience heat generation primarily due to copper and iron losses, as well as mechanical friction. overheating can lead to insulation degradation, efficiency loss, and irreversible demagnetization of permanent magnets. to counteract these issues, various cooling strategies have been developed, categorized into active and passive methods. active cooling techniques, including forced air convection, liquid cooling via water jackets or microchannels, and advanced methods like direct oil spray cooling, enhance heat dissipation but require additional energy. in contrast, passive cooling solutions such as phase change materials (pcms), heat pipes, and finned heat sinks offer efficient thermal management without external power consumption. recent advancements, such as direct slot cooling (dsc), have further improved thermal regulation in modern permanent magnet synchronous motors (pmsms), enabling higher efficiency and future energy open access journal https://doi.org/10.55670/fpll.fuen.4.1.5 february 2025| volume 04 | issue 01 | pages 43-49 journal homepage: https://fupubco.com/fuen issn 2832-0328 mailto:amin.m.andwari@oulu.fi https://doi.org/10.55670/fpll.fuen.4.1.5 https://fupubco.com/fuen j. moradi et al. /future energy february 2025| volume 04 | issue 01| pages 43-49 44 torque density [3,4]. similarly, power electronic components, including inverters, converters, and semiconductor chips, face significant thermal stress due to electrical resistance, switching losses, and parasitic effects. excessive temperatures in pecs can lead to reduced performance, shorter lifespan, and potential component failure. various cooling techniques are employed to address this issue, including solid-state methods such as thermoelectric cooling, thermotunneling, and heat sinks with thermal interface materials. air-based cooling, through either natural or forced convection, remains a common solution, while more advanced technologies such as piezoelectric fans, synthetic jet cooling, and electrohydrodynamic cooling offer innovative approaches to heat dissipation. liquid-based cooling methods, including cold plates, microchannels, electrowetting, immersion cooling, and jet impingement, provide superior heat transfer efficiency. additionally, twophase cooling systems, such as heat pipes and spray cooling, leverage phase transition properties to enhance thermal performance, ensuring that power electronics operate within safe temperature limits [5]. battery thermal management is equally crucial in evs and hevs, as battery performance is highly sensitive to temperature fluctuations. the optimal operating temperature range for lithium-ion batteries is typically between 15°c and 35°c; deviations beyond this range can lead to increased internal resistance, capacity loss, and severe safety risks such as thermal runaway. battery thermal management systems (btms) are classified into active, passive, and hybrid methods. active btms technologies, such as forced air cooling, liquid cooling, and immersion cooling, provide effective temperature control, with some manufacturers, like tesla and audi, adopting direct dielectric coolant immersion for enhanced thermal regulation. thermoelectric cooling (tec) and thermoelectric generators (tegs) are also gaining attention for their ability to convert excess heat into usable power. passive btms techniques, including phase change materials (pcms) and heat pipes, offer energy-efficient solutions by leveraging latent heat storage and efficient heat transport. hybrid btms approaches combine active and passive methods, such as liquid-pcm or air-pcm hybrid systems, to optimize heat dissipation while minimizing energy consumption and design complexity [6]. given the rapid advancements in ev technology, the development of effective thermal management systems is paramount to ensuring higher efficiency, prolonged component durability, and improved safety. this paper provides a comprehensive review of thermal management strategies across electric traction motors, pecs, and batteries, evaluating the strengths, limitations, and emerging trends in cooling technologies. the integration of innovative thermal solutions, such as immersion cooling, direct slot cooling, and hybrid cooling techniques, represents a critical step toward optimizing ev and hev performance. by addressing thermal challenges, manufacturers can enhance energy efficiency, extend vehicle lifespan, and contribute to the broader adoption of sustainable electric mobility. 2. thermal management in evs thermal management methods are as essential as control strategies in pcu. temperature has a great impact on the performance and durability of electronic components, and it also determines the magnetic flux of electric motors. thermal management aims to dissipate heat from evs’ components to limit failure, optimize energy consumption, improve reliability, enhance power and flux density, and extenuate device quantity. in evs, there are various systems, such as batteries, electric traction motors, and pcus with subcategories, including electronic boards and pecs, each of which has different thermal management methods. in evs that are equipped with engines (hevs), using the term thermal management for the engine is not correct, and whr is more appropriate instead, while applying whr systems in other components of evs is not justified, since they do not generate much heat [7]. 3. thermal management in electric traction motor the main source of heat in high-torque traction motors in evs is stator windings resistance, which brings copper loss as the most heated unit and major energy loss, respectively, although there is iron loss due to hysteresis in magnetic field and mechanical loss from the bearing’s friction. hightemperature regions emerge in the winding copper core, air gaps between the stator and rotor, around the axial center of the rotor bar, and stator section. the high temperature must be managed seriously since a 10 c increase in temperature halves the lifetime of the insulation across the conductors and demagnetizes the permanent magnets irreversibly. active and passive cooling are two main categories of ev electric traction motor cooling methods. active methods refer to forced convection using fans or pumps to circulate the coolant with more capability to dissipate heat, although they consume extra energy, while passive cooling methods are based on natural convection such as fins and heat pipes, which limit the absorbing heat while they do not need energy and much maintenance cost. solid-liquid phase change material (pcm) is one of the passive cooling methods applied around the stator coil and does not affect the reluctance much. pcm with high melting heat capacity can absorb the large heat generated from the coil by changing its phase from solid to liquid and back again to the previous state by transferring heat to the environment when the motor turns off. the heat pipe, as a passive cooling, does not use any moving parts and is able to transfer large amounts of heat over long distances at a constant temperature. generally, water is used as a cooling fluid in electric traction motors. heat pipes could be installed in different locations, including motor housing, winding, stator shaft, rotor shaft, and stator core. there are so many methods to dissipate heat from ev electric traction motors, such as air-cooling, water jacket cooling, liquid/oil-based cooling, oil spray cooling, cooling tubes and microchannels, and potting silicon gelatin (psg) cooling. in modern pmsms, a direct spray of dielectric oil to cool the stator and windings with water jacket cooling has shown the highest torque achievement of electric motors compared to all other methods. recent alternative optimal methods remove heat more accurately. direct slot cooling (dsc) uses heat pipes applying a cooling channel to cool motor windings directly in the open slot of a motor stator as the cooling channel [8]. j. moradi et al. /future energy february 2025| volume 04 | issue 01| pages 43-49 45 4. thermal management in pecs and electronic chips electrical resistance in semiconductors is the main heat source in electronic devices. the heat generation from switching losses, conduction losses, and parasitic effects degrade the performance, durability, and reliability of pecs. the essentials of innovative cooling technologies should be achieved by both high absorbing heat capacity and small module size. thermal stress is the main reason for capacitor and semiconductor failures. developing wide bandgap devices (wbg) with high heat generation in power electronic topologies requires more effective cooling techniques [9]. an appropriate cooling system must contain three proficiencies in absorbing, transferring, and removing heat out of the module. as indicated in table 1, the cooling of power electronics is classified according to different heat transfer mechanisms or coolant agents. the cooling technologies are as follows [10]: a) solid-state cooling is employed in the technologies of solid materials with high thermal conductivity or thermoelectric effects. 1. heat sinks, thermal interface materials, and conduction plates: based on the amount of heat generation, different materials could be applied with various thermal conductivities, from conventional cheap devices like aluminum with limited ability in terms of heat dissipation and density to high-performance devices like pyrolytic graphite. they are used to eliminate the gap between a semiconductor and a heat sink instead of air. their main restriction is uncontrollable heat spread that requires thin plates. 2. magnetic cooling: in this method, integrating magnetocaloric devices and a temporary magnetic field leads to a drop in the temperature of the electronic components. this method is performed according to a four-stage cycle of increasing the temperature of the device, magnetizing it, releasing heat, decreasing the temperature, and finally, demagnetizing. the importance of this method is determined when volume and weight are constrained and high efficiency is considered. 3. thermoelectric cooling: this method works exactly the opposite of the tegs. dc low voltage current flows through the device to enable heat transfer based on the peltier effect. this method, despite its low efficiency, low heat transfer capability and high cost, is used in applications where there is volume and weight limitation, and temperature changes are extremely transient and require precise control. 4. thermotunnelling and thermionic cooling: the operation of this method is inverse of a battery and uses two electrodes, one to absorb heat as an emitter and the other to repel as a collector, then transmission the front of electrons, and finally to drive an electric current and generate electricity. no mechanical moving parts like other solid-state methods, high power density, high reliability, good stability, and high efficiency are the main advantages of this method. its main restrictions are only supporting localized cooling and low cooling power from ambient temperature. b) air cooling technologies: this method does not have complications of liquid heat transfer, and it is done in two ways: natural and forced convection. table 1. thermal management strategies in power electronics heat transfer mechanisms \ coolant agent solid gas (air) liquid two-phases conduction conduction plates and heat sinks, thermal interface materials, advanced conduction plates not applicable not applicable not applicable natural convection not applicable air cooling immersion cooling immersion cooling forced convection not applicable standard fans, piezoelectric devices, synthetic jet impingement, electrohydrodynamics, thermoacoustic cooling cold plates, microchannel cooling, electrowetting, immersion cooling, jet impingement cooling cold plates, microchannel cooling, electrowetting, immersion cooling, jet impingement cooling, heat pipes, spray cooling, phase change materials magnetocaloric effect magnetic cooling not applicable not applicable not applicable peltier effect thermoelectric cooling not applicable not applicable not applicable tunnel and thermionic effects thermotunnelling and thermionic cooling not applicable not applicable not applicable j. moradi et al. /future energy february 2025| volume 04 | issue 01| pages 43-49 46 1. natural air convection: this heat transfer mechanism is the simplest way to cool electronic boards, and it is done due to the bouncy force and the density difference between the hot device and the cool surrounding air. limiting the amount of heat transferred is the main challenge of this method. 2. forced air convection: the combination of fan and thermal heat sinks causes more heat transfer than natural convection. this method is the most common way to cool pecs. the main limitations of this method are fan energy consumption, high volume-to-weight ratio, and lower capability than other novel methods based on energy efficiency. 3. piezoelectric devices: piezoelectric fans use vibrating cantilevers instead of rotating fans to generate cooling flowing air. this method has higher preferences than conventional fans in positional accuracy, reliability, and flow direction, although limiting heat dissipation is its main obstacle. 4. synthetic jet impingement: a pump with a controlled diaphragm is equipped to jet turbulent airflow to dissipate heat from the electric device. this method is restricted by a low heat dissipation capability, while high reliability, low energy consumption, and noise are its main benefits. 5. electrohydrodynamic: by increasing the voltage difference between two electrodes with different thicknesses until the electric arc does not occur, the electric field around the anode electrode is enhanced. as a result, the gases around the anode are ionized, leading to the phenomenon of corona discharge. the collision of ions with neutral molecules causes the transfer of momentum and cooling of the power device. silent operation, high cooling power density, and low energy consumption are the best options, although degradation of the electrodes, high operating voltage, and complex equipment are its main disadvantages. 6. thermoacoustic: this property refers to producing sound waves and, consequently, pressure fluctuations from heat for a cooling mechanism. no moving parts, silent operation, and simplicity are the charms of this method, and the low capability to dissipate heat is its major restriction. c) liquid cooling technologies: the conductivity coefficient in liquids is significantly more than in air, and as a result, their cooling capacity is higher. although air cooling causes additional weight and volume to be imposed on the system due to the fan and heat sink, the main challenges of liquids are leakage, corrosion, electrical conductivity, and flammability. 1. cold plates: cold plates are the main alternative to air cooling with heatsinks. in this method, a pump replaces the fan to circulate the liquid in a heat exchanger. although it has more ability to dissipate heat, it increases weight and reduces reliability. 2. microchannel: microchannel is a much more efficient method than cold plates because they are more capable of dissipating heat from the power device with less volume and weight. different types of fluids and even nanofluids are used in them, but their main challenge is high-pressure drop. 3. electrowetting: applying an electric field to the fluid causes its surface tension to change, and a droplet is sprayed on the power device. this spray can be applied directly on the part board (wetted surface) or at a distance from it (dry surface). the fluid must be dielectric, such as de-ionized water, liquid electrolytes, or ethanol. this method has a very high ability to absorb heat with low pump energy consumption. 4. immersion: in this method, the whole power device is submerged in the dielectric coolant fluid through natural convection or forced with a pump. the coolant fluid can even reach the boiling point, which is called nucleate boiling. this method has a great ability to dissipate heat due to its highpower density and high efficiency. this method is mostly used in microelectronics. 5. jet impingement: in this method, liquid jet spraying in the form of regular matrices on the electric board with a high flow rate as a free surface or immersed with a dielectric fluid that causes significant heat transfer. the arrangement and number of nozzles, spray flow velocity, and properties of the coolant fluid are among the most important factors that determine the amount of heat dissipated in this method. d) two-phase cooling technologies: two-phase cooling methods can absorb considerable heat from the high latent heat capacity of phase change, also due to their low volumeto-weight ratio, they have a higher power density and efficiency than other methods, but their most important challenge is the selection of coolant fluid and complexity of their control and design. 1. heat pipes: a heat pipe uses evaporative cooling to transfer thermal energy from one point to another. the operation is based on evaporation and condensation, relies on the temperature difference between the two ends of the pipe, and cannot reduce the temperature on both sides. the heated side of the heat pipe evaporates the coolant and increases the vapor pressure inside the heat pipe. the latent heat of vaporization absorbed by the fluid causes the temperature to drop on the tube's hot side. high thermal convection, isothermal operation, durability, and low costs are the most important strengths of the heat pipe, despite the control of the temperature range that depends on the material and fluid of the coolant since the liquid in hot temperature evaporates completely, and in low temperature there is no evaporation, to create a two-phase flow. 2. spray: spray cooling is defined as the passage of a highpressure liquid through a nozzle and its atomization. liquid droplets have a great ability to absorb heat and consume low power but choosing the right fluid that has the right chemical properties, dielectric constant, and adequate non-conduction thermal due to direct contact with the power device is its main challenge. the performance of this method depends on the number and arrangement of nozzles, flow rate, and many other parameters. 3. phase change materials: phase change materials (pcms) store energy in the form of latent heat of fusion. pcm absorbs heat as part of a continuous cycle, which has high heat dissipation density and does not need a heat sink. high melting point, high volumetric storage density, uniform melting ability, stable chemical properties, high fusion temperature, and reliability are its strengths, but low thermal conductivity in the solid state is its main weakness. 4. thermal management in batteries: the electricity produced in the battery is created during the electrochemical process, which is accompanied by heat generation. therefore, the temperature of the battery increases and affects its performance. the ideal temperature for battery operation is between 15 and 35 degrees celsius; providing this condition, j. moradi et al. /future energy february 2025| volume 04 | issue 01| pages 43-49 47 along with creating a uniform temperature distribution in cells, is the responsibility of the battery thermal management system (btms). temperatures below 15 degrees increase resistance and charge failure, and temperatures above 35 degrees intensify side reactions and cause thermal runway [11]. a conventional classification of btms is presented in figure 1. figure 1. classification of btms technologies 1. active btms: forced heat transfer of air or liquid coolant, as an active method, is the most common btms technology in evs. toyota and lexus use a fan to circulate air over the battery cells, but tesla and audi use direct contact immersion with dielectric coolant. indirect cooling technology causes the loss of an important part of the cooling power due to the conduction resistance in the pipe. table 2. the advantages and disadvantages of btms technologies btms technologies advantages disadvantages air 1-simple design, low cost and maintenance, 2-low volume occupation 3compatible with different batteries 1-low efficiency and heat transfer rate 2-high energy consumption 3non-uniform temperature distribution liquid 1-high efficiency and heat transfer rate 2uniform temperature distribution 1leakage risk 2high occupied volume 3complexity 4short system lifespan thermoelectric system 1-switching capability between cooling and heating mode 2-no coolant nor mechanical component 3light-weighted 1-high cost 2-low conversion efficiency pcm 1-simple design 2-light weight 3-low volume occupation 4low maintenance 5-no power consumption 1-low thermal conductivity 2continuous operation difficulty 3leakage risk 4risk of supercooling 5limited thermal storage capacity. heat pipe 1-high thermal conductivity 2no power consumption 3-reliable 4low maintenance 5-compact and light 1-low efficiency and capacity due to the limited contact area 2-high initial costs 3leakage risk hybrid btms 1-light weight 2-high cooling performance 1-complex structure 2-expensive j. moradi et al. /future energy february 2025| volume 04 | issue 01| pages 43-49 48 immersion technology is at the cutting edge of science, and there is a long way to go in its development. usually, a mixture of water and ethylene glycol, besides acetone and oil, is used as a dielectric fluid in this method. on the other hand, the design of the system using coolants that experience phase change conditions in the operating temperature range of the battery can enhance the heat transfer rate up to 10 times. thermoelectric cooling (tec) and thermoelectric generator (teg) are the other approaches in active btms, which require electrical power to cool the battery. tec application had been considered before when it could be integrated with teg. teg converts the lost heat from the battery to power tec to improve heat absorption capability. they need no coolant fluid or moving components, which gives them high heat absorption density and low weight. 2. passive btms: these methods are not very popular, but they have advantages that can cover the challenges of active technologies. its most famous subcategories are phase change materials (pcms) and heat pipes (hps). pcm has two attractive features: one is to create a uniform temperature through the battery, and the other is to operate at the melting temperature, which causes suitable heat absorption. paraffins, fatty acids, or hydrated salts are the most important materials that can work in the operating temperature range of batteries between 30-50 degrees celsius. low thermal conductivity is the most important challenge for the advancement of pcms, which restricts heat transfer since researchers have been trying to solve it with different approaches, including porous structures combined with nanoparticles, fibers, and graphite. heat pipes are an alternative option in the passive approach, whose main application is in pecs and electronic chips and not in btms. hps are vacuum tubes consisting of three sections of an evaporator, an adiabatic fragment, and a condenser. hps have a great ability to absorb heat, do not need external energy, are adaptable and flexible, and do not have maintenance costs, but their design is complex and expensive. 3. hybrid btms: hybrid methods are a combination of active and passive technologies that enhance strengths and eliminate weaknesses of them alone. in this approach, pcm is central to creating a uniform temperature distribution throughout the battery, while the integrated method could be air or liquid to improve the heat transfer rate or hps to increase natural heat transfer. although the results of this approach meet expectations, their main problem is the expensive design and their complexity. in short, the advantages and disadvantages of these technologies are mentioned in table 2. 5. conclusion effective thermal management is essential for ensuring the efficiency, reliability, and safety of electric and hybrid electric vehicles (evs and hevs). as these vehicles continue to evolve, advanced cooling strategies are required to address the heat dissipation challenges in key components, including electric traction motors, power electronic components (pecs), and batteries. each of these systems generates significant heat during operation, which, if not properly controlled, can lead to performance degradation, reduced lifespan, and critical failures. electric traction motors face thermal challenges due to copper and iron losses, which impact efficiency and durability. a range of cooling methods, from conventional air cooling to advanced liquid cooling techniques such as direct oil spray cooling and microchannel cooling, have been developed to enhance thermal regulation. additionally, passive methods like phase change materials (pcms) and heat pipes offer energy-efficient solutions without the need for additional power consumption. similarly, power electronic components experience substantial heat generation due to electrical resistance and switching losses. innovative cooling solutions, including solid-state methods like thermoelectric cooling, air-based convection techniques, and liquid immersion cooling, have significantly improved heat dissipation, increasing the efficiency and lifespan of pecs. battery thermal management remains one of the most critical aspects of ev and hev performance, as temperature fluctuations directly affect battery capacity, charging efficiency, and safety. active cooling techniques such as liquid immersion and forced air circulation provide effective temperature regulation, while passive methods like pcms and heat pipes contribute to improved heat distribution. hybrid approaches, combining both active and passive cooling, have emerged as optimal solutions to maximize efficiency while minimizing energy consumption and design complexity. the continuous development of innovative thermal management technologies is crucial for advancing ev and hev performance. emerging trends, such as direct slot cooling, advanced two-phase cooling systems, and immersion-based cooling, are pushing the boundaries of heat dissipation efficiency. by integrating these advanced solutions, automakers can achieve higher energy efficiency, extend the operational lifespan of components, and enhance overall vehicle safety. as the demand for sustainable transportation grows, refining thermal management strategies will play a pivotal role in the future of electric mobility, ensuring that evs and hevs continue to provide a reliable and efficient alternative to internal combustion engine vehicles. ethical issue the authors are aware of and comply with best practices in publication ethics, specifically concerning authorship (avoidance of guest authorship), dual submission, manipulation of figures, competing interests, and compliance with policies on research ethics. the authors adhere to publication requirements that the submitted work is original and has not been published elsewhere in any language. data availability statement the manuscript contains all the data. however, more data will be available upon request from the corresponding author. conflict of interest the authors declare no potential conflict of interest. references [1] a. maiorino, c. cilenti, f. petruzziello, and c. aprea, “a review on thermal management of battery packs for electric vehicles,” appl therm eng, vol. 238, p. 122035, feb. 2024, doi: 10.1016/j.applthermaleng.2023.122035. 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[11] m. r. cosley and m. p. garcia, “battery thermal management systems,” intelec, international telecommunications energy conference (proceedings), pp. 119–160, jan. 2023, doi: 10.1016/b978-0-443-18862-6.00003-3. this article is an open-access article distributed under the terms and conditions of the creative commons attribution (cc by) license (https://creativecommons.org/licenses/by/4.0/). https://creativecommons.org/licenses/by/4.0/ n. meco & c. firat /future energy may 2025| volume 04 | issue 02| pages 12-22 12 article exploring the impact of nano-enhanced phase change materials on trombe wall efficiency nazlıcan meco1, coskun firat2* istanbul technical university, energy institute, istanbul, turkiye a r t i c l e i n f o article history: received 14 january 2025 received in revised form 25 february 2025 accepted 07 march 2025 keywords: trombe wall, nano-enhanced phase change materials (nepcm), energy efficiency, thermal energy storage, finite element method simulation *corresponding author email address: coskun.firat@itu.edu.tr doi: 10.55670/fpll.fuen.4.2.2 a b s t r a c t a novel trombe wall design that incorporates highly thermally conductive materials along with nano-enhanced phase change material is presented. performance analysis is conducted using finite element method simulations. a comparative study of nepcm and pcm in a room with a trombe wall revealed minor differences in thermal performance during january, february, and december, but a significant discrepancy in march due to higher solar radiation levels. the enhanced latent heat storage capability of nepcm contributed to a more sustained temperature increase during periods of intense solar radiation. over seven months, nepcm demonstrated a 16% higher average energy gain compared to pcm, attributed to its improved thermal conductivity and heat transfer efficiency. these findings indicate that nano-enhanced phase change materials are more effective than their non-nano counterparts. the results indicate a substantial impact of the system, raising room temperatures to 22°c during the day and resulting in significant energy savings. 1. introduction historically, numerous researchers have sought new energy sources in response to global energy crises. in this context, extensive studies have been conducted on alternative fuels and solutions that can replace fossil resources. to achieve sustainable development, countries require a reliable supply of clean and safe energy that minimizes environmental impacts [1]. consequently, the exploration of renewable energy sources has become a crucial area of focus. this increasing interest in renewable energy has attracted considerable attention. turkey, in particular, emphasizes the development of domestic and renewable energy sources, in line with the goals set forth in the national energy policy of 2017. as a testament to this commitment, turkey has risen to the fifth position in europe and twelfth globally in terms of installed renewable energy capacity. by the end of 2022, renewable sources accounted for 54% of turkey's total installed energy capacity [2]. the global energy crisis and the urgent need for sustainable solutions have driven intensive research into renewable energy sources. turkey, endowed with significant solar potential, has emerged as a key player in the renewable energy landscape. this study examines turkey's impressive growth in solar energy, particularly in istanbul, a city characterized by unique weather conditions. by analyzing statistical data from the international renewable energy agency [3] and national energy ministries [4], this research investigates the critical role of solar energy in residential heating within the specific context of istanbul. the building sector is responsible for 30-40% of global energy consumption, with nearly half of this energy allocated to heating and cooling systems to maintain indoor comfort [5,6]. this significant energy usage contributes substantially to global greenhouse gas emissions, highlighting the urgent need for reduction strategies. the united states aims to decrease building energy consumption by 70% by 2020 as part of federal policy initiatives [7], while china has set ambitious targets to cut energy usage in new constructions by 50% [8]. furthermore, rising fossil fuel consumption and electricity demand underscore the necessity for more efficient building practices. addressing these challenges is essential for mitigating environmental impacts and promoting sustainable energy practices. various methods utilizing solar energy are implemented in construction, including passive walls with solar facades, natural ventilation systems, architectural solar roofs, solar chimneys, and trombe walls [9,10]. passive heating and cooling systems capture solar radiation and ambient temperature variations to store energy, which is then released into indoor spaces at optimal times. trombe walls represent a pioneering approach in passive solar technology, effectively harnessing solar energy to provide space heating in buildings for several decades. these thermal mass walls, typically composed of masonry or concrete, absorb sunlight through a glass facade and subsequently release the stored heat into the interior future energy open access journal https://doi.org/10.55670/fpll.fuen.4.2.2 may 2025| volume 04 | issue 02 | pages 12-22 journal homepage: https://fupubco.com/fuen issn 2832-0328 mailto:coskun.firat@itu.edu.tr https://doi.org/10.55670/fpll.fuen.4.2.2 https://fupubco.com/fuen n. meco & c. firat /future energy may 2025| volume 04 | issue 02| pages 12-22 13 space. despite their potential, the thermal performance of trombe walls can be hindered by various factors, including heat loss through conduction and convection, as well as their dependency on direct sunlight exposure. the well-established trombe wall functions similarly to a solar thermal collector; it consists of a large wall with an external glazing area that stores solar energy within its mass for later use, particularly after sunset. other passive systems include solar chimneys, unglazed transpired solar facades, and green walls—all designed to effectively harness natural energy sources. trombe walls are also known as thermal or storage walls [11]. trombe walls come in various forms, including classic trombe walls, aquatic trombe walls, water trombe walls, zigzag trombe walls, composite trombe walls, solar compound walls, and the widely utilized pv trombe wall [12]. in existing literature, the trombe wall stands out as one of the most extensively studied passive systems with numerous configurations explored. in traditional designs, openings are integrated into the solid wall to enable air circulation. during winter months, circulation occurs internally; conversely, during summer months, an external connection is established to enhance ventilation rates [13]. a study by abbassi et al. [14] examined the effectiveness of trombe walls in tunisia's climate and found that a 4 m² wall could reduce annual auxiliary heating energy needs by approximately 50%, while an 8 m² version could achieve a remarkable 77% reduction. similarly, bojic et al. [15] studied a residence in lyon, france, demonstrating that a south-facing trombe wall could decrease yearly heating consumption by up to 20%. these studies collectively highlight the versatility and efficiency of trombe walls across various climates, making them a focal point for research in passive energy systems. hu et al. [16] investigated the use of venetian blinds placed between glazing and thermal mass walls and emphasized how blind tilt angles significantly influence natural convection within the air gap. likewise, hong et al. [17] focused on optimizing venetian blinds integrated into trombe walls; their findings indicated that an optimal distance of 9 cm between the blinds and glass was effective with a 14 cm air gap. duan et al. [18] explored placing an absorber plate within the middle of the air gap rather than on the thermal mass wall surface; they demonstrated that this configuration outperformed conventional trombe walls regarding both energy efficiency and interpretative aspects. innovative designs for trombe wall systems have also been explored. rabani et al. [19] developed a trombe wall that captures solar irradiation from eastern, western, and southern directions while covering half of the south-facing wall; this cost-effective system provided satisfactory thermal comfort due to its reduced surface area. shen et al. [20] conducted a comparative analysis between classical and composite trombe walls and highlighted superior performance for composite designs under cold and overcast weather conditions. li et al. [21] researched thermal efficiency in pcm-integrated trombe wall systems through comparative experiments conducted during summer months in hot and humid regions of china; results indicated that pcmintegrated designs exhibited better heat insulation properties compared to standard building envelopes and traditional trombe wall designs. recent advancements in materials science have introduced nanoparticles and phase change materials (nepcms) as promising solutions to enhance the thermal efficiency of trombe walls. nanoparticles can significantly improve thermal conductivity, while pcms are capable of increasing thermal storage capacity by absorbing and releasing heat during phase transitions. the integration of these materials into building energy systems has attracted increasing attention due to their potential to enhance energy efficiency, reduce carbon emissions, and improve occupant comfort. however, despite the growing interest in nepcms, there remains a substantial gap in research regarding their application in trombe walls specifically. this study aims to address this gap by investigating the incorporation of nepcms into trombe wall systems to enhance their energy efficiency. through a theoretical analysis of thermal performance, this research seeks to contribute valuable insights into passive solar heating technologies and building energy efficiency strategies. 1.1 trombe walls a typical unvented trombe wall consists of a southfacing masonry structure with a thickness ranging from 10 to 40 cm. the exterior surface of this wall is coated with a dark, heat-absorbing material and is covered by one or two layers of glass. these glass layers are spaced 2 to 5 cm away from the masonry wall, creating a small air gap between them. when sunlight enters through the glass, the dark surface absorbs heat, which is then stored within the wall and gradually conducted inward through the masonry. using hightransmission glass enhances the solar heat gains captured by the masonry. additionally, incorporating patterned glass can serve as an architectural feature that obscures the view of the dark concrete wall from outside while still allowing light to pass through. trombe walls are architectural components designed for passive solar heat absorption, storage, and distribution. typically made from high-mass materials such as concrete or stone, these walls collect solar radiation during the day and slowly release it into the interior at night, providing consistent and sustainable heating. however, their successful implementation relies on various factors, including orientation, thermal properties, and local climate conditions. the efficiency of trombe walls across different scenarios has attracted interest from both researchers and building professionals. different configurations are employed to adapt trombe walls for various climates, purposes, and seasons, as illustrated in figure 1 [22]. several types of trombe walls exist, including classic and modified designs, zigzag trombe walls, solar water walls, solar trans walls, solar hybrid walls, trombe walls with phase change materials (pcm), composite trombe walls, fluidized trombe walls, and photovoltaic (pv) trombe walls [23]. a conventional trombe wall, also known as a standard trombe wall, features glass and an air gap that separates it from the outdoor environment [24]. the concept of the trombe wall was first patented by edward morse, an american engineer, in 1881 but gained widespread recognition thanks to felix trombe and architect jacque michel [25], leading to its common designation as a trombe wall. figure 2 shows a pvtrombe wall equipped with photovoltaic cells that enhance thermal comfort while contributing to electricity generation [26]. 1.2 solar radiation in istanbul turkey has a vast land area well-suited for capturing solar energy, attributed to its favorable geographical position. the country lies between latitudes 36° and 42° n. historical data gathered by the turkish state meteorological service from 1971 to 2000 indicates a significant solar potential across the nation. on average, turkey has 2,573 hours of sunshine annually (approximately 7 hours per day) and an average total radiation of 1,474 kwh/m² per year (or about 4 kwh/m² daily). figure 3 illustrates the global irradiation levels for turkey [27]. n. meco & c. firat /future energy may 2025| volume 04 | issue 02| pages 12-22 14 figure 1. operating schemes: non-ventilated solar wall (a); trombe wall in winter mode with air thermo-circulation (b); trombe wall in summer mode with cross ventilation [22] figure 2. schematic diagram and photograph of pv-trombe wall for winter heating [26] figure 3. global irradiation levels for turkey [27] n. meco & c. firat /future energy may 2025| volume 04 | issue 02| pages 12-22 15 with a population exceeding 80 million, turkey is facing a rising demand for energy, leading to a continuous increase in energy consumption. in 2022, turkey's per capita energy consumption reached 3,360 kwh [28]. according to the turkey energy efficiency development report, approximately 20% of the country's energy and around 22% of total electricity consumption is utilized in households. of this energy usage, about 60% is allocated to heating in buildings [29]. the average cooling requirement for a typical building in istanbul is approximately 33.52 kwh/m² per year, while the heating requirement is around 84.49 kwh/m² per year [30]. alarmingly, over 75% of this energy is currently supplied through imports, a figure that continues to rise annually. therefore, it has become increasingly urgent to diversify energy sources by focusing on both domestic nonrenewable and renewable resources. among these alternatives, solar energy stands out as a crucial option with significant potential that remains largely untapped in turkey. the nation has an average of 200 sunny days each year, providing a solid foundation for developing a comprehensive solar energy strategy. the primary objective of this research is to evaluate the performance of a trombe wall system integrated into a room within istanbul. located at a latitude of 40.58° n, longitude of 29.05° e, and an elevation of 39 meters, istanbul is one of turkey's most densely populated urban areas in the northwestern part of the country. figure 4 presents data on global solar radiation and sunshine hours for istanbul. in istanbul, the average annual global solar radiation is recorded at 1,612 kwh/m² per year, with an average annual sunshine duration of 2,446 hours. these values are relatively low compared to many other cities in turkey. to promote solar energy utilization, the istanbul metropolitan municipality's geographic information system (gis) directorate has developed the istanbul solar energy potential map. a snapshot from this map is shown in figure 5 [31]. 2. methodology 2.1 material selection n-octadecane, a paraffin-based organic phase change material (pcm), was selected for the present study due to its advantageous properties for industrial applications. the key factors influencing this choice include: • thermal comfort range: n-octadecane has a phase change temperature that closely aligns with the optimal range for thermal comfort in indoor environments. this characteristic allows it to effectively absorb and release thermal energy within a temperature range conducive to human comfort. • high thermal conductivity: compared to other organic pcms, n-octadecane exhibits relatively high thermal conductivity. this property facilitates efficient heat transfer both within the material and between the pcm and its surrounding environment. figure 4. monthly averaged daily global solar radiation and sunshine duration hours in istanbul [27] figure 5. istanbul solar energy potential map [31] n. meco & c. firat /future energy may 2025| volume 04 | issue 02| pages 12-22 16 • latent heat storage capacity: n-octadecane possesses a significant latent heat of fusion, enabling it to store a substantial amount of thermal energy per unit mass during its phase transition. this maximizes its potential for energy storage. in the study, n-octadecane (c₁₈h₃₈) was chosen as the primary pcm due to its melting point of 28°c, which is wellsuited for maintaining thermal comfort in occupied spaces. this property allows n-octadecane to effectively store and release thermal energy within the desired temperature range. to enhance the pcm's performance the nano-enhancement expandable graphite (eg), a carbon-based compound, was selected for its compatibility with n-octadecane. both materials share graphite as a common source, ensuring chemical compatibility and minimizing potential adverse interactions within the composite. 2.2 trombe wall construction the trombe wall was designed with two essential components: • highly thermal conductive encapsulation: the outer layer was constructed using pyrolytic graphite, a highly ordered form of graphite known for its exceptional thermal conductivity (approximately 1800 w/m·k in-plane). this high conductivity ensures efficient heat transfer from the solar-heated exterior surface to the pcm layer within the wall. • energy storage substance (pcm): the core of the trombe wall consisted of the pcm layer containing n-octadecane, with or without nano-enhanced eg for comparative analysis. during daylight hours, the pcm absorbed thermal energy from the sun-heated pyrolytic graphite and released it back into the room as temperatures dropped, thereby providing passive heating during colder periods. 2.3 room construction the surrounding room walls were constructed from concrete, selected for its robust thermal mass, which helps regulate fluctuations in room temperature. additionally, a glass window was incorporated into the design to allow direct solar radiation onto the trombe wall, optimizing its potential for thermal gain. detailed properties of the materials used in this system are summarized in table 1 for reference. the subject of this study is a small room with an approximate area of 15.5 m², which includes four external walls, a roof, and a ground floor. a window is situated on the south side, adjacent to the trombe wall (tw). the configuration of the room featuring the trombe wall is depicted in figure 6, showcasing a unique setup regarding both its placement and operational mechanism. the tw is constructed from a highly thermally conductive material (pyrolytic graphite) and utilizes phase change material (pcm) for energy storage. this innovative design presents several advantages, making it an intriguing subject for examinations. firstly, it does not include any ventilation gaps, setting it apart from other types of trombe walls documented in the literature. secondly, it functions as a hybrid system that allows the wall to transfer heat into the room while storing some energy in the pcm for use during nighttime. the dimensions and configuration of the tw considered in the calculations are shown in figure 7. the thermal and mechanical properties of the materials used in the tw are summarized in table 2. although the trombe wall is primarily intended for use during the eight cold months in istanbul, analyses and calculations were conducted for all twelve months. weather and solar data specific to istanbul for each month are detailed in table 3. figure 6. dimensions and configuration of the analyzed trombe wall table 1. material properties [32] property pyrolytic graphite pcm (n-octadecane) nepcm (n-octadecane/eg) concrete wall glass window density (kg/m3) 2100 814 2300 2203 specific heat (j/kgk) 850 2660 880 703 thermal conductivity (w/mk) 1800 0.36 1.11 1.8 1.38 melting point (oc) 28 23 latent heat (kj/kg) 244 196.8 n. meco & c. firat /future energy may 2025| volume 04 | issue 02| pages 12-22 17 figure 7. dimensions of the trombe wall table 2. properties of tw materials [32, 33] thermal and mechanical property pyrolytic graphite pcm (paraffin) density (kg/m3) 2100 912 specific heat (j/kgk) 850 2310 thermal conductivity (w/mk) 1800 0.21 melting point (oc) 31.9 table 3. the weather and solar data specific to istanbul months dni (w/m2) sunshine (hrs./day) ambient temperature, ta, (oc) wind speed, v, (m/s) h (w/m2k) jan 491.33 3.46 6.00 4.81 24 feb 493.12 4.43 6.10 4.81 24 mar 671.05 5.32 7.70 4.36 22 apr 655.18 6.85 12.00 4.03 21 may 621.95 8.61 16.70 3.97 21 jun 549.14 10.51 21.40 4.28 22 july 516.70 11.17 23.80 4.78 24 aug 508.83 10.14 23.80 4.78 24 sep 552.55 7.83 20.10 4.92 24 oct 609.00 5.22 15.70 4.36 22 nov 523.25 3.85 11.70 4.25 22 dec 516.89 2.96 8.20 4.83 24 the weather data, including solar radiation (dni) and sunshine hours, were averaged for each day of a specific month for these calculations, while convective heat loss due to wind was calculated using equation (1), as described by hong et al. [34]. ℎ𝑤𝑖𝑛𝑑 = 5.7 + 3.8𝑣𝑤𝑖𝑛𝑑 (1) where 𝑣𝑤𝑖𝑛𝑑 represents wind speed. simulation of the system was performed regarding time dependent finite element method. simulation model is calculating the heat load with respect to the effect of the conduction, convection and radiation heat transfer rates as given below. 𝑑𝑄 = (𝑞𝑐𝑜𝑛𝑑 ′′ + 𝑞𝑐𝑜𝑛𝑣 ′′ + 𝑞𝑟𝑎𝑑 ′′ )𝑑𝑡 (2) in the fem, the navier-stokes equations are used which govern conservation of mass, momentum, and energy as given trough eq (3) to eq (7). for the conduction calculations in the system following equations are used. 𝜌𝐶𝑝 𝜕𝑇 𝜕𝑡 + 𝜌𝐶𝑝𝑢𝛻𝑇 + 𝛻𝑞 = 𝑄 (3) 𝑞 = −𝑘𝛻𝑇 (4) for the laminar flow of air which is newtonian in the room and the gravity calculations, equation below was used. 𝜌 𝜕𝑢 𝜕𝑡 + 𝜌(𝑢𝛻)𝑢 = 𝛻[−𝑝𝐼 + 𝐾] + 𝐹 + 𝜌𝑔 (5) where, 𝜕𝜌 𝜕𝑡 + 𝛻(𝜌𝑢) = 0 (6) 𝐾 = 𝜇(𝛻𝑢 + (𝛻𝑢)𝑇 − 2 3 𝜇(𝛻𝑢)𝐼 (7) i is the identity tensor, 𝜌 is the density, u is the velocity vector , 𝑝 is the pressure, 𝜇 is the dynamic viscosity, 𝐶𝑝 is the specific heat capacity at constant pressure, t is the absolute temperature, q is the heat flux vector, q contains the heat sources, k is the thermal conductivity, f is the buoyancy force and 𝑔 gravitational acceleration. ambient radiation to the surface was calculated as below. −𝑛𝑞 = 𝜀𝜎(𝑇𝑎𝑚𝑏 4 − 𝑇4) (8) 𝜀 is the emissivity of the surface, 𝜎 is stefan-boltzmann constant, 𝑇𝑎𝑚𝑏is the ambient temperature, 𝑛 is the surface normal vector. phase change interface calculations were performed regarding the equations below. in stationary and timedependent studies, the temperature is set to the phase change temperature, 𝑇𝑝𝑐 , on the interface: 𝑇 = 𝑇𝑝𝑐 (9) in addition, in time-dependent studies, the stefan condition defines the phase change interface velocity 𝑣𝑛 from the conductive heat flux jump across the interface, q, the latent heat of phase change from solid to fluid, 𝐿𝑠→𝑓, and the solid density, 𝜌𝑠: 𝑣𝑛 = 𝒒 𝜌𝑠𝐿𝑠→𝑓 (10) with, 𝑞 = −𝑘𝑠𝛻𝑇𝑠 + 𝑘𝑓𝛻𝑇𝑓 (11) where 𝑘𝑠 and 𝑇𝑠 are the solid heat coefficient and temperature, 𝑘𝑓 and 𝑇𝑓 are the fluid heat coefficient and temperature of pcm. a portion of the solar energy entering the room heats the air, helping to achieve a comfortable temperature of 22°c. additionally, some of this energy is stored in the trombe wall for use at night. the energy stored within the trombe wall can be calculated using the following equation: 𝑄𝑇𝑊 = 𝑚𝑇𝑊 × 𝑐𝑇𝑊 × 𝑇𝑇𝑊 (12) where 𝑇𝑇𝑊 is the temperature of trombe wall, 𝑚𝑇𝑊 is the total mass, 𝑐𝑇𝑊 is the total specific heat which are calculated as below: 𝑚𝑇𝑊 = 𝑚𝑝𝑔 + 𝑚𝑝𝑐𝑚 (13) n. meco & c. firat /future energy may 2025| volume 04 | issue 02| pages 12-22 18 where 𝑚𝑝𝑔 and 𝑚𝑝𝑐𝑚 are the mass of pyrolytic graphite and pcm respectively. 𝑐𝑇𝑊 = ( 𝑚𝑝𝑔 𝑚𝑇𝑊 ) × 𝑐𝑝𝑔 + ( 𝑚𝑝𝑐𝑚 𝑚𝑇𝑊 ) × 𝑐𝑝𝑐𝑚 (14) where 𝑐𝑝𝑔 and 𝑐𝑝𝑐𝑚 are the specific heat of pyrolytic graphite and pcm respectively. the increased temperature, 𝑇𝑟, by the utilization of energy, 𝑄𝑇𝑊 is given as below: 𝑇𝑟 = 18 + 𝑄𝑇𝑊 (𝑚𝑎𝑐𝑎)⁄ (15) where 𝑚𝑎 is mass and 𝑐𝑎 is specific heat of air. the fundamental thermal model for the room-trombe wall system is depicted in figure 8, providing a schematic representation of thermal transfer within the system. figure 8. thermal model for the room-trombe wall system several assumptions were made based on thermal transfer principles: • the thermal physical properties used in this model are considered constant. • pyrolytic graphite exhibits high thermal conductivity inplane but low conductivity through-plane; it is assumed to be utilized as an in-plane conductive material. boundary conditions of the simulation model are given below. • room is a closed system that has no fluid in or out from the system. • outlet temperature and heat flux inlet from solar radiation is taken according to the weather data. • initial temperature and pressure of the room is taken as 18℃ and 1 atm. • all the walls of the room except trombe wall and window are insulated. • heat flux from solar radiation is applied to window and trombe wall. • no slip condition is applied to the walls. • acceleration of gravity is assumed as constant. • pressure point constraint point is taken the left corner of the room. • given the minimal nano-enhancement present in the noctadecane/eg composite (nepcm), its density is considered equivalent to that of pure n-octadecane. 3. results and discussion this section presents the simulation results obtained from the two-dimensional finite element method (fem) model. the simulations were conducted for the seven coldest months of the year: january, february, march, april, october, november, and december. the initial simulation utilized nepcm, specifically a combination of n-octadecane and expandable graphite (eg), yielding promising results. temperature readings for the trombe wall, pcm, and the room were recorded and are illustrated in figure 9. figure 9. first simulation temperature data the initial room temperature was set at 18°c. in figure 9, the blue line represents the average ambient temperature. the simulations, which incorporated weather and solar radiation data, revealed an increase in room temperature over the simulation period. december, january, and february recorded the lowest average room temperatures at 19.57°c, 19.23°c, and 19.40°c, respectively. this increase can be attributed to the trombe wall's high thermal conductivity. the heating effect of the trombe wall extended beyond the room itself, resulting in an increase in the temperature of pcm as well. the pcm serves as a thermal energy storage medium, absorbing heat until the room temperature drops below that of the trombe wall. during these periods, the stored energy in the pcm is released to provide additional heating to the room. the sunshine duration for each month was factored into the simulation, with corresponding temperature distributions shown in figure 10. to further investigate the impact of nano-enhancement on phase change materials (pcms), a second simulation was conducted using n-octadecane pcm without any nanoenhanced components. this simulation employed the same weather data for istanbul as used in the nepcm scenario. to ensure consistency, the trombe wall design, room layout, and material characteristics were identical to those in the first simulation. this approach allows for a controlled comparison between nepcm and standard n-octadecane pcm performance under identical environmental conditions and physical constraints. the primary goal was to isolate and evaluate the specific effects of nano-enhancement on the thermal behavior of the pcm and its interaction with the trombe wall system. figure 11 shows the second simulation temperature data. the results indicated a positive correlation among the temperatures of the room, pcm, and trombe wall. the trombe wall consistently exhibited higher temperatures than both the room and pcm, likely due to its superior thermal conductivity that facilitates efficient heat transfer from the wall to both areas. the months of december (19.56°c), january (19.15°c), and february (19.28°c) recorded the lowest average room temperatures. this trend can be attributed to a combination of lower ambient temperatures during these months and an increased thermal demand for heating. overall, these simulations demonstrate how both standard n-octadecane and its nano-enhanced counterpart perform under winter conditions, highlighting significant differences in thermal behavior that could influence future designs of passive solar heating systems using trombe walls. n. meco & c. firat /future energy may 2025| volume 04 | issue 02| pages 12-22 19 figure 10. temperature distribution of the room for the month: (a) january, (b) february, (c) march, (d) april, (e) october, (f) november, (g) december n. meco & c. firat /future energy may 2025| volume 04 | issue 02| pages 12-22 20 the analysis of room temperature data indicated that the use of nano-enhanced phase change material (nepcm) resulted in a noticeable increase in temperature, especially during the colder months as shown in figure 12. figure 11. second simulation temperature data figure 12. room temperature comparison between pcm materials while the differences between the nepcm and nonnepcm scenarios were minimal in january, february, and december, march showed the most significant variation. this pattern can be attributed to two main factors: increased solar radiation: in march, there was a relatively higher level of solar radiation, even though the sunshine duration was shorter compared to april. this additional solar energy contributed to greater thermal gain in the trombe wall, thereby amplifying the temperature difference associated with nepcm. latent heat storage capacity: the latent heat storage capacity of nepcm likely played a vital role during this month. when solar radiation was high, the pcm absorbed and stored thermal energy, which was then gradually released during cooler periods of the day or on subsequent days when solar input was less available. this ability to act as a latent heat buffer allowed for a more sustained increase in temperature compared to scenarios that did not utilize nepcm. the performance of two different phase change materials (pcms) was examined: n-octadecane (pcm, represented by the blue line) and a composite of n-octadecane with expanded graphite (nepcm, represented by the orange line). the temperature profiles for both materials showed a high degree of similarity; however, the nepcm consistently recorded slightly higher temperatures as shown in figure 13. the trombe wall was exposed to solar radiation, allowing for an assessment of the effects of both pcm and nepcm. the analysis indicated that the average temperature of the trombe wall was slightly higher when nepcm was employed as seen in figure 14. the temperature difference observed between the trombe wall conditions with pcm and nepcm closely mirrored the temperature variation between the two materials themselves. this suggests that the enhanced thermal conductivity of the nepcm, attributed to its nanoengineered structure, significantly influenced both its own temperature and that of the trombe wall. this indicates that the nano-enhancement primarily affects the material's energy storage capacity rather than its temperature-dependent phase transitions. further analysis revealed a notable difference in the amount of stored energy between the two pcms. during the colder months, the nepcm demonstrated an average of 16% more stored energy compared to the standard pcm. this enhancement can be attributed to the improved thermal conductivity and heat transfer capabilities provided by the nano-engineered structure of the nepcm, which facilitates more efficient absorption and retention of thermal energy within the material. using the stored energy, it is possible to adjust the room temperature by approximately 0.2°c in december; although this change may seem minor and not significantly impact nighttime comfort, it is sufficient to maintain a pleasant sleeping environment. figure 13. temperature comparison between pcm materials figure 14. tw temperature comparison between pcm materials 4. conclusion this study is confined to a theoretical analysis and numerical simulation focused on the thermal performance of single-sided trombe walls utilizing two types of phase change materials (pcms): standard n-octadecane and a nanoenhanced composite of n-octadecane with expandable graphite (nepcm). through a series of simulations conducted over the coldest months of the year, key findings were obtained that highlight the advantages of incorporating nepcm into passive solar heating systems. the results demonstrated that the use of nepcm led to a noticeable increase in room temperature, particularly during colder months. the contribution of nepcm compare to pcm was observed the most in march. this enhancement was attributed to two primary factors: the higher solar radiation received in march, despite a shorter sunshine duration compared to april, and the superior latent heat storage capacity of nepcm. the ability of nepcm to absorb and n. meco & c. firat /future energy may 2025| volume 04 | issue 02| pages 12-22 21 gradually release thermal energy significantly contributed to maintaining comfortable indoor temperatures, even during periods of limited solar input. for instance, in december, the room temperature rises from 18°c to 19.5°c while consuming approximately 71.6 kj of energy, equivalent to a cost of 0.02 kwh. this research offers valuable insights into sustainable building design practices, equipping architects and engineers with crucial information for optimizing passive solar heating systems. ultimately, the study promotes environmentally friendly and energy-efficient building designs, supporting global efforts to address climate change and reduce greenhouse gas emissions. furthermore, the analysis revealed that the average temperature of the trombe wall was slightly elevated when nepcm was utilized, reflecting its enhanced thermal conductivity. this characteristic not only improved the energy storage capacity of the material but also positively influenced the overall thermal performance of the trombe wall system. the findings indicate that integrating nano-enhanced materials like nepcm can substantially improve the efficiency of passive solar heating systems. by optimizing energy absorption and retention, nepcm serves as a valuable component in designing more effective and sustainable building systems. in conclusion, this research underscores the potential of utilizing nano-enhanced phase change materials in trombe walls to enhance energy efficiency and occupant comfort. future studies should explore the long-term performance and economic viability of these materials in real-world applications, as well as their environmental impact, to fully understand their role in advancing sustainable building practices. the significance of this study lies in its contribution to advancing sustainable building design practices. by conducting numerical investigations of trombe walls using finite element method simulations, this research aims to provide architects and engineers with practical insights for optimizing passive solar heating systems. the findings may influence architectural and engineering decisions by offering a clearer understanding of trombe wall behavior and their potential role in reducing building energy consumption. ultimately, this study seeks to promote environmentally friendly and energy-efficient design strategies aligned with global efforts to combat climate change and reduce greenhouse gas emissions. ethical issue the authors are aware of and complies with best practices in publication ethics, specifically concerning authorship (avoidance of guest authorship), dual submission, manipulation of figures, competing interests, and compliance with policies on research ethics. the authors adhere to publication requirements that the submitted work is original and has not been 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[34] hong x., he w., hu z., wang c., ji j., 2015. threedimensional simulation on the thermal performance of a novel trombe wall with venetian blind structure, energy and buildings, 32-38. this article is an open-access article distributed under the terms and conditions of the creative commons attribution (cc by) license (https://creativecommons.org/licenses/by/4.0/). https://creativecommons.org/licenses/by/4.0/ aa. rifat et al. /future energy february 2026| volume 05 | issue 01| pages 01-09 1 article effect of piston bowl geometry on combustion, performance, and emission characteristics of a dual-fuel engine abdullah al rifat, md. mizanur rahman, md. arafat rahman* department of mechanical engineering, chittagong university of engineering and technology, chittagong-4349, bangladesh a r t i c l e i n f o article history: received 05 august 2025 received in revised form 14 september 2025 accepted 30 september 2025 keywords: piston bowl, dual-fuel, engine, energy share, combustion and emission *corresponding author email address: arafat@cuet.ac.bd doi: 10.55670/fpll.fuen.5.1.1 a b s t r a c t the piston bowl shape plays a crucial role in turbulence, swirl, and subsequent fuel-air mixing, which in turn affect combustion, emissions, and performance attributes. a cylinder stepped and modified re-entrant combustion chamber was investigated through ansys forte 2023 r1 cfd software to analyze combustion, emission, and performance characteristics in a diesel-methane dual-fuel engine. numerical investigation is performed under 0.44 mpa load, 50% methane energy contribution, 7° start of injection btdc, and with a 120° spray angle. methane is injected into the inlet manifold to be premixed with air. the maximum thermal efficiency was found to be 34.11%, and a specific fuel consumption of 270.44 g/kw-h was indicated by the modified re-entrant bowl shape. the combustion duration for a modified re-entrant is 6.73% and 14.38% higher than that of a cylinder and stepped bowl. higher combustion efficiency, combustion duration, and total apparent heat release demonstrate sustained combustion in the modified re-entrant bowl. strong early premixed combustion in a cylinder-shaped bowl gives the highest percentage of nox. the stepped bowl has fuel-rich zones near the center after 19° ca, with lower temperatures near the center, giving higher amounts of uhc and voc emissions. the amount of o and oh radical formation in the modified re-entrant bowl was lower, and delayed oxidation resulted in a higher amount of co emission. the modified reentrant bowl offered the best combustion, performance, and emission attributes among the bowl shapes. 1. introduction internal combustion engines (ice) persist as a significant part of the energy cycle. the global impact of vehicle emissions on the environment is increasing. ices must meet high-performance and minimal-emission regulations, which complicates engine design [1]. engine manufacturers have expanded their research on reducing exhaust emissions in response to growing awareness of air pollution and increasingly restrictive emission regulations. in addition, several studies are conducted on the parameters that influence the performance of engines and combustion [2]. the efficiency, combustion characteristics, and emissions of a compression ignition engine are influenced by various factors, including fuel standards, operating conditions, and engine structural design [3]. a more rapid and efficient blend of air and fuel is the most significant requirement for lowering exhaust emissions, boosting engine performance, and enhancing combustion characteristics [4]. the piston bowl, or upper section of the piston, creates the combustion chamber alongside the cylinder bowl. the design of the piston bowl alters the turbulent nature of the flow and the consistency of the air-fuel mixture [1]. improving the geometry of the combustion space, adjusting injection parameters, and optimizing air movement characteristics can enhance the mixing ability of diesel fuel with air. for optimal geometry, the ratio of air to fuel should be adjusted, and for better evaporation, there ought to be greater circulation of air in the cylinder in the form of swirl, squish, and turbulence [2]. the effect of piston bowl shape on engine flow, turbulence, mixing, and burning has been widely studied in the literature [5–11]. advances in fuel-air mixing across the cylinder have an opportunity to significantly improve combustion and thereby increase engine performance [12]. the gas flow inside the cylinder is primarily influenced by swirl alongside turbulent kinetic energy, which in turn affects flame propagation [13]. over the last decade, researchers have shown a strong interest in diesel engine combustion chamber design, which offers various approaches for enhancing airflow within the future energy open access journal https://doi.org/10.55670/fpll.fuen.5.1.1 february 2026| volume 05 | issue 01 | pages 01-09 journal homepage: https://fupubco.com/fuen issn 2832-0328 mailto:arafat@cuet.ac.bd https://doi.org/10.55670/fpll.fuen.5.1.1 https://fupubco.com/fuen aa. rifat et al. /future energy february 2026| volume 05 | issue 01| pages 01-09 2 engine's cylinders. optimal bowl shape increases air/fuel mixture creation while reducing rich regions [14]. both nitrogen oxide (nox) emissions and local temperature rise can be reduced by eliminating rich mixing regions [15]. the impact of combustion chamber shape on the performance of the engine, flow field, and air-fuel interaction is extremely complex. the ices intricate structure has hampered experimental studies into the shape of the piston bowl. the investigation will be costly and time-consuming. as a result, numerical modeling has become a helpful tool for evaluating and improving engine control systems due to its greater versatility and lower cost when compared to experimental approaches [16]. kakaee et al. [17] studied numerically three piston bowl shapes, namely stock, bathtub, and cylindrical, in a diesel engine at medium load. reported that the bathtub shape turned out to have the best performance and emission values. the bowl profile did not significantly affect the combustion of the reactivity-controlled compression ignition (rcci) engine at low engine speeds, but it had a substantial impact at higher engine speeds. the bowl profile had a considerable effect on nox, but a negligible effect on unburned hydrocarbons (uhc) and carbon monoxide (co). singh et al. [18] studied various combustion chamber shapes, finding that the required tumble, swirl, squish, and turbulence attributes in the chamber can be enhanced, resulting in lower emissions and improved performance. the re-entrant piston bowl is best for generating turbulent kinetic energy and swirl during the compression stroke. hariharan et al. [19] studied with reentrant bowl and shallow bowl geometry. under identical conditions, there was a slight variation in the combustion aspect between these two geometries; however, the shallow bowl design performed somewhat better in terms of thermal efficiency. saito et al. [20] evaluated traditional and re-entrant bowls in a diesel engine to evaluate performance, emissions, and combustion characteristics. consequently, the ignition delay is minimized because the re-entrant configuration is hotter than the opposite wall where the fuel strikes. furthermore, as the number of air motions in the cylinder increased, turbulence also increased, and combustion attributes improved. gülcan and ciniviz [10] studied the effects of toroidal and toroidal re-entrant chamber geometry on a methane diesel engine. the testing results revealed that the toroidal re-entrant combustion chamber (trcc) design eliminates the long ignition delay caused by methane addition and provides more stable combustion under all torque settings. in summary, the trcc geometry has been demonstrated to be a practical approach for achieving improved combustion and reduced emission levels in dual fuel mode under torque conditions ranging from 3 to 9 nm. yaliwal et al. [21] found that the re-entrant design combustion chamber performed best at an injection pressure of 23 mpa and a nozzle opening of 0.25 mm, with 4 holes. dempsey et al. [22] demonstrated that at a low load, the shallow cylinder has much higher combustion efficiency than the re-entrant bowl piston due to lower heat transfer losses and greater combustion efficiency. using the typical reentrant piston bowl design, these fuel combinations achieve minimal nox and particulate matter (pm) emissions while reaching a maximum gross required efficiency of 48%. over the whole load and speed range, the redesigned piston produced minimal nox and pm emissions, with a peak gross stated efficiency of around 51%. bapu et al. investigated the modified hemispherical combustion chamber (mhcc) and traditional hemispherical combustion chamber (hcc) designs in a diesel engine using ansys fluent software. according to the results, mixing was improved when flow motions at different places of the piston were studied instead of the hcc [23]. pham et al. [24] studied the impact of piston bowl shape on combustion and emissions in a heavy-duty marine diesel engine. three different piston bowl configurations were numerically investigated. the study found that ω-type and re-entrant piston chambers increased cylinder power and decreased specific fuel consumption compared to u-type chambers. ω-type and re-entrant piston heads have lower peak temperatures than u-type piston crowns, resulting in decreased nox emissions. piston bowl design was also discovered to have no influence on soot and carbon dioxide (co2). the application of re-entrant piston chambers is strongly suggested for improving engine efficiency and fuel economy while lowering nitrogen monoxide (no) emissions. mobasheri and peng [25] employed computational fluid dynamics (cfd) modeling to investigate the impact of a reentrant chamber on mixture preparation, combustion, and engine performance. when determining the influence of the combustion chamber, thirteen alternative designs were analyzed and categorized into four key aspects: bowl depth, breadth, bottom surface, and lip area. the findings indicated that the shape of the combustion chamber has a substantial impact on the combustion process. it was demonstrated that by modifying the shape of the bowl, the level of emission pollutants could be lowered while other engine performance metrics remained constant. the purpose of this research is to assess the performance, combustion, and emission characteristics of a dual-fuel diesel engine with different piston bowl shapes via ansys forte 2023 r1 cfd numerical software. while piston bowl design has a substantial impact on air-fuel mixing, ignition delay, and combustion parameters in diesel engines, it draws little attention in studies of methane-diesel dual-fuel combustion. this study conducts a complete cfd-based analysis of various bowl shapes to determine their effects on in-cylinder pressure, thermal efficiency, and emissions. the findings demonstrate the piston bowl effect as a viable strategy for enhancing performance and lowering emissions in dual-fueled engines. 2. computational methodology 2.1 governing equation the gas-phase working fluids are modeled using a mixture of several gas species in cfd. the continuity equation for a whole gas-phase fluid can be obtained by combining the equations for all species. their composition changes while the engine is running due to molecular diffusion, flow convection, turbulence transport, contact with fuel sprays, and combustion. governing equations are essentially dictated by the perfect gas law during the gas phase, newtonian fluid dynamics, fick's law governing mass diffusion, and fourier's law governing thermal diffusion. the species conservation equation [26] is stated in eq (1). here, n=1, 2, … n, subscript n is the species index, n is the total species number, �̃� is the density, �̅� is the velocity, 𝑦𝑛 = 𝜌𝑛 𝜌 is the mass fraction of species n; and �̃�𝑛 𝑐 𝑎𝑛𝑑 �̃�𝑛 𝑠 are chemical reactions and spray evaporation terms, respectively. the term, 𝜙 is the effect of the ensemble's mean convection factor [27] stated in eq (2). 𝛿�̃�𝑛 𝛿𝑡 + 𝛻. (�̃�𝑛�̅�) = 𝛻. [�̃�𝐷𝛻�̃�𝑛] + 𝛻. 𝜙 + �̃�𝑛 𝑐 + �̃� 𝑛 𝑠 (1) 𝜙 = �̃�𝑛�̅� − 𝜌�̇�𝑣̅̅ ̅̅ ̅ (2) aa. rifat et al. /future energy february 2026| volume 05 | issue 01| pages 01-09 3 the continuity equation of the gas phase fluid is stated in eq (3) [27,28]. 𝛿�̃� 𝛿𝑡 + ∇. (�̃��̅�) = �̃�𝑠 (3) equation (4) is the momentum equation used in ansys forte, which accounts for convection, pilot fuel spray, viscous stress, pressure force, gravity force, and turbulence transport effect [26]. where, �̅�, �̅�𝑠, �̃� and �̅� are the pressure, momentum gain rate for spray per unit volume, stress due to the effects of ensemble-averaging the nonlinear convection, and body force, respectively. the viscous shear stress, �̃�, is stated in eq. (5) where, 𝐼 and 𝜐 accounts for the identity tensor and kinematic viscosity, respectively. 𝛿�̃��̅� 𝛿𝑡 + ∇. (�̃��̅��̅�) = −∇�̅� + ∇. �̃� − ∇. γ̃ + �̅�𝑠 + �̃��̅� (4) �̃� = �̃�𝜐 [∇�̅� + (𝛻�̅�)𝑇 − 2 3 (𝛻�̅�)𝐼] (5) from 1st law of thermodynamics, a change in internal energy needs to be equalized by pressure work and heat transfer. eq (6) is the internal energy transport mathematical equation [27,28]. where, �̃�, 𝜀̂, �̅�𝑟 , �̅� and h ̃ are the specific internal energy, dissipation rate, radiation heat loss, heat flux vector and effect of convection parameter filtering, respectively. the �̅�𝑐 and �̅�𝑆 are the source effects due to chemical heat release parameters and spray interactions, respectively. 𝛿�̃��̃� 𝛿𝑡 + ∇. (�̃��̅��̃�) = − �̅� ∇. �̅� − ∇. �̅� − ∇. �̃� + �̃�𝜖̂ + �̃�𝑐 + �̃�𝑆 − �̃�𝑟 (6) the flow turbulence model is for solving the reynoldsaveraged navier-stokes (rans) equations. the focus of rans is to simulate the ensemble-mean flow. the ensemble is an average that enables the understanding of incidents depending on the repeatability of multi-component flow streams. the reynolds stress tensor, �̃�, and the turbulent kinematic viscosity, 𝜐𝑇, are shown in eqs (7) and (8), respectively [27], where, 𝐶𝜇 is the model constant that varies with various turbulence models. the turbulent kinetic energy, 𝑘�̃� , is represented in eq (9) [29]. �̃� = −�̃�𝜐𝑇 [∇�̅� + (𝛻�̅�)𝑇 − 2 3 (𝛻. �̅�)𝐼] + 2 3 �̃�𝑘�̃�𝐼 (7) 𝜐𝑇 = 𝐶𝜇 𝑘�̃� 2 �̂� (8) 𝑘�̃� = 1 2�̃� 𝑡𝑟𝑎𝑐𝑒 (γ̃) = 1 2 �̅�. �̅�̅̅ ̅̅̅ (9) the turbulence flux parameter in the species transport numerical model [29] is represented in eq. (10). equations (11) and (12) refer to the turbulence flow factor, �̃�, [27], and the reynolds stress, �̃�, respectively [28]. where dt and �̅�𝑡𝑐 are the turbulence diffusivity and turbulence thermal conductivity, respectively. 𝜙 = �̃�𝐷𝑇∇�̅�𝑡𝑐 (10) �̃� = −𝑘∇�̅� − �̃�𝐷𝑇 ∑ ℎ̃𝑛∇�̅�𝑛𝑛 (11) �̃�𝑟 = �̃�(𝑣𝑣̅̅ ̅ − �̅��̅�) (12) 2.2 bowl geometry and mesh three different piston bowl geometries, namely cylinder, stepped, and modified re-entrant, shown in figure 1(a)-(c), respectively, are analyzed at 110° spray angle. to account for the symmetry of the combustion chamber, the bowl of eight injectors is divided into one-eighth sections. for injectors that are uniformly spaced, factors like injection pressure, temperature, air-fuel mixing, and combustion events are considered to be similar across each hole in the injector and the corresponding spray [27]. in this study, the sector angle is set to 45°, having periodic boundary conditions applied at the periodic faces. figure 1. piston bowl shape, (a) cylinder, (b) stepped, and (c) modified re-entrant the peak cylinder pressure (pcp) values for the cylindershaped bowl model range from 7.78 mpa to 8.31 mpa, as illustrated in figure 2(a). mesh count 20600 has a pcp of 8.31 mpa and is used as the final mesh for modeling a cylindrical bowl. the pcp in a stepped bowl occurs at 15660 and 18375 mesh counts; these two pcp are close enough, and the highest is shown in figure 2(b). the final mesh number for the stepped bowl is 18375. for the modified re-entrant bowl, mesh number 18120 is used for the final mesh. hydrocarbon (hc) and co pollutants firstly increased and then decreased over different methane energy share (mes), and a maximum reduction of nox by 35% at a 50% mes level [30]. co decreased when the mes was increased from 0 to 50%. co emissions increase significantly as the mes reaches 75%. methane absorbs a considerable portion of the oxygen inside the intake manifold, minimizing co oxidation. at 75% mes, the diesel amount is extremely low to ensure complete combustion of methane, and it cannot burn on its own because of its greater auto-ignition temperature. incomplete combustion causes higher co emissions [31]. this study uses 50% mes to examine combustion, performance, and emissions. the engine operating conditions for the bowl shapes are given in table 1. table 1. engine parameters type of engine single cylinder, 4stroke piston diameter 139.7 mm piston stroke 152.4 mm squish 5.6 mm connecting rod dimension 304.8 mm crevice width 1.67 mm crevice height 37.2621 mm geometric compression ratio 11.1957 total nozzle count 8 nozzle orifice diameter 0.1961 mm speed 1200 rpm start of diesel injection −7° atdc spray angle 110° inflow droplet temperature 384 k discharge co-efficient 0.7 aa. rifat et al. /future energy february 2026| volume 05 | issue 01| pages 01-09 4 table 2 demonstrates the initial and boundary conditions utilized in this simulation. these values are useful in scenarios involving three different piston bowl shapes. the piston, head, and liner all have a wall model, which allows for more accurate capture of the influence of the wall boundary layer. 2.3 chemistry and sub-models to set out the chemical reaction process for dual fuel combustion, a chemkin file was developed by combining the diesel and methane chemkin mechanism data with the chemkin 2023 r1. the n-heptane [32] describes how diesel fuel burns in a conventional diesel engine. the gri-mech 3.0 [33] is a popular chemical kinetics instrument for modeling methane combustion. the total number of species and reactions was below the individual sums of the two processes. the explanation is that both processes contain the same species and reactions. this merged chemkin file is added to the chemical set in the chemistry model. table 2 lists some of the other cfd sub-models required for this study. 2.4 model validation the numerical findings of pcp for diesel combustion are then compared with in-cylinder pressure by musculus's reported data [34], demonstrating appropriate consistency as shown in figure 3. the pcp fluctuations of approximately 2.45% were discovered when compared to the current study. table 2. initial and boundary conditions parameters correspondent data intake valve closing 165° btdc exhaust valve opening 125° atdc intake pressure 2.33 bar intake mixture temperature 384 k primary swirl ratio 0.5 primary swirl shape factor 3.11 turbulent kinetic energy 10,000 cm2/sec2 wall temperature of piston 400 k head temperature of piston 375 k liner temperature of piston 365 k figure 2. optimum mesh: (a) cylinder, (b) stepped, and (c) modified re-entrant aa. rifat et al. /future energy february 2026| volume 05 | issue 01| pages 01-09 5 figure 3. validation for cylinder pressure with musculus 3. results and discussion 3.1 bowl shape effect on combustion the pcp of the modified re-entrant bowl is 0.28% and 0.7% higher than the cylinder and stepped bowl, respectively. the highest pcp of modified re-entrants suggests an early start of combustion. the area under the cylinder pressure (cp) and crank angle (ca) demonstrates the net release of heat during combustion. figure 4 represents cp variation for three different bowl shapes. the modified re-entrant bowl promotes more complete burning compared with the cylinder and stepped bowl. the uniform pressure variation of the modified re-entrant suggests turbulence increased in the combustion chamber, which enhances mixing of the premixed charge and diesel. the peak cylinder temperature (pct) of the modified re-entrant shape is 1.24% and 0.46% higher than that of the cylinder and stepped bowl, respectively. figure 5 represents cylinder temperature variation over crank angle. the modified re-entrant bowl leads to more efficient heat transfer inside the combustion chamber. improved mixing and turbulence can lead to higher pct. the peak apparent heat release rate (ahrr) is 0.075% and 9.53% higher in cylinder shape than in the modified re-entrant shape and steeped, respectively. the peak ahrr in the cylinder and the modified re-entrant shape are almost the same. ahrr for the three bowl shapes is shown in figure 6 at various ca. from 5° ca to -1.75° ca, ahrr increases and then decreases at the same rate; and at this range, values are close enough for both the modified re-entrant and cylinder shapes. after -1.75° to 3° ca, the ahrr curve for the cylinder shape is above the modified re-entrant. after 3° ca, the ahrr curve of the modified re-entrant curve surpasses the cylinder bowl. figure 4. in-cylinder pressure variation for three different piston bowl shapes this phenomenon exhibits weaker swirl, less turbulence, and early burning of the premixed phase, resulting in weaker diffusion-controlled combustion. the modified re-entrant bowl enhances air-fuel mixing, allowing more of the methaneair mixture to participate in sustained combustion after the premixed phase. the total apparent heat release (ahr) for the modified re-entrant is 8.07% and 2.74% higher than the cylinder and stepped bowl, respectively, as shown in figure 7(d). the longest duration for combustion is for the modified re-entrant shown in figure 7(b) and is for a maximum heat release of 2046.18 j. during the premixed phase, the combustion fuel burns rapidly. main diffusion phase combustion, which follows the premixed phase, is related to combustion duration with heat release rate (hrr) [35]. combustion efficiency (ce) of the modified re-entrant is 2.12% and 7.41% higher than that of the cylinder and stepped chamber, respectively, as shown in figure 7(a). the 10% to 90% heat release duration for the modified re-entrant is 6.73% and 14.38% higher than that for the cylinder and stepped bowl, respectively, as shown in figure 7(b). lower combustion duration (cd) signifies a short diffusion stage of combustion and improved premixed phase combustion [36]. a longer duration of heat release and the highest ce indicate sufficient time to oxidize fuel, more sustained combustion, and an increase in total heat release. for the stepped bowl, the peak ahrr, ce, and cd are lower than for the cylinder shape, but the total ahr is 5.19% higher. figure 5. cylinder temperature variation for three different piston bowl shapes figure 6. ahrr variation for three different piston bowl shapes aa. rifat et al. /future energy february 2026| volume 05 | issue 01| pages 01-09 6 ce demonstrates how much chemical energy is released from fuel into useful work. ce for stepped bowl signifies mixing is poor and a larger amount of fuel is oxidizing incompletely. figure 9 shows the highest percentage of uhc and voc emissions from the stepped bowl. a strong late diffusion burn can give a large area under the ahrr curve without a significant amount of complete oxidation. peak pressure rise rates (pprr) are almost the same for both the cylinder and the modified re-entrant bowl, as shown in figure 7(c). the modified re-entrant bowl has high pprr with high ce. besides, the cylinder has similar pprr, but less overall oxidation, demonstrating it is less favorable than the modified re-entrant bowl. figure 7. comparison of, (a) combustion efficiency, (b) combustion duration, (c) maximum pressure rise rate, and (d) total ahr for three different bowl shapes 3.2 bowl shape effect on performance the amount of fuel consumed per kwh is indicated by specific fuel consumption (isfc). the isfc is 1.5% and 7.05% higher in the cylinder bowl than in the stepped and modified re-entrant shapes, respectively, as shown in figure 8 (a). thermal efficiency is the fraction of fuel energy that is converted into work. the thermal efficiency for the modified re-entrant is 4.86% and 6.5% higher than the stepped and cylinder bowl, respectively, as shown in figure 8 (b). enhanced swirl and turbulence are generated by the reentrant lip, which improves mixing and sustained oxidation during the diffusion phase in the modified re-entrant bowl. a modified re-entrant bowl yields lower isfc and higher thermal efficiency, enabling a significant fraction of chemical energy to be converted into useful work. despite the intermediate ce and cd of the cylinder bowl, it has a higher isfc and lower thermal efficiency. the rapid burning of premixed fuel increases nox, as shown in figure 9 for the cylinder bowl shape, and weaker diffusion burn decreases total ahr, as shown in figure 7(d). 3.3 bowl shape effect on emission nox emissions of the cylinder bowl are 15.91% and 15.16% higher than those of the stepped and modified reentrant bowls, respectively, as shown in figure 9. the pct of the modified re-entrant shape is 1.24% and 0.46% higher, and the pcp is 0.28% and 0.7% higher than the cylinder and stepped bowl, but nox emission is higher in the cylinder bowl. the pct and pcp differences are not enough to define nox formation dependency due to temperature. in the cylinder bowl, pcp and pct occurred at 3° ca and 4° ca, respectively, as in figure 5. but, in the modified re-entrant bowl, pcp and pct occurred at 4° ca and 7° ca, respectively, and in the stepped bowl, they occurred at 4° ca and 6° ca, respectively. the cylinder-shaped bowl’s pcp and pct occurred earlier, close to top dead center (tdc), and pprr was also high. early pcp and pct conditions strongly favor zeldovich thermal nox formation. early pcp and pct with pprr indicate a very fast premixed burn near tdc. although the modified re-entrant has a longer cd than the cylinder bowl, the stronger, earlier, and instantaneous combustion in the cylinder bowl provides a larger integrated nox. the superior mixing inside the modified re-entrant shape lowers local fuel-rich hot spots; this lowers local nox formation. figure 8. comparison of (a) isfc, and (b) thermal efficiency, for three different bowls figure 9. comparison of emissions for three different piston bowl shapes at 0.44 mpa load the co emission of the modified re-entrant is 6.32% and 37.41% higher than that of the cylinder and stepped bowl, respectively, as shown in figure 9. the presence of highly active o and oh free radicals increases the oxidation of co into co2 [37,38]. figure 10 shows the active o and oh radicals for three different bowls. from -165° ca to 125° ca simulation, the stepped bowl has a higher amount of o and oh radical formation than the cylinder bowl, and then the modified re-entrant bowl shape. as free radical formation is lower in the modified re-entrant, co emission is higher, as shown in figure 9. co emission is lower in stepped bowls due to higher o and oh radicals. in a steeped bowl, though radical formation is delayed, the cumulative radical formation is large and effectively converts co into co2. aa. rifat et al. /future energy february 2026| volume 05 | issue 01| pages 01-09 7 figure 10. reactive species, (a) oh radical, and (b) o radical the uhc emission of the stepped bowl is 17% and 35.62% higher than that of the cylinder and modified reentrant bowl, respectively, as shown in figure 9. a modified re-entrant bowl enhances very good mixing, and a longer cd and total ahr demonstrate a sustained diffusion phase and enable more oxidation, which lowers uhc. a short cd in a stepped bowl means weak diffusion-controlled combustion. the voc emission of the stepped bowl is 16.48% and 34.4% higher than that of the cylinder and modified re-entrant bowl, respectively, as shown in figure 9. voc evaporates easily, and uhc is a specific type of voc that results from the byproduct of incomplete combustion. 3.4 qualitative analysis at 3° ca, the stepped bowl has a higher small fuel vapor mass fraction (fvmf) shown in figure 11, which demonstrates that locally rich pockets remained unmixed into oxidant streams. the cylinder and modified re-entrant have fewer pockets; comparing these two, the modified reentrant provides slightly better mixing. at 7° ca, there are local rich hot zones for the cylinder and stepped bowl, and the rich cold zones of the steeped are highest at the head. overall, fvmf is the highest in the stepped bowl and then the cylinder bowl. from 11° to 19°, fvmf pockets almost remained unreacted by the cylinder and stepped bowl; that is a sign of much lower diffusion oxidation. fvmf still burns slowly from 11° ca to 19° ca, suggesting sustained diffusion oxidation. all bowls showed the fvmf reduction towards the centerline. fvmf concentrated near the cylinder axis much more for the stepped, then the cylinder, and then the modified re-entrant bowl. the modified re-entrant bowl better summarizes net mixing and steps down the lower net mixing. piston bowls showed higher and wider temperature distribution along the spray direction, as shown in figure 12, representing the premixed combustion region. the stepped bowl has a higher temperature zone near the bowl axis for 3° ca. at 11° ca, bowls have hot spots at the center, and stepped bowls show higher temperature distribution at the center. figure 11. fuel vapor mass fraction for different piston bowl shapes figure 12. temperature distribution for three different piston bowl shapes aa. rifat et al. /future energy february 2026| volume 05 | issue 01| pages 01-09 8 the stepped bowl has a hot spot at the squish zone and has a higher temperature distribution along the step curvature, but a much lower temperature distribution at the bowl radius periphery. the modified re-entrant bowl showed the higher temperature distribution along the bowl radius periphery and in the squish zone. cylinder bowls have a much higher temperature distribution along the lower bowl depth surface. at 19° ca, the modified re-entrant maintains a wide and uniform range of higher temperatures, reflecting sustained diffusion oxidation. around 3° ca, early wide hotspots with high pprr produce higher amounts of thermal nox. the contours demonstrate that the stepped bowl captures and maintains higher fuel vapor in the near middle, which remains unreacted because of the short diffusion phase and causes higher uhc and voc levels. the cylinder generates intense, early hotspots that cause the greatest nox levels, while its weaker diffusion burns result in modest uhc. the modified re-entrant generates a more uniform vapor distribution and sustains late oxidation, decreasing uhc and voc and boosting thermal efficiency. 4. conclusion this study investigates how a dual-fuel (df) engine at 50% mes is affected by different bowl geometries on combustion, emission, and performance attributes. the piston bowls are investigated with 45° sections for eight injectors with periodic boundary conditions at the periodic faces to reduce computational time. ansys forte 2023 r1 software was used for the analysis of the cylinder, stepped, and modified re-entrant bowl. there are some observations that have been found in this investigation as follows: • modified re-entrant’s longer combustion duration with higher combustion efficiency indicates enough time to oxidize fuel, more sustained combustion, and an increase in total heat release. for the stepped bowl, the peak ahrr, combustion efficiency, and combustion duration are lower than those of the cylinder shape, but the total ahr is 5.19% higher. the cylinder bowl has a similar pprr but less overall oxidation, demonstrating it is less favorable than the modified re-entrant bowl. • the modified re-entrant bowl has the highest thermal efficiency with lower isfc. the enhanced swirl and turbulence in the modified re-entrant chamber improve mixing and sustained oxidation during the diffusion phase. • in the cylindrical bowl, nox emissions peaked. nox emissions in stepped and modified re-entrant bowls are close enough. the uhc and voc emissions peaked in the stepped bowl with a larger fraction; the modified reentrant bowl was the lowest by 35.62% and 34.4%, respectively. the modified re-entrant bowl has the lowest amount of free radical formation results and the highest amount of co fraction. • a larger amount of fvmf remained unreacted in the middle of the stepped chamber, and a low temperature distribution at 19° ca results in a higher percentage of uhc and voc emissions. the temperature distribution from 7°ca to 19°ca, modified re-entrant bowl, showed a stable and uniform temperature distribution throughout the combustion chamber, demonstrating diffusion burn is superior to the cylinder-shaped bowl. it is noted that the best performance was shown by the modified re-entrant bowl. its lower isfc ensures the best fuel economy with higher combustion efficiency and thermal efficiency. sustained diffusion burning confirms complete fuel oxidation; that’s why there are lower uhc and voc. the only drawback is the higher co emission for delayed oxidation. acknowledgements this work is financially supported by chittagong university of engineering & technology (cuet), bangladesh through research grant no. cuet/chsr-47-47.4.11. the corresponding author is responsible for ensuring that the descriptions are accurate and agreed by all authors. 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[38] g. tripathi, a. dhar, performance, emissions, and combustion characteristics of methane-diesel dualfuel engines: a review, front. therm. eng. 2 (2022) 870077. this article is an open-access article distributed under the terms and conditions of the creative commons attribution (cc by) license (https://creativecommons.org/licenses/by/4.0/). https://creativecommons.org/licenses/by/4.0/ m. abdoos et al. /future energy february 2025| volume 04 | issue 01| pages 08-18 8 article evaluating zero-energy strategies in mixed-use buildings: a case study mahmood abdoos, mohammad mahdi mobaraki, hossein yousefi*, younes noroollahi school of energy engineering and sustainable resources, college of interdisciplinary science and technology, university of tehran, tehran, iran a r t i c l e i n f o article history: received 19 october 2024 received in revised form 24 november 2024 accepted 04 december 2024 keywords: zero energy building, mixed-use development, energy efficiency, thermal insulation, sustainable design, hvac systems *corresponding author email address: hosseinyousefi@ut.ac.ir doi: 10.55670/fpll.fuen.4.1.2 a b s t r a c t the building sector is responsible for over 40% of global energy consumption, necessitating innovative strategies to minimize energy usage in both commercial and residential buildings, ultimately striving for zero-energy status. this study addresses the relatively overlooked area of zero-energy buildings within the context of a combined commercial-residential structure, utilizing carrier (hap) software for precise thermal and cooling load calculations. the research introduces a multifaceted approach, examining various scenarios that influence energy demand reduction, including wall color modifications, the application of noble gases for window insulation, shading effects, and technical innovations in window dimensions. notably, this study emphasizes insulation as a cost-effective strategy for achieving zero-energy objectives, revealing that the optimal scenario incorporating krypton insulation, color adjustments, and effective shading achieves a significant 21.36% reduction in energy consumption. this research not only contributes novel insights into mixed-use building design but also provides a practical framework for future energyefficient building projects. 1. introduction in numerous countries across the globe, residential buildings account for approximately 40% of the energy demand in residential areas, with an impressive 60% of the total energy consumption specifically allocated towards maintaining optimal heating conditions within living spaces [1, 2]. moreover, it is worth noting that a predominant portion of this energy is consumed by air conditioning systems [3]. however, implementing thermal insulating materials in buildings yields a substantial reduction in energy load. furthermore, there has been a notable surge in the adoption of innovative technologies within the realm of building construction in recent years. this technical advancement has consistently resulted in improved building management practices and has paved the way for the successful administration of building systems [4]. implementing fundamental measures to conserve energy can result in a significant economic boost for the country. within this arena, design and construction play crucial roles, as energy consumption can be substantially reduced by applying innovative design and construction techniques [5]. the global concerns of energy scarcity and environmental pollution invoke apprehension, and it is widely acknowledged that curtailing energy demand in buildings presents an efficacious solution to address this pressing issue [6, 7]. researchers worldwide exhibit unwavering dedication in their endeavors to optimize the design and functionality of both buildings and energy systems [8-10]. accurate thermal-cooling load assessments are fundamental for designing efficient hvac systems. studies utilizing advanced software tools have demonstrated that proper load analysis can lead to reductions in energy consumption by up to 20% in office buildings, emphasizing the importance of integrating technology into building design processes [11, 12]. ramesh, g et al. [13] assert that buildings contribute to approximately thirty-eight percent of greenhouse gas emissions, with twenty percent attributed to residential buildings and eighteen percent to commercial structures, thereby placing them as significant contributors to global warming [14]. implementing effective insulation strategies is crucial for reducing energy consumption in buildings. a study assessing various insulation scenarios found that buildings could achieve up to 30% reduction in heating and cooling loads when combined with renewable energy systems (e.g., solar photovoltaic panels). this synergy is vital for reaching netzero targets, as highlighted in multiple building performance analyses [15, 16]. consequently, research conducted by felimban et al. [17] and colleagues posits that the demand for future energy open access journal https://doi.org/10.55670/fpll.fuen.4.1.2 february 2025| volume 04 | issue 01 | pages 08-18 journal homepage: https://fupubco.com/fuen issn 2832-0328 mailto:hosseinyousefi@ut.ac.ir https://doi.org/10.55670/fpll.fuen.4.1.2 https://fupubco.com/fuen m. abdoos et al. /future energy february 2025| volume 04 | issue 01| pages 08-18 9 electricity in the residential sector of saudi arabia is projected to double by 2025, in comparison to the statistics recorded in 2009. in their research, boemi et al. [18] contend that a pivotal advancement lies in the realm of sustainable design for residential and commercial buildings, coupled with the resilience of existing structures, all geared towards achieving reduced and optimized energy consumption. as elucidated by baetens. in their research, harnessing renewable energy sources to meet the energy demands of buildings constitutes a noteworthy means of curbing energy consumption [19, 20]. integrating solar panels in commercial properties has emerged as a transformative approach to achieving energy efficiency. a report noted that less than 3% of commercial buildings currently utilize solar panels; however, with over 8 billion square meters of suitable rooftops in the u.s., there is potential to generate approximately 1,400 terawatt-hours of electricity annually, nearly 40% of total utility sales. this transition from cost centers to profit centers underscores the financial viability of solar investments in commercial real estate [21, 22]. a comprehensive bibliometric analysis of renewable energy integration in zero-energy carbon buildings reveals critical gaps in research methodologies and implementation strategies. machine learning techniques are increasingly being applied to forecast energy needs and optimize the integration of renewable technologies, which is essential for enhancing building performance and achieving sustainability goals [23]. expounding on building energy modeling, robertson j. j. and colleagues propose various approaches to enhance energy efficiency, including the optimization of passive resilience [24], refinement of building position geometry [25], optimization of cooling tower exergy [26], and optimization of control systems for variable refrigerant flow [27]. using phase change materials has been shown to significantly enhance thermal comfort while reducing energy demands. research indicates that buildings employing pcm can reduce cooling energy consumption by up to 25%, particularly in climates with high-temperature variability. this innovative approach allows buildings to maintain comfortable indoor conditions with minimal reliance on mechanical cooling systems [28, 29]. the innovation of this research is distinguished by its comprehensive analysis of a large-scale mixed-use building, integrating both commercial and residential elements to achieve zero-energy status. unlike previous studies focusing on smaller, single-use structures, this research addresses the complexities associated with a 4072 square-meter facility, which presents unique thermal characteristics and energy management challenges. this study innovatively employs carrier (hap) software to model various scenarios that consider the impact of building colors, the use of noble gases like krypton for window insulation, and shading effects on energy consumption. by pioneering a comparative analysis between noble gases and traditional air insulation methods, this research provides valuable insights into enhancing energy efficiency in large buildings. furthermore, it incorporates an economic perspective by evaluating cost-effective insulation strategies while ensuring that the commercial integrity of the building is maintained. it fills a critical gap in the literature regarding mixed-use developments and sets a precedent for future studies to optimize energy performance in large-scale buildings. the findings underscore the viability of achieving zero-energy status through innovative insulation techniques and strategic design modifications, reinforcing the importance of such approaches in sustainable urban development. 2. mathematical expression building walls commonly comprise multiple layers composed of different materials, thereby transforming the wall into a composite structure. consequently, the thermal resistance exhibited by a composite wall can be determined by summing the resistances of its constituent layers. the composite thermal resistance of the wall is expressed in equation (1): thermal resistance composite wall: r1 + r2 + x1 k1 + x2 k2 + ⋯ (1) during the heat transfer process between the indoor and outdoor air of a building, a thin layer of air forms along the surface of the building wall, creating a thermal resistance that hinders the flow of heat. this layer, commonly referred to as the air film, exhibits a unit thermal coefficient denoted as f. the resistance of this air film, analogous to the resistance of the surrounding air, is represented by 1/f, where f is the value determined by the speed of the airflow. u = 1 1 fi +r1+r2+⋯+ 1 fo (2) u=the overall coefficient of thermal conductivity 1/fi=inner air film resistance r1, r2=thermal resistance of layers 1/fo=outdoor air film resistance the calculation of heat transfer through various building components, including walls, ceilings, floors, windows, and glass, can be determined using the following equation (3): 𝑄 = 𝐴𝑈(𝑡1 − 𝑡2) (3) q=heat transferred from the wall btu/hr. a=wall area ft2 t1=temperature on the warmer side ) f) t2=temperature on the cooler side) f) every building has certain rooms or spaces that we intentionally do not desire to be heated or cooled to the same extent. if there exists an unheated room adjacent to the space where we are assessing the thermal load, and this adjacent room does not undergo cooling. the temperature of the adjacent uncooled room is expressed in equation (4): adjacent uncooled room temperature = ti + (to − ti) ∗ 0.667 (4) 3. methodology 3.1 software hap software exemplifies the amalgamation of two formidable tools, offering a comprehensive package that encompasses the design of hvac systems for commercial buildings, as well as robust energy analysis capabilities to ascertain energy consumption and operational costs for various design typologies. the fusion of these two tools yields substantial time savings, as input data and calculations from the system design calculation can seamlessly transition into energy studies, obviating the need for redundant input. m. abdoos et al. /future energy february 2025| volume 04 | issue 01| pages 08-18 10 furthermore, the carrier (hap) hourly analysis software, an esteemed component of the carrier (hap) hvac design software family, holds the distinction of being one of the oldest and most all-encompassing software solutions available for accurately computing the cold and heat load of buildings across diverse applications [30]. 3.2 case study the average rainfall in tehran varies from 230 mm to 500 mm annually. tehran is one of the most climatic cities and four seasons in iran . precipitation is usually high in winter. the cold season starts in march but a little earlier in the mountains. cold seasons last three or four months. in february, the cold decreases gradually, and in late february, the weather warms up more quickly, and in early may, the weather is relatively warm. the climate of tehran province is warm and dry in the desert and south, in the cold and semihumid basin areas, and in the cold highlands with long winters. the warmest month of the spring year is reported with an average maximum temperature of 37 ° c, and the coldest month of the year with an average minimum temperature of zero ° c. the temperature in tehran is slightly cold in the mild winter and warm in the summer. for these reasons, this site was chosen over several other potential locations. the selection was primarily driven by two key factors. first, the site allows for the implementation and comparison of various scenarios, enabling the identification of the optimal option. second, the region's unique climate contributes significantly to the natural cooling and heating of the building, which is crucial for sustainable design. additionally, the study's scope is intentionally focused on facilitating the practical application of the best scenario. the project is situated within tehran, serving as a tangible real-world case study. it encompasses both commercial and residential functionalities, comprising six floors dedicated to residential use, four floors designated for parking, and an additional commercial floor supplemented by a half-floor extension. spanning an area of 4072 m2, this project represents a unique example not previously explored in the literature concerning the integration of commercial and residential spaces. particularly noteworthy are the numerous thermal waste spaces inherent in the design, offering opportunities for mitigation through the implementation of existing strategies. given the considerable size of the project, the imperative of energy reduction is underscored. table 1 provides insight into the climatic characteristics of the city, as elucidated within the carrier (hap) software, further informing the project's development. in this modeling endeavor, the selection of air conditioning systems emerges as a pivotal consideration, given the thermal demands inherent in both the commercial and residential sectors. the convergence of energy supply and coordination poses a significant challenge in this context. the ventilation system adopted for the modeled building comprises a fan coil system supplemented with fresh air intake. notably, the introduction of fresh air in the commercial sector plays a crucial role in alleviating thermal stress. furthermore, the heating system chosen for this mixed-use project is a packaged system. table 1. weather conditions in tehran city region middle east iran tehran location city latitude 35.5 deg longitude 51.4 deg elevation 5418 ft summer design db 104 f summer coincident wb 75 f summer daily range 25 f winter design db 25 f winter coincident wb 18 f soil conductivity 1 btu/hr/ft/f the selection of air conditioning units is meticulously aligned with the climatic nuances of tehran, where both cooling and heating functionalities are requisite owing to the climatic fluctuations. in this regard, neither system holds superiority over the other, and thus, they are not prioritized based on singular efficiency metrics. instead, the choice of air conditioning systems is calibrated to ensure optimal performance under diverse climatic conditions prevalent in tehran. 3.3 scenarios used in modeling 3.3.1 walls examining walls and their efficacy in mitigating energy consumption is a viable avenue for addressing energy and environmental concerns. according to table 2, it is stated that according to previous research, choosing the most appropriate color can significantly reduce energy consumption throughout the year. this reduction manifests in a cooling effect of approximately 1.5 degrees celsius during warm seasons and a corresponding increase in temperature of approximately one degree celsius during colder periods. the analysis reveals that the wall's design is crucial in minimizing heat transfer between the interior and exterior environments. the high absorptivity (0.900) of the dark exterior surface color suggests that while it may absorb more heat from sunlight, effective insulation strategies can mitigate excessive heat gain during warmer months. the total r-value indicates how well the wall resists heat flow; higher values correlate with better-insulating properties, essential for achieving zero-energy goals. the u-value reflects the rate at which heat is transferred through the wall assembly; lower uvalues are desirable as they signify reduced heat loss or gain. incorporating advanced insulation techniques and understanding the thermal dynamics of building materials is vital for achieving zero-energy buildings. this analysis not only underscores the importance of selecting appropriate materials but also advocates for innovative design considerations—such as wall color and layered construction, that can lead to substantial energy savings. by focusing on these elements within a mixed-use context, this research provides valuable insights for future developments to m. abdoos et al. /future energy february 2025| volume 04 | issue 01| pages 08-18 11 enhance energy efficiency in large-scale buildings, thus contributing to sustainable urban development goals. analysis of table 3, the enhanced thermal performance of wall type number 2 illustrates the importance of selecting appropriate materials and configurations for achieving zeroenergy buildings. the higher r-value signifies better insulation against heat transfer, critical for maintaining comfortable indoor temperatures while minimizing energy consumption. the significantly lower u-value suggests that this wall type will reduce heating and cooling loads, contributing to overall energy savings and supporting zeroenergy objectives. including r-7 board insulation represents a strategic advancement in building design to enhance energy efficiency. the shift to a lighter exterior color demonstrates an understanding of passive solar design principles, which can further optimize energy performance. in summary, the comparison between wall type number 1 and wall type number 2 underscores the critical role that material selection and design choices play in achieving zero-energy buildings. the advancements seen in wall type number 2, particularly through integrating high-performance insulation and strategic color selection, demonstrate a clear pathway toward enhanced energy efficiency in mixed-use developments. these findings reinforce the necessity for continued exploration and implementation of innovative building strategies that align with sustainability goals in the construction industry. according to table 4, wall 1's high absorption coefficient (0.9) implies it will absorb more solar heat, potentially leading to higher cooling loads in the summer months. in contrast, walls 2 and 3 have lower absorption coefficients (0.45), making them more favorable for energy conservation as they reduce the heat gained from solar radiation. the uvalue is a critical measure of thermal performance; wall 1 has the highest u-value (0.225), indicating poorer insulation and greater heat loss or gain compared to walls 2 and 3, which both have a much lower u-value (0.096). this substantial difference highlights the superior insulating properties of walls 2 and 3. the choice of color significantly affects energy performance; the dark color of wall 1 results in higher heat absorption and, consequently, increased cooling requirements. walls 2 and 3 utilize a dark and light color, respectively, both contributing to lower energy consumption due to their reflective properties and reduced heat gain. in summary, the analysis of table 4 reveals that walls 2 and 3 are more advantageous for achieving energy efficiency in building designs aimed at zero-energy goals when compared to wall 1. these walls' lower absorption coefficients and uvalues indicate better thermal performance and reduced energy demands for heating and cooling. this analysis underscores the importance of material selection and color choice in optimizing building envelopes for enhanced energy efficiency, particularly in mixed-use developments where diverse thermal characteristics must be managed effectively. table 2. details of wall type number 1 outside surface color dark absorptivity 0.900 layers: inside to outside thickness density specific .ht. r-value weight in lb/ft3 btu/lb/f hr-ft2-f/btu lb/ft2 inside surface resistance 0 0 0 0.68500 0 gypsum board 0.625 50 0.26 0.56000 2.6 air space 0.000 0.0 0.00 0.91000 0.0 lw concrete block 4.000 38.0 0.20 1.51500 12.7 face brick 4.000 125.0 0.22 0.43300 41.7 outside surface resistance 0.000 0.0 0.00 0.33300 0.0 total 8.625 4.44 56.9 overall u-value 0.225 btu/hr/ft2/f table 3. details of wall type number 2 outside surface color light absorptivity 0.450 layers: inside to outside thickness density specific.ht. r-value weight in lb/ft3 btu/lb/f hr-ft2-f/btu lb/ft2 inside surface resistance 0 0 0 0.68500 0 5/8 -in gypsem board 0.625 50 0.26 0.56004 2.6 r-7 board insulation 1.000 2.0 0.22 6.94445 0.2 4-in lw concrete block 4.000 38.0 0.20 1.51515 12.7 face brick 4.000 125.0 0.22 0.43300 41.7 outside surface resistance 0.000 0.0 0.00 0.33300 0.0 total 9.625 10.47 57.1 overall u-value 0.096 btu/hr/ft2/f m. abdoos et al. /future energy february 2025| volume 04 | issue 01| pages 08-18 12 table 4. technical specifications of walls defined in different scenarios 3.3.2 windows the window plays a crucial role in reducing energy consumption as an integral component of a building. widely regarded as a vital element in construction, the window serves multiple functions essential to the built environment. among these functions, providing ventilation, natural light, and illumination to the interior space is paramount. additionally, windows serve as filters, regulating the influx of sunlight and controlling the airflow to prevent excessive entry into the designated environment. when utilized effectively within a building, windows contribute significantly to enhancing the interior environment, thereby optimizing their impact on energy efficiency and overall comfort. according to table 5, window type number 1 features dimensions of 6.00 feet in height and 10.00 feet in width, constructed from aluminum without thermal breaks. this design choice may result in higher heat transfer compared to windows with thermal breaks, potentially leading to increased energy costs for heating and cooling. the overall uvalue of 0.779 btu/hr/ft²/°f indicates a moderate level of thermal performance, suggesting that this window may allow more heat loss compared to more efficient alternatives. furthermore, the overall shade coefficient of 0.827 signifies that the window provides a reasonable level of solar control, which can help mitigate excessive heat gain from sunlight. the absence of internal shading may enhance natural light entry but also necessitates careful temperature regulation within the space. in summary, while this window offers ample daylighting opportunities, its thermal performance may limit its effectiveness in energy-efficient building designs. the properties outlined in table 6 are critical for understanding how window type number 1 will perform in various thermal scenarios. the high transmissivity coupled with low reflectivity means this window type will allow substantial solar heat gain. while this can be beneficial in colder months for passive heating, it may pose challenges during warmer months when cooling demands increase. the relatively low absorptivity indicates that only a minor amount of solar energy is retained by the glass, which helps mitigate excessive heat buildup within the window assembly. table 5. details of window type number 1 however, in combination with high transmissivity, it suggests that careful consideration must be given to shading strategies to manage heat gain effectively. when comparing window type number 1 with other potential window configurations (not detailed here), several factors should be considered. unlike more advanced window types that may utilize multiple glazing layers or low-emissivity coatings to enhance thermal performance, window type number 1's simplicity may limit its effectiveness in extreme climates or high-performance applications. the gap type (¼-inch air space) provides some insulation; however, it may not be sufficient compared to windows employing argon or krypton gas fills or thicker air spaces that significantly improve thermal resistance. in practical terms, the characteristics of window type number 1 suggest several applications and considerations for building design. passive solar design: given its high transmissivity, this window type could be effectively utilized in passive solar design strategies where maximizing natural light and heat gain during winter months is desired. shading and control mechanisms: to counteract potential overheating during summer months, integrating external shading devices or using interior shading solutions will be essential to maintain comfort levels and reduce reliance on mechanical cooling systems. in summary, table 6 highlights the fundamental thermal characteristics of window type number 1, emphasizing its role in influencing energy efficiency within mixed-use buildings aimed at achieving zero-energy status. the balance between transmissivity, reflectivity, and absorptivity underscores the need for strategic design choices that optimize natural light while managing heat gain effectively. as part of a comprehensive energy strategy, this window type can contribute positively to overall building performance when integrated with appropriate shading and insulation techniques. according to table 7, window type number 2, with dimensions of 6.00 feet in height and 4.00 feet in width, is constructed from aluminum with thermal breaks, which aids in reducing heat transfer. this feature enhances energy efficiency and lowers heating and cooling costs. with an overall u-value of 0.557 btu/hr/ft²/°f, this window demonstrates relatively good performance in preventing heat loss. absorption coefficient u-value color different types of walls 0.9 0.225 dark wall 1 0.45 0.096 dark wall2 0.45 0.096 light wall3 height 6.00 ft width 10.00ft frame type aluminum without thermal breaks internal shade type none overall u-value 0.779 btu/hr/ft2/f overall shade coefficient 0.827 table 6. details of window type number 1 glazing glass type transmissivity reflectivity absorptivity outer glazing 1/8” clear 0.841 0.078 0.081 glazing#2 1/8” clear 0.841 0.078 0.081 glazing #3 not used gap type ¼” air space m. abdoos et al. /future energy february 2025| volume 04 | issue 01| pages 08-18 13 table 7. details of window type number 2 additionally, the overall shade coefficient of 0.796 indicates that this window effectively controls solar radiation, helping to maintain indoor temperatures within a comfortable range. the absence of internal shading may contribute to increased natural light; however, it also raises the need for temperature management. overall, this window presents a suitable option for spaces that require both natural light and energy efficiency. the properties outlined in table 8 are critical for understanding how window type number 2 will perform in various thermal scenarios. the high transmissivity coupled with low reflectivity means that this window type will allow substantial solar heat gain. while beneficial for passive heating during colder months, effective shading strategies may be necessary during warmer months to mitigate excessive heat gain. the relatively low absorptivity indicates that only a minor amount of solar energy is retained by the glass itself, which helps mitigate excessive heat buildup within the window assembly. however, combined with high transmissivity, it suggests that careful consideration must be given to shading strategies to manage heat gain effectively. the introduction of a ½-inch krypton gap is significant as krypton gas has a lower thermal conductivity compared to air. this enhances the overall insulation performance of the window assembly, reducing heat transfer through conduction and improving energy efficiency. when comparing window type number 2 with window type number 1 (previously analyzed), several key differences and improvements can be observed. while both window types utilize clear glass with similar transmissivity and reflectivity values, window type number 2 benefits from using krypton gas in its gap, offering superior insulation properties compared to the air-filled gap in window type number 1. using krypton gas significantly lowers the u-value for window type number 2 compared to window type number 1. this reduces heat transfer rates and enhances thermal resistance, making it more effective in maintaining indoor temperatures and reducing energy consumption. combining high transmissivity and improved insulation through krypton gas positions window type number 2 as a more energy-efficient option than window type number 1. this improvement is particularly relevant for buildings aiming for zero-energy status where minimizing energy loss is critical. combining high transmissivity and improved insulation through krypton gas positions window type number 2 as a more energy-efficient option than window type number 1. this improvement is particularly relevant for buildings aiming for zero-energy status where minimizing energy loss is critical. in practical terms, the characteristics of window type number 2 suggest several applications and considerations for building design. given its high transmissivity, this window type could be effectively utilized in passive solar design strategies where maximizing natural light and heat gain during winter months is desired while ensuring adequate measures are in place to control heat gain during summer months. to counteract potential overheating during summer months, integrating external shading devices or using interior shading solutions will be essential to maintain comfort levels and reduce reliance on mechanical cooling systems. in summary, table 8 highlights the fundamental thermal characteristics of window type number 2, emphasizing its role in influencing energy efficiency within mixed-use buildings aimed at achieving zero-energy status. the balance between transmissivity, reflectivity, absorptivity, and enhanced insulation through krypton gas underscores the need for strategic design choices that optimize natural light while managing heat gain effectively. as part of a comprehensive energy strategy, this window type can contribute positively to overall building performance when integrated with appropriate shading and insulation techniques. according to table 9, window 1 has a higher u-value (0.779), indicating less insulation effectiveness compared to windows 2 and 3 (both at 0.551). this suggests that windows 2 and 3 will provide better energy efficiency by minimizing heat transfer. the use of krypton gas in windows 2 and 3 enhances their thermal performance significantly compared to the air insulation used in window 1. krypton provides superior insulation properties due to its lower thermal conductivity. while all three windows have comparable shcoefficients, windows 2 and 3 maintain a balance between solar heat gain reduction and thermal resistance, making them more suitable for energy-efficient designs in varying climates. the combination of lower u-values and effective solar heat gain management in windows 2 and 3 positions them as favorable options for achieving zero-energy building goals, whereas window 1 may require additional strategies to enhance its energy performance. 3.3.3 roofs the walls of a building serve as its outermost shell, exposed to direct air and temperature fluctuations, thus playing a pivotal role in heat exchange and energy regulation. among these walls, the roof wall holds particular significance due to its expansive horizontal surface area. this orientation exposes it to prolonged periods of sunlight and other atmospheric elements, leading to heightened heat exchange compared to other walls of the building. consequently, the heat exchange dynamics of the roof wall are accentuated, rendering it a critical focal point in building design and energy management considerations. this recognition underscores its importance as a key scenario warranting thorough analysis and optimization strategies. according to table 10, the provided table details the specifications of roof type number 1, including the outside surface color, thermal absorptivity, and characteristics of various roof layers. the dark outside surface color, with an absorptivity of 0.900, indicates a high capacity for heat absorption. the layers of the roof consist of inside surface resistance, steel deck, board insulation, and built-up roofing, each with specific thicknesses, densities, and thermal properties. the total thickness of the layers is 1.410 inches, with an r-value of 8.29 hr-ft²-f/btu, indicating effective insulation performance. height 6.00 ft width 4.00ft frame type aluminum with thermal breaks internal shade type none overall u-value 0.557 btu/hr/ft2/f overall shade coefficient 0.796 m. abdoos et al. /future energy february 2025| volume 04 | issue 01| pages 08-18 14 finally, the overall u-value of the roof is calculated to be 0.121 btu/hr/ft²/f, reflecting its adequate thermal efficiency and contributing to reduced heat transfer. these characteristics enhance energy efficiency and improve comfort within the building. table 11 presents the specifications for roof type number 2, characterized by a light outside surface color and a thermal absorptivity of 0.450, indicating a lower capacity for heat absorption compared to darker roofs. the roof layers include inside surface resistance, steel deck, board insulation, and built-up roofing, each with defined thicknesses, densities, and thermal properties. the total thickness of the roof assembly is 1.410 inches, with an rvalue of 8.29 hr-ft²-f/btu, demonstrating effective insulation capabilities. the overall u-value is calculated at 0.121 btu/hr/ft²/f, suggesting efficient thermal performance and minimal heat transfer. these attributes contribute positively to energy efficiency and occupant comfort within the building structure. table 12 analyzes roof types in the context of net zero energy buildings and reveals significant differences in thermal performance based on their absorptivity and color. roof type 1, characterized by a dark color and an absorptivity of 0.900, is likely to absorb a substantial amount of solar heat, which can benefit colder climates but may lead to increased cooling demands in warmer conditions. in contrast, roof type 2 features a light color with an absorptivity of 0.450, indicating a reduced capacity for heat absorption, which can enhance energy efficiency by minimizing cooling loads during hot weather. roof type 3, also light in color with an absorptivity of 0.90, presents a unique case where, despite its light appearance, it retains a high absorptive capacity similar to roof type 1. these variations highlight the importance of selecting appropriate roofing materials and colors in the design of net zero energy buildings, as they directly influence energy consumption patterns and overall building performance. effective roof design can significantly contribute to achieving the energy efficiency goals essential for net zero energy status, particularly by optimizing thermal comfort and reducing reliance on mechanical heating and cooling systems. 3.3.4 shade another scenario involves the strategic deployment of shading to minimize sunlight penetration and optimize energy consumption within the building space. harnessing sunlight and energy efficiently in buildings constitutes a fundamental principle for energy optimization, with shades in architecture serving as a viable solution. awnings, in particular, represent an effective means of harnessing energy resources judiciously. the judicious utilization of solar energy within buildings plays a pivotal role in examining the impact of shading on reducing energy consumption. according to figure 1, shading is exclusively implemented in scenario 3, aimed at influencing the necessity for shading and its role in diminishing energy consumption. the introduction of shading in the form of a canopy has resulted in decreased energy usage attributable to the creation of a form of insulation and thermal barrier. table 8. details of window type number 2 glazing glass type transmissivity reflectivity absorptivity outer glazing 1/8” clear 0.841 0.078 0.081 glazing#2 1/8” clear 0.841 0.078 0.081 glazing #3 not used gap type 1/2” krypton table 9. technical specifications of windows defined in different scenarios sh-coefficient u-value insulation type types of windows 0.827 0.779 air window1 0.796 0.551 krypton window2 0.796 0.551 krypton window3 table10. details of roof type number 1 outside surface color dark absorptivity 0.900 layers: inside to outside thickness density specific.ht. r-value weight in lb/ft3 btu/lb/f hr-ft2-f/btu lb/ft2 inside surface resistance 0 0 0 0.68500 0 steel deck 0.034 489.0 0.12 0.00011 1.4 board insulation 1.000 2.0 0.22 6.94400 0.2 built up roofing 0.376 70.0 0.35 0.33200 2.2 outside surface resistance 0.000 0.0 0.00 0.33300 0.0 total 1.410 8.29 3.7 overall u-value 0.121 btu/hr/ft2/f m. abdoos et al. /future energy february 2025| volume 04 | issue 01| pages 08-18 15 table 12. specifications of technical ceilings defined in different scenarios the selection of an appropriate canopy is contingent upon factors such as location, climate, and the sun's angle, which fluctuates throughout the day. in a building, windows represent areas susceptible to high levels of light and heat ingress. employing awnings for windows serves to deter the entry of heat and sunlight. since glass has a greater propensity for heat absorption compared to walls, the strategic use of various types of canopies holds promise for reducing energy consumption and maintaining interior coolness. shading windows or glass walls effectively curtails interior heat buildup, diminishing the reliance on cooling systems and reducing overall energy consumption. 4. results and discussion according to table 13, in the normal mode, the building spans an area of 4072 square meters. the walls are constructed using standard materials, while the glass features regular insulation with an air layer. the walls and ceiling are also dark in color, with an absorption coefficient of 0.9. figure 1. details of shade type number 1 notably, no shading elements are incorporated into the building design. in this normal mode configuration, the thermal load of the building amounts to 1090681 btu/hr. according to table 14, the output from the carrier (hap) software for scenario 2 is obtained under specific conditions. the wall incorporates r7 insulation, while the color of the wall remains dark. however, the ceiling color is light in this scenario. the absorption coefficient is maintained at 0.45. the space between the double-glazed window is filled with krypton gas for enhanced insulation compared to air. notably, no shading elements are present. additionally, the thermal load of the building has been recalculated to 916152 btu per hour after implementing the specified scenarios. based on table 15, in this scenario, the color of the wall is lightened, and the absorption coefficient remains at 0.45. the specifications for the roof and window are consistent with those of scenario 2. additionally, all windows are equipped with shades. this configuration represents the optimal scenario, resulting in a thermal load calculated at 857610 btu /hr. 1090681𝐵𝑇𝑈/ℎ𝑟−916152𝐵𝑇𝑈/ℎ𝑟 1090681𝐵𝑇𝑈/ℎ𝑟 ∗ 100 = 16% 1090681𝐵𝑇𝑈/ℎ𝑟−857610𝐵𝑇𝑈/ℎ𝑟 1090681𝐵𝑇𝑈/ℎ𝑟 ∗ 100 = 21.36 % 916152𝐵𝑇𝑈/ℎ𝑟−857610𝐵𝑇𝑈/ℎ𝑟 916152 ∗ 100 = 6.38 % absorptivity the color of the modeled ceilings types of roofs 0.900 dark roof1 0.450 light roof2 0.90 light roof3 table 11. details of roof type number 2 outside surface color light absorptivity 0.450 layers: inside to outside thickness density specific.ht. r-value weight in lb/ft3 btu/lb/f hr-ft2-f/btu lb/ft2 inside surface resistance 0 0 0 0.68500 0 steel deck 0.034 489.0 0.12 0.00011 1.4 board insulation 1.000 2.0 0.22 6.94400 0.2 built up roofing 0.376 70.0 0.35 0.33200 2.2 outside surface resistance 0.000 0.0 0.00 0.33300 0.0 total 1.410 8.29 3.7 overall u-value 0.121 btu/hr/ft2/f m. abdoos et al. /future energy february 2025| volume 04 | issue 01| pages 08-18 16 table 13. implementation of base scenario table 14. implementation of the most balanced scenario m. abdoos et al. /future energy february 2025| volume 04 | issue 01| pages 08-18 17 table 15. implementation of the best scenario 5. conclusion the significance of zero-energy buildings (zebs) is increasingly recognized as a crucial strategy in addressing the building sector's substantial contribution to global energy consumption, which exceeds 40%. this study highlights the potential of zebs in mixed-use developments, particularly focusing on a unique case involving a large-scale commercial residential structure. by employing advanced modeling techniques with carrier (hap)software, this research not only identifies effective energy-saving strategies but also emphasizes the need for innovative approaches tailored to complex building types. the findings reveal that implementing a combination of advanced insulation methods, such as krypton gas for window treatments, alongside strategic design modifications like wall color optimization and shading techniques, can lead to significant reductions in energy consumption up to 21.36% in the most effective scenario. the exploration of diverse thermal characteristics and the integration of commercial and residential functionalities present new challenges and opportunities that have been insufficiently addressed in prior studies. as such, this article serves as a vital contribution to the field, advocating for the adoption of zero-energy principles in large mixed-use buildings. future efforts should focus on refining these strategies across various climates and building types, reinforcing the role of zebs as a cornerstone in sustainable urban development and energy management practices. ethical issue the authors are aware of and comply with best practices in publication ethics, specifically concerning authorship (avoidance of guest authorship), dual submission, manipulation of figures, competing interests, and compliance with policies on research ethics. the authors adhere to publication requirements that the submitted work is original and has not been published elsewhere in any language. data availability statement the manuscript contains all the data. however, more data will be available upon request from the corresponding author. conflict of interest the authors declare no potential conflict of interest. references [1] chwieduk, d., towards sustainable-energy buildings. applied energy, 2003. 76(1-3): p. 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[30] zahedi, r., et al., analysis and evaluation of thermalcooling loads of office buildings using carrier software in iran. journal of smart buildings and construction technology, 2022. 4(2): p. 61-74. this article is an open-access article distributed under the terms and conditions of the creative commons attribution (cc by) license (https://creativecommons.org/licenses/by/4.0/). https://creativecommons.org/licenses/by/4.0/ m. abdoos et al. /future energy november 2025| volume 04 | issue 04| pages 22-30 22 article managing risk and volatility in oil-dependent economies: the role of advanced predictive analytics mahmood abdoos, amirali saifoddin*, hossein yousefi, sattar zavvari, ali majnoon school of energy engineering and sustainable resources, college of interdisciplinary science and technology, university of tehran, tehran, iran a r t i c l e i n f o article history: received 15 july 2025 received in revised form 20 august 2025 accepted 05 september 2025 keywords: oil price forecasting, neural networks, economic policy, risk management, investment strategies *corresponding author email address: saifoddin@ut.ac.ir doi: 10.55670/fpll.fuen.4.4.3 a b s t r a c t the forecasting of oil production, demand, and prices holds critical significance for global economic stability and growth. oil plays a crucial role in determining economic performance, making reliable price estimations essential for shaping public policy and guiding investment decisions. in this study, advanced neural network models were employed to enhance the accuracy of oil market forecasts, with a particular focus on their economic implications. using pythonbased implementations of long short-term memory (lstm), radial basis function (rbf), and multilayer perceptron (mlp) networks, the research compares the effectiveness of these approaches in crude oil price forecasting. the evaluation of model outputs using technical indicators revealed that the multilayer perceptron network yielded the best results. during training, it reached an average squared error of 55.28, a root mean squared error of 7.43, and a mean absolute error of 5.55; while in testing, the values were 116.01, 12.96, and 10.73, respectively. overall, the comparative analysis indicates that the multilayer perceptron consistently surpassed both lstm and rbf models in minimizing prediction errors. the economic relevance of these findings is underscored by the model's potential to enhance decision-making processes for investors, policymakers, and oil producers by offering more reliable forecasts. by improving accuracy by 20 to 30 percent compared to previous studies, this research provides valuable insights into optimizing resource allocation and mitigating the economic risks associated with oil price volatility. 1. introduction the production of oil is undoubtedly a critical input. all countries that produce and export oil are affected by changes in their market indicators, including price fluctuations and instability. additionally, crude oil market shocks can have a profound economic impact. in this regard, an increase in crude oil prices, for example, results in a decrease in energy demand and, consequently, a decrease in capital productivity. an event that will increase unemployment, assuming nominal wages remain stable. oil shocks have numerous and widespread consequences. several studies on oil prices and demand are cited in the background of the research. furthermore, the oil market has always been a volatile market characterized by unpredictable events. an examination of the recent changes in oil prices and several major oil shocks proves this fact. this not only motivates researchers to conduct research in this field but has also served as a platform for innovative efforts and new models, as evidenced by its substantial research output. economic enterprises and governments have a great deal of interest in accurately forecasting oil market indicators [1]. oil price changes, like other assets, are based on efficient markets. for this reason, the price for the previous period will be predicted. the changes can estimate price fluctuations in the following periods. for this reason, forecasting takes a significant share of oil financial market studies. in most countries, the stability of crude oil prices plays an essential role in their national security and economic development. research on predicting petroleum prices using neural networks has led to the development of several methodologies and strategies for analyzing different crude oil price data forms. research has shown the significance of crude oil pricing and its influence on corporate operations. international trade, global commerce, and macroeconomic policy [2]. additionally, artificial intelligence techniques are being applied to many research projects. researchers are continually exploring neural network-based approaches to forecasting crude oil prices. the two main directions are as future energy open access journal https://doi.org/10.55670/fpll.fuen.4.4.3 november 2025| volume 04 | issue 04 | pages 22-30 journal homepage: https://fupubco.com/fuen issn 2832-0328 mailto:saifoddin@ut.ac.ir https://doi.org/10.55670/fpll.fuen.4.4.3 https://fupubco.com/fuen m. abdoos et al. /future energy november 2025| volume 04 | issue 04| pages 22-30 23 follows. the first direction is to develop forecasting tools that utilize neural networks as a standalone tool or in combination with other tools. without considering the uncertainty in the price of crude oil, theoretical development and practical implementation will suffer detrimental effects, which is why forecasting is necessary. as a result, we anticipate that crude oil prices will become increasingly challenging. neural networks are utilized to investigate the correlation between crude oil price fluctuations and predict trends in critical crude oil markets [3]. in this article, an improved deep neural network is employed to achieve a more accurate prediction of oil prices and demand, as numerous factors, including global supply and demand, economic and political developments, climate change, and others, influence the price and demand of oil. better results are achieved due to the use of deep neural networks. this article utilizes a developed deep neural network to analyze oil prices and demand. this article fills in the gaps in previous articles. as a result, it is possible to design a deep neural network model with layers appropriate for each feature or characteristic of the data. it is possible to model price and demand using two separate neural networks or a hybrid model. moreover, the model must be optimized by changing the network architecture, adding new layers, or updating parameters. one of the goals of this research is to improve the performance of these three methods compared to previous research. in addition to comparing them with each other to select the best prediction model, this study also compares them with previous studies mentioned in the introduction and literature review sections for the single selected method. crude oil is a vital component in the manufacturing industry. crude oil prices fluctuate according to the economic principles of supply and demand, making them challenging to predict accurately. zhang et al. [4] suggested that an additional reason for using oil price fluctuations is the reaction of oil-related companies along the economic value chain. in contrast, when oil prices continue to decline, the appetite for oil refineries and chemical companies will decrease, resulting in lower operating profits. companies that can accurately predict oil price fluctuations will be able to reduce cost risk and maintain sustainable growth. based on zhang et al. [5] findings, oil price fluctuations significantly impact both the real economy and the virtual economy of crude oil. these factors impact the export and import sectors of oil-producing and exporting nations. as a result, it is appropriate to focus on crude oil price forecasting. forecasting models can be classified into classical econometric and machine learning approaches [6]. wei et al. [7] employed arima stochastic implementation models and garch conditional heterogeneity models to predict crude oil prices. garch-type models were used to capture volatility, and crack spread futures outperformed mass random walk models. as a result, it has been found that nonlinear garch models outperform linear models in accurately reflecting both long-term memory and volatility asymmetry in prices, more so than linear models [8]. lin et al. [9] reported in their study that, in addition to classical econometric approaches, machine-learning methods have also been employed in recent years to forecast crude oil prices. among these methods, neural networks [10] and support vector machines (svms) [11] have been used most often to simulate the complex characteristics of oil prices. yu et al. [12] propose that all methods and external and internal factors in oil prices are aimed at achieving short-term effects to maximize performance. deep learning models such as cnn [13] neural networks, deep belief networks (dbns) [14], and long short-term memory (lstms) [15] may be helpful for investors and market analysts dealing with increasingly complex data. using more layers in these models is intended to help investors make informed investment decisions. these components are used in neural networks [16]. crude oil price forecasting aims to predict price movement one step ahead. to accomplish this, a modeled relationship is used in conjunction with data and crude oil prices. cnn is considered one of the most effective methods [17]. a combination of lstm and rnn models is recommended for long-term forecasting of oil prices and demand [18]. lstm is most important for long-term storage. based on historical price data, bousari et al. [19] reported that many studies employ the ann approach to predict crude oil prices using time series analysis. additionally, according to research, a short-term memory neural network (lstm) is applied to sequential data to learn the pattern of past price fluctuations and predict the future. different approaches have been attempted to generate and utilize neural networks in studies on predicting crude oil prices. wang et al. developed a model that examines variations in data networks. crude oil price forecasting using time series data involves artificial intelligence methods, such as backpropagation neural networks, radial basis function neural networks, and learning machines. crude oil price volatility remains influenced by sentiment data from news sources, particularly in the short term. the price of crude oil can be impacted directly and indirectly by emotional data [20]. according to zhang et al. [21], factors such as the persian gulf war or russia's attack on ukraine significantly impact oil prices. due to the covid19 outbreak, the crude oil market has also experienced shortterm volatility [22]. studies have shown that news is a crucial source of information for gauging market sentiment [23]. the accuracy of forecasting short-term stock returns can also be improved, which is extremely important for businesses [24]. as crude oil prices fluctuate daily, forecasts based on longterm historical data may not be accurate. 2. mathematical equations 2.1 criteria for evaluation to evaluate the performance of rmse mean root errors and mea mean absolute errors, considering the evaluation criteria, which are used for the accuracy of the evaluation in question, the following equations are used: rmse = √ 1 n ∗ ∑ (y1t in i=1 − yt i) (1) mae = √ 1 n ∑ |y1t i − yt i|n i=1 (2) where y1 is the predictive value, y is the actual value, and n is the number of test samples. 2.2 multilayer perception equations the neural network changes the connection weight after processing each piece of data, based on the amount of error in the output compared to the expected result. this example is done by monitoring and through backtracking and generalizing the least squares algorithm in linear perception. error in the output node, we show n data points. node values are adjusted based on corrections that minimize the amount of error in the total output and are: 𝜀(𝑛) = 1 2 ∑ 𝑒𝑗 2 𝑗 (𝑛) (3) using the gradient, the change in weight is: m. abdoos et al. /future energy november 2025| volume 04 | issue 04| pages 22-30 24 ∆𝜔𝑗𝑖(𝑛) = −𝜂 𝜕𝜀(𝑛) 𝜕𝜗𝑗(𝑛) 𝑦𝑖(𝑛) (4) where in yi is the output of the previous neuron and ƞ is the learning rate chosen to ensure that the weights quickly converge to the oscillation-free response. the calculated derivative depends on the induced local field. it is ʋi that changes itself. it is easy to prove that for the output node, this derivation can be simplified. −𝜕𝜀(𝑛) 𝜕𝜗𝑗(𝑛) = 𝑒𝑗(𝑛)∅~ (𝜗𝑗(𝑛)) (5) where ϕ is the derivative of the activation function described above, and does not change itself. the analysis for changing the weights to a hidden node is more difficult, but it can be shown that the corresponding derivative is: − 𝜕𝜀(𝑛) 𝜕𝜗𝑗(𝑛) = ∅~ (𝜗𝑗(𝑛)) ∑ − 𝜕𝜀(𝑛) 𝜕𝜗𝐾(𝑛) 𝜔𝑘𝑗𝐾 (𝑛) (6) it depends on the change in the weights of the k nodes that represent the output layer; therefore, to change the weights of the hidden layer, the output layer changes according to the derivative of the activation function, and thus this algorithm represents a function of the activation function. 3. methodology 3.1 software an improved deep-learning model was used in this study to forecast production, demand, and price. deep learning requires significant computing power. there is a parallel architecture available in high-performance gpus that makes them suitable for deep learning. deep learning models are often called deep neural networks because they utilize neural network architecture. deep neural networks have a large number of hidden layers. in deep learning, data sets are labeled, and neural network architectures are used to learn features directly from the data without manually extracting them. data characteristics include the collection and processing of oil market data (table 1). in addition to oil price information, demand and supply information, global events, and other related information are included. moreover, model training is conducted to develop a model that can forecast price and demand based on training data. adjusting parameters, applying improved techniques, and evaluating model accuracy are all part of this process. several metrics, such as mean square error, assess the model's accuracy on test data over different periods. additionally, it includes criteria for predicting, analyzing, and modeling. the program also offers optimization and analysis of model prediction results and solutions. optimizing the model for higher accuracy in future predictions is also very effective. the project aims to predict the final price of oil using the prices and demand of oil in different parts of the world, and to analyze the developments, which include three key components: data preprocessing, modeling, and model evaluation. 3.2 data preprocessing the primary purpose of data preparation is to arrange the data for the following modeling step. data preprocessing is a crucial component of machine learning, involving the application of mathematical and logical filters to refine the data. to achieve this, the following steps will be implemented sequentially for data cleaning: • eliminate columns with more than 15 missing values. in this step, columns with several missing values exceeding ten percent of the total dataset (approximately 15 instances) will be removed. • exclude the year column. as the year feature consists of unique values, it does not contribute significantly to model training. consequently, it will be excluded from the dataset due to its lack of relevance. by following these steps, the dataset will undergo effective cleanup, enhancing its suitability for subsequent modeling and analysis. 3.3 standardizing data the scaling of data varies across different columns and can have distinct impacts on the learning of data models. to address this, we employ the method of min-max standardization, which rescales the entire dataset to a range of 0 to 1. additionally, we undertake the following steps for data refinement: • remove columns with a correlation exceeding 90%. • exclude data that contains null values. table 1. variables impact the supply and demand of crude oil technical factors economical factors political factors factors influencing the market environmental factors crude oil quality cost of equipment political struggles transaction volume pressure on communities to use renewable energy new manufacturers economic recession socio-political conditions of oil extractor countries the pricing of energy hubs temperature changes and seasons crude oil transportation gold price oil crisis population growth completion of green fields and production from brownfields the amount of oil extraction in the world enhancing the value of the dollar global crisis opec production risk and decisions focus on renewable energy sources oil storage and products geopolitical occurrences and oil market shock politics of oil companies non-alignment with opec plus geographical disasters innovation and technology economic development supply a-nd dem-and m. abdoos et al. /future energy november 2025| volume 04 | issue 04| pages 22-30 25 in our predictive analysis, we utilize three distinct methods, which we shall briefly introduce. the objective of neural networks is to emulate the patterns generated by the human brain. neural networks operate by generating an output pattern based on the provided input pattern. comprising multiple processing elements called artificial neurons, neural networks receive and process data within the neurons, ultimately generating an output. 3.4 introduction to the lstm method (long short-term) long short-term memory (lstm) networks are an improved iteration of recursive neural networks that are designed to effectively retain past data within memory. the choice of utilizing the lstm method for predicting oil prices and supply-demand dynamics aims to address the inherent issue of vanishing gradients common in recurrent neural networks. by overcoming this challenge, lstm enhances the quality of forecasting models for price and demand analysis. 3.5 introduction to the rbf method the rbf (radial basis function) method serves as the secondary network employed for predicting oil prices and demand. esteemed for its application in time series prediction, this method is commonly employed by industry analysts within oil prediction models. the radial basis function (rbf) neural network is designed as a feed-forward model in which radial basis functions are applied as the activation mechanism. its structure consists of an input layer, one or more hidden layers, and an output layer. owing to this architecture, rbf networks are widely recognized as effective tools for handling forecasting tasks. 3.6 introduction to the multilayer perception (mlp) method the multilayer perceptron model represents a prominent category of neural networks, characterized by interconnected layers of neurons. unlike other deep learning algorithms, such as recurrent neural networks, the mlp operates solely in a unidirectional manner, transmitting data only in a forward direction across the network. mlps, consisting of several elements such as the input, output, and hidden layers, are widely acknowledged as the most often used architecture in neural networks. their applicability in forecasting oil prices and demand is highly regarded within the field. 4. results and discussion following the data preprocessing stage, 149 instances and 120 columns remain. in this section, two models, namely lstm and rbf, were utilized. the results of the error and the accuracy of each model were presented separately. to evaluate the performance, the dataset was divided into two subsets, namely training and testing, with 70% used for training and 30% reserved for testing. before splitting, to avoid selection bias, the data was randomly shuffled. each model was then trained for a total of 300 iterations. 4.1 lstm model (long short-term memory) the long short-term memory (lstm) model shown in figure 1 follows a sequential neural network structure, with an lstm layer with 60 neurons as the main layer. the neurons of the lstm layer capture temporal dependencies and learn patterns in time series data, such as changes in oil prices. the first layer is an input layer that encapsulates past oil price data; this data is then analyzed by the lstm layer. at this time, the information across different intervals is remembered by the 60 neurons of the lstm layer. the lstm layer specifically adapts to work with challenges, like vanishing and exploding gradients, usually raised in conventional recurrent neural networks (rnns). this underlying layer is followed by other layers that fine-tune the extracted features, ultimately sending the information to the output layer, which provides accurate price predictions. the diagram in figure 1 illustrates how data flows through these layers and through the 60 neurons in the lstm layer; the 60 neurons express long-term dependencies. the figure shows how the model converts the input data into trusted predictions, additionally helping the decision-making process, in the economic and energy sectors, more specifically. according to figure 2, the long short-term memory (lstm) method demonstrates a training loss of 509.70 and a testing loss of 529.98, placing it in the middle performance range compared to the other two selected methods. while this indicates that the lstm model performs reasonably well, it neither outperforms nor underperforms the best and worst methods evaluated in the study. this level of loss suggests that the lstm model successfully captures key patterns in the data during training but exhibits some level of prediction error during testing, which is characteristic of time-series forecasting challenges. compared to the other models, the lstm strikes a balance between training and testing accuracy, making it a viable option for oil price forecasting, although further tuning or alternative methods may provide additional improvements. figure 2 visually highlights the lstm's relative position, showing how it balances accuracy and loss compared to the other models (the model error diagram). figure 1. python code model ™ for price and demand forecasts figure 2. error chart using the lstm method to predict demand and oil prices 4.2 rbf model (radial base function) the model consists of two fully connected layers and one rbf layer. a view of the model is shown in figure 3. the model error diagram is shown in figure 4. according to figure 4, the radial basis function (rbf) method had the highest m. abdoos et al. /future energy november 2025| volume 04 | issue 04| pages 22-30 26 casualty rates of the three models, with rbf training casualty rates of 763.51 and rbf testing casualty rates of 836.33. in terms of minimizing loss, this indicates it performs poorly and is much worse than both the lstm and mlp methods. the increased casualty rates suggest that the rbf model is having trouble estimating patterns in the data during the training and testing phases. the higher error rates in both environments indicate a greater challenge in providing a discerning outcome, which highlights the limitations of the rbf model for forecasting oil prices. on the contrary, both the lstm model and the mlp models performed significantly better based on their reduced casualty rates. figure 4 visually underscores the rbf method’s comparatively poor performance, making it less favorable for applications that require high accuracy, such as economic and energy market forecasting. figure 3. python code of the rbf model for price and demand forecasts figure 4. rbf model error in python software for predicting demand and oil prices 4.3 multilayer perceptron model multilayer neural networks, particularly multilayer perception networks, are widely acknowledged by researchers as powerful approximations. it is believed that these networks, provided they possess sufficient layers and neurons, can estimate any nonlinear transformation with the desired level of accuracy. as such, the multilayer perception network stands as one of the most versatile and successful prediction models. the multilayer perception neural network, also known as mlp, utilizes the post-error learning rule. this learning method serves as a generalization of the least squares error algorithm, based on the principle of error correction learning. the algorithm consists of two essential paths: the forward path and the backward path. during the forward pass, the input vector moves through the intermediate layers to the output layers, producing their effects. on the return path, the network parameters are adjusted, following the principles of the error correction law. despite the proficiency of the aforementioned models, they do not perform optimally on data lacking a recursive structure, where the order of properties is significant, such as in text data. to address this limitation, a three-layer perception with a configuration of 60, 50, and 40 neurons, respectively, was employed, yielding the best performance. a visual representation of the model is displayed in figure 5, while the error chart is illustrated in figure 6. figure 5. python code for the three-layer perceptron model for price and demand forecasts figure 6. error graph of the 3-layer perceptron model for forecasting demand and oil prices as depicted in figure 5, each neuron within these layers plays a critical role in transforming the inputs from the preceding layer. the inputs are combined using weights specific to each neuron, determining the influence of each input on the neuron's output. after that, the sum of inputs is passed through an activation function, which causes nonlinearity in the network. nonlinearity is crucial for enabling the model to learn complex patterns and relationships within the data. at this stage, each neuron generates an output that is specific to each neuron and reflects a new feature or attribute that is the nonlinear combination of the inputs. the outputs of the neurons of this layer establish a feature vector of the data that is comprised of the processed input. the feature vector will be reassigned as input to the next layer, and the process of transformation will continue. the feature vector will be reassigned as input to the next layer, and the process of transformation will continue. figure 5 illustrates the effect of this structure. from this figure, it can be seen that each layer in the network transforms the data, developing to deeper levels of abstraction and therefore extracting increasingly refined features from the initial data, and leading to more reliable predictions. neural networks utilize this hierarchical m. abdoos et al. /future energy november 2025| volume 04 | issue 04| pages 22-30 27 structure, which can lead to more reliable information management and modeling in complex systems, such as oil price fluctuations. in figure 6, it can be observed that the multilayer perceptron (mlp) approach has the lowest loss rates among the models under evaluation, with a training loss rate of 55.28% and a testing loss rate of 116.01%. this indicates that, in terms of minimizing loss, the multilayer perceptron model is comparatively the best, and it performed significantly better than the lstm and rbf models. the notably low loss rates indicate that the mlp model is highly effective in capturing patterns during both the training and testing phases, achieving superior predictive accuracy. this reduction in loss makes it an ideal choice for applications where minimizing prediction error is critical, such as oil price forecasting. the mlp method’s ability to consistently deliver the lowest casualty rates positions it as a top choice among the models studied. figure 6 visually emphasizes the mlp method's clear advantage in the discussion of casualties, highlighting its potential for making highly accurate predictions and ensuring reliability in decision-making processes in volatile markets. 4.4 comparison of oil forecast models the results of the models are presented in table 2. the average squared error in the training mode for the lstm, rbf, and perceptron models decreased significantly, reaching 55.28 (from the initial values of 509 and 763.51, respectively). similarly, in the testing mode, the average squared error was reduced to 116.01 (from the initial values of 529.98 and 836.33) for the respective models. in terms of the root mean squared error, the lstm, rbf, and perceptron models achieved values of 7.43 (initially starting at 22.57) and 12.96 (from the initial values of 23.02 and 28.91) in the training and testing modes, respectively. regarding the mean absolute error, the lstm, rbf, and perceptron models obtained values of 5.55 (from the initial values of 19.56 and 21.95) and 10.73 (initially starting at 20.84 and 23.71) in the training and testing modes, respectively. 4.5 validation by performing validation using the lstm method, it has been analyzed that this study performed better than the previous studies in the compared parameters, and it can be used for more accurate predictions with a lower percentage of error (table 3). the study's results on oil price forecasting using neural networks, specifically lstm, rbf, and multilayer perceptron (mlp) models, indicate a significant improvement in predictive accuracy compared to previous methodologies. model performance metrics: the multilayer perceptron (mlp) model demonstrated superior performance with the following metrics: training phase: average squared error (ase): 55.28 root mean squared error (rmse): 7.43 mean absolute error (mae): 5.55 testing phase: average squared error (ase): 116.01 root mean squared error (rmse): 12.96 mean absolute error (mae): 10.73 the study asserts that the mlp model outperformed both lstm and rbf models in terms of error metrics. this supports the claim that the mlp method is more effective for oil price forecasting, achieving a performance improvement of 20-30% over traditional models that utilized only one or two methodologies. data preprocessing involved cleaning and standardizing the dataset, which consisted of 149 instances and 120 columns after the initial data cleaning process. the dataset was split into training (70%) and testing (30%) sets, ensuring unbiased selection through shuffling. model training: each model was trained for 300 iterations, with the lstm model configured with 60 neurons in its layers. the training process aimed to minimize prediction errors, as indicated by the performance metrics. the results confirm the success of the multilayer perceptron model in predicting oil prices, consistently outperforming lstm and rbf in terms of error rates. the method applied, which includes detailed data preprocessing, rigorous model training, and evaluation, ensures that the findings presented are trustworthy and relevant, meeting the research specifications outlined in the article. this thorough process not only fosters confidence in the quality of the findings but also contributes to the growing discourse on oil price prediction techniques. accurate oil price forecasts are crucial in developing global economic policy, risk management, and resource allocation as oil remains a critical pillar of the economy. 4.6 global economic policy oil prices have significant effects on the rate of inflation, the value of exchange rates, and the economic activity of what are typically oil-importing nations, as well as oil-exporting nations. with credible forecasts, countries can: formulate effective monetary and fiscal policies: central banks and finance ministries rely on oil price forecasts to adjust interest rates, manage inflation, and design fiscal policies that strike a balance between growth and stability. for instance, governments may take steps to cushion inflationary impacts during periods of forecasted high oil prices. stabilize currency and trade balances: for oil-exporting countries, a good forecast allows for an assessment of export revenues, which, in many cases, constitute a significant portion of gdp. conversely, oil-importing countries can better plan their foreign exchange requirements, allowing them to control currency volatility. develop energy policies: governments utilize forecasts to adjust different energy subsidies, taxes, and strategic reserve levels. governments forecast and plan for energy security while facilitating transitions to renewable energy sources. table 2. comparison of errors between lstm & rbf and perceptron models test train model mae rmse mse loss mae1 rmse1 mse1 loss 20.84 23.02 529.98 529.98 19.56 22.57 509.70 509.70 lstm 23.71 28.91 836.33 836.33 21.95 27.63 763.51 763.51 rbf 10.73 12.96 116.01 116.01 5.55 7.43 55.28 55.28 perceptr on m. abdoos et al. /future energy november 2025| volume 04 | issue 04| pages 22-30 28 accurate forecasts can enable policymakers to reduce their reliance on oil when prices are expected to rise and to make more informed decisions about replacing new investments in energy with alternative energy sources. table 3. validation of predictions made with previous studies model mse mae rmse proposed lstm 529.98 20.84 23.02 proposed arima [4] 1047.851 28.699 lstm-ann [25] 699.98 14.56 4.7 risk management unpredictable oil prices lead to enormous risks for a firm, the financial market, and the economy as a whole. reliable forecasting substantially reduces these risks by allowing them to use some key strategies: facilitating hedging strategies: firms that have a lot of exposure to oil prices, such as petroleum companies, airlines, and energy-dependent firms, can employ accurate forecasts to hedge against price movements. these firms protect themselves against unforeseen spikes in oil prices or dramatic declines by locking in prices based on the previous forecasts in the future contracts or similar documents. improving investment planning: investors in the oil sector can utilize forecasting for investment purposes in order to analyze the profit potential of long-term projects, including exploration of oil reserves and capital projects. accurate forecasting will help companies avoid overinvestment, and equally important, under-investment, while aiding in faster capital utilization. managing macroeconomic risks: countries that rely on oil revenues can experience sudden growth problems and deterioration of public finances due to price shocks. forecasting tools permit governments to set stabilization processes into motion (e.g., sovereign wealth funds, countercyclical fiscal policies) to help insulate their economy against unexpected shocks. 4.8 resource allocation reliable oil price forecasts are essential for government and industry sector productivity as they guide the effective use of resources, and economic stabilization and growth potential. optimizing investment in energy projects: oil industry players use forecasts to make decisions about where and when to explore, drill, and produce. adequate planning based on accurate predictions will enable oil and gas companies to invest their capital efficiently, preventing production during times of low demand and underproduction during periods of higher prices. optimizing the energy mix: forecasts regarding oil prices can help public policymakers know how to steer the national energy portfolio. oil prices can have a cyclical effect, where higher oil prices may support quantitative investment in renewable energy, and lower prices are likely to result in increased dependence on fossil fuels. if decisions are based on accurate forecasts, public agencies and corporations can make informed and productive arguments against diversification as a factor of security, and as a cost management concern. guiding infrastructure development: forecasting is critical for states, provinces, or countries that rely on oil imports, as they must make long-term capital investments in infrastructure such as pipelines, refineries, and storage facilities. the integrity of forecasting efforts, i.e., a better price trend analysis, better identifies when you are overspending or underusing facilities based on what was inaccurately forecasted. 4.9 policy implications better forecasts, particularly in oil-dependent economies, can aid the policy-making process by providing greater clarity on price movements now and into the future. being able to project prices accurately enables policymakers to create policies that mitigate the potential effects of price volatility. by considering and revising their policy frameworks and strategies, they can proactively limit the impacts of price movements, such as inflationary or abrupt cuts resulting from fiscal practices. having better forecasts provides considerable opportunities for the government to enhance fiscal indicators, such as oil production, prices, and demand, similar to those from this study, which allows the government to adjust fiscal instruments, i.e., subsidies/taxation, etc., accordingly in regard to changes in oil revenues. if the government starts relying on accurate forecasting of price movements, it will be able to prepare well in advance to update its fiscal budget and economic plan, thereby reducing the possibility of unexpected deficits or inflationary policy practices caused by sudden exogenous shocks. reliable forecasting also supports the establishment of long-term energy trajectories. with price projections, policymakers can decide whether to diversify the economy, further invest in renewable energy, or expand strategic oil reserve inventories. using one of the more accurate forecasting methods described in hinter, namely, neural network models, and particularly the multilayer perceptron model used in this study, gives governments a better basis for these decisions on weighing the advantages and risks of continued dependency on oil, with transitioning toward alternative energy sources. in summary, reliable oil price forecasts not only provide policymakers with the capacity to support stability in national economies and improve public financial management but also enable a measured approach towards policies that balance the viability of short-term resilience with long-term sustainability. 4.10 management and strategy the upgraded forecasting model developed in this research offers an excellent opportunity for oil producers and investors to enhance decision-making, mitigate uncertainty, and hedge against market fluctuations. several potential applications are outlined below: • optimizing investment timing: with the accuracy of the multilayer perceptron model in predicting oil prices, companies and investors can use the model to better predict price movements. this allows them to plan when to make major decisions, such as increasing or decreasing production, increasing capacity, or investing in a new exploration program, so that capital expenditures align with prices and yield a stronger return on investment. • hedging and risk management: in the context of hedging, accurate price forecasting is the key to crystallizing effective hedging strategies. the greater the specificity in price forecasted moves, the better firms will be able to utilize contracts, options, etc. to protect themselves from unpredictable and unforeseen moves, which will preserve their profit margin and certainly make their revenue m. abdoos et al. /future energy november 2025| volume 04 | issue 04| pages 22-30 29 streams from incredibly volatile markets to some predictable extent. • reducing market uncertainty: the level of accuracy attached to the neural network model, an improvement of 20–30% against previous studies, fundamentally improves the uncertainty normally attached to oil price volatility. more sophisticated oil price forecasting enables firms to make less speculative decisions regarding supply chain management, long-term contracts, and selling prices. furthermore, greater predictability will improve investor confidence in firms' ability to deliver returns over the investment horizon they need, making it easier for them to choose a stable sector and return, thereby placing them in a less volatile risk position. • capital allocation and portfolio diversification: investors can measure the type of exposure they want to oil-related assets or sectors and decide if they want to gain exposure at any point going forward to other sectors. the investment was about helping improve the forecast capabilities so that there is more clarity on future market fundamentals and conditions around the oil price. this helped with optimizing the risk and opportunity balance in their portfolios across the investment buckets. in conclusion, as the leading user of cost principles, applying new generation forecasting models has significantly assisted both the company and investors in improving profit generation, developing and maintaining risk prudence, and enhancing mechanisms for capitalizing on potential trading opportunities. 5. conclusion this research makes a significant contribution to economics and management, as it offers a broader and more reliable method for forecasting oil pricing and demand using deep neural networks. of the models employed, the threelayer perceptron exhibited the greatest predictive power, which is a significant finding for decision-making in oildependent economies, where oil prices can create significant uncertainty and can jeopardize fiscal stability and influential investment decisions. this improvement, which identifies that the model's accuracy is improved by 20%-30% compared to prior models, provides stakeholders with opportunities to make the best and most informed capital allocation, risk management, and long-term decisions. from an economic perspective, employing these models can mitigate some of the adverse impacts of price volatility, as they enable governments and businesses to implement steadier fiscal policies, reduce uncertainty surrounding revenues, and allocate resources more effectively. for oil companies, such projections can help firms make better decisions around production scheduling, capital investment timing, and apply them to hedging strategies, which will improve profitability and reduce their vulnerability to sudden market shocks. this information also enables investors to utilize it more effectively in protecting their portfolios and refining risk management strategies in energy markets. moreover, the use of advanced neural networks in conjunction with forecasting processes, specifically economic forecasting, makes analyses of what drives energy markets more systematic and transparent for stakeholders, providing them with additional valuable data to predict trends and take action based on facts rather than speculation. when economic forecasting incorporates the use of artificial intelligence, it has the potential to be influential in reducing uncertainty and facilitating more consistent, sustainable development and growth. ultimately, this research also demonstrates the expanding role of intelligent predictive models that futures and options possess in addressing global oil market challenges, and highlights the need for economists and students to consider investing in advanced analytical capabilities, both in economic and managerial contexts. ethical issue the authors are aware of and comply with best practices in publication ethics, specifically concerning 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[25] a. l. zahouani and h. boubaker, "forecasting crude oil price with hybrid approaches," rev. econ. financ., vol. 21, pp. 564-576, 2023. this article is an open-access article distributed under the terms and conditions of the creative commons attribution (cc by) license (https://creativecommons.org/licenses/by/4.0/). https://creativecommons.org/licenses/by/4.0/ m. sambane et al. /future energy november 2024| volume 03 | issue 04| pages 67-79 67 review advanced neural network and hybrid models for wind power forecasting: a comprehensive global review malixole sambane1, bongumsa mendu1,2*, bessie baakanyang monchusi1 1department of electrical and smart systems engineering, university of south africa, pretoria, south africa 2national transmission company south africa soc ltd, maxwell dr, sunninghill, sandton, 2157, south africa a r t i c l e i n f o article history: received 01 september 2024 received in revised form 05 october 2024 accepted 14 october 2024 keywords: neural network, hybrid models, forecasting, wind power *corresponding author email address: mendubongumsa@gmail.com doi: 10.55670/fpll.fuen.3.4.5 a b s t r a c t neural network algorithms (nnas), modeled after the workings of biological neurons, are increasingly utilized in areas like data mining and robotics to address complex challenges in artificial intelligence (ai). this research will undertake a systematic review based on advanced neural networks and hybrid models for wind power forecasting. using the scopus database, a methodical search, acquisition, and filtering procedure was utilized to find pertinent publication documents; vosviewer software was utilized to analyze trends. the emphasis on improving prediction accuracy and stability in wind power forecasting through the application of cutting-edge machine learning techniques and hybrid models is a prominent feature that unites the literature. furthermore, attention is being paid to resolving issues pertaining to the production of wind energy, such as wind power fluctuation management, grid integration problems, wind speed prediction, and turbine health monitoring. a rising trend involves multi-dimensional, multi-step forecasting and incorporating factors like weather data and spatial-temporal features to enhance reliability. this paper contributes by exploring the integration of optimization techniques with neural networks, investigating hybrid models to improve wind power predictions, assessing lstm-based approaches in forecasting, and suggesting directions for future research. 1. introduction today, neural network algorithms (nnas) are computational models inspired by biological neural networks designed to process information and solve complex ai problems [1]. these algorithms have gained prominence in various fields, including robotics [2], and data mining [3]. nnas are crucial for their ability to learn from data, adapt to new information, and make predictions [4]. recent advancements in deep learning have further enhanced their capabilities, particularly in computer vision, speech processing, and iot applications [5]. the effectiveness of nnas depends on selecting appropriate architectures and training algorithms. ongoing research focuses on developing innovative topologies, optimization methods, and applications in quantum computing and differential equations [6]. as nnas continue to evolve, they offer powerful tools for handling high-dimensional data and automating feature extraction processes [7]. furthermore, in engineering and construction, nnas are used for structural analysis, materials optimization, energy efficiency forecasting, and smart city technologies [8]. they excel in pattern recognition tasks like character and handwriting recognition [9, 10]. in business, nnas are employed for hedge fund analytics, marketing segmentation, and fraud detection [11]. unsupervised nnas, such as autoencoders and selforganizing maps, are particularly useful in exploratory data analysis, biomedical imaging, and financial applications when labeled datasets are unavailable [12]. in healthcare, nnas can predict disease severity, as demonstrated in epidermolysis bullosa simplex, with 78% accuracy [13]. nnas are also applied in system identification, vehicle control, quantum chemistry, and natural resource management [14]. their ability to simulate nonlinear phenomena and identify hidden patterns in large databases makes them valuable tools across various industries. in this work, the discussion will be narrowed specifically to its application for wind power generation. wind power generation is a rapidly growing renewable energy source with significant potential for addressing global energy demands and environmental concerns [15]. it offers numerous advantages, including low carbon emissions, resource conservation, and flexible applications [16]. the development of wind energy future energy open access journal https://doi.org/10.55670/fpll.fuen.3.4.5 november 2024| volume 03 | issue 04 | pages 67-79 journal homepage: https://fupubco.com/fuen issn 2832-0328 mailto:mendubongumsa@gmail.com https://doi.org/10.55670/fpll.fuen.3.4.5 https://fupubco.com/fuen m. sambane et al. /future energy november 2024| volume 03 | issue 04| pages 67-79 68 technology has been dramatic since the 1980s, with many countries setting ambitious targets for its implementation [17]. key aspects of wind power systems include importance analysis for identifying critical components [18], integration with smart grids and storage systems [19], and advanced control strategies for efficient operation [20]. however, challenges remain, such as technological limitations, environmental impacts, and grid integration issues [21]. despite these obstacles, wind power is expected to play an increasingly important role in the global energy landscape, driven by ongoing research, technological advancements, and supportive government policies [22]. neural networks have emerged as powerful tools for improving wind power efficiency and forecasting. they have been applied to turbine control, wind farm optimization, and blade design [23]. various machine learning approaches, including artificial neural networks (anns), recurrent neural networks, support vector machines, and extreme learning machines, have shown promising results in wind power forecasting [24]. multilayer perceptron structures with purelin and sigmoid activation functions are commonly used [25]. recent advancements include combining anns with dependability models to enhance short-term production estimation. time-series methods, fuzzy logic, and hybrid models have also been explored [26]. the integration of physical, statistical, and hybrid methods has improved forecasting accuracy across different time horizons [27]. overall, neural network applications in wind power forecasting have increased significantly, offering improved accuracy compared to individual methods [28]. in summary of the key obversions from the previous related literature analyzed above, neural networks have emerged as powerful tools for enhancing wind power efficiency and forecasting. it is evidence that they have been effectively applied to turbine control, wind farm optimization, and blade design. various machine learning approaches, including artificial neural networks (anns), recurrent neural networks, support vector machines, and extreme learning machines, have shown promising results in wind power forecasting. commonly used structures include multilayer perceptrons with purelin and sigmoid activation functions. recent advancements involve combining anns with dependability models to improve short-term production estimation. additionally, time-series methods, fuzzy logic, and hybrid models have been explored, leading to better forecasting accuracy. the integration of physical, statistical, and hybrid methods has further improved accuracy across different time horizons. overall, the application of neural networks in wind power forecasting has significantly increased, offering enhanced accuracy compared to individual methods. however, there is a notable gap in the literature regarding a comprehensive review of neural network algorithms in wind power generation. thus, the aim of this work is to conduct a systematic review of the applications of neural network algorithms in wind power generation, focusing on key contributions, among others, such as: • reviewing the applications of lstm models in wind power generation, highlighting their effectiveness in improving long-term forecasting accuracy. • exploring the use of short-term memory-based models • examining the integration of various optimization techniques with neural network models to enhance the accuracy and reliability of wind power forecasts. • analyzing different neural network methodologies applied to time series data in wind farms, focusing on their predictive capabilities. • investigating the combination of hybrid models and machine learning techniques to improve the prediction of wind speed and power output. • detailing various algorithms and neural network models specifically designed for predicting wind energy, and their performance in different scenarios. • reviewing the application of neural network models in accurately predicting wind speed and power output, emphasizing recent advancements. • proposal for possible future work directions will be discussed. the remaining part of the paper is organized as follows: section 2 introduces the relevant theory of similar or related work explored or completed, while section 3 explores the methods or processes utilized to search, retrieve, collect, and analyze relevant information and documents on the different search engines and software. section 4 consists of analyzed literature papers, and section 5, summarizes the analyzed literature papers' observations. section 5 interprets and discusses results, while section 6 discusses the results under network and overlay visualization. section 7, suggests and recommends proposals for future research, and section 8 summarizes the main conclusions of this work. 2. wind energy systems to combat climate change and achieve a sustainable energy future, offshore wind energy is becoming more and more important. real-time performance monitoring and predictive maintenance are now possible thanks to the revolution in industrial systems brought about by advances in data-driven and machine-learning technologies. for fault detection and operational optimization, accurate wind turbine models are essential. notwithstanding, there are obstacles, including wind direction, speed, power generation, and performance statistics [29]. since wind energy doesn't produce pollution like hydropower or coal does, it is an essential alternative energy source. its potential regions remain unidentified, and the variability of wind speed impacts its generation capacity. statistics on the availability of wind energy are essential for inventory preparation. the generation of wind energy capacity is predicted using soft computing techniques, such as weather and historical data modeling. artificial intelligence techniques such as neural networks and fuzzy logic have been used by researchers to develop energy estimation and prediction methods that are more accurate and efficient than conventional statistical methods [30]. the economic, social, political, and environmental aspects of renewable resources are the main subjects of research, with wind energy receiving special challenges for the operation of the electrical network. with a variety of storage technologies available, energy storage systems in conjunction with wind power can improve gridconnection capability [31]. in the past, researchers have proposed various statistical approaches related to wind power, wind speed, and energy prediction [32]. the artificial neural network structure comprises three layers: input, hidden, and output. the input layer receives network inputs, the hidden layer processes information, and the output layer provides network response. the number of neurons in the input layer equals the number of inputs, while the number of neurons in the output layer corresponds to the number of outputs, see figure 1, where x1, x2 are the input functions m. sambane et al. /future energy november 2024| volume 03 | issue 04| pages 67-79 69 (wind speed, temperature etc) wij is the signal weight, and f is an activation function [33]. figure 1. artificial neural network structure artificial neural network activation functions map inputs and hidden layers, advancing the node output from one layer to the following and introducing irregularities into the network's modeling abilities. a neuron's functional form is determined by its activation function; for example, a linear activation function multiplies the neuron's value by the learned weight [34]. the activation function is expressed as: 𝑓 = 1 1+exp(𝑥) (1) a set of '𝑖′ synapses with weight 𝑊𝑖 that are supplied by a signal 𝑋𝑖 can have either a positive or a negative weight; a negative weight inhibits the sum of the junction's output, while a positive weight has a remarkable impact [35], signal weight is expressed as: 𝑊 = 𝑊𝑖𝑗 + ∆𝑊𝑖𝑗 (2) the wind system's power production fluctuates depending on a few factors, including air density and rotor blade area, but it changes more dramatically in response to wind speed. air density, blade area, and wind speed all affect the wind energy system's output power. the wind power distribution equation for a certain wind turbine can be calculated by utilizing its power curve. the wind speed distribution function at an area is determined by the mean wind speed. one can calculate the mean power density (mean power available) per unit of surface. getting power from the wind, considering betz's law, realistic values, and wind turbine factors like cut-in and cut-out wind speed, rated speed, and rated power can all be used in this procedure [36]. one helpful tool for simulating the operation of a wind turbine is its power curve. it displays the power output at a given wind speed. figure 2 displays a typical power curve for a pitch-regulated wind turbine. the lowest speed at which there is no power output is known as the cut-in speed. power grows quickly in the second zone, which is between the rated speed and the cut-in. the output in the third region doesn't change until the cut-off speed is reached. after this, the turbine is turned off to shield its internal parts from strong winds [37]. therefore, accurate wind speed and power forecasting are crucial for reducing wind power fluctuations in system dispatch planning. deep learning-based models are increasingly being considered due to their ability to handle complex nonlinear problems. however, scheduling, management, and optimization remain the main challenges for high penetration of renewable energy sources like wind power [38]. figure 2. wind turbine power curve model the following depicts the equation: where:𝑃𝑤 is the power extracted from the wind source in watts (w), 𝜌 is the density of air in ( 𝐾𝑔 𝑚3 ), 𝐴 is the area of blades of a rotor in (𝑚2), and 𝑣 is the speed of wind in ( 𝑚 𝑠 ) [39]. 𝑃𝑤 = 0.5𝜌𝐴𝑣3 (3) 3. methodology the prisma approach was employed to systematically identify and refine the focus on the intersection of neural networks and wind power generation using the scopus database. this comprehensive method followed the four key stages of prisma: identification, screening, eligibility, and inclusion. 3.1 identification the scopus database was selected as the primary source for downloading relevant information. the process began by accessing the scopus database and configuring the search parameters. initially, the "article title, abstract, and keywords" option was chosen from the dropdown menu in the search box. keywords "neural network" and "wind power generation" were entered, ensuring that the search would return documents containing both phrases exactly as specified. this search yielded an initial result of 811 documents. 3.2 screening to refine the search results, several filters were systematically applied. first, the results were sorted by relevance, ensuring that the most pertinent documents appeared at the top. then, the publication year range was set from 2019 to 2023, reducing the document count to 435. to narrow the focus further, the subject area was limited to engineering, which brought the count down to 285 documents. document type was then filtered to include only articles, resulting in 169 documents. the language filter was set to english, reducing the count to 158 documents. finally, the year range was further restricted to 2021–2023 to ensure the most recent information, leaving 110 documents. table 1 is an overview of inclusions and exclusions considered in this study. 3.3 eligibility in the eligibility phase, the relevant papers were selected and exported for detailed analysis. all documents were highlighted, and the csv format was chosen for export, successfully exporting 234 documents. this file was saved under a new folder on the desktop as the master file, which was preserved without any editing. a copy of this file, named "scopus documents," was created for editing and analysis purposes. m. sambane et al. /future energy november 2024| volume 03 | issue 04| pages 67-79 70 table 1. inclusions and exclusions 3.4 inclusions the next step involved a thorough review of the data. the scopus documents excel file was opened, and the abstracts in column r were reviewed to assess the relevance of each document. to facilitate this process, three new columns (s, t, and u) were created. column s was used to identify the aim, objective, or purpose of each document, the problems addressed, and the methods or techniques used. column t listed all variables used as inputs and outputs in each document, while column u identified the type of forecasting (short-term, medium-term, or long-term) if applicable. documents that were deemed irrelevant were highlighted in red and subsequently deleted from both the scopus documents file and the scopus master file, ensuring consistency between the two files. initially, both files contained 110 documents, but after removing non-relevant entries, the count was reduced to 64 documents. 3.5 analysis using vosviwer for deeper analysis, vosviewer software was downloaded and installed. the software was used to identify research gaps (network visualization) and current trending field patterns (overlay visualization). the process began by selecting the option to create a map based on bibliographic data, specifically choosing the scopus csv file for upload. cooccurrence analysis was performed, focusing on all keywords with a full counting method. a threshold of a minimum of five occurrences was set, resulting in 22 keywords meeting the criteria. the resulting map highlighted key topics and trends within the research area. the map was saved and exported for further analysis. clusters identified in the map were copied to an excel spreadsheet, where they were edited and analyzed. this detailed analysis helped to identify current trends and gaps in the research on neural networks and wind power generation. 4. literature review results analysis 4.1 long short term forecasting hong et al. [40] developed a mixed classical-quantum model that predicts wind speeds forecast for twenty-four hours ahead using a long term short term memory and a quantum network model to address the issue of power planning uncertainty of renewable energy by power companies in different countries, including south korea, taiwan, china, and philippines. in switzerland, basel, sun et al. [41] established a wind energy forecasting system using 2 stage attention and a short long term memory system. the approach significantly increased forecast accuracy while reducing the variable nature of climatic circumstances. with a focus on a wind farm in hunan province, wang et al. [42] explored a wind energy forecasting model that made use of a long-term short-term memory system and incorporated gaussian mutation technique and erratic sequence for enhanced stability and search performance. using statistically learned methods, ahmad t and zhang d [43] improved feature reliability and performance across belgian, distribution system operators (dso)-connected, and elia sites by using an in-depth sequence to sequence; long term short term memory regression approach for accurate wind energy projection. they employed the week ahead prediction. 4.2 short term memory based forecasting anushalini t and sri revathi b [44] identified a deep learning model appropriate for wind power forecasting with the aim to correctly predict power produced per hour using wind speed, air temperature, pressure, and air direction as inputs and power produced as output. cheng l et al. [45] explored a novel spatial temporal approach using an enhanced neural system for short-term forecasting of wind energy to address the issue of fluctuating. in australia, hossain et al. [46], in the boco rock wind plant, used a combined model of deep learning to precisely forecast wind power production in intervals of five and ten minutes. in australia, to accurately predict wind power production. hossain et al. [47] explored a deep hybrid learning model to accurately enhance a short-term wind power prediction at the bodangora wind plant. an et al. [48] analyzed data provided by three organizations to predict accurately wind power using a short-term model that entailed a diverse wind velocity combination. li et al. [49] explored a short-term adjustable graph network model based on temporospatial to accurately predict wind power. sopena et al. [50] presented a comparative analysis of up to thirty minutes ahead of the short-term prediction of wind energy utilizing a collection of artificial models based on neural systems and the primary decomposition techniques from a wind plant in ireland. in ireland, gonzalez et al. [51] presented a researched shortterm wind energy prediction system that utilized a spiked neural system that was tailored to the processing capabilities of intel’s loihi. 4.3 optimization techniques and neural network models for wind power forecasting to precisely forecast wind power values, tarek et al. [52] proposed a novel optimization method based on swarm particle optimization and fractal stochastic search to enhance long-term short memory network parameters. wu et al. [53] proposed a technique model to enhance the factors of longshort term memory using particle swarm adjustment and erratic fractal to forecast precise values of wind power. becanin et al. [54] proposed a forecasting energy method that utilizes long short-term memory and gated recurrent units to address the issue of managing the grid power, which also explored an improved algorithm of swarm intelligence. grace r.k, and manimegalai r [55] integrated a novel model that entails grey wolf optimization and back propagation neural system to predict wind speed; wavelet transform to divide item no. description criteria inclusion exclusion 1 database scopus other databases 2 publication period 2021-2023 documents published in 2020 and before. 3 document type articles book chapters, books, notes, letters, editorials reviews, conferences. 4 subject area engineering energy, mathematics, physical, life, social, health and humanities sciences 5 language english all other languages 6 file type csv ris, bibtex, plain text, etc. (please list all as i showed you) 7 8 design keywords “neural network” and “wind power generation” all documents outside specified used keywords m. sambane et al. /future energy november 2024| volume 03 | issue 04| pages 67-79 71 wind speed into an in-depth band. to accomplish precise and effective power forecasting. zhang et al. [56] suggested a wind energy forecasting system that used a logistic chaotic atom seek optimized enhanced back propagation neural system. huang et al. [57] developed an ideal ensemble approach in taiwan’s changhua for an hourly prediction of wind energy one day ahead of time. three steps made up the suggested optimum ensemble approach. in order to forecast wind speed in northwest china, zhu l and hu w [58] suggested a technique method that processed wind speed data by combining an optimized variational modal breakdown method with an optimized depth belief neural network. wang et al. [59] introduced a deep neural system to anticipate wind energy production, and it suggested a storage hydrogen windpumped storage combination that employs deep learning as well as intelligent optimization. 4.4 neural network approaches for predictive time series in wind farms in china’s xinjiang wind farm, ai et al. [59] explored the use of neural networks with erratic attribute analysis to create a predictive time series system. the wind farm data was analyzed using an integrated prediction approach, which improved the precision of predictions. to deal with the unpredictable and resolved nature of wind plants in local energy forecasting, a unique multiple-purpose optimal continuous neural system with time pattern awareness was explored by chen et al. [60]. qu et al. [61] explored multidimensional power time series, intrinsic mode signals, and convolutional neural systems which are combined with bidirectional long short-term memory and attention mechanisms to estimate wind energy in a wind farm located in liaoning province, china. to estimate wind speed in the short term, chen et al. [63] explored a mixed approach that combined neural networks, time-varying restrictions, modal degradation, permutation entropy, adaptive noise, neurofuzzy inference, packet data analysis, and an enhanced monarch butterfly optimization method. drawing inspiration from the remarkable capabilities of deep neural systems in machine vision, liu et al. [64] provided a novel method for forecasting short-term wind energy by utilizing the machine learning system to analyze time series pictures. 4.5 hybrid models and machine learning techniques for wind speed and power prediction in canada, saskatchewan, abbasipour et al. [65] addressed the issue of wind speed prediction using a twentyfour-hour ahead hybrid model of neural network that entailed 5 algorithms of networks. xiong et al. [66] worked on a hybrid design prediction system built on descent and meta-heuristic planning to accurately predict wind power and lessen computing load. hong y and santos j [67] suggested a unique hybrid model that combines period and latent long-term, short-term memory improved by optimizing particle swarms to forecast a day wind speed. in italy, finamore et al. [68] explored a hybrid wind power prediction model that used an organized framework method that grouped weather data and then used the person’s scrutiny method to locate key elements in each group. peng et al. [69] proposed a 1 stepahead power prediction method using a hybrid long-term short-term memory and a convolutional deep learning method. shah et al. [70] explored a hybrid prediction model that entails ripple transform and swarm particle optimization to address the issue of stability in wind power generation integration. in indonesia, barus and dalimi [71] presented an extensive hybrid machine learning solution that integrated a seasonal moving average on daily hourly operational reserves with specific neural system variables. long-term short-term memory produced the most precise results. wang et al. [72] developed a combined innovative forecasting technique consisting of data preprocessing and combination strategy to accurately predict wind speeds for power generation. in this paper, xiao et al. [73] explored a hybrid model with optimized hyperparameters gated recurrent unit neural network model and feature-weighted principal component analysis, which lessened the effects of unpredictability, noisy data, and instability in wind energy production. 4.6 hybrid and neuro-fuzzy models for enhanced wind power prediction in singapore, abdullah and hassan [74] used a neurofuzzy short-term hybrid forecast over a twenty-four-hour ahead model to improve the wind power generation prediction, and the results showed 94% accuracy. roy et al. [75] forecasted 1 hour ahead wind speed accuracy using a synthetic neural network model that compares the input to output data and maps it out, and uses a changeable neurofuzzy system to precisely estimate grid power reference for the forecasted hour period. in this paper, xu et al. [76] presented a reiterative neuro fuzzy hammerstein approachbased projective control system for wind turbines, which addressed the issue of regulating power output. 4.7 algorithms and neural network models for wind energy prediction peiris et al. [77] created an artificial neural system algorithm to predict the amount of wind energy generated at sri lanka’s operational pawan danawi wind farm. the algorithm utilized the produced wind energy as a dependent factor and wind direction, wind speed, and local temperature as independent factors. xiong et al. [78] suggested and explored a multiple-view deep learning network architecture to estimate wind energy using a wide range of information, including wind speed, wind direction, and wind power. chen and han [79] advanced to balance and stabilize the accuracy and wind speed control by using a control method of reward adaptive that entailed controlling the pitch angle and torque of the generator in different conditions. xia et al. [80] explored and enhanced a stacked gated recurrent unit neural network. they used it to predict the production of wind energy and electrical load in both single and multiple-variable scenarios. to improve calculations and uncover hidden features, liu et al. [81] presented a novel deep and transfer learning framework that developed efficient data-driven wind energy forecasting algorithms for wind turbines. liu et al. [82] explored a sophisticated forecasting technique that allowed for both precise and accurate wind power estimates using a standard differential equation system with attention support paired with a long-term short-term memory system. in montreal, shirzandi et al. [83], due to the erratic behavior of wind power production, developed a forecasting model of 48 hours ahead using arithmetic weather forecasting, comparing wind speed inputs and output power generation. a synthetic neural network architecture for wind energy prediction was examined in detail by huang et al. [84] using just historical wind speed and wind energy production statistics for a half hour ahead from a wind plant in southeast australia. gu et al. [85] used collected wind speed information from chuanshan port area, ningbo-zhoushan port, and developed an improved wavelet neural network wind speed prediction model. in northwest china, qu et al. [86] investigated the high association properties of wind farm groups and learned their spatial features using a spatialtemporal deep learning system. ozbek et al. [87] explored a m. sambane et al. /future energy november 2024| volume 03 | issue 04| pages 67-79 72 machine intelligence method for precise prediction of wind speeds in turkey's marmara and mediterranean regions. it does this by predicting short-term wind speed data 1 hour ahead of time using neural networks and the adaptive neuro fuzzy inference system. an algorithm for projecting the production of wind energy, both probabilistic and predictable, as well as related methods, were explored by wu et al. [88]. wind speed from taiwan’s central weather bureau was used. sun et al. [89] to address wind power fluctuations on the grid. they explored a hybrid model of regulating disturbance with an inverter on the grid side. for wind energy projections in the netherlands and germany, wahdany et al. [90] explored a neural network topology that directly considered changing energy system conditions to optimize system costs. 4.8 neural network models for wind speed and power prediction li et al. [91] used eight models to accurately predict wind speeds. results showed that the convolutional neural model performed better. song y et al. [92] presented a method used to precisely forecast wind power using convolutional graphs and convolutional neural systems, mixing spatiotemporal features. wang et al. [93] created a comprehensive multiple variates mix short-term forecasting of wind speeds system. it consisted of sophisticated feature selection techniques and angle prediction models built on convolutional neural systems. in this research, nguyen et al. [94] proposed a layered temporal convolutional system method to handle the multi-step forward prediction and increase the reliability of short-term wind energy predictions. this technique tackles the problem of depending on long-term memory. in japan, sari et al. [95] explored deep learning that is based on a wind model of one-hour ahead prediction with the intention of establishing a precise prediction model that is made of 3dimensional neural network convolutional and long-shortterm deep convolutional memory. 4.9 stability and predictability in renewable energy systems enhancement alzain and liu [96] undertook to resolve the issue of uncertainty stability of voltage in the system caused by renewable loads by exploring a model that extracts data between sources using a deep kernel emulator. to tackle the issue of turbine power imbalance causing frequency deviations, sun et al. [97] explored the use of a load frequency control as a secondary measure for power systems. in denmark and the netherlands, yu t and yang r [98] explored a wind prediction method to address the wind generation issue by implementing a changeable model that retrieves wind data from different meteorological sources. in this paper, memmel et al. [99] proposed a selection method of n-1 to address the issue of congestion on the grid. to overcome blade health issues through an additional task and data enhancement neural systems, an independently overseen approach method was presented by sun et al. [100]. zhang et al. [101] used wind speed prediction and wind power simulations as its two main elements, developed a system of management for windfarms. to improve renewable system dependability, tan et al. [102] presented an hour-ahead wind power production forecasting model that used wind speeds as input data. wang et al. [103] explored a model free adaptable fifteen seconds ahead wind predicting controller to pitch-varying systems, including speed disruption suppression to address variations in wind output. 5. literature review analysis observations the literature provided presents a comprehensive overview of various methodologies and models employed for wind power forecasting across different regions globally. one key noticeable aspect throughout the literature is the emphasis on enhancing prediction accuracy and stability in wind power forecasting through the utilization of advanced machine learning techniques and hybrid models. these techniques include deep learning architectures such as convolutional neural networks (cnns), long short-term memory (lstm) networks, gated recurrent units (grus), and their combinations with optimization algorithms like particle swarm optimization and fractal stochastic search. additionally, there is a focus on addressing specific challenges related to wind energy production, such as wind speed prediction, wind power fluctuation management, grid integration issues, and turbine health monitoring. moreover, there is a notable trend towards incorporating multidimensional and multi-step forecasting methods, as well as considering various environmental factors such as weather data and spatial-temporal features to improve forecasting reliability. the literature highlights the significance of accurate wind power forecasting for optimizing energy system operations, enhancing grid stability, and facilitating the integration of renewable energy sources into the power grid. 6. trends analysis 6.1 network visualization the tables below represent the network visualization or gaps within this topic. the table consists of keywords, namely clusters, links, total link strength, and occurrences as headings. they are categorized according to clusters, which range from clusters 1 to 5. table 2 is the combination of clusters 1 and 2, where cluster 1 consists of 16 keywords, and long short-term memory has a higher number of 243 total link strength, indicating a higher association and relation strength for the keyword. this normally indicates that the higher the total link strength, the higher the occurrence for the keyword, and this is observable from table 2. cluster 2 consists of 14 keywords, and electric load dispatching has a higher number of 89 total link strengths, which indicates that there is a higher association and relation strength for the keyword. this normally indicates that the higher the total link strength, the higher the occurrence for the keyword, and this is observable from table 2 below. table 3 represents clusters 3, 4, and 5, and in cluster 3, it can be observed that it consists of 9 keywords. wind power has a higher number of 487 total link strength, which indicates that there is a higher association and relation strength on the keyword. this normally indicates that the higher the total link strength, the higher the occurrence for the keyword, which is observable from the table below. cluster 4, it can be observed that it consists of 8 keywords. wind power generation has a higher number of 214 total link strengths, which indicates that there is a higher association and relation strength on the keyword. this normally indicates that the higher the total link strength, the higher the occurrence for the keyword, and this is observable from table 3. cluster 5, it can be observed that it consists of 5 keywords. particle swarm optimization (pso) has a higher number of 128 total link strengths, which indicates that there is a higher association and relation strength on the keyword. this normally indicates that the higher the total link strength, the higher the occurrence for the keyword, which is observable from table 3. m. sambane et al. /future energy november 2024| volume 03 | issue 04| pages 67-79 73 table 2. keywords with links, total link strength, occurrences based on application of neural network regression algorithms in wind power generation cluster 1 red keywords cluster links total link strength occurrences long short-term memory 1 50 243 24 wind speed 1 49 185 17 mean square error 1 45 133 12 learning systems 1 43 112 11 deep learning 1 45 111 12 wind speed forecasting 1 38 98 9 convolution 1 38 90 9 machine learning 1 39 84 7 errors 1 44 83 7 stochastic systems 1 32 72 8 machine-learning 1 34 69 6 learning algorithms 1 35 62 5 multilayer neural networks 1 36 60 5 deep neural networks 1 32 59 7 time series 1 28 56 6 convolutional neural networks 1 29 52 5 cluster 2 green keywords cluster links total link strength occurrences electric load dispatching 2 36 89 9 brain 2 37 77 7 electric utilities 2 35 61 7 energy utilization 2 24 61 7 neural-networks 2 48 61 15 optimization 2 36 61 8 power generation 2 49 61 26 recurrent neural networks 2 30 61 7 weather forecasting 2 51 61 40 wind farm 2 37 61 10 wind power forecasting 2 40 61 12 wind power prediction 2 27 61 5 wind power predictions 2 36 61 9 algorithm 2 34 54 5 table 3. keywords with links, total link strength, occurrences based on application of neural network regression algorithms in wind power generation cluster 3 blue keywords cluster links total link strength occurrences wind power 3 51 487 56 electric power generation 3 51 311 36 forecasting 3 47 122 12 wind 3 35 86 11 electric power transmission networks 3 39 72 8 speed 3 32 70 8 fuzzy inference 3 30 57 6 fuzzy neural networks 3 30 57 6 fuzzy systems 3 28 50 5 cluster 4 yellow keywords cluster links total link strength occurrences wind power generation 4 49 214 25 artificial neural network 4 47 128 13 neural networks 4 35 92 11 predictive models 4 39 79 8 wind turbines 4 34 70 9 short term prediction 4 32 57 5 short-term prediction 4 32 57 5 wind forecasting 4 25 50 5 cluster 5 purple keywords cluster links total link strength occurrences particle swarm optimization (pso) 5 43 128 12 particle swarm 5 40 92 8 swarm optimization 5 36 81 7 particle swarm optimization 5 33 63 5 meteorology 5 27 55 5 m. sambane et al. /future energy november 2024| volume 03 | issue 04| pages 67-79 74 figure 3 is a network visualization, which consists of different colors that represent a gap between the different research topics. the bigger the circle means that much research has been done on that topic, and the smaller the circle means less work or research has been done on that topic and needs further research. the lines between the topics show how the topics are related to each other; the more lines you will have between two topics, the more strength exists between them, and the closer the topics are, the more relationships can be observed between the topics. the graph has five different colors, which are clustered accordingly, namely, cluster number 1 is indicated in red. it can be observed that long short-term memory has a bigger circle, meaning more research has been done on the topic, with machine learning having a smaller circle, indicating less research work being completed on the topic. cluster number 2 is indicated in green. it can be observed that weather forecasting as well as power generation have bigger circles, meaning more research has been done on those topics, with algorithm and optimization having smaller circles, indicating less research work being completed on the topics. cluster number 3 is indicated in blue. it can be observed that wind power as well as electric power generation have bigger circles, meaning more research has been done on those topics, with fuzzy inference and fuzzy systems having smaller circles indicating less research work being completed on the topics. cluster number 4 is indicated in yellow. it can be observed that wind power generation, as well as artificial neural networks, has bigger circles, meaning more research has been done on those topics, with wind turbines and neural networks having smaller circles, indicating less research work being completed on the topics. cluster number 5 is indicated in purple. it can be observed that particle swarm optimization (pso) has a bigger circle, meaning more research has been done on the topic, and meteorology has a smaller circle, indicating less research work is being completed on the topic. 6.2 overlay visualization results figure 4 illustrates an overlay visualizing which represents a research trend on the topics. it shows the most recently researched topics and areas by using different colors. the periods have been averaged as depicted on the scale; it starts from 2021.8; this means that 2021 is the year, and the .8 represents month 8; this follows the same trend for the other periods. from 2021.8 to 2022.0, it shows that the investigation has been more on speed, wind, etc., and moving towards 2022.0 to 2022.2, the trends were more into learning systems and errors, then by 2022.2 to 2022.4, the investigation was more based on weather foresting and wind power. from around 2022.4 to 2022.6, the focus was more on particle swarm optimization artificial neural networks. the research topic for the above graph shows the yellow color that from the year period of 2022.6 coming towards 2022.8, the researched topics have been under power generation, which has a bigger circle representing that much research has been explored on the subject and also a few topics namely, electric load dispatching, algorithm, neural networks having smaller circles representing less researched or explored topics for the future. 7. future proposal recommendation owing to the wind's sudden changes in density, speed, and other important factors, the following topics are recommendations that still need to be thoroughly researched to guarantee consistent generation and a larger role for this source in the electrical power framework. • examine how learning algorithms like convolutional neural networks (cnns) and multilayer neural networks can be combined to increase the accuracy of wind power prediction time series forecasting. • create innovative wind power prediction algorithms by combining knowledge from cutting-edge machine learning techniques and conventional forecasting methods. figure 3. network visualization based on the application of neural network regression algorithms in wind power generation m. sambane et al. /future energy november 2024| volume 03 | issue 04| pages 67-79 75 • investigate how to incorporate fuzzy neural networks and fuzzy inference systems into wind power prediction models to address imprecision and uncertainty in meteorological data. • by utilizing particle swarm optimization algorithms and incorporating knowledge from meteorology research, create sophisticated short-term prediction models for wind forecasting. • create optimization frameworks that improve the accuracy and dependability of short-term wind power predictions by fusing meteorological data with particle swarm optimization techniques. 8. conclusion this research undertook a systematic review based on the advanced neural network and hybrid models for wind power forecasting. using the scopus database, a methodical search, acquisition, and filtering procedure was utilized to find pertinent publication documents; vosviewer software was employed to analyze trends. numerous studies demonstrate the critical role that precise wind power forecasting plays in improving grid stability, accelerating the integration of renewable energy sources into the grid, and optimizing the performance of the energy system. by applying sophisticated machine learning algorithms and hybrid models, wind power forecasting can be made more accurate and stable. deep learning techniques involve the use of various designs, such as convolutional neural networks (cnns), long short-term memory (lstm) networks, and gated recurrent units (grus), along with optimization algorithms like particle swarm optimization and fractal stochastic search. in addition to analyzing the integration of optimization techniques with neural networks and offering a thorough review of lstm and short-term memory-based models in wind power generation, this paper contributed by examining hybrid models that can enhance predictions of wind speed and power output. along with outlining the effectiveness of different neural network approaches and algorithms used in wind energy forecasting, it also provided recommendations for future research directions. acknowledgment the authors gratefully acknowledge the university of south africa, 28 pioneer ave, florida park, roodepoort, for providing the resources essential to this research. ethical issue the authors are aware of and comply with best practices in publication ethics, specifically concerning authorship (avoidance of guest authorship), dual submission, manipulation of figures, competing interests, and compliance with policies on research ethics. the authors adhere to publication requirements that the submitted work is original and has not been published elsewhere in any language. 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[103] wang s.; li j.; hou z.; meng q.; li m., “composite model-free adaptive predictive control for wind power generation based on full wind speed”, csee journal of power and energy systems, vol. 8 (6), 2022, pp. 1659-1669. this article is an open-access article distributed under the terms and conditions of the creative commons attribution (cc by) license (https://creativecommons.org/licenses/by/4.0/). https://creativecommons.org/licenses/by/4.0/ i. hossen et al. /future energy february 2026| volume 05 | issue 01| pages 20-29 20 article advanced passive heat transfer enhancement: numerical analysis of tio₂-water nanofluid flow in tubes fitted with twisted tape and conical ring inserts itquan hossen*, prasanjit das, ashraful zannat akhi department of mechanical engineering, chittagong university of engineering and technology, chittagong-4349, bangladesh a r t i c l e i n f o article history: received 10 september 2025 received in revised form 25 october 2025 accepted 09 november 2025 keywords: twisted tape, tio2 nanofluid, passive heat transfer enhancement, friction factor, nusselt number, thermal performance factor *corresponding author email address: itquan2013@gmail.com doi: 10.55670/fpll.fuen.5.1.3 a b s t r a c t the primary objective of this study is to investigate the heat transfer enhancement, friction factor, and thermal performance factor of a plain tube with single and double twisted tapes, combined with a semicircular cut with and without dimples, a perforated v-cut, and conical rings, using a tio2-water nanofluid. numerical simulations of tube flow and heat transfer were conducted. the nanofluid used in the simulations contains tio2 nanoparticles at concentrations of 0.5% and 1.5% by volume. the nanofluid inlet temperature was set at 300 k, and boundary conditions were applied. the maximum heat transfer coefficient increases from plain tube to 88.2% and 71.42% at double twisted tape with perforated v-cut and semi-circular cut, respectively, with dimples in 0.5% and 1.5% tio₂ concentrations. the maximum nusselt number increased by 115.53% and 100.9% at double twisted tape with perforated v-cut and semi-circular cut with dimples compared to the plain tube in 0.5% and 1.5% tio2 concentrations, respectively. the simple tube with a perforated v-cut and a conical ring insert exhibits a 94.44% higher friction factor at a 1.5% tio2 concentration. the maximum thermal performance factor was found to be 2.04 for double twisted tapes at a 0.5% tio2 concentration. additionally, this study presents contour plots of the velocity distribution, pressure distribution, temperature distribution, and turbulent kinetic energy. 1. introduction in thermal engineering, a device used for transferring thermal energy between fluids, whether that's between a solid surface and a liquid or between solid particles and a gas, is called a heat exchanger. without the exchange of work or the application of external heat, these machines are used in heating, cooling, evaporation, condensation, and heat recovery [1]. heat exchange performance improvement is of special significance, as improved heat transfer performance can translate into more compact systems, lower costs, and substantial energy savings [2,3]. heat transfer improvement techniques are an effective way to realize these advantages. active, passive, and compound are three significant classifications of heat transfer improvement methods. active techniques involve the application of external sources of power, such as fluid injections, electric or magnetic fields, mechanical assistance, or surface vibration, to enhance heat transfer. passive techniques utilize turbulators, roughened surfaces, fine surfaces, coiled tape, dimples, and protrusions or nanofluids to enhance the thermal efficiency of the system without introducing any supplementary energy. to attain greater heat transfer rates than by each method alone, composite techniques combine active and passive solutions [4,5]. passive solutions include twisted tape inserts, which have received substantial attention due to their ease of application, economy, and simplicity of installation [6]. strips of metal are shaped into particular geometries and placed in fluid flow conduits to improve heat transfer. these inserts create interference with the thermal boundary layer, increasing convective heat transfer through swirl flow and turbulence. they also lead to a pressure drop, and hence a compromise between heat transfer improvement and frictional loss is unavoidable. to maximize thermal performance and minimize pressure loss, various twisted tape geometries have been investigated in recent studies [5]. future energy open access journal https://doi.org/10.55670/fpll.fuen.5.1.3 february 2026| volume 05 | issue 01 | pages 20-29 journal homepage: https://fupubco.com/fuen issn 2832-0328 mailto:itquan2013@gmail.com https://doi.org/10.55670/fpll.fuen.5.1.3 https://fupubco.com/fuen i. hossen et al. /future energy february 2026| volume 05 | issue 01| pages 20-29 21 the following is an overview of recent studies that investigate the thermal performance outcomes of various twisted tape designs. wongcharee et al. [6] examined the thermal-hydraulic behavior of u-cut twisted tapes (u-tts) under homogeneous heat flow conditions when inserted into a circular tube. their work focused on twist ratios (y/w = 3.5 and 4.0) and u-cut ratios (s/t = 0.5 to 3.0). the thermal performance factor (tpf) was found to be 1.28 when s/t = 0.5 and y/w = 3.5, which was better than any other configuration. they observed that u-tts with smaller u-cut ratios (s/t = 0.5 to 2.0) exhibited a significantly higher nusselt number compared to regular twisted tapes. for u-tts, however, friction losses were regularly larger than for standard tapes [6]. li et al. [7] quantitatively investigated employing hollow twisted tapes for heat transfer enhancement in laminar flow. their studies showed that cross-hollow twisted tapes enhanced general heat transfer performance by 28.1% over ordinary tapes. reducing the gap between the tube and the twisted tape also improved heat transfer, and four unilateral twisted tapes at reynolds numbers above 600 produced ideal performance. abed et al. [8] investigated forced convection heat transfer in a horizontal pipe with twisted-tape inserts under constant heat flow using a numerical method. their working fluid was water; they investigated reynolds number (4000 ≤ re ≤ 9000), twist ratio (4.0 ≤ tr ≤ 6.0), and heat flow (5000 ≤ q ≤ 10000 w/m²). their results showed that v-cut twisted tapes with a twist ratio of 4 offered the highest thermal performance factor (tpf = 4.45), surpassing simple twisted tapes (tpf = 4.19). promvonge et al. [9] investigated heat transmission in a circular tube combined with conical-ring and twisted-tape inserts. their tests, using air as the working fluid, revealed that the combined inserts raised the nusselt number by up to 367%, thanks to the formation of reverse and swirl flows, which improved fluid mixing. abbasian arani and amani studied the effect of tube diameter on the heat transmission ability of tio₂-water nanofluids [10]. by increasing turbulence, they demonstrated that tube size increases enhanced heat transfer and led to greater pressure drops. kumar et al. [11] also demonstrated that double v-cut perforated twisted tapes significantly enhanced heat transfer, with the optimum result achieved at a twist ratio of 2. nanofluid developments in recent years have also further extended the scope for enhancing heat transfer. dagdevir and ozceyhan [12] conducted a comparison study utilizing plain tube, perforated twisted tape, and dimpled twisted tape. working with mixes of ethylene glycol and water, they found that the concentration of ethylene glycol in the mixtures degraded thermal-hydraulic performance. for instance, eiamsa-ard et al. [13] found that tio₂water nanofluids with a volume concentration of 0.21% improved heat transmission by 9.9–11.2%, while weerapun [14] noted that nanofluids displayed a 6–11% greater convective heat transfer coefficient than baseline fluids. s. eiamsa-ard [15] investigated the twin-twisted-tape heat exchanger tube tio2-water nanofluid heat transfer improvement. heat transmission improved by 9.9-11.2% and thermal performance by 4.5% at 0.21% tio2 volume concentration. according to a review of previous studies, various approaches have been employed over the years to optimize heat exchange performance. passive techniques have previously been employed, utilizing a variety of inserts with different types of cuts, various types of fluids, including nanofluids, and surface modifications to reduce the thickness of the thermal boundary layer. as a result, the search for a suitable insert remains a significant challenge. this study focuses on the numerical investigation of heat transfer improvement with tio₂-water nanofluid in a tube fitted with conical rings and modified twisted tapes. the combinations of twisted tapes used in this study are: single twisted tape with perforated v-cut (stpv), single twisted tape with semicircular cut (stsc), perforated v-cut twisted tape with conical rings (pvtc), double twisted tape with perforated v-cut and semicircular cut (dtt-1), double twisted tape with perforated v-cut and semicircular cut with dimples (dtt-2), and plain tube. as can be seen, these combinations of twisted tapes have not been used in previous studies. therefore, the effect of these combinations on heat transfer enhancement remains unknown. for nanofluids, tio2 is utilized due to its superior performance compared to other nanomaterials. tio2 nanoparticles exhibit exceptional capabilities for enhancing thermal conductivity in nanofluids. tio2-water nanofluids have been reported to exhibit a thermal conductivity enhancement of up to 37% at elevated temperatures. thermal conductivity for tio2 nanofluids ranges from 4-11.8 w/m·k, which is significantly higher than that of most base fluids, and hence is extremely suitable for use in heat transfer applications [16,17]. the thermal stability of tio2 is particularly noteworthy, as the material maintains its structure and function up to 1000-1200°c. this heat resistance is superior to that of several other nanomaterials, which can break down or become less effective at lower temperatures [18,19]. moreover, tio2 is non-toxic and safe for humans, giving it a significant advantage over other nanoparticles that may pose health or environmental risks. tio2 nanoparticles possess fairly good dispersibility in polar and nonpolar base fluids, especially with the use of sufficient dispersants [20]. in contrast to other commonly used nanoparticles, tio2 exhibits similar or improved performance. this study investigates the effects of heat transfer enhancement of stsc, stpv, pvtc, dtt-1, and dtt2, and assesses the nusselt number, friction factor, and thermal performance factor (tpf) over a range of reynolds numbers (5000–49800) and tio₂ volume concentrations (0.5% and 1.5%). however, optimization of twisted tape design and volume concentration percentage of tio2 in water are not done in this study. there is a scope for future study by optimizing these combinations of twisted tapes and nanofluids. the results of this study seek to shed light on heat exchanger designs for refrigeration, power plants, chemical processing, and electronic cooling systems. 2. numerical modelling 2.1 physical modeling three types of twisted tape were used to insert into a plain tube. the tapes were semicircular cut, perforated v-cut, and semicircular cut with dimples. the working fluid used was a tio2-water nanofluid with varying concentrations. the fluid entered the tube at a specific inlet temperature and flowed through the 70 mm diameter section, where the testing would take place. the investigation was conducted within the range of reynolds numbers of 5000 to 49800. i. hossen et al. /future energy february 2026| volume 05 | issue 01| pages 20-29 22 detailed information on the geometry is given in table 1. figure 1 shows the physical model of the plain tube, stsc, stpv, pvtc, dtt-1, and dtt-2. in this study, air will be used as the working fluid in the plain tube validation, and tio2-water will be used as the working fluid with different concentrations. the thermophysical properties of tio2 are given in table 2. the properties of air are listed in table 3, which are used as the defaults in ansys. table 1. dimensions of the physical model figure 1. (a) 3d view of plain tube, (b) stsc, (c) stpv, (d) pvtc, (e) dtt-1, (f) dtt-2 2.2 mesh generation the term "mesh" refers to the abstract mathematical space utilized to generate polygons, tetrahedra, or hexahedra and other geometrical structures. different mesh types are chosen based on geometric complexity, desired accuracy, and computational resources. inadequate grid development, on the other hand, might reveal discrepancies from the intended mathematical design [22]. in this study, tetrahedron meshes were applied to the fluid domain for all of the geometries. the mesh size was 25 mm. a refined mesh was utilized along the tube wall to ensure the effect of the viscous sublayer. the first layer thickness inflation option was used to ensure that the y+ value remained below 1. edge sizing with a particular number of divisions was applied to maintain meshing quality. meshing criteria, such as orthogonal quality, skewness, and element quality, will be evaluated to determine mesh quality. table 4 shows the meshing elements and summary. figure 2 illustrates the meshing for the pipe wall, insert, and rings, which include holes and dimples. table 2. properties of tio2 [21] table 3. properties of air table 4. meshing details plain tube length, l 1500mm tube inner diameter, d 70mm twisted tape length, l 1440mm tape width, w 24mm tape thickness, t 2mm pitch length of insert, y 48mm twist ratio, tr= y/w 2 v cut width, w 7mm depth of cut 6mm perforated hole diameter 6mm distance between two holes 12mm radius of semicircular cut 6mm opposite semicircular cut distance 24mm diameter of dimple 2 mm conical ring length, y 60mm ring inlet diameter, 𝐷1 15mm ring outlet diameter, 𝐷2 25mm pitch length of ring, p 240mm pitch ratio, pr=p/𝐷1 4 volume concentration, φ (%) density, ρ (kg/m3) specific heat, cp (j/kg.k) thermal conductivity, k (w/m k) viscosity, µ (kg/m.s) 0 1055.39 3502.0 0.413 0.00240 0.5 1071.26 3446.5 0.418 0.00251 1 1087.14 3392.7 0.418 0.00265 1.5 1103.01 3392.7 0.441 0.00279 dynamic viscosity, μ 1.7894×10-5 kg/m-s specific heat, cp 1006.43 j/kg-k prandtl number, pr 0.744 air density, ρ 1.225 kg/m3 thermal conductivity, k 0.242 w/m k orthogonal quality 0.99 transition ratio 0.272 element size 20 mm maximum layer 10 edge sizing number of divisions inflation option smooth transition number of elements 12000-19000 node 32096 i. hossen et al. /future energy february 2026| volume 05 | issue 01| pages 20-29 23 figure 2. (a) meshing profile for solid tube, (b) inflation layer for tube wall, (c) meshing profile for perforated v-cut twisted tape, (d) meshing profile for semicircular cut twisted tape, (e) meshing profile for perforated v-cut twisted tape with conical ring, (f) meshing profile for double twisted tape with perforated v-cut and semi-circular cut with dimples 2.3 governing equations mathematical modeling will be applied to anticipate flow and heat transfer characteristics. the finite difference method was used to evaluate the partial governing equations for boundary layers and swirling flows. three governing equations characterize the properties of a fluid. the governing equations are solved by ansys fluent, assuming the fluid is steady. the governing equations are used from xie et al. [23]. the governing equations are given below. 𝜕 𝜕𝑥𝑖 (𝜌𝑢𝑖) = 0 (1) where 𝜌 is fluid density, 𝑢𝑖 is the ith-direction of flow velocity. momentum equation: 𝜕 𝜕𝑥𝑗 (𝜌𝑢𝑖𝑢𝑗) = − 𝜕𝜌 𝜕𝑥𝑖 + 𝜕 𝜕𝑥𝑗 (µ + µ𝑡)( 𝜕𝑢𝑖 𝜕𝑥𝑗 + 𝜕𝑢𝑗 𝜕𝑥𝑖 ) (2) where, 𝑢𝑖 is the ith-direction of flow velocity, 𝑢𝑗 is the jthdirection of flow velocity, µ is dynamic viscosity, µ𝑡 is the eddy viscosity. energy equation: 𝜕 𝜕𝑥𝑖 (𝑢𝑖𝑇) = 𝜕 𝜕𝑥𝑖 [( µ 𝑃𝑟 + µ𝑡 𝑃𝑟𝑡 ) 𝜕𝑇 𝜕𝑥𝑖 ] (3) where 𝑢𝑖 is the ith-direction of flow velocity, t is temperature, µ is dynamic viscosity, µ𝑡 is the eddy viscosity, pr is the prandtl number, and 𝑃𝑟𝑡 is the prandtl number of the turbulent flow. turbulent kinetic (г) energy equation: 𝜕 𝜕𝑥𝑗 (𝜌𝑘𝑢𝑗) = 𝜕 𝜕𝑥𝑗 [(μ + µ𝑡 σ𝑘 ) 𝜕𝑘 𝜕𝑥𝑗 ] + г − ρɛ (4) where 𝜌 is fluid density, 𝑢𝑗 is the jth-direction of flow velocity, µ is dynamic viscosity, µ𝑡 is the eddy viscosity, γ is the turbulent kinetic energy production rate, and ɛ is the dissipation rate of turbulent kinetic energy. specific dissipative rate (ɛ) equation: 𝜕 𝜕𝑥𝑗 (𝜌ɛ𝑢𝑗) = 𝜕 𝜕𝑥𝑗 [(𝜇 + µ𝑡 𝜎ɛ ) 𝜕ɛ 𝜕𝑥𝑗 ]+𝐶1гɛ -𝐶2 ɛ2 𝑘+√ʋɛ (5) where, σ𝑘 = 1 and σɛ = 1.3 , 𝐶1 = 𝑚[0.43 µ𝑡 µ𝑡+5 ] and 𝐶2 = 1 and ʋ is the kinematic viscosity. 2.4 simulation setup in this investigation, the energy equation was used in the ansys setup. when nakhchi et al. [24] evaluated various turbulence models, including the standard k-model, the renormalized group (rng) k-model, and the shear stress transport (sst) k-model, they discovered that the (rng) kmodel provides good accuracy. the rng model of turbulence is derived from the instantaneous navier-stokes equations using a statistical method called "renormalization group" (rng) methods. the rng model improves accuracy for swirling flows by considering the effects of swirling on turbulence. the rng viscous model with enhanced wall treatment was applied in this study. the use of y+ with enhanced wall treatment gives scalable benefits over standard wall functions. for solver parameters in the fluent model setup, the pressure-based and steady-state models were used. then, the rng kmodel for viscosity was chosen. the inlet temperature of air was taken to be 300k. the walls of stsc, stpv, pvtc, dtt-1, and dtt-2 were set to adiabatic walls. the boundary conditions are shown in table 5. table 5. boundary conditions 2.5 numerical procedures the pressure-based solver is used in this study to solve the steady-state problem. the governing equations are solved by the finite volume method. the simple (semi-implicit method for the pressure-linked equations) algorithm was selected for the numerical study. twisted tapes fitted with a plain tube were utilized with presto (pressure staggering option). the quadratic upstream interpolation for convective kinematics (quick) approach employed momentum, energy, turbulent kinetic energy, and specific dissipation rate to obtain accuracy. when the residuals dropped below 10-3 the numerical solutions converged, except for the energy equation, which dropped below 10-6. 3. results and discussion 3.1 validation of simulations in order to validate the simulation results for a plain tube to calculate heat transfer augmentation, the results are compared with the gneilski correlation for nusselt number comparison and the petukhov correlation for friction factor [25]. a previous experimental work of promvonge et al. [26] using a conical ring and a previous experimental investigation by bhuiya et al. [27] was validated by simulation results. surface thermal momentum inlet 300k velocity inlet outlet pressure outlet tube wall 7500 w/𝑚2 no-slip condition walls of all twisted tapes and conical rings 0 w/𝑚2 i. hossen et al. /future energy february 2026| volume 05 | issue 01| pages 20-29 24 0 0.005 0.01 0.015 0.02 0.025 0.03 0.035 0 20000 40000 60000 f ri ct io n f ac to r, f reynolds number, re petukov current study (b) the gneilnski correlation was used to verify the plain tube for the nusselt number. the nusselt number deviation percentage ranges from 3.78% to 5.18% with an rms error of 3.079%. the friction factor for the simple tube was confirmed using the petukhov correlation [25]. the friction factor's deviation percentage varied from 6.3778% to 13.405%. with an rms error of 2.837%. figure 3 illustrates the validation results for the nusselt number and friction factor. figure 3. (a) nusselt number validation for plain tube, (b) friction factor validation to ensure the simulation procedure validated a previous experimental work done by promvonge et al. [28]. the working fluid for this experiment was air. the deviation percentage of the nusselt number varied from 16.5% to 18.01%. the validation of the nusselt number for a conical ring is shown in figure 4. 3.2 heat transfer enhancement characteristics heat transfer coefficient results from ansys fluent were gathered. the connection between the reynolds number and the heat transfer coefficient of double and single twisted tape inserts at various concentrations of tio2 is shown in figure 5, which demonstrates that, in all cases, the heat transfer coefficient increased as the reynolds number increased. the heat transfer rate increased because the twisted tapes created vortices and turbulence in the fluid flow, which ensured better fluid mixing and, consequently, increased the heat transfer rate [29]. besides, twisted tapes create a larger effective surface area, which improves overall heat transfer performance. the maximum heat transfer coefficient is increased from plain tube to 88.2% and 71.42% at pvtc and dtt-2 in 0.5% and 1.5% tio₂ concentrations, respectively. figure 4. nusselt number validation for a conical ring (a) (b) figure 5. (a) comparison of the reynolds number and the heat transfer coefficient for 0.5% tio2, (b) comparison of the reynolds number and the heat transfer coefficient for 1.5% tio2 figure 6 depicts the relationship between the nusselt number and the reynolds number. the maximum nusselt number increased by 115.53% and 100.9% for double twisted tape with perforated v-cut and semi-circular cut with dimples, compared to the plain tube in 0.5% and 1.5% tio2 concentrations. figure 6 illustrates that, in all instances, the nusselt number increased as the reynolds number increased. 0 20 40 60 80 100 120 0 20000 40000 60000 n u ss el n u m b er , n u reynolds number, re gneilnski current study (a) 0 20 40 60 80 100 120 140 160 0 5000 10000 15000 20000 25000 30000 n u ss el t n u m b er , n u reynolds number, re promvonge et al. current study i. hossen et al. /future energy february 2026| volume 05 | issue 01| pages 20-29 25 convective heat transfer was amplified as the intensity of turbulent flow increased with the reynolds number. the twisted and double-twisted tapes swirl generators have a considerable impact on the heat transfer rate for all reynolds numbers. this may produce secondary or swirl flow, which provides a longer channel for the fluid to flow through the tube. intense fluid and pressure gradient mixing might also have been formed in the radial direction. (a) (b) figure 6. (a) comparison of the reynolds number and nusselt number for 0.5% tio2, (b) comparison of the reynolds number and nusselt number for 1.5% tio2. the friction factor was computed using the darcyweisbach equation after collecting the pressure drop from the inlet to the outlet in the ansys fluent results. figure 7 shows the effects of double twisted tape inserts on friction factor characteristics. the friction factor of the tape-inserted tube steadily decreased as the reynolds number rose. it is shown that the friction factor increased by a vast amount at lower reynolds number values and by a relatively small amount at higher reynolds number values. this might be explained by the fact that at lower reynolds number values, which correspond to lower flow rates, air can travel over the tape and produce large frictional forces, as tiny vortices are present behind the tape. the friction coefficients of pvtc were 94.44% greater than those of the plain tube. when designing heat exchangers, the thermal performance factor (tpf) is very important. the tpf demonstrated the usefulness of using twisted tape in heat exchangers [29]. with an increase in reynolds number, the performance characteristics for all twisted tapes tended to decline. this suggested that the energy-saving devices for usage at lower reynolds numbers were the enhancement devices. figure 8 shows the thermal performance factor using double and single twisted tapes for 10000 to 55000 reynolds numbers. the maximum thermal performance factor was found at dtt2. the maximum value of tpf is 2.04 and 1.88 at 0.5% and 1.5% tio2 concentrations, respectively. (a) (b) figure 7. (a) comparison of the reynolds number and friction factor for 0.5% tio2, (b) comparison of the reynolds number and friction factor for 1.5% tio2 3.3 contour plots the velocity contour for the plain tube and stsc, pvtc, dtt-1, stpv, dtt-2 are shown in figure 9. the fluid velocity reaches the free stream velocity at the center of the pipe and becomes zero adjacent to the pipe wall. also, velocity increases at the tube's inlet region and decreases when the insert geometry restricts the passage. the temperature distribution contour for the plain tube and stsc, stpv, pvtc, dtt-1, and dtt-2 are shown in figure 9. for a plain tube, the temperature increases at the boundary layer adjacent to a solid surface. figure 10 illustrates the temperature range from high to low at the boundary surface fluid. after using the insert on a plain tube, the heat was distributed everywhere, enhancing the heat transfer. the pressure distribution contour for the plain tube and stsc, stpv, pvtc, dtt-1, and dtt-2 are shown in figure 11. at the inlet section, pressure was higher, but a pressure drop occurred at the outlet section due to frictional forces. after using conical rings, fluid flow creates more disturbance because more pressure drop occurs in the outlet section. figure 12 shows the turbulent kinetic energy for various sections of plain tubes and tubes equipped with inserts. the contour figure shows that tke is higher where the boundary is closest to the tube wall and also where the alternate axis dimpled twisted tape is located, indicating high shear stress. i. hossen et al. /future energy february 2026| volume 05 | issue 01| pages 20-29 26 (a) (b) figure 8. (a) comparison of the reynolds number and tpf for 0.5% tio2, (b) comparison of the reynolds number and tpf for 1.5% tio2 figure 9. (a) plain tube, (b) stsc, (c) pvtc, (d) dtt-1, (e) dtt-2, (f) stpv figure 10. (a) plain tube, (b) stsc, (c) stpv, (d) pvtc, (e) dtt-1, (f) dtt-2 i. hossen et al. /future energy february 2026| volume 05 | issue 01| pages 20-29 27 velocity increases in the tube's inlet region and decreases when the insert geometry restricts the passage. for a plain tube, the temperature increases at the boundary layer adjacent to a solid surface. after using the insert on a plain tube, the heat was distributed everywhere, enhancing the heat transfer. at the inlet section, pressure was higher, but a pressure drop occurred at the outlet section due to frictional forces. after using double-twisted tape inserts, fluid flow creates more disturbance because a greater pressure drop occurs in the outlet section. 4. conclusion in the present research, the heat transfer and friction factor characteristics of turbulent flow for stsc, stpv, pvtc, dtt-1, and dtt-2 at varying tio2 concentrations were investigated numerically. when compared to the plain tube, the dtt-2 significantly boosted the heat transmission rate. the following are the primary findings of this numerical study: • the double twisted tapes offered a higher heat transfer rate, friction factor, and thermal performance factor as compared to the plain tube. as the reynolds number increased, so did the nusselt number. the maximum heat transfer coefficient is increased from plain tube to 88.2% and 71.42% at dtt-2 in 0.5% and 1.5% tio₂ figure 11. (a) plain tube, (b) stsc, (c) dtt-1, (d) stpv, (e) dtt-2, (f) pvtc figure 12. (a) plain tube, (b) stsc, (c) stpv, (d) dtt-1, (e) pvtc, (f) dtt-2 i. hossen et al. /future energy february 2026| volume 05 | issue 01| pages 20-29 28 concentrations, respectively. also, the maximum nusselt number rose by 115.53% and 100.9% at dtt-2 compared to the plain tube in 0.5% and 1.5% tio2 concentrations, respectively. the nusselt number increased because the twisted tapes with insertion create vortices and turbulence in the fluid flow, which ensured better fluid mixing that increased the heat transfer rate. besides, twisted tapes create a larger effective surface area, which improves overall heat transfer performance. there were four different cases. the nusselt number was enhanced for double twisted tapes, perforated v-cut with and without conical ring, semicircular cut tape by 74.52%, 101.2%, 29.19%, 18.49% respectively for 1.5% of tio2 nanofluid and by 67.7231%, 97.32%, 26.2%, 18.23% respectively for 0.5% tio2 nanofluid. • the friction factor decreased with the increase of the reynolds number. the friction factor of a tube with a double twisted tape insert was higher than that of the plain tube. the maximum friction factor increased from that of a plain tube to 94.44% with a double twisted tape at a 1.5% tio2 nano-fluid concentration. the friction factor was increased for double twisted tapes, perforated v-cut with and without conical ring, semicircular cut tape by 75.4%, 94.44%, 55.32%, 33.3078%, respectively for 1.5% of tio2 nano fluid, and by 71.757%, 82.86%, 45.29%, 28.75% respectively for 0.5% tio2 nano fluid. • the thermal performance factor was also evaluated. the thermal performance factor decreased with increased reynolds number. the maximum thermal performance factor was found to be 2.04 at a reynolds number of 14000 for dtt-2 at a 0.5% concentration of tio2. for further investigation, the cuts on the twisted tape can be modified. also, the conical rings configuration can be changed as well. since in this study conical rings with v-cut have been used, the hexagonal ring with v-cut or rectangular cut can be utilized to analyze the heat transfer enhancement. besides, the pressure drop analysis can be done between the v-cut with conical ring configuration and the v/rectangular cut with hexagonal configuration. ethical issue the authors are aware of and comply with best practices in publication ethics, specifically concerning authorship (avoidance of guest authorship), dual submission, manipulation of figures, competing interests, and compliance with policies on research ethics. the authors adhere to publication requirements that the submitted work is original and has not been published elsewhere in any language. data availability statement the manuscript contains all the data. however, more data will be available upon request from the corresponding author. conflict of interest the authors declare no potential conflict of interest. references [1] shah rk, sekulib dr. handbook of heat transfer 3 heat exchangers. 1998;3:17.1-17.169. 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[21] hamid ka, azmi wh, mamat r et al. effect of temperature on heat transfer coefficient of titanium dioxide in ethylene glycol-based nanofluid. journal of mechanical engineering and sciences 2015;8:1367– 75. [22] mesh types in cfd: a comprehensive guide. https://www.ansys.com/products/fluids [23] v. gnielinski. new equations for heat and mass transfer in turbulent pipe and channel flow. international chemical engineering 1976. [24] nakhchi me, esfahani ja. performance intensification of turbulent flow through heat exchanger tube using double v-cut twisted tape inserts. chemical engineering and processing process intensification 2019;141:107533. [25] petukhov bs. heat transfer and friction in turbulent pipe flow with variable physical properties. adv heat transf 1970;6:503–64. [26] moria h. compound usage of twisted tape turbulator and air injection for heat transfer augmentation in a vertical straight tube with upward stream. case studies in thermal engineering 2021;25:100854. [27] bhuiya mmk, chowdhury msu, saha m et al. heat transfer and friction factor characteristics in turbulent flow through a tube fitted with perforated twisted tape inserts. international communications in heat and mass transfer 2013;46:49–57. [28] promvonge p, eiamsa-ard s. heat transfer behaviors in a tube with combined conical-ring and twistedtape insert. international communications in heat and mass transfer 2007;34:849–59. [29] kumar sahu m, kumar singh s. double-sided semicircular-wing tape inserts to enhance thermal performance of a double-pipe heat exchanger. international journal of recent research in civil and mechanical engineering (ijrrcme) 2020;7:1–8. this article is an open-access article distributed under the terms and conditions of the creative commons attribution (cc by) license (https://creativecommons.org/licenses/by/4.0/). https://creativecommons.org/licenses/by/4.0/ wb. noor & t. amin /future energy november 2024| volume 03 | issue 04| pages 01-17 1 review towards sustainable energy: a comprehensive review on hydrogen integration in renewable energy systems wahid bin noor, md. tanvir amin* department of mechanical engineering, chittagong university of engineering and technology, bangladesh a r t i c l e i n f o article history: received 23 april 2024 received in revised form 01 june 2024 accepted 13 june 2024 keywords: renewable energy, fossil fuels, hydrogen technology, electrolysis, hydrogen integration *corresponding author email address: u1903021@student.cuet.ac.bd doi: 10.55670/fpll.fuen.3.4.1 a b s t r a c t as the world shifts towards sustainable energy sources, incorporating hydrogen into renewable energy systems emerges as a critical pathway. this thorough analysis delves deeply into the various facets of hydrogen integration, exploring its potential to revolutionize the energy landscape. drawing upon recent advancements and research findings, the review examines the production, storage, and utilization of hydrogen within renewable energy frameworks. key topics include electrolysis methods, storage technologies, and diverse applications spanning transportation, residential sectors, and industry. furthermore, the review examines the obstacles and prospects linked with hydrogen integration, shedding light on policy frameworks, economic implications, and technological innovations driving its adoption. by offering insights into the multifaceted role of hydrogen, this review aims to inform researchers, stakeholders, and policymakers about the transformative potential of integrating green hydrogen into renewable energy systems for a sustainable future. 1. introduction the annual growth of primary energy demand is forecasted to be 1.3%, driven by factors such as economic expansion, technological advancements, and population growth, consequently leading to increased demand for energy services, which is projected until 2040 [1-3]. fossil fuels, encompassing coal, oil, and natural gas, have historically served as primary sources of energy generation and are projected to maintain their significant role in energy production until 2050 at least [4-6]. the utilization of fossil fuels results in the release of greenhouse gases, including volatile compounds, nitrogen oxides, and carbon dioxide, alongside solid particles, thereby playing a role in the alteration of the earth's climate [7, 8]. furthermore, carbonbased fuels currently fulfill 85% of the requirements of the world's energy [5,9]. in 2019, the yearly global energy-related co2 emissions amounted to 33.3 metric gigatons (gt), increasing at a rate that poses a significant threat to elevate the earth's temperature by multiple degrees unless mitigative measures are taken [10]. “green” hydrogen serves as an alternative to fossil fuels, which is generated via the process of water electrolysis, wherein an electric current splits water into oxygen and hydrogen. this procedure results in zero greenhouse gas emissions, contingent upon the electricity powering it is sourced entirely from renewables. the lightweight properties, high mass-energy density, and efficient electrochemical conversion of hydrogen facilitate its ability to transport energy across geographical regions through pipelines or in the guise of liquid fuels like ammonia transported via freight ships [11]. additionally, hydrogen can be produced locally, diminishing countries' reliance on external energy providers. moreover, hydrogen can be derived from a diverse array of substances, including oil, sewage sludge, water, gas, biofuels, and more [12]. in the current era, the application of renewable-energy-driven green hydrogen production stands out as a progressively favored method for mitigating greenhouse gas emissions (ghgs) and environmental contamination in the global shift aimed at carbon reduction [9, 13]. hydrogen (h2) presents an economical and sustainable alternative for both storage and energy consumption [14, 15]. moreover, it has the potential to actualize a carbon-neutral society and significantly increase the utilization of hydrogen [16]. hydrogen technologies have emerged as a strategy to fortify diverse economic sectors following the covid-19 outbreak. there is currently a notable consensus surrounding the potential of hydrogen, driven in future energy open access journal https://doi.org/10.55670/fpll.fuen.3.4.1 november 2024| volume 03 | issue 04 | pages 01-17 journal homepage: https://fupubco.com/fuen issn 2832-0328 mailto:u1903021@student.cuet.ac.bd https://doi.org/10.55670/fpll.fuen.3.4.1 https://fupubco.com/fuen wb. noor & t. amin /future energy november 2024| volume 03 | issue 04| pages 01-17 2 part by an increasingly ambitious climate policy agenda [17, 18]. moreover, hydrogen finds applications in fuel cell technology across various sectors, including industry, power generation, residential settings, and transportation, underscoring its potential for facilitating decarbonization [19-21]. many nations view hydrogen as the upcoming generation solution for energy supervision and are progressively endorsing the adoption of hydrogen technology to foster a low-carbon economy. consequently, numerous plans and strategies have been formulated for the development and implementation of hydrogen [22]. green hydrogen holds significant potential to contribute significantly to the energy transition by serving as a means to store renewable energies as chemical energy carriers over an extended period. moreover, current infrastructure like underground gas storage facilities and natural gas grids in germany can be repurposed, mitigating the need for additional investment costs [23]. green hydrogen demonstrates remarkable capability for transportation and storage within the natural gas grid with minimal loss. consequently, this green gas can be effectively provided to industrial sectors and households, offering flexibility for applications such as heating through heating systems powered by fuel cells or industrial operations like steel production. additionally, industries can utilize hydrogen for producing ammonia-based fertilizers, food processing, metal treatment, and various other purposes [24, 25]. in the past, review papers covering diverse focal points within the hydrogen energy systems domain have been published. thema et al. [26] conducted a review of energy-to-gas projects, which generate either renewable or hydrogen substitutes for natural gas. their study includes a forecast and analysis of the cost evolution concerning carbon dioxide methanation and electrolysis. abe et al. [27] conducted a comprehensive review exploring the potential of hydrogen serving as a primary energy transporter, with a specific emphasis on the storage capabilities utilizing metal hydrides. mazloomi et al. [28] outlined hydrogen as a highly encouraging option, serving not only as fuel for forthcoming vehicles but also as a pivotal energy preservation solution within expansive power systems. their study comprehensively examines production and storage methods while also addressing the risk and safety considerations inherent in hydrogen technologies. parra et al. [29] present a thorough technical-economic analysis of hydrogen-based energy systems. they outline strategies aimed at hastening the integration of hydrogen technologies, emphasizing key measures such as mass production, standardization, and the implementation of supportive policies. moradi et al. [30] conducted a review of alternatives concerning the storage and delivery of hydrogen alongside an analysis of associated risk and safety considerations. dutta [31] explored storage and production methodologies for hydrogen, with particular attention to risk and safety considerations. yue et al. [9] conducted an extensive survey on hydrogen technologies within power systems, leveraging real-world projects as exemplars to elucidate diverse technologies and applications. their techno-economic analysis integrated cost and technical considerations, emphasizing the imperative for ongoing focus on project scalability, technical advancements, political endorsement, and production expansion to attain cost competitiveness in hydrogen technologies. bailera et al. [32] conducted a review encompassing the diverse methodologies employed to transform renewable energy into methane within power-to-gas initiatives, complemented by a summary of practical projects. gahleitner [33] scrutinized pilot facilities for power-to-gas, focusing on instances where sustainable electricity was employed for hydrogen production via water electrolysis. hanley et al. [34] conducted a survey on the integration of hydrogen within energy frameworks, examining potential drivers and policies that could promote hydrogen as a preferred option above alternative lowemission energy technology. to the best of the author's understanding, scientific research has largely overlooked the environmental expenses associated with green hydrogen generation. thus, this paper, which delves into the environmental implications of green hydrogen production as a means of renewable energy storage, presents a novel contribution and addresses a growing sphere of focus [35]. the study encompasses alternative energy sources such as solar, wind, and hydro energy, which are predominant in europe, in addition to biomass [36]. 2. the generation of hydrogen from renewable energy resources the utilization of renewable energy sources for hydrogen production stands as a highly promising avenue within the domain of sustainable energy. ongoing endeavors in this field encompass a spectrum of technologies, notably encompassing the utilization of solar and wind power for water electrolysis [37], biomass-to-hydrogen processes including gasification and pyrolysis [38], and the deployment of solar energy-driven thermochemical reactions for water splitting [39]. the collaboration between renewable energy sources and hydrogen presents advantages like energy storage capabilities and the provision of on-demand energy supply [40]. electrolysis, employing various types of electrolyzers, emerges as a pivotal step in green hydrogen production from renewables, with the prospect of achieving notable efficiency levels through optimization with renewable energy systems [41]. on the whole, the integration of renewable energy sources into hydrogen production holds considerable promise for realizing a sustainable and clean energy future. in broad terms, compounds originating from biomass or water have the capacity to be employed for hydrogen production via the process of extraction from natural resources [42]. 2.1 utilization of biomass for hydrogen generation biomass emerges as a promising avenue for hydrogen production, outstripping fossil fuels owing to its abundant supply, facile oxidation, and substantial annual output [43]. diverse biomass sources, ranging from agricultural waste to microalgae, exemplify the vast array of plant and animal components convertible into biomass, constituting a renewable primary energy source [44]. thermochemical and biological mechanisms serve as the two primary methodologies for hydrogen production from biomass, detailed in subsequent sections. the technical and economic feasibility of hydrogen production from biomass and residual wastes is evident in numerous developed nations, underscoring a projected contribution of over 25% to global energy demands by 2050 [45]. in stark contrast to fossil fuels, wb. noor & t. amin /future energy november 2024| volume 03 | issue 04| pages 01-17 3 biomass-to-power processes mitigate the emissions of co2 and facilitate co2 absorption from the atmosphere, fostering a net-zero emissions scenario for greenhouse gases. figure 1 illustrates various pathways for hydrogen production from biomass, delineating gasification to yield syngas, pyrolysis for bio-oil generation, and cellulose hydrolysis for sugar monomer extraction [46]. syngas, resulting from gasification, can undergo a water gas shift (wgs) reaction for hydrogen conversion, albeit necessitating co removal from the gas stream. while pyrolysis-derived bio-oil can be transformed into liquid fuel, the conversion processes are intricate with limited efficiency. conversely, hydrogen production from biooil via autothermal reforming, particularly employing catalytic membrane reactors, boasts high conversion efficiency. additionally, hydrogen generation from sugars and sugar alcohols, such as sorbitol, through aqueous phase reforming (apr) stands as a viable method. although alternative biological pathways exist, encompassing enzymatic and bacterial routes, this article confines its discourse to heterogeneous catalytic approaches. table 1 outlines the fundamental technologies employed in both processes, detailing the biomass type utilized, operational parameters, and technological maturity levels. figure 1. diverse strategies for extracting hydrogen from biomass table 1. summary of techniques for hydrogen production from biomass methods principle source of energy operating conditions maturity pyrolysis thermochemical dried biomass 3001000°c in the absence of oxygen commercial hydrothermal liquefaction thermochemical wet biomass 250-370°c research and development gasification thermochemical dried biomass 800-900°c commercial 2.1.1 gasification biomass gasification stands as a versatile and sustainable method for clean energy generation, with various approaches, such as steam gasification, demonstrating efficacy in hydrogen production [47, 48]. particularly noteworthy is catalytic steam gasification utilizing calcium oxide (𝐶𝑎𝑂), which exhibits the capacity to yield high-purity hydrogen through simultaneous 𝐶𝑂2 absorption and catalytic action [49]. moreover, the utilization of waste biomass or agricultural residues presents dual benefits in renewable energy production and waste management [50]. gasification, occurring at temperatures surpassing 1000k, entails a complex interplay of pyrolysis, partial oxidation, and steamreforming reactions [51]. oxygen or air facilitates partial oxidation, yielding gaseous products, including 𝐻2 and 𝐶𝑂𝑥 , alongside bio-oils, tar, and charcoal [51]. optimization of parameters such as temperature and residence time minimizes tar formation, with thermal cracking and the introduction of catalytic additives further augmenting efficiency [51, 52]. advanced technologies like hypr-ring integrate gasification with the water-gas shift reaction, aimed at enhancing hydrogen yield while curbing pollutants [53]. a diverse range of organic materials can undergo gasification using various agents, like oxygen, air, carbon dioxide, or steam, each imparting distinct effects on gas composition. despite its heightened energy cost, steam gasification produces a gas with superior heating value and higher hydrogen content in comparison to air gasification. furthermore, the presence of 𝐶𝑂2 in the synthesis, gas holds promise for specific process applications [54]. in summary, biomass gasification represents a pivotal pathway for sustainable clean energy production, with ongoing advancements in technology and process refinement aimed at optimizing efficiency and minimizing environmental impact. 2.1.2 pyrolysis biomass pyrolysis emerges as a promising avenue for hydrogen production, particularly when accompanied by innovative methodologies. notably, investigations reveal that the fast pyrolysis of algae pellets in molten 𝑁𝑎𝑂𝐻-𝑁𝑎2𝐶𝑂3 at elevated temperatures can yield stable hydrogen, boasting a notable theoretical efficiency of 84.86% [55]. furthermore, the integration of advanced artificial intelligence models, combining support vector machines and artificial bee colony optimizers, enhances our understanding of the generation of hydrogen gas from biomass composition and pyrolysis processes [56]. these advancements underscore the pivotal role of thermochemical processes such as pyrolysis and biomass gasification in deriving hydrogen from renewable biomass, emphasizing the necessity for enhanced selectivity and efficiency to realize economically viable industrial applications [47]. the efficacy of pyrolysis is contingent upon a multitude of parameters, incorporating heating rate, pressure, residence time, biomass type, and moisture content. notably, the absence of air or oxygen during pyrolysis eliminates the risk of dioxin production and mitigates emissions. additionally, the exclusion of air or water obviates the requirement for secondary reactors to produce carbon dioxide (co2) or carbon monoxide (co), further contributing to emission reduction. pyrolysis presents numerous benefits, incorporating fuel flexibility, reduced cox emissions, and operational simplicity, compactness, and a clean carbon byproduct. nevertheless, the existence of air or water can result in significant cox emissions. pyrolysis operations can be conducted at high (>800°c), moderate (500-800°c), or low (500°c) temperatures, with fast pyrolysis (fp) serving as a method to convert organic matter into products with wb. noor & t. amin /future energy november 2024| volume 03 | issue 04| pages 01-17 4 increased energy content, albeit with challenges such as potential fouling from carbon buildup [57]. 2.1.3 hydrothermal liquefaction hydrothermal liquefaction (htl) is emerging as a promising method for harnessing hydrogen from biomass. htl processes involve the conversion of wet biomass into biocrude oils and valuable biochemicals under high temperature and pressure conditions, utilizing water or water-alcohol blends, often with the incorporation of catalysts [58]. studies have demonstrated that the use of catalysts such as ni/al2o3 and fe can significantly enhance bio-crude yields, with optimal performance achieved at 330°c and a reaction duration of 10 minutes, leading to improved higher heating values for the biomass [59]. additionally, research has explored hydrogen production from household mixed waste through htl and hydrothermal gasification (htg). htg exhibits a maximum hydrogen yield of 39 wt%, while htl yields a bio-oil output of 33 wt% with notable heating values [60]. 2.2 water electrolysis in contemporary industrial contexts, primary methodologies for hydrogen production include coal gasification, steam reforming, and water electrolysis. although alternative approaches such as ethanol and sugar reforming, photocatalytic water splitting, water biophotolysis, and high-temperature water splitting are currently undergoing development, they have yet to achieve widespread industrial deployment. presently, there is a growing fascination with hydrogen production via water electrolysis, attributable to the declining costs associated with renewable electricity. this method entails utilizing electricity to separate hydrogen from water, thereby circumventing the generation of carbon byproducts such as co2 [9]. within the configuration of a water electrolysis cell, two electrodes are immersed in an electrolyte solution and linked to a power source to enable the flow of electrical current, as demonstrated in figure 2. upon application of a sufficiently elevated voltage between the electrodes, water undergoes decomposition, yielding hydrogen at the cathode and oxygen at the anode. the introduction of the electrolyte serves to augment the conductivity of the water medium, thus enabling uninterrupted electrical flow. commonly employed electrolytes in water electrolysis encompass acids and solid polymer materials, which utilize a variety of ions, including 𝐻+, 𝑂𝐻−, 𝑂2 −, and others, as charge carriers [9]. during water electrolysis, water acts as the input reactant and undergoes dissociation into hydrogen and oxygen due to the application of direct current. anode: 𝐻2𝑂 → 1 2 𝑂2 + 2𝐻+ + 2𝑒− (1) cathode: 2𝐻+ + 2𝑒− → 𝐻2 (2) overall: 𝐻2𝑂 → 𝐻2 + 1 2 𝑂2 (3) an array of electrolyte systems has been devised for water electrolysis, encompassing alkaline water electrolysis (awe), solid oxide water electrolysis (soe), alkaline anion exchange membranes (aems), and proton exchange membranes (pems). these systems are distinguished by their employment of diverse materials and operational parameters while adhering to shared foundational operating principles. furthermore, depending on the temperature regimes applied, both high and low-temperature water electrolysis configurations are viable [61]. figure 2. water electrolysis principle 2.2.1 pv-electrolysis system this system comprises photovoltaic cells, which generate electricity to operate an electrolysis unit, as depicted in figure 3. water electrolysis, an electrochemical reaction delineated in figure 4, facilitates the disintegration of water molecules (h2 o) into oxygen (o2) and hydrogen (h2) gases [62]. the o2 and h2 ions migrate to the anode and cathode, respectively, within the water medium. the resultant hydrogen boasts numerous merits, including its utility in welding applications and fuel cells, particularly when blended with o2 to produce oxyhydrogen gas. this approach yields a substantial volume of high-purity hydrogen with minimal ecological ramifications, leveraging solar energy as its power source. figure 3. diagram illustrating the pv-electrolysis apparatus [63] wb. noor & t. amin /future energy november 2024| volume 03 | issue 04| pages 01-17 5 figure 4. electrolysis of water [63] 2.2.2 hybrid photovoltaic/thermal (pv/t)-electrolysis system a hybrid pv/t-electrolysis system represents a sophisticated integration of photovoltaic (pv) and thermal technologies to concurrently produce electricity and heat, thereby offering a sustainable solution for hydrogen production [64]. this sophisticated system harnesses solar energy through both electricity generation and thermal absorption, driving an electrolyzer via water electrolysis and presenting a renewable substitute for conventional hydrogen production methods. consisting of photovoltaic panels and a proton exchange membrane (pem) electrolysis unit, its components include a pv-thermal array, a dc/dc converter, and the electrolysis unit, as delineated in figure 5. 2.2.3 wind-electrolysis system a wind-electrolysis system is engineered to utilize wind energy for hydrogen production via electrolysis. this innovative setup incorporates wind turbines to capture kinetic energy from the wind and transform it into electricity. figure 5. a schematic representation of the envisaged system [63] this electricity then powers an electrolyzer, facilitating the separation of hydrogen and oxygen from water. by harnessing wind power, this system presents a sustainable and renewable approach to hydrogen production, thereby contributing significantly to the transition towards cleaner energy sources and reducing dependency on fossil fuels. the components of a wind-electrolysis device typically include a wind turbine generator, a water electrolyzer, and a converter (ac/dc) [65]. this system can be deployed in various configurations tailored to different operational scenarios: firstly, the direct wind-electrolysis configuration is suitable for remote regions equipped with wind farms [66]. secondly, the hybrid wind/grid-electrolysis setup enables the grid to provide supplementary energy during periods of low wind activity. thirdly, surplus wind energy can be supplied back to the grid while hydrogen is concurrently produced. lastly, in the fourth scenario, excess hydrogen can be stored for future utilization, facilitating electricity generation through a fuel cell [67]. figure 6 illustrates the distinct elements comprising the wind-electrolysis system. 2.2.4 thermolysis system the thermolysis system utilizes solar energy to drive the disintegration of water into hydrogen and oxygen gases by concentrating solar radiation onto a reactor containing water, achieving elevated temperatures conducive to the endothermic water-splitting reaction. this approach presents potential advantages over conventional electrolysis, including enhanced efficiency and reduced costs, particularly when integrated with high-temperature electrolysis. nevertheless, significant challenges persist in scaling up and optimizing this technology for large-scale hydrogen production. ongoing research endeavors are dedicated to surmounting these hurdles and fully realizing the potential of thermolysis for sustainable hydrogen production. wb. noor & t. amin /future energy november 2024| volume 03 | issue 04| pages 01-17 6 figure 6. the fundamental concept of the wind-electrolysis system entails harnessing wind energy to drive the process of electrolysis for hydrogen generation [63] furthermore, the amalgamation of solar thermal dissociation with high-temperature electrolysis has demonstrated a lower production cost compared to pv-electrolysis, as evidenced in reference [68]. through the strategic utilization of concentrators, thermal energy is generated to heat water or fossil fuels within the thermolysis system, thus presenting a promising avenue for hydrogen production. additionally, the high-temperature decomposition of natural gas emerges as a particularly promising method for producing hydrogen. 2.2.5 thermochemical system the thermochemical system employs both heat and chemical reactions to initiate the disintegration of water into hydrogen and oxygen. this intricate process involves the recycling of chemicals through successive thermochemical cycles. three critical prerequisites for its success include the availability of a high-heat source, the use of materials resilient to such extreme temperatures, and the application of sophisticated chemical methodologies for the effective separation of hydrogen and oxygen [69]. this thermochemical process entails the breakdown of water into its constituent elements through the synergistic application of heat sources and chemical reactions. figure 7. depiction of an electrochemical cell [63] these reactions rely on chemicals that undergo recycling within a series of thermochemical cycles. the successful execution of this method hinges upon meeting three fundamental conditions: the provision of a high-heat source, the utilization of materials capable of enduring these elevated temperatures, and the implementation of intricate chemical techniques to facilitate the separation of hydrogen and oxygen. 2.2.6 steam electrolysis steam electrolysis is a process utilized for hydrogen production by passing steam through an electrolyzer. within the electrolyzer, electrical energy is applied to split water molecules (h2o) into oxygen gas (o2) and hydrogen gas (h2). this method is regarded as environmentally benign as it emits no greenhouse gases when powered by renewable energy sources. its utility lies in its ability to utilize water as a readily available resource, albeit it demands substantial energy input. ongoing research endeavors aim to enhance its efficiency and cost-effectiveness. the cornerstone of hightemperature steam electrolysis (htse) is the electrochemical cell, typically composed of ceramics due to the elevated operating temperature [70]. this cell, referred to as the solid oxide electrolysis cell (soec), comprises three ceramic layers: a dense electrolyte and two porous electrodes (a cathode for h2 and an anode for o2), as depicted in figure 7. table 2 presents a comparative analysis of different methods, outlining their respective benefits, drawbacks, and associated references. 3. hydrogen's role in storing energy within renewable systems according to forecasts by the iea, approximately onethird of the world's electricity generation is projected to come from intermittent renewable sources such as wind and solar by 2040 [86]. to meet this demand, long-term solutions for large-scale electricity storage are necessary. hydrogen storage and production emerge as prospective technology, as depicted in figure 8 [87]. wb. noor & t. amin /future energy november 2024| volume 03 | issue 04| pages 01-17 7 the extensive utilization of hydrogen as a sustainable and clean energy source, applicable to various sectors, including energy storage and transportation, hinges on advancements in storage technologies. therefore, the immediate development of improved storage methods with the potential for higher energy density is imperative. in contemporary times, hydrogen is stored for onboard applications using high-pressure tanks for compressed gas, in cryogenic liquid form (below the critical temperature of 33 k), or in solid-state compounds like complex hydrides, metal hydrides, or porous materials. figure 9 illustrates the practical methods for hydrogen storage, which are categorized into four main types: hydrogen liquefaction, physical adsorption, chemical absorption, and pressurized gas storage. hydrogen gas possesses remarkable energy value per unit mass due to its high molar combustion heat and low molecular weight [88]. currently, the most common method for hydrogen storage is compressed gas. commercial hydrogen storage tanks, such as those utilized in toyota's mirai fuel cell car, can accommodate hydrogen gas at pressures reaching 700 bar [90]. typically, the compression process consumes roughly 20% of the energy held within the hydrogen [91]. utilizing compressed hydrogen storage offers advantages in terms of technical simplicity and relatively low cost. downsides involve relatively lower system energy density compared to fossil fuel-based systems, alongside safety considerations due to high pressure [92]. hydrogen can alternatively be stored in liquid form, significantly boosting its volumetric energy density compared to storage as a compressed gas. liquid hydrogen exhibits an energy density of 2.2 kwh/l, while compressed hydrogen gas provides 1.3 kwh/l at 700 bar and 0.8 kwh/l at 350 bar [93]. the drawbacks of liquid hydrogen encompass the significant energy consumption during the liquefaction process, hydrogen boil-off, and the considerable expense of storage systems. due to the boil-off issue, liquid hydrogen is primarily suited for applications where rapid consumption is anticipated, such as transport scenarios with frequent refilling options. consequently, it is not regarded as a feasible option for long-term energy storage in stationary power systems [92]. table 2. a comparison of various methods for producing hydrogen utilizing wind and solar energy h2 production methods advantages disadvantages ref. wind-electrolysis system • suitable in remote areas • wind intermittency • low electricity production cost • technically mature and has already been commercialized • power fluctuation varies according to wind speed [66], [67], [71], [72], [73], [74], [75], [76] steam electrolysis • less energy is needed to separate steam compared to liquid water. • the lifespan of the hydrogen electrode is constrained by degradation. [77] pv-electrolysis system • quick response time and rapid startup. • elevated levels of hydrogen purity. • reduced cost of electricity production. • delayed loading response. • decreased current density. [62], [71] hybrid pv/t-electrolysis system • readily adjustable to achieve the desired rate of hydrogen production or to correspond with the output of pv energy. • the feedwater undergoes preheating. • it generates highly pure hydrogen while simultaneously demanding significantly lower maintenance. • distilled or deionized water is required instead of tap water. [7882] thermolysis system • optimal efficiency. • cost-effective. • necessitates elevated temperatures. • inapplicable for practical use because of the elevated temperature requirement. • challenging to timely separate hydrogen and oxygen. [68], [83], [84] thermochemical system • significant potential for theoretical efficiency. • minimal or absent greenhouse gas emissions. • sophisticated chemical techniques are employed for the separation of h2 and o2. • produces a substantial amount of waste. [69], [77], [85] wb. noor & t. amin /future energy november 2024| volume 03 | issue 04| pages 01-17 8 figure 9. processes and phenomena of different hydrogen storage systems [89] solid-state storage emerges as a secure, promising, and efficient method for hydrogen storage. this approach involves storing hydrogen within a material, either in atomic form or as h2 molecules, through two established processes: physisorption and chemisorption [94]. physisorption presents an additional approach to hydrogen storage. in this method, hydrogen gas molecules adhere to the surface of a solid material through adsorption and are subsequently released as gas when required, such as in fuel cell applications. the prevalent materials utilized for hydrogen gas adsorption include metal-organic frameworks and carbon-based materials [91]. hydrogen storage through physisorption offers advantages such as simplified system design, low-pressure requirements, and the use of relatively inexpensive materials. challenges include the relatively low hydrogen density achieved on carbon and the requirement for low temperatures [95]. another method for hydrogen storage is chemisorption in metal hydrides, where hydrogen gas is absorbed and retained within a metal powder, which can be either a metal alloy or a pure metal. heat is generated during the absorption of hydrogen gas into the metal hydride material, and conversely, applying heat is essential to facilitate the release of hydrogen from the metal hydride. a limitation of the metal hydride storage method, observed with certain materials, is the strong bonding between hydrogen and the metal hydride, requiring relatively high temperatures for hydrogen release. for instance, temperatures exceeding 650°c are necessary for lithium. yet, one advantage is that certain materials boast remarkably high gravimetric hydrogen capacities, reaching up to 18 wt% for libh4 [91]. hydrogen stands at the forefront of renewable energy storage solutions, offering a versatile and scalable option to address the intermittent of renewable sources. its potential for long-term storage, coupled with its versatility in various applications, makes it a compelling choice for integration into renewable energy systems. 4. hydrogen's role in future energy generation and applications both developed and developing nations increasingly acknowledge the significance of hydrogen energy as an energy carrier for achieving sustainable growth on a global scale [96]. despite its remarkable power generation capacities, hydrogen is predominantly utilized in sectors beyond power generation. a considerable portion of commercially generated hydrogen finds application in diverse sectors such as oil refining, recycling, metalworking, chemical processing, and fertilizer production, as shown in figure 10. figure 8. analyzing storage capacity and discharge time across diverse energy storage solutions [87] wb. noor & t. amin /future energy november 2024| volume 03 | issue 04| pages 01-17 9 figure 10. present and prospective industrial uses of hydrogen while hydrogen products currently serve as foundational resources within the industrial sector, their potential as a comprehensive energy carrier remains largely untapped. of the approximately 50 million metric tons produced annually worldwide, the primary application is as a feedstock for ammonia production, with oil refining accounting for 35% of its usage [34]. fuel cells and hydrogen are widely regarded as pivotal technologies for a sustainable future energy source. projections suggest that increasing renewable energy shares to 36% by 2025 and 69% by 2050 could result in hydrogen shares rising to 11% by 2025 and 34% by 2050, contributing significantly to meeting total energy demand [97]. hydrogen holds the potential to generate electricity, produce synthetic fuels, and perform mechanical work [98]. fuel cells possess the capability to convert hydrogen into electrical energy, facilitating its transfer and storage for subsequent use [99]. one of the main reasons for considering hydrogen is its ability to complement electricity in energy transport. currently, a prominent application of hydrogen occurs within the transportation sector. while electric vehicle users often express concerns about limited range and long recharge times, these worries are alleviated by hydrogen-powered fuel cell electric vehicles, which offer significantly faster refueling times, minimal behavioral adjustments, and extended range compared to electric vehicles [100]. hydrogen shows promising potential for utilization in spark ignition engines [101]. internal combustion engines (ices) utilize the energy from a fuel, like hydrogen, to generate mechanical power, which in turn drives a shaft. in power generation, a generator is coupled to convert this mechanical energy into electrical power. hydrogen-fueled ices emit fewer pollutants, mainly nitrous oxides, compared to traditional ices. moreover, they exhibit up to 25% higher fuel efficiency than standard gasoline engines, with conventional car fuels typically achieving efficiencies of only 20-25%, while hydrogen ices can reach rates of 30-40% [102]. hydrogen is regarded as a promising energy source with the potential to mitigate co2 emissions. figure 11 illustrates a comparison between fossil fuels and hydrogen technologies. it is estimated that employing hydrogen derived from conventional methods can reduce carbon emissions by nearly 20% when utilized in fuel cells. thus, the production of hydrogen using rs could substantially mitigate carbon emissions [103]. the research conducted by the hydrogen council indicates that demand and supply for hydrogen (h2) could potentially reach 10 exajoules annually by 2050, with further anticipated growth of approximately 5%–10% per year beyond 2050. therefore, it can be asserted that hydrogen is poised to emerge as a formidable contender in the future global energy landscape [104]. 5. challenges and perspectives the cost dynamics associated with hydrogen production are contingent upon numerous factors, with the primary determinant being the expense linked to the electricity wb. noor & t. amin /future energy november 2024| volume 03 | issue 04| pages 01-17 10 required for electrolysis. additional considerations include investments in diverse equipment for establishing sustainable energy sources, land procurement expenses, and the anticipated lifespan of the infrastructure. these financial commitments can be categorized into two main areas: production and logistical costs. furthermore, local regulatory frameworks and financial variables such as capital outlays play a significant role in determining the final delivery cost. throughout the production process, the pricing mechanisms governing renewable energy and fossil fuels, like coal and natural gas, significantly influence variable costs, thereby shaping the comparative competitiveness of each technology. figure 11. the influence of combustion and hydrogen production on carbon emissions [103] the data illustrated in figure 12 indicates that renewable electricity, both on average and in the best-case scenario, may present competitive supply costs when compared to fossil fuels with carbon capture and storage (ccs). this suggests that under specific circumstances, renewables could potentially emerge as one of the most economically feasible options for producing hydrogen, even in the current landscape. in this optimal scenario, a low-cost electrolyzer priced at usd 200/kw is considered, a milestone expected to be widely achievable by 2040, although some chinese manufacturers claim its present feasibility. furthermore, there are instances of low-cost renewable power, exemplified by wind projects in countries like brazil and saudi arabia, where electricity costs are as low as usd 23/mwh [105]. electricity, the primary output of renewable energy sources, is important for powering electrolysis units in hydrogen generation. consequently, electricity price plays a significant role in determining the overall expense of hydrogen production. this cost is contingent upon various factors, including the installation of renewable energy infrastructure, geographical considerations, land costs, and the design and scale of renewable energy systems. figure 13, which outlines the cost ranges associated with hydrogen production utilizing different renewable energy sources [106, 107], illustrates pertinent insights. it reveals that conventional energy sources like nuclear and coal generally offer lower production costs compared to renewables. however, their environmental impact, characterized by greenhouse gas emissions, poses notable concerns. figure 12. the expenses associated with generating hydrogen from renewable sources and fossil fuels are currently being examined [105] wb. noor & t. amin /future energy november 2024| volume 03 | issue 04| pages 01-17 11 in contrast, despite the relatively higher costs associated with hydrogen production from green energy sources, there exists a prevailing global preference for their adoption due to their emission-free attributes. efforts are actively underway to mitigate the costs associated with renewable energy sources. as delineated in figure 13, renewable energy systems for hydrogen production typically entail higher expenses compared to conventional energy sources. achieving optimal, reliable, cost-effective, environmentally sustainable, and efficient hydrogen generation presents a multifaceted challenge, as no single technique can satisfy all these objectives simultaneously. hence, additional investigation is warranted to address the remaining complexities outlined as follows [108]. given that hydrogen is not naturally occurring and must be synthesized, there is a pressing need to innovate manufacturing methods that consume less energy and facilitate large-scale production. moreover, prioritizing water as a feedstock is advantageous due to its potential to mitigate environmental impact by eliminating co2 emissions. as hydrogen exists in a gaseous state at room temperature, it possesses a notably low volumetric density, necessitating a volume exceeding 3000 times that of typical liquid fuels to produce equivalent energy. thus, it is pertinent to decrease the volume of hydrogen to streamline its storage and transportation processes. due to hydrogen's increased flammability relative to other fuels, safety becomes a significant concern. additionally, as an asphyxiant gas, it can result in suffocation by depleting oxygen levels in the atmosphere. consequently, meticulous attention to various safety and security protocols is essential when handling or storing hydrogen. once hydrogen is prepared for utilization, it should be employed with utmost efficiency to generate heat or power. due to its production process rather than natural occurrence, hydrogen commands a cost threefold higher than fossil fuels. moreover, storage considerations may exacerbate expenses, particularly with the utilization of high-pressure technologies. a projection of production costs for renewable hydrogen can be extrapolated and juxtaposed against fossil fuel alternatives integrating carbon capture and storage (ccs). a portion of co₂ remains unsequestered in ccs facilities, prompting consideration of carbon pricing, as delineated in figure 14. forecasts indicate that hydrogen production from low-cost solar and wind photovoltaic (pv) projects is poised to attain competitiveness with fossil fuels within the upcoming five years, particularly in comparison to steam methane reforming (smr) from natural gas with ccs, assuming a natural gas price of usd 8 per million british thermal units (btus). in the case of low-cost pv projects, this equilibrium is anticipated within eight years. subsequently, from 2030 to 2040, renewable hydrogen costs are projected to fall below those of fossil fuels with ccs across all scenarios. figure 13. the expense of generating hydrogen fluctuates depending on the energy source used [63] wb. noor & t. amin /future energy november 2024| volume 03 | issue 04| pages 01-17 12 6. conclusion the transition to utilizing renewable energy sources, like wind and solar, for hydrogen production is a pivotal step toward achieving sustainable energy objectives. cutting-edge technologies, including water electrolysis and biomass conversion, offer efficient pathways to produce environmentally friendly hydrogen. emphasizing the potential for energy storage and reliable supply underscores the strategic importance of this approach. future initiatives are focused on optimizing electrolysis systems and enhancing biomass conversion techniques to accelerate the transition to a cleaner energy landscape. in tandem with renewable energy production, hydrogen offers diverse storage options, ranging from compressed gas to liquid and solid-state storage. each method presents unique advantages and challenges related to energy usage and safety. ongoing efforts are directed toward enhancing storage technologies to minimize energy consumption and ensure broader acceptance. the versatility and scalability of hydrogen position it as a promising candidate for integrating renewable energy solutions, thus fostering sustainability across various sectors. recognized as a cornerstone of sustainable global development, hydrogen is increasingly valued for its multifaceted applications. projections indicate a substantial rise in its role in meeting energy demands by 2050, particularly as renewable energy adoption accelerates. its versatility extends to electricity generation, synthetic fuel production, and beyond, with fuel cell electric vehicles offering enhanced efficiency and range. additionally, hydrogen holds promise in reducing co2 emissions, particularly when derived from renewable sources. to fully capitalize on its potential, ongoing efforts are essential to advance production, storage, and utilization technologies, ensuring maximum efficiency and sustainability. despite the complexities associated with hydrogen production costs, renewable energy sources offer promising avenues for achieving competitive pricing. addressing challenges such as innovative manufacturing, storage optimization, and safety protocols is paramount for cost-effective and efficient hydrogen generation. future endeavors should prioritize research into enhancing electrolysis efficiency, storage, and transportation alongside advancements in renewable energy technologies. these collective efforts will facilitate the widespread adoption of hydrogen as a renewable energy solution, thus contributing to a greener and more resilient energy landscape. ethical issue the authors are aware of and comply with best practices in publication ethics, specifically concerning authorship (avoidance of guest authorship), dual submission, manipulation of figures, competing interests, and compliance with policies on research ethics. 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[109] d. gielen, e. taibi, and r. miranda, hydrogen: a renewable energy perspective. 2019. this article is an open-access article distributed under the terms and conditions of the creative commons attribution (cc by) license (https://creativecommons.org/licenses/by/4.0/). https://creativecommons.org/licenses/by/4.0/ a. fathi et al. /future energy november 2025| volume 04 | issue 04| pages 01-08 1 article toward a 100% renewable energy future in iceland: scenario analysis of geothermal, biofuel, and electric vehicle integration armita fathi, ahmadreza abedkhani, hossein yoosefi*, mahmood abdoos, helia salaripoor school of energy engineering and sustainable resources, college of interdisciplinary science and technology, university of tehran, tehran, iran a r t i c l e i n f o article history: received 10 june 2025 received in revised form 21 july 2025 accepted 01 august 2025 keywords: renewable energy, energy transition, carbon emissions reduction *corresponding author email address: hosseinyousefi@ut.ac.ir doi: 10.55670/fpll.fuen.4.4.1 a b s t r a c t this study investigates the transition paths towards a 100% renewable energy system in iceland through scenario analysis and simulation using the energy plan software. because of its unique geographical location and abundant geothermal resources, iceland is a case study for renewable energy. in the present research, three primary scenarios are considered. the ev scenario is the substitution of fossil-fuel vehicles with evs, which would imply that the proportion of renewable energy rises to 91.2% and co₂ emission falls from 1.98 million tons in 2022 to 1.27 million tons by 2035. the hybrid scenario, beyond the expansion of evs, also includes the use of biofuels in industrial and maritime sectors, leading to an increase in the share of renewable energy to 96.6% and reducing co₂ emissions down to 0.49 million tons. in contrast, the business as usual (bau) scenario keeps the current system without structural changes, resulting in only a marginal increase in renewable energy share and an escalation of co₂ emissions to 2.58 million tons. alongside technical and environmental analysis, this study assesses the economic, social, and political aspects of the transition to a sustainable energy system. it highlights the importance of supportive policies, stronger regulations, and greater public awareness as key factors for success. overall, the comprehensive insights provided by this research offer valuable guidance for policymakers and stakeholders aiming to reduce reliance on fossil fuels and enhance iceland’s environmental performance. 1. introduction the urgent global shift from fossil fuels to renewable energy has intensified research into sustainable solutions, and iceland, with its vast, easily accessible geothermal resources, stands out as an ideal candidate for a 100% renewable energy system. although substantial fossil fuel reserves continue to exist and new discoveries further expand these resources, the current trajectory of fossil fuel consumption is incompatible with the stringent emission limits set by the paris agreement. therefore, it is imperative for countries to shift their focus towards harnessing domestic renewable energy potential in order to meet climate targets and ensure long-term environmental sustainability [1-4]. reliance on fossil fuels increases system vulnerability, underscoring the need to minimize this dependency. although global studies highlight various regional challenges, our focus remains on iceland’s unique energy landscape. prior research has modeled individual renewable scenarios using energy planning software, yet few have integrated the interdependencies among various energy sectors. the united nations predicts rising global temperatures, which, coupled with persistent fossil fuel dependency, may jeopardize energy security worldwide. for instance, portugal, one of the european union countries with significant energy dependency, could face national or international crises in the future [5-8]. thanks to iceland’s strategic position in europe and its close integration within the european economic area, the nation’s renewable energy strategy has increasingly come under the influence of continental policy frameworks. in particular, the european green deal stands out as a comprehensive strategic initiative designed to curtail greenhouse gas emissions, bolster sustainable technologies, and foster the development of a green economy within the european union. by incentivizing green investments and promoting clean technology advancement, this initiative is driving a fundamental transformation in the continent’s environmental and economic policies, thereby creating a strategic context that reinforces iceland’s efforts. aligning future energy open access journal https://doi.org/10.55670/fpll.fuen.4.4.1 november 2025| volume 04 | issue 04 | pages 01-08 journal homepage: https://fupubco.com/fuen issn 2832-0328 mailto:hosseinyousefi@ut.ac.ir https://doi.org/10.55670/fpll.fuen.4.4.1 https://fupubco.com/fuen a. fathi et al. /future energy november 2025| volume 04 | issue 04| pages 01-08 2 with these ambitious targets not only enhances iceland’s energy security and environmental sustainability but also establishes it as a benchmark for best practices across the region [9-11]. a study conducted by elizabeth paloma and colleagues examined the potential of geothermal energy (temperature-based) to supply 85% of the industrial activities in spain. they found that spain's industry has the potential to utilize at least 1.13% of geothermal energy, indicating the country's economic potential in harnessing this resource [12, 13]. lebbihiat et al. [14] explored the potential of geothermal energy in algeria, citing its relatively abundant low-enthalpy resources. they suggested that algeria could partially meet its energy needs using this source, positioning the country as a pioneer in direct geothermal energy utilization in africa, with a total installed heat capacity of 54.64 megawatts. manish ram et al. [15], in a study utilizing the lut energy system transition model, investigated the technical and economic potential for achieving 100% renewable energy in delhi. this included heating, desalination, electricity, and transportation sectors in india. their findings indicate that delhi could benefit from reducing primary energy consumption by over 40%, lowering energy costs by over 25%, decreasing greenhouse gas emissions, air pollution, and health impacts, thus facilitating regional energy transfer. connolly conducted a technical and economic study on achieving 100% renewable energy for the european union. they utilized the energy plan software to optimize the technical performance of a system and provide multiple scenario options. their findings. revealed that the european smart energy scenario outperforms conventional energy scenarios by 10 to 15% in key economic and technical performance indicators. this advantage arises from reallocating investments from fuel imports to domestic job creation, which, in this context, would result in the generation of an additional 10 million direct jobs [16]. parrado-hernando et al. [17], in a study for bulgaria on achieving 100% renewable energy, utilized the energy plan and modass tools. they identified a flexibility gap between two selected methods and proposed a new approach that is more beneficial for variable renewable energies in energy transition scenarios. although bulgaria's potential is limited by its three main industries, introducing hydrogen-based fuel results in a decrease in the system's energy return on investment (eroi, which measures the ratio of usable energy produced to the energy invested in production) while simultaneously increasing the share of renewable energies [18]. meschede et al. [19] highlighted the renewable energy potential of islands, where over 740 million people reside. their results indicated that islands have significant potential to use solar pv and wind as primary technologies to reach a 100% renewable energy source (res) system. dominković and colleagues described the transition process to a 100% renewable energy system for southeast europe by 2050. they emphasized that no single source should have more than a 30% share to enhance supply security. economically, this transition would be beneficial, with primary energy supply expected to be nearly 51% lower than the baseline year [20]. reyseliani et al. [21] assessed indonesia's power system transition path using the veda-times method to achieve 100% renewable energy. they evaluated and optimized the cost-minimizing path and considered reliability using a monte carlo-based approach. daneshvardehnavi et al. [22] embarked on a challenging inquiry into renewable energy systems, focusing on a city in west texas with a peak load of 100 megawatts. they estimated the associated costs using two methods—real-time temporal data and load data—to attain an optimal model. additionally, they utilized monte carlo simulations to enhance their analysis, comparing results to converge on an optimal blend and factoring in cost calculations to achieve a renewable energy system, considering reliability through a monte carlo-based analysis. akuru et al. [23] raised a challenging question regarding the reliability and cost-effectiveness of res systems in nigeria. they initiated a study to outline the country's starting point toward reaching a 100% renewable energy system. al katsaprakakis et al. [24] examined the prospects of a 100% renewable energy system for the faroe islands. they defined systems and numerically simulated their performance to optimize dimensions. their findings suggested that achieving an annual penetration of over 90% res is entirely feasible both technically and economically, demonstrating the strong potential for a widespread renewable energy transition. reycosta et al. [25], in their study for australia, asserted the costeffectiveness of renewable energies due to declining costs. they provided the most extensive geographical analysis and longest-term time series of solar pv and wind in the australian electricity market. they identified areas better suited for industrial and commercial expansion through surplus renewable energy generation. additionally, it was estimated that energy storage systems, designed to operate for durations ranging from 1 to 8 hours, could result in cost savings equivalent to nearly twice the annual energy demand—approximately 167 billion dollars—if battery storage is utilized, and up to four times that amount if nonbattery storage solutions are implemented. daniel icaza alvarz et al. [26] proposed a zero-carbon energy system with 100% renewable energy for the galapagos islands, ecuador, as the second-largest marine reserve in the world, designated a unesco world heritage site in 1978, with the project aiming for 2050. michael child et al. [27], by delineating two transition paths using the lut energy system transition model, examined and plotted the path to 100% renewable energy for europe by 2050. they deemed a 100% res system technologically achievable and financially competitive for europe, emphasizing the need for cost reduction and storage. al-ghussain et al. [28] investigated the security challenges of res from a different perspective. they presented a novel method for assessing the security of integrated res power systems, considering primary frequency regulation. their evaluation, based on an improved accumulation-based plf model using a multi-linear approach, creates a generalized power flow profile to rapidly identify operational violations. previous works assumed ideal primary frequency control, compensating for fluctuations by conventional generating units over short time intervals, which may be invalid for small or isolated systems with highres penetration. thus, incorporating primary frequency regulation into plf analysis is crucial for a comprehensive system risk assessment. the proposed method has proven highly effective. palomba et al. [29] outlined the implementation of a solar biomass system for multi-family homes to achieve 100% renewable energy. they reported that typical energy demand profiles for these buildings allocate about 70% of total consumption to heating, while cooling requires full capacity (100%). moreover, even in northern climates, renewable energy sources can supply nearly 60% of the overall energy demand [30]. tabrizi et al. [31] used a topsis-based multi-criteria decision-making method to evaluate renewable energy adoption in g7 countries. they collected data on power generation, renewable outputs, carbon emissions, and economic indicators to calculate metrics such as carbon emissions per a. fathi et al. /future energy november 2025| volume 04 | issue 04| pages 01-08 3 dollar of gdp. their results revealed significant disparities, with the uk ranking highest and canada lowest. the study shows that european nations with lower fossil fuel dependence perform better, providing valuable insights for policymakers. previous research has explored geothermal potentials in various contexts, from industrial applications in spain to low-enthalpy exploitation in algeria, but these studies typically address isolated components rather than a full-system perspective. the research gap addressed in this article lies in the limited understanding and comprehensive analysis of the transition to a fully renewable energy system in iceland, specifically focusing on the integration of geothermal energy with other renewable sources. despite extensive studies on individual renewable resources, a comprehensive analysis that integrates the economic, social, and political challenges of transitioning iceland’s energy system remains lacking. moreover, existing literature often overlooks the dynamic relationship between energy policy, technological innovation, and public acceptance in shaping the shift toward renewables. this article fills this gap by using the energyplan model to analyze various energy mix scenarios and their impact on iceland’s energy security, environmental sustainability, and economic feasibility. the study also critically examines the influence of government incentives and regulatory frameworks in encouraging the adoption of renewable technologies, helping to highlight both the obstacles and the opportunities involved. by addressing these underexplored aspects, this research not only contributes to the academic discourse on sustainable energy transitions but also provides practical insights for policymakers and stakeholders in iceland and other regions with similar renewable energy goals. the findings underscore the importance of an integrated approach to energy planning, where technical, economic, and social factors are considered simultaneously to ensure a successful transition to a 100% renewable energy system. 2. methodology 2.1 current state of iceland's renewable energy system this research aims to model the transition to a 100% renewable energy system in iceland and to analyze its technical and environmental impacts. geothermal energy, the dominant energy source, accounts for 65% of the energy mix, utilizing earth's residual heat to generate both heat and electricity. hydroelectric energy contributes 20%, underscoring its important role in iceland's energy portfolio. in contrast, solar energy represents a minimal share, with a 2022 capacity of 7 mw and production of 5 gwh, reflecting iceland's low solar radiation levels, particularly during winter. wind energy, primarily from coastal sources, had a reported capacity of 2 mw and produced 6 gwh in 2022. although iceland's long coastline offers significant wave energy potential, estimated at 1,524 twh annually, commercial development remains improbable due to the lower costs associated with geothermal and hydroelectric power. although iceland has one of the lowest hydrogen fuel prices globally, its usage is currently limited, with minimal advancements in hydrogen infrastructure. bioenergy usage is negligible, and the country has no nuclear facilities or plans for nuclear energy production. fossil fuels, comprising 15% of the total energy mix, are predominantly used in transportation. iceland's energy strategy emphasizes the use of diverse renewable resources that contribute to environmental sustainability. in the biofuels sector, 2022 data indicate limited use, with biofuel consumption in industry and fishing registering 0.8 twh, compared to 2.3 twh of oil consumption. in 2021, iceland's renewable energy production totaled 19,617 gwh, with hydroelectric power generating 13,804 gwh, geothermal energy 5,802 gwh, and both wind and solar energy contributing 6 gwh and 5 gwh, respectively. the reliance on hydroelectric and geothermal energy illustrates iceland's commitment to a sustainable, lowcarbon energy system. this transition involves optimizing energy resources, enhancing energy efficiency, and promoting low-carbon consumption patterns to mitigate environmental impacts and reduce greenhouse gas emissions. iceland was chosen as the focus of this study due to its unique energy profile and the relative simplicity of modeling its renewable energy system [32]. table 1 shows the monthly temperature variations in iceland, which are crucial for assessing the seasonal impacts on renewable energy production, particularly for geothermal and solar systems. similarly, figure 1 illustrates the moisture status of reykjavík throughout the year, providing valuable insights into local climatic conditions that affect energy demand and system performance. table 1. temperature of iceland in different months of the year daylight hrs. (c) coldest ever(c) warmest ever(c) average low(c) average high(c) month 4 1 50 28 36 jan 7 7 50 28 37 feb 10 7 57 32 39 mar 15 9 59 33 45 apr 18 19 70 39 50 may 20-22 32 70 45 54 jun 19 34 74 50 60 jul 16 32 70 48 57 aug 13 25 68 43 52 sep 9 14 61 37 45 oct 6 10 54 34 39 nov 4 1 52 28 36 dec figure1. moisture status of reykjavik, iceland in different months of the year a. fathi et al. /future energy november 2025| volume 04 | issue 04| pages 01-08 4 2.2 energy plan software in this study, the energy plan model is employed. it is a deterministic simulation tool that has been specifically designed for comprehensive energy system analysis. unlike many generic models, energy plan uniquely features an 'endpoint' approach, which is used to forecast future system configurations rather than merely replicating current conditions. multiple sectors (heat, transportation, industry, and electricity) are integrated by this tool through the consideration of various inputs such as renewable resource capacities, system demands, and cost parameters for both renewable and non-renewable sources. the application of energy plan has been successfully carried out across diverse contexts, from industrialized nations to developing countries, for the development of regional and national energy strategies. its capability to simulate the economic, environmental, and technical impacts of different energy scenarios is particularly well-suited for the evaluation of iceland’s transition towards a 100% renewable energy system. within the methodology of this study, energy plan has been tailored to capture the unique interdependencies among energy sectors in iceland, thereby enabling a detailed scenario-based analysis of pathways such as evs, hybrid, and bau models. the overall flow of the model is illustrated in figure 3, which is segmented into inputs, processes, and outcomes [33]. peter tozzi j.r. and jane jo [34] discussed renewable energy simulation using the energy plan software. they described it as a cost-free, open-layer tool designed to analyze the energy, environmental, and economic impacts of various energy scenarios. the main objective is to model various scenarios and compare them. what makes it different is that the "endpoint" modeling approach focuses on the future of the energy system rather than its current state [35]. 2.3 scenario descriptions the first scenario, which is basically bau, models the continuation of the current trend without any structural changes. this scenario serves as a depiction of the country's current status and highlights the importance and urgency of implementing the two previous scenarios to improve the energy situation in iceland. in the second scenario, named the evs (s2) scenario, the development of electric vehicles as an alternative to fossil fuel vehicles is expected to increase energy efficiency and reduce environmental impacts. this scenario is proposed as a significant solution for the transition of iceland's transportation sector. in the last scenario, named the hybrid (s3) scenario, not only are evs developed, but industrial energy consumption and ships are also converted to biofuel. this step will harness the full potential of clean and sustainable energy from biofuel sources, contributing to the realization of energy sustainability goals in iceland. these three scenarios together present a balanced and coherent approach towards achieving sustainable energy supply and reducing negative environmental impacts. table 2 provides a summary of scenario descriptions. as population growth directly affects increasing demand, the described scenarios were implemented based on population data up to 2023 and projections until 2035. figure 2 demonstrates the icelandic population trend up to 2023. 3. results and discussion as clearly shown in figure 3, the results revealed that the share of renewable energies in supplying energy demand, known as res, is different for each scenario. in the ev scenario, res percentage reached 91.2%, while in the hybrid scenario, it reached 96.6%, which shows that the implementation of this scenario can be considered an effective step in reaching the goal of 100% renewable system in iceland. the bau scenario remains significant despite having a lower capacity for reducing greenhouse gas emissions. it represents an improvement compared to the situation in other countries. additionally, it can serve as a valuable benchmark for comparing other scenarios, helping us make informed decisions for future environmental and energy policies. table 2. scenario descriptions figure 2. iceland’s population trend (blue points are available data and orange points are predictions) figure 3. res percentage trends scenarios abbreviation code scenario 1continuation of the current trend in iceland’s energy system without any structural changes bau scenario 2conversion of fossil fuel cars to electric cars. evs (s2) scenario 3 conversion of fossil fuel cars to electric vehicles alongside conversion of industrial and maritime energy consumption to biofuel. hybrid (s3) a. fathi et al. /future energy november 2025| volume 04 | issue 04| pages 01-08 5 according to figure 4, in terms of co2 emissions, as expected, both ev and hybrid scenario implementation lead to a reduction of carbon dioxide emissions, proving their positive and effective environmental impact and their role in mitigating the adverse effects of climate change. as can be seen in figure 4, carbon dioxide emissions in 2022 amounted to 1.98 million tons. this number is reduced to 1.27 and 0.49 million tons by 2035 in evs and the hybrid scenario, respectively. this experience underscores that implementing changes in transportation and industrial systems towards clean fuels and sustainable energy systems is an effective strategy for achieving environmental compatibility and reducing the harmful effects of human activities on the earth. however, the study also has its weaknesses. the accuracy of the model is highly dependent on the quality and availability of input data, which may vary and therefore affect the reliability of the results. the outcome is specific to iceland’s unique energy system and may not be directly applicable to other regions with different conditions. furthermore, while the study focuses on technical and environmental aspects, it does not delve deeply into economic considerations such as cost implications and financial feasibility, which are crucial for practical implementation and policy-making. figure 4. carbon dioxide production rate bau scenario: in the bau scenario, which assumes no significant changes to the current energy system, the share of renewable energy only increases slightly by 0.1%. this scenario reflects a continuation of current trends, with little progress in adopting renewable energy sources. although the rate of increase is relatively modest, co2 emissions are projected to rise to 2.58 million tons by 2035. this indicates that without structural changes, iceland’s energy system will remain dependent on fossil fuels, resulting in a continued growth in greenhouse gas emissions. evs scenario (s2): in this scenario, fossil fuel vehicles are replaced with evs; therefore, the share of renewable energy sources in iceland's energy supply reaches 91.2% by 2035. this represents a significant shift toward cleaner energy consumption. co2 emissions decrease from 1.98 million tons in 2022 to 1.27 million tons by 2035. this reduction highlights the positive environmental impact of transitioning to evs, which contribute to cleaner energy consumption and lower greenhouse gas emissions. hybrid scenario (s3): the hybrid scenario goes a step further by combining ev adoption with biofuel utilization. in this scenario, fossil fuels are replaced with biofuels in the industrial and maritime transportation sectors, resulting in an even higher res share of 96.6% by 2035. this scenario demonstrates the potential for near-total reliance on renewable energy sources in iceland. the hybrid scenario achieves the most substantial reduction, lowering emissions to just 0.49 million tons by 2035. this substantial reduction underscores the effectiveness of integrating multiple renewable energy strategies to mitigate climate change. 3.1 economic consequences of transitioning to a 100% energy system cost reductions in energy supply: transitioning to a 100% renewable energy system, particularly through scenarios such as evs and hybrid models, is projected to lead to significant reductions in energy costs. the ev scenario, which focuses on electric vehicles, reduces reliance on fossil fuels, leading to lower fuel expenditures and operational costs. the hybrid scenario extends the noticed benefits by incorporating biofuel, which can stabilize energy prices in the long term by diversifying the energy mix. both scenarios contribute to lowering the overall energy demand and enhancing energy efficiency, leading to cost savings across various sectors, including transportation, industry, and residential energy consumption. these reductions in energy costs can improve the economic competitiveness of iceland's industries and reduce the cost of living for its citizens. model estimates indicate that the evs scenario could reduce total energy costs by approximately 12% compared to the bau scenario, translating into annual savings of around $500 million by 2035. the hybrid scenario, by integrating biofuels into sectors such as maritime transport, is forecasted to deliver cost reductions of up to 18%, as energy diversification contributes to long-term energy price stability. job creation and economic growth: investments in renewable energy infrastructure, such as the development of ev charging infrastructure and biofuel production facilities, are expected to create jobs in construction, operation, and maintenance. the hybrid scenario, which includes both evs and biofuels, is likely to generate more employment opportunities than the ev scenario alone. the transition to a 100% renewable energy system also has the potential to attract foreign direct investment, particularly in green technologies and clean energy sectors, contributing to the diversification of iceland's economy and economic growth. according to the model, the ev scenario could directly generate around 3,000 new jobs in areas related to the deployment and maintenance of ev infrastructure. the hybrid scenario is projected to deliver even more employment benefits, potentially creating an additional 5,000 direct jobs due to the broader scope of investments in both electric vehicle and biofuel production facilities. these employment gains, alongside enhanced industrial competitiveness, contribute to overall economic growth and diversification. financial evaluation and investment opportunities: the financial evaluation of the proposed scenarios highlights the critical need for upfront capital investments in renewable energy infrastructure. while the ev scenario demands considerable initial investment, it offers long-term financial benefits through reduced fuel imports and lower operational costs. the hybrid scenario requires even more extensive investments, particularly in biofuel production and distribution networks. however, these additional costs can be justified by the long-term advantages of enhanced energy security and reduced sensitivity to fuel price fluctuations. early investments in these scenarios would play a pivotal role in realizing these economic benefits. by supporting the development of renewable energy infrastructure, investors a. fathi et al. /future energy november 2025| volume 04 | issue 04| pages 01-08 6 can ensure the financial viability of these projects and gain significant returns on investment through the growing demand for clean energy. 3.2 recommendations for policymakers and stakeholders incentivize investments in renewable energy: our results indicate that both the evs and hybrid scenarios yield significant cost savings and emission reductions. policymakers can build on these insights by offering targeted tax incentives, grants, and low-interest loans focused on expanding ev infrastructure and developing sustainable biofuel systems. such measures will further drive investment into areas where our model shows the greatest potential for improvement. enhance energy policy frameworks: given iceland’s unique strengths in geothermal and hydroelectric power, existing energy policies should be revised to integrate additional renewable measures demonstrated in our scenarios. it’s not just about increasing the share of renewables overall; it's also about enabling specific measures, like scaling up biofuels for maritime transport, which can play a decisive role in improving energy security and reducing fossil fuel dependency. promote public awareness and education: a successful transition to a 100% renewable energy system is not only a technical or economic challenge, but also a social one. our findings underscore the importance of public engagement. designing public awareness campaigns is recommended to highlight the specific benefits of evs and hybrid scenarios, such as reduced operational costs and improved air quality. educational programs can also foster greater understanding of how everyday choices connect to iceland’s long-term sustainability and resilience. 3.3 social and political challenges of the transition to a 100% renewable energy system addressing policy and infrastructure gaps: although the simulation results indicated promising technical and environmental potential, overcoming institutional and infrastructural barriers is essential in order to achieve these benefits in practice. policymakers must address the existing gaps in the current system. for instance, the growing share of renewable energy sources requires modernizing the national grid and expanding electric vehicle charging infrastructure. managing the socioeconomic transition: the scenarios also pointed to potential economic gains, such as job creation within renewable energy sectors. nevertheless, these advantages must be weighed against the disruptions caused by restructuring traditional industries. strategic support is needed for employee retraining and local economic diversification to mitigate any short-term employment disruptions. securing political and public support: given the innovative nature of integrating biofuels with existing renewable resources in the hybrid scenario, it is crucial to build a broad consensus. government incentives, coupled with transparent communication of study findings (e.g., quantified reductions in co₂ emissions and cost savings), can help secure both political support and public approval for the necessary structural reforms. these recommendations and challenges are directly derived from the findings of our energy plan-based scenario analysis, ensuring that policy and stakeholder strategies are both targeted and feasible. 4. conclusion this study explored a new pathway for iceland’s energy transition by integrating geothermal energy, biofuels, and electric vehicles into a unified, scenario-based model using the energy plan software. unlike earlier studies that often examined renewable energy sources in isolation, this paper focused on how different energy sectors interact within broader policy frameworks. three distinct scenarios were compared: in the evs scenario, replacing fossil fuel vehicles with electric vehicles significantly boosted the share of renewable energy and led to a noticeable reduction in co₂ emissions; in the hybrid scenario, which combined the adoption of evs with the use of biofuels in industrial and maritime sectors, the renewable energy share reached approximately 97% while co₂ emissions dropped to 0.49 million tons by 2035. conversely, the bau scenario showed only a marginal increase in renewable energy share, with co₂ emissions rising to 2.58 million tons. these findings demonstrated that integrated renewable strategies can substantially enhance energy security and environmental sustainability. the outcomes also aligned with growing research supporting the necessity of comprehensive energy planning. compared to earlier studies that treated individual energy sources separately, this work underscored the added value of a multifaceted approach and highlighted the importance of supportive policies such as those promoted by the european green deal in driving the transition. in summary, the study confirmed that strategic interventions and the adoption of a diverse renewable energy mix are essential for overcoming fossil fuel dependency. it offered both a theoretical contribution to academic discourse and practical guidance for policymakers and stakeholders in iceland and similar regions pursuing a low-carbon future. ethical issue the authors are aware of and comply with best practices in publication ethics, specifically concerning authorship (avoidance of guest authorship), dual submission, manipulation of figures, competing interests, and compliance with policies on research ethics. the authors adhere to publication requirements that the submitted work is original and has not been published elsewhere in any language. data availability statement the manuscript contains all the data. however, more data will be available upon request from the corresponding author. conflict of interest the authors declare no potential conflict of interest. references [1] pambudi, n.a. and d.k. ulfa, the geothermal energy landscape in indonesia: a comprehensive 2023 update on power generation, policies, risks, phase and the role of education. renewable and sustainable energy reviews, 2024. 189: p. 114008. 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[31] tabrizi, a., yousefi, h., abdoos, m. et al. evaluating renewable energy adoption in g7 countries: a topsis-based multi-criteria decision analysis. discov energy 5, 2 (2025). https://doi.org/10.1007/s43937025-00064-w [32] irena. reneweble energy statistic 2023. 2023, file:///c:/users/muhyeddin/downloads/statistical review of world energy.pdf. a. fathi et al. /future energy november 2025| volume 04 | issue 04| pages 01-08 8 [33] lund, h., et al., energyplan–advanced analysis of smart energy systems. smart energy, 2021. 1: p. 100007. [34] tozzi jr, p. and j.h. jo, a comparative analysis of renewable energy simulation tools: performance simulation model vs. system optimization. renewable and sustainable energy reviews, 2017. 80: p. 390398. [35] jahangir, m.h., et al., reducing carbon emissions of industrial large livestock farms using hybrid renewable energy systems. renewable energy, 2022. 189: p. 52-65. this article is an open-access article distributed under the terms and conditions of the creative commons attribution (cc by) license (https://creativecommons.org/licenses/by/4.0/). https://creativecommons.org/licenses/by/4.0/ 1. introduction the urgent global shift from fossil fuels to renewable energy has intensified research into sustainable solutions, and iceland, with its vast, easily accessible geothermal resources, stands out as an ideal candidate for a 100% renewable energy system.... parrado-hernando et al. [17], in a study for bulgaria on achieving 100% renewable energy, utilized the energy plan and modass tools. they identified a flexibility gap between two selected methods and proposed a new approach that is more beneficial for... daniel icaza alvarz et al. [26] proposed a zero-carbon energy system with 100% renewable energy for the galapagos islands, ecuador, as the second-largest marine reserve in the world, designated a unesco world heritage site in 1978, with the project ai... 2. methodology 2.1 current state of iceland's renewable energy system this research aims to model the transition to a 100% renewable energy system in iceland and to analyze its technical and environmental impacts. geothermal energy, the dominant energy source, accounts for 65% of the energy mix, utilizing earth's residu... table 1. temperature of iceland in different months of the year figure1. moisture status of reykjavik, iceland in different months of the year 2.2 energy plan software in this study, the energy plan model is employed. it is a deterministic simulation tool that has been specifically designed for comprehensive energy system analysis. unlike many generic models, energy plan uniquely features an 'endpoint' approach, whi... 2.3 scenario descriptions the first scenario, which is basically bau, models the continuation of the current trend without any structural changes. this scenario serves as a depiction of the country's current status and highlights the importance and urgency of implementing the ... 3. results and discussion as clearly shown in figure 3, the results revealed that the share of renewable energies in supplying energy demand, known as res, is different for each scenario. in the ev scenario, res percentage reached 91.2%, while in the hybrid scenario, it reache... table 2. scenario descriptions figure 2. iceland’s population trend (blue points are available data and orange points are predictions) figure 3. res percentage trends according to figure 4, in terms of co2 emissions, as expected, both ev and hybrid scenario implementation lead to a reduction of carbon dioxide emissions, proving their positive and effective environmental impact and their role in mitigating the adver... figure 4. carbon dioxide production rate bau scenario: in the bau scenario, which assumes no significant changes to the current energy system, the share of renewable energy only increases slightly by 0.1%. this scenario reflects a continuation of current trends, with little progress in adopt... evs scenario (s2): in this scenario, fossil fuel vehicles are replaced with evs; therefore, the share of renewable energy sources in iceland's energy supply reaches 91.2% by 2035. this represents a significant shift toward cleaner energy consumption. ... hybrid scenario (s3): the hybrid scenario goes a step further by combining ev adoption with biofuel utilization. in this scenario, fossil fuels are replaced with biofuels in the industrial and maritime transportation sectors, resulting in an even high... 3.1 economic consequences of transitioning to a 100% energy system cost reductions in energy supply: transitioning to a 100% renewable energy system, particularly through scenarios such as evs and hybrid models, is projected to lead to significant reductions in energy costs. the ev scenario, which focuses on electric... job creation and economic growth: investments in renewable energy infrastructure, such as the development of ev charging infrastructure and biofuel production facilities, are expected to create jobs in construction, operation, and maintenance. the hy... financial evaluation and investment opportunities: the financial evaluation of the proposed scenarios highlights the critical need for upfront capital investments in renewable energy infrastructure. while the ev scenario demands considerable initial i... 3.2 recommendations for policymakers and stakeholders incentivize investments in renewable energy: our results indicate that both the evs and hybrid scenarios yield significant cost savings and emission reductions. policymakers can build on these insights by offering targeted tax incentives, grants, and ... enhance energy policy frameworks: given iceland’s unique strengths in geothermal and hydroelectric power, existing energy policies should be revised to integrate additional renewable measures demonstrated in our scenarios. it’s not just about increasi... promote public awareness and education: a successful transition to a 100% renewable energy system is not only a technical or economic challenge, but also a social one. our findings underscore the importance of public engagement. designing public aware... 3.3 social and political challenges of the transition to a 100% renewable energy system addressing policy and infrastructure gaps: although the simulation results indicated promising technical and environmental potential, overcoming institutional and infrastructural barriers is essential in order to achieve these benefits in practice. po... managing the socioeconomic transition: the scenarios also pointed to potential economic gains, such as job creation within renewable energy sectors. nevertheless, these advantages must be weighed against the disruptions caused by restructuring traditi... securing political and public support: given the innovative nature of integrating biofuels with existing renewable resources in the hybrid scenario, it is crucial to build a broad consensus. government incentives, coupled with transparent communicatio... these recommendations and challenges are directly derived from the findings of our energy plan-based scenario analysis, ensuring that policy and stakeholder strategies are both targeted and feasible. 4. conclusion the manuscript contains all the data. however, more data will be available upon request from the corresponding author. conflict of interest the authors declare no potential conflict of interest. references [1] pambudi, n.a. and d.k. ulfa, the geothermal energy landscape in indonesia: a comprehensive 2023 update on power generation, policies, risks, phase and the role of education. renewable and sustainable energy reviews, 2024. 189: p. 114008. [2] marczinkowski, h.m. and l. barros, technical approaches and institutional alignment to 100% renewable energy system transition of madeira island—electrification, smart energy and the required flexible market conditions. energies, 2020. 13(17): p. ... [3] yousefi, h., et al., developing the geothermal resources map of iran. geothermics, 2010. 39(2): p. 140-151. [4] rasaei, fateme, et al. “optimal selection of csp site for desalination system using gis and ahp method in hormozgan province, iran.” energy reports, vol. 13, 2025, pp. 2255–68, https://doi.org/10.1016/j.egyr.2025.01.082. [5] porubova, j. and g. bazbauers, analysis of long-term plan for energy supply system for latvia that is 100% based on the use of local energy resources. environmental and climate technologies, 2010. 4(1): p. 82-90. [6] raza, m.a., et al., towards achieving 100% renewable energy supply for sustainable climate change in pakistan. sustainability, 2022. 14(24): p. 16547. [7] yousefi, h., s. ehara, and y. noorollahi. geothermal potential site selection using gis in iran. in proceedings of the 32nd workshop on geothermal reservoir engineering, stanford university, stanford, california. 2007. [8] razeghi, marziyeh, et al. “evaluating the economic impact of solar energy on local industries in semnan, iran.” future sustainability, vol. 03, no. 01, pp. 49–58, https://doi.org/10.55670/fpll.fusus.3.1.5. [9] https://commission.europa.eu/strategy-and-policy/priorities-2019-2024/european-green-deal_en [10] fardnia, khashayar, et al. “a bibliometric analysis of carbon and water footprints in renewable energy: the post-covid-19 landscape.” green technologies and sustainability, vol. 3, no. 3, 2025, https://doi.org/10.1016/j.grets.2024.100162. 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[35] jahangir, m.h., et al., reducing carbon emissions of industrial large livestock farms using hybrid renewable energy systems. renewable energy, 2022. 189: p. 52-65. s. tiwari et al. /future energy february 2025| volume 04 | issue 01| pages 19-29 19 review how electricity utility practitioners in the united states approach power system resilience shardul tiwari1, aritra chakrabarty2, chelsea schelly2*, mostafa sahraei-ardakani3, gaby ou4, jianli chen3 1university of toronto, canada 2michigan technological university, united states 3university of utah, united states 4university of florida, united states a r t i c l e i n f o article history: received 16 december 2024 received in revised form 18 january 2025 accepted 30 january 2025 keywords: energy resilience, electricity utility, energy services, resilient energy system, united states *corresponding author email address: cschelly@mtu.edu doi: 10.55670/fpll.fuen.4.1.3 a b s t r a c t this study explores the understanding and practice of resilience among electrical utilities in the united states, focusing on how practitioners in the utility sector conceptualize and apply resilience in their work. as electricity becomes increasingly central to modern life, powering critical infrastructure and essential services, the resilience of power systems has gained prominence in energy policy and planning. however, there is a lack of standardized definitions and approaches to resilience in both academia and practice, particularly from an energy service perspective. the research employs a qualitative approach, utilizing semi-structured interviews with experts (practitioners) from transmission and distribution utilities in the united states to examine their definitions, understanding, and applications of resilience. by adopting a grounded theory approach, the study aims to identify key themes and concepts that practitioners associate with power system resilience. the findings outline that there is no clear definition of resilience amongst utility practitioners, and resilience and reliability are often used interchangeably/synonymously as there are no fixed indicators for resilience amongst practitioners. at present, unlike reliability, utilities are not including resilience as a term in their long-term resource planning, and neither are they reporting resilience-based indicators to any of the government agencies. the findings contribute to the ongoing dialogue on energy resilience and offer a foundation for developing more comprehensive and context-specific approaches to building resilient energy systems that prioritize critical services and vulnerable populations. 1. introduction electricity is key to deriving almost every energy service required for modern human comforts and is critical to building resilient communities [1, 2]. power systems now serve as the lifeline for critical infrastructures such as health, education, defense, communications, and overall national security [3, 4]. economic and human development indicators often depend on the capability and resiliency of access to energy services [5]. the most evident example is in the case of any climate-induced disaster or during the war, power system protection is considered a priority to derive other forms of services. further, impacts on the electricity system have cascading effects on multiple aspects of community resiliency [6, 7]. the resiliency of a power system is a proxy indicator for understanding the energy services adaptability of a community to respond, recover, and rebound from a disaster. historically, energy planning predominantly relied on the trilemma of energy security, affordability, and sustainability, a relatively new application of energy resilience is gaining traction as a key element in energy policymaking [8, 9]. this shift to an increased focus on energy resilience stems from the study of the resilience of centralized oil and gas systems, other energy generation systems, and energy services access [10]. the increased influx of renewable electricity and utilization of electricity as end-use energy, even in the traditionally bereft transportation sector, has led to an increased focus on power system resilience [11]. this focus on power system resilience has primarily focused on system capabilities modeled through various software, with limited consideration for human agency, particularly for future energy open access journal https://doi.org/10.55670/fpll.fuen.4.1.3 february 2025| volume 04 | issue 01 | pages 19-29 journal homepage: https://fupubco.com/fuen issn 2832-0328 mailto:cschelly@mtu.edu https://doi.org/10.55670/fpll.fuen.4.1.3 https://fupubco.com/fuen s. tiwari et al. /future energy february 2025| volume 04 | issue 01| pages 19-29 20 electrical utilities [10]. the socio-technical nature of power systems and socio-technical system resiliency is largely under-researched, with a primary focus on developing a technically resilient power system. electrical utilities are the primary stakeholders that apply, define, and shape the application of energy system resiliency [12]. given the evolving restructured competitive electricity markets in the usa, which is primarily led by utilities, the practitioners' understanding of power system resiliency is of critical importance [13]. currently, utility practitioners’ understand resilience as reliability, with a limited understanding of resilience in practice within the energy industry. researchers and power system scholars are continually debating how utility professionals understand and define resiliency at the transmission and distribution levels [14, 15]. scholars have argued that resilient energy services is an enigma even when it is a prerequisite to understanding the nature of electricity system resilience for the community [16]. given the importance of understanding the power sector's resilience and how it impacts energy services access, it is imperative to understand how practitioners working in the utility sector understand energy resilience. the energy resilience of a power system and its capabilities are typically understood and captured using reliability indicators. power system scholars utilize metrics such as system average interruption duration index (saidi) and system average interruption frequency index (saifi) to understand the average power interruption to consumers and outages in the system [17]. however, these indicators do not tell us which customers are affected in what ways, particularly for the people who are most vulnerable in a particular power system. the current lack of a standard definition for resiliency, particularly energy system/service resiliency, in academia and practice has created a challenge to comprehensively develop and build models that look at community resiliency through an energy service approach. energy systems resilience must prioritize access to energy services for those who are vulnerable in the case of energy services disruption [18]. this paper aims to explore the understanding and practice of resilience among electrical utilities in the us. as there is currently limited research on how utility practitioners utilize resilience in their work, this paper serves as an initial foray into examining the meaning and utilization of resilience in transmission and distribution utilities. the paper uses a qualitative semi-structured interview approach to interview experts from utilities at the transmission and distribution level to understand and explore the practitioners' current definition of resiliency. we explore the current themes discussed by the practitioners to apply the concept of resilience coherently. based on this grounded theory approach, we situate energy resilience into community resiliency through an energy service approach, which is under-represented in the study of energy resilience yet is key in developing a resilient power system. 2. background: electric utility & resilience in the united states 2.1 resilience of the current utility sector in the united states the electric utility in the us has its roots in a decentralized system, with initial regulations starting at municipal, thereafter state, and only later at the federal level [19]. the role of electricity has expanded since the enactment of the rural electrification act in 1935, which led to the uswide electrification of rural us households through electric cooperatives with the foremost goal of providing electricity services to rural farms [20, 21]. however, the expansion of utilities through the late 1990s till today involves a centralized system with vertical integration of a sector that has been considered a natural monopoly of the public utility commission (puc) or public service commission (psc) operating at the state level [22]. vertical integration involves a single company's ownership of three main parts of the power system: generation, transmission, and distribution [23]. this vertically integrated sector required regulation, as they were deemed natural monopolies. the major focus of scholarship has been on the economic argument for regulating monopolies to provide people with electricity at a reasonable price. however, given the nature of the power system, where electricity cannot easily be stored and maintaining grid frequency is of utmost importance in the power system, system reliability was also a major concern for the regulators [20]. following the deregulation of the electric power industry, wholesale power markets were formed in parts of the us, with separate entities owning generation, transmission, and distribution. administration of the wholesale markets in deregulated regions is the responsibility of independent system operators (isos)/regional transmission system operators (rtos). isos/rtos are also responsible for maintaining grid reliability and resiliency [19, 24]. both regions with vertically integrated utilities and restructured markets in north america must adhere to north american electric reliability corporation (nerc) standards to ensure the reliability and security of the bulk power system (figure 1). some of these standards encompass various aspects of system operation, including critical infrastructure protection (cip), which safeguards physical and cyber assets. utilities must follow transmission operations (top) standards, ensuring real-time system monitoring and coordination and transmission planning (tpl), which involves assessing future system needs and reliability. utilities have to maintain the nerc standards, such as the development of emergency plans (eop) for system disturbances, modeling, data, and analysis (mod) to support accurate system simulations, and resource and demand balancing (bal) to maintain system stability. the electrical utility sector today is complex, involving multiple layers of actors, institutions, and interests. the us electricity segment contains over 24,645 electricity generation power plants with over 11,000 utility-scale plants with a nameplate capacity of over 1 mw. with the growing utilization of electricity as a means of service, the utilities' transmission and distribution network capacity is expected to grow at a brisk pace, particularly after the implementation of the inflation regulation act (ira) aimed at infrastructure improvement. the increase in central dependency on the s. tiwari et al. /future energy february 2025| volume 04 | issue 01| pages 19-29 21 power grid to provide end-use energy makes electrical utilities' understanding and application of resilience even more critical in the restructured electricity market. restoration and recovery of services are of prime importance. electricity is seen as a means for people to incur services, and the need for services can range across multiple dimensions of social vulnerability; hence, it is essential to understand the meaning and application of resilience amongst professionals in the transitioning electrical utility sector. figure 1. regional transmission organizations (rtos)/independent system operators (isos) 2.2 electricity utility services & resiliency electricity is a core commodity required to derive a multitude of services for human needs and comforts. any attack on the supply or distribution of electricity can disrupt those multitude of human services. the national academy of sciences (nas) has outlined that power systems are increasingly vulnerable to physical and nonphysical attacks, such as cyber-attacks and extreme weather [24]. the current us electric system is increasingly vulnerable to climateinduced disasters, which impacts community resilience as well since it is tied to electricity system resilience [18]. however, unlike other commodities, utilities cannot independently improve resiliency because they are linked to each other through distribution, and supply purchase and sale and work within a market response model since each is competing to gain consumers and remain profitable [24]. hence, the overall goal of providing resilient energy services and maintaining a resilient grid (both at transmission and distribution levels) sits at a crossroads of myriad economic, climate, and social priorities. power outages translate into direct service disruptions, which can vary across a spectrum from a minor inconvenience to a fight between life and death for some community members. for instance, in a recent power outage in michigan, 467,000 people were left without power in freezing cold weather [25]. the same was observed during the texas power crisis, where 4.5 million people were left without power [18], and those with access to electricity paid very high electricity bills because of the market principles of increased prices with constrained electricity supply and high demand [26, 27]. the impact of power outages is compounded by the fact that utilities are not required by federal law to report power outages. there are no rules to report the resiliency of a power system till a recent ruling by the federal energy regulatory commission (ferc) that requires interstate electric transmission providers to file one-time informational reports assessing the susceptibility of their systems to extreme weather events to the nerc. however, this rule is only applicable to power outages caused by extreme weather events. the scope of this rule is limited to current and planned policies of transmission providers when exposed to extreme weather events. apart from this rule, power utilities are mandated to report reliability data to nerc. the nerc then assigns ‘cause codes’ from the reported data that identify the cause of the power outage event. these cause codes cover momentary (less than a minute) and sustained (more than a minute) outages. the cause codes are the basis of our current understanding of the energy resilience of a power system. the nerc data reporting requirement notwithstanding, scholars have increasingly attempted to develop metrics to gauge power outages and report power system resilience [28]. technical standards of reliability, such as the system average interruption duration index (saidi)/system average interruption frequency index (saifi), measure the reliability of electricity service. saifi and saidi are international standards created by the institute of electrical electronics engineers (ieee). these indicators are used by transmission and distribution companies across the world to measure, report, and track the reliability of power systems. each of the participating utility managers in this study submitted data to eia through form 861, which is the annual electric power industry report and contains reliability indicators such as saidi, saifi, and caidi. form eia 861 collects annual information on the status of electric power industry participants involved in the generation, transmission, and distribution of electric energy. power outage reporting requirements are in the form of standards set by nerc (event reporting standard eop-004-4) [29], according to which utilities are to report events that cause outages exceeding a certain threshold of either a loss of a load of more than 300 megawatts (mw), and/or impacts over 50,000 customers. however, these metrics are associated with restoring and/or improving the physical infrastructure and exclude the impact on community resilience. there is a lack of academic agreement on defining or measuring resilience in the context of power systems. often, it is used synonymously with reliability, which is extensively used in power system studies and has agreed-upon indicators and metrics. reliability has been defined by the department of energy as “the ability of the system or its components to withstand instability, uncontrolled events, cascading failures, or unanticipated loss of system components”. on the other hand, resilience encompasses human factors as well, as its scope includes the differential and compounding impact of power outages on communities [30, 31]. to put it simply, a power system can be reliable but not resilient because of limited consideration of the impact of outages on different groups of people over time-based on a range of vulnerabilities caused by energy service disruption. reliability, when used as a synonym with resilience, only captures limited information of who is getting impacted by the power system design failures and the ways in which utilities are trying to minimize s. tiwari et al. /future energy february 2025| volume 04 | issue 01| pages 19-29 22 this failure. through this study, we are trying to bridge this gap by understanding how utility managers understand and define resilience and how they foresee the future of developing a resilient power system that can cater to the energy service needs of all people. 3. research methodology this study is an initial foray into understanding energy resilience through conversations with professionals about the use and definition of the energy resilience term in their practical work. semi-structured interviews are considered an appropriate method for inductive research when the intent is to understand the meanings and how stakeholders use a particular concept, which in our case is energy resilience in the context of energy and disaster policymaking [32-34] have stated that semi-structured interviews are one of the best forms of data collection during the exploratory phase of a study. this qualitative research tool suits our study as our goal is to answer ‘how utility managers think, define, and take action on energy resilience’. we do not intend to test any hypothesis about the utility functions. we use the data collected from the interviews to identify new insights and propose further research. this method is criticized for being vulnerable to bias, particularly social desirability bias, and not providing a means to generalize the research result [35]; however, our goal is to provide new conceptual insights that can be explored further in future empirical work. given the exploratory nature of our study with no intention to prove a particular hypothesis, we make no claim to generalize the research results. hence, this is an appropriate method and form of analysis. we structured the interview into two modules: prevention of transmission & distribution (t&d) losses and restoration/recovery. 3.1 data collection utility experts were selected for the interviews to explore understanding and use of resilience in power systems operations in the us. the potential respondents were selected through an iterative process of snowball sampling [35]. the interviews were conducted between august 2022 and february 2023. we interviewed utility providers with territories in roughly tens of states in the contiguous us and one unincorporated territory of the us. twelve interviews were conducted with eighteen participants. out of the twelve interviews, one interview was telephonic; two were in-person interviews; one company submitted written responses to the interview questions, and the other eight were conducted online. the choice of the means to conduct the interview (inperson, over the phone, online) was based on the preference of the interviewee. out of the eighteen respondents, nine were one-to-one interviews, and the rest were group interviews one with a team of four people, one with a team of three people, and another with a team of two people. in the united states, electric utilities operate in a highly competitive market and hence are apprehensive of sharing information that might hurt their profitability due to asymmetric information. the initial respondents were recruited through available professional referrals and by contact through information available on utility websites. over forty emails for interview recruitment were sent to different utilities, including utilities working at the transmission and distribution system levels. the unit of study is electrical utility; hence, utility managers were interviewed depending on the scale of the utility. for small utilities, we had a single participant, while in large transmission system operators, once we had a team of four people, and one was a team of three people. 3.2 data analysis stake [36] and later sovacool et al. [37] state that qualitative data analysis involves segregating data into themes and understanding those themes and their relation to each other. miles and huberman [38] summarized qualitative data analysis as a means to dissect meaning from the text while keeping the relations between the parts intact. creswell [35] provides the foundation steps of qualitative data analysis, regardless of the type of methodology employed. we utilized nvivo to do manual coding following the creswell [35] guidelines using the following interactive steps for data analysis. • anonymizing and cleaning transcripts as raw data for analysis; • echo reading to get a general sense of the data; • coding data based on themes; • contextualizing and finding linkages between the themes; • interpretation of data. 4. findings the analysis of the text data from the interviews reveals that utilities have a well-defined scope and activities regarding the reliability of the power system, metrics to measure the reliability, and a systemized process of reporting power outages to federal authorities. however, the understanding of resilience goes beyond the scope of reliability, tracking, and reporting power outages. resilience also encompasses community resilience and disaster resilience in the aftermath of extreme weather events. five themes emerged based on the data the cause of outages in power systems, the process of system maintenance, understanding of resilience, the cooperation among utilities, and regulations on resilience. the most important finding was the gap in understanding resilience as something that goes beyond grid reliability (table 1). 4.1 causes of outage all interviewees identified weather-related outages as the most common in power systems. the participants classified them as significant disturbances, including big storms hitting the power system or smaller ones, such as when a bird accidentally blows out a transformer or local winds leading to a tree falling and damaging a particular distribution system line. the utilities working in the distribution system highlighted more frequent impacts on their grid and services when compared with transmission utilities. utilities with relatively new infrastructure have the advantage of having a higher tolerance to weather-related events due to new equipment and no legacy challenges. falling trees or vegetation are the most common reasons outlined for electricity outages. one utility outlined that "over 70% plus of all of our outages are either tree or weatherrelated, and they're intertwined because trees fall down a lot more during bad weather." the type of weather-related outage varies depending on the utility territory, with the most common ones identified as a hurricane, extreme wind events, earthquakes, floods, and ice storms. it is important to note s. tiwari et al. /future energy february 2025| volume 04 | issue 01| pages 19-29 23 that these events were not classified as mutually exclusive and can happen simultaneously. in general, utilities use approximately 30 different cause codes to categorize the reason for an outage. however, these cause codes are not uniform and can vary in terms of the nomenclature used across utilities, as the regulatory authorities do not mandate these codes at the federal or state level. in the case of minor outages, utilities do not maintain a clear demarcation of understanding if a tree-related outage is caused by weather or by humans. for instance, as explained by one respondent, "an amateur lumberjack dropped a tree into the easement of their property and happened to dent a nearby transmission line." most participants agreed that when a significant event impacts the system, it is generally an extreme weather-related outage. some third-party interference, such as vehicle accidents, were relatively common; however, these occur at a relatively small scale. table 1. summary of findings issues summary of theme scale of the issue relevance to resilience causes of outage extreme weather events, followed by small local incidents, and lastly humancaused events distribution systems are more severely impacted compared to transmission systems. utilities with new infrastructure can withstand impacts better than older utilities with legacy issues. while outages and restoration is part of system resilience, restoration practices are not uniform across utilities and resilience to extreme weather events is not part of planning at either transmission or distribution scale. system maintenance most utilities conduct full system maintenance every 10 12 years, but there is no standard regulation nor any oversight to govern system maintenance. age of the system and its geographical spread determine the cost and frequency of maintenance. distribution utilities depend on human inspection while transmission utilities have automated the process. the lack of standard regulations reflects how utilities conduct maintenance, which is based on an informal understanding of best practices. a resilience-based regulation could involve not only maintenance but also impacts on communities. resilience vs reliability utility managers understand resilience from a reliability perspective. while there are standard metrics to measure reliability of a system, resilience is a new concept that has not been defined yet. reliability is measured through saidi and saifi indicators that a utility submits to the eia. the data is available through nerc in regions throughout the entire us. resilience is not measured or reported by the utilities either at the transmission or distribution level. resilience measurement is absent. there is no metric to understand the scale of impact an outage has on consumers. the absence of indicators is a result of no agreement amongst utilities regarding the scope of resilience beyond reliability. cooperation among utilities cooperation is based on informal agreement among neighboring distribution utilities to provide man hours prior to and post-disaster events. municipal utilities depend on investor owned utilities (iou) for restart of substation after outage events. there are organizational barriers that prevent formal cooperation agreements among ious and municipal utilities regarding the scope of maintenance at distribution level. cooperation is a factor of the extent of the damage, the geographical coverage of each utility, and dependence on iou. however, with lack of formal agreements and/or rules, restoration (reliability), and resilience is open to interpretation across utilities. regulations there are reliability standards at the transmission and distribution levels. however, there are no strict guidelines for resilience, particularly in the aftermath of an outage. the absence of standardized rules and regulations is felt the most at the transmission and distribution scale. this is a top-down issue where the absence of standardization from the federal level flows down in the form of an informal understanding of what is considered essential services by utilities independently. this is the most critical issue which influences how the transmission and distribution companies invest on resilience. technical parameters aside, resilience is also the impact of power outage on utility services (electricity, water, gas, water, wastewater, and steam) that define community lives [39]. s. tiwari et al. /future energy february 2025| volume 04 | issue 01| pages 19-29 24 4.2 system maintenance system age and the utility's size in terms of its geographical spread significantly impact how it is maintained. a smaller, newly established utility has a more robust system than an old one with significant stranded assets, particularly when another firm acquires the old system following the restructuring of the electricity sector of the us in various states. one participant outlined “the legacy costs create a significant challenge to maintaining system reliability and resiliency.” this statement highlights the synonymous use of reliability and resilience in practice. at the distribution system, a lot of maintenance and restoration work still relies on human inspection, and technology use is largely restricted to outage management systems integrated with supervisory control and data acquisition (scada) systems. using scada depends on the utility budget and territorial spread, which is common for transmission utilities and not so common amongst small distribution utilities. some utilities are bringing in new systems, particularly for vegetation management, to enhance the system's resilience from minor storms and weather events. however, significant penetration of such maintenance systems is still needed. software for monitoring and inspection is more common at the transmission level, which can be attributed to the availability of more resources with the transmission companies. the average maintenance cycle for distribution companies is 1214 years, which means one-twelfth to one-fourteenth of the system is replaced yearly in the utility geographical territory. different utilities have varying standards for the maintenance of their system, even though most of them are based on the best practices from the industry. each utility is free to maintain its system the way it deems fit. hence, one utility can have a pole cycle of 12 years and others of 10 years; the same is true for other parts of the system. as one utility representative outlined, "we are in the service industry, and we have to satisfy our customers, and we choose to do it in a way which we deem best for consumers." hence, there is no regulatory standard for the operation of utility services. the findings highlight the need for the implementation of regulations on the use of advanced technologies and systems at the distribution level for effective maintenance and restoration work. while scada systems are commonly used in transmission utilities, their implementation in distribution utilities is often limited due to budget constraints and the geographical spread of the distribution network. the maintenance cycle for distribution companies, which typically ranges from 10 to 14 years, further emphasizes the need for efficient monitoring and inspection systems to ensure the reliability and resilience of the distribution system. the type of technology notwithstanding, the findings point to the lack of and the need for policies at the federal level on use of technologies that can significantly improve the maintenance and restoration processes, enhance system resilience, and enable more efficient asset management. 4.3 resilience vs reliability across interviews, there was consensus that resiliency is a new buzzword in the electrical utility industry. however, there is yet to be a clear and standard definition and description of the term. resiliency was often described as synonymous with reliability; however, during the interview, three interviewees outlined that they are used synonymously but are different. there was also an expressed need to define resiliency and specify how the term should be used in the utility sector. one participant mentioned, “there are many metrics for reliability that have long existed and are well understood; there are no known metrics for resilience today.” interviewees substantiated the claim that reliability is often associated with the saidi and saifi indicators. furthermore, the integrated resource planners within the utility outlined that they do not use resiliency as a term for future energy systems planning and that they need quantifiable metrics for resiliency before it can be incorporated into planning and practice. another participant defined resilience as "reliability informs the resiliency of a power system," suggesting that reliability is a prerequisite for resilience rather than the two being synonymous. participants further clarified that reliability refers to the ability to keep the majority of the lights on most of the time, while resilience is the capacity to respond to and recover from high-impact events. one interviewee mentioned that the definition of resilience should also account for the resilience of the relationship between the utility and its consumers and how waning trust between customers and the utility can be restored. the common theme regarding power system resilience is the need to develop temporal indicators that can measure the system's bearing capacity for different levels of impact, its level of adaptability, and the amount of transformation required for the system to remain reliable. findings suggest the importance of distinguishing reliability and resilience in the context of power systems. critical to this distinction is the temporal aspect of resilience, wherein indicators for pre-, during, and post-event impacts are needed to understand the impact on communities. enhancing community resilience is tied to the temporal aspect trust and communication between utilities and consumers before, during, and after extreme events. another aspect of community resilience is understanding how energy services are differentiated among customers; people living in older housing are more vulnerable to disruptions to heating and cooling services, as are residents with very young or very old household members. medically vulnerable consumers who need electric power to maintain access to necessary medical equipment face different vulnerabilities than those who are healthy. based on the interviews, this aspect of community resilience, recognition of energy services access, and its link to social vulnerabilities is currently missing from considerations of reliability and resilience in the power sector. 4.4 cooperation among utilities interviewees outlined that utilities have signed and, more commonly, unsigned agreed upon understandings for helping neighboring electrical utilities, particularly in the distribution system. in case of an anticipated disaster, helping other utilities by sending the crew at standard labor rates is practiced. in case of more significant disasters in terms of geographical scale and scope, the crew also arrives from further away utilities, and that time lag to accessing the necessary labor for restoration work to begin cannot s. tiwari et al. /future energy february 2025| volume 04 | issue 01| pages 19-29 25 currently be classified under the resiliency of the system as it is not based on any of the reliability indicators within the power sector. during high-impact events, cooperation among utilities can also be hindered by organizational barriers and arrangements. interviewees mentioned that cooperation is a key element of recovery because, in case of an event requiring additional workforce and equipment for pre-staging or postevent work, utilities cooperate in providing the services. one respondent stated, "in my mind, the biggest thing we need to do is better coordinate for preparing for mutual aid activities,” which, in most cases, is based on informal understandings as identified in this statement, "it's just an understanding basis, say hey, you know, come on over and help us out; we'll send you a bill and help you during your situation." the structure and geography of a particular utility system can significantly influence its response to outages. as explained by several participants, when an outage occurs in a small municipal utility proximate to the service territory of an investor-owned utility (iou), or vice versa (although the former scenario is more common), even after the municipal utility restores its distribution system, they may still have to wait for the iou to restore or reboot the substation, leading to a delay in power restoration. the municipal utility typically pays kneeling charges to the iou for maintaining the substation. this situation arises when an iou has a significant territory and does not, or to some extent, cannot maintain a contractual relationship authorizing the municipal utility to work on the substation. while the municipal utility can repair distribution lines, the substation may fall under the iou's jurisdiction, and interviews discussed this exact situation as one highlighting the need for cooperation between utilities. 4.5 regulations for resilience one crucial aspect of the restoration process is the prioritization of essential services and critical infrastructure. these terms refer to facilities and services that are vital for the functioning of a community, such as hospitals, emergency services, water treatment plants, and communication networks. ensuring the continuous operation or prompt restoration of these services is crucial for public safety and minimizing the impact of outages. while utilities follow reliability standards at the transmission and distribution levels, there are no strict guidelines dictating restoration processes. instead, utilities rely on their own best practices, which leads to inconsistencies in priorities and procedures. there are 16 critical infrastructure (ci) sectors according to the national infrastructure protection plan (nipp) [40]. within those cis are “lifeline functions,” which refers to a sector that provides indispensable services that enable the continuous operation of critical business and government functions and that would risk human health and safety or national and economic security if compromised or not promptly restored. these lifeline functions include communications, energy, transportation, and water. however, the participants highlighted that the definition of what constitutes an essential service or critical infrastructure is not uniformly defined by external agencies; instead, each utility determines its own criteria, particularly at the distribution level. this lack of standardization can lead to discrepancies across different utility service areas, where certain facilities, such as nursing homes or schools, may be prioritized in one area but not in another. 5. discussion the future of energy resilience from a utility perspective is increasingly intertwined with reliability concerns, particularly in light of emerging technologies, changing energy consumption patterns and a changing global climate. utilities are grappling with the challenge of adapting their infrastructure to accommodate the growth of electric vehicles (evs) and the increasing electrification of various services. as one participant noted, "one of the things we're looking at is upgrading our distribution system to meet the demand for electric vehicles and other things; we are going to have to have something more robust if everybody is plugging in a car." this sentiment reflects a broader concern among utilities, especially municipal entities, as they strive to enhance system capacity and robustness to meet evolving electricity demands. the increasing reliance on electricity for essential services such as heating, cooling, lighting, communication, and food storage amplifies the potential impact of even minor outages. as stated earlier, the nipp (2013) has defined 16 critical infrastructure (ci) sectors, and within those cis, it has defined “lifeline functions,” which refers to a sector that provides indispensable services that enable the continuous operation of critical business and government functions, and that would risk human health and safety or national and economic security if compromised or not promptly restored. to address the challenge of ensuring lifeline functions, utilities are considering various technical solutions to enhance both reliability and resilience. these include investments in storm hardening measures, such as reinforcing poles and wires and transitioning from overhead to underground distribution lines. additionally, utilities are exploring the implementation of distribution automation and remote supervisory control and data acquisition (scada) systems to improve system monitoring and control capabilities. however, different utilities prioritize different aspects of resilience, and there is no specification on what constitutes essential services in a utility territory. the implementation of these identified resilience-enhancing measures presents a significant economic challenge. the costs associated with modernizing transmission and distribution systems are substantial and would likely be passed on to customers. this economic burden creates a tension between the need for infrastructure upgrades and the imperative to maintain affordable electricity rates. utilities face the complex task of justifying these investments to both regulators and customers, often in unfavorable regulatory and public opinion environments. the findings suggest the need for further research on defining the scope and measurement of resilience at the transmission and distribution levels. this research can be expanded upon by including the perspectives of the impacted communities and resilience impacts after power outage events. the lack of consideration of the impact of power outages on essential services and challenges faced by vulnerable communities during outages requires broadening of our understanding of resilience and establishing standard s. tiwari et al. /future energy february 2025| volume 04 | issue 01| pages 19-29 26 metrics for measuring resilience impacts of outages. participants are aware that climate-induced disasters will increase in the future, leading to a higher probability of system outages. this finding confirms current research on how increasing climate disaster events would risk power system reliability [41, 42]. extreme weather events are now a significant cause of power system failure beyond the contingency of n-1-1 for the events that are financially unfeasible to plan for as they are once-in-a-lifetime events. hence, the participants agreed that they need indicators and a framework for applying resilience in the utility sector. currently, resilience is being used synonymously with reliability without any specific framework on how and on whom the benefits and the costs associated with adapting to resilience are to be distributed. the lack of focus on energy service vulnerabilities also leads to a lack of not understanding of how consumers energy service needs are differentially impacted. as power systems are only a means to serve people's energy needs, there is a need to look at people's energy service needs while considering the power system's resilience [43]. the increasing reliance on electricity for essential services such as heating, cooling, lighting, communication, and food storage amplifies the potential impact of even minor outages. this heightened vulnerability underscores the need for improved system resilience [42]. the absence of standardization on what constitutes critical or essential services across utilities is another cause of concern. communities' specific needs and vulnerabilities can vary based on their geographic location, socioeconomic characteristics, and existing infrastructure [44]. although the importance of different categories of services at times might not vary across groups, the communities' specific needs and vulnerabilities still vary since these needs could depend on housing characteristics (e.g., house insulation level), specific comfort requirements across individuals, and health needs of occupants [45]. research also indicates that utilities can prioritize different services based on their customer base, revenue considerations, and organizational priorities [46]. this understanding reflects a broader concern among utilities, especially municipal entities, as they strive to enhance system capacity and robustness to meet evolving electricity demands [47]. a key finding that has been prominent in the field of disaster resilience [48], is the importance of stakeholder cooperation. as highlighted by most interviewees, utilities support each other in case of emergencies and system failure. however, this is mainly done through mutual understanding and rarely with written agreements. utilities in most of the us have eminent domain and now they are trying to compete with each other for customers [49]. therefore, in cases of competing interests and nested jurisdictions, cooperation during system failures requires a more nuanced understanding. lack of agreement among transmission and distribution utilities in the us regarding resilience indicators is further evidenced by other studies. bie et al. [50] note that different utilities prioritize different aspects of resilience based on their region-specific vulnerabilities and experiences with past disruptions. with electricity being a central element in providing services for every aspect of human life, it is important to articulate how resilience is defined for people and the criteria for restoration and recovery of energy services. this disparity in focus can lead to inconsistent approaches to measuring and improving resilience across the power sector. there is a need to develop a common understanding of the meaning of resilience in the utility sector and develop the means of measuring it and including resilience in integrated resource planning. the practitioners interviewed in the electrical utility sector did not identify a single definition of energy resilience. as often done in engineering studies, participants articulated energy resiliency as synonymous with reliability. there is a clear agreement that reliability indicators are clearly defined and measurable through data submitted to eia and other reporting requirements of utilities regarding power outages to nerc. however, the scope and definition of resilience are vaguely understood and misplaced with reliability in terms of standard metrics. resilience is temporal in nature and includes aspects of recovering after a disaster. this element is not covered in any reliability indicator on how long the distribution system should deter the impact of an event and how quickly it has to recover from the impact and be prepared for the subsequent failure. furthermore, differential impacts on different segments of the population are also a key factor missing from practitioners’ understanding of resilience. umunnakwe et al. [51] have proposed a categorization scheme for quantitative power system resilience metrics. the categorization scheme in the study by umunnakwe et al. [51] reflects the multifaceted nature of resilience, encompassing aspects such as robustness, resourcefulness, rapid recovery, and adaptability. however, the development of universally accepted quantitative indicators remains challenging due to lack of agreement among utilities on what constitutes resilience. 6. conclusion through the study, we explored how electrical utilities think of, and practice resilience in the context of power systems, which are increasingly affected by the increasing impacts of climate change. our analysis of the interviews provides valuable insights into how electrical utilities conceptualize and implement resilience in the face of increasing climate change impacts. this case study on resilience is novel because academic literature has not looked into understanding resilience from an energy service perspective and the ways in which practitioners in the electrical utility sector understand and use the term. it highlights the need for a more contextualized understanding of resilience that goes beyond grid stability, emphasizing the importance of clearly defined critical services and vulnerable populations. however, this study does not represent the understanding of the entire utility sector in the us. hence, no attempt is made to generalize the results of this study using a small sample of interviews conducted. the scope of the study was limited as the approach was to dig deep into understanding the perspective of a wide range of utilities from different geographical regions in the us. the findings are still relevant given the methodology of studying resilience and understanding a particular sector’s perspectives. as electricity becomes increasingly central to all aspects of human life and the energy landscape evolves with electrification and retail choice, a nuanced approach to power system resilience that considers both technical and social s. tiwari et al. /future energy february 2025| volume 04 | issue 01| pages 19-29 27 dimensions is crucial for future planning and policy development. ethical issue the authors are aware of and comply with best practices in publication ethics, specifically concerning authorship (avoidance of guest authorship), dual submission, manipulation of figures, competing interests, and compliance with policies on research ethics. the authors adhere to publication requirements that the submitted work is original and has not been published elsewhere in any language. data availability statement the manuscript contains all the data. however, more data will be available upon request from the corresponding author. conflict of interest the authors declare no potential conflict of interest. references [1] kuang, b., schelly, c., ou, g., sahraei-ardakani, m., tiwari, s., & chen, j. 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(2021). quantitative analysis of power systems resilience: standardization, categorizations, and challenges. sciencedirect. retrieved june 29, 2024, from https://www.sciencedirect.com/science/article/pii/s 1364032121005396 this article is an open-access article distributed under the terms and conditions of the creative commons attribution (cc by) license (https://creativecommons.org/licenses/by/4.0/). https://creativecommons.org/licenses/by/4.0/ bm. smith /future energy may 2025| volume 04 | issue 02| pages 41-49 41 review from novel turbine designs to artificial intelligence: a review of cutting-edge innovations in hydropower systems brooklyn mckenzie smith* department of mechanical engineering, arkansas tech university, 1811 n boulder ave, russellville, ar, 72801, usa a r t i c l e i n f o article history: received 02 march 2025 received in revised form 10 april 2025 accepted 25 april 2025 keywords: hydropower technology, kinetic energy, efficiency, renewable energy, electricity *corresponding author email address: bsmith160@atu.edu doi: 10.55670/fpll.fuen.4.2.5 a b s t r a c t this paper explores the breakthroughs made in hydropower technology and efficiency. the research aims to assess and highlight the advances in hydropower technology and efficiency by investigating the different breakthroughs such as improved turbine designs, aquatic life preservation in relation to the hydropower industry, the utilization of ai, simulations, and digitalization, advancements made in artificial channeling, exploring and advancing marine and hydrokinetic technologies, along with the methods used to optimize operations in the hydropower industry. hydropower, as a clean and reliable renewable energy source, utilizes various types of structures to harness the kinetic energy of moving water to generate electricity. the main initiatives in advancing hydropower include increasing efficiency, improving cost effectiveness, exploring new technologies, and minimizing environmental impacts. hydropower generates roughly six percent of the energy produced in the united states and roughly fifteen percent of all electricity worldwide. over the last 20 years, global hydropower capacity has increased by seventy percent and is projected to grow by an additional seventeen percent between the years 2021 and 2030. this energy source shows a strong, steady upward trend in the advances made in hydropower technology and efficiencies. 1. introduction hydropower was one of the first energy sources to be explored and utilized. this renewable energy source has been used for thousands of years. early civilizations utilized this form of renewable energy to generate mechanical energy and complete tasks such as grinding grain [1]. the modern form of hydropower used to generate electricity began to gain traction in the late 1800’s when the first hydroelectric power plant in the united states became operational in 1882 [2]. over the last century, hydroelectric power has made many advances in design, technology, and efficiency. the conventional dam is one of the more commonly utilized hydroelectric power generation systems. the water collected in the man-made lake or reservoir flows through the intake valve and into a pipe also referred to as a penstock. the water then spins a turbine, which in turn spins a generator, ultimately producing electricity [3]. the conversion from water to wire is roughly 90% efficient. this is at the higher end of the spectrum as coal, natural gas, and oil plants typically achieve roughly only 30% to 40% efficiency [4]. once the energy is produced, it is fed into the electrical grid for distribution. many of the largest hydropower dams are located in the western united states [5]. roughly 60% of the state of washington’s electricity comes from hydropower. currently, hydroelectric power is used in every state in the usa besides delaware and mississippi [6]. hydropower has the potential to advance and improve environmental performance. with rising concerns for the environment and economic impacts, this energy source could potentially solve a multitude of global economic and environmental concerns. however, hydropower has its faults, such as negative environmental effects, including habitat loss, the effect on fish and wildlife, and the unnatural alterations made to the river flows, sediment deposition, water temperature, and water quality [7]. potential advances focused on solving these environmental concerns could cause hydropower to become more desirable and mainstream. economically, hydropower offers significant benefits such as reduced reliance on fossil fuels and low-cost electricity generation [8]. this outweighs the economic challenges that are associated with hydropower, such as the high initial cost of establishing a future energy open access journal https://doi.org/10.55670/fpll.fuen.4.2.5 may 2025| volume 04 | issue 02 | pages 41-49 journal homepage: https://fupubco.com/fuen issn 2832-0328 mailto:bsmith160@atu.edu https://doi.org/10.55670/fpll.fuen.4.2.5 https://fupubco.com/fuen bm. smith /future energy may 2025| volume 04 | issue 02| pages 41-49 42 hydroelectric power plant and the environmental impacts that can potentially take place. 2. the different types of hydropower plants there are four main types of hydropower plants. the main types of hydropower facilities consist of reservoir hydropower, diversion hydropower, offshore hydropower, and pumped storage [9]. each of these projects harnesses the energy of moving water in a different way. the type of hydropower facility implemented depends on factors such as water flow availability, type of water source available, and the potential amount of energy generated [10]. hence, the use of offshore hydropower is often utilized along the coasts, while reservoir hydropower is implemented mainly along rivers or large bodies of water. 2.1 pumped storage hydropower pumped storage hydropower (psh) is the technique used to store energy by pumping water from a lower reservoir uphill to a higher reservoir during periods of low energy demand (figure 1). once the demand for energy increases, the water is released from the upper reservoir. as the water flows through turbines and moves towards the lower reservoir, it generates electricity [11]. an example of a low energy demand period would be when other renewable energy sources, such as wind and solar, are producing excess power or during the night [12]. the psh system was first utilized in 1907 in switzerland at the engeweiher pumped storage facility [13]. the first pumped storage hydropower facility in the u.s., known as the rocky river plant, became operational in 1929 [14]. the psh system helps create grid stability by storing energy during periods of low energy demand and ensuring a source of reliable power when the energy demand is high. psh is the only technology for prolonged energy storage on the market and is known for its predictability and reliability [15]. previously used psh systems have been found to have negative environmental impacts, such as changes to ecosystems and water levels. one advancement made would be the design of the closed-loop psh system. the closed-loop psh is contained between two reservoirs but does not flow into or out of any natural bodies of water. this minimizes the effect on existing ecosystems and water levels in natural water bodies. figure 1. pumped storage hydropower plant system [19] another benefit of the closed-loop systems is that they can be located in areas that are not near rivers or lakes and utilize man-made sites such as mines that are no longer used and converted into reservoirs [16]. psh technology has also undergone other advances such as new equipment controls, improved reversible pump-turbines, and adjustable speed turbines. these advances allow the pumping cycle to increase efficiency by 5% over the last 25 years [17]. psh has several advantages in comparison to other forms of energy storage, including a low economic lifetime cost and a high power capacity [18]. 2.2 impoundment hydropower impoundment hydropower, which is also referred to as reservoir hydropower, is a type of hydropower plant that utilizes either a natural or man-made river. a dam is built to halt the flow of the river and create a reservoir of water. this allows the storage of water, which can then be released as needed to create a steady flow of generated electricity. when the water is released from the reservoir, it flows through a pipe also known as a penstock. the water flow causes the turbine blades to turn. the turbine is connected to a generator, which converts the mechanical energy of the turbine into electrical energy. the electrical energy generated can then be released into the electrical grid for distribution [20]. impoundment hydropower allows for the storage of water for long periods of time, even when river levels begin to decrease. impoundment hydropower plants allow control over the release of water, which allows operators to generate hydroelectricity on demand [21]. disadvantages of reservoir hydropower facilities include the disruption of natural river flows, ecosystems, fish and wildlife populations, and water quality. dams can also disrupt the natural formation of sediment, leading to poor water quality downstream and a potential negative impact on agricultural lands. impoundment hydropower facilities require large areas of land, which can lead to land disputes [22]. annually, reservoir hydropower plants generate roughly 4,000 terawatt-hours of electricity [23]. bm. smith /future energy may 2025| volume 04 | issue 02| pages 41-49 43 a key advancement involving impoundment hydropower facilities would be the creation of a more efficient turbine design, which could be implemented in currently existing dams without the need to construct new dams. this would be a cost-efficient design advancement that would solve problems associated with impoundment facilities without the high costs of building a new dam site. the natel’s restoration hydro turbine (rht) is the first turbine in the hydropower industry that allows for the safe passage of fish and wildlife while still meeting high performance standards. this effort shows advances in efforts to preserve biodiversity while continuing the progression of renewable energy production [24]. in the united states alone, there are over 90,000 dams (figure 2). the national inventory of dams (nid) states there are 92,075 dams currently in the united states. only 3% or 2,500 of all dams in the u.s. actually generate power [25]. the non-powered dams (npd) can be retrofitted to generate power. this would significantly increase the united states’ hydropower capacity without the construction of any new dams [26]. 2.3 diversion hydropower diversion hydropower is a run-of-river (ror) hydropower system that harnesses the electricity generation of a river's naturally occurring downward flow (figure 3). unlike an impoundment facility that flows directly through turbines, the ror systems divert water into a channel or penstock to power turbines and generate electricity. the water is then returned to the river downstream, and the electricity produced is released into the grid for distribution [27]. this type of hydropower facility is convenient because it does not require a dam or reservoir to store water. diversion hydropower offers minimal environmental impacts in comparison to other hydropower facilities by not disrupting the natural flow of rivers [28]. run-of-river systems provide a great source of clean, renewable energy and have predictable seasonal outputs. this is convenient during the hotter seasons, where water levels may periodically deplete [29]. ror systems are ideal only if there is a steadily flowing river or channel [30]. figure 2. hydroelectric dam diagram figure 3. run of river 2.4 offshore hydropower offshore hydropower is a newly established method of harnessing waves and the power of tidal currents to produce hydroelectricity [31]. the largest body of water available in the world is the ocean. the two main types of offshore hydropower are tidal power and wave power [32]. tidal power utilizes the constant and predictable fall and rise of tides to generate electricity [33]. wave power relies on the potential energy produced from ocean waves [34]. tidal barrages are structures commonly placed at the entrance of an estuary or bay. this allows water to be trapped in a reservoir during high tide and run through turbines to generate power as the tide recedes during the ebb current [35]. tidal power is also harnessed through tidal stream turbines. this form of tidal power technology utilizes underwater turbines to harness the energy of tidal currents [36]. bm. smith /future energy may 2025| volume 04 | issue 02| pages 41-49 44 the global tidal energy market is expected to grow at a compound annual growth rate (cagr) of 12.5% from 2024 to 2030 [37]. wave power is utilized by two main types of technology. the wave energy converters (wec) are devices placed in the ocean near areas of high wave activity. the wec devices often utilize specialized buoys or other devices to convert the kinetic energy of the waves into electricity [38]. wave power can also be harnessed through offshore power plants. offshore power plants allow for the utilization of the higher potential energy of waves while minimizing the environmental impacts that are associated with being near the shore [39]. wave hydropower is still in the early stages of development, with many advances yet to be made. the international panel on climate change (ipcc) estimates that the world’s oceans could produce nearly 29,500 terawatthours of electricity annually from wave energy [40]. since 2010, the cumulative global deployment for wave energy has reached 27 mw. 1.6 mw was deployed in 2023 alone [41]. currently, offshore hydropower is more expensive than offshore wind power plants [42]. the u.s. department of energy’s water power technologies office (wpto) is funding research and projects to advance the commercial readiness of wave energy technologies through testing and system validation [43]. by utilizing the predictable wave and tidal cycles, we could substantially increase hydropower production and the utilization of renewable energy. 3. advancements in hydropower the hydropower industry is advancing and growing yearly, nearly doubling its market value from $282.6 billion to $422.13 billion by 2025 [44]. global electricity demand is a major factor in the growth of the hydropower market. investing in hydropower is important, especially for developing countries, because it is a reliable and accessible renewable resource [45]. the traditional designs for hydropower facilities have not changed significantly since they were first introduced nearly two decades ago [46]. due to cost concerns and environmental factors, it is not ideal to completely construct new hydropower plants. therefore, upgrading and advancing already established facilities and technologies would increase efficiency and increase the appeal of hydropower. issues faced within the hydropower industry that could potentially see advancements include measures that preserve aquatic life, improvements to turbine design, harnessing ai, and upgrades made to technology and hydropower plant sites already in place. 3.1 aquatic life preservation the main disadvantage of the hydropower industry is the negative impact that hydropower facilities have on aquatic wildlife. 22.3% of all fish that pass through hydropower turbines are killed or severely injured [47]. natel energy has teamed up with pacific northwest national laboratory to design and test a new turbine design that allows for the safe passage of both small and large fish. the natel’s restoration hydro turbine (rht) is uniquely designed with thicker blades, rounded leading edges, and a forward slant from the blade’s hub to tip. the research team tested the turbine’s efficiency with the passage of rainbow trout, sturgeon, salmonids, alosines, and american eel. these fish ranged in size from 8-20 inches in length. more than 99% of fish passed through the turbine while still allowing for maximum performance output of energy [48]. advancements are still being made to restore aquatic habitats, preserve endangered species, and improve dam operations. statkraft, a leading global renewable energy producer in europe, is working to rehabilitate the population of the endangered european eel. european eels are heavily affected due to the many hydropower plants and other man-made structures that disrupt their natural migration patterns to their spawning grounds. statkraft has implemented plans to transport the eels upriver past hydropower plants in order to allow them a chance to breed and repopulate. this is an uncommon practice, but it is a step in conserving wildlife that is threatened by the construction of hydropower plants [49]. 3.2 improved turbine design the most commonly used turbine design in hydropower plants is the francis turbine (figure 4). the francis turbine is used mainly for larger-scale hydropower plants, while the kaplan and pelton turbines are used for specific head and flow conditions ranging from low to high [50]. figure 4. francis turbine although these designs are efficient, there are still many improvements that can be made. as previously discussed, the rht has been designed to preserve aquatic life that passes through the turbines. hydropower plants have begun implementing the novel turbine. the novel turbine design allows for improved efficiency, reduced costs, and the implementation in areas not normally associated with hydropower generation, such as urban and offshore areas [51]. novel turbines often differ from traditional turbine designs through the materials, geometries, or operation principles [52]. a popular example of a novel turbine being introduced is the fin-ring turbine. the fin-ring turbine consists of seven rings and 88 connecting cambered fins that optimize hydrodynamic performance [53]. novel turbines provide a multitude of benefits that will help aid in the advancements and growth of hydropower. statkraft has broken ground on the hydroflex project, which focuses on the development of turbine systems that can withstand fastpaced starts and stops. this focuses on the response time by allowing the turbine to run as needed and respond in real time to energy demands [54]. research and implementation of turbines that focus on the speed of a turbine have also been introduced within the last decade. the goldisthal psh plant in bm. smith /future energy may 2025| volume 04 | issue 02| pages 41-49 45 germany was the first plant in europe to utilize large variable speed turbines [55]. variable speed technology allows for power regulation during pumping operations, improved efficiency, and optimized control of the power delivered into the grid [56]. a large variable-speed hydropower plant can go from idleness to maximum capacity in approximately 100 seconds [57]. 3.3 harnessing ai, simulations, and digitalization artificial intelligence (ai) technology has improved the hydropower industry’s efficiency and accuracy [58]. ai has improved water management, operations, grid integration, and allows facilities to accurately predict when maintenance on turbines, generators, and other machinery is required [59]. the wuqiangxi hydropower plant in hunan province, china, has implemented ai-based technology to inspect it. the hydropower smart remote o&m system utilizes a fleet of drones and robots to collect data using sound and image recognition tools and infrared thermometers, among other devices. this system allows for repairs and maintenance to be made as needed and not solely during scheduled inspections completed by plant personnel [60]. simulations allow researchers focused on advancing the hydropower industry to develop, design, and test potential designs for hydropower technology without the cost of fabricating and testing an actual prototype [61]. the national renewable energy laboratory (nrel) has developed the aries platform, which creates a controlled, real-world environment that allows researchers to emulate and evaluate prototype controls and advance hydropower technologies [62]. nrel is also developing a platform called the real-time hydropower emulation platform, which mimics hydropower facilities in real time, allowing researchers to test technologies and controls and minimize the risks involved [63]. hydropower digitalization has become a turning point in the advancement of hydropower technologies and efficiencies. digitalization is the process of incorporating digital technologies into various aspects of operations to increase efficiency and lead to advancements [64]. hydropower digitalization has created platform solutions to aid in areas such as digital simulation, predictive maintenance, water monitoring, and asset management [65]. 3.4 marine and hydrokinetic technology marine energy utilizes the kinetic energy created during the movement of water [66]. it focuses on natural occurrences such as waves, tides, and ocean currents [67]. this differs from traditional hydropower, which relies on facilities such as dams and impoundments to generate electricity. the five main types of ocean energy technologies are tidal stream, ocean waves, river hydrokinetic, ocean thermal, and ocean current [68]. marine and hydrokinetic (mhk) technologies were developed to aid in harnessing marine energy [69]. mhk technologies include tidal stream generators (figure 5), barrage systems, and instream hydrokinetic devices [70]. these systems allow for the generation of clean energy, are a reliable energy source, and are considered cost-effective due to relying on naturally replenishing energy sources [71]. this is a promising and reliable future option for areas that are remote or off-grid [72]. research and development for marine and hydrokinetic technology are advancing and focused on the improvement of mhk technologies’ efficiency, durability, and cost-effectiveness [73]. figure 5. diagram of tidal stream power generation 3.5 artificial channeling advancements in artificial channeling focus on improving efficiency, cost effectiveness, and the environmental concerns caused. artificial channeling is an advancement in the hydropower industry that works closely with mhk technology [74]. to harness marine energy, barrage systems, instream hydrokinetic devices, and tidal stream generators are implemented [75]. a barrage system works similarly to a dam by creating a controlled water flow by utilizing the difference in water levels that naturally occur as the tide levels alternate from low to high. as the water levels rise, the barrage gates open, allowing the water to pool into a water basin. as the tide recedes, the collected water is released through the sluice gates as it flows through a turbine, generating electricity [76]. instream hydrokinetic devices and tidal stream generators are both mhk technologies that harvest power from the currents [77]. the innovation of novel turbine designs, such as fish-friendly turbines, hydrokinetic turbines, and vortex turbines, has improved both the efficiency and environmental impacts of artificial channeling [78]. fish-friendly turbines allow for fish to safely pass through turbines [79]. vortex turbines and hydrokinetic turbines are a potential breakthrough in harnessing power in areas with limited water flow or low-speed flows captured in artificial channels such as canals [80]. this is ideal for areas where traditional hydropower is not suitable (figure 6). 3.6 repairing and advancing outdated hydropower plant sites while advancing the hydropower industry is of utmost importance, preserving and maintaining the hydropower plant sites already in use is crucial. the annual operations and maintenance (o&m) cost for hydropower plants can range from 1.5% to 2.5% of the initial investment. for a major hydropower plant, this converts to roughly 15 to 30 million dollars [81]. smaller plants have lower operation and maintenance costs. hydropower plants have a lifespan of 50 to 100 years, but often exceed that when properly maintained [82]. advancing outdated hydropower plants involves bm. smith /future energy may 2025| volume 04 | issue 02| pages 41-49 46 upgrading technologies, improving infrastructure, replacing or repairing aging components, and integrating new technologies that could potentially optimize operations. the modernization of hydropower facilities can have a multitude of benefits, including potentially cost savings due to lower maintenance requirements, extending plant lifespans, and improved energy security. figure 6. a barrage hydroelectric power plant 4. conclusion hydropower is a promising renewable energy source that is steadily improving and evolving. the main goal in advancing hydropower is to increase efficiency, improve cost effectiveness, explore new technologies, and minimize environmental impacts. as covered in this paper, prominent renewable energy companies such as natel and statkraft, amongst others, have made headway in advancing the hydropower industry and overall promoting the use of hydropower. over the last two decades, global hydropower capacity has increased by 70% and is projected to grow by an additional 17% between the years 2021 and 2030. with hydropower on the rise, the possibilities of novel designs and technology in the hydropower industry are on the horizon. ethical issue the author is aware of and complies with best practices in publication ethics, specifically concerning authorship (avoidance of guest authorship), dual submission, manipulation of figures, competing interests, and compliance with policies on research ethics. the author adheres to publication requirements that the submitted work is original and has not been published 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[81] u.s. hydropower market report 2023 edition. 2023. https://www.osti.gov/biblio/2006921 [82] u.s. energy information administration. “hydropower and the environment u.s. energy information administration (eia).” eia.gov, 7 nov. 2022, www.eia.gov/energyexplained/hydropower/hydropo wer-and-the-environment.php. this article is an open-access article distributed under the terms and conditions of the creative commons attribution (cc by) license (https://creativecommons.org/licenses/by/4.0/). https://creativecommons.org/licenses/by/4.0/ r. hajimineh et al. /future energy february 2026| volume 05 | issue 01| pages 10-19 10 article the expansion of brics and its impact on the use of renewable energy sources: a case study of hydrogen energy rahamat hajimineh1*, parisa sabri2, ebrahim rezaei rad3 1department of law, et.c., islamic azad university, tehran, iran 2faculty of world studies, university of tehran, tehran, iran 3science and research branch, islamic azad university, tehran, iran a r t i c l e i n f o article history: received 28 august 2025 received in revised form 06 october 2025 accepted 20 october 2025 keywords: brics, renewable energy sources, hydrogen energy, new development bank, eco-industrial park *corresponding author email address: rahmat.hajimineh@iau.ac.ir doi: 10.55670/fpll.fuen.5.1.2 a b s t r a c t considering the increasing energy needs and environmental challenges in the world, brics members have also put in place a policy of reducing dependence on fossil fuels and moving towards more sustainable energy sources. this study aims to investigate the role and impact of the expansion of this bloc on the development and use of renewable energies, with a special focus on hydrogen energy. in this article, the combined method (quantitative and qualitative) and the theoretical framework of sustainable development and energy transition have been employed. based on the results, brics can play an important role in accelerating the development of hydrogen energy by using policies such as knowledge and technology exchange between member countries, increasing investment in research and development of hydrogen energy, and financing hydrogen energy production infrastructure projects by the new brics development bank. 1. introduction regional organizations have attracted the attention of the international community since the end of world war ii due to their roles in global governance. the hegemony of the west led countries from various parts of the world to establish organizations that could represent their interests, particularly those in the global south, in the division between the north and south. one of these organizations is brics. the brics organization, which includes emerging global powers. brics is actually a group of emerging economic powers of the world, namely brazil, russia, india, china, and south africa. initially, the name of this group was called brics, but after south africa joined, it was changed to brics. this organization has tried to expand its role in global equations by expanding economic cooperation or plans, such as removing the us dollar from its equations. the main text of the article discusses the structure and policies of brics. the issue of renewable energy has attracted the attention of the world due to the high cost and price fluctuations of fossil fuels, environmental problems, and the impact of crises. the presence of two energy consumption giants in the world, namely china and india, has led to the issue of energy and its sustainable supply being given attention. in this regard, china and india are seeking to expand the use of renewable energy and reduce dependence on fossil fuels. the presence of the world's energy giants, namely china, india, iran, and russia, in this organization has made the role of energy and its policies very important in the brics organization. this study aims to investigate the role and impact of the expansion of this bloc on the development and use of renewable energies, with a special focus on hydrogen energy. in this article, the combined method (quantitative and qualitative) and the theoretical framework of sustainable development and energy transition have been used. based on the results, brics can play an essential role in accelerating the development of hydrogen energy by using policies such as knowledge and technology exchange between member countries, increasing investment in research and development of hydrogen energy, and financing hydrogen energy production infrastructure projects by the new brics development bank. renewable energy-led growth hypothesis: new insights from brics and n-11 economies. it has been argued that although brics and n-11 economies have experienced tremendous economic growth in recent years, the energy required is mainly consumed from conventional sources. therefore, policymakers have turned their attention towards promoting future energy open access journal https://doi.org/10.55670/fpll.fuen.5.1.2 february 2026| volume 05 | issue 01 | pages 10-19 journal homepage: https://fupubco.com/fuen issn 2832-0328 mailto:rahmat.hajimineh@iau.ac.ir https://doi.org/10.55670/fpll.fuen.5.1.2 https://fupubco.com/fuen r. hajimineh et al. /future energy february 2026| volume 05 | issue 01| pages 10-19 11 the production and consumption of renewable energy in all economic activities. the findings of this paper show that the renewable energy-based growth hypothesis is present in brics countries in amg and in all quantiles in mmqr, but surprisingly, it is absent in n-11 economies using both estimates [1]. perspective of renewable energy in the brics countries: the brics countries (brazil, russia, india, china, and south africa) have separately embarked on a transition to sustainable energy sources. khare et al. [2] examined the renewable energy networks of the brics countries. it compares and assesses the potential of different renewable energy technologies. the study presents the positive and negative impacts of renewable energy on economic development, foreign investment, domestic production, energy sustainability, and environmental protection across all brics countries. examining the drivers of renewable energy consumption, evidence from brics nations: sachan et al. [3] studied the factors affecting renewable energy consumption by analyzing data from brics countries from 1990 to 2015. panel quantile regression methods and other robustness tests show that the environmental policy stringency index and the human development index have a significant and positive effect on renewable energy consumption. other variables, including carbon dioxide emissions and gross fixed capital formation, show a statistically significant and negative relationship with renewable energy consumption. role of renewable energy investment and geopolitical risk in green finance development, empirical evidence from brics countries: renewable energy-led growth hypothesis: new insights from brics and n-11 economies. dong et al. [4] employed panel data from brics countries from 2000 to 2020 to examine the interactions among economic growth, green finance, green credit, renewable energy investment, and geopolitical risk (gpr). furthermore, the findings of the paper show that renewable energy adoption in brics countries is significantly and favorably affected by gpr. as studied and reviewed, no article has addressed the use of hydrogen energy from various types of renewable energy and the impact of brics on expanding its use, and this has made this article even more important. 2. theoretical framework growing environmental concerns and the rising economic costs associated with fossil fuel dependence have accelerated global attention toward renewable and clean energy solutions. this shift aligns with both sustainable development objectives and international climate commitments. energy transition represents a long-term, strategic process that necessitates tailored approaches, incorporating context-specific technologies and policies to achieve net-zero emissions while balancing national energy security and economic considerations. from an analytical perspective, while environmental protection remains a central driver of energy transition, the process must also account for critical factors such as energy security and economic viability—particularly for resource-rich nations, including those within the brics bloc. at the international level, organizations such as the international energy agency (iea) and the international renewable energy agency (irena) have identified six key pillars for successful energy transition: • expansion of renewable energy infrastructure • enhancement of energy efficiency and demand-side optimization • strategic electrification of energy systems • integration of hydrogen as a clean energy carrier • implementation of carbon capture technologies for fossilbased systems • bioenergy with carbon capture and storage (beccs) energy transition, as a transformative process within energy systems, has been examined through various theoretical lenses by prominent scholars. below, we outline the most significant theoretical frameworks in this field. 2.1 socio-technical systems theory frank geels and johan schot [5] pioneered this theoretical approach through their multi-level perspective (mlp framework. they conceptualize energy transition as the outcome of interactions across three levels: • niche level (emerging technologies) • regime level (dominant energy systems) • landscape level (macro-political, economic, and social trends) 2.2 governance of energy transitions theory anadon and nemet [6] emphasized the critical role of policy-making and institutional frameworks in accelerating or impeding energy transitions. their work highlights how regulatory structures, subsidies, carbon pricing mechanisms, and market regulations determine the pace of transition. 2.3 path dependency theory pierson and arthur [7] demonstrated that energy systems exhibit inertia due to sunk costs and entrenched infrastructure, leading to resistance against rapid shifts. this theory explains why some nations lag in adopting renewable energy despite global pressures. 2.4 political economy of energy transitions timothy mitchell [8], in his seminal work carbon democracy (2011), argues that energy systems are not merely technological but deeply political. he asserts that a successful transition requires transformations in power relations and the political structures governing energy. 2.5 energy justice theory benjamin sovacool et al. [9] advocate for a socially inclusive approach to energy transitions, emphasizing three core principles: • distributive justice (equitable allocation of costs and benefits) • procedural justice (public participation in decisionmaking) • recognition justice (respect for marginalized communities' rights). figure 1 illustrates the conceptual model of the study's theoretical framework. within the theoretical framework of sustainable development, greenhouse gas mitigation and environmental preservation emerge as fundamental imperatives, particularly for major emerging economies like the brics nations. notably, brics countries have demonstrated a strong commitment to renewable energy advancement, with hydrogen economic development receiving particular emphasis as a strategic priority. the convergence of sustainable development principles and energy transition strategies provides a robust analytical foundation for examining the energy policies of brics members. these frameworks are particularly relevant given the bloc's concerted efforts to harmonize climate objectives with energy security and economic growth imperatives, r. hajimineh et al. /future energy february 2026| volume 05 | issue 01| pages 10-19 12 making them indispensable to any scholarly examination of contemporary energy geopolitics. figure 1. conceptual model of the theoretical framework 3. hydrogen energy as an alternative fuel the rise of global warming caused by the emission of greenhouse gases, especially carbon dioxide, and the emergence of environmental crises, the limitation of fossil fuel resources, and the increase in world population growth as three sides of a triangle, have required countries to revise their energy policies and prevent the collapse of human societies under the influence of the reduction of fossil fuel resources. although during the corona virus pandemic, the amount of crude oil production in the world decreased significantly due to transportation restrictions and reached 88 million barrels per day according to the statista report, it is still observed that during the last two decades, the amount of crude oil production has made a big jump and has reached from 74.570 million barrels in 2000 to 96.376 million barrels per day in 2023 [10], which is the highest amount in this period. therefore, in order to reduce the global emissions of these gases, the process of "decarbonization", which means energy transition from fossil fuels to low-carbon energy sources, is the only solution that must happen. figure 2. global primary energy consumption by source [11] as can be seen in figure 2, in 2023, the three nonrenewable energy sources of oil, coal and natural gas account for the largest amount about 75% of the share of energy supply in the world, while renewable energy sources such as nuclear, wind, solar and hydropower have produced nearly 17% which is only a small percentage of the world's energy. this means that the energy transition is in its early stages and has not been fully implemented by countries. among the clean and sustainable energy sources, hydrogen is considered a suitable alternative to fossil fuels. hydrogen, represented by the chemical symbol h, is a chemical element in the periodic table with atomic number 1 and has three isotopes, namely protium, deuterium, and tritium [12]. hydrogen is the most abundant chemical substance in the world, which makes up approximately 75% of the mass of the world and is found in molecular forms such as water and organic compounds. as can be seen in table 1, there are 8 different types of hydrogen, among which green hydrogen is the most suitable type for energy supply. although hydrogen is known as the lightest element, it has the highest amount of energy per unit weight among all fuels [13]. in the last decade, according to energy reports published by statista [15], many countries such as australia, germany, spain, the netherlands, and the united kingdom have made the transition from an economy based on fossil fuels to the hydrogen economy. in the list of the top 10 countries that have the largest number of green hydrogen production facilities around the world, the names of china and russia are also visible. the russian federation and china are two leading countries in the brics group in the field of hydrogen policy and projects. in figure 3, the components that an economy transitioning to a hydrogen economy should pay attention to are categorized. one of the most essential points to pay attention to in the hydrogen energy system is choosing the right source for hydrogen production. to achieve a sustainable and environmentally friendly hydrogen economic system, the required hydrogen energy must be produced from clean, abundant, accessible, and affordable sources. as can be seen in the diagram, hydrogen production sources can be divided into renewable and non-renewable sources or fossil fuels. r. hajimineh et al. /future energy february 2026| volume 05 | issue 01| pages 10-19 13 hydrogen production from renewable sources such as geothermal, water, wind, solar energy, and biomass accelerates the decarbonization process and significantly reduces environmental pollution. table 1. different types of hydrogen [14] figure 3. the hierarchy of a hydrogen economy hydrogen production systems must be efficient on small and large scales and be available in a fixed and portable form. according to pareek et al. [16], there are several paths of hydrogen production such as steam methane reforming, in this method, which uses natural gas extracted from the earth's crust as an energy source, extracted methane can be combined with steam using thermal processes such as steam methane conversion and partial oxidation to produce hydrogen. coal gasification, coal gas can be converted into energy, liquid fuel, chemicals and hydrogen in a process where coal reacts with hydrogen (h2), oxygen (o2) and steam under high pressure and constitutes a mixture of carbon monoxide and hydrogen. electrolysis, in this process, by the application of electrical current, water splits into hydrogen and oxygen. photoelectrochemical, in this method, hydrogen is produced from two abundant renewable sources such as water and sunlight. in this process, two electrodes are used in which one electrode acts as an anode for oxygen production and the other electrode acts as a cathode for hydrogen production. thermochemical water splitting, thermochemical processes, whose heat can be provided by nuclear or solar sources, is a chemical reaction that produces hydrogen at high temperatures (500-2000 degrees celsius). in cases where the source of hydrogen production, such as solar energy, is not permanent and continuous, a suitable storage system is required in hydrogen production. the produced hydrogen can be stored in different ways such as chemical hydrides, compressed gas, cryogenic liquid and metal hydrides. the main expectations from the hydrogen storage system can be specified as high power generation, low electricity and energy consumption, zero emission of pollutants, availability, effective operation, long life and minimal hydrogen waste during discharge and storage [17]. among the most important fields of application of the final hydrogen energy produced are chemical industries, electricity production, transportation and construction. since the transportation sector in the world remains largely dependent on fossil fuels and the share of this sector in the global production of carbon dioxide according to figure 4, especially cars, is more than 48% in 2022, one of the applications of hydrogen energy can be considered in the transportation sector. by substituting hydrogen fuel instead of fossil fuels, the pollutants in the transportation sector will be significantly reduced. grey hydrogen gray hydrogen, the most commonly known form of hydrogen production, is created using natural gas or methane and methane steam reforming, without absorbing greenhouse gases. blue hydrogen like gray hydrogen, blue hydrogen is produced from natural gas using a steam reforming process that combines natural gas and heated water in the form of steam. green hydrogen green hydrogen is produced using renewable energy sources such as solar or wind energy, and this type of hydrogen is produced using the electrolysis process that splits water into hydrogen and oxygen. black and brown hydrogen in the production of this type of hydrogen, which is the opposite of green hydrogen, black coal or brown coal is used, and for this reason, the most damage to the environment occurs in this type of production process. turquoise hydrogen newly entered into this category, turquoise hydrogen is made using a process called pyrolysis of methane to produce hydrogen and solid carbon, and in the future, it may be valued as a low-emission hydrogen. pink hydrogen pink hydrogen produced through electrolysis with nuclear energy can also be called purple hydrogen or red hydrogen. since co2 gas is not released in the production process of pink hydrogen, it is usually considered as green hydrogen. yellow hydrogen yellow hydrogen is the term used to produce hydrogen through electrolysis using solar energy. white hydrogen white hydrogen, which is a form of natural hydrogen, is found in underground deposits and is created through the process of fracking. but so far there is no suitable method to use this hydrogen production. r. hajimineh et al. /future energy february 2026| volume 05 | issue 01| pages 10-19 14 figure 4. co2 emissions by transportation [18] 4. performance of brics (old and new mem) in hydrogen energy projects one of the important issues that has become the concern of developed and developing countries is establishing a balance between economic growth and environmental issues [19]. the increase in greenhouse gas emissions has forced the countries that have become the largest consumers of fossil fuels due to their economic growth to look for ways to achieve the transition to a green and low-carbon economy. since countries with emerging economies are experiencing a stage where achieving economic growth and well-being is a priority for them over environmental well-being, policies such as decarbonization, reducing dependence on fossil fuels, and replacing them with clean fuels are more challenging [20]. the brics member countries, which increased to 10 countries from 2024, can be considered as an example of emerging economies that directly face the priorities related to economic growth on the one hand and environmental issues on the other hand. table 2 indicates variables such as the amount of carbon dioxide emissions and each country's share in global emissions for former brics members and countries that newly joined this organization in 2024. china, with the largest population and the largest amount of carbon dioxide production, with 12.667.428.430 billion tons in 2022, is ranked first, and ethiopia ranks tenth among these countries with the lowest amount of carbon dioxide production of 21,106,910 million tons. according to the table, the amount of carbon dioxide emission by the main brics members, except india, first increased and then faced a noticeable decrease. but the new members who have joined brics have all had an increasing trend in carbon dioxide emissions. changes in the amount of carbon dioxide emissions in the brics countries can be due to the adoption of decarbonization strategies by these countries, which will be explained further. one of the most important steps of the transition from an economy based on fossil fuels to a green hydrogen economy based on renewable energy sources is the formulation of long-term and short-term policies and strategies in this field. in this regard, the most important policies and agreements of the main brics members in the field of renewable energy projects, especially hydrogen, will be reviewed first, and then the situation of the countries that have recently joined brics will be examined in relation to decarbonization projects and hydrogen policies. as can be seen in figure 5, the percentage of renewable energy consumption of brics members in china, brazil, and south africa has maintained its upward trend since 2020. but this trend has been accompanied by fluctuations in russia and india, and in 2023, due to the increase in carbon dioxide emissions by both countries, they have experienced some reduction in the consumption of renewable energies. among brics members, it can be seen that brazil has the highest amount of renewable energy consumption, and south africa has the lowest amount. in recent years, the brics countries have increasingly cooperated in the field of energy and decarbonization of their economy. following the brics summit in johannesburg in 2018, the leaders of the five countries adopted a joint johannesburg declaration, which called for full implementation of the paris agreement and the 2030 agenda, noting that “the five countries will strengthen their energy cooperation, indicating a transition to a cleaner, sustainable energy system [22,23]. the brics countries are working together to promote renewable energy sources such as wind, solar, and hydropower. for example, in 2019, the brics energy research cooperation platform was created to expand cooperation in the field of energy research and promote the use of renewable energy sources (communique adopted in the brics energy ministers meeting, 2021). brics members also cooperate closely with international organizations such as the united nations framework convention on climate change (unfccc) and the international renewable energy agency (irena) to promote sustainable development and climate change. in the meeting held by the brics members on june 23, 2022, virtually, under the chairmanship of the president of china, the leaders emphasized the cooperation of the brics members in the new era of global development [24]. r. hajimineh et al. /future energy february 2026| volume 05 | issue 01| pages 10-19 15 table 2. fossil co2 emissions in brics members [21] country fossil co2 emissions (tons) population co2 emissions per capita share of world's co2 emissions (%) china 2022 12.667.428.430 1.425.179.569 8.89 34.94 2021 12.717.655.300 1.426.437.267 8.92 35.08 2020 12.037.316.110 1.426.106.093 8.44 33.20 india 2022 2,693,034,100 1,425,423,212 1.89 7.43 2021 2,528,133,480 1,414,203,896 1.79 6.97 2020 2,320,678,660 1,402,617,695 1.65 6.40 russia 2022 1,909,039,310 145,579,899 13.11 5.27 2021 1,932,695,430 145,836,175 13.25 5.33 2020 1,789,251,420 146,371,299 12.22 4.94 iran 2022 686,415,730 89,524,246 7.67 1.89 2021 677,815,330 88,455,488 7.66 1.87 2020 656,798,170 87,723,443 7.49 1.81 saudi arabia 2022 607,907,500 32,175,352 18.89 1.68 2021 590,582,460 31,328,375 18.85 1.63 2020 571,341,980 30,991,207 18.44 1.58 brazil 2022 466,770,410 210,306,415 2.22 1.29 2021 503,538,680 209,550,294 2.40 1.39 2020 447,695,430 208,660,842 2.15 1.23 south africa 2022 404,974,510 62,378,410 6.49 1.12 2021 418,965,260 61,502,603 6.81 1.16 2020 419,865,030 60,562,381 6.93 1.16 egypt 2022 265,961,280 112,618,250 2.36 0.73 2021 249,642,460 110,957,008 2.25 0.69 2020 228,165,980 109,315,124 2.09 0.63 united arab emirates 2022 218,799,350 10,242,086 21.36 0.60 2021 214,451,290 9,789,048 21.91 0.59 2020 201,002,140 9,448,524 21.27 0.55 ethiopia 2022 21,106,910 125,384,287 0.17 0.06 2021 20,552,520 122,138,588 0.17 0.06 2020 18,841,280 118,917,671 0.16 0.05 figure 5. renewable energy consumption of brics during 2020-2023 r. hajimineh et al. /future energy february 2026| volume 05 | issue 01| pages 10-19 16 in this meeting, the latest report of the intergovernmental panel on climate change (ipcc) was mentioned, according to which "the triple crisis of climate change, biodiversity loss, and pollution is intensifying. there is an overview of the decarbonization and hydrogen strategy of the 5 main brics countries: regarding compliance with the paris agreement, brazil announced strategic measures to meet its climate neutrality commitments by 2050, including zero illegal deforestation by 2028, restoring and reforesting 18 million hectares of forests by 2030, and encouraging the expansion of the national rail network [25]. policymaking in the field of hydrogen energy has always been the focus of the brazilian government in recent years. for example, in the national energy plan 2050 (pne 2050), which was launched under the ministry of mines and energy of brazil in 2020 [26], hydrogen is also part of the brazilian energy strategy. in the brazil 2050 energy plan, published in 2021, the increase in quality, safety, transport infrastructure, and incentives for the adoption of innovative hydrogen energy technology are also considered. in brazil's three-year national hydrogen plan 2025-2023, the country's strategy is defined by three time frames: until 2025, the establishment of pilot low-carbon hydrogen power plants throughout the country, the establishment of brazil as a competitive low-carbon hydrogen producer, until 2030. and integration of low-carbon hydrogen hubs in brazil by 2035. climate doctrine of the russian federation, approved by decree of the president of the russian federation of december 17, 2009. the russian federation signed the paris agreement on climate change in 2015, but only ratified it in september 2019. decarbonization was not a priority as the country was able to meet the agreement's requirement to reduce its emissions compared to 1990. the first official document of the russian government in the field of hydrogen energy was approved in 2020 under the title roadmap for the development of hydrogen energy in russia until 2024 [27]. during the implementation of the road map, in 2021, the russian government approved another document called the concept of hydrogen energy development in russia, which outlines the goals, tasks, initiatives, and critical measures for the development of hydrogen energy in russia in the medium term until 2024 and long-term until 2035 [28]. as reported on behalf of india's ministry of environment, forest and climate change, india submitted its long-term low emission development strategy to the united nations framework convention on climate change (unfccc) in november 2022 [29]. the indian government has taken measures such as promoting a sustainable lifestyle based on conscious consumption and reducing waste, as well as policies in the sectors of energy economy, transportation, and industry, to combat climate change. the joint statement 2022, released at the brics high level meeting on climate change, noted that india has launched a national hydrogen mission to produce hydrogen from clean energy sources to create alternatives to fossil fuels. the joint statement released at the brics high-level meeting on climate change in 2022 reported that china is pursuing proactive national strategies to address climate change. based on exceeding the 2020 climate action target promised to the international community, china further announced a goal and vision to strive to peak carbon dioxide emissions by 2030 and achieve carbon neutrality by 2060. in 2019, the phrase "promoting the implementation of hydrogen charging and refueling facilities" was included in china's "government work report" for the first time [30] according to the latest report of the international energy agency in 2021 [31], one of china's projects in renewable energy is the sinopec green hydrogen plant, which aims to be the first green hydrogen project of the state-owned china oil company and produce zero carbon fuel from renewable sources. south africa is making progress towards its climate goals in response to the paris agreement. south africa established a presidential climate commission in 2020, adopted a national strategy, introduced an enhanced mitigation system with robust monitoring and assessment, and developed a long-term low-emission development strategy [32]. south africa has shown interest in hydrogen energy since 2007. in 2021, a report on power fuels and green hydrogen was published by the country's council for scientific and industrial research (csir) [33]. then, in a speech on 17 february 2022, the minister of higher education, science and innovation of the republic of south africa announced the launch of the hydrogen society roadmap (hsrm). finally, in february 2022, the south african hydrogen community roadmap (hsrm) was published by the south african government [34]. egypt is one of the five countries that recently joined brics. egypt's membership, because it is the largest nonopec oil producer in africa and the second largest gas producer on the continent, can have many advantages for brics members, especially in the energy sector. as one of the leaders of the arab world, egypt plans to increase the supply of electricity produced from renewable sources to 42% by 2035 [35], so egypt's experience in this field should accelerate the transfer of clean energy in other brics member countries. it should be noted that in the last few days, on august 15, 2024 and at the time of writing this article, egypt has unveiled a national low-carbon hydrogen strategy with the aim of strengthening its green economy and achieving climate change goals [36]. as a new member of brics and africa's sixth-largest economy, ethiopia has grown at an average of 10 percent annually over the past 15 years [37]. ethiopia has significant potential for energy installations and is capable of generating more than 60,000 megawatts (mw) of electricity from hydro, wind, solar, and geothermal sources [38]. about 90% of ethiopia's production capacity is made up of hydropower, and wind and thermal resources make up 8% and 2%, respectively. ethiopia has formulated its climate resilience and green economy strategy (crge) with the goal of keeping greenhouse gas emissions low and building climate resilience and achieving middle-income status by 2025 [39]. in its energy policies, ethiopia has also paid attention to the production of clean and hydrogen energy. in this regard, ethiopia's ministry of water and energy (mowe) has announced that research on green hydrogen production is underway as a solution to meet the world's growing energy needs [40]. the islamic republic of iran, as a country that has the largest oil reserves in the world, with the fourth rank, as well as large gas reserves, is considered one of the new brics members. the potential of different regions of iran in wind, solar, and geothermal energy can provide the basis for the development of iran's energy markets among brics members. despite having significant amounts of minerals as well as renewable resources, iran has not been able to invest properly in energy production from renewable sources due to severe economic sanctions. saudi arabia is the most powerful new brics member as the largest arab economy with an annual gdp of more than one trillion dollars [41]. despite saudi arabia's dependence on traditional fossil energy markets, the country also has goals in the renewable energy sector and aims to provide 50% of its electricity from r. hajimineh et al. /future energy february 2026| volume 05 | issue 01| pages 10-19 17 renewable sources by 2030 [42]. saudi arabia is a country with a huge potential for clean hydrogen production and, therefore, is exploring ways to become the largest supplier of blue and green hydrogen in the world and targets clean hydrogen production of 2.9 million tons per year. 2030 and 4 million tons per year by 2035 [43]. the united arab emirates has joined the brics as one of the top three energy powers of the persian gulf. in addition to being one of the top 10 oil producers in the world, the uae recently announced plans to triple the share of renewable energy in the economy in line with the uae energy strategy 2050 [44]. according to its strategy, the united arab emirates plans to use 44% of renewable energy, 38% of gas, 12% of clean coal, and 6% of nuclear energy sources to produce half of its electricity by 2050. in relation to hydrogen energy, the uae has set its national hydrogen strategy 2050 to support local low-carbon industries and promote the uae's position as one of the largest hydrogen producers by 2031 [45]. according to the global hydrogen review 2023 [46], the uae's strategy includes forecasting the production of 1.4 million tons of hydrogen by 2030, 7.5 million tons by 2040, and 15 million tons by 2050, through a combination of electrolysis with renewable and nuclear electricity, and natural gas, by absorbing, using, and storing carbon. 5. role of brics in expanding hydrogen energy among member countries the challenges brics members face in achieving clean energy, especially hydrogen, can be divided into two categories: internal and external. internal challenges can be considered as the presence or absence of policies, potential, and infrastructure of countries in the field of hydrogen energy. external challenges also include factors influencing a country's policy-making, such as sanctions and shocks, as well as the establishment of bilateral and multilateral relations between brics members and the lack of a unified strategy among them. among the former members of brics, brazil is the country with the highest consumption of renewable energy and can be considered a leader in the transition to a hydrogen economy. about the new members who have recently joined brics, it can be said that iran is considered a country that has not made adequate progress and investment in the field of renewable energies despite its great potential and resources. in general, because the process of energy transfer involves investment, social and political issues that are very different in each country, the transition from fossil fuels to renewable sources such as hydrogen energy, which requires the creation of appropriate infrastructure, is not a simple matter. one of the main challenges of brics is the geographical distance among members, very different socioeconomic and legal models, as well as the competition among group members in influencing the energy market. therefore, it seems difficult and almost impossible for brics to integrate the direction of member countries in obtaining hydrogen energy by formulating a general strategy. therefore, according to the existing challenges, the main question of the article can be answered here, which is “how can brics expand the use of renewable energy sources, especially hydrogen energy, in the member countries?” the three main components of the transition from fossil fuels to renewable energies can be categorized as follows: to achieve clean hydrogen production, a country must have the three i's: investment, infrastructure, and innovation. one of the unique features of brics that can act as a catalyst to accelerate longterm and expensive projects is the brics development bank. this bank, which was established in 2015 by 5 main members, plays a vital role in financing and supporting the infrastructure and development projects of brics member countries (brazil, russia, india, china, and south africa). the role of the brics development bank in providing its members with access to hydrogen energy production can be categorized as follows: • funding projects: the brics development bank can lead major projects in this field in member countries by providing the necessary financial resources for research and development of technologies related to the production, storage, and distribution of hydrogen. • international cooperation: the brics development bank can act as a bridge between member countries to exchange knowledge and technologies related to hydrogen to accelerate the development of hydrogen infrastructure. • encouraging private investment: the brics development bank can encourage private sector investment in the field of hydrogen energy by providing financial guarantees and facilities. • government policy support: the brics development bank can help member countries optimize their national policies and strategies to achieve hydrogen energy by providing advice on financial, environmental, and industrial policies. • eco-industrial park plan: the brics development bank, by building eco-industrial parks in member countries, can help in the production of hydrogen and realize the goals of sustainable development in these countries simultaneously. 6. conclusion in recent decades, issues such as the increase in environmental pollution caused by non-renewable fuels and fossil fuel price fluctuations on the one hand and the benefits of renewable energy sources, such as the absence of pollution or their permanent availability on the other hand, have expanded the desire of many countries in the world to replace non-renewable energy sources in their energy sector. among the types of clean renewable fuels, hydrogen energy has become a sustainable energy source because it can be produced from renewable sources such as water, solar, and wind energy, and is considered the best alternative fuel. since the members of brics are countries with emerging economies, the issue of using renewable energy in the form of long-term and short-term policies and strategies has also received the attention of this bloc. by analyzing the energy policies and carbon dioxide emissions of each of the former and new brics countries, this article has examined the ways to promote and develop hydrogen energy in these countries. the findings of the research show that the new members of brics, such as iran, saudi arabia, ethiopia, egypt, and the united arab emirates, have suitable conditions for the development of hydrogen energy production, but some of them are facing problems in the investment and infrastructure sectors. while the former brics members have taken a little step forward in the transition to clean energy under the influence of the paris agreement, brazil, among them, can take the leadership role. despite the fact that the current state of hydrogen development is still in its early stages and due to the high cost of hydrogen production, significant investment in the infrastructure and technology of this fuel is necessary to achieve its full potential. the brics development bank can finance the project, encouraging private investment as well as building eco-industrial parks to accelerate this process. r. 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[46] energy i, agency. globalhydrogenreview2023 2023 [available from: (https://iea.blob.core.windows.net/assets/cb9d5903 -0df2-4c6c-afa1 4012f9ed45d2/globalhydrogenreview2023.pdf. this article is an open-access article distributed under the terms and conditions of the creative commons attribution (cc by) license (https://creativecommons.org/licenses/by/4.0/). https://creativecommons.org/licenses/by/4.0/ mn. rahman et al. /future energy february 2026| volume 05 | issue 01| pages 41-52 41 article ammonia as a hydrogen carrier: les of ammonia-solid fuel firing at varying air staging ratios mohammad nurizat rahman1*, muhamad shazarizul haziq mohd samsuri2, suzana yusup3, ismail shariff 2 1energy markets and strategy, energy systems, dnv, 118227 singapore 2generation unit, generation and environment, tnb research, kajang, selangor, 43000, malaysia 3faculty of engineering and technology, sunway university, selangor, 47500, malaysia a r t i c l e i n f o article history: received 02 october 2025 received in revised form 17 november 2025 accepted 15 december 2025 keywords: large eddy simulation (les), solid fuel, coal, ammonia, power generation, air-staging combustion *corresponding author email address: mohammadnurizatrahman@gmail.com doi: 10.55670/fpll.fuen.5.1.5 a b s t r a c t hydrogen carriers, such as ammonia (nh3), is anticipated to be used as a carbon-free alternative for solid fuels, such as coal. hence, the effect of air staging ratio (asr) on emissions from nh3 co-firing with sub-bituminous coal was numerically investigated in a small-scale coal combustor via a large eddy simulation (les) method. the validation with experimental data demonstrated a difference in nitrogen oxides (nox) and temperature profiles of less than 10 %. carbon dioxide (co2) and sulphur dioxide (so2) levels are decreasing as the nh3 percentage rises, but asr has minimal influence. increasing the asr from 20 to 60 % resulted in nox reduction, except for 60 calorific (cal.) % nh3, where nox began to grow at asr 60 %. in the said case, peak temperature was recorded in the over-fire air (ofa) zone due to considerable unburned carbon (uc) oxidation, resulting in an increase in thermal nox. due to oxygen deficiency, coal volatiles and nh3 are thought to burn in the firing zone due to dominant devolatilization, resulting in significant uc/char oxidation in the ofa zone. overall, with proper asr tuning, nh3 co-firing can produce low co2, so2, and nox, and existing coal-fired utility asr technology can be used. 1. introduction nowadays, the electricity sector accounts for a significant share of worldwide carbon dioxide (co2) emissions [1-2], primarily because coal-fired thermal power plants supply a substantial share of global electricity demand, owing to their large reserves and affordability [2-6]. it is a known fact that coal-fired thermal power plants emit more co2 than other generation systems [7], since coal has a relatively higher carbon content than almost all other fossil fuels [8]. and it serves as one of the main anthropogenic co2 emission sources [9], accounting for 41 % of worldwide co2 emissions in 2023 [10]. a reduction in greenhouse gas (ghg) emissions is critical as a key control measure for climate change issues, and it is now becoming a worldwide accord [913]. the attainment of a sustainable society is extensively spoken about, and the pressure on coal-fired utilities to decarbonise is heightening [5]. at the un's climate change conference (cop26), more than 40 nations made pledges to abandon coal. despite the excitement surrounding the netzero carbon transition, the global energy crisis in recent years has led to a rush for coal demand once more, demonstrating that the rapid switch to renewable energy is, in fact, more difficult than anticipated. one of the solutions to this issue is to gradually phase out coal, so that there is an adequate amount of time for lowand/or zero-carbon technologies to reach economies of scale [2]. therefore, while waiting for these technologies and their associated supply chains to fully mature, decreasing negative emissions from existing coalfired thermal power plants is critical for reducing the carbon footprint and eventually establishing the targeted net-zero society [9-10]. therefore, various techniques are being established to reduce co2 emissions from the said plants, including integrated gasification combined cycle (igcc), ultra-supercritical technology [10], oxy-fuel combustion, carbon capture and storage (ccs) [7], double reheat technology [10], and the use of low-/zero-carbon fuels [11]. when it comes to employing these types of fuels, biofuels (such as biogas and biomass) are appealing fuels for co-firing applications. yet, variability in harvesting periods indicates fluctuations in feedstock supply and presents significant hurdles for both operations and market sentiment. carbonfree fuels, such as hydrogen, are another option, expected to play an increasingly important role in creating a net-zero society, especially in hard-to-abate sectors [11-15]. however, owing to its unique properties [11], the storage and transportation of hydrogen remain relatively complex future energy open access journal https://doi.org/10.55670/fpll.fuen.5.1.5 february 2026| volume 05 | issue 01 | pages 41-52 journal homepage: https://fupubco.com/fuen issn 2832-0328 mailto:mohammadnurizatrahman@gmail.com https://doi.org/10.55670/fpll.fuen.5.1.5 https://fupubco.com/fuen mn. rahman et al. /future energy february 2026| volume 05 | issue 01| pages 41-52 42 [13,16]. hydrogen carriers, such as ammonia (nh3), are effective alternatives to pure hydrogen, as demonstrated in a report by rahman [13], owing to their relatively high hydrogen density compared with other hydrogen carriers, such as organic hydrides [16-17]. additionally, nh3 is a desirable vector for hydrogen because it retains roughly 90% of the energy from the hydrogen feedstock and is much easier to store due to its ease of liquefaction [18]. having said that, nh3 is an enabler of the hydrogen economy, not a competitor [19]. furthermore, as a fuel, nh3 can be employed in existing plant-related combustion systems without the need for a procedure to extract its hydrogen content [18], albeit with tuning works to be done where necessary. nh3 has been regularly and widely employed as a denitrification material in boilers and plants. the latest movement in decarbonising the shipping industry with nh3 as a marine fuel is an obvious indication of some of its benefits that can be potentially adapted to power generation systems, such as production scalability, a comparatively adequate energy density with relatively simple storage needs as opposed to pure h2, and secured usage in existing industrial processes. nh3 is already an essential commodity chemical worldwide, with a mature storage and distribution supply chain that is becoming increasingly crucial to vital aspects of global society, such as the fertiliser industry [17]. as such, infrastructures for nh3 storage and delivery are well developed [3, 12], and its initial and operational costs are expected to be relatively lower than those of other low-carbon/carbon-free fuels and hydrogen carriers [7], with several techno-economic studies indicating that it has the potential to be the lowest cost zero-carbon option. hence, nh3 could be a preferable candidate for widespread use in the future because it is both a hydrogen carrier and a potential replacement for conventional fossil fuels. hence, it is clear that interest in nh3 as an electricitygenerated component is growing, especially with its prospect as a crucial fuel/feedstock for decarbonising power generation [2]. co-firing of coal and nh3 has recently been regarded as a promising method for minimising co2 emissions from coalfired thermal power plants [17]. for the production of nh3 as a fuel, the "blue nh3" is expected to be created using ccs to capture carbon emissions [10]. the "green nh3" could be produced from hydrogen electrolysis from water, utilising the excess renewable electricity (e.g., wind and solar power) [9]. hence, “green nh3” is a derivative renewable fuel that functions as a transporter and a storage option for renewable energy [17]. at the same time, it is important to note that the reduction in emissions from nh3 co-firing is also highly affected by the nh3 production method [18]. yet, nh3 cofiring remains one of the most realistic and appealing options compared to most strategies for fuel blending scenarios [19]. co-firing methods aim to maximise the utilisation of facilities in existing coal-fired power plants, potentially reducing resource waste and financial/opportunity losses due to power plant early retirement [20]. moreover, reducing the carbon content of the main fuel stream (in this case, coal) could help cut co2 emissions. however, given the limited capacity of nh3 production facilities worldwide, it is unlikely that nh3 will fully replace coal in the short to medium term [3]. possibly in the future, especially in the scenario of nh3 yield sees an exponential increase due to its use as a hydrogen carrier (combined with government fuel incentives), the associated cost of nh3 procurement has the potential to fall even further, and it can thus be used as one of the main energy vectors for power generation systems [7]. by utilising green nh3 as a carbon-free fuel, the integration of existing coal-fired power plants and low-carbon renewable options could be realised, providing an essential engineering pathway for a potentially cleaner coal-fired power generation [10]. thus, at the moment, co-firing nh3 with pulverised coal in a boiler is seen as a quick and viable means of effectively lowering co2 emissions from these systems, as the world waits for the eventual full phase-out of coal-fired power plants [17]. despite this, co-firing nh3 in coal-fired boiler systems could result in elevated nitrogen oxide (nox) emissions, owing to its much higher fuel-nitrogen content [9, 12]. these impacts must be investigated in advance, including their emissions and combustion aspects, if nh3 co-firing is to be widely used in the future. various organisations worldwide have researched the combustion properties of nh3 [7]. in the context of combustion assessments, comprehensive data on nh3 flame propagation across varying operational scenarios aid combustion dynamics assessment and the development of comprehensive reaction mechanisms [12, 16]. recent advances in research on nh3 co-firing technology with pulverised coal have been published [3,20]. ihi corporation, for instance, successfully tested nh3 co-firing in a pulverised coal combustor system (10 mw size), with nh3 accounting for 20% of the co-firing ratio. moreover, the results from these experimental works have demonstrated that for the case of nh3 co-firing, unburned carbon (uc) in fly ash and nox emission could be comparable to those in the scenario of full coal firing, if a proper nh3 injection technology is adopted. in separate experimental research, the characteristics of pulverised coal+nh3 co-firing were explored in detail via a horizontally shaped single burner with the feeding rate of 100 kg/hr (coal) [3]. their results have shown that when the nh3 was injected from the burner’s centre with nh3 of 20 cal.%, nox concentration in the flue gas has been seen to be elevated by roughly 20 % from the pure coal firing case, and uc in fly ash increased in a moderate manner. these findings suggest that controlling/tuning nh3coal co-firing while preserving both flame stability and nox emissions is a significant challenge that requires further research to achieve acceptable combustion characteristics. tuning the air staging ratio (asr) is another potential approach for decreasing nox emissions when co-firing coal and nh3. this is the same strategy employed in existing coalfired power plants, where airflow is distributed via the combustion air and then separated into the burner zone and the over-fire air (ofa) zone above the burner regions [21-22]. the existing air staging system in most coal-fired utility furnaces is a technical advantage. as a result, its start-up and operating costs are expected to be relatively low, as it requires essentially no alteration to the existing coal-fired power system. the only significant change in co-firing nh3 is at the burner, where a novel nh3-co-fired burner is required to inject nh3 with coal [20]. while several studies have examined the co-firing of coal and nh3 to evaluate its combustion and emission properties, there have been very few investigations into the effects of asr on these properties. moreover, a number of important works on nh3 co-firing mn. rahman et al. /future energy february 2026| volume 05 | issue 01| pages 41-52 43 mostly assumed an ideal reactor network model [4, 5, 7, 9, 12]. this assumption is known to neglect the 3d effects of fluid dynamics. weng [5], for instance, examined the presence of sulphur and alkali species in nh3 conversion processes in a post-flame environment using ideal reactor networks (chemkin pro software), with a focus on the characteristics of no emissions and the slip of nh3 in flue gases. despite the fact that nh3 and low-rank coals have comparable energy density [19], it is clear that important nh3 properties, for example its relatively low laminar burning velocities and energy [16, 23], as well as elevated ignition energies and high auto-ignition temperatures [19], make it more difficult to combust nh3 efficiently and achieve the operational and combustion performances required by existing coal-fired power plants. in fact, more assessment is necessary before nh3 is used in existing coal-fired power plants to better understand its combustion and emission properties, mainly through further research on the kinetics and fluid dynamics of nh3 co-firing/full-firing, to aid flow tuning, such as asr control. one viable option is computational fluid dynamics (cfd), which can be a useful tool for detailed investigations of the impact of asr on nh3 co-firing. subsequently, it can aid in the tuning of the asr for actual coal-nh3 firing for nox reduction in power plants. cfd has been frequently utilised to examine heat transmission and combustion dynamics in pulverised coal-fired utility furnaces. zhang [3], for instance, used cfd approaches to examine the impact of nh3 ratio on coal+nh3 co-firing in a pulverised coal combustor facility. the modelling findings were compared with experimental data on nox, co2, and uc levels. however, when compared to nox readings from experimental data, the modelling approaches that use the reynolds-averaged navier-stokes (rans) model to resolve turbulence flow produced a 35 % and 47 % difference in nox and uc levels, respectively. cardoso [2] has also used one of the rans-based models, the krealizable model, to investigate nh3 and biomass cofiring in a pilot-scale fluidised bed reactor system. the predicted co2 and no emissions from coal+biomass co-firing were compared to the actual co2 and no emissions from coal+biomass co-firing experiments. while the validations show reasonable agreement in terms of trend, there is no direct validation with real coal-nh3 co-firing. therefore, it is still not entirely safe to assume that it can reliably simulate coal-nh3 co-firing when the validation basis is for different fuel blends (coal-biomass). furthermore, post-processing is the most commonly used approach for nox modelling, in which the main gas compositions, temperature, and velocity distributions are first obtained from combustion numerical calculations; then nox-related reactions are added [3]. as a result, it is advised to use the combustion simulation parameter to evaluate a reasonable validation. furthermore, actual nh3 co-firing test data should be used as a validation benchmark. in terms of resolving turbulence flow, while the use of the rans model is beneficial to account for the accuracy and efficiency of the computational processes of nh3 co-firing [2], there is still more research required to fully comprehend the coal-nh3 flame dynamics and its associated emissions, which can only be achieved through the use of large eddy simulation (les). the key advantage of les over rans approaches is that it treats turbulence-chemistry interactions (tci) more realistically [24]. as a result, higher fidelity to simulation results can be achieved. through the low-pass filtering method, the les reduces the computational burden by ignoring small length scales that require significant computational effort. instead, the effect of these small length scales will be modelled using sub-grid scale models [25]. therefore, les is a powerful algorithm with a good tradeoff between reliable combustion dynamics predictions and computational cost. while les has been commonly used for nh3 combustion simulations, the majority of these studies have been focused on co-firing with gaseous fuel, primarily natural gas and methane (ch4) [26-28]. the use of les for coal+nh3 co-firing research is still lacking. furthermore, the effect of varying asr on nh3 co-firing must be studied further for future implementation in coal-fired power plants. hence, reliable prediction of flame structures, temperature dynamics, and nox levels is an important goal in the numerical modelling of coal+nh3 co-firing via les in order to provide a holistic risk assessment for coal+nh3 co-firing at varying asrs. as a result, in this study, cfd assessments using a detailed les were performed to examine the effects of nh3 co-firing on emissions in a small-scale coal combustor facility at various asrs. among the studied pollutants are co2, so2, and nox. sub-bituminous coal rank was used since it is the most commonly used coal rank in malaysia’s coal-fired power plants [29-30]. the prediction accuracy of the cfd approach was first evaluated by comparing it to actual testing data from the pulverised coal combustor testing facility. 2. experimental setup the coal+nh3 co-firing test was carried out in tnb research's pulverised coal combustor facility, as shown in figure 1. the thermal input of 150 kw is employed for the cofiring assessment. nh3 was inserted radially and concentrically from the centre of the coal injector burner, allowing direct mixing with the entering coal and air. this is also to lower the flow velocity of nh3, allowing for a longer residential mixing time with the coal+air mixture. the coal combustor facility has been built with a flue gas analyser, ktype thermocouples at combustor sections, and a single swirl burner. the air and fuel inlets, the main combustion section, the heat exchanger, and the cyclone are the main parts of the combustor. the facility also includes a high-temperature glass window for viewing the flame profile and temperature measurements. within the facility, the embedded combustor is configured in an l-shape to simulate a typical coal-fired boiler layout. this allows for the distinction between radiation, where the high-temperature combustor/flame zone occurs, and convection zones. the coal sample was transported using primary air (pa). another flow of air, known as secondary air (sa), acts as an oxidising component for the primary combustion process. throughout the test program, the pa flow rate was held constant at 9 nm3/hr, while the coal, sa, and nh3 volume flow rates were calculated on a calorific/thermal input basis and maintained at 150 kw. the combustor main body, or the longer section of the lshape, is made up of four tube sections that measure 3.3 m in length and have an internal diameter of 0.6 m each. each tube section contains one k-type thermocouple for temperature measurement. section 1 is upstream, and sections 2, 3, and 4 mn. rahman et al. /future energy february 2026| volume 05 | issue 01| pages 41-52 44 come after it. the downstream part of the combustor (the shorter length) is about 0.91 m long and has an internal diameter of 0.3 m. figure 1. tnb research's pulverised coal combustor facility the gas temperatures and compositions at the combustor outlet, comprising co2, so2, and nox, were constantly measured. one of the key aspects of ensuring the success of the testing is to ensure that the temperature from the combustion process within the combustor reaches a sufficiently high temperature condition and then maintains that temperature condition throughout the testing process so that it can mimic the actual temperature condition within the combustion zone of the actual boiler temperature condition. hence, to achieve this flame temperature, liquefied petroleum gas (lpg) was also fed at a certain range of mass flow rate, roughly 2 kg/hr, with manual flow rate tuning required intermittently to maintain the desired temperature. the presence of nh3 was also assessed in the flue gas via a detector tube to ensure that no slip of nh3 occurred. discharge of nh3 into the surrounding area is prohibited due to its toxicity [20]. for modelling validation purposes, out of all the testing cases that were done, one test case of pure coal firing and one test case of nh3 co-firing with a 60 cal.% proportion were selected. the asr (fraction of ofa) in both of these cases was around 20 %. the properties of the fuels utilised in experiments and numerical studies are shown in table 1. 3. numerical setup cfd techniques were used to simulate the combustion dynamics of pure coal firing and nh3 co-firing at various asrs and nh3 co-firing ratios. ansys fluent 19.0 was used, and the majority of the default cfd solvers and models were already embedded. yet, a new model establishment was needed to account for coal kinetics. the coal-firing simulation accounts for three key stages of the coal combustion process: devolatilization of coal, the subsequent conversion/reaction of char, and volatile reactions (from volatiles released during early devolatilization). the coal network model and the coal database from tnb research’s analytical fuel laboratory were used to determine the composition of volatiles and the corresponding rate constants for coal devolatilization. our prior studies [29-30] show the chemical reactions and coal combustion models employed in the current cfd assessments. the compressible and reacting navier-stokes (ns) equations were used in the numerical model. the pressure-based solver was used to solve the governing equations. turbulence was solved using the large eddy simulation (les) model [31]. wan [32] and sun [33] provide detailed information on the formulations utilized in the ns equations and les model for coal combustion. all of the equations were discretised using second-order upwind methods. the coal particle trajectories were traced via a lagrangian approach, which took into account turbulent dispersion factors in the coal trajectories, an important consideration due to the turbulence mixing of the coal that occurs in the combustor facility. another consideration is radiation, which was simulated using the discrete ordinate (do) approach. the radiation model setup includes discretisation, which includes an angular direction of 5 divisions, as well as polar and azimuthal orientations of 3 pixels each. the weighted-sum-of-gray-gases model (wsggm) [3] was used to predict gas emissivity. within the entire cfd frameworks, a different method known as a post-processing technique was employed to predict nox emissions from the simulated combustion processes of these fuels. the technique first allowed all combustion iterations to occur, during which all key modelling results were obtained, including temperature, major gas composition, and velocity distributions. then, reactions of hydrogen cyanide (hcn), nh3, thermal nox, and the eventual nox reduction by released/residual char were incorporated after these key iterations in the combustion computation had finished. having said that, it occurred during post-processing, not during the main processing. accordingly, nox-related species such as no, nh3, hcn, o, hydroxide (oh), and n were computed at this stage. turbulence, flow, other major gas compositions such as co2, oxygen, hydrogen, and carbon monoxide (co), as well as energy and radiation equations, were already solved during the main processing phase. figure 2 summarizes the calculation approaches for the kinetics of coal-nh3 combustion and the corresponding nox emissions. table 1. fuel properties proximate analysis, wt. %, ad., coal (tm-total moisture, vm-volatile matter, fc-fixed carbon, ac-ash content) ultimate analysis, wt. %, ad., coal (c-carbon, h-hydrogen, n-nitrogen, o-oxygen, ssulphur) gcvgross calorific value, ad., coal (kcal/kg) tm vm fc ac c h n o s coal a nh3 lpg 24 41 39 2 68.7 4.4 0.9 23.7 0.2 6,449 5,374 11,775 mn. rahman et al. /future energy february 2026| volume 05 | issue 01| pages 41-52 45 figure 2. calculation approaches for the coal-nh3 combustion kinetics and nox table 2 depicts the main conditions of simulated cases. this study included 16 cases. the same heat input utilised in the experiment was employed in all numerical cases. as previously stated, the co-firing ratio was calculated on a calorific/thermal input basis and set at 150 kw. the coal, nh3, and lpg flow rates are shown in table 2. all cases have an equivalence ratio (ø) of 1, indicating a stoichiometric condition. the combustion air (pa + sa) flow rate was determined using the coal/nh3/lpg ratio at a stoichiometric condition. the coal-to-nh3 co-firing ratio was varied, and nh3 co-firing was increased from 0 to 60 cal.% at various asrs. while the maximum asr for a coal-fired air-staged combustion system is typically no more than 40 % due to fuel burnout issues, the asr was set to 60 % for the current assessment to gain combustion insights for future asr tuning of coal-nh3 firing in actual coal-fired power plants. the overall ratio of coal+nh3 to lpg was kept constant to ensure a constant lpg flow rate, with the lpg ratio kept at 27 cal.% and the rest being coal+nh3 ratio (83 cal.%). the exact drawing of the combustor facility was used to generate the 3d model of its computational domain, which was later discretised mainly with hexahedral meshes using the assembly meshing method. a mesh-independent test was performed to ensure that the modelling results were not affected by the number of meshes. table 3 presents the properties of the meshes used in the computational domain. since the quality of meshes affects the spatial discretisation error, meshes were generated with both skewness and orthogonality taken into account to reflect overall mesh quality. orthogonality indicates how closely the angles between consecutive mesh faces approach the ideal mesh angle. the scale of orthogonal quality ranges from 0 to 1, with 1 indicating the highest quality [34]. skewness reflects how close the mesh is to an optimal equiangular mesh. heavily skewed meshes and their corresponding faces are unsuitable, as the governing equations are solved under the assumption that meshes are roughly equiangular. skewness also ranges from 0 to 1, where values close to zero have the slightest deviation from a normalised equiangular angle [34]. all meshes were optimised to achieve high quality across both mesh quality metrics, as shown in table 3. the predicted velocity and nox (case c12) at the coal combustor outlet as the mesh count changes are shown in figure 3. when the mesh number is increased from 2.412 million to 4.171 million, nox and velocity change little, with variations of less than 1 %. hence, 2.412 million meshes were selected for the coal combustor domain. figure 4 illustrates the mesh-independent model of the coal combustor’s computational (fluid) domain, as well as the boundary inlet details. since the upstream region (inlet) entails intricate reactions and mixing of nh3, coal, air, and lpg, a finer mesh was generated in that zone. table 2. primary conditions of simulated cases cases asr (%) coal + nh3 = 82 cal.% lpg (cal.%) coal (kg/hr) nh3 (kg/hr) lpg (kg/hr) ø coal (cal.%) nh3 (cal.%) c10 0 100 0 27 10.00 0.00 2.00 1 c12 20 80 20 8.00 2.40 c13 40 60 40 6.00 4.79 c14 60 40 60 4.00 7.19 n20 0 100 0 10.00 0.00 n22 20 80 20 8.00 2.40 n23 40 60 40 6.00 4.79 n24 60 40 60 4.00 7.19 n30 0 100 0 10.00 0.00 n32 20 80 20 8.00 2.40 n33 40 60 40 6.00 4.79 n34 60 40 60 4.00 7.19 n40 0 100 0 10.00 0.00 n42 20 80 20 8.00 2.40 n43 40 60 40 4.00 4.79 n44 60 40 60 4.00 7.19 mn. rahman et al. /future energy february 2026| volume 05 | issue 01| pages 41-52 46 table 3. mesh characteristics figure 3. predicted velocity and nox at varying mesh counts (location: combustor outlet) (a) (b) figure 4. coal combustor domain with (a) mesh model and (b) boundary inlets in plane aa view 4. results and discussion figures 5 and figure 6 display the validation results for nox levels and temperature profiles from experiments and numerical simulations. the numerical results from the simulated cases with varied asrs were thoroughly evaluated in subsequent sections based on predicted co2, so2, and nox. for validation, nox and temperature profile data from experimental coal firing and nh3 co-firing were compared to the numerical results from cases c12 and n42, respectively. 4.1 validation i: nox concentrations according to figure 5, nh3 co-firing results in higher nox concentrations at the combustor exit in both the simulation and the experiment than in coal combustion. based on the validation cases, the nox concentrations in the coal-firing and nh3-cofiring cases are 265 and 1,573 ppm, respectively (according to the experimental results). therefore, as the fraction of nh3 climbs to 60 cal.%, the nox concentration increases by around 494 %, roughly five times more than that produced by the pure coal combustion scenario. it is well known that decreasing prompt and thermal nox is always challenging in combustion involving carbon-dominant fuels. yet, it appears that adding nh3 enhances the likelihood of fuel-bound nitrogen to interact with oxygen in the air, as seen in the experimental results in figure 5. the synergistic effect of the fuel-bound nitrogen results in a considerable increase in the total nox emissions, which consists of fuel, prompt, and thermal nox. according to the numerical results, the established model appears to perform reasonably well when comparing the nox results from both the model and the testing, with discrepancies in nox concentrations between the two (for both coal firing and nh3 co-firing) being below 10 %. despite the model's ability to simulate a broadly similar increasing trend in nox emissions when nh3 co-firing is employed compared to the 100% coal firing case, there remains a slight variation between nox values simulated by the established model and the ones obtained from the actual tests. one explanation for the minor discrepancies is that the techniques for nox modelling used in this study, as previously mentioned, are based on a method that relies heavily on a set of mechanism that is semi-empirical in basis [3]. of course, in the actual kinetics process from these fuels’ combustion, the reaction pathways for the nox production are substantially more intricate, necessitating a greater computing cost to resolve the key chemical kinetics that are involved [12]. therefore, semi-empirical mechanisms, while excellent for parametric and/or scaling assessments, may not be fully sufficient to provide absolutely correct nox emissions. nonetheless, when compared to the testing data, the simulation results shown in figure 5 still showed a nox difference with testing results below 10 %. furthermore, quantitatively, it can be observed that the trend in the testing data matches the trend in nox emissions simulated by the established numerical model. hence, adequate validation can be reasonably claimed as the model can model nox emissions with reliable accuracy for both pure coal firing and nh3 cofiring. safety-wise, it is important to note that the slip of nh3 was not detected at the outlet of the combustor facility throughout the tests, which can be safely assumed to mean that there are no safety issues related to toxic nh3 slip being detected. figure 5. nox results from numerical and experimental works (asr 20 %) average element size (mm) meshes, 106 orthogonal quality skewness 300 0.069 0.916 0.094 200 0.081 0.936 0.079 100 0.120 0.971 0.051 50 0.162 0.990 0.024 30 0.273 0.991 0.041 20 0.530 0.993 0.037 15 0.958 0.992 0.025 13 1.425 0.990 0.016 10 2.412 0.995 0.014 8 4.171 0.996 0.019 mn. rahman et al. /future energy february 2026| volume 05 | issue 01| pages 41-52 47 it can be reasonably postulated that this is mainly because of the direction in which the nh3 was injected into the combustor, where it is injected radially and concentrically from the coal injector’s centre at the burner inlet. this allows for a higher residence time for mixing with incoming combustion air and coal, hence reducing the jet velocity of nh3 entering the combustor. with the combined effects of these higher mixing rates, the potential for nh3 to escape from the recirculation zone is lower as well (as supported by a previous study [7]). this recirculation zone is important for flame stability in the combustor. hence, the directional injection factor of nh3 is potentially the key reason for the inexistence of nh3 slip. 4.2 validation ii: temperature profiles as shown in figure 6, the one-point temperature in each tube section of the coal combustor testing facility was measured using thermocouples. the testing data showed that the temperature difference (average) between the nh3 cofiring and 100% coal firing cases varied between 0.9 and 6.1 %. the average difference in numerical data between the two cases ranged from 0.4% to 4.9%. due to the constant thermal input, differences in temperature were almost negligible in both cases: 100% coal firing and nh3 co-firing. of the four tube sections of the combustor, section 2 had the highest temperature (testing data), and it also had the highest temperature in the modelling assessments. the ofa enrichment between the two middle sections, sections 2 and 3, which serves as a thermal nox mitigation method and also stops the flame front from elongating to reach between sections 3 and 4, resulted in a significant temperature drop after section 2. from the experimental data, the maximum temperatures are 1,149 °c for 100% coal firing and 1,121 °c for nh3 co-firing, indicating a measured peak temperature difference of 2.4%. the numerical model predicts maximum temperatures of 1,222 and 1,184 °c for the 100% coal-firing and nh3 co-firing cases, respectively. therefore, there is a 3% difference in peak temperature between these two fuel scenarios, according to modelling results. peak temperature differences between testing and numerical results are 5.9 and 5.3 % for 100% coal and nh3 co-firing cases, respectively. a possible cause of these minor differences is the calculation of the turbulence-chemistry model in the current cfd frameworks. it is important to note that the turbulencecombustion model used in the current study provides one of the best possible balances between the efficiency and accuracy of reacting flow cfd modelling. however, it remains a known fact that the les algorithm filters the comparatively small-sized eddies to be modelled purely via the sub-grid formulation [31]. as a result, the current cfd framework does not fully capture the overall range of length scales. this could result in minor regional differences in flame front dynamics and corresponding temperatures. still, the peak temperature difference between experimental and numerical results is less than 6 %. qualitatively, the numerical predictions for the temperature profile positioning and trend nearly match those measured from test data. therefore, the validation can be considered satisfactory, and the model can reliably predict temperature behaviour in both nh3 co-firing and 100% coal-firing cases. 4.3 impacts on co2 emission co2 compositions in flue gas changed dramatically when nh3 was co-fired in the coal combustor, as illustrated in figure 7. in nh3 co-firing situations, the fraction of co2 in flue gas was much lower than in the coal-fired base case. as anticipated, the co2 fraction decreased as the nh3 co-firing ratio increased. when the nh3 co-firing ratio reached 60 cal.%, the co2 emission dropped to 7.8 % (for 0 % asr), equal to a 41 % reduction in co2 emissions as compared to the coalfired base scenario. co2 emissions fell to 7.9, 8.0, and 8.1 % at asrs of 20, 40, and 60 %, respectively (co-firing ratio 60 cal.%). this equates to a reduction in co2 emissions of 41 to 42 % when compared to the coal-fired base scenario. the numerical results show that the co2 emission ranges for coal firing, 20, 40, and 60 cal.% nh3 cases are 13.2 to 14.0 %, 11.2 to 12.1 %, 9.7 to 10.5 %, and 7.8 to 8.2 %, respectively. as a result, increasing the percentage of nh3 in the fuel to 20, 40, and 60 cal.% reduces co2 emissions by roughly 13.1, 25.7, and 41.7 %, respectively, when compared to the coal-fired case. since nh3 is a carbon-free fuel, replacing coal with nh3 reduces co2 emissions directly, with the decline ratio roughly equalling the fuel replacement ratio on a heating value basis. the percentage difference between the lowest and highest co2 emissions when the asrs were varied is less than 10% in all cases shown in figure 7. hence, the difference in asr has no substantial effect on co2 emissions. while greater asrs will result in a considerable increase in uc from the main combustion zone due to the lack of oxygen caused by reduced airflow, the remaining airflow was subsequently injected into the ofa zone to complete the oxidation of uc to generate co2. since the combustion temperature has a relatively lesser effect on co2 production than thermal nox [35], the considerably lower temperature of injected ofa could still complete the oxidation of uc to generate co2. hence, despite the obvious co2 decrement as nh3 increased, the main finding from this assessment is that the staging air element has literally no impact on co2 emissions during coalnh3 combustion. figure 6. temperature results from numerical and experimental works (cases c12 and n42) figure 7. co2 data at varying nh3 ratios and asrs mn. rahman et al. /future energy february 2026| volume 05 | issue 01| pages 41-52 48 4.4 impacts on so2 emission as shown in figure 8, the so2 concentrations in flue gas altered significantly when nh3 was co-fired in the coal combustor. the concentration of so2 in flue gas was substantially lower in nh3 co-firing scenarios than in the coalfired base case. as the nh3 co-firing ratio increased, the so2 concentration decreased. when the nh3 co-firing ratio reached 60 cal.%, so2 emissions plummeted to 12 ppm (for 0 % asr), representing a 75 % reduction in so2 emissions as opposed to the coal-fired base case. when the nh3 co-firing ratio reached 60 cal.%, so2 emissions dropped to 13.0, 13.1, and 13.2 ppm at asrs of 20, 40, and 60 %, respectively. when compared to the coal-fired base scenario, this translates to a 71 to 72 % reduction in so2 emissions. the numerical results show that the so2 emission ranges for coal firing, 20, 40, and 60 cal.% nh3 cases are 45.5 to 47.0 ppm, 34.1 to 36.7 ppm, 23.0 to 25.1 ppm, and 12.0 to 13.2 ppm, respectively. hence, raising the amount of nh3 in the fuel to 20, 40, and 60 cal.% reduces so2 emissions by approximately 24.1, 47.9, and 72.5 %, respectively, as compared to the coal-fired case. because this assessment was conducted at a pilot coal combustor testing facility, the injected fuel flow rates are significantly lower than the actual fuel flow rates in coal-fired power plants. as a result, the predicted so2 concentration values in figure 8 are very low in comparison to the actual so2 emissions from industrial coal combustion systems such as coal-fired power plants. moreover, it is crucial to note that the sulphur concentration of the sub-bituminous coal utilised in the current assessment (table 1) is lower than the sulphur content of common sub-bituminous coals. hence, the so2 concentration in the coal-fired base scenario is already substantially lower. nonetheless, for parametric analysis, the percentage reduction of so2 when nh3 was co-fired is one of the most relevant research outcomes. nh3 is not only a carbon-free fuel, but it also contains no sulphur. as a result, increasing the amount of nh3 has resulted in a significant decrease in so2 concentrations due to a lack of sulphur as a portion of coal is replaced by nh3. the percentage disparity in so2 emissions between the lowest and highest asrs is likewise less than 10 % in all cases shown in figure 8. as a result, the variation in asr has no discernible influence on so2 emissions. however, notable discoveries can be found in the coal-fired base case, where no asr was used. it was predicted that a slightly higher so2 concentration would occur in this case. the rise in so2 emissions might be explained by the leaner fuel condition (main combustion zone) in the coal firing case, where no asr was used. with greater oxygen available in the main combustion zone, it reduces the likelihood of other sulphurous substances such as hydrogen sulphide (h2s), carbonyl sulphide (cos), and carbon disulphide (cs2) being created, as most of the available oxygen oxidises to become so2. this is also corroborated by prior findings that a fuel-rich region will lead to a reduction in so2 emissions from coal combustion [35]. as a result, for the coal firing situations depicted in figure 8, the adoption of an asr is predicted to result in lower so2 emissions than the no staging ratio case due to the fuel-rich condition in the primary combustion zone as oxygen availability decreases. furthermore, during coal devolatilization, a portion of sulphur is liberated from the coal as one of the volatiles, and the remainder of sulphur remains within the char (residual of coal after devolatilization) [35]. as a result, sulphur retention in char/uc is suggested to be another explanation for slightly reduced so2 in the asr cases. this is because, in the asr cases, the fuel-rich zone occurs within the main combustion zone, so the devolatilization intensity decreases, lowering the char combustion intensity, which is mostly affected by volatiles combustion. hence, in a fuel-rich environment of coal firing, the sulphur in char/uc has the tendency to release a lesser amount of sulphur than in a fuel-lean environment. figure 8. so2 data at varying nh3 ratios and asrs 4.5 impacts on nox emission the nox concentrations in flue gas changed greatly when nh3 was co-fired in the coal combustor, as shown in figure 9. nox concentrations in flue gas were notably higher in nh3 cofiring scenarios than in the coal-fired baseline case. the nox concentration grew as the nh3 co-firing ratio increased. when the nh3 co-firing ratio reached 60 cal.%, nox emissions soared to 1,918 ppm (for 0 % asr), reflecting a staggering 632.06 % increase in nox emissions, approximately six times that of the coal-fired base case. the numerical findings show that the nox emission ranges for coal firing, 20, 40, and 60 cal.% nh3 cases are 250 to 282 ppm, 492 to 895 ppm, 685 to 1,460 ppm, and 1221 to 1918 ppm, respectively. therefore, compared to the coalfired scenario, increasing the amount of nh3 in the fuel to 20, 40, and 60 cal. % increases nox emissions by an average of 146.5, 311.1, and 480.2 %, respectively. however, as the nh3 co-firing ratio reached 60 cal.%, nox emissions reduced to 1,670 and 1,221 ppm for asrs of 20 and 40 %, respectively. yet, as soon as the staging ratio for the aforesaid nh3 co-firing ratio hit 60 %, the nox emission began to increase. the nox reduction trend is also visible in 20 and 40 cal.% of nh3 co-firing cases. nox emissions were reduced to 672, 532, and 492 ppm in nh3 20 cal.% co-firing cases with asr increases of 20, 40, and 60 %, respectively. with an increase in asr of 20, 40, and 60 % for nh3 40 cal.% co-firing, nox emissions were lowered to 1,383, 793, and 685 ppm, respectively. furthermore, with an asr of 60 %, the nox emission from the 20 and 40 cal.% nh3 co-firing approaches the nox emission from the coal firing base case. using a 60 % asr, the percentage difference between the coal firing base case and nh3 co-firing cases was reduced to 74.5 (20 cal.% nh3) and 142.9 % (40 cal.% nh3). these percentage differences are much lower than those obtained when no air staging was used, which are 241.6 (40 cal.% nh3), 457.3 (40 cal.% nh3), and 632.1 % (60 cal.% nh3). therefore, it was expected that the use of air staging would greatly aid in reducing nox when nh3 was co-fired. mn. rahman et al. /future energy february 2026| volume 05 | issue 01| pages 41-52 49 figure 9. nox data at varying nh3 ratios and asrs adopting a 60 % asr severely curtailed the airflow for the main combustion zone, resulting in an extremely rich in fuel state with a large deficit in oxygen concentration. as a result, it significantly reduces the oxidation intensity with the nitrogen in fuel, resulting in a reduction in fuel nox. furthermore, the very fuel-rich main combustion zone reduces temperature, which reduces the creation of thermal nox [36]. the remaining injected airflow (60 %) is supplied by the ofa technology above the main combustion zone via a separate injector situated above the said zone. the firing process is effectively terminated in this ofa zone. consequently, the relatively low temperature in the ofa injection zone helps to further reduce the production of thermal nox. furthermore, the injected sa surrounded the core combustion zone. as a result, a relatively low temperature in the oxygen-enriched afterburning zone provides a further reduction in the generation of thermal nox. this is a common approach used in coal-fired boiler low nox burners [36]. previous kinetic studies have also supported the aforementioned findings, revealing that for nh3 co-firing with coal, thermal nox and fuel nox are the dominant nox types produced [4, 12]. thus, it can be observed that limiting oxygen availability during the crucial stage of coal devolatilization is the most efficient way to reduce nox formation from the nh3 co-firing. the coal devolatilization is hypothesised to occur primarily in the primary combustion zone due to its relatively short processes as opposed to the char oxidation [30, 37] since the combustion zone in the current coal combustor is relatively smaller than that in the actual coal-fired boiler. later on in the operation, more air (oxygen) can be introduced by the ofa technology to finish char reactions, lower uc, and maintain high combustion efficiency [22]. however, as the asr surpasses 40 %, the nox reduction gradient begins to decrease for 20 and 40 cal.% nh3 but begins to climb for 60 cal.% nh3. previous research has also indicated that when the asr crosses a particular quantity, nox levels begin to rise [38]. this is because when the asr exceeds a particular threshold value, a large proportion of nox production is repressed at the primary combustion zone, where the air ratio is small. yet, a significant amount of uc stays in the said position and is burned at the ofa zone to complete its oxidation. since a substantial quantity of uc is burned in the ofa zone, the combustion intensity increases, causing the nitrogen content in the fuel to oxidize and produce nox in the ofa zone. in other words, while the main combustion zone generates the highest temperature along the coal combustor, the high uc content at the ofa zone generates another peak combustion temperature, commonly known as delayed combustion, resulting in nitrogen oxidation in fuel at a high temperature in the ofa zone. figure 10 depicts temperature contours within the coal combustor model (excluding the convection zone – shorter length region) at nh3 60 cal.% at various asrs. there is a completely visible second temperature peak at the ofa zone, especially at 60 % asr. hence, it promotes the development of thermal nox at the ofa zone. the temperature distribution near the outlet, where the temperature is higher as opposed to lower/no asrs, can also indicate delayed combustion at high asrs. figure 10 also shows that the flame temperature is higher in the absence of asr than in its presence, indicating that more oxygen is available to achieve a higher combustion temperature. the flame temperature has been observed to decrease as asr increases due to a reduction in available oxygen in the main firing area. figure 10. temperature contours (nh3 60 cal. %) at (a) 0 %, (b) 20 %, (c) 40 %, and (d) 60 % asrs in figure 9, the degree of asr has a smaller effect on nox emissions in the coal-firing base scenario than in the nh3 cofiring scenarios. the predicted nox levels decreased slightly, from 262 to 250 ppm, as the asr increased from 0 to 20 % in the coal-fired base scenario. however, when the staging ratio reaches 40% and 60 %, there is a slight increase in nox in the coal-firing base scenario. the increase, however, is not as significant as in the nh3 60 cal.% case. as previously stated, devolatilization occurred primarily in the main combustion zone. because the char reaction has a faster ignition rate than coal, the vm of coal and nh3 are assumed to burn in the primary firing zone [32], resulting in a slight increase when asr 40 and 60 % were implemented in the coal firing base scenario. the amount of these components in nh3 co-firing, however, is greater than in coal firing. therefore, it is postulated that when nh3 co-firing reaches 60 cal.%, along with a high asr (60 %), the air-to-vm ratio in the main combustion zone is lower than in the coal-only case. hence, a substantially larger amount of char/uc remains, which is burned at the ofa position, causing thermal nox to be much higher than in the coal firing case. mn. rahman et al. /future energy february 2026| volume 05 | issue 01| pages 41-52 50 furthermore, these findings were supported by a comprehensive kinetics reactor network 0d modelling by ishihara [7]. despite the fact that their analysis ignored the impacts of fluid dynamics and 3d characteristics, their kinetics pathway showed that for a relatively high nh3 cofiring ratio, complete nh3 reactions cannot be achieved in the primary firing area. as a result, it demonstrates the prospect of nitrogen-related radicals being combusted further upstream in the coal combustor region, such as the ofa zone with significant oxygen availability, as predicted by current numerical assessments. the devolatilization, volatiles reaction, and nh3 reaction are more prominent in the combustion zone than the char/uc reactions due to the significant amount of vm and nh3 in 60 cal.% nh3 co-firing. the aforesaid hypothesis has also been supported by prior research, which indicated that nh3 co-firing, both in fuel-rich and fuel-lean conditions, promoted coal devolatilization and volatile release [8]. furthermore, with the use of subbituminous coal in the current study, which is known to have a higher vm than common bituminous coals [25], the devolatilization and volatiles reactions will dominate even more. therefore, the current findings support prior 0d kinetic modelling studies that revealed that nh3 reactions inhibit char oxidation [7]. 5. conclusion in the context of reducing co2 emissions from pulverised coal-fired boilers, the paper studied the potential of nh3 to be utilised as a carbon-free substitute for coal, at least partially, to aid in the progressive phase-out of coal. in this research, the co-firing of nh3 with sub-bituminous coal was numerically studied via a detailed les assessment at various asrs in a small-scale coal-fired testing combustor. in-depth insight into predicted emissions, including co2, so2, and nox, was successfully obtained, and an appropriate asr for a number of nh3 co-firing percentages was discovered to enable the reduction of such emissions. the prediction accuracy of the model’s results was first evaluated by validating it with actual testing data from tnb research’s coal combustor testing facility, which revealed a below 10 % difference in nox emissions and temperature results for both 100% coal firing and nh3 co-firing cases. as a result, the validation can be deemed satisfactory, and the model can forecast the expected emissions with reliable accuracy for both these cases. all in all, the research has demonstrated that coal+nh3 co-firing can produce low co2, so2, and nox emissions as opposed to pure coal-firing with proper asr tuning. as the variation of asrs was studied, important findings regarding emission characteristics were discovered, where the synergistic effect of nh3 co-firing with coal plays a significant part in the selection of asr to be used at a specific nh3 co-firing case. the increase in nox when the staging ratio reached 60 % revealed that devolatilization occurred primarily in the main combustion zone due to the smaller firing space compared to actual coal-fired power plants, as well as the shorter devolatilization duration compared to char reaction. as a result, reaction, vm of coal, and nh3 are assumed to be what burns at the primary firing zone, with the amount of these components in nh3 co-firing being greater than in a pure coal firing scenario. this causes considerable uc oxidation in the ofa zone, which has high oxygen availability, and results in a relatively higher combustion temperature in the ofa zone. these findings contribute to vital information for combustion tuning in actual coal-fired power plants to achieve nh3+coal co-co-firing and reduce co2 emissions. the numerical results also confirmed that nh3 can be used as an alternative fuel to reduce co2 emissions in actual coal-fired power boilers. the air staging method has been shown to provide reduced co2, so2, and nox emissions when the asr is properly tuned to ensure acceptable staging combustion within the furnace. as a result, existing coal-fired power plant air staging technology can be utilised to provide proper nh3 co-firing while attaining low nox emissions. this is critical information for retrofit setups because it is possible that the only adjustment required is the addition of a new nh3 burner. however, in the current work, the combustion zone is simplified, and the effects of multiple burners (which actual coal-fired boilers have), such as flame interplay, are not fully examined. plus, the size of the coal combustor employed is smaller than that of a typical coal-fired utility boiler. when several burners are used, as in commercial boilers, it is expected that estimating the amount of emissions will become more complex due to the presence of additional flame interaction and/or the stronger influence of mixing residence time. further research can be conducted to investigate the impact of multiple burners and different nh3 burner designs on emission and combustion characteristics. it is also expected that a higher nh3 co-firing ratio will be required in the future to accomplish further co2 emission reductions. hence, future research can include an increase in the nh3 cofiring ratio. ethical issue the authors are aware of and comply with best practices in publication ethics, specifically concerning authorship (avoidance of guest authorship), dual submission, manipulation of figures, competing interests, and compliance with policies on research ethics. the authors adhere to publication requirements that the submitted work is original and has not been published elsewhere in any language. data availability statement the manuscript contains all the data. however, more data will be available upon request from the corresponding author. conflict of 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commons attribution (cc by) license (https://creativecommons.org/licenses/by/4.0/). abbreviations cfd computational fluid dynamics cop26 un's climate change conference igcc integrated gasification combined cycle ccs carbon capture and storage uc unburned carbon asr air staging ratio tm total moisture fc fixed carbon gcv gross calorific value h hydrogen element o oxygen element ofa over-fire air pa primary air do discrete ordinate hcn hydrogen cyanide co carbon monoxide h2s hydrogen sulphide cs2 carbon disulphide nox nitrogen oxides nh3 ammonia so2 sulphur dioxide co2 carbon dioxide sa secondary air lpg liquefied petroleum gas vm volatile matter ac ash content c carbon element n nitrogen element s sulphur element ns navier–stokes les large eddy simulation wsggm weighted-sum-of-gray-gases model oh hydroxide ad air-dried basis cos carbonyl sulphide https://creativecommons.org/licenses/by/4.0/ ahad bin azad et al. /future energy november 2025| volume 04 | issue 04| pages 09-21 9 review an extensive examination of the potential of waste cooking oil biodiesel in bangladesh ahad bin azad, priyam chakraborty, fahim hossain, tahmidur rahman siam, nure alam siddiki* department of mechanical engineering, chittagong university of engineering & technology, bangladesh a r t i c l e i n f o article history: received 11 june 2025 received in revised form 20 july 2025 accepted 03 september 2025 keywords: biodiesel, sustainability, emission, esterification *corresponding author email address: nurealamsiddiki456@gmail.com doi: 10.55670/fpll.fuen.4.4.2 a b s t r a c t waste cooking oil (wco) has gained attention as a valuable resource for biodiesel production due to its availability and potential for waste management. this study examines the viability of wco as a biodiesel feedstock in bangladesh, addressing the increasing demand for sustainable energy alternatives. this paper explores multiple facets of wco biodiesel, encompassing feedstock types, pretreatment techniques, and the production process. the study analyzes the physicochemical properties, emission characteristics, performance, and combustion behavior of biodiesel derived from wco. the findings indicate that wco biodiesel presents considerable potential as an economically viable and environmentally sustainable alternative fuel for diesel engines in bangladesh. challenges in wco collection, commercialization, and public awareness must be addressed to realize its full potential. the paper concludes by proposing avenues for further research in bangladesh, emphasizing the enhancement of collection systems, the refinement of policy frameworks, and the optimization of conversion technologies to facilitate the broader adoption of wco biodiesel. 1. introduction the rapid industrialization and urbanization that have occurred since the mid-20th century have driven the global surge in diesel production, providing the backbone for transportation, energy generation, and industrial operations [1]. although diesel has played a crucial role as a fuel source, its associated environmental and economic issues, such as greenhouse gas emissions, pollution, and resource depletion, have ignited a global quest for sustainable alternatives. carbon dioxide (co₂) is the primary contributor to global warming, increasing from roughly 3.34 million tons in 1970 to around 124.79 million tons in 2023. in 2022, global energyrelated co₂ emissions totaled approximately 36.8 gigatons, representing a 0.9% increase from the previous year. in 2022, the transportation sector contributed nearly eight gigatons of co₂ emissions, representing approximately 23% of global energy-related co₂ emissions [2]. the ongoing dependence on fossil fuels, particularly diesel, has intensified environmental degradation through air pollution and climate change, while also raising concerns about resource depletion and energy security. crude oil reserves are expected to be depleted by 2052, given the current annual consumption rate of 4 billion tons [3]. this projection indicates a looming energy crisis if alternative solutions are not adopted promptly. bangladesh's energy sector is heavily reliant on fossil fuels, with more than 85% of electricity generation coming from conventional sources, predominantly natural gas, which accounts for over 50% of annual electricity production [4]. even with a rise in electricity generation to support industrial expansion, the nation faces challenges stemming from dwindling fossil fuel reserves and insufficient oil resources, necessitating expensive imports [5]. the rising global fuel prices, geopolitical conflicts, and supply chain disruptions further strain bangladesh’s energy security, prompting efforts to explore alternative energy solutions. additionally, the country’s rapid industrialization and urbanization have led to a surge in co₂ emissions, with fossil fuel combustion contributing significantly to environmental degradation. bangladesh’s per capita co₂ emissions have risen from approximately 0 tons in 1946 to 0.7 tons in 2023 [6]. in 2021, fuel combustion resulted in the emission of 17.17 million tons of co₂, positioning bangladesh as the 13th highest emitter in the asia-pacific region in terms of carbon emissions [7]. despite accounting for only 0.09% of global carbon emissions, bangladesh is significantly vulnerable to climate change, ranking eighth on the 2021 global climate risk index [8]. the government has pledged to reduce emissions by 21.8% by 2030, in line with the paris agreement, underscoring the urgent need for a transition to renewable energy sources [9]. the currently available number of renewables, particularly solar energy, hovers between 2-4%, highlighting the necessity for legislative reforms, financial incentives, and technological improvements to minimize reliance on fossil fuels and foster future energy open access journal https://doi.org/10.55670/fpll.fuen.4.4.2 november 2025| volume 04 | issue 04 | pages 09-21 journal homepage: https://fupubco.com/fuen issn 2832-0328 mailto:nurealamsiddiki456@gmail.com https://doi.org/10.55670/fpll.fuen.4.4.2 https://fupubco.com/fuen ahad bin azad et al. /future energy november 2025| volume 04 | issue 04| pages 09-21 10 sustainable energy alternatives [10]. facing the threat of declining fossil fuel reserves and potential energy crises, nations worldwide are increasingly exploring a variety of alternative energy sources [11]. bioethanol, biomethanol, biobutanol, biogas, and biodiesel have emerged as promising alternatives to fossil fuels, offering renewable and environmentally friendly energy sources. bioethanol, sourced from agricultural feedstocks, demonstrates energy balance and enhances combustion efficiency; however, it is notably corrosive and necessitates modifications to engines [12]. biomethanol, recognized for its biodegradability and compatibility with the current petrol distribution infrastructure, encounters obstacles stemming from its toxicity and the necessity for elevated temperature conditions [13]. biobutanol, a multifaceted biofuel, can be utilized directly in gasoline engines without necessitating modifications. it offers a high energy content; however, its production is challenging, and it has a reduced heating value compared to gasoline [14]. biogas, produced from plant and animal waste, is a cost-effective and sustainable fuel that reduces greenhouse gas emissions, yet its high impurity content necessitates additional refining processes [15]. biodiesel, currently the most widely recognized alternative, is recognized for its low sulfur emissions, non-toxic characteristics, and ability to reduce particulate matter in diesel engines. nonetheless, it presents certain challenges, such as heightened viscosity, which affects the efficiency of fuel injection. despite showing great promise in addressing energy security and sustainability challenges, their inherent limitations necessitate further technological advancements to enable large-scale adoption. biodiesel production continues to grow worldwide, with europe leading both output (34%) and consumption (35%). however, raw feedstock costs—constituting up to 80% of total production expenses—remain a significant barrier [16]. since approximately 95% of the world’s biodiesel relies on edible oils, the resulting increase in raw material prices has made biodiesel 1.5 to 2 times more expensive than diesel [17]. this escalation hinders commercial viability and spurs interest in alternative feedstocks such as non-edible oils and waste cooking oil (wco), which can potentially lower production costs by up to 70% [18]. in bangladesh, where an estimated 1-1.2 lakh tons of wco is generated annually, only a small fraction is properly managed; the majority is blackmarketed or reused in restaurants, contrary to the country’s food safety act [19]. such practices pose serious health and environmental risks, yet the abundance of wco presents a cost-effective option for biodiesel production, especially amid rising edible oil prices [20]. recent efforts by local and international companies to collect and convert wco into biodiesel underscore its promise as an advanced biofuel feedstock, highlighting the potential for both environmental and economic benefits. hence, the focus of this paper is to examine wco-based biodiesel within the bangladeshi context and explore strategies for its sustainable large-scale implementation. 2. biodiesel and its feedstock biodiesel is a renewable alternative fuel produced through transesterification, where oils or fats react with alcohol (usually methanol) in the presence of a catalyst to form fatty acid methyl esters (fame), which are biodiesel [21]. the advantages of biodiesel include its biodegradability, non-explosiveness, non-flammability, and non-toxicity, alongside the crucial benefit of being renewable [22]. the feedstocks for biodiesel can be categorized into four generations, shown in figure 1, with each offering distinct benefits and challenges. figure 1. generation of biodiesel feedstock 2.1 first-generation feedstocks (1g) first-generation feedstocks include edible oils like palm oil, soybean oil, sunflower oil, and rapeseed oil, which are commonly used for biodiesel production due to their high oil content and availability [23]. however, their use has led to the "food vs. fuel" debate, as they compete with food crops, raising the cost of biodiesel production. 2.2 second-generation feedstock (2g) second-generation feedstocks, such as jatropha, jojoba, neem, and waste cooking oil (wco) are derived from nonedible oils that do not compete with food production [24]. while these oils help mitigate the food vs. fuel issue, their cultivation still requires significant land, which could otherwise be used for food crops [25]. however, some nonedible oils, like jatropha, can be grown on marginal lands, reducing the pressure on arable land [26]. wco, in particular, reduces biodiesel production costs by up to 70–80% and prevents environmental pollution [27]. however, wco requires pretreatment due to its high impurity content [28]. 2.3 third-generation feedstock (3g) third-generation feedstocks, such as microalgae and animal fats, offer significant potential for biodiesel production due to their low cost and availability [29]. microalgae, with high lipid content and rapid growth, also hold promise but face challenges in large-scale cultivation due to high nutrient demands and land requirements. 2.4 fourth-generation feedstock (4g) fourth-generation feedstocks, such as electro-fuels and solar fuels, are an emerging area of research in biodiesel production [30]. these feedstocks offer the potential for high lipid content and superior co2 absorption, contributing to sustainability. however, they are still in the early stages of development, and the main challenge lies in making their production economically viable at a large scale [31]. 3. waste cooking oil (wco) production waste cooking oil (wco) is produced from repeatedly used edible oils, which increases impurities such as free fatty acids (ffas) and water, necessitating pretreatment before biodiesel production [32]. globally, large quantities of wco— running into millions of tons—underscore its potential as a cheap, non-food feedstock [33]. in bangladesh, annual edible oil consumption exceeds 20 lakh tons, with discarded oil often ahad bin azad et al. /future energy november 2025| volume 04 | issue 04| pages 09-21 11 reused or disposed of improperly, posing health and environmental threats [34]. converting wco into biodiesel can significantly cut production costs, avert reintroduction into the food chain, and reduce waste. companies like muenzer bangla exemplify this potential by collecting wco from restaurants and transforming it into cleaner energy, marking a promising path toward sustainable fuel solutions in bangladesh [35]. 4. pretreatment of wco removing impurities, free fatty acids (ffa), and water from waste cooking oil (wco) is crucial for efficient biodiesel production [36]. high ffa can cause saponification, lowering biodiesel yield and increasing catalyst consumption. common techniques include acid esterification with methanol and sulfuric acid, neutralization with alkalis, and heating above 100 °c or vacuum distillation to eliminate water. additionally, filtration and centrifugation help remove solids and phospholipids. 5. biodiesel production from wco biodiesel can be produced from waste cooking oil (wco) using several distinct processes, including gasification, catalytic pyrolysis, hydrocracking [37], and fast pyrolysis [38]. having said that, transesterification is the most widely used and practical method due to its effectiveness and low cost. one of the key benefits of biodiesel is its ability to be blended with conventional diesel in different ratios, such as b5 (5% biodiesel and 95% diesel) or b20 (20% biodiesel and 80% diesel), making it a viable alternative for fueling internal combustion engines [39]. biodiesel has approximately 9% less energy content than conventional diesel [40]; yet, it is frequently preferred for its enhanced combustion characteristics and significantly reduced emissions, making it an ecologically sustainable option. 5.1 transesterification the transesterification, also known as methanolysis, process involves reacting triglycerides (fats and oils) with alcohol (usually methanol) in the presence of a catalyst to produce biodiesel (fatty acid methyl esters, fames) and glycerol as by-products [41]. figure 3. general transesterification reaction this method is preferred for large-scale biodiesel production because it requires minimal modifications to diesel engines and integrates easily into existing industrial systems. the process occurs in three consecutive reversible reactions: triglycerides are first converted to diglycerides, then to monoglycerides, and finally to glycerol, with each step producing an ester. this results in three ester molecules from one triglyceride [42]. when methanol is used, the product is methyl esters (fames), while ethanol produces ethyl esters (faees). the reaction is typically catalyzed by inorganic catalysts like koh or naoh, which accelerate the process and improve the yield. the general chemical equation for this reaction is shown in figure 2 and figure 3. figure 2. flow diagram of biodiesel production from wco ahad bin azad et al. /future energy november 2025| volume 04 | issue 04| pages 09-21 12 6. physicochemical properties of wco wco–based biodiesel exhibits several key physicochemical properties that impact its suitability for compression ignition engines. these properties are influenced by free fatty acid content, production methods (e.g., transesterification conditions), and purification steps [43]. below is a brief overview of major properties—namely, kinematic viscosity, density, cetane number, flash point, cloud point, pour point, acid value, and higher heating value—as gleaned from the literature. table 1 presents a comparative analysis of the physicochemical properties of wco, as reported by various authors. 6.1 density density plays a pivotal role in injection mass flow. wco biodiesel generally has a higher density than petro-diesel. this is attributed to the presence of saturated and unsaturated fatty acids [44]. overly high densities (e.g., >880 kg/m³) may increase brake-specific fuel consumption, while blending with diesel or removing impurities can mitigate this issue [45]. 6.2 kinematic viscosity kinematic viscosity critically affects fuel injection, spray atomization, and overall combustion efficiency. wco biodiesel often displays higher viscosity than mineral diesel [32]. if viscosity is excessive, larger fuel droplets form, leading to incomplete combustion and potential deposit buildup. however, viscosity that is too low can reduce lubricity and harm the injection system. most studies report that properly produced wco biodiesel falls between 4–5 mm²/s at 40 °c, in line with astm d445 standards [45]. en iso 3104 (3.5 mm²/s to 5.0 mm²/s) and astm d445 (1.9 mm²/s to 6.0 mm²/s) are employed to assess the viscosity of biodiesel [46]. 6.3 pour point pour point is the lowest temperature at which the fuel remains pourable. high pour points are common in wco biodiesel, especially if the source oil contains elevated saturated fat content (e.g., palm-derived wco) [47]. this property can pose challenges in colder climates [48]. typical improvement strategies include blending with lowerviscosity fuels or adding pour-point depressants [49]. 6.4 flash point flash point indicates the temperature at which fuel vapors ignite [50]. wco biodiesel typically exhibits a higher flash point than diesel [51], enhancing transport and storage safety. yet residual alcohol from transesterification can reduce flash points below the astm minimum (100 °c), emphasizing the need for thorough processing [52]. 6.5 cloud point the cloud point is the temperature at which wax crystals emerge, posing potential blockages in filters or injectors under cold conditions [45]. due to the presence of saturated fatty acids, many wco biodiesels do not meet the astmrecommended sub-zero cloud point [44]. 6.6 iodine number iodine number signifies the degree of unsaturation in the fatty acid chains constituting biodiesel. a higher iodine number implies more double bonds, which can influence oxidative stability and cold-flow behavior [53]. wco feedstocks that contain greater amounts of unsaturated fatty acids tend to produce biodiesel with elevated iodine numbers [54]. 6.7 cetane number the cetane number measures ignition quality; higher values translate into shorter ignition delays and improved cold starting [55]. most wco biodiesel samples exhibit cetane numbers of≥47 [44], which meet the astm d6751 guidelines. 6.8 higher heating value (hhv) the higher heating value represents the total energy content of the fuel. wco biodiesel typically shows an hhv around 39 mj/kg, slightly lower than petroleum diesel (~43 mj/kg) [56]. consequently, engines may consume a marginally greater volume of wco biodiesel for the same power output, though the difference is often acceptable for most ci applications. 6.9 acid value acid value reflects free fatty acids and oxidation byproducts [57]. exceeding ~0.5 mg koh/g can promote corrosive effects and fuel instability [58]. pre-treatment steps such as esterification and subsequent purification are therefore crucial to bring acid values within astm limits [59]. 7. types of catalysts catalysts are essential for enhancing the transesterification process, playing a key role in determining the efficiency, cost, and reaction time of biodiesel production. based on their physical state and chemical properties, these catalysts are broadly categorized into homogeneous and heterogeneous types [66]. homogeneous catalysts, including both acids and bases, are widely used due to their high activity and simple reaction setups, while heterogeneous and enzymatic catalysts offer benefits such as reusability and environmental compatibility. figure 4 illustrates the main types of transesterification catalysts, and table 2 compares their effectiveness under various reaction conditions. figure 4. types of catalysts for transesterification 8. emission characteristics biodiesel produced from waste cooking oil (wco) has garnered considerable interest as a sustainable substitute for traditional diesel fuel. the emission characteristics, specifically regarding cox, nox, unburned hydrocarbons (hc), and particulate matter (pm), have been thoroughly examined [92]. ahad bin azad et al. /future energy november 2025| volume 04 | issue 04| pages 09-21 13 table 1. comparison of physicochemical properties property unit diesel wco density (15-20° c) kg/m3 828.54 871 874 865 880 881 884 kinematic viscosity (40° c) cst 2.7 4.3 3.69 4.18 6 3.58 4.95 pour point ° c -37 2 -3.4 -4.5 -3 -8.4 -6 flash point ° c 65 133 175 202 140 170 178 cloud point ° c -5 6 1.6 1 -1 -1.43 0 iodine value g i2/100 g 66.52 33 128.4 146.44 cetane number ci 54.1 46 70.24 56.67 44.315 49.14 higher heating value mj/kg 43.386 37.4 44.13 39.48 41.4 37.114 acid value mmg koh/g 0.2 0.92 0.39 0.3 0.8 0.48 ref. [60] [61] [62] [63] [64] [65] [60] table 2. comparison of physicochemical properties types of catalyst catalyst methanol to oil ratio reaction conditions fame (%) reference temperature time homogeneous base catalyst koh 6:1 65 ◦ c 1 h 93.2 [67] naoh 12:1 65 ◦ c 0.03 h 98.2 [68] ch3ona 3.9:1 120 ◦ c 6 h 91 [69] ch3ok 6:1 60 ◦ c 0.5 h 99 [70] homogeneous acid catalyst h2so4 245:1 70◦ c 4 h 99 [71] heterogeneous base catalyst cao 3.5:1 130 ◦ c 1.5 h 94 [72] mgo 24:1 65 ◦ c 1 h 93.3 [73] mgo-naoh 6:1 50 ◦ c 6 h 97 [74] sro 9:1 65 ◦ c 0.07 h 93 [75] k3po4 6:1 60 ◦ c 2 h 97.3 [76] α-fe2o3-al2o3 15:1 65 ◦ c 3 h 87.78 [77] heterogeneous acid catalyst zs/si 18:1 200◦ c 10 h 98 [78] rs-so3h 18:1 70 ◦ c 1 h 90.38 [79] zrhpw 20:1 65 ◦ c 8 h 98.9 [80] sher 12:1 60 ◦ c 2 h 97 [81] fe-al-tio2 10:1 90 ◦ c 2.5 h 96 [82] enzyme candida antarctica lipase b 4:1 40 °c 30 h 96 [83] geotrichum candidum 1.15:1 40 °c 1.33 h 94.1 [84] immobilized penicillium 1:1 35 °c 7 h 92.8 [85] pseudomonas cepacia 6.6:1 38.4 °c 2.47 h 96 [86] bifunctional cao/fe2o3 18:1 65 ◦ c 3 h 98.3 [87] cao/al2o3 12:1 60 ◦ c 3 h 98.23 [88] fly ash/cao, so3 3.1:1 59 °c 6 h 100 [89] sn/cao 16.1:1 85.15 ◦ c 3.42 h 97.39 [90] tio2/prso3h 15:1 60 ◦ c 9 h 98.3 [91] ahad bin azad et al. /future energy november 2025| volume 04 | issue 04| pages 09-21 14 its oxygen content improves combustion efficiency, typically reducing carbon monoxide (co), hydrocarbons (hc), and particulate matter (pm) when compared to diesel. table 2 summarizes the emission findings documented by multiple researchers. 8.1 cox emission co emissions generally decrease with wco biodiesel, benefiting from its higher oxygen content [93]. cox emissions may either stay similar or increase, depending on combustion efficiency and blend ratio [94]. co2 emissions from wco biodiesel can be higher or similar to those from diesel, depending on the combustion efficiency and blend ratio [95]. enhanced oxidation typically leads to higher co2 emissions, although some studies report only moderate differences [96]. 8.2 nox emissions increased wco biodiesel usage typically leads to higher noₓ emissions, attributed to the fuel’s higher oxygen content and increased combustion temperatures. advanced injection timing and higher bulk modulus may exacerbate noₓ levels, though mitigation strategies like exhaust gas recirculation have proven effective. noₓ emissions often increase with higher biodiesel content, likely due to elevated in-cylinder temperatures and changes in ignition timing. 8.3 unburned hc and pm hc emissions typically decrease with wco biodiesel, due to better combustion. pm and smoke opacity also reduce, especially under higher load conditions, where soot oxidation improves. however, some studies report minimal or increased pm at low loads or specific conditions [97]. 9. performance characteristics the reduced calorific value, increased viscosity, and increased density of wco biodiesel affect brake thermal efficiency (bte), brake-specific fuel consumption (bsfc), and brake power (bp), according to numerous studies. however, the use of additives and the optimization of engine parameters have shown promise in mitigating these drawbacks and, in some cases, enhancing performance. table 3 collates the findings from multiple studies. 9.1 brake thermal efficiency (bte) brake thermal efficiency (bte) indicates the effectiveness with which an engine transforms the chemical energy of gasoline into mechanical work. numerous studies demonstrate that waste cooking oil (wco) biodiesel and its blends typically produce a somewhat reduced bte relative to petroleum diesel, chiefly due to their diminished calorific value and increased viscosity. some authors report modest bte reductions of about 1–2% at higher loads or higher biodiesel blend ratios. 9.2 brake-specific fuel consumption (bsfc) bsfc serves as an essential metric that reflects the quantity of fuel utilized per unit of brake power (kw) over the span of one hour. a prevalent observation in the literature indicates that wco biodiesel demonstrates a greater bsfc in comparison to diesel. the primary factors involve the reduced heating value, increased density, and elevated viscosity of wco biodiesel, which require a marginally greater fuel mass injection to attain equivalent power output. certain studies indicate that there are increases in bsfc within the range of 2–17%. while others have observed more pronounced rises at specific loads or for higher blends. table 3. comparison of emission characteristics oil blend co co2 nox hc pm ref. wcmo b100 significant reduction gradual increase significant reduction vast reduction in smoke [98] wco b100 up to 58.9% reduction up to 8.6% reduction up to 37.5% reduction [99] wco b100 slightly lower increased slightly lower significantly reduced [92] wco b100 8.59% reduction 2.62% increase 5.03% increase 30.66% reduction 63.33% reduction [100] wco (coconut) b5 7.3% reduction 1% reduction 23% reduction [101] wco b100 17.14% reduction 8.05% reduction 1.45% reduction [102] wco b100 significant decrease slight increase significant decrease sharp reduction [103] wco b100 7% reduced lower [104] wco b100 higher lower [105] wco b100 decreased increased decreased [106] wco b100 reduced higher reduced reduced [107] wcmo b100 111% reduced 12% increased 9% increased 600% decreased [108] wco b100 minimum minimum unreliable minimum [109] wco b100 24.76% decreased 15.67% increased 22.95% decreased 48.13% decreased [97] ahad bin azad et al. /future energy november 2025| volume 04 | issue 04| pages 09-21 15 interestingly, a few studies point to optimized blends (e.g., b40) or additive use (nanoparticles) mitigating the bsfc penalty [110]. one notable exception to this rule of thumb is the finding that biodiesel has a lower bsfc than diesel, put out by altun et al. [111]. this raises questions about the validity of the results and may indicate the presence of an unusual experimental design or a statistical outlier. 9.3 brake power (bp) brake power (bp) is fundamentally influenced by the calorific value of the fuel as well as the quality of the air-fuel mixture. the reduced energy density of wco biodiesel may result in diminished brake power output in comparison to diesel. decreases in bp or torque are frequently associated with a rise in the proportion of wco biodiesel within the blend. the power loss is negligible, however, for low or moderate blend levels and lower engine speeds, according to some experimental study [112]. engine adjustments, such as altering injection pressure or timing, can also help to make up for some of the power disadvantage [113]. 10. combustion characteristics the combustion properties of waste cooking oil (wco) biodiesel, such as ignition delay, peak pressure, and heat release, vary from those of diesel [120]. wco blends demonstrate reduced ignition delays attributable to their elevated cetane number and oxygen content, which improve combustion. due to improved combustion, wco blends have a slightly greater peak pressure than diesel. however, the rate of pressure rise is lower since there is less fuel accumulation during the ignition delay. while wco blends have a lower calorific value and hence a slower heat release rate, the higher oxygen concentration improves combustion efficiency at higher speeds. 11. conclusion this research emphasizes the viability of waste cooking oil as a sustainable and cost-effective feedstock for bangladesh. the key findings of the study are as follows: waste cooking oil serves as a viable and economical feedstock for biodiesel production in bangladesh, with an annual availability surpassing one hundred thousand tons. wco biodiesel typically complies with international physicochemical property requirements, encompassing acceptable limits for viscosity, density, and cetane number. wco is an optimal feedstock for the production of biodiesel due to its ability to produce a significant quantity of fame under optimal transesterification conditions, regardless of the type of catalyst used. the combustion of wco biodiesel results in a reduction of hazardous emissions, including carbon monoxide (co), hydrocarbons (hc), and particulate matter (pm), as compared to diesel. despite these benefits, it presents certain trade-offs, including slightly reduced brake thermal efficiency (bte), higher brake-specific fuel consumption (bsfc), and elevated nox emissions. the findings indicate that wco biodiesel is not technically viable; nevertheless, it is significantly pertinent to bangladesh's energy and environmental requirements. its use provides a dual advantage, such as functioning as a renewable energy source while also delivering an effective solution for managing waste cooking oil. large-scale use could minimize production costs, reduce pollution, and prevent the harmful usage of wco in the food chain. moreover, it fulfils bangladesh's commitments regarding climate change under the paris agreement and decreases dependency on costly fossil fuel imports, hence improving national energy security. future research should focus on developing practical and economical collection networks, enhancing pretreatment procedures, and advancing conversion technologies. in addition, continuous investigations into advanced catalysts, optimal blending techniques, and engine modifications are necessary to overcome performance limitations and ensure that wco biodiesel becomes a feasible and sustainable contributor to bangladesh's clean energy transition. table 4. comparison of performance characteristics reference oil blend bte bsfc bp load condition [114] wco similar to diesel similar to diesel different loads, constant speed [105] wco pure ~1–1.5% efficiency loss at higher loads vs. diesel higher than diesel at a higher speed slightly lower than diesel various loads [115] wco b100 ~6% lower than diesel ~10% higher than diesel maximum load [116] wco pure almost similar to diesel ~17.8% higher than diesel full load [60] wco pure ~11.5% drop ~ 28.67% increased ~34.5% drop 0.16–0.65 mpa [104] wco pure ~1.5% higher than diesel ~11.6% ↑ than diesel ~13% lower than diesel various loads [117] wco b40 slightly higher lower than diesel comparable to diesel various loads, varying compression [118] wco b100 ~14.2% increase than diesel ~3% higher than diesel 5.56% drop in power [111] wco lower for wco than diesel lower torque than diesel [119] wco b10 ~6.45% decreased ~3.3% increased ~3.8% lower than diesel various loads ahad bin azad et al. /future energy november 2025| volume 04 | issue 04| pages 09-21 16 acknowledgements the authors sincerely thank the research team at green lead society for creating the platform for its contributions in carrying out this research project. ethical issue the authors are aware of and comply with best practices in publication ethics, specifically concerning authorship (avoidance of guest authorship), dual submission, manipulation of figures, competing interests, and compliance with policies on research ethics. the authors adhere to publication requirements that the submitted work is original and has not been published elsewhere in any language. data availability statement the manuscript contains all the data. however, more data will be available upon request from the corresponding author. conflict of interest the authors declare no potential conflict of interest. references [1] l. rocha-meneses et al., “recent advances on biodiesel production from waste cooking oil (wco): a review of reactors, catalysts, and optimization techniques impacting the production,” fuel (london, england), vol. 348, no. 128514, p. 128514, 2023, doi: 10.1016/j.fuel.2023.128514. 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[120] t. k. sahu, s. sarkar, and p. c. shukla, “combustion investigation of waste cooking oil (wco) with varying compression ratio in a single cylinder ci engine,” fuel, vol. 283, p. 119262, 2021. this article is an open-access article distributed under the terms and conditions of the creative commons attribution (cc by) license (https://creativecommons.org/licenses/by/4.0/). https://creativecommons.org/licenses/by/4.0/ a. naseri et al. /future energy august 2025| volume 04 | issue 03| pages 18-34 18 article renewable energy in transportation: economic and environmental trade-offs amir naseri1, amirali saifoddin1,2*, amin zahedi1, mahmood abdoos1, younes noorollahi1 1school of energy engineering and sustainable resources, college of interdisciplinary science and technology, university of tehran, tehran, iran 2institute of soft technologies, faculty of energy engineering and sustainable resources, college of interdisciplinary science and technologies, university of tehran, iran a r t i c l e i n f o article history: received 15 april 2025 received in revised form 28 may 2025 accepted 13 june 2025 keywords: energy economics, energy system modeling, electric vehicles, renewable energy, greenhouse gas emission reduction, sustainable transportation *corresponding author email address: saifoddin@ut.ac.ir doi: 10.55670/fpll.fuen.4.3.3 a b s t r a c t this paper explores the benefits and challenges of transitioning from fossilfueled vehicles to electric vehicles in iran, with a focus on economic and environmental analysis. to this end, three different scenarios were considered to evaluate the impacts of this transition: the baseline system (fossil-fueled vehicles only), electric vehicles powered by fossil-based electricity, and electric vehicles powered by renewable energy. each scenario was analyzed using various criteria, including fuel and maintenance costs, greenhouse gas emissions, required infrastructure investments, and return on investment. the results reveal that in the baseline scenario, annual co₂ emissions of 73.25 million tons and total annual costs of $1.92 billion are among the main challenges. in the second scenario, with a 50% penetration of electric vehicles powered by fossil-based electricity, co₂ emissions are reduced by 36.76 million tons, and the return on investment is achieved within five years. in the third scenario, assuming renewable energy sources supply electricity and a 70% penetration of electric vehicles, co₂ emissions are reduced by 114.49 million tons, and a return on investment of 32.6% is achieved. these findings underscore the importance of integrating electric vehicles with renewable energy to achieve economic and environmental sustainability. the study highlights the critical need for developing renewable energy infrastructure and implementing appropriate policies to accelerate the transition to electric vehicles. 1. introduction due to global concerns such as climate change and environmental pollution, various countries are moving toward sustainable and green economic development [1, 2]. among the critical sectors underpinning any country's economic development is the transportation sector. this highlights the importance of focusing on transportation to achieve sustainable and green economic development. according to data published by the iea in 2023, global co₂ emissions exceeded 30 billion tons in 2021, serving as a serious warning to the international community. the transportation sector is responsible for 25% of these emissions and accounts for 55% of global oil consumption [36]. in recent years, governments worldwide have prioritized replacing fossil fuels with renewable energy sources in the transportation sector to achieve sustainable and green economic growth [1, 2]. one of the key strategies to reduce greenhouse gas emissions in transportation is the adoption of evs, provided that their electricity is generated using renewable energy sources such as wind and solar power. according to statistics from the iea, the sales of electric vehicles across various regions from 2012 to 2024, illustrated in figure 1, demonstrate a growing global inclination toward ev adoption, especially in developed countries [7]. so far, extensive research has been conducted on the use of electric vehicles and their role in addressing environmental, economic, and energy network challenges across different countries, some of which are discussed below. li et al. [8] investigated various scenarios for the deployment of electric vehicles in their country, focusing on their impact on the energy mix, economic outcomes, and environmental consequences, considering expected developments by 2030. li et al. [8] also aimed to develop the electric vehicle market through improving charging strategies and power system design in china. future energy open access journal https://doi.org/10.55670/fpll.fuen.4.3.3 august 2025| volume 04 | issue 03 | pages 18-34 journal homepage: https://fupubco.com/fuen issn 2832-0328 mailto:saifoddin@ut.ac.ir https://doi.org/10.55670/fpll.fuen.4.3.3 https://fupubco.com/fuen a. naseri et al. /future energy august 2025| volume 04 | issue 03| pages 18-34 19 their findings indicated that, from an environmental perspective, the adoption of electric vehicles in china does not effectively reduce co₂ emissions. this is primarily because the electricity required for these vehicles is generated using coal rather than renewable energy sources. as a result, the electrification of vehicles merely shifts the energy mix rather than improving co₂ emissions, with coal replacing gasoline as the energy source. economically, electric vehicles outperform gasoline vehicles in terms of average fueling costs. the study suggested that, from both environmental and economic perspectives, it would be more beneficial for electric vehicles to rely on renewable energy or even natural gas for electricity generation. additionally, establishing co₂ emission regulations for electricity production and transmission could significantly contribute to the development of electric vehicles. in another study conducted by garcía-olivares et al [9], a 100% renewable energy system for the transportation sector was proposed. this study examined existing and emerging technologies for replacing fossil fuels in transportation and estimated the energy requirements and costs associated with transitioning to a fully renewable transportation system. the results revealed that such a system could reduce global transportation energy consumption by 18%, with a 69% reduction expected in road transportation. however, aviation and maritime transportation are projected to see increases of 149% and 163%, respectively. the study concluded that transitioning to a 100% renewable transportation system is feasible but would require careful management of natural resources and overcoming challenges related to material and energy consumption across various sectors. another study by ding et al [1] focused on promoting sustainable and green economic development. using a two-stage least squares regression approach, this research analyzed the impact of renewable energy adoption on achieving sustainability in china’s transportation sector. the results indicated that renewable energy utilization and investments in green financing are two key factors for establishing an environmentally friendly transportation system. furthermore, these factors play a significant role in reducing carbon emissions and fostering green economic growth. the research by zahoor et al. [10] focused on the development of electric vehicles and their role in reducing carbon emissions. it examined technologies and policies that could facilitate the adoption of electric vehicles in china. the findings revealed that government policies, such as tax exemptions, advancements in innovative technologies, expansion of charging infrastructure, and easing traffic restrictions, could significantly boost the adoption of electric vehicles and reduce co₂ emissions. the analysis showed that the share of renewable energy in china’s electricity mix could increase from 42% in 2030 to 93% by 2060, while the reliance on fossil fuels could decrease from 55% to 4%. in another study conducted by taghizad et al. [5], the focus was on the role of electric vehicle charging stations and load distribution management within power grids to support electric vehicle development. the researchers emphasized that establishing charging stations powered by renewable energy sources could further enhance the adoption of electric vehicles and reduce environmental pollution. the study analyzed global standards for ev charging, different types of evs, and converter architectures (ac-dc and dc-dc) to address challenges related to peak demand and ensure the efficiency of charging infrastructure. the results indicated that smart and controlled charging strategies could alleviate grid pressures, enhance the integration of renewable energy sources, and optimize the design and implementation of ev charging infrastructure. abbreviations bevs battery electric vehicles cpvt concentrated photovoltaic-thermal evs electric vehicles fcevs fuel cell electric vehicles ho highway operator iea international energy agency iluc indirect land use change mesv mobile energy storage vehicle milp mixed integer linear programming res renewable energy systems figure1. the number of sales of electric cars in different regions of the world [7] a. naseri et al. /future energy august 2025| volume 04 | issue 03| pages 18-34 20 table 1 (appendix i) presents additional research that reviews the articles in terms of content, furthering our understanding of previous research. considering the review of previous studies, although various research efforts have sought to highlight the role of renewable energy in the transportation sector by introducing diverse technologies and assessing the environmental benefits of these resources, as well as analyzing the impact of incorporating renewable energy into transportation from the perspective of national energy networks, a comprehensive study addressing the balance and trade-offs between the economic and environmental advantages and disadvantages of using such energy sources remains absent. the significance of this research lies in the fact that merely examining environmental and technical aspects is insufficient for the development of renewable energy in the transportation sector. a thorough and simultaneous evaluation of economic costs and benefits alongside environmental aspects is essential. consequently, this study aims to achieve a deeper understanding of how to create a relative balance between environmental and economic factors in a manner that fosters the sustainable development of renewable energy in transportation. it can serve as a foundation for policymaking and the sustainable development of renewable energy in this sector. this paper seeks to provide a comprehensive analysis of the economic and environmental impacts of utilizing renewable energy in transportation, focusing on how to balance economic benefits, such as reducing operational costs and improving energy efficiency, with environmental advantages, such as reducing emissions and preserving ecosystem sustainability. through a quantitative and qualitative analysis of these aspects, the study aims to identify the opportunities and challenges of sustainable renewable energy development in transportation and offer policy recommendations to optimize this balance. the ultimate goal of this research is to propose an approach that minimizes the negative economic and environmental impacts while paving the way for more informed and effective decision-making toward sustainable transportation development. 2. methodology this section explains the research process, various scenarios, and data used in the economic and environmental analysis of transitioning from fossil-fuel vehicles to evs in iran. the statistics and figures employed in this research, which serve as the foundation for calculations in subsequent sections, are based on the most recent and reliable data from the iranian energy balance sheet (2021). these data form the primary basis for all calculations and analyses. the main objective of this research is to analyze the economic and environmental advantages and disadvantages of using electric vehicles powered by various energy sources. 2.1 research objectives the primary goal of this paper is to examine and analyze the economic and environmental impacts of transitioning from fossil-fuel vehicles to electric vehicles in iran. the specific objectives of this research are: • to compare the economic and environmental costs of using fossil-fuel vehicles versus electric vehicles. • to analyze various energy supply scenarios for electric vehicles and their impact on reducing co2 emissions. • to evaluate the environmental and economic benefits of using electric vehicles powered by renewable energy sources. 2.2 research methodology and models this research is based on three main scenarios and three sub-scenarios, which are explained in detail below: • scenario 1 (baseline system): in this scenario, all vehicles are fossil-fuel-based, and no electric vehicles are used. this scenario serves as the baseline for comparison with other scenarios. • scenario 2 (electric vehicles with fossil-fuel electricity): in this scenario, it is assumed that electric vehicles are solely powered by fossil-fuel energy sources. this scenario is analyzed under the following three conditions: o case 1 (30%): 30% of vehicles are electric. o case 2 (50%): 50% of vehicles are electric. o case 3 (70%): 70% of vehicles are electric. • scenario 3 (electric vehicles with renewable electricity): in this scenario, it is assumed that electric vehicles are powered solely by renewable energy sources (e.g., solar, wind, etc.). this scenario is also analyzed under the following three conditions: o case 1 (30%): 30% of vehicles are electric. o case 2 (50%): 50% of vehicles are electric. o case 3 (70%): 70% of vehicles are electric. table 2 contains the economic and environmental data used for analyzing the transition from fossil-fuel vehicles to electric vehicles in iran. all statistics and figures in this study are extracted from the iranian energy balance sheet (2021) and are considered the most up-to-date and reliable data available in this field. to determine the required investment for charging stations, equation (1) will be used. total investment for charging stations = number of stations × cost per charging station (1) in equation (1), the number of charging stations will be calculated using equation (2). ncar nday×ncs = ns (2) in this context, ncar represents the number of electric vehicles, nday is the number of operational days for a station in a year, ncs refers to the daily capacity of a station for charging vehicles, and ns represents the number of charging stations. the number of operational days will be considered as 365 days, and the daily capacity of the station will be set to 20 vehicles in this study. additionally, the cost for equipment, installation, and necessary infrastructure for one charging station in iran is approximately 875 usd. the internal rate of return is calculated using the cash flow of the project over time, as expressed in equation (3). ∑ (𝑁𝐶𝐹)𝑡 (1+irr)t n t=0 = 0 = 𝑁𝑃𝑉 (3) ncf refers to the net cash flow, which is obtained according to equation (4). ncf=annual income−annual operational costs (4) a. naseri et al. /future energy august 2025| volume 04 | issue 03| pages 18-34 21 table 2. comparison of economic and environmental data of fossil and electric vehicles item details total number of fossil-fuel vehicles 41 million units average fuel consumption of fossil-fuel vehicles 6.9 liters per 100 kilometers average distance traveled per vehicle per month 400 kilometers annual gasoline consumption 31,851.4 million liters annual lpg consumption 2,545 million cubic meters annual crude oil equivalent natural gas consumption 54.6 million barrels of oil equivalent cost per liter of gasoline 2.8 cents fuel cost per kilometer for fossil-fuel vehicles 0.18 cents charging cost per kilometer for electric vehicles 0.09 cents average purchase price of fossil-fuel vehicles $437.50 average purchase price of electric vehicles $4,375 annual maintenance cost of fossil-fuel vehicles $25 annual maintenance cost of electric vehicles 33% less than fossil-fuel vehicles ($16.75) electricity cost for electric vehicles 0.68 cents per kilowatt-hour the average battery capacity of electric vehicles 50 kilowatt-hours range of electric vehicles on a single charge 400 kilometers co2 emissions from fossil-fuel vehicles 2.3 kilograms of co2 per liter of gasoline co2 emissions from electric vehicles using fossil-fuel electricity 0.6 kilograms of co2 per kilowatthour co2 emissions from electric vehicles using renewable electricity negligible (can be ignored) average energy consumption of evs 12.5 kilowatt-hours per 100 kilometers the annual income is derived from equation (5). annual income=number of electric vehicles×average annual kilometer×charging rate (5) • number of electric vehicles: variable in each scenario • average annual kilometers: 4,800 kilometers (400 kilometers per month) • charging rate: 0.09 cents • annual operational costs: these include maintenance costs of the stations and electricity consumption, which in this study are considered to be approximately 10% of the initial investment cost. the payback period is calculated using equation (6). 𝐶𝐴𝑃𝐸𝑋 ncf = payback period (6) 𝐶𝐴𝑃𝐸𝑋 the cost is the initial investment. 2.3 analysis method for each scenario and its respective sub-cases, separate economic and environmental calculations are conducted. these calculations include costs associated with fuel, maintenance, and vehicle purchase, as well as co2 emissions resulting from fuel consumption and energy supply. finally, the results are presented comparatively among the scenarios. in the results section, these calculations are fully examined, and comparisons between the proposed scenarios are carried out. 3. results and discussion this section analyzes and interprets the economic and environmental results related to the transition from fossil fuel vehicles to electric vehicles in iran. using the provided data, three different scenarios for this transition are evaluated. each scenario is assessed based on economic criteria (e.g., purchase cost, maintenance cost, electricity cost, and return on investment) and environmental criteria (e.g., reduction of greenhouse gas emissions). the ultimate goal is to identify the most suitable strategy for developing electric vehicles in iran and mitigating the environmental impacts of fossil fuel vehicles. • scenario 1: base system (only fossil fuel vehicles) this scenario serves as the baseline for comparison, and its economic and environmental results are shown in table 3. the baseline system represents the current conditions with widespread use of fossil fuel vehicles. this scenario imposes substantial economic and environmental costs. emitting 73 million tons of co2 annually from road transportation alone poses a significant environmental challenge for iran. additionally, annual fuel and maintenance expenses place a heavy financial burden on households and the national economy. • scenario 2: electric vehicles powered by fossil-fueled electricity in this scenario, it is assumed that the electricity required for electric vehicles (evs) is generated using fossil fuel-based energy sources. the penetration of electric vehicles in this scenario is divided into three levels: 30%, 50%, and 70%. case 1: 30% electric vehicles table 4 presents the economic and environmental status of the transportation sector, assuming 30% adoption of electric vehicles. the fuel cost for the remaining fossil fuel vehicles decreases to $0.63 billion, while the electricity cost for electric vehicles reaches $0.18 billion. the maintenance cost for electric vehicles amounts to $0.2 billion. the reduction in co2 emissions in this scenario is 22,077,160 tons. the required investment for charging infrastructure is $105,000, with an internal rate of return (irr) of 29.5%, and a payback period of 5.2 years. a. naseri et al. /future energy august 2025| volume 04 | issue 03| pages 18-34 22 table 3. current status of iran's transportation system (baseline scenario) parameter value total number of fossil fuel vehicles 41 million vehicles annual fuel consumption of fossil vehicles 31,851.4 million liters of gasoline annual fuel cost $0.9 billion (at a rate of $0.028 per liter) annual co2co_2co2 emissions (tons) 73,257,220 tons co2co_2co2 (considering 2.3 kg co2co_2co2 per liter of gasoline consumed) annual maintenance costs $1.02 billion ($25 per vehicle) total annual costs $1.92 billion (fuel and maintenance costs) table 4. economic and environmental status of transportation in the second scenario, assuming 30% electric vehicle use parameter value number of electric vehicles 12.3 million units fuel cost for remaining fossil fuel vehicles $0.63 billion electricity cost for electric vehicles $0.18 billion (at $0.085 per kilometer for 12.3 million vehicles) maintenance cost for electric vehicles $0.2 billion ($16.75 per year for 12.3 million vehicles) annual co2co_2co2 emissions from fossil-fueled electricity 27,720,000 tons co2co_2co2 (based on 60.8 billion kwh electricity generated from fossil fuel sources) reduction in co2co_2co2 emissions 22,077,160 tons co2co_2co2 (compared to the baseline scenario) total investment in charging stations $105,000 internal rate of return (irr) 29.50% payback period 5.2 years case 2: 50% electric vehicles table 5 presents the economic and environmental status of the transportation sector, assuming 50% of vehicles are electric. the fuel cost for the remaining fossil fuel vehicles decreases to $0.45 billion, while the electricity cost for electric vehicles rises to $0.3 billion. the maintenance cost for electric vehicles increases to $0.34 billion. the reduction in co2 emissions reaches 36,760,000 tons. the investment required for charging infrastructure rises to $175,000, with an irr of 30.2% and a payback period of 5 years. case 3: 70% electric vehicles table 6 presents the economic and environmental status of the transportation sector, assuming 70% electric vehicle penetration. in this scenario, fuel costs for fossil vehicles decrease to $0.27 billion, while electricity costs for electric vehicles rise to $0.41 billion. the maintenance costs for electric vehicles increased to $0.48 billion, and co2 emissions decreased by 51,443,040 tons. the investment required for charging infrastructure is $5,000, with an irr of 30.8% and a payback period of 4.8 years. despite reduced fuel and maintenance costs, the environmental benefits are limited due to reliance on fossil-based electricity. this highlights the need for a transition to renewable energy sources to fully harness the potential of electric vehicles. table 5. economic and environmental status of transportation in the second scenario, assuming 50% electric vehicle use parameter value number of electric vehicles 21 million vehicles fuel cost for remaining fossil fuel vehicles $0.45 billion electricity cost for electric vehicles $0.3 billion (0.085 cents per km for 21million vehicles) maintenance cost for electric vehicles $0.34 billion annual co2 emissions from fossilfueled electricity 46,200,000 tons co2 reduction in co2 emissions 36,760,000 tons co2 total investment in charging stations $175,000 internal rate of return (irr) 30.20% payback period 5 years scenario 3: electric vehicles with renewable energy in this scenario, it is assumed that the electricity consumed by electric vehicles is entirely sourced from solar energy. the impacts of this scenario are evaluated under three levels of electric vehicle penetration: 30%, 50%, and 70%. case 1: 30% electric vehicles table 7 presents the economic and environmental status of the transportation sector in scenario 3, assuming 30% adoption of electric vehicles. the fuel cost for the remaining fossil fuel vehicles decreases to 0.63 billion dollars, while the electricity cost for electric vehicles reaches 0.18 billion dollars, and the maintenance cost amounts to 0.2 billion dollars. the co2 reduction is equivalent to 49,797,160 tons. the required investment for the solar power plant is 480,343.75 dollars, with an internal rate of return (irr) of 31.67% and a payback period of 5 years. table 6. economic and environmental status of transportation in the second scenario, assuming the use of 70% electric vehicles parameter value number of electric vehicles 29million units fuel cost for remaining fossil vehicles $0.27 billion electricity cost for electric vehicles $0.41 billion maintenance cost for electric vehicles $0.48 billion annual co2 emissions from fossil electricity 64,680,000 tons co2 reduction in co2 emissions 51,443,040 tons co2 total investment in charging stations $245,000 internal rate of return (irr) 30.80% payback period 4.8 years a. naseri et al. /future energy august 2025| volume 04 | issue 03| pages 18-34 23 table 7. economic and environmental status of transportation in the third scenario and assuming the use of 30% electric vehicles parameter value number of electric vehicles 12 million units fuel cost for remaining fossil vehicles $0.63 billion electricity cost for electric vehicles $0.18 billion maintenance cost for electric vehicles $0.2 billion investment in solar power plants $480343.75 reduction in co2 emissions (tons) 49,797,160 tons co2 rate of return on power plant investment 31.67% payback period for power plants 5 years case 2: 50% electric vehicles table 8 shows the economic and environmental status of the transportation sector in scenario 3, assuming the use of 50% electric vehicles. the fuel cost for fossil fuel vehicles has decreased to 0.45 billion usd, while the electricity cost for electric vehicles reaches 0.3 billion usd. the maintenance cost increases to 0.34 billion usd, and the reduction in co2 emissions amounts to 39,837,728 tons. the investment in solar power plants rises to 800,573.75 usd, with an internal rate of return (irr) of 32.1% and a payback period of 4.8 years. case 3: 70% electric vehicles table 9 presents the economic and environmental status of the transportation sector in scenario 3, assuming 70% adoption of electric vehicles. table 8. economic and environmental status of transportation in the third scenario, assuming 50% electric vehicle use table 9. economic and environmental status of transportation in the third scenario, assuming 70% use of electric vehicles the fuel cost for fossil fuel vehicles decreases to 0.27 billion usd, while the electricity cost for electric vehicles rises to 0.42 billion usd. maintenance costs increase to 0.48 billion usd, and co2 reduction reaches 31,870,182 tons. the investment required for solar power plants reaches 1.12 million usd, with an irr of 32.6% and a payback period of 4.6 years. this scenario is the most optimal in terms of both environmental and economic factors. in this scenario, due to the use of renewable energy sources, a significant reduction in co2 emissions is achieved, and a favorable and quick return on investment in solar power plant projects is observed (figure 2). this scenario highlights the importance of integrating renewable energy sources with the transition to electric vehicles to achieve both economic and environmental sustainability. figure 2. carbon dioxide emissions in different scenarios the findings of this study demonstrate that electric vehicles have significant potential in reducing economic costs and environmental impacts. the results show that even with fossil fuel-based electricity, the adoption of electric vehicles will lead to a substantial reduction in operational costs and co2 emissions. however, the greatest environmental benefits are achieved when the electricity used to charge electric vehicles comes from renewable energy sources. an analysis of various electric vehicle penetration scenarios indicates that parameter value number of electric vehicles 21million units remaining fuel cost for fossil vehicles 0.45 billion usd electricity cost for electric vehicles 0.3 billion usd maintenance cost for electric vehicles 0.34 billion usd investment in solar power plant 800,573.75 usd co2 emission reduction (tons) 39,837,728 tons co2 internal rate of return (irr) for power plants 32.10% payback period for power plants 4.8 years parameter value number of electric vehicles 29 million units fuel cost for remaining fossil fuel vehicles 0.27 billion usd electricity cost for electric vehicles 0.42 billion usd maintenance cost for electric vehicles 0.48 billion usd investment in solar power plants 1.12 million usd co2 emission reduction (tons) 31,870,182 tons co2 internal rate of return (irr) 32.60% payback period for solar power plants 4.6 years a. naseri et al. /future energy august 2025| volume 04 | issue 03| pages 18-34 24 increasing the share of electric vehicles, coupled with the integration of renewable energy, can result in a substantial reduction in greenhouse gas emissions. furthermore, investments in charging infrastructure and renewable energy generation provide attractive returns, with payback periods ranging from 4.6 to 5.2 years. as a result, the transition to electric vehicles, supported by renewable energy infrastructure, presents a promising path for economic and environmental sustainability in iran. to fully capitalize on the benefits of this transition, efforts must be made to accelerate the adoption of electric vehicles and renewable energy sources. 4. conclusion the findings of this research show that the transition to electric vehicles has a significant impact on reducing economic costs and greenhouse gas emissions. even in the scenario of using electricity generated from fossil fuels, a reduction of 36.76 million tons of co2 and an investment return rate of 30.2% reflect the positive impact of this transition. however, the greatest environmental benefits are realized when the electricity used by electric vehicles comes from renewable sources. in this case, a reduction of 114.49 million tons of co2 and an investment return rate of 32.6% are achieved, showing a remarkable improvement in environmental impact reduction. additionally, the payback period for solar power plant projects is estimated to be between 4.6 and 5 years, highlighting the economic importance of utilizing renewable energy. an analysis of various scenarios shows that increasing the share of electric vehicles, particularly when combined with the integration of renewable energy, can provide a sustainable solution to reduce dependence on fossil fuels and strengthen energy security. in this process, investment in charging infrastructure and the development of renewable energy are essential. this research emphasizes the importance of precise planning and policymaking to accelerate the transition to electric vehicles and optimally leverage the economic and environmental benefits. ultimately, the development of electric vehicles alongside renewable energy infrastructure can play a key role in achieving economic and environmental sustainability. this strategy not only leads to a significant reduction in greenhouse gas emissions but also provides a favorable investment return. therefore, the transition to electric 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[26] de schepper, e., et al., economic and environmental multi-objective optimisation to evaluate the impact of belgian policy on solar power and electric vehicles. journal of environmental economics and policy, 2016. 5(1): p. 1-27. [27] wei, w., et al., the effectiveness and trade-offs of renewable energy policies in achieving the dual decarbonization goals in china: a dynamic computable general equilibrium analysis. international journal of environmental research and public health, 2022. 19(11): p. 6386. [28] ogden, j.m., e.d. larson, and m.a. delucchi, a technical and economic assessment of renewable transportation fuels and technologies. 1994. https://escholarship.org/uc/item/1n69849j this article is an open-access article distributed under the terms and conditions of the creative commons attribution (cc by) license (https://creativecommons.org/licenses/by/4.0/). https://creativecommons.org/licenses/by/4.0/ a. naseri et al. /future energy august 2025| volume 04 | issue 03| pages 18-34 26 appendix i table 1. summary of past research on using renewable energy in the transportation sector ref papers results research gap challenges methods used [11] management of environmental and economic tradeoffs for the optimization of renewable energy scheme • the study employed two qualitative methods: bibliometric analysis and systematic literature review, focusing on scopus-based articles related to renewable energy optimization. • vosviewer software was utilized to conduct the analysis, which helped in identifying prevalent environmental and economic tradeoffs in renewable energy schemes. • the study identifies prevalent environmental tradeoffs in renewable energy schemes, such as habitat loss, fragmentation, sediment transportation, and deforestation, but does not explore specific case studies or empirical data that illustrate the extent and impact of these tradeoffs in different contexts. • while the research suggests solutions for managing economic tradeoffs like high initial costs and supply chain risks, it lacks a detailed analysis of the effectiveness of these solutions in real-world applications or their potential barriers to implementation. • the study identifies prevalent environmental tradeoffs in renewable energy schemes, which include habitat loss, fragmentation, sediment transportation, and deforestation, highlighting the negative impacts on ecosystems and biodiversity associated with renewable energy development. • economic tradeoffs are also discussed, such as high initial costs, intermittency, reliability challenges, job security, resource scarcity, and supply chain risks, which pose significant challenges to the economic viability and stability of renewable energy initiatives. • the study identified significant environmental tradeoffs in renewable energy schemes, including issues such as habitat loss, fragmentation, sediment transportation, and deforestation, which need to be addressed to enhance sustainability in energy production. • economic tradeoffs were also highlighted, including high initial costs, intermittency, reliability challenges, job security concerns, resource scarcity, and supply chain risks, leading to the recommendation of strategic planning, continuous monitoring, and diversification of renewable energy sources to manage these challenges effectively. [12] a comprehensive study of effects of renewable energy based electric vehicles on environment • the study conducts a thorough analysis of existing literature, empirical studies, and modeling approaches to evaluate the environmental implications of electric vehicles (evs) powered by renewable energy sources. this comprehensive review helps in understanding the life cycle emissions of evs compared to conventional cars, considering factors such as production, electricity generation, and endof-life disposal. • it examines the integration of renewable energy sources like solar, wind, and hydropower into the electrical grid for powering evs, highlighting the synergistic effects on both the energy and transportation sectors. the study also addresses potential opportunities and challenges associated with the widespread adoption of renewable energypowered evs, including infrastructure requirements, legislative incentives, and consumer behavior. • the study addresses the environmental implications of renewable energy-powered electric vehicles (evs) but does not explicitly identify specific research gaps or areas that require further investigation, such as the long-term impacts of ev adoption on biodiversity or the socio-economic effects on communities transitioning to renewable energy sources. • while the paper discusses the integration of renewable energy sources into the electrical grid for powering evs, it does not delve into the technological advancements or innovations needed to enhance this integration, nor does it explore the potential barriers to widespread adoption of such technologies in different regions. • the study addresses potential challenges associated with the widespread adoption of electric vehicles (evs) powered by renewable energy, including infrastructural needs that must be met to support the integration of evs into existing transportation networks and the electrical grid. • it also highlights the importance of legislative incentives and customer behavior as factors that could influence the successful implementation and acceptance of renewable energy-powered evs, indicating that these elements may pose challenges to achieving a sustainable transition in transportation. • the study highlights that electric vehicles (evs) powered by renewable energy sources can significantly reduce air pollution and greenhouse gas emissions compared to conventional internal combustion engine vehicles, emphasizing the potential for cleaner transportation networks as the world shifts towards greener energy solutions. • it provides insights into the life cycle emissions of evs, comparing them to traditional cars by considering factors such as manufacturing processes, electricity generation methods, and end-of-life disposal, ultimately guiding decisionmaking for sustainable transportation and energy transitions. a. naseri et al. /future energy august 2025| volume 04 | issue 03| pages 18-34 27 [13] the environmental footprint of transport by car using renewable energy • the paper compares and contrasts the carbon, land, and water footprints per driven kilometer in midsize cars that utilize different energy sources, including conventional gasoline, biofuels, bioelectricity, solar electricity, and solar-based hydrogen. • the analysis focuses on assessing the environmental impacts of these various fuel types to understand the trade-offs involved in replacing fossil fuels with renewable energy in the transport sector. • the transition from fossil fuels to renewable energy in the transport sector may lead to trade-offs concerning land and water resources, which could impact environmental sustainability. • while renewable energy sources can lower greenhouse gas emissions, the environmental footprints associated with different fuel types vary significantly, with biofuel-driven cars exhibiting the largest footprints compared to solar-powered electric and hydrogen cars. • solar-powered electric cars have the smallest environmental footprints per kilometer driven, indicating they are the most sustainable option among the alternatives analyzed. • biofuel-driven cars have the largest environmental footprints per kilometer, suggesting that while they are an alternative to fossil fuels, they may not be the most environmentally friendly choice. [14] renewable energy systems implementation in road transport: prospects and impediments • the paper conducts a detailed literature review to assess the current state of major renewable energy systems in road transport, focusing specifically on the european union. this review includes an analysis of the prospects and impediments for the future use of biofuels, renewable electricity, and green hydrogen in road transport. • the authors discuss the implications of various policies implemented and emission reduction targets set for the future, particularly in relation to passenger car transport, to provide a comprehensive overview of the challenges and opportunities for renewable energy systems in the transport sector. • the paper highlights that most literature focuses either solely on biofuels, battery electric vehicles, or hydrogen and fuel cell vehicles, indicating a research gap in comprehensive analyses that consider all these renewable energy systems together. this lack of integrated studies limits the understanding of the overall potential and challenges of renewable energy systems in the transport sector. • there is a noted immaturity in the production processes of advanced biofuels, which could be produced from lignocellulosic materials and do not compete with food production. the paper suggests that further research is needed to improve these production processes and reduce costs, indicating a gap in the development and commercialization of advanced biofuels. • the high investment costs associated with bevs and fcevs present a significant barrier to their faster market penetration. although these costs may decrease in the future due to technological advancements, they currently hinder the widespread adoption of these alternative automotive technologies. • the competition for arable land between biofuels production and food/feed production poses a critical challenge for the future of renewable energy in the transport sector. the sustainability issues related to biofuels, particularly the iluc, complicate their viability as a low-carbon fuel option, raising concerns about their overall environmental benefits. • the paper concludes that while there are prospects for increased use of res in the transport sector, particularly in the eu, the overall life-cycle emissions must be carefully considered to avoid negative environmental impacts, such as those associated with the green paradox. the competition between biofuels and food production is highlighted as a critical issue for the future of biofuels. • it identifies high investment costs as a significant barrier to the faster market penetration of bevs and fcevs. although the number of bevs is increasing globally, the costs of green hydrogen remain prohibitively high compared to fossil fuelderived hydrogen, which limits the growth of hydrogen and fuel cell technologies in the automotive sector. a. naseri et al. /future energy august 2025| volume 04 | issue 03| pages 18-34 28 [15] enhancing the utilization of renewable generation on the highway with mobile energy storage vehicles and electric vehicles • the paper proposes a cooptimization method for the evcharging scheme and mesv scheduling on the highway, which takes into account locational marginal price, renewable generation, and the benefits for ev users. • a bi-level optimization model is developed to simulate the interaction between ev users and the ho, where the upper-level model focuses on optimizing ev charging pricing and mesv scheduling to maximize ho profit, while the lower-level model aims to minimize ev users' charging-parking costs. • the paper does not address the potential impacts of varying traffic patterns and their influence on the scheduling of mesvs and ev charging loads, which could affect the overall efficiency of the proposed co-optimization method. • there is a lack of exploration into the integration of different types of renewable energy sources and their specific characteristics, which may further enhance the utilization of renewable generation on the highway beyond the current focus on scheduling mesvs and ev charging. • the paper discusses the challenge of reshaping ev charging loads to address the imbalance between energy supply from renewable generation and the electricity demand from traffic on the highway. this imbalance is expected to grow with the increasing number of evs and renewable energy sources. • another challenge highlighted is the optimization of scheduling mesvs to consume renewable energy effectively. this involves developing a cooptimization method that considers various factors such as locational marginal price, renewable generation, and the benefits to ev users, which complicates the scheduling and charging strategies. • the study demonstrates a 32.0% increase in the utilization of renewable energy on the highway, indicating a significant improvement in the integration of renewable generation with electric vehicle charging demands. • there is a reduction of 3190.1 kwh in electricity purchased from the main grid, which contributes to promoting both environmental and economic sustainability for the highway operator. [16] optimization of renewable energy usage in public transportation: mathematical model for energy management of plug-in pv-based electric metrobuses • the study employs a metrobus charging station optimization model that integrates grid and renewable energy systems, allowing for energy exchange with the grid when necessary. this model is specifically designed for the iett avcılar metrobus garage in istanbul, focusing on static conditions and optimal scheduling. • a single objective milp approach is utilized to maximize the usage of renewable energy while minimizing the cost associated with non-renewable energy usage. the model also determines the best assignment of metrobuses to their scheduled departures, ensuring an environmentally friendly and cost-effective solution. • the study focuses specifically on the optimization of renewable energy usage in the context of metrobuses in istanbul, turkey, but does not address the potential applicability of the proposed model to other cities or public transportation systems, which could limit the generalizability of the findings. • while the model aims to maximize the usage of renewable energy and minimize costs, it does not explore the long-term impacts of integrating such systems on the overall sustainability of public transportation or the potential challenges in implementation, such as infrastructure requirements or policy support. • the paper highlights the challenge of reducing carbon emissions from public transportation systems that traditionally rely on internal combustion engines, emphasizing the need for greener solutions to meet sustainability targets and decrease the carbon footprint associated with these vehicles. • another challenge addressed is the optimization of energy management for electric metrobuses, specifically in the context of integrating renewable energy systems with the grid, which requires effective scheduling and assignment of metrobuses to ensure maximum utilization of renewable energy while minimizing costs associated with non-renewable energy usage. • the study developed a metrobus charging station optimization model that integrates renewable energy systems with the grid, allowing for energy exchange when necessary, specifically designed for the iett avcılar metrobus garage in istanbul. this model focuses on maximizing the usage of renewable energy while minimizing the costs associated with non-renewable energy usage. • the model was solved using the gams solver, and the results indicated that adopting an environmentally friendly approach to public transportation through the electrification of metrobuses is not costly, demonstrating the feasibility of sustainable energy management in public transport systems. a. naseri et al. /future energy august 2025| volume 04 | issue 03| pages 18-34 29 [17] a review of the integrated renewable energy systems for sustainable urban mobility • the paper reviews various renewable energy integration methods for electric vehicle charging stations, including the use of cpvt systems, wind turbines, and biomass-based rankine cycles to generate electricity and thermal energy for vehicle charging and hydrogen production. • it discusses the prioritization of energy storage systems, starting with hydrogen fuel cells, followed by ammonia fuel cells, and lastly conventional battery storage, to ensure a reliable power supply for electric vehicles when renewable energy generation is insufficient. • the paper highlights the challenges of integrating renewable energy into existing electric power systems, pointing out the technical and economic difficulties due to the varying and unreliable nature of renewable energy sources compared to traditional methods. • the research identifies the need to understand the three main operational planning scopes crucial to renewable energy integration before considering how renewable resources impact these planning processes, indicating a gap in comprehensive understanding and analysis in this area. • the integration of renewable energy into existing electric power systems is technically and economically challenging due to the ingrained nature of these systems in daily life and the variability and unreliability of renewable energy sources compared to traditional methods. • there are several implementation challenges related to consumer incentives, infrastructure, and the need for a sustainable energy supply for charging stations in urban regions, which are crucial for promoting the use of cleaner vehicles and reducing pollution. • the paper highlights the adverse impacts of air pollutants emitted from internal combustion engine vehicles, emphasizing the need for transitions to cleaner fuels and electric vehicles to reduce pollution and encourage the use of clean vehicles for urban mobility. • it discusses the integration of electric vehicle stations with renewable energy sources, showcasing how certain components within the integrated system can provide uninterrupted power supply to electric vehicles, leading to less pollution and promoting the adoption of clean vehicles. [18] externalities of transportation fuels: assessing trade-offs between petroleum and alternatives • the study utilized the greet lifecycle analysis model to assess the environmental externalities associated with different types of transportation fuels, providing a comprehensive evaluation of their impacts throughout their life cycles. • additionally, the research employed several other models, including the fasom-ghg model for agriculture and forestry, the apeep integrated assessment model for calculating the marginal damage of emissions, the gtap-bio computable general equilibrium model for estimating land use changes, and the osiris model for estimating species extinctions due to deforestation. • the study indicates that many previous analyses have not included all elements that constitute the true cost of oil, suggesting a gap in comprehensive assessments of oil dependence costs across various studies. this highlights the need for more inclusive research that captures the full spectrum of economic and environmental impacts associated with oil consumption. • there is a call for a holistic framework to assess the relative costs and benefits of alternative transportation fuels, indicating a gap in existing research methodologies that fail to integrate economic, environmental, and societal costs comprehensively. this suggests that future studies should aim to develop and apply such frameworks to better inform policy initiatives related to transportation infrastructure. • achieving energy security by reducing dependence on imported oil is highlighted as a foremost challenge for the united states, which currently imports about 50 percent of its oil consumption, accounting for 25 percent of world oil consumption. • the study indicates that many existing analyses do not account for the full range of costs associated with oil dependence, suggesting that a comprehensive understanding of these costs is necessary for effective policy-making regarding transportation fuels. • the study estimates the costs associated with energy security and the dependence on oil, highlighting that many studies have not fully accounted for the true costs of oil, which include various economic and environmental factors. • the research utilizes multiple models, such as greet and apeep, to assess environmental externalities of different transportation fuels, suggesting a need for a holistic framework to evaluate the relative costs and benefits of alternative fuels for future energy needs. a. naseri et al. /future energy august 2025| volume 04 | issue 03| pages 18-34 30 [19] energy system implications of demand scenarios and supply strategies for renewable transportation fuels • the paper employs a combination of bottom-up and top-down energy modeling approaches to address shortcomings in energy planning for renewable transportation fuels. this dual methodology allows for a more comprehensive analysis of energy demands and supply strategies. • the study designs a set of eight scenarios that vary in climate ambition, the share of indirect electrification of transport final energy demand, and biofuel availability, enabling a detailed examination of the implications of different demand scenarios on energy supply infrastructure. • the impacts of sustainable biofuels on the required electricity supply infrastructure are not well understood, indicating a gap in knowledge regarding how biofuel availability influences energy demand and infrastructure needs in the transport sector. • there is a lack of sufficient justification for the assumption of large shares of imported gaseous and liquid energy carriers, which neglects the needs of local societies and highlights a gap in addressing the socio-economic implications of renewable fuel imports in energy planning. • the transport sector faces significant challenges in reducing greenhouse gas (ghg) emissions due to the complex interplay of social behavioral, technical factors, political decisions, and economic conditions, necessitating detailed sub-sector demand modeling for effective energy planning. • the energy supply for climateneutral transportation services is expected to strain electricity supply infrastructure, with studies often overlooking local societal needs while assuming large shares of imported renewable fuels, highlighting a gap in understanding the impacts of sustainable biofuels on electricity supply infrastructure. • the study finds that bottom-up demand modeling of transport final energy demand significantly narrows down the ranges of renewable fuel energy demands that were previously assumed in top-down approaches. this indicates that more accurate demand modeling can lead to better energy planning and infrastructure development. • the availability of biofuels may considerably reduce the demand for e-fuels, which in turn lowers the required expansion of energy infrastructure. this results in a more gradual distribution of renewable energy expansions over the next 25 years and reduces the cost-optimal hydrogen production capacity and necessary grid expansion in germany beyond 2030. [20] electric vehicles and renewable energy • the paper discusses various charging methods for electric vehicles, including home solar systems, public charging stations with renewables, and smart charging systems. • it highlights the importance of integrating electric vehicles with renewable energy sources like solar, wind, and hydropower to minimize their carbon footprint and promote sustainability. • the paper demonstrates that the environmental impact of electric vehicles (evs) is significantly influenced by the source of their electricity, highlighting the importance of renewable energy sources such as solar, wind, and hydropower in reducing the carbon footprint of evs. • it presents the advantages of electric vehicles over gasoline vehicles, including lower maintenance needs, costeffectiveness, quieter operation, energy efficiency, and a positive impact on air quality, thereby promoting the transition towards a more sustainable and environmentally friendly energy landscape. a. naseri et al. /future energy august 2025| volume 04 | issue 03| pages 18-34 31 [21] energy saving in public transport using renewable energy • the paper evaluates the economic viability of hydrogen production through a discounted cash flow analysis, considering two different hypotheses: one focusing on the installation of a hydrogen station powered by grid electricity and the other incorporating the initial investments of renewable energy sources (biomass, wind, and sea wave) alongside the hydrogen station. • hydrogen production is primarily analyzed through the electrolysis process, which utilizes electrical energy supplied by various renewable sources, including wind, biomass, and sea wave, to generate hydrogen, thereby facilitating the replacement of diesel buses with hydrogenpowered vehicles in urban transport. • the paper does not provide a comprehensive analysis of the long-term sustainability and economic viability of the proposed hydrogen production methods, particularly regarding the operational and maintenance costs of the renewable energy sources (wind, biomass, and sea wave) over time, which could impact the overall feasibility of the project. • there is a lack of detailed exploration into the potential challenges and limitations associated with the implementation of hydrogen filling stations and the infrastructure required for supporting fuel cell vehicles, including regulatory, logistical, and technological barriers that may arise in the transition from diesel to hydrogen-powered public transport. • the variability of the sea wave energy source presents a challenge, as its availability is higher during the winter season and lower in the summer season. this variability can be addressed through the use of appropriate storage tanks to ensure a consistent supply of energy for hydrogen production. • the economic analysis of the hydrogen production system requires consideration of initial investments for the biomass power plant, wind farm, wave farm, and hydrogen station. the viability of the project depends on accurately estimating these costs and the potential avoided purchase of fossil fuels, which complicates the financial planning and investment decisions. • the study demonstrates that utilizing renewable energy sources such as wind, biomass, and sea waves for hydrogen production can effectively replace the entire fleet of dieselpowered buses in trapani with hydrogen vehicles, leading to significant reductions in greenhouse gas emissions. in the best-case scenario, the annual avoided emissions are quantified as 1444 tons of co2, 7.64 tons of co, 1.12 tons of pm10, 2.1 tons of nmvoc, and 22.85 tons of nox. • the economic analysis indicates that while the production of hydrogen from a self-sufficient renewable energy plant is not economically viable without incentives, the discounted cash flow for purchasing electrical energy for hydrogen production becomes comparable within five years under different scenarios, highlighting the financial challenges associated with transitioning to hydrogen fuel in public transport. [22] renewable energy generation and impacts on emobility • the paper highlights the need for a fundamental change in the road transportation sector to achieve a long-term transition to a low-carbon economy, which poses challenges in adapting existing infrastructure and services to meet demographic and economic growth without increasing pollution and congestion. • it emphasizes the requirement for affordable, secure, and inclusive sustainable solutions that are integrated with customer-centric infrastructure, indicating the challenge of developing such systems while ensuring they are efficient and effective for all users. • the paper highlights that the integration of electric vehicles (evs) with renewable energy sources can significantly reduce future emissions of greenhouse gases and air pollutants from road transport, contributing to a long-term transition to a lowcarbon economy. • it emphasizes the necessity for a fundamental change in the road transportation sector, advocating for the development of affordable, secure, and sustainable infrastructure and services that are customercentric, in order to adapt to demographic and economic growth while minimizing pollution and congestion. a. naseri et al. /future energy august 2025| volume 04 | issue 03| pages 18-34 32 [23] do patents, renewable energies and energy taxes in the transport sector reduce transportation carbon emissions in the european union? • the study analyzes the impact of renewable energy use, patent development, and energy taxes in the transport sector on the three different modes of transportrelated emissions (aviation, road, and rail) in the 10 highestincome countries of the european union over the period 2008–2020. • the study uses the novel halfpanel jackknife estimator for the analysis of the impact of patents, renewable energies, and energy taxes on carbon dioxide (co2) emissions in the transportation sector. • the transportation industry in the european union has not succeeded in reducing greenhouse gas emissions, making it the sole economic sector with increasing emissions, which poses a significant challenge in meeting climate targets. • the study highlights the need for effective strategies, such as promoting electric vehicles and eco-friendly transportation through energy taxes, and supporting renewable energy sources and patents for green innovations, to address the ongoing issue of co2 emissions in various modes of transport. • patents have been found to contribute to the reduction of co2 emissions specifically in aviation and rail transportation, indicating that innovation in these sectors can lead to lower greenhouse gas emissions. • renewable energies are effective in reducing emissions only in rail transportation, while energy taxes are effective in mitigating co2 emissions in road transportation, suggesting that different strategies may be needed for different modes of transport. [24] reducing transport sector co2 emissions patterns: environmental technologies and renewable energy • the research employs panel corrected standard error methods to analyze the data, which helps in addressing potential issues of heteroscedasticity and autocorrelation in the panel data set. • additionally, feasible generalized least squares methods are utilized to estimate the relationships between environmental technologies, renewable energy, and co2 emissions, allowing for more efficient and consistent parameter estimates in the presence of panel data characteristics. • the research does not explicitly identify specific gaps in existing literature or methodologies related to the impact of environmental technologies and renewable energy on co2 emissions in the eu transport sector, which could provide a clearer context for the study's contributions and limitations. • there is a lack of detailed exploration into the socioeconomic factors that may influence the adoption of renewable energy and environmental technologies in transportation, which could affect the overall effectiveness of the proposed strategies for emission reduction. • the study emphasizes the necessity for heightened eu investment in sustainable transport infrastructure and clean energy solutions, indicating that a lack of investment could hinder the adoption of environmental technologies and renewable energy, which are crucial for reducing co2 emissions in the transport sector. • it highlights the need for a multifaceted approach that includes comprehensive strategies for cleaner transportation, innovation, and education, suggesting that without these elements, the transition towards sustainable practices in the eu may be slowed or obstructed. • the study reveals a significant and variable effect of environmental technologies and renewable energy on co2 emissions in the eu transport sector, indicating that increased adoption of renewable energy is positively correlated with emission reduction. • the research emphasizes the necessity for heightened eu investment in sustainable transport infrastructure and clean energy solutions, recommending initiatives such as electric vehicles, hydrogen fuel cells, and biofuels to align with the goals of the european green deal and the eu climate law. a. naseri et al. /future energy august 2025| volume 04 | issue 03| pages 18-34 33 [25] utjecaj obnovljivih izvora energije na prijevoz • the paper discusses the use of photovoltaic modules in various vehicles, including solar and biodiesel vehicles, highlighting their ability to convert solar energy into electricity to power electric motors and other devices within the vehicles. this method emphasizes the importance of renewable energy sources in reducing greenhouse gas emissions and promoting environmental protection. • it also examines the integration of solar technology in marine applications, where photovoltaic modules are used to maintain battery charge levels in boats, addressing the increasing demand for electricity during periods of inactivity and preventing battery damage, thereby extending their lifespan. • the paper does not explore the economic feasibility and costeffectiveness of implementing renewable energy sources in transportation, particularly in comparison to traditional fossil fuels. a detailed analysis of the financial implications for consumers and manufacturers could provide insights into the broader adoption of these technologies. • there is a lack of discussion on the long-term sustainability and environmental impact of the production and disposal of renewable energy vehicles, such as solar and electric vehicles. research could focus on the lifecycle assessment of these vehicles, including the sourcing of materials, manufacturing processes, and end-of-life recycling or disposal methods. • not all renewable energy technologies are perfect, indicating that while they contribute significantly to environmental protection, there are still limitations and challenges in their efficiency and implementation in the transport sector. • electric vehicles, although environmentally friendly, face challenges related to their range and the need for recharging, which can limit their practicality compared to hybrid vehicles that can utilize both electric and fossil fuel power sources. • the increasing use of renewable energy sources in transportation, such as solar and biodiesel vehicles, significantly reduces greenhouse gas emissions, contributing to environmental protection and addressing global warming caused by nonrenewable energy depletion. • the integration of photovoltaic systems in vehicles, including boats, enhances battery longevity and efficiency, particularly during periods of inactivity, thereby addressing common issues related to battery depletion and damage, which ultimately supports the sustainability of marine and land transportation. [26] economic and environmental multi-objective optimisation to evaluate the impact of belgian policy on solar power and electric vehicles • the research employs a multiobjective branch and bound algorithm, originally developed by mavrotas and diakoulaki, which has been improved for the bi-objective case. this algorithm is designed to find all efficient solutions of multi-objective mixed integer linear programming (momilp) problems exactly, ensuring that the solutions are not dominated by any other feasible solutions. • the methodology distinguishes between energy generating technologies and transportation technologies, incorporating constraints that account for economies of scale. the model uses binary variables to indicate active technology intervals, allowing for a structured comparison of the economic and environmental impacts of various energy and transportation technologies while satisfying specific demand constraints. • the paper acknowledges the limitations of the model, particularly in differentiating between rational investors who consider life cycle costs and bounded rational investors who focus on required investments only. this distinction suggests a gap in understanding how different investor behaviors impact the adoption of energy and transportation technologies under varying policy measures. • the research highlights the need for further exploration of the impact of subsidies on the pareto frontier, indicating a gap in assessing how different subsidy structures could influence the optimal mix of energy and transportation technologies, particularly in terms of economic and environmental outcomes. • the paper highlights the challenge of differentiating between rational investors, who consider life cycle costs, and bounded rational investors, who often focus solely on required investments. this distinction affects the effectiveness of current policy measures aimed at promoting technologies like solar power and electric vehicles. • another challenge discussed is the limitation of grid-powered battery electric vehicles (bevs) in significantly reducing greenhouse gas (ghg) emissions compared to solar panels, despite their lower costs. this raises questions about the optimal mix of technologies and the impact of policy on achieving environmental goals. • the research demonstrates the use of multi-objective mixed integer linear programming (momilp) to identify optimal solutions for energy and transportation technologies, highlighting the differences in outcomes when considering the minimisation of total economic life cycle costs versus solely the initial investment. the results are illustrated through the pareto frontier, which shows the trade-offs between life cycle emissions and life cycle costs, both with and without the impact of policy measures. • the findings indicate that current policy measures effectively target rational investors who prioritize life cycle costs, while private investors, who may exhibit bounded rationality, tend to focus on required investments. this distinction reveals the limitations of policy effectiveness in addressing the needs of all investor types, particularly in the context of reducing greenhouse gas emissions through the adoption of various energy and transportation technologies. a. naseri et al. /future energy august 2025| volume 04 | issue 03| pages 18-34 34 [27] the effectiveness and trade-offs of renewable energy policies in achieving the dual decarbonization goals in china: a dynamic computable general equilibrium analysis • the study employs a dynamic general equilibrium model to assess the effectiveness and trade-offs of various renewable energy policies in achieving china's dual decarbonization goals by 2060. this model captures both direct and indirect effects of changes in the economy and identifies impact mechanisms across different sectors. • an indicator measuring the efficiency of carbon emission abatement is calculated by dividing the percentage changes in china's gdp by the amount of carbon emission abatement. this indicator helps evaluate the average economic loss associated with abating per billion tons of co2 through renewable energy policies, allowing for a comparative analysis of the policies' impacts on gdp and carbon emissions. • the paper highlights that previous studies have shown great disparity in the effectiveness and suitability of renewable energy policies in abating carbon emissions, indicating a lack of consensus and comprehensive understanding in the existing literature regarding the impact of these policies on carbon reduction. • while the study evaluates the effectiveness and trade-offs of various renewable energy policies, it acknowledges that the implications and limitations of the results are discussed, suggesting that further research is needed to explore the long-term effects and potential unintended consequences of these policies on the economy and energy structure. • the effectiveness of renewable energy policies in abating carbon emissions varies significantly, with some policies like the renewable energy cost (rec) showing greater effectiveness in reducing co2 emissions while also benefiting gdp, whereas others like the carbon market (crp) and renewable portfolio standards (rep) can lead to greater gdp losses despite their ability to reduce emissions. • most renewable energy policies tend to sacrifice internal and external demand in the economy, which poses a challenge for policymakers who must balance the need for carbon emission reductions with the potential negative impacts on economic growth and demand. • the study finds that renewable energy policies could abate china’s co2 emissions by 2.57 billion tons by 2060, with varying effectiveness among the policies. the reduction of renewable energy costs (rec) is identified as the most effective policy, followed by renewable portfolio standards (rep) and carbon market (crp). • while most renewable energy policies may lead to a sacrifice in china’s internal and external demand, they are expected to benefit employment and cause relatively slight damage to the gdp, with the rec actually raising gdp by 1.1713%. [28] a technical and economic assessment of renewable transportation fuels and technologies • the paper does not explicitly identify specific research gaps, but it implies a need for further exploration into the economic feasibility of producing renewable transportation fuels on a large scale from domestic resources, as well as the technological advancements required to enhance the efficiency of vehicles that utilize these fuels. • there is a lack of detailed analysis on the integration of renewable fuels with existing transportation infrastructure and the potential challenges that may arise in transitioning from petroleumbased fuels to renewable alternatives, particularly in terms of supply chain logistics and consumer acceptance. • the current transportation system is heavily reliant on petroleum-based fuels, making it vulnerable to supply and price volatility in the world oil market, which poses a significant challenge for energy security and stability. • despite advancements in reducing tailpipe emissions, motor vehicles still contribute significantly to urban air pollution and greenhouse gas emissions, indicating a need for the development and adoption of lower-polluting alternatives to internal combustion engines. • the paper highlights that transitioning to renewable transportation fuels derived from sources such as solar, wind, hydropower, and biomass could significantly reduce greenhouse gas emissions and local air pollutants, especially when used in zero or near-zero emission vehicles like batterypowered electric vehicles or fuel cell electric vehicles. • it emphasizes the potential for large-scale economic production of renewable fuels from domestic resources, which could alleviate the vulnerabilities associated with petroleum-based fuels and contribute to a more sustainable and environmentally friendly transportation system. mfi chowdhury et al. /future energy november 2024| volume 03 | issue 04| pages 18-46 18 review unlocking the potential of green hydrogen for a sustainable energy future: a review of production methods and challenges md farhan imtiaz chowdhury*, md fahim sadat bari, muhaiminul islam, wasif sadman tanim, redoy masum meraz department of mechanical engineering, chittagong university of engineering and technology, bangladesh a r t i c l e i n f o article history: received 10 june 2024 received in revised form 12 july 2024 accepted 25 july 2024 keywords: sustainable energy, green hydrogen, water electrolysis, biomass gasification, decarbonization *corresponding author email address: u1903002@student.cuet.ac.bd doi: 10.55670/fpll.fuen.3.4.2 a b s t r a c t the buzz around green hydrogen is growing louder as a game-changer in the fight for a clean and sustainable energy future. this article dives into the coolest ways to create this eco-friendly fuel, exploring methods like splitting water with electricity, turning plant matter into gas, and even some cutting-edge techniques in the pipeline. this research dives deep into the latest breakthroughs in electrocatalyst and electrode materials, the secret ingredients that could supercharge hydrogen production, making it cleaner and cheaper. while good old water electrolysis using alkaline and pem electrolyzers is the current champ, it's still a bit pricey and not as efficient as we'd like. thankfully, innovative ways to design these "fuel-splitting champions" and integrate them with renewable energy sources are showing promise as solutions. but green hydrogen isn't just some cool science experiment; it's a potential game-changer for cleaning up our transportation, factories, and even the way we power our homes, all to fight climate change. the study also identifies areas where we need more research and ironing out of kinks before widespread use. it emphasizes the importance of keeping the innovation train rolling, smart investments in this technology, and government policies that give it a green light. by pushing green hydrogen forward, we can slash greenhouse gasses, become more energy-independent, and finally build that sustainable energy future we've all been dreaming of! 1. introduction our planet's running on fumes! we desperately need to eliminate dirty fuels like coal and gas, and luckily, there are some awesome alternatives on the horizon. sunshine, wind, heat from the earth's core, and even the power of moving waterthese renewable sources hold immense promise (but they're not without their quirks) [1-2]. enter hydrogen: this champion packs a serious energy punch, way more than other contenders, making it a strong candidate for the future of clean energy. it is also essential in significant quantities for hydroprocessing in petroleum refineries, cleaning natural gas, and upgrading biofuels. however, hydrogen gas is not naturally available on earth and must be extracted from various resources like fossil fuels, organic materials, and water. extracting hydrogen from these sources remains a prevalent but challenging task. currently, most of the hydrogen we use comes from revamping natural gas, particularly methane. this process, known as steam methane reforming (smr), is like breaking down natural gas molecules to get the hydrogen out. it's the most popular and affordable way to do this, and it is responsible for around half of all hydrogen production globally. in the us, smr is the champion, churning out a whopping 95% of the country's hydrogen from natural gas [3-4]. pretty much everyone agrees: our co2 emissions are climbing, fueled by a growing population and developing countries needing more energy. this is why there's a big push for sustainable energy sources, and guess what's getting a lot of buzz? hydrogen. some experts even think it could be the key to a future "hydrogen economy" [5]. the allure of hydrogen lies in its clean, burning natureit creates no co2 when used for power. but here's the catch: to get that hydrogen, we currently rely heavily on fossil fuels, which pump out tons of co2 in the process. to cut these emissions, scientists are looking at ways to cook up hydrogen from renewable sources like plants and waste. they're experimenting with different methods, like superheating plant matter with water or turning plant-based fuels into hydrogen gas. this focus on bio-stuff for hydrogen production future energy open access journal https://doi.org/10.55670/fpll.fuen.3.4.2 november 2024| volume 03 | issue 04 | pages 18-46 journal homepage: https://fupubco.com/fuen issn 2832-0328 mailto:u1903002@student.cuet.ac.bd https://doi.org/10.55670/fpll.fuen.3.4.2 https://fupubco.com/fuen mfi chowdhury et al. /future energy november 2024| volume 03 | issue 04| pages 18-46 19 is a win-win. it not only cleans things up, but the variety of plant sources available also makes our energy supplies more secure and boosts the economy in developing countries, which is a big deal [6]. a method for producing hydrogen without using fossil fuels is essential [7–10]. fossil-free methods include photocatalysis, thermochemical water splitting, and electrolysis. of these methods, only electrolysis in alkaline electrolyzers at moderate temperatures around 75°c is commercially available. although advanced in development, alkaline electrolysis requires an entirely electric energy input, which increases operating costs. some of this electric energy can be replaced with cheaper thermal energy if electrolysis is conducted in solid oxide electrolyzers at temperatures between 500-1000°c. however, even at high temperatures, the proportion of energy that can be substituted with thermal energy is limited to less than 30%. unlike electrolysis, thermochemical water-splitting processes use only thermal energy to split water and are theoretically highly efficient. electrolyzers are classified into four main types: polymeric, alkaline, and solid oxide electrolyzers [11]. the process of direct water splitting by using sunlight is termed a photolytic process, which involves using light energy to separate water molecules into hydrogen and oxygen [12]. the replacement of fossil fuels with green hydrogen presents an effective means of alleviating the environmental impact attributed to energy-related industries, notably climate change, global warming, and acid rain. green hydrogen is anticipated to exert a significant influence on forthcoming power and electricity systems and will be indispensable for cutting carbon emissions of energyintensive domains like transportation and buildings. producing green hydrogen from renewable resources is key to promoting sustainable energy production. it holds the potential to meet the hydrogen demand of these sectors while yielding markedly reduced environmental effects compared to fossil fuels [13]. countries worldwide want to decarbonize by 2050 to combat climate change, with green hydrogen playing a critical part. green hydrogen, produced through water electrolysis, is essential for renewable energy power plants as well as a variety of industrial and transportation applications. this paper examines water electrolysis technologies, pricing, and current advancements in electrode materials and identifies research gaps and commercial electrolyzer limits. it also investigates hydrogen synthesis from ammonia breakdown with mixed metal oxide catalysts, addressing the issues of hydrogen storage and distribution. the review focuses on recent developments in electrocatalysts and electrolyzers, such as seawater electrolysis, as well as innovations in biomass steam gasification for hydrogen production, emphasizing the importance of renewable electricity in these processes. 2. water electrolysis electrolysis of water is an electrochemical method for producing green hydrogen that uses power and produces no emissions. the following equation shows the fundamental reaction for water electrolysis. h2o + electricity (237.2 kj mol−1 ) + heat (48.6 kj mol−1 )= h2 + 0.5o2 (1) the concept of dividing water into oxygen and hydrogen fuel is quite intriguing: in theory, it shouldn't take much zap (around 1.23 volts) to do the trick at room temperature. but in the real world, things get a bit trickier – we actually need a little more juice (around 1.48 volts) to overcome some roadblocks and inefficiencies in the process [14]. while scientists have known about water splitting for hundreds of years, making it affordable hasn't been easy. that's why, even today, only a small fraction (around 4%, or 65 million tons) of the world's hydrogen comes from this eco-friendly method. most of the hydrogen we use is actually a leftover from a different industrial process [15] . the evolution of water electrolysis technologies boasts a rich history, dating back to the 18th century [16]. this continuous development has been driven by various trends, leading to roughly five distinct generations of the technology. notably, this journey has witnessed the emergence of four key types differentiated by their electrolytes, operating conditions, and ionic agents (hydroxyl (oh-), proton (h+), and oxide (o2-): • alkaline water electrolysis • aem water electrolysis • pem water electrolysis • solid oxide water electrolysis despite these variations in the underlying mechanisms, the fundamental principle of water splitting remains consistent across all types [17]. 2.1 alkaline water electrolysis alkaline water electrolysis (figure 1), a long-established and mature technology, is widely used for industrial hydrogen production. it has been operational since the late 18th century, with significant advancements leading to the first large-scale plant in 1939. this process, which operates at temperatures between 30° and 80°c with a concentrated alkaline solution (5m koh/naoh), uses diaphragms made of asbestos and zro2 and electrodes made of stainless steel coated with nickel. alkaline water electrolysis is not only a well-established technique that can reach multiple megawatts, but it is also economically viable for large-scale operations. it costs usd 500-1000/kw and boasts a system lifespan of 90,000 hours, making it a practical choice for industrial applications [18]. despite its advantages, the technology faces limitations, such as low current densities (0.1–0.5 a/cm²) due to the moderate mobility of oh⁻ ions and the corrosive nature of koh. the electrolyte’s sensitivity to co₂ results in the formation of k₂co₃, which clogs the anode, impeding ion transfer and reducing hydrogen production. additionally, the system yields gases of lower purity (99.9%) because the diaphragm fails to entirely obstruct gas crossedover between the half-cells [18–22]. many firms worldwide have successfully deployed and employed this technique for industrial applications. nevertheless, there is a need for further advancements in this technology, including enhancing current density and minimizing gas crossover. new electrode materials and separators need to be developed to solve these problems. additionally, integrating a renewable energypowered electrolyzer for acidic water (e.g. solar, wind) helps save capital costs. some research institutes and organizations are still attempting to improve efficiency and reduce hydrogen production costs. by development of low-cost and noble metal-free mos2@ni0.96s as a heterojunction hybrid mailto:mos2@ni0.96s mailto:mos2@ni0.96s mailto:mos2@ni0.96s mailto:mos2@ni0.96s mailto:mos2@ni0.96s mfi chowdhury et al. /future energy november 2024| volume 03 | issue 04| pages 18-46 20 electrodes designed for the hydrogen evolution reaction (her) and oxygen evolution reaction (oer) in alkaline surroundings. mos2@ni0.96s-1. the electrocatalyst demonstrated the most significant response, with a considerably lower overpotential of 104 mv at 10 macm−2, in contrast to the overpotential of 182 mv for both the her and oer at the same temperature. additionally, obtained a lower cell voltage of 1.86v to separate water in the aggregate and displayed greater stability during 15 hours of nonstop operation [23]. the improvement of this material is attributed to the numerous heterojunction interfaces present within it, the increased exposure of active sites, and the strong integration between ultrathin mos₂ nanosheets and nonstoichiometric ni₀.₉₆s nanocrystals mos₂@ni₀.₉₆s-1h [24]. researchers have created a bifunctional electrocatalyst in nanostructure, nico-nicoo₂@cu₂o@cf, designed for overall water splitting and evaluated its performance in a 1m koh mixture. this electrocatalyst exhibited enhanced electrochemical performance for both the hydrogen evolution reaction (her) and the oxygen evolution reaction (oer) in alkaline media, with low overpotentials of 133 mv and 327 mv, respectively, to achieve a current density of 10 ma cm². it also showed small tafel slopes of 119 mv dec⁻¹ for her and 118 mv dec⁻¹ for oer. the electrocatalyst's effectiveness was further confirmed through single-cell electrolysis, where it achieved a cell voltage of 1.69 v at a current density of ≥10 ma cm⁻². it remained stable for 12 hours of continuous electrolysis within a very acidic solution due to the strong physical cling of nico-nicoo₂ nanoparticles. the enhanced efficiency is attributed to the compact dimensions and even spread of the nano heterostructures across the surface of the copper foam after oxidation. this facilitated optimal utilization of active sites during electrochemical reactions [25]. researchers created a very effective bifunctional electrocatalyst using nicop nanoflakes (nico(nf)-p) derived from the 2d metal-organic framework (mof) for overall water splitting in alkaline conditions. they assessed its functionality by employing a threeelectrode cell configuration and conducting linear sweep voltammetry (lsv) with a cycling rate of 2 mv s⁻¹ in a 1m koh solution. the electrocatalyst nico(nf)-p exhibited excellent electrocatalytic performance, with a lower onset mili-voltage of 37 mv for the hydrogen evolution reaction and 1.435 v for the oxygen evolution reaction at a current density of 100 ma cm⁻², outperforming the commercial 5% pt/c (43 mv) and iro₂ (1.504v). furthermore, nico(nf)-p had low overpotentials of 0.119v for her and 0.315v for oer, compared to 291 mv for pt/c and 400 mv for iro₂, to achieve a current density of 100 ma cm⁻². the tafel slopes were also much lesser for nico(nf)-p (0.112v dec⁻¹ for her and 0.066v dec⁻¹ for oer) than for pt/c (164 mv dec⁻¹) and iro₂ (88 mv dec⁻¹), indicating efficient electric current flow at the surfaces of electrocatalytic materials. furthermore, the stability of the developed nico(nf)-p electrocatalyst was tested at various current densities (100, 500, and 1000 ma cm⁻²) for both. through chronopotentiometric (v-t) measurements of continuous operation, the data indicated consistent electrochemical performance over a 30-hour period for both her and oer, as depicted in figure 2. this study involved the synthesis of a carbon-supported ni-mo-o/ni₄mo electrocatalyst having nanointerface doped-up with n (nimo-o/ni₄mo@nc) using calcination and electrodeposition methods. the electrocatalysis performance of this catalyst for an evolutionary process using hydrogen in a 1m koh alkaline solution was thoroughly evaluated. the ni-mo-o/ni₄mo@nc electrocatalyst unequivocally demonstrated remarkable electrocatalytic activity, exhibiting a significantly lower overpotential of 61(mv) at a current density of 10 ma cm⁻². this astounding performance, 50% lower than that of ni-mo-o (0.120v), can be attributed to the n-doped layers of carbon. under neutral conditions in a 1m pbs solution, ni-moo/ni₄mo@nc exhibited an overpotential of less than 60 mv, while ni-mo-o showed an overpotential of around 100 mv. figure 1. diagram depicting the working principle of alkaline water electrolysis [24] about:blank about:blank about:blank about:blank about:blank mfi chowdhury et al. /future energy november 2024| volume 03 | issue 04| pages 18-46 21 the tafel slope for ni-mo-o/ni₄mo@nc was 0.099v dec⁻¹, which is less than the tafel slope of ni-mo-o, which was 135 mv dec⁻¹ [26]. creating an efficient her electrocatalyst, co₂p/n@ti₃c₂tx@nf, with 3-dimensional porous architectures and interactions between heterostructures. they utilized a process that included nitriding and electrodeposition in two steps on mxene-modified nf. this electrocatalyst performed well in 1m koh solution, with an excessive potential of 15 mv at 10 ma cm⁻² and a tafel incline of 0.030v dec⁻¹. it also remained stable after 3000 cv cycles. dft simulations revealed significant binding energy (−0.822 ev) and ideal hydrogen adsorption energy, showing its potential as an effective electrocatalyst for her [27]. 2.2 anion exchange membrane (aem) water electrolysis aem water electrolysis is an emerging method for producing green hydrogen. aemwe is gaining popularity among research organizations and institutions due to its low cost and superior performance compared to traditional electrolysis technologies. we and scott published the first scholarly article on aemwe in 2011. since then, several researchers have contributed to its advancement [28]. aem water electrolysis technology is comparable to traditional alkaline water electrolysis [29]. alkaline water electrolysis differs from aem water electrolysis in that it replaces traditional asbestos diaphragms with quaternary ammonium ion exchange membranes. aem water electrolysis has various advantages, including using cost-effective transition metal catalysts instead of noble metal catalysts and using purified water or a low-concentration alkaline solution (1m koh) as the electrolyte instead of a high-concentration solution (5 koh solution) [30]. aem water electrolysis utilizes an anion exchange membrane and electricity to split water through electrochemical reactions. the process involves two main reactions: the hydrogen evolution reaction (her) and the oxygen evolution reaction (oer). at the cathode, water molecules are reduced to produce hydrogen gas (h₂) and hydroxyl ions (oh⁻) by gaining electrons. hydrogen is released at the cathode, while oh⁻ ions move across the membrane towards the anode, attracted by its positive figure 2. the electrocatalytic activity of the following synthesized electrocatalysts will be evaluated: ldh(ns), nico(ns)-p, mof(nf), nico(nf)-p, nico(nr)-p, as well as the commercial 5% pt/c and iro2.(a) polarization curves for the hydrogen evolution reaction (her), (b) her potential failures at varying current densities of 100, 500, and 1000 macm−2, (c) tafel slopes for the her, (d) polarization curves for the oxygen evolution reaction (oer), (e) different current densities of 100, 500, and 1000 ma cm−2 used to measure oer overpotentials.(f) tafel incline for the oer, (g, h) stability studies (v-t curves) of the nico(nf)-p electrocatalyst for both her and oer at current densities of 100, 500, and 1000 ma cm−2,(i) polarization curves of nico(nf)-p and nico(nf)-p; commercial iro2 and 5% pt/c for overall water splitting. the inset shows the v-t curves of nico(nf)-p at the specified current densities for the overall water splitting process [25]. mfi chowdhury et al. /future energy november 2024| volume 03 | issue 04| pages 18-46 22 charge. simultaneously, electrons flow through an external circuit to the anode. at the anode, oh⁻ ions recombine to form water and oxygen gas (o₂), which is released. this describes the fundamental operation and half-cell reactions involved in aem water electrolysis figure 3. significant advances and challenges characterize the field of aem water electrolysis. the technology is currently in the developmental stage, steadily progressing towards kwscale applications. many international research organizations and institutions are currently engaged in the advancement of aem water electrolyzers, as outlined in table 1. however, substantial advancements and enhancements are necessary to expand the utilization of this technology for business purposes. key challenges include achieving sufficient stability, with current targets aiming for operational lifetimes of up to 100,000 hours, and reducing the high cost of hydrogen production. as of 2020, the production cost was approximately usd 1279 per kw/h₂, with a target of reducing this cost to usd ≤ 300 per kw/h₂ by 2050. recent progress has been achieved in tackling these obstacles, including the creation of a 3d electrode for producing oxygen using noncrystalline nifeooh on activated carbon fiber paper. this electrode showed excellent electrochemical performance in a 1m koh solution, with an overpotential of just 170 mv at 10 ma cm⁻², a low tafel slope of 39 mv dec⁻¹, and exceptional stability over 240 hours of continuous operation. synthesis report of cu-co-p on carbon paper via electrodeposition techniques optimized for her in alkaline solutions and enhancement of electrochemical performance through surface modification and copper (cu) incorporation. the modified cu-co-p1200/cp electrode demonstrated significant enhancements, having an excessive potential of 59 mv at 0.010a cm⁻² and a tafel incline of 0.038v dec⁻¹ presented in figure 4. this electrode also demonstrated promising performance in a single-cell aem water electrolyzer setup. additionally, the development of a nonnoble metal electrocatalyst cu₀.₅co₂.₅o₂ anodes by means of co-precipitation techniques showed improved performance with an overpotential of 285 mv at 10 ma cm⁻² in 1m koh solution. this electrode maintained high stability during extended operation, including achieving a current density of 1.3 a cm⁻² at 1.8 v and demonstrating durability over 2000 hours at 10 ma cm⁻². furthermore, advancements in poly (fluorenyl-coaryl piperidinium) (pfap)-based anion exchange materials as electrolytes and binders have contributed to achieving high ionic conductivity and durability under alkaline conditions. combined with platinum group metal (pgm) catalysts, these materials achieved impressive cell performances and durability, highlighting their potential for practical applications in aem water electrolysis. overall, while significant progress has been made in improving the performance and durability of aem water electrolysis technologies, ongoing research and development efforts are essential to overcome remaining challenges and commercialize this technology effectively [32–35]. 2.3 pem water electrolysis in pem water electrolysis, water undergoes electrochemical splitting into hydrogen and oxygen. initially, at the anode, water molecules decompose to produce oxygen (o₂), protons (h⁺), and electrons (e⁻). oxygen is released from the anode surface, while protons migrate through the protonconducting membrane to the cathode. simultaneously, electrons flow through an external circuit to the cathode. at the cathode, protons and electrons combine to form hydrogen gas (h₂). this process outlines the fundamental principle of pem water electrolysis, as depicted in figure 5. pem water electrolysis technology has achieved a high level of technical maturity and is currently available for industrial and transportation applications on the megawatt (mw) scale. this is facilitated by several prominent manufacturers, as indicated in table 1. further enhancements are required to effectively lower the cost of hydrogen production, which currently ranges from usd 700 to 1400 per kw/h₂ (2020), with a targeted reduction to usd ≤ 200 per kw/h₂ by 2050. challenges include replacing or reducing platinum group metals, minimizing costs associated with bipolar plate coatings, and optimizing membrane thickness to enhance cell efficiency (figure 6). figure 3. schematic representation of the working principle of aem water electrolysis electrolysis [31] mfi chowdhury et al. /future energy november 2024| volume 03 | issue 04| pages 18-46 23 figure 4. a) the her diagrams depicting polarization of cu-co-p1200/cp electrodes were rigorously tested with varying concentrations of cu2+ in a 1m koh sol. at a scanned rate of 0.005v/s. b) investigating the impact of changing cu2+ concentrations on overpotential while upholding a constant current density of 10 ma/cm2. c) tafel slopes. d) current-voltage polarization curves of a single cell aem water electrolyzer with iro2/cp as the anode, paired with the as-synthesized cu10-co-p1200/cp electrode as the cathode, and a comparison with the commercial pt/c/cp [32]. figure 5. schematic illustration of the pem water electrolysis operating principle [31] mfi chowdhury et al. /future energy november 2024| volume 03 | issue 04| pages 18-46 24 efforts towards cost reduction include innovative approaches such as integrated electrode architectures. for instance, integrated pt nanowires on ultrathin titanium gas diffusion layers (ptnw/ti) have demonstrated promising performance in pem water electrolyzers, achieving a lower overpotential of 63 mv at 100 ma cm⁻² and a cell voltage of 1.643 v at 1 a cm⁻² with significantly reduced catalyst loadings compared to conventional meas. additionally, synthesized ionomer-free electrodes (1t-2h mos₂ns/cfp) for hydrogen evolution, showing a minimal overpotential of 192 mv and a cell voltage of 2.25 v at 2 a/cm² in pem water electrolyzers. despite commercial pt/c catalysts exhibiting slightly lower cell voltages (2.18 v), the performance of these integrated electrodes represents a notable advancement over non-noble catalysts. these innovations underscore ongoing efforts to enhance the efficiency and cost-effectiveness of pem water electrolysis technologies for broader market adoption [37]. 2.4 solid oxide water electrolysis solid oxide water electrolysis typically operates at elevated temperatures, utilizing water in the form of steam to produce green hydrogen and oxygen. during the process, at the cathode, water molecules are initially reduced to hydrogen (h₂) and oxide ions (o₂⁻) through the addition of two electrons. hydrogen is released from the cathode, while oxide ions migrate through an ion exchange membrane to the anode. at the anode, oxide ions undergo further reduction to produce oxygen and electrons. oxygen is then released from the anode, and electrons travel back to the cathode through an external circuit due to the positive charge attraction. this outlines the fundamental operational principle of solid oxide water electrolysis, depicted in figure 7. solid oxide water electrolysis technology is currently advancing towards commercialization, with various global research institutions and organizations actively involved in its development. several commercial manufacturers of solid oxide electrolyzers are listed in table 1. this technology offers high energy efficiency by operating at elevated temperatures and utilizing non-noble metal electrocatalysts. however, challenges such as long-term stability and high hydrogen production costs remain significant. presently, stability is around 20,000 hours, with a targeted improvement to 100,000 hours, while the current hydrogen production cost stands at usd 2000 per kw/h₂ (2020), with a goal to reduce it to usd ≤ 200 per kw/h₂ by 2050.to address these challenges, efforts are focused on enhancing long-term stability through electrochemical fluctuations of electrode materials and exploring new perovskite materials for improved durability. additionally, scaling up electrolyzer production with renewable energy sources is being pursued to reduce costs. recent advancements include the development of ni1−xcdxo-sdc composite oxide materials for hydrogen electrodes in reversible solid oxide cells. their r-ni0.9cd0.1o-sdc electrode exhibited high electrocatalytic activity and stability under various conditions (figure 8 and figure 9). figure 6. this is a graphical illustration of an electrolyte without ionomers featuring ultra-low-loading, defect-rich 1t-2h mos2 nanosheets synthesized in situ. the haadf-stem visuals in (a–f) confirm the presence of boundaries, fissures, and atomic holes simultaneously in defect-rich 1t-2h mos2ns/cfp. the polarization curves of mos2 assemblies/cfp and 1t-2h mos2ns/cfp with defects are displayed in (g), along with the corresponding tafel plots in (h). moreover, (i) demonstrates the polarization curves of defected 1t-2h mos2ns/cfp and mos2 assemblies/cfp in a pemec at 353k [36]. mfi chowdhury et al. /future energy november 2024| volume 03 | issue 04| pages 18-46 25 figure 7. schematic view of solid oxide water electrolysis working principle [31] figure 8. physicochemical and electrochemical performance of the developed irru@wo3 nanorods.(a) the diagram shows the synthesis procedure of irru@wo3. (b) the left image is a scanning electron microscope (sem) image, and the right image shows a sectional view of the array. (c) a transmission electron microscope (tem) image displays a single nanorod.(d) a high-resolution tem (hr-tem) image demonstrates the irru coating, with blue indicating ru and purple indicating ir. inset images provide magnified views of specific areas. (e) a selected area electron diffraction image is displayed. (f) a scanning tem (stem) image illustrates a single nanorod with overlapping element mapping. (g) a high-angle annular dark-field (haadf)-stem image displays an irru grain. elemental mapping of ir, ru, w, and o is presented, along with a merged picture and scanning lines parallel to the pink line. (h) cv curves are included, with a darked/marked area representing the oer stabilities.(i) oer lsv curves are shown. (j) i-v polarization curves for a single electrolyzer at 353k are displayed. (k) durability testing at 353k at same current density is also included [37]. (to understand the color references in the figure legend, please consult the online version of the article.) mfi chowdhury et al. /future energy november 2024| volume 03 | issue 04| pages 18-46 26 figure 9. (a) patterns from xrd analysis; (b) images from tem and hrtem; (c, d) patterns from corresponding fourier transforms of iro2; (f) images from tem and hrtem; (h) images from haadf; and the corresponding mapping of ir, o, c, and n elements in iro2/cn; (i) images from tem and hrtem; (k) images from haadf; and the corresponding edx mapping of ir, o, c, and n elements in iro2/n-cn. (l) i-v polarization curves, (m) iro2/n-cn stability over 300 hours at 1.6 a cm2, and (n) iro2, iro2/cn, and iro2/n-cn mass and specific activities at 12.48 v [38] table 1. global main electrolyzer manufacturers and their specifications alkaline water electrolysis manufactured by origin of country generic name h2 capacity (m3/h) pressure (psi) energy used (kwh/nm3) ref. nel. norway a3880 2784–4500.8 2900.75 3.8–4.4 [39] cummins canada hystatâ® -100–10 116 145.038 5.0–5.4 [31] john cockerill belgium dq-500 580 435.113 4.0–4.3 [31] mcphy france melyzer 800–30 928 435.113 4.5 [40] sunfire germany hylink alkaline 2586.8 435.113 4.7 [41] nuberg peric china–india zdq-600 696 290.075 4.6 [42] tianjin mainland china fdq800 1160 72.5189 4.4 [35] greenhydrogen denmark hyprovide a-90 104.4 507.632 4.3 [43] aem water electrolysis enapter germany aem multicore 210 35 4.8 [44] pem water electrolysis nel. norway m5000 5800 435.113 4.5 [45] cummins canada hylyzerâ® -4.000-30 4640 435.113 4.3 [31] siemens germany silyzer 300 116–2320 507.632 n/a [46] proton onsite usa m400 483.72 435.113 n/a [47] itm power uk hgasxmw 127.6–2204 290.075 n/a [48] plug power usa genfuel 5 mw 1160 580.151 5.2 [31] elogen france elyte 260 301.6 435.113 4.9 [49] solid oxide water electrolysis sunfire germany hylink soec 870 580.151 3.6 [41] mfi chowdhury et al. /future energy november 2024| volume 03 | issue 04| pages 18-46 27 introduction of cobalt-free ba1−xndxfeo3−δ perovskite materials as oxygen electrodes in solid oxide cells, demonstrating high electronic conductivity and low thermal expansion coefficients, along with significant current densities at high temperatures. these developments underscore ongoing efforts to improve the efficiency, stability, and cost-effectiveness of solid oxide water electrolysis technology for broader commercial applications [50–52]. 2.5 biomass gasification hydrogen can be produced through various methods, as illustrated in figure 10. these methods include thermochemical processes, which require heat, organic reactants like water or ammonia, and fossil fuels to be effective [53]. the biological technique uses microbes (bacteria and microalgae) to convert biomass into hydrogen through a biological reaction [55]. sunlight or organic molecules serve as the activator for this approach. two biological processing technologies, microbial biomass conversion (mbc) and photobiological techniques, are employed to produce hydrogen. the most common method for producing hydrogen is through electrolysis using electricity, assuming the electricity comes from zero-carbon sources such as solar and photovoltaic energy [50,56–59]. variable electricity generation from sources such as solar and photovoltaics is insufficient to guarantee a consistent hydrogen supply. consistent production methods, which are currently reliant on fossil fuels, need to be supplemented. utilizing established technologies, biomass energy has the potential to play a significant role in producing energy carriers like biomethane or syngas, which can be converted into hydrogen as required. there is a wealth of scientific literature [60–65], which showcases the different methods of converting biomass into hydrogen, which can be categorized into two main groups. these processes involve biochemical reactions driven by microorganisms and photo-fermentation, as well as thermochemical reactions like pyrolysis & gasification. after that, the subsequent procedures involve syngas upgrading and biomethane reforming. in order to generate a gas that contains a high proportion of hydrogen and minimal carbon content, it is essential to utilize a hydrogenizer to alter the hydrogen-rich syngas. this process involves reducing the carbon monoxide (co) content by converting it into carbon dioxide (co₂) and hydrogen (h₂), and then eliminating the co₂. figure 10. production methods of hydrogen [54] specialized water-shift reactors with steam injection that are pressurized and co₂ removal systems can be employed to effectively eliminate the carbon content [66]. 2.6 experimental gasification plant an early version of the gasifier, designed for the process of converting a substance into gas using air, was adapted for oxy-gasification experiments, requiring technical and mechanical modifications to the feed framework, piping, and gasification agent allocation to guarantee consistent reaction conditions (figure 11). special attention was given to sealing the gasifier to prevent air infiltration during the oxy-steam gasification process, which operates at higher temperatures. oxygen was kept in pressurized tanks at 200 bars for gasification, while a small electric boiler produced saturated steam at 4 bars, with a capacity of up to 10 kg/h. the process line had different meters and sensors to control and oversee the conditions during experiments. the gasifier functions in a semi-batch manner, where biomass is held in a tightly sealed container, allowing for around 8 hours of self-sufficiency. the biomass is transported into the reactor by a screw conveyor in an automated manner. upon ignition with a removable external heater, the process becomes auto-thermal. the gasifier is maintained at near-atmospheric pressure by a blower and oxygen supply, with downstream sections at slightly lower pressure to prevent air leakage. a mobile scraper is used to frequently clean the grate supporting the reaction bed in order to avoid the accumulation of char along with ash. the system for removing impurities from syngas consists of three cyclones in a row and a filter made of biomass and fabric. after the experiment, the ash is kept in a sealed tank for later removal. an agilent 3000 micro-gas chromatograph is used to constantly check the composition within the syngas. it measures significant elements like co, co2, h2, ch4, n2, o2, and other hydrocarbons. this allows for ongoing evaluation of the gasification process. analysis of tar and solid particles is conducted once the operating conditions become stable, following the guidelines outlined in cen/ts 15439:2006. the facility is outfitted with an electronic system that gathers data to oversee and document the primary operational variables, such as temperatures, pressures along with syngas flow. this ensures accurate control and assessment of the gasification process [67,68]. mfi chowdhury et al. /future energy november 2024| volume 03 | issue 04| pages 18-46 28 3. hydrogen generation from syngas evaluation of effectiveness enhancing the level of hydrogen concentration in syngas generated by oxy-steam gasification can reduce its carbon content. a hydrogenation plant capable of producing large amounts of h2 and co2 gases and the system was constructed and tested using the aspen plus® tool. the hydrogenizer, depicted in figure 12a, relies on syngas generated from the oxy-steam gasification process. to lower co content, we employed a straightforward configuration with a single water-shift. to reduce the amount of steam used and minimize its effect on the energy requirements of the hydrogenizer, the method employs absorption using a heated potassium carbonate solution to remove co2. this method is chosen for its well-established efficiency in co2 removal; the off-gas experiences low hydrogen loss, and the rich solution requires modest heat for regeneration. the hydrogenizer efficiently recovers sensible heat from several streams to improve energy sustainability [69]. 3.1 configuration of the plant the plant operates by first cooling high-temperature syngas to 300°c to prevent tar condensation, producing some steam in the process. the resulting syngas is subsequently cooled to the surrounding temperature by employing a water-based scrubber, which eliminates small particles and condensable tar. the treated water is utilized on steam generators downstream. a portion of the purified syngas is directed towards a boiler in order to provide the steam required for the complete gasification and hydrogen production facility. a three-way modulating valve ensures the correct amount of syngas is sent to the boiler, making the system self-sufficient and not reliant on external energy sources. the carbon dioxide emissions resulting from this technique are deemed to be carbon neutral due to the bioorigin of the syngas. the remaining syngas is used for hydrogen production. operating at 3.9 bar, prior to entering the co-shift catalytic reactor, the syngas undergoes compression and is combined with steam, where co reacts with steam to produce co2 and h2. the mixture needs to enter the reactor at 320°c, so it is preheated using a heat regenerator that recovers heat from the reactor's exothermic reaction. the reaction that occurs is, co(g) +h2o(g) → co2(g) +h2(g) (2) the gas produced by the co-shift reactor contains a significant amount of co2, which is captured using a hot potassium carbonate solution. this process involves an absorber to separate co2, a heat exchanger for heat recovery between lean and rich solvents, and a heat exchanger is used to recycle heat within lean and rich solvents, while a stripper is employed to extract carbon dioxide (co2) from the rich solution by utilizing heat from medium-pressure steam condensation. the reaction taking place for co2 capture, co2(g) +k2co3(aq) +h2o(l) → 2 khco3(aq) (3) the plant requires a significant amount of steam for various processes: in order to make gas with oxygen in the gasification process, to keep the exact molar ratio of steam to carbon in the co-shift reactor, and to strip co2 in the reboiler. to ensure the system's independence from external energy sources and to maintain the renewable origin of the hydrogen, part of the syngas is used to meet the thermal power demand. a syngas cooler located downstream of the gasifier is responsible for the production of steam and additional steam is generated in a syngas-fired boiler, ensuring the hydrogen production system is energetically autonomous. 3.2 photocatalytic water splitting photocatalysis, sometimes termed artificial photosynthesis because it mimics the process of photosynthesis in plants, involves enhancing or altering the rate of redox reactions with the help of solar energy and a stable semiconductor that remains unaffected and unconsumed during the reaction [70]. the core of photocatalytic hydrogen production is a semiconductor photocatalyst capable of converting solar energy into chemical energy. ideal photocatalysts should be efficient, affordable, recyclable, and non-toxic, with proper band alignment and bandgap. when these criteria are met, the photocatalyst can generate excitons that participate in redox reactions to split water into hydrogen and oxygen. figure 11. diagram illustrating the flow of the experimental gasification plant [54] mfi chowdhury et al. /future energy november 2024| volume 03 | issue 04| pages 18-46 29 figure 12. a) aspen plus process flow diagram; b) process flow diagram for the hydrogenation of syngas plant [54] (the reader is suggested to use the referred paper for a better view of the image). mfi chowdhury et al. /future energy november 2024| volume 03 | issue 04| pages 18-46 30 the fundamental steps in photocatalytic water splitting to produce hydrogen fuel are illustrated in figure 13. when a photocatalyst is exposed to solar energy equal to its bandgap, it generates charge carriers (electrons and holes). electrons move to the conduction band, while holes stay in the valence band. figure 13. illustration of the fundamental steps in the process of photocatalytic hydrogen production [71] these carriers then reach the surface and engage in redox reactions, producing hydrogen and oxygen. this rapid water-splitting process occurs in nanoseconds to microseconds and competes with charge recombination. it involves two half-reactions: hydrogen evolution (her) and oxygen evolution (oer), which together make up the overall water splitting reaction (owr). these reactions are given below one by one [70], her: 4h+ + 4e= 2h2 oer: 2h2o = 4h+ + 4e+ o2 owr: 2h2o = 2h2 + o2 when energetic photons are absorbed, they generate and separate charge carriers. the holes in the valence band split water molecules into protons and oxygen gas, as described by the second reaction. these protons then react with the free electrons in the conduction band to produce hydrogen gas, as shown in the first reaction. 4. methane pyrolysis methane pyrolysis offers a way to produce cox-free hydrogen through an endothermic reaction: ch4(g) = c(s)+2h2(g), δh(1000k)=89.8kj mol (4) noncatalytic methane pyrolysis requires very high temperatures, around 1300°c, to decompose methane effectively and achieve high hydrogen selectivity, which is impractical for industrial use. therefore, research has focused on two main areas to commercialize this process: 1. developing commercially viable catalysts to lower the reaction temperature and enhance methane conversion and hydrogen selectivity. 2. controlling and producing valuable, separable carbon allotropes. since solid catalysts have been extensively reviewed, this paper will provide a detailed and updated analysis of liquid catalysts and discuss the main challenges to commercializing methane pyrolysis. it will also review the latest advancements in each type of catalyst, outlining their advantages and disadvantages see figure 14. figure 14. an overview of the different catalysts used in methane pyrolysis [72] the autocatalytic pathway for methane pyrolysis is a multifaceted, high-temperature process with various routes and intermediates [73]. abanades and colleagues detected hydrocarbons, besides methane, along with radicals in the outlet stream while investigating methane's thermal decomposition [74]. the authors did not specifically pinpoint the types of species present. matheu and collaborators constructed a simulated mechanism for methane pyrolysis that closely matched existing literature [75]. so, methane pyrolysis is seen as a practical and economical way to produce hydrogen with minimal emissions at a low cost. 5. techno-economic analysis for green hydrogen production the ever-present threat of climate change propels green hydrogen into the spotlight as a potential game-changer in the global energy discussion. experts and analysts around the world are highlighting its potential as a game-changer in reducing carbon emissions and paving the way for a lowcarbon future. if we're going to unlock the true potential of green hydrogen and fight the urgent climate crisis, we need a deep understanding of the technologies and economic factors surrounding its production right now [76–79]. the future of clean energy is getting a significant boost from green hydrogen, a fuel produced using renewable sources like sunshine and wind [80]. this eco-friendly option is showing immense promise across various industries, with significant advancements in the technologies that create it. these advancements include electrolysis, biomass gasification, and mfi chowdhury et al. /future energy november 2024| volume 03 | issue 04| pages 18-46 31 even splitting water directly using solar power. one fascinating area of exploration is using renewable biomass resources like plant matter to generate green hydrogen through gasification [80,81]. additionally, the integration of solar water splitting, which directly converts sun energy converted to hydrogen [82], displays creative methods that are influencing the growth of the green-hydrogen industry. electrolysis advancements, gasification of biomass, and water splitting by the sun have accelerated the development of green hydrogen production methods figure 14. green hydrogen (table 2) is a game-changer due to its versatility across various sectors. from powering our industries and transportation to generating cleaner electricity, this cleanburning fuel offers a promising solution for a sustainable future (figure 15). several techno-economic frameworks have been developed to evaluate the viability of green hydrogen-generating systems. one of the most popular methods is electrolysis, specifically proton exchange membrane (pem) technology, which has evolved dramatically. studies showed pem electrolysis as an ecofriendly method of hydrogen production. this approach enables the generation of green hydrogen from clean energy sources, wind, and solar, whose prices vary from 2.94-3.32 usd/kgh2 [85,86]. in the research [80] also investigated the feasibility of integrating a ten-megawatt pem electrolysis apparatus with an organic rankine cycle with waste heat recovery to establish economically viable large-scale storage of green hydrogen that is sustainable. the study investigates the manufacture of hydrogen utilizing solar energy, namely photovoltaic systems. it demonstrates the potential for this technology to serve as a green hydrogen production method in iraq, playing a part in a global zero-emissions economy. this research highlights the potential of biomass gasification technology as a game-changer in producing clean, sustainable hydrogen. this technology holds particular promise for tackling decarbonization challenges in sectors like industrial heating and even home heating systems [86]. the study especially looked at whether gasification of biomass might be used in the us to produce hydrogen. it yielded valuable insights regarding the economic costs, environmental impact of biomass sources, and the technical hurdles and successes of generating hydrogen through this method [87]. the research investigates the generation of hydrogen from combustion of biomass and gives a thorough analysis of the current challenges and possible prospects, particularly in establishing a comprehensive pathway for this process. edou et al. [39] researched the production of a significant amount of hydrogen using gasification using a fluidized bed , steam reformation of biogas from breaking down anaerobically (ad) , and various other thermo-chemical technologies. among these, fluidized bed gasification (fb) emerged as the most cost-effective method, producing hydrogen at $3.40/kg for potential use in public transportation buses. ad-biogas reforming followed at $4.20/kg. additionally, arcos et al. [40] discussed photocatalysis, a method that utilizes light to produce hydrogen gas [88,89]. the research explores thermochemical water splitting (tws) as a viable method for largescale production of clean hydrogen, emphasizing that optimization can reduce costs and environmental impact. it introduces ceria thermochemical water-splitting (tcws) as an innovative technique for solar hydrogen synthesis, improving hydrogen production with solar-heated nitrogen. another advanced technology, developed by mehrpooya et al., incorporates solar thermal energy, an overheated heat pump, a natural cycle of rankine, and a four-phase thermochemical cycle for cu-cl, achieving a hydrogen production rate of 21.75 kg/h. additionally, the power-to-hydrogen-to-combined heat and power (pth2tchp) system offers a cost-effective, low-emission approach that supports a low-carbon, clean energy infrastructure. the study also indicates that the generation of hydrogen using renewable resources could become as cost-effective as conventional techniques in countries with strict carbon pricing [91–95]. figure 15. indicators of both technological advancements and economic viability across different global technologies for green hydrogen production [60,83,84]. mfi chowdhury et al. /future energy november 2024| volume 03 | issue 04| pages 18-46 32 6. recent advances and innovations in recent years, significant progress has been made in green hydrogen production technologies, improving their efficiency, cost-effectiveness, and scalability. the current cost of green hydrogen typically falls between $2.50 and $6.80 per kilogram [96]. however, the declining costs of renewable energy and electrolyzers are driving down the price of green hydrogen, making it increasingly competitive with blue hydrogen. the decreasing costs of renewable energy and electrolysers are effectively lowering the price of green hydrogen, making it more competitive with blue hydrogen. the united states department of energy aims to reduce hydrogen production costs to $1 per kilogram by 2030. table 3 outlines recent hydrogen production technologies, detailing their sources, processes, benefits, drawbacks, and maturity. due to data limitations, life cycle assessments and technoeconomic analyses are not included. figure 16 summarizes these technologies, focusing on esmr, soec, aem, bpv and dae as key methods. electrolysis powered by wind or hydrogenerated electricity is considered one of the most effective methods for producing green hydrogen [97]. of the three electrolysis methods, solid oxide electrolysis cells (soecs) are regarded as the most efficient for hydrogen production. table 3 (appendix) indicates that soecs outperform other methods, achieving efficiencies of up to 90%, the highest among hydrogen production technologies [98]. soecs use ceramic electrolytes instead of hydroxide exchange membranes, resulting in lower material costs despite a longer initial setup time. they are currently at a technology readiness level (trl) of 6–7, indicating readiness for demonstration and commercialization. however, their lifespan of less than two to three years contrasts with pem and alkaline electrolysis technologies, which typically last 1020 years. the current emphasis of our research and development endeavors is on extending the operational lifespan of solid oxide electrolysis cells (soecs) [99]. aems represent a new era in high-efficiency energy devices, characterized by their strong mechanical, thermal, and chemical properties that address fuel crossover and carbonation challenges seen in traditional alkaline fuel cells utilizing aqueous koh [100]. aems are approaching readiness for demonstration and commercialization, while esmr holds promise in reducing ghg emissions but faces methane leakage and high energy consumption issues. hydroxide exchange membrane water electrolyzers show potential for efficient hydrogen production, yet improvements are needed in durability and commercial viability [101]. a range of emerging green hydrogen technologies, such as aem and pem electrolysis, soecs, esmr, dae, and mecs, are progressing towards applications in transportation and industry. these innovations aim to mitigate emissions, improve energy efficiency, and support the shift towards cleaner energy sources. as these technologies advance and achieve greater cost efficiency, they will undoubtedly play a pivotal role in catapulting us into a sustainable energy future. figure 16. latest innovations in green hydrogen production [118] 7. challenges and solutions clean hydrogen's potential for a global energy shift is hampered by two main challenges. first, the infrastructure needed to use hydrogen widely is still under development. this lack of infrastructure is a major roadblock to widespread adoption. second, producing clean hydrogen using renewable energy sources is currently too expensive (figure 17). table 2. various studies conducted for the advancement of the green hydrogen production literature perspective on the various studies conducted for the advancement of green hydrogen production year technology yield of h2 cost of h2 production capital cost operational cost ref. 2023 proton exchange membrane (pem) electrolysis – 2.94–3.32 usd/kgh2 600 usd/kw 1.5% of capex [86] 2023 photovoltaic energy system – 3.79–4.11 usd/kgh2 1.29 × 106 usd 7,166.76 usd/yr [90] 2023 pem coupled with waste heat recovery and an orc – – 79.29 × 106 £ 133.92–283.80 £/mw [80] 2023 biomass gasification 94.9–99.1 kg h2/ ton of biomass 3.47–4.11 usd/kgh2 1.7–2.51 × 108 usd 24.55–29.95 usd/kgh2 [87] 2023 thermochemical water-splitting 168.3 kg/h 3.92 usd/kg h2 48.3 × 106 usd 15.6 × 106 usd/yr [91] 2022 integrated systems of power-to hydrogen-to combined heat and power – 5.76 v/kg 700-1500 v/kw 3 v/mw [92] mfi chowdhury et al. /future energy november 2024| volume 03 | issue 04| pages 18-46 33 as a result, most hydrogen production relies on fossil fuels like natural gas and coal, which undermines its environmental benefits [119]. despite current regulatory hurdles, the clean hydrogen industry is making significant progress, with many industries and companies incorporating green hydrogen into their products. the growing demand for green hydrogen indicates its potential to become a highly sought-after renewable energy source shortly. the increasing recognition of its significance spurs the advancement of more environmentally friendly technologies and global approval. the significant recent decrease in the costs of renewable energy clearly indicates that producing hydrogen from renewable power through the power-to-gas process will become more cost-effective [120]. some methods of making hydrogen, like electrolysis, use a lot of water. in fact, it takes roughly 9 kilograms of water to produce just 1 kilogram of hydrogen [121]. for over 200 years, scientists and engineers have been refining water electrolysis techniques for industrial use. this development can be broadly categorized into five distinct phases. each phase is characterized by its own set of challenges, technological advancements, and contributions to the overall progress of water electrolysis technology (as illustrated in figure 18). hydrogen can indeed be used in traditional engines, but it unfortunately produces nitrogen oxide emissions and is not as efficient as fuel cells. nevertheless, the environmental advantages of hydrogen fuel cannot be disregarded. the scarcity of hydrogen stations and fuel cells' exorbitant prices are the principal factors contributing to the limited presence of h2-powered cars on the roads today. the limited availability of hydrogen fueling stations presents an opportunity for expanding the market for hydrogen vehicles. as more stations are built, it will encourage more people to consider purchasing hydrogen vehicles, leading to a positive cycle of growth for the industry. it is a chicken-and-egg situation [123]. storing hydrogen in its liquid form is tricky because it needs super cold temperatures and special equipment. that's why scientists are putting a lot of effort into developing technology that can convert hydrogen from electrolysis (made with renewable energy sources) into liquid fuels like diesel, methanol, or ammonia. this would be a game-changer! these fuels are easier to transport, allowing us to move clean energy from places with lots of renewable resources to areas with limited options [124]. adding to the challenges, safety is a major concern with hydrogen. because it's highly flammable and can ignite easily under many conditions, there are significant worries about its safe handling and use. 8. solution to the challenges the fight against climate change hinges on researchers developing clean ways to produce hydrogen. but for it to be truly impactful, industries need solutions for transporting, storing, and distributing hydrogen – including making it readily available in rural areas. governments also have a critical role. they need to craft policies that make green hydrogen a key player in the global shift towards a clean, reliable, and affordable energy system. this includes securing domestic supplies of zero-carbon hydrogen, as current production methods are expensive and limited in scale. the current infrastructure simply can't handle large-scale storage, long-distance transportation, and distribution of liquefied hydrogen [125]. no country is currently selfsufficient in carbon-neutral or zero-carbon hydrogen, meaning imports will be necessary. hydrogen energy's potential for the future relies on global competition and consumer demand. for instance, for hydrogen-powered vehicles to succeed, they need to be priced competitively compared to other options. right now, the lack of hydrogen stations and high refueling costs are major roadblocks for fuel cell vehicles. however, with increased demand, economies of scale could bring down refueling costs. hydrogen might find its biggest advantage in powering heavy-duty vehicles like buses, trains, and industrial trucks used in mining. this is because fuel cells excel where high energy storage per weight is crucial [126]. figure 17. current challenges and potentials of hydrogen production [118] mfi chowdhury et al. /future energy november 2024| volume 03 | issue 04| pages 18-46 34 figure 18. water electrolysis generation wise development [122] the utilization of hydrogen in sectors such as methanol production and refining is expected to experience gradual expansion by the year 2050, a major shift is expected for hydrogen as a fuel. the use of hydrogen as an energy source is anticipated to increase significantly by the year 2030, making up a significant portion (35%) of total hydrogen demand by 2050 [127]. our present energy infrastructure, which has evolved over decades, is a complicated network of extraction, processing, and transportation. the transition to a hydrogen-based system will be sluggish, maybe spanning many decades. rebuilding or changing a huge percentage of existing infrastructure is a significant challenge for hydrogen. furthermore, hydrogen will face fierce competition from alternative energy sources. the economic effect of the covid19 epidemic may postpone this transformation even further. policymakers must identify cost-effective ways to incorporate hydrogen and investigate how the hydrogen and natural gas businesses might collaborate, possibly complementing one another. 9. applications and impact hydrogen is employed in various industries, such as electricity generation, transportation, processing, medicine, chemical production, heating, and steelmaking [128]. environmentally friendly hydrogen's benefits include its compatibility with existing natural gas pipelines for storage and transport, which can be readily adapted for hydrogen use. green hydrogen offers the advantage of being stored and transported through existing natural gas pipelines, making it distinct from other energy storage types. the natural gas infrastructure can be easily adapted for hydrogen transport transportation across air, sea, and land can become carbonfree with hydrogen. some examples of such cars include hfcvs, evs, and ngvs, which stand for natural gas vehicles [129]. given its advantages compared to alternative energy storage technologies, p2h could be an extremely efficient option for addressing challenges in transitioning to renewable energy, offering reliable, cost-effective, efficient, long-term, and high-capacity storage [129]. 10. production method wise applications in water electrolysis, external energy flows through a circuit to drive a reaction that splits water molecules into hydrogen and oxygen atoms, a process known as dissociation. combining photocatalysis with electrocatalysis, the technique behind photoelectrocatalysis (pec), which work together to enhance this electrochemical reaction [130]. at the anode, water undergoes oxidation, producing oxygen gas, protons, and electrons. these protons pass through the proton exchange membrane electrolysis (pemel) and are then reduced, where they react with electrons to produce gaseous hydrogen at the cathode. future work on proton exchange membrane electrolyzers (pemel) includes the following: higher temperature operation: operating at temperatures between 60°c and 120°c is critical for enhancing voltage efficiency. however, higher temperatures can dehydrate the pem, so maintaining adequate water content is essential [131]. increased operating pressure: another important area of research is increasing the operational pressure of pemel systems. higher pressure is crucial for the widespread use of hydrogen, particularly in hydrogen plants, due to the very low volumetric energy density of hydrogen gas under ambient conditions. currently, mechanical compressors are used to pressurize hydrogen gas, but they are inefficient and noisy (figure 19). ael can create significant volumes of clean hydrogen. featuring an 8-year membrane and electrode exchange, an operational efficiency of 62-82%, and a lifespan of up to 30 years, this equipment is reliable and safe. fundamentally, two terminals are immersed in an aqueous solution containing 25-30% koh or naoh. koh is used for its higher ionic conductivity and lower co2 solubility. the positive electrode generates oxygen, while the negative electrode generates hydrogen [132]. mfi chowdhury et al. /future energy november 2024| volume 03 | issue 04| pages 18-46 35 figure 19. the basic methods of green hydrogen technology [131] 11. photovoltaic (pv) systems with electrolyzers a. one cutting-edge method of producing and storing energy is a pv system that incorporates an electrolyzer. b. this system harnesses solar power to produce electricity, which is then used by the electrolyzer to split water into hydrogen and oxygen. c. a research examines photovoltaic (pv) on-grid systems that include electrolyzer technology. the paper presents a techno-economic model for pv-linked electrolysis facilities that takes into account the dynamics of the system. d. water electrolysis-coupled pv off-grid systems are efficient. 11.1 solar-powered water-splitting system a. three state-of-the-art pemels with a total area of 730 cm² and a bifacial (shj) solar module make up a dependable solar-powered water purification system. b. the system parameters, including the cell count, inclination, and elevation of the solar panel, were finetuned for optimal performance. c. at an irradiation level of 1000 w/m², the system achieves an 11.55% efficiency in converting solar energy to hydrogen. 12. wind turbines with electrolyzers a. wind turbines are a promising renewable energy source, but their intermittent nature poses challenges. b. wind turbines generate extra power that electrolyzers may store and utilize as fuel. c. this technique improves wind energy dependability and efficiency, enabling clean energy transition. d. electrolysis wind turbines produce green hydrogen and sell excess energy to the grid when hydrogen storage is full. e. factors affecting wind energy production include wind speed at the site, tower height, and blade diameter. f. frequent wind power fluctuations can cause electrolyzers (ael) to start up and shut down frequently, reducing hydrogen production. g. supercapacitors can be integrated into a wind/hydrogen (w/h₂) grid-tied system for attenuating wind power variations. 13. hybrid microgrid (hµg) a. the proposed hybrid microgrid comprises three distributed generation (dg) units: two that are wind-and solar-powered, and remaining using proton exchange membrane fuel cell (pemfc) technology (figure 20). b. the ael in the system balances the variable renewable energy sources (vres) by producing hydrogen. c. when there is excess generation, hydrogen is stored in a hydrogen tank and used to feed the fuel cell during low generation periods. d. the hydrogen microgrid demonstrates the benefits of using hydrogen to store energy produced by sun and wind systems, enhancing system self-sufficiency [133–136]. 14. policy and regulatory framework the world bank group is actively advancing green hydrogen initiatives in latin america, with countries such as brazil, costa rica, colombia, panama, and chile actively exploring its potential for fuel and energy storage. this renewable energy option is gaining attention on a global scale, with australia, china, india, japan, bangladesh, and germany all emphasizing its significance in their energy shifts [137]. it's worth noting that sub-saharan africa holds the greatest potential for producing green hydrogen (2715 ej), followed by the middle east and north africa (2023 ej), north america (1314 ej), and oceania (1272 ej). india's national hydrogen mission exemplifies this global focus. the recently unveiled initial phase of its green hydrogen policy aims to position the country as a leader in this domain. targeting a production capacity of 5 million metric tons per annum (mmtpa) by 2030, the policy also emphasizes boosting renewable energy sources and offering incentives to attract investment in green hydrogen and ammonia production. this initiative comes amid projections of india's hydrogen consumption doubling to 6.7 million tonnes per year by 2030 [138]. currently, most hydrogen is utilized by industries like steel mills, fertilizer plants, and oil refineries as a process fuel. the challenge? while green hydrogen boasts a lower environmental impact, it is not yet cost-competitive with its "grey" counterpart derived from valuable fossil fuel sources like natural gas or naphtha, despite its decreasing costs of renewable electricity [139]. looking towards the future, japan's ministry of economy, trade and industry (meti) is outlining a roadmap for establishing a global hydrogen supply chain by 2030. their strategic roadmap and basic hydrogen plan for hydrogen and fuel cell highlight the potential of nh3 as a low-carbon fuel option. bangladesh is expanding its energy diversification efforts with a hydrogen research facility, emphasizing a cost-efficient solar-wind hybrid power plant model along its coastline [140]. germany's forward-looking hydrogen policy involves significant state funding for green hydrogen initiatives, alongside research into low-carbon hydrogen options, positioning the country as a leader in technology development and international partnerships to ensure energy security [141]. mfi chowdhury et al. /future energy november 2024| volume 03 | issue 04| pages 18-46 36 figure 20. hybrid system for green hydrogen production china's 2021–2035 hydrogen energy plan aims to establish a robust industry by 2025 and scale up renewable hydrogen production, targeting significant carbon emissions reductions. by 2035, china plans to rely heavily on renewable hydrogen to advance its transition to sustainable energy sources [142]. the uk is working to build a hydrogen economy with flexible guidelines focused on long-term decarbonization and economic benefits, in alignment with national goals. by 2030, it aims to lead in low-carbon hydrogen production, supporting both carbon reduction and economic growth. the strategy emphasizes adaptability to market changes and explores various technologies to meet carbon budget 6 and net zero targets by 2050 [143]. 15. future directions and research gaps future research should prioritize advancing green hydrogen technologies to trl 5–6. researchers need to improve production methods, industries must develop better systems for storage, transportation, and distribution, and governments should create policies that support a sustainable and secure energy future. addressing the high costs and infrastructure limitations is crucial for making green hydrogen a viable energy source [125]. governments in every country depend significantly on importing carbonneutral and zero-carbon hydrogen to meet their domestic needs. the effectiveness of hydrogen energy systems in the future hinges on competitive market conditions and demand. challenges such as insufficient refueling infrastructure and expensive hydrogen refueling costs are barriers to the widespread use of fuel cell vehicles at present, but increased demand could drive down costs as economies of scale come into play [126]. while traditional hydrogen applications, like making methanol and refining oil, are expected to grow slowly by 2050, the future looks bright for its use as a fuel. demand in this sector is predicted to skyrocket after 2030, accounting for a significant portion (35%) of total hydrogen demand by mid-century [127]. however, transitioning our energy infrastructure to accommodate this shift is a complex undertaking, potentially spanning decades. the challenge lies in adapting existing systems and navigating competition from other energy sources. economic hurdles, like the recent covid-19 pandemic, could further slow down this progress. to address these obstacles, policymakers must find costeffective transition strategies and encourage collaboration between the hydrogen and natural gas sectors (figure 21). figure 21. to ensure the successful development of green hydrogen, it is crucial for the government, hydrogen producers, and researchers to work together actively [118] mfi chowdhury et al. /future energy november 2024| volume 03 | issue 04| pages 18-46 37 16. conclusion green hydrogen is at the forefront of the global energy transition, presenting a versatile and sustainable alternative to conventional fossil fuels. this comprehensive review has elucidated the multifaceted approaches to green hydrogen production, including water electrolysis, biomass gasification, and thermochemical processes. among these, water electrolysis stands out due to its maturity and scalability, particularly through the use of alkaline and pem electrolyzers. however, the efficiency and cost-effectiveness of these technologies remain challenges that require continued research and development. significant advancements in electrocatalysts and electrode materials have shown promise in enhancing the efficiency of hydrogen production. for instance, the development of bifunctional electrocatalysts and heterostructured interfaces has led to lower overpotentials and increased stability, crucial for both hydrogen evolution reactions (her) and oxygen evolution reactions (oer). additionally, the integration of renewable energy sources, such as solar and wind, with hydrogen production systems offers a pathway to further reduce environmental impacts and improve energy security. the importance of green hydrogen extends beyond energy production; it is integral to decarbonizing sectors like transportation, industry, and power generation. this transition is critical as nations worldwide strive to meet their climate goals, particularly the ambitious goal of reaching zero emissions by the year 2050. the successful implementation of green hydrogen technologies can significantly mitigate co2 emissions, combat climate change, and foster sustainable economic growth. despite the progress, several research gaps and commercial limitations need to be addressed. key areas for future research include improving the efficiency of electrolysis processes, developing low-cost and durable materials, and enhancing hydrogen storage and distribution systems. policy support and strategic investments are essential to accelerate the deployment of green hydrogen technologies and realize their full potential in the energy transition. ethical issue the authors are aware of and comply with best practices in publication ethics, specifically concerning authorship (avoidance of guest authorship), dual submission, manipulation of figures, competing interests, and compliance with policies on research ethics. the authors adhere to publication requirements that the submitted work is original and has not been published elsewhere in any language. data availability statement data sharing does not apply to 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(accessed on 22 june 2024). this article is an open-access article distributed under the terms and conditions of the creative commons attribution (cc by) license (https://creativecommons.org/licenses/by/4.0/). https://creativecommons.org/licenses/by/4.0/ mfi chowdhury et al. /future energy november 2024| volume 03 | issue 04| pages 18-46 44 appendix i table 3. latest innovations in green hydrogen production [118] process sources process and range advantages challenges trl cost of production ref. solid oxide electrolyser cells (soecs) steam heat sources include: 1. utilization of thermal energy waste from industry. 2. harnessing heat energy from solar and geothermal systems. 3. generation of heat through nuclear power. 1202–1832 ◦ f, <25 bar 1. able to maintain very high rates of electrochemical reactions, with current densities greater than 1 a/cm². 2.demonstrates excellent loadfollowing ability, thus well-suited for use with intermittent renewable energy. 3.produces compact systems that take up less space than those using liquid-alkaline electrolytes. 4.perfect for on-site usage. 5.less-cost materials, utilizing ceramics for the electrolyte. 6.can function in alter mode. 1. cellular constituent parts deterioration. 2.the gasket or electrolyte fails, allowing the gas to escape. 3. unstable mechanical conditions caused by thermal stress. 4. extended start-up and break-in durations. 6–7 capital expenditures for solid oxide electrolysers are estimated to be around $2,000/kw based on irena's estimations for 2020. [102,103] methane pyrolysis/ splitting source of energy: electricity feedstock: methane >1472 ◦ f 1.straight co2 emissions are absent. 2.forms solid carbon, resulting in carbon black. 1. significant heat wastages may impair its efficiency. 2. needs hightemperature plasma. 3–6 hydrogen produced by methane pyrolysis now costs between $2,600 and $3,200 per metric ton, with the exact amount dependent on the price of carbon. [104] electrified steam methane reforming (esmr) (methane) extracted from natural gas 1. the formative years 2.reforming 3.shift change 4.co2 removal 5.compression and purification 6.utilisation 1.amenable to incorporating carbon capture, utilization, and maintain (ccus) to lower co2 emissions. 2.can decrease the cost of decarbonizing h2 production. 1. as of right now, the procedure costs more than conventional smr. 2. the possibility of methane seepage. 3–4 a particular investment cost of about 422 euros/kw net equivalent is associated with traditional steam reforming that does not use ccs. [105] anion exchange membranes (aems) membrane: solid polymer electrolyte using catalyst of transition metals (ceo2– la2o) 1.doesn’t rely on pt. 2.utilizes an aem to serve as a solid electrolyte, thereby obstructing damage from corrosive electrolytes. 3.operates effectively in acidic settings. 1. not as robust. 2. not as steady. 3. poor performance in hot and high pressure environments. 6–7 (for lab scale system) hydrogen generation costs utilizing aem-based water electrolysis are anticipated to be $2 to $3/kg. the use of metals from the nonplatinum group and the effectiveness of the aems in facilitating hydroxide conduction and limiting fuel [106,107] mfi chowdhury et al. /future energy november 2024| volume 03 | issue 04| pages 18-46 45 4.demonstrates reduced internal resistance and high levels of conductivity. crossover both contribute to the competitive cost and improve the electrolyzers' overall performance and durability. hydroxide exchange membrane water electrolyzers highly-purified water as the feedstock make use of an electrolyte that is hydroxide exchange membrane to separate oxygen and hydrogen from water. 1.utilizes catalysts devoid of platinum group metals. 2.enables the use of economical stack components such as stainless steel, preserving the advantages of membrane-based technologies. 1. in order to function, electrolytes must be supported, rather than liquid water. 2. the solid-state ionomers are immature. 3. not very long-lasting. 4. not fully developed technology. 5. ionomer breakdown occurs quickly. 3-5 depending on the exact configurations and operating circumstances used, the projected production cost of hydrogen utilizing heme ranges from around $2.50 to $4.50 per kilogram. factors such as material cost, manufacturing size, and electrolyser efficiency determine this price range. [108– 110] direct air electrolysis (dae) external input: such as solar panels, tidal, geothermal, or wind water source: water oxygen source: atmospheric air electrolyte: alkaline solution such as koh directly produce hydrogen from atmospheric co2 using an electrochemical technique 1.harnesses renewable energy sources. 2.scalable in size. 3.demonstrates high efficiency. 4.cost-effective by eliminating the need for expensive membranes or electrodes. 1. the expense of initial investment is great. 2. a number of variables, such as catalysts, pressure, and temperature, must be carefully controlled. 3. hydrogen production is low. 4-6 the cost of hydrogen production using dae is estimated to be around $2.5 to $3 per kilogram of hydrogen. this cost is comparable to other environmentally friendly methods for producing hydrogen that harness renewable energy [111] biophotovoltaics (bpv)/ biophotoelectrolysis cell (bpe)/microbial electrolysis cells (mec) employing photosynthetic microorganisms like algae and cyanobacteria by using biological photosynthetic materials, solar energy may be transformed into electrical current. 1. converts industrial co2 waste into a feed for microorganisms, offering a sustainable and economical route for hydrogen production. 2. the technology is environmentally sound and generates almost less harmful emissions or pollutants. 1.the goal is to use microbial electron transport pathways to transfer electrons to a solid-state anode. 2. the experimental setup lacks comparability and standardisation. 3. the devices' current outputs are quite low. 1-3 hydrogen generation with bpe devices is now estimated to cost between $2.5 and $3/kg, which is competitive with other environmentally friendly ways of hydrogen production.depending on the design and operating conditions, mecs can create hydrogen for $2.75 to $4.00 per kilogram, according to recent study. [102,112– 114] membrane-less electrolysers source: different types of highconductivity aqueous electrolytes the electrodes that evolve h2 and o2 do not have a diaphragm or membrane divider. 1. requires fewer and simpler components (anode, cathode, and device body), leading to reduced manufacturing and assembly costs. 2. simplifies device complexity. 3.shows potential for robust devices that can withstand severe operating conditions without membrane damage, have high impurity tolerance, and long operational lifetimes. 4.capable of functioning with a variety of aqueous conductive electrolytes. 1. the decreased voltage efficiency was caused by the high operational current densities (≥0.5 a cm-2) that resulted from the increased ohmic solution (ir) losses. the ohmic voltage loss is larger in most membrane-less electrolysers because the ion transport distance is longer, which increases the total ohmic resistance (rs) of the electrolytic solution. 2. it is difficult to produce and sustain a large enough pressure gradient between the electrodes to conduct electrochemical hydrogen compression. 4.3 an estimated $2 to $2.5 per kilogram of hydrogen may be produced utilizing electrolysers that do not use membranes. [101,115] mfi chowdhury et al. /future energy november 2024| volume 03 | issue 04| pages 18-46 46 no, it can't manufacture hydrogen with a purity level of 99.99% when compared to pem. fourthly, difficulties associated with materials. 5. issues with scalingup. redox decoupling source: water or solutions with alkaline properties 1) use electricity to separate water into its component hydrogen and oxygen. has a two-step process: (i) the oer is the process by which oxygen is formed; (ii) the her is the process by which hydrogen is formed. 1.utilizes redoxmediated reactions in dual electrochemical cycles to produce highpurity hydrogen from alkaline solutions. 2.shows consistent and rapid hydrogen production with nearly perfect steady-state faradaic efficiency. because of the inherent relationship between oer and her, any changes or improvements to one will have an effect on the other. 2-4 one method that might bring the price of hydrogen generation down to about $2/kg is an electrochemical and thermally-activated chemical (etac) cycle, which has shown an efficiency of 98.7 percent. [116,117] 