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34 

 

 

 

Review 

A review of the integration of the copper-

chlorine 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 thermo-
chemical 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 copper-
chlorine 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 low-
temperature 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 

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February 2024| Volume 03 | Issue 01 | Pages 34-49 

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ISSN 2832-0328 

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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 [32-
34]: 

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), Cu-
Cl 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 triple-

production 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 four-

step 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 Cu-

Cl 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 tri-

generation 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 high-

temperature 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 non-

renewable 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 its temperature can meet the required heat 

for cycles that work with low-temperature sources 

(Goswami, ORC, Kalina cycle). 

4. The output oxygen of the Cu-Cl cycle can be used as a heat 

source for cycles that work with low-temperature 

sources. 

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. 

 

 

 



MA Ehyaei et al. /Future Energy                                                                                                February 2024| Volume 03 | Issue 01| Pages 34-49 

47 

 

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