An innovative multigeneration energy system driven by solar energy is proposed in this paper. The integrated model produces electricity, hydrogen, oxygen, and steam for heating purposes . The energy system comprises of pressurized cavity based solar power tower, latent thermal energy storage (TES) unit, unfired gas turbine (GT) unit, regenerative steam Rankine cycle (SRC), copper -chlorine (Cu -Cl) thermochemical cycle, and heat recovery units. By utilization of a high temperature ternary eutectic phase change material (PCM), a dynamic model is developed to deal with the intermittency of the solar energy. Using energy and exergy approaches, the proposed system is investigated to assess exergy destruction rates and the overall system performance . A parametric study is performed to investigate the influence of design parameters such as numb er of heliostats, pressure ratio of GT, and temperatures of reactions on the system performance. The results showed that the energy system produces electricity, steam , hydrogen, and oxygen at a rate of 41.9 MW, 12.6 kg/s, 0.19 kg/s, and 0.76 kg/s, respectively. Energy and exergy efficiencies of the integrated system are found to be 49.9%, and 44.9%, respectively. Keywords Thermal Energy Storage; Multigeneration System ; Thermochemical Cycle ; Heat Recovery; Phase Change Material . Nomenclature ph Physical Cpo Specific heat (J/mol.k) pp Pinch point Dp Depletion number th Thermal 2 Eẋ Exergy (W) turb Turbine ṁ Mass flow rate (kg/s) Greek symbols Q̇ Heat transfer rate (W) ηI Energy efficiency Ẇ Power (W) ηII Exergy efficiency A Area (m2) ∆ Difference ex Specific exergy (kJ/kg) Abbreviations h Specific enthalpy (kJ/kg) AC Air compressor P Pressure (kPa) CFWH Close feedwater heater s Entropy (J/kg.K) Cu-Cl Copper Chlorine T Temperature (K) DNI Direct normal irradiance V Volume (m3) GT Gas turbine Subscripts HRSG Heat recovery steam generator ch Chemical HX Heat exchanger Cond Condenser LHV Lower heating value D Destruction OFWH Open feedwater heater Elec Electrolyzer PCM Phase change material ex Exergy SI Sustainability index i Inlet SRC Steam Rankine cycle 3 L Loss ST Steam turbine o Dead state TES Thermal energy storage P Pump 1. Introduction Total energy consumption of the world is growing 3.2% annually [1]. Additionally, with the deterioration of natural resources, it is necessary to use more sustainable energy sources, manage the energy consumption/production more effectively, and use more e fficient energy systems [2]. Using renewable energies such as solar or wind energies is important to achieve sustainability goals . Energy storage systems are also required due to intermitten cy of renewable energy sources [3]. Multigeneration systems which are capable to produce more than one product should be considered to improve the overall performance [4-6]. Pure oxygen is used in industry, medica l, space , and marine applications [7]. It is currently used in respiratory devices in hospitals, life support in the space or underwater conditions , and even in industry to produce steel from iron ore [7,8]. Additionally, h ydrogen which is a carbon -free energy carrier with high energy density c an be of great use for energy management purposes [9]. It is an important substance which can be used as a chemical agent in chemical plants such as refineries to produce high quality fuels such as diesel and gasoline, and also, in petrochemical plants to produce ammonia, methanol, and other chemicals [ 10]. Currently, h ydrogen is mostly produced from fossil fuels. Over 95% of the current hydrogen demand in the world is produced from natural gas and coal, and less than 5% is produced through water electrolysis [ 11]. Therefore, it is required to investigate more sustainable methods for large -scale hydrogen production. There are few methods in which water splitting processes are used to dissociate water molecules into hydrogen and oxygen 4 [12]. These methods include thermochemical cycles, photo -electrochemical cells, and electrolysis [ 12-14]. Thermochemical water splitting is one of the most promising methods for sustainable hydrogen production. A thermochemical cycle decomposes water into hydro gen and oxygen through a series of chemical reactions. All of the chemical compounds produced in the cycle, are used within the cycle. Therefore, the net outputs are only oxygen and hydrogen [ 15,16 ]. Some of the thermochemical cycles require thermal energy , and some others, called hybrid cycles, need both thermal energy and electricity [ 17]. Among over hundreds of different thermochemical cycles presented in the literature, Sulfur -Iodine (S -I) and Copper -Chlorine (Cu -Cl) are known as the most promising thermochemical cycles for hydrogen production [ 12,13,17 ]. Heat is required at the maximum temperature of around 900 and 500 ℃ for the S -I and Cu -Cl cycle, respectively [ 18,19 ]. A comparative analysis between S -I and CuCl cycle was carried out by Wang et al. [ 20]. It was shown that the Cu -Cl cycle is more suitable for integration with various renewable energy sources [ 20]. Due to high temperature requirement of the thermochemical cycles, limited sources of energy are available for integration . Solar energy as one of the most abundant and available renewable energy resources is a good candidate for integration with the Cu -Cl cycle [ 21,22 ]. However, due to its intermittency, for a continuous operation of the plant, TES systems should be utilized to store the solar energy during the sunny hours and recover it during cloudy hours or nights. Molten salts, as sensible energy storag e materials, are usually used as the TES media in the solar plants [ 23]. However, considering high costs, limited operating temperature, and large required volumes of the molten salts, PCM can be considered as alternative TES media in the solar plants [ 24,25]. Some studies explored solar cogeneration/multigeneration systems for producing various outputs especially oxygen and hydrogen. Coupling of a solar system with a five -step Cu -Cl thermochemical cycle was investigated [26] . Solar salt which is a binary mixture of KNO 3 5 and NaNO 3 was selected as the thermal energy storage medium and a thermal efficiency of 49% was reported [ 26]. A four -step Cu -Cl cycle integrated with a solar parabolic trough collector system was proposed for Algeria. Energy and exe rgy efficiencies of the Cu -Cl cycle were reported as 48.14% and 92.25%, respectively [ 27]. In another study, three different types of hydrogen production systems including an ocean thermal powered water electrolysis system, solar Cu -Cl cycle and wind power ed water electrolysis system were investigated and compared. It was concluded that the solar Cu -Cl cycle has the highest energy efficiency which is 32.7% [2 8]. An integrated solar powered Cu -Cl cycle coupled with a hydrogen compression unit was proposed an d investigated in another study. The overall energy efficiency of the system was 12.6% [2 9]. Thermodynamic performance of multigeneration which produced potable water, hydrogen, power, and heating -cooling based on solar energy was investigated in another study. The system utilized solar power tower with Brayton cycle and electrolysis . However, no TES system was considered for continuous operation of the system. The overall system energy and exergy efficiencies were reported as 78.93%, and 47.56%, respectively [30]. In another study, a multigeneration system was investigated which used parabolic solar dish collector to produce electrolytic hydrogen, cooling -heatin g, and power. Molten salt was considered for sensible TES. The energy and exergy efficiencies of this system were reported as 48.19% and 43.57%, respectively [31]. A hybrid system based on solar and biomass energies were investigated to produce hot water, cooling, hydrogen, and power. A four-step Cu -Cl cycle was used to produce the hydrogen. The energy and exergy efficiencies of the system were evaluated as 29.9% and 31.5%, respectively [32]. Past studies used conventional molten salts as the TES media of their solar subsystems [28,29, 31,32]. Also, molten salt was used to produce steam which served as a heat transfer fluid to provide the required heat to the reactors and heat exchangers [28,29,32] . The operating temperature of the molten salt ranges from 29 0 to 565 ℃ [33] which limits the 6 hydrogen production yield of the plant. Also, the integrated systems were dependent on the grid electricity for the electrolysis step [ 26-28]. In this study , a novel solar multigeneration system with thermochemical cycle is proposed for sustainable production of oxygen, hydrogen , power, and steam for heating purposes . This energy system does not rely on the external electricity source. Also, air is used as the heat transfer fluid in the plant. The proposed multigeneration system includes a solar heliostat field, pressurized cavity receiver, PCM tank, unfired gas turbine cycle, four -step Cu -Cl cycle, heat recovery steam generator unit and regenerative Rankine cycle. The TES material selected for this stu dy is an eutectic mixture of CaF 2(49)-CaSO 4(41.4) -CaMoO 4(9.6) fluoride salt with melting temperature of 943 ℃ and fusion enthalpy of 237 kJ/kg [ 34]. Main objective s of this study are to conduct energy and exergy analyses for the proposed solar multigeneration energy plant to assess the overall system and subsystems performance, and finding the exergy destruction of various components , and also, to compare with the previous studies in the literature . Exergy analysis is a useful tool which can help the design engine ers identify the source, type, and amount of lost availability in the system which are caused by irreversibility . Therefore, it is possible t o achiev e higher efficiencies which result in improving the sustainability . The effects of varying input parameters on the overall energy system performance are also investigated in this study . The results provide insight for design enginee rs to determine the major input influencers on the energy system performance. 2. System Description The schematic of the proposed integrated solar -based hydrogen production plant is shown in Fig . 1. The outputs of the proposed energy system in this study are hydrogen, oxygen, electricity, and steam for heating purposes . The proposed energy system comprises of five subsystems including solar heliostat field and receiver, unfired gas turbine 7 cycle with PCM , four -step c u-cl cycle, regenerative steam Rankine cycle , and heat recovery unit. The air is pressurized by the compressor of the unfired gas turbine unit at state 21 and goes to the pressurized cavity receiver tower . Meanwhile, s olar radiation s are reflected by the heliostat mirrors to top of the receiver tower to heat up the air. The heated air at state 23 passes through the PCM unit. When the solar radiations are high, the PCM begins to charge up and when the solar radiations are low the PCM disch arges. The air then goes through the gas turbine unit in which electricity is generated. The low -pressure air at the exit of the gas turbine unit at st ate 25 returns to the PCM unit to get heated again. It is because the required temperature for the Cu -Cl cycle is about 530 ℃, and therefore, the temperature of air leaving the PCM unit at state 26 has to be higher tha n 530 ℃. For the base case, the temperature at state 26 is 600 ℃. Afterwards, the hot air splits into three streams to supply the required heat for the various heat exchangers, reactors , and steam generators in Cu-Cl and Rankine cycle s. The air exiting the heat exchangers at states 31, 32, and 33 are used in a heat recovery steam generator unit to produce steam for heating purposes . Four-step Cu -Cl cycle considered here includes hydrolysis, thermolysis, drying, and electrolysis steps. The first step is the hydrolysis in which water and cupric chloride (CuCl 2) react to produce copper oxychloride (Cu 2OCl 2) and hydrogen chloride (HCl) gas at 375 -400 ℃ [35]: 2CuC l2(s)+H2O(g)→Cu2OCl2(s)+2HCl (g) (1) Second step is thermolysis in which decomposition of copper oxychloride occurs at high temperatures of 500 -530 ℃. The products of this step are oxygen and cuprous chloride (CuCl) [ 35]: Cu2OCl2(s)→1 2O2(g)+2CuCl (l) (2) The third step is drying of aqueous cupric chloride which occurs at temperatures ranging from 30 to 80 ℃ [35]: 8 CuC l2(aq)→CuCl2(s) (3) The last step is electrolysis in which hydrogen gas and cupric chloride are produced from the electrochemical reaction of aqueous HCl and CuCl at around 25 ℃ [35]: 2CuCl (aq)+2HCl (aq)→H2(g)+2Cu Cl2(aq) (4) Heat is recover ed from the oxygen and molten CuCl leaving the thermolysis reactor at about 530 ℃, and also the HCl leaving the hydrolysis reactor at about 400 ℃. The recovered heat is used to heat up CuCl 2 and copper oxychloride , to produce steam, and also to preheat the Rankine cycle ’s working fluid . Four heat exchangers are used in the Rankine cycle to produce superheated steam. HX9 and HX10 are the preheaters, HX11 is the evaporator, and HX12 is the superheater. Open and closed feedwater heaters use extract ed steam at states 52 and 53 to improve the performance of the SRC . The required electricity of the Cu - Cl cycle’s electrolyzer is supplied from the produced power of the GT cycle. Additionally, the excess electricity of the GT, and also, the SRC are exported to the electrical grid. 9 Figure 1 Schematic of the integrated solar -based multigeneration energy plant 3. Methodology Energy and mass convers ions are expressed as follow s [36]: Q̇−Ẇ=∑(ṁh)i−∑(ṁh)e (5) ∑ṁi−∑ṁe=0 (6) And exergy balance is developed as [36]: 10 Eẋd=EẋQ−Eẋ𝑊+∑(ṁex)i−∑(ṁex)e (7) where, Eẋ, Ẇ, Q̇, and ṁ denote rate of exergy, work, heat, and mass, respectively. Also, ex and h are the specific e xergy and e nthalpy , respectively. Other terms are calculated from the equations (8) to (11) [36]: EẋQ=(1−T0 Ti)Qi̇ (8) EẋW=Ẇ (9) ex=exph+exch (10) exph=(hi−ho)−To(si−so) (11) Here, exch and exph represent chemical and physical specific exergy, respectively. Temperature and pressure of reference environment is considered as 25 ℃ and 101 kPa. To relate between the environment impacts and exergy, sustainability index is defined as follows [37]: SI=1 Dp (12) Dp is the depletion number and is defined as the ratio of exergy destruction to exergy input of the integrated system [ 37]. 3. Analysis 3.1. Solar Heliostat Field and Pressurized Cavity Receiver Input and reflected solar radiation to and from the heliostat mirrors are calculated as follow s [38]: 11 Q̇Solar =Ah×N×DNI (13) Q̇Heliostats =Q̇Solar ×ηOpt (14) where, ηOpt, N, and Ah represent the optical efficiency of heliostats, number of heliostats, and aperture area of a single heliostat mirror, number of heliostat mirrors , and aperture area of a single heliostat , respectively. In this study, conduction heat losses are negligible [39,40 ]. Heat losses associated with convection and radiation heat transfe r from the pressurized cavity receiver are determine d by [39]: Q̇loss=Q̇loss ,conv +Q̇loss ,rad (15) Q̇loss ,conv =hairAr(Trec,surf−To) (16) Q̇loss ,rad=σε(Trec,surf4−To4) (17) where, σ, ε, Trec,surf, and Ar represent Stefan -Boltzmann constant, receiver emissivity, receiver surface temperature, and receiver aperture area , respectively. hair is convection heat transfer coefficient which is obtained from [39]: hair=10.45−Va+10√Va (18) The heat absorbed by the pressurized air is evaluated from the following equation : Q̇abs=Q̇Heliostats −Q̇loss =ṁ(h23−h22) (19) As mentioned earlier, a high temperature latent heat TES medium is utilized to achieve higher efficiency in the unfired gas turbine cycle. The PCM considered here is a eutectic mixture of CaF 2(49)-CaSO 4(41.4) -CaMoO 4(9.6) with the melting temperature of 943 ℃ [34]. 12 Heat loss during the storage of the PCM unit is considered as 1% [41]. Changes in energy content of the PCM is evaluated by [42,43 ]: dEPCM dt=Q̇net,PCM (20) where Q̇net,PCM and EPCM are the heat transfer rate to the PCM and total energy content of PCM, respectively. Rate of liquefaction/solidification of the PCM is calculated as [42,43 ]: dM PCM dt=Q̇net,PCM ∆hmelt (21) where MPCM and ∆hmelt represent mass of the liquified PCM and enthalpy of fusion of the eutectic fluoride salt, respectively. Figure 2 shows the variations of direct normal irradiation and wind velocity for the city of Isfahan in central Iran. Figure 2 Variations of DNI level and wind velocity for various seasons in Isfahan 3.2 Copper -Chlorine and Rankine Cycle s 13 The s pecific heat, enthalpy and entropy of various compounds in the Cu -Cl cycle are evaluated as follow s [44-47]: Cpo=A+B×t+C×t2+D×t3+E/t2 (22) ho−hrefo=A×t+B×t2 2+C×t3 3+D×t4 4−E t+F−H (23) So=A×ln(t)+B×t+C×t2 2+D×t3 3−E 2×t2+G (24) t=(T 1000) (25) In the above equations , A-H are the Shomate constants [ 46]. Rate of thermal energy associated with steam flow and the net power output are calculated as follows: Q̇Steam =ṁ63h63+ṁ41h41 (27) ẆNet=(ẆGT+ẆSRC)−(ẆAC+ẆElec +ẆP) (28) Here, subscripts p, SRC, GT, AC, and Elec denote pump, steam Rankine cycle, gas turbine, air compressor, and electrolyzer, respectively. Integrated system overall energy and exergy efficiencies are expressed as: ηI=(ṅH2LHVH2+ẆNet+Q̇Steam )Q̇Solar⁄ (29) ηII=1−(Eẋd,total EẋSolar⁄ ) (30) Input data and assumptions for the base case study are listed in Table 1 [34,48-52]. Table 1 Input data and assumption s of various subsystems for the base case study Subsystem Parameter Value 14 Solar Heliostat Field Optical efficiency (%) 75 Number of heliostats 5,000 Aperture area of each heliostat (m2) 11×11 Pressurized Cavity Receiver Receiver aperture area (m2) 60 Average s urface temperature of the receiver (℃) 1,100 Receiver emissivity (%) 88 Unfired gas turbine cycle Pressure ratio 8.2 Air compressor isentropic efficiency (%) 80 Gas turbine isentropic efficiency (%) 86 Temperature of air entering the turbine ( ℃) 943 PCM unit Melting temperature ( ℃) 943 Enthalpy of fusion (kJ/kg) 237 Temperature of air entering the CuCl cycle ( ℃) 600 Cu-Cl cycle Temperature of hydrolysis step ( ℃) 400 Temperature of thermolysis step ( ℃) 530 Temperature of electrolysis step ( ℃) 25 Temperature of drying step ( ℃) 70 Steam Rankine cycle Condenser pressure (kPa) 10 First bleed pressure of steam turbine (kPa) 2,500 Second bleed pressure of steam turbine (kPa) 1,500 Boiler pressure (kPa) 15,000 Turbine inlet temperature ( ℃) 400 Steam turbine isentropic efficiency (%) 86 15 Pumps isentropic efficiency (%) 80 4. Results and Discussion 4.1. Validation The results for the Cu -Cl cycle are compared with those presented by previous studies [53] and [ 54]. For heat exchanger effectiveness of 75%, and 100%, the results of current model are presented and compared with previous studies in Fig. 3 . As can be seen , the results are in good agreement with past reported studies . 16 Figure 3 A comparison between the results for the Cu -Cl cycle with past studies The main results for the integrated system are shown in Table 2. The overall energy and exergy efficienc ies of the integrated system are obtained as 49.9% and 44.9%, respectively. For the base case, electricity, hydrogen, oxygen, and steam are produced at the rates of 41.9 MW, 0.19 kg /s, 0.76 kg/s, and 12. 6 kg/s, respectively. The sustainability index of the plant is obtained as 1.81. 17 Table 2 Main results of the integrated energy system for the base case study Parameter Value Overall energy efficiency (%) 49.9 Overall exergy efficiency (%) 44.9 Amount of produced hydrogen (kg/s) 0.19 Amount of produced oxygen (kg/s) 0.76 Net generated electricity (MW) 41.9 Produced steam (kg/s) 12.6 Total exergy destruction (MW) 111 Sustainability index 1.81 The Sankey diagram shown in Fig . 4 presents the exergy destruction of various subsystems and components of the integrated system. As can be seen, 37.8% of the input exergy which is equal to 76.5 MW is destroyed in the solar heliostat field and the receiver. The exergy destruction rates associated with Cu -Cl cycle, Rankine cycle, and heat recovery units are 4.4%, 3.25%, and 2.5% of the total exergy input , respectively . Advantage of Sankey diagram is in improving the sustainability of the proposed energy plant. The exergy destruction of different components shows the prioritization for the next advancement in the energy plant . Additionally, it can be used to identify the large sources of system irreversibility. This way it is possible to focus on each source and reduce the deficiencies i n energy system performance by selecting right input parameters or refining the overall design in future studies. 18 Figure 4 Sankey diagram for the exergy flow and exergy destruction of the integrated energy system Variations of solar input heat and heat losses for different seasons are shown in Fig. 5. The maximum heat input from the heliostat mirrors ranges from 387 MW in winter to over 623 MW in summer. Additionally , heat losses associated with solar heliostat fie ld and pressurized cavity receiver increase from 101 MW in winter to 159 MW in summer which indicates a 57% increase in the heat loss es. 19 Figure 5 Performance of solar power tower system in different seasons: (a) heliostats input heat, (b) heliostats output heat, (c) absorbed heat by air , and (d) overall solar heat losses Effects of various input parameters on the overall integrated system performance are investigated in this paper . The effect of the number of heliostat mirrors on the overall integrated system performance is shown in Fig . 6. Ascan be seen, n et power output, hydrogen production rate , and exergy destruction increase linearly with an increase in the heliostat numbers. As the number of heliostat mirrors increase from 3,000 to 6,000, t he hydrogen production rate and net power output increase from 0.11 kg/s and 24.94 MW to 0.27 kg/s and 58.90 MW , respectively. 20 Figure 6 Influence of the number of heliostat mirrors on the overall integrated system performanc e The effect of the gas turbine pressure ratio on the overall integrated system performance are shown in Fig . 7. Maximum power output and overall energy efficiency occur at pressure ratios of around 6-8. However, at these pressure ratios, the rate of hydrogen production is minimized . 21 Figure 7 Influence of gas turbine pressure ratio on the overall integrated system performance The i nfluence of the inlet hot air temperature to the Cu -Cl cycle (T 26) on the overall integrated system performance is shown in Fig . 8. As it can be seen, b y increasing the temperature of this state in the second phase of heating the hot air, higher amount of energy will be discharged from the PCM tank and therefore, the mass flow rate of air which enters the air compressor is reduced and hence all of the integrated system outputs are reduced. There is one exception and that is the molar flow rate of produced hydrogen which is directly related to the temperature of state 26. Because the temperature difference between state 26 and state 27 is quite low (less th an 100 ℃ for the base case); whenever the temperature of state 26 increases the flow rate of air entering the thermolysis reactor reduces and therefore, more air is left to run the Cu -Cl cycle and produce higher amount of hydrogen. 22 Figure 8 Influence of T 26 on the overall integrated system performance Figure 9 shows the effect of variation s in the hydrolysis temperature on the overall integrated system performance. As it is observable, b y increasing the hydrolysis reaction temperature, more air has to flows through the hydrolysis reactor which causes a decrease in the net power output and the hydrogen production rate of the energy system . However, energy and exergy efficiencies of the int egrated system increase due to an increase in the steam production rate. 23 Figure 9 Influence of hydrolysis reaction temperature on the overall integrated system performanc e As shown in Fig. 10, by increasing the thermolysis reaction temperature , net power output, and rate of produced hydrogen increase. This causes an improvement in the energy and exergy efficiencies of the integrated system . It is noted that if the integrated system did not include a heat recovery steam generator unit, an increa se in the thermolysis reaction temperature would reduce the energy system performance. 24 Figure 10 Influence of thermolysis reaction temperature on overall integrated system performance and output The results for the novel integrated system proposed in this paper are compared with those for other solar -based hydrogen production systems investigated in past studies . As shown in Fig. 1 1, the present energy system has the highest overall energy efficiency among other systems . This is mainly because of the heat recovery unit included in the integrated system . Also, d espite relatively high exergy destructions in the heat recovery unit and the gas turbine cycle, the overall exergy efficiency of the proposed energy system is desirable . 25 Figure 11 Comparison between the overall efficiency of the proposed integrated system and other solar systems 5. Conclusions A novel solar powered integrated system for the production of thermochemical hydrogen, oxygen, power, and steam for heating purposes is analysed in this study . The proposed integrated system utilizes a solar power tower with pressurized cavity receiver, unfired gas turbine cycle with PCM thermal ene rgy storage, four-step Cu -Cl cycle, regenerative steam Rankine cycle , and heat recovery unit. The impact of the thermal energy storage on the hydrogen production cycle can be concluded as : • Overall integrated system energy and exergy efficiencies are 49.9% and 44.9%, respectively. • For the baseline of this study, 0.19 kg/s of hydrogen, 0.76 kg/s of oxygen , 41.9 MW of electricity , and 12.6 kg/s of steam are produced . 26 • Heat losses associated with solar heliostat field and pressurized cavity receiver increases over 57% from 101 MW in winter to 159 MW in summer. • Highest exergy destruction s occur in the solar power tower system and unfired gas turbine cycle which consume 37.8 % and 6.98% of the overall integrated system exergy input . Influence s of various input parameters , including the number of heliostats, pressure ratio of the gas turbine, air inlet te mperature to the Cu -Cl cycle , hydrolysis reaction temperature, and thermolysis reaction temperature on the overall energy system performance are investigated . It was concluded that by increasing the number of heliostats mirrors from 3,000 to 6,000, it is p ossible to increase the power generation of the cycle by 33.96 MW . Additionally, investigation on the influence of gas turbine pressure ratio on system performance showed that the energy efficiency, and power generation of the cycle is maximized at the pressure ratio of 7. Our results indicated that by increasing the temperature of hydrolysis and thermolysis reactions, both energy and exergy efficiencies will be increase d. A comparison between the proposed integrated and other solar systems studied in th e past shows the proposed integrated system has the highe st performance compared to previous solar hydrogen systems in terms of energy and exergy efficiencies.