BIBECHANA Vol. 22, No. 3, December 2025, 195-204 ISSN 2091-0762 (Print), 2382-5340 (Online) Journal homepage: http://nepjol.info/index.php/BIBECHANA Publisher:Dept. of Phys., Mahendra Morang A. M. Campus (Tribhuvan University)Biratnagar Study of photovoltaic system performance across different geographical region of Nepal Sanjay Lal Karna1,2, Ajay Kumar Jha3,∗, Kishori Yadavi4 1Central Department of Physics, Tribhuvan University, Kirtipur, Nepal 2Department of Physics, Tri-Chandra Multiple Campus, Tribhuvan University, Kathmandu, Nepal 3Department of Mechanical and Aerospace Engineering, Institute of Engineering, Tribhuvan University, Pulchowk Campus, Lalitpur, Nepal 4Department of Physics, Patan Multiple Campus, Tribhuvan University, Lalitpur, Nepal ∗Corresponding author. Email: akjha@ioe.edu.np Abstract The objective of this work is to study the photovoltaic system performance across different geographical region of Nepal and its economic benefits. Nepal's solar irradiation varies sig- nificantly by season, from 4.5 kWh/m² in December to 7.2 kWh/m² in May. Notably, May has the highest irradiance levels, whereas December has the lowest. The Himalayan region, including Mustang, Kehami, and Jomsom, has greater irradiance levels ranging from 6 to 6.5 kWh/m²/day. The eastern half of Nepal has lower irradiance values, below 4.4 kWh/m²/day. The palce of high irradiance, has current output ranges from 19 A to 27.5 A, with peak PV power of 375 W when simulated with secondary data. The simulation observation shows temperature fluctuations has influence power output, with higher power at lower temperatures. Also, the power generation by PV rises with decreasing temperature and shifts to optimization voltage. The relationship between global horizontal irradiance and photocurrent is linear and increase from 9 to 19 A. At considered temperatures range the optimum creased photocurrent observed at 45°C. The economic analsyis was done considering 365 W solar PV system in Nepal’s Himalayan region and Eastern Half. The parameters use for economic analysis are Payback Period, Return on Investment (ROI), and Net Present Value (NPV). The analysis show that at higher solar irradiance in the Himalayan region leads to a shorter payback (15.7 years), higher ROI (59.4%), and a less negative NPV in comparative to the Eastern Half of Nepal. These findings highlight the importance of knowing solar irradiance and temperature dynamics for optimizing PV system performance throughout Nepal's different geographical regions. Keywords Global horizontal irradiance, Himalayan, Hilly and Terai region, photocurrent, temperature, PV system performance Article information Manuscript received: March 3, 2025; Revised July 12, 2025; Accepted: July 16, 2025 DOI https://doi.org/10.3126/bibechana.v22i3.76287 This work is licensed under the Creative Commons CC BY-NC License. https://creativecommons. org/licenses/by-nc/4.0/ 195 http://nepjol.info/index.php/BIBECHANA akjha@ioe.edu.np https://doi.org/10.3126/bibechana.v22i3.76287 https://creativecommons.org/licenses/by-nc/4.0/ https://creativecommons.org/licenses/by-nc/4.0/ Sanjay Lal Karna et al./ BIBECHANA 22 (2025) 195-204 196 1 Introduction Photovoltaic (PV) cells are tools for transforming radiant energy from the solar to electrical in a sus- tainable manner. PV systems, which are typically consist of interconnected solar cells are shown in Figure 1. These cells are designed to produce to maximum output energy. Recent advances have enabled in the production of high-efficiency pho- tovoltaic cells. They include certain multijunction solar cells approaching 50% of efficiency. The com- mercially accessible PV panels typically have con- verted efficiencies from 17% to 20% [1]. Now a days, manufacturers give the electrical requirements of photovoltaic devices on the basis of standard test settings (STC). They include a controlled tempera- ture of 25°C along with incident irradiance of 1000 W/m². To capture non-linear electrical behavior and environmental unpredictability, limited data exists on actual annual energy yield. Nepal enjoys around 300 sunny days per year, offering strong po- tential for solar power. This makes it an ideal envi- ronment for photovoltaic technology to meet grow- ing energy demands. However, many sites in Nepal still lack essential research on solar energy. This study addresses that gap by highlighting the im- portance of renewable energy in Nepal's context. Figure 1: Different types of photovoltaic cells de- pending on configuration [2] 1.1 Research related to solar Irradiance in Nepal Nepal's solar resource has inspired increased inter- est within photovoltaic systems. It is reported that roughly 1.1 million solar household systems. The Nepal Electricity Authority has recently introduced net billing to encourage the use of rooftop solar panels. Also the potential of technologies to assist governmental decisions on expanded power genera- tion. A report by Kadle et al. shows Kathmandu, Pokhara, Butwal, Nepalgunj, and Biratnagar has tr rooftop solar panels potential, like 637 GWh per year in Kathmandu to 50 GWh per year in But- wal [3]. Nepal has favourable geography and abundant solar radiation, which averages between 3.6 and 6.2 kWh/m2/day and roughly 300 days of sunshine per year. The current statistics show that both the Thabang Solar Mini-Grid (TSMG) and Sug- arkhal Solar Mini-Grid (SSMG) experience their peak energy generation in April. TSMG generated 83.206 MWh/year in 2021 with 112.140 MWh/year in 2022, having a peak sun hour (PSH) of 5.5 h. SSMG produced 64.14 MWh/year in 2021 as well as 68.79 MWh/year in 2022, with a PSH of 5.7 h [4]. A potential solution to the energy crisis in remote areas like Karnali Province where about 67% of the population lacks access to the national grid is the use of PV solar mini grids. Due to the region's rugged geographical region, extending the grid is challenging, making solar mini grids a more eco- nomical and efficient option with high generation potential [5]. 1.2 Significant of research Understanding solar energy in Nepal has impacts beyond research. Studying how solar radiation, temperature, and power generation interact can guide major improvements in the country’s energy system. This knowledge can help create tailored plans to optimize solar power production, boosting energy independence and protecting against price changes. Identifying the best locations for solar PV can help use Nepal’s vast solar resources for economic growth and rural development. Develop- ing solar infrastructure can create jobs, attract in- vestments, and support local industries, improving socioeconomic conditions. As Nepal faces climate change and environmental challenges, solar energy can reduce greenhouse gas emissions and reliance on fossil fuels. Closing research gaps and fully using renewable energy can lead Nepal toward a greener and more prosperous future. 1.3 Research Gap Although there are studies on solar irradiance and power generation in Nepal, important gaps re- main. One key gap is understanding how geog- raphy, solar irradiance, and temperature together affect photovoltaic system performance. Research on how these factors interact in Nepal’s different re- gions, Himalayan, hilly, and eastern Terai is limited. These regions have diverse climates and geograph- ical region, which likely influence solar power out- put differently. Additionally, economic feasibility studies comparing PV system performance across these regions are rare. Few studies combine tech- nical data like irradiance, temperature effects, and Sanjay Lal Karna et al./ BIBECHANA 22 (2025) 195-204 197 power output with financial measures such as Pay- back Period, Return on Investment (ROI), and Net Present Value (NPV). This lack of integrated anal- ysis makes it hard to determine the most suitable locations for solar energy projects. Overall, there is a strong need for comprehensive research that includes both technical performance and economic viability. Such studies would help identify optimal areas for solar power deployment throughout Nepal, considering its varied geography and climate condi- tions. 2 Methods and Materials 2.1 PV module used in this research For the computation detial of studying the nature of power generated, voltage and current, Solarex MSX60 PV module, a conventional 60W module made up of 36 polycrystalline cells connected in se- ries, was used in the investigation. The PV mod- ule more detial is shown in Table 1. These criteria served as the foundation for analysing the PV mod- ule's performance and attributes in the study. Table 1: Specification of solar PV module used in this research: Solarex MSX60 [6] at 25°C Parameter MSX60 Specifica- tion Maximum power (Pmax) 60 W Voltage at Pmax (Vmp) 17.1 V Current at Pmax (Imp) 3.5 A Short-circuit current (Isc) 3.8 A Open-circuit voltage (Voc) 21.1 V 2.2 Theory Solar cells serve an important role in transform- ing solar energy into electricity, providing an en- vironmentally friendly and renewable source of en- ergy. Solar cell technology has progressed through- out time, from single-crystal silicon to flexible film, organic, dye-sensitized, perovskite cells, etc. Ma- terial enhancement, construction, contact systems, characterization techniques are used to improve so- lar cell performance. The Shockley diode model is a popular model for solar cell analysis. It allows for extensive analysis and modelling to optimize the efficiency of solar cells and capacity, a single-diode model demonstrated in Figure 2. Figure 2: Circuit diagram of shockley diode model of solar cell [7] The output current of an ideal solar cell is found as I = Iph − Is [ exp ( qVOC NsKAT0 ) − 1 ] (1) where Iph is photogenerated current, Is is satu- ration current, q is elementary charge of an electron, VOC is open-circuit voltage of the solar cell, Ns is Number of cells/modules in series, k is boltzmann constant, A is Ideality factor of the diode (typically between 1 and 2) and T0 is reference or operating temperature. In the ideal scenario, beam produced power is directly proportional to irradiation bright- ness, and photovoltaics provide a reasonable esti- mate. The mathematical representation of a pho- tovoltaic cell (real/practical cell type) containing infinite Rs (series resistance) along with Rp (paral- lel resistance), then the diode current becomes Id = Is [ exp ( q (V + IRs) NsKAT0 ) − 1 ] (2) When Rs is taken into account, the resulting cur- rent of the module with Ns cells in series becomes: I = Iph − Is [ exp ( q (V + IRs) NsKAT0 ) − 1 ] (3) When the solar energy system is coupled in se- ries and parallel, the current using equation (3) is I = Np × Iph −Np × Is [ exp ( q (V + IRs) NsKAT0 ) − 1 ] (4) The incident flux has a relationship to the pho- tocurrent (Iph), and thus not dependent on voltage (or Rs). The photocurrent generated by solar radi- ation along with the temperature influenced by it can be computed as Iph = [ISC +Ki(T0 − Tr)]× G Gref (5) Sanjay Lal Karna et al./ BIBECHANA 22 (2025) 195-204 198 Where Ki is temperature coefficient of the short- circuit current (in A/°C), Tr is reference tempera- ture (typically 25°C), G is actual solar irradiance (sunlight intensity) on the panel surface (in W/m²) and Gref is reference irradiance, usually 1000 W/m² (Standard Test Conditions). The single-diode model, which consists of a single diode component including five electrical parameters, constitutes one of the simplest representations of PV panels' in- trinsic nonlinear features. Castaner and Silvestre (2002) created an implicit mathematical formula known as the usual I-V characteristic equation. I = Iph − Is [ e V +IRs A0NVt − 1 ] − V + IRs Rsh (6) The thermal voltage (Vt) can be mathematically stated as Vt = kT/q. Further circuit analysis can create a mathematical association between along with the incident ambient condition of the photo- voltaic cell (radiation, G, and temperature, T) as reported [8]. 2.3 parameters analysis of deploying PV systems in different regions The methodology of this research involves a finan- cial assessment of a solar photovoltaic system by calculating three key economic parameters: Pay- back Period, ROI, and NPV. First, the total ini- tial investment cost is determined by summing the prices of solar panels, MPPT controllers, installa- tion, and battery replacements over the system’s 25-year lifespan. Next, the annual energy output is estimated based on the panel’s rated power, local Peak Sun Hours (PSH), and system performance ratio. Using these values, the Payback Period is calculated by dividing the initial investment by the annual monetary savings, derived from multiplying annual energy output by the local electricity rate. ROI is then computed as the percentage difference between the total revenue generated over the sys- tem lifetime and the initial investment. Finally, NPV is calculated by discounting annual savings over 25 years at a chosen discount rate (6%) and subtracting the initial investment to assess the sys- tem’s present economic value. This methodology allows comparison of the solar system’s financial viability across different geographic locations with varying solar irradiance levels. 3 Results and Discussion 3.1 Solar Irradiance in Nepal According to NASA's Surface Meteorology along with Solar Energy dataset, the average daily so- lar radiation on a horizontal plane in Nepal varies significantly by season. The annual irradiation rate ranges from 4.5 kWh/m² in December to 7.2 kWh/m² in May [9]. Notably, May has the highest average monthly sun irradiation, whereas Decem- ber has the lowest amounts. This seasonal pattern represents the shifts in solar angle during daylight length caused by the tilt that occurs in the Earth's axis with its orbit around the solar system. Previ- ous research, such as that undertaken by Neupane et al. [10], has found comparable seasonal variations in sun irradiance across Nepal's different geograph- ical regions. Figure 3 from the 2023 Global Solar Atlas depicts the geographic distribution of solar radiation over Nepal, offering a spatial picture of the region's solar energy potential. Figure 3: Solar Irradiance above Nepal ( [9] 3.2 Current generated by PV modules at varying irradiation levels in Nepal. Solar irradiation varies significantly in Nepal, af- fected primarily by topographical considerations. Solar irradiation levels in the Himalayan region, including Mustang, Kehami, as well as Jomsom, are significantly higher, ranging from 6 to 6.5 kWh/m²/day. This increased irradiance causes higher current generation, with values ranging from 19 A to 27.5 A. Tinje, Saldang, Dolphu, as well as Mugu have high sun irradiation, which ranges from 5.6 kWh/m²/day to 6 kWh/m²/day, result- ing in current outputs within this range. In con- trast, the western area of Nepal experiences signif- icantly lower sun irradiation, average around 4.8 kWh/m²/day. In the eastern section of the country, solar irradiance values are below 4.4 kWh/m²/day. Sanjay Lal Karna et al./ BIBECHANA 22 (2025) 195-204 199 Figure 4: PV current generated at different geo- graphical region at 45 oC, at different region of Nepal on the basis of irradiance level Figures 4–6 demonstrate current-voltage char- acteristics at various temperatures and solar irra- diation levels. It has been found that as the tem- perature drops, the voltage increases while the cur- rent flowing decreases. Also, the current-voltage graphs show that when temperature decreases, the current switches to higher voltages before rapidly falling beyond particular voltage thresholds. The convergence of current with rising voltage occurs at around 20V at 45°C (Figure 4), 22V at 25 °C (Fig- ure 5), along with 24V at 0°C (Figure 6). These findings are comparable with prior research con- ducted on the Pulchowk campus [11], indicating the validity and dependability of the provided results. The observation drops in power and current with increasing temperature is similar with the results of [12]. Figure 5: V current generated at 25 oC, at different geographical region of Nepal on the basis of irradi- ance level Figure 6: PV current generated at 0 oC, at different geographical region of Nepal on the basis of irradi- ance level The findings show solar irradiation and tem- perature variations across Nepal significantly influ- ence PV current output. High-irradiance areas like Mustang and Jomsom (6–6.5 kWh/m²/day) gener- ate higher currents (19–27.5 A), making them ideal for solar PV system installation. In contrast, re- gions with lower irradiation, especially in the east and west, produce less current and require more efficient system design. Additionally, lower tem- peratures enhance voltage, improving system per- formance. These support researchers, developers, and installation organizations in selecting optimal locations, designing efficient systems, and planning region-specific solar energy projects in Nepal. . 3.3 Power generated by PV at various irra- diation levels in Nepal The solar photovoltaic module's power output varies greatly across different geographical region of Nepal, particularly in the Himalayan region demon- strating significantly better power generation po- tential. Specifically, in Mustang, Kehami, as well as Jomsom, solar PV generated electricity is sub- stantially higher than in other places, ranging up to 250 W, as illustrated in figure 7. The maximum electrical output of a solar PV module is often ob- served within a specified voltage range, usually be- tween 10 and 15 V. This range shows the best work- ing circumstances under which the PV module may produce the most power effectively. This improves the performance of solar PV system for energy ex- traction in specific region of Nepal. Sanjay Lal Karna et al./ BIBECHANA 22 (2025) 195-204 200 Figure 7: Solar PV generated power at 45 oC, at different geographical region of Nepal at difference irradiance level Considering different possible temperature in context of Nepal the solar power generated by PV module generated as shown in Figures 7–9. On comparing the power generated across the different region of Nepal with solar irradiance (figure 3 as references). The observation shows at 45°C, power generation in western part of Butwal can produce up to 150 W across the terai and up to 200 W across hilly region of different places of Nepal. Similarly, in the region of the Himalayas, solar PV systems gen- erate significantly more power than terai and hilly region i.e. up to 250 W. The difference in power generated by solar PV is due to higher solar irra- diation in the western Himalayas compared to the eastern region, leading to greater power generation. Figure 8: Solar PV generated power at 25 oC, at different geographical region of Nepal at difference irradiance level On comparison of higher irradiance level in Hi- malayan region of Nepal, especially Mustang, Ke- hami, as well as Jomsom region photovoltaic so- lar energy generation is significantly higher than in other regions of Nepal and observed up to 345 W as shown in figure 8. Power output is higher in the western Himalayas due to greater solar irradiation, peaking at 345 W compared to 270W in the east. This shows how geographic differences in sunlight directly affect solar PV performance, less pollution, sunshine peak hour, good orientation of solar panel, etc. In general, the solar PV power generation differs between the western along with eastern Himalayas shows western Himalayan region maximum at 375 W, whereas in the eastern Himalayan region it can reach 300 W at considered temperature. The ex- amination of the effect temperatures have on power generation finds a consistent pattern across many regions and conditions. With decreasing temper- ature, power output increases, accompanied by a shift to higher voltages. Figures 7–9 show that the power convergence occurs approximately 20 V at 45°C, 22 V at 25°C, along with 24 V at 0°C. These findings are consistent with prior studies [8,13], sup- porting the observed phenomenon of power gener- ation increasing voltage under varied irradiation. Studying these dynamics is critical for optimising the deployment as well as efficiency of solar PV sys- tems across various geographical locations, hence supporting the country's sustainable energy devel- opment. 3.4 Impact of Global Horizontal Irradiance on Photocurrent Figure 10 shows, how global horizontal irradiance effect photocurrent generated by solar PV mod- ule at different temperature in Nepal (the region is consider for Nepal from figure 3). On the ab- sis of real data the three temperature scenarios (- 40°C, 25°C, along with 45°C) were used to measure photocurrent fluctuation. The study analysed pho- tovoltaic cells' photocurrent production at various worldwide horizontal radiation levels, which varied from 3 kWh/m²/day to 7 kWh/m²/day. The obser- vation shows photocurrent was linear with regard to the global horizontal irradiance as shown in figure 10. Photocurrent readings ranged from 9 to 19 A at different irradiance level. Also, at higher tempera- ture the yield in photocurrent higher than lower temperature as example amount of photocurrent at 45°C is greater than that at 25°C and -40°C, empha- sising the effect of temperature on the photocurrent generation. 3.5 Impact of Cell Temperature on Pho- tocurrent Figure 11 depicts the fluctuation in photocurrent depending on cell temperature, which ranges from 10.7 A to 11.5. The observation shows as the cell temperature increase photocurrent also increases. However, the fluctuation was small, and photocur- rent values remained within a narrow range. Also, Sanjay Lal Karna et al./ BIBECHANA 22 (2025) 195-204 201 the global irradiance has impact on photocurrent at different irradiance level means higher the level of irradiance higher the production of photocur- rent. This shows that both irradiance and tem- perature have effects on photocurrent and consider panel generated current up maximum at the region of Nepal where irradiance as well as temperature is both high. Figure 9: Photocurrent generate with global hori- zontal irradiance at differential temperature Figure 10: Photocurrent generate with global hori- zontal irradiance at differential temperature Figure 11: Cell Working Temperature vs Photocur- rent 3.6 -benefit analysis of deploying PV sys- tems in different regions For cost-beneficial analysis of different geographical region of Nepal on the basis of solar irradiances and power generation. A solar system setup consists of a 365 W panel costing NPR 57,300, an MPPT con- troller priced at NPR 12,190, and installation ex- penses of NPR 2,000. A battery system with a lifes- pan of 8 years, requiring three replacements over the 25-year system lifespan, adds NPR 156,900 to the cost (3 batteries × NPR 52,300 each). The total investment amounts to NPR 228,390. The system assumes a performance ratio of 0.8, with average Peak Sun Hours (PSH) of 6.5 kWh/m²/day at Hi- malayan region location and 4.4 kWh/m²/day at Himalayan region location. Electricity is valued at 15 NPR/kWh, and the system is designed to op- erate over a 25-year lifespan. The annual energy output of a 365 W solar panel is calculated using the formula: E = 0.365 × PSH × 365 × 0.8, where 0.8 is the assumed performance ratio. For the Hi- malayan region place, with Peak Sun Hours (PSH) of 6.5 kWh/m²/day, the panel generates approxi- mately 693.31 kWh/year, while for the Eastern half place, with 4.4 PSH, it produces 469.46 kWh/year. Over a 25-year system lifespan, the total energy output is 17,332.75 kWh for Himalayan region and 11,736.5 kWh for Eastern half. The Levelized Cost of Energy (LCOE) is then calculated as the total system cost divided by the lifetime energy output. With a total investment of NPR 228,390, the LCOE is 13.18 NPR/kWh for Himalayan region and 19.46 NPR/kWh for Eastern half. The solar system, equipped with a 365 W panel and designed for daily use, can effectively sup- port a combination of common household appli- ances. These include five 9W LED bulbs (to- taling 45W), five 5W mobile chargers (totaling 25W), and two 60W laptops (totaling 120W), re- Sanjay Lal Karna et al./ BIBECHANA 22 (2025) 195-204 202 sulting in a combined power demand of 190W. Since the panel provides 365W of peak power and generates approximately 693.31 kWh/year (1.9 kWh/day) at Himalayan region location and 469.46 kWh/year (1.29 kWh/day) at Eastern half location, it can comfortably run these 190W loads for several hours daily—around 10 hours/day at Himalayan re- gion and about 6–7 hours/day at Eastern half — demonstrating its suitability for basic residential or off-grid use. To meet a daily energy consumption of 950 Wh (0.95 kWh) for 5 hours of use, a battery capacity of about 1,140 Wh is needed after adding a 20% buffer for losses and cloudy days. For a 12V system, this equals roughly 95 Ah, but considering a 50% depth of discharge (DoD) for lead-acid bat- teries, the total required capacity becomes 190 Ah at 12V. This setup can reliably power 5 LED bulbs, 5 mobile chargers, and 2 laptops running for 5 hours daily. Table 2 compares the electricity prices between solar systems and government-supplied electricity in different regions. While the Levelized Cost of Energy (LCOE) from the solar system ranges from 13.18 to 19.46 NPR/kWh—higher than the urban government rate of 10 NPR/kWh—it is notably cheaper than the rural-hilly government rate of 21 NPR/kWh, especially in the Himalayan region where solar is about 37% cheaper. Despite the higher per-unit cost of solar electricity in some ar- eas, the overall investment in extending the gov- ernment grid to remote, geographically challenging locations like mountainous villages in Nepal is sig- nificantly greater. This is because the difficult ter- rain and dispersed settlements increase infrastruc- ture costs, making solar systems a more viable and cost-effective solution for electrification in such off- grid areas. 3.7 Payback period Payback Period is defined as the amount of time re- quired for an investment to generate enough savings or revenue to recover the initial cost. It is calculated using the formula: Payback Period=Initial Invest- ment/Annual Savings. where Initial Investment is the total upfront cost of the system, and An- nual Savings represents the yearly financial bene- fit or revenue generated from the investment. A shorter payback period indicates quicker recovery of the invested capital. The solar system, with a total investment of NPR 228,390, demonstrates different payback periods depending on location. In the Himalayan region, the system generates 693.31 kWh/year, resulting in annual savings of NPR 14,559.5 based on an electricity rate of 21 NPR/kWh. This leads to a payback period of ap- proximately 15.7 years. In the Eastern Half, with a lower annual output of 469.46 kWh/year, the an- nual revenue is NPR 9,858.66, resulting in a longer payback period of around 23.2 years. These figures highlight that the system is more financially favor- able in locations with higher solar radiation like the Himalayan region. 3.8 Return on Investment Return on Investment (ROI) measures the prof- itability of an investment by comparing the net gain to the initial cost. It is calculated as: ROI = Total Savings over lifetime−Investment Investment ×100% where Total Savings over Lifetime is the cumu- lative financial benefit gained from the investment, and Investment is the initial cost. ROI expresses the percentage return relative to the original in- vestment, indicating how much profit (or loss) was made. The Return on Investment (ROI) of the so- lar system varies significantly between regions due to differences in solar energy availability. In the Himalayan region, the system generates a total of 17,332.75 kWh over 25 years, translating to a to- tal revenue of NPR 364,000 at the rural electricity Sanjay Lal Karna et al./ BIBECHANA 22 (2025) 195-204 203 rate of 21 NPR/kWh. This results in an ROI of approximately 59.4%, indicating a substantial gain over the initial investment of NPR 228,390. In con- trast, the Eastern Half yields a lower total energy output of 11,736.5 kWh, generating NPR 246,465 in revenue over the same period, which gives an ROI of only 7.9%. This means the system is much more economically beneficial in high-irradiance areas like the Himalayan region, where energy production is higher and payback is quicker, while returns are minimal in lower-irradiance regions like the East- ern Half. 3.9 Net Present Value Net Present Value (NPV) evaluates the profitability of an investment by calculating the present value of future cash flows discounted at a specific rate. As- suming a discount rate r=6%, NPV is calculated as: NPV = 25∑ t=1 Annual Saving (t+ 0.6)t − Inverstemnt Assuming a discount rate of 6%, the Net Present Value (NPV) analysis reveals that the solar system yields negative returns in both locations over the 25-year lifespan. In the Himalayan region, with an annual cash flow of NPR 14,559.5, the NPV is calculated as 14,559.5 × 11.9247 228,390 = NPR 54,727.5, indicating that the system does not recover its initial investment in today's monetary terms. Similarly, in the Eastern Half, the lower an- nual cash flow of NPR 9,858.66 results in an even more negative NPV of NPR 110,850. These find- ings suggest that while the system performs bet- ter in high-irradiance areas like the Himalayas, it still falls short of being financially viable when dis- counted future earnings are considered, highlighting the need for either cost reduction or subsidy sup- port for greater feasibility. 3.10 Limitations of research This study is subject to several limitations. Solar irradiance in Nepal varies significantly by season and region, ranging from 4.5 kWh/m² in Decem- ber to 7.2 kWh/m² in May, with the Himalayan regions such as Mustang, Kehami, and Jomsom exhibiting higher irradiance (6–6.5 kWh/m²/day) compared to the eastern half, which remains be- low 4.4 kWh/m²/day. These variations, along with temperature fluctuations that affect current out- put and voltage, directly impact solar PV per- formance. However, the financial analysis in this study—covering Payback Period, ROI, and NPV— was conducted based solely on a single 365 W solar panel, MPPT controller, installation, and battery replacement over a 25-year lifespan. Furthermore, the simulation of power generation and energy out- put relied on secondary data rather than real-time field measurements, which may limit the accuracy and generalizability of the results across diverse ge- ographic and climatic conditions in Nepal. 4 Conclusion The observation shows Nepal's enormous possibili- ties for solar energy harnessing, specifically in the Himalayan region with high irradiation levels. Also, findings indicate a clear relationship between so- lar irradiance, the outside temperature, along with PV system performance. That means greater ir- radiance along with lower temperatures producing larger current and power outputs. The linear re- lationship between horizontal global irradiance and photocurrent demonstrates the predictability of PV system performance under changing environmental condition. These findings can help policymakers and stakeholders promote renewable energy adop- tion while encouraging sustainable development ac- tivities in Nepal. The Himalayan region is the more favorable location for solar PV deployment due to greater solar energy availability, resulting in faster cost recovery and higher returns. Although both regions exhibit negative NPVs, the system is more economically viable in the Himalayas, while cost re- ductions or subsidies may be needed to improve feasibility in lower-irradiance areas like the East- ern Half. Further study might concentrate on en- hancing PV system models and incorporating en- ergy storage options to improve grid resilience as well as stability when faced with of climate change risks. References [1] K. Yoshikawa, H. Kawasaki, W. Yoshida, T. Irie, K. Konishi, K. Nakano, T. Uto, D. Adachi, M. Kanematsu, H. Uzu, et al. Sil- icon heterojunction solar cell with interdigi- tated back contacts for a photoconversion effi- ciency over 26%. Nature Energy, 2:17032, 2017. [2] D. Hernández-López, E. R. de Oña, M. A. Moreno, and D. González-Aguilera. 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Implementation of modified incremental con- ductance mppt algorithm in grid connected pv system under dynamic climatic conditions. Indian Journal of Science and Technology, 15(17):819–828, 2022. [13] N. Mohammad, M. Quamruzzaman, M. R. T. Hossain, and M. R. Alam. Parasitic effects on the performance of dc-dc sepic in photovoltaic maximum power point tracking applications. Smart Grid and Renewable Energy, 4:113–121, 2013. https://www.solarelectricsupply.com/media/custom/upload/Solarex-MSX64.pdf https://www.solarelectricsupply.com/media/custom/upload/Solarex-MSX64.pdf https://www.solarelectricsupply.com/media/custom/upload/Solarex-MSX64.pdf Introduction Research related to solar Irradiance in Nepal Significant of research Research Gap Methods and Materials PV module used in this research Theory parameters analysis of deploying PV systems in different regions Results and Discussion Solar Irradiance in Nepal Current generated by PV modules at varying irradiation levels in Nepal. Power generated by PV at various irradiation levels in Nepal Impact of Global Horizontal Irradiance on Photocurrent Impact of Cell Temperature on Photocurrent -benefit analysis of deploying PV systems in different regions Payback period Return on Investment Net Present Value Limitations of research Conclusion