The theoretical approach of the solar organic Rankine cycle integrated with phase change material for the Hungarian region

Hungary is not only dependent on imports of natural gas and fossil fuels, but Hungary is also the lowest in renewable energy utilization; otherwise, only 11.3% compared to other Central European countries in renewable energy utilization, above 13%. The percentage of renewables in power generation quadrupled from 8% to 16% between 2010 and 2020, with most of the gains coming from the rapid expansion of solar energy, particularly after 2016. Regarding solar energy resource potential, Hungary has a daily total of around 3.2–3.6 kWh/m2 and a yearly total of about 1168–1314 kW.h/m2. This makes it a suitable location for putting solar thermal collectors in conjunction with an organic Rankine cycle (ORC) system. In this study, the authors analyzed solar thermal as a heat source to generate electricity with ORC using two types of working fluids (R245fa and R123). Hungary's weather data for a whole year is used as primary data to look for solar radiation characteristics and ambient temperature. Based on the general solar collector equation, the parabolic tube collector was selected as the best solar collector to utilize solar radiation by producing a maximum heat of around 654.68 kW. Therefore, the evacuated flat plate collector was selected as the solar collector that can produce the maximum outlet temperature of around 372.15 K with a similar size aperture area. Producing a temperature output from the solar collector for heat transfer in the ORC system and from the performance showed that R245fa resulted in better Wnet performance compared with R123 with values of 45.82 and 28.17 kW, respectively, under the same solar collector. Meanwhile, the material suitable for the thermal energy storage‐evaporator combination is organic phase change material using N‐Octacosane, which in the same temperature range (350–375 K) has the smallest ζ(T) value (1.08–1.103), so the mass required for the system is very efficient.


| INTRODUCTION
Hungary is attempting to become an energy-independent country by enacting various acts and policies.Hungary now imports the majority of its energy primarily from Russia.Although Hungary's natural gas use has declined since 2008, natural gas accounts for the majority of imported energy.Approximately 80% of this natural gas is transported from Russia via Ukraine and Austria. 1 Therefore, Hungary's energy policy strategy for 2022 focuses on increasing the country's energy independence, especially in the recent tragedy of Russia's invasion of Ukraine in February 2022.Russia completely stopped Nord Stream 1 gas flows, which has presented Europe with a new set of energy security issues.Hungary responded by declaring an energy emergency in July 2022.To solve the crisis, the administration intends to boost local gas and coal production, secure additional gas imports, and boost the country's lignite-fired power plant output.Furthermore, the lifespan of nuclear power plants is extended. 2Hungary is not only dependent on imports of natural gas and fossil fuels, but Hungary is also the lowest in renewable energy utilization.That is, only 11.3% compared to other Central European countries in renewable energy utilization, above 13%. 3he data shows that the Hungarian government is trying to increase the utilization of renewable energy for electricity consumption every year, especially in the solar energy utilization sector.Most of the use of solar energy is through solar photovoltaic (PV), solar drying, or a combination of solar PV-thermal.In addition, the use of solar thermal using an organic Rankine cycle (ORC) has long been carried out, especially in areas prone to disasters and isolated.The use of ORC is the same as the conventional Rankine cycle.However, it uses hydrocarbons/refrigerants with a lower boiling point than water, so using ORC from various sources is possible.These include heat sources from geothermal waste heat, [4][5][6] biomass and biogas, 7,8 and industrial or power plants flue gas.
In terms of solar energy resource potential, Hungary has a daily total of around 3.2-3.6kWh/m 2 and a yearly total is about 1168-1314 kWh/m 2 , and can be seen in Figure 1 shows Hungary's global solar radiation (GHI) intensity. 9These numbers distinguish Hungary as having a relatively high potential for solar energy use. 10 This makes it a suitable location for installing solar thermal collectors with an ORC system.In solar thermal applications, the two main subsystem components are solar collectors and heat storage.In solar thermal applications, a solar collector is the component that transforms solar irradiation energy to heat energy via a working fluid, a strong optical performance is essential to absorb as much heat as possible.The heat transported by the working fluid can be used to charge thermal energy storage (TES) systems or to provide residential hot water. 11,12A recent study suggests that small-scale Solar Thermal systems paired with ORC power may compete with PV and diesel generators for off-grid duty on a levelized cost-of-energy basis. 13Not only that, solar-ORC has several advantages as an alternative to ORC, namely: (1) Low-cost components from heating ventilating and air conditioning engineers or chiller, (2) It can be combined for household heating or desalination, (3) use of TES for heat storage intermittently, which will be used at critical hours.
5][16] Some authors 17,18 investigated ORC employing a solar parabolic through concentrator (PTC).Kumar 18 used the PTC model to examine a solar thermal power plant, reflecting solar energy on the receiver.While it has been completed a hybrid ORC powered with solar collector PTC type of low-grade temperature (>423 K), the prototype produces power ranging from 479 to 845 kW, with system efficiency ranging from 11.6% to 19.7%, respectively. 17illarini et al. 19 offered another scenario in which they evaluated the solar ORC and focused on various typologies and technological viewpoints.
It was mentioned before that the Solar-ORC is unable to operate all day long, TES can support the system by storing excess heat during the day hours and using it during the night time or low solar irradiation. 20,21TES systems are classified as sensible, latent, and thermochemical storage.Latent storage is known as phase change material (PCM) storage. 22Alvi et al. 23 evaluated the performance of direct and indirect solar ORC designs using water and R245fa in both cases.Although the direct design had better yearly efficiency and output power than the indirect, the indirect configuration had a more considerable annual heat stored by the PCM and a higher capacity factor.Bellos et al. 24 investigated the influence of three different TESs on the PTC-driven solar-ORC.Compared to sensible thermal oils and thermal oil-ceramic pebbles, the PCM acquired 13.97% and 128.66k€ thermal and net present value (NPV), respectively.Freeman et al. 25 investigated a residential solar ORC system paired with PCM storage based on UK meteorological conditions.It was stated that employing PCM storage instead of sensible storage increased daily power production by 20%.Jafari Mosleh and Ahmadi. 26sed the TRNSYS program to evaluate the influence of PCM storage on the solar Rankine cycle every year.The solar fraction was enhanced by around 90.5% compared to the system without the PCM.Several PCMs' effects were investigated, and NaNO 3 acquired the most significant solar fraction (34.14%).Daniarta et al. 27 recently did a complete review related to ORC integrated with TES under low-medium temperatures.Moreover, the authors give an advanced insight into designing a cascade model of TES-evaporator considering the selection of TES materials.
We propose evaluating the variety of TES media used in a domestic solar-ORC system, focusing only on the prediction of sizing PCMs as storage media.The selection of optimum storage temperatures that maximize the solar-ORC system's total to solar-to-electric conversion efficiency is being examined in Godollo, Hungary, where research for solar-ORC still needs to be improved.It is essential.To ensure the optimum fit between the systems' electrical outputs and the residential seasonal load profiles in the individual locales, the needed TES volumes and system operational methods are also examined.Furthermore, the energy and exergy analysis of the Solar-ORC system is also analyzed to find out how much potential power and the characteristics of the power produced and to find out the details of how much exergy loss is caused by each component of the Solar-ORC system.

| Climate condition characteristics
To comprehend the features of solar energy storage needed for Godollo, the maximum and average global F I G U R E 1 Global solar irradiation (GHI) in Hungary. 9olar irradiance characteristics were accessible in Solargis data during 2021.Figure 2 shows the solar irradiation on average and peak days in Godollo for each month of the year.The figures show that the average Godollo solar irradiation is more plentiful and varies less on a daily and seasonal timeframe than maximum Godollo solar irradiation.It can be seen in the figure that August is the peak for both the maximum and the average of global solar irradiation, with around 507 and 316.9 Wh/m 2 , respectively.Therefore, this study chose June as the month to use as simulation data.Figure 3 shows the characteristics of the daily average of global solar irradiation and the ambient temperature.The plot confirms that both characteristics (Gb and T ambient ) have different peak values of the time.For solar irradiation, the maximum value happens around 9-10 o'clock, around 447 Wh/m 2 , while the highest ambient temperature happens around 16-17 o'clock with a temperature of around 304 K.It happens due to the accumulation that occurs during solar irradiation at the last time to make the ambient temperature rise at the end of daylight.

| Solar collector subsystem
Therefore, for the solar collector, the current research looks at two types of nonconcentrating collectors: (1) a new generation of high-performance evacuated flat-plate collector (EFPC) explicitly designed for medium-temperature process-heating applications (including ORC systems), and (2) a standard, lower-cost evacuated-tube heat-pipe collector (ETC) designed for low-temperature DHW heating applications, and (3) parabolic tube collector (PTC).According to an experiment by Alshibil et al., 28 the collector array is designed to be south-facing, with a 30°i nclination angle facing south for maximum thermal power and electrical output.The solar-collector array is modeled as functioning under quasi-steady state circumstances, with the collectors' thermal capacity ignored.The sizing calculations assume that the collector subsystem is only active during the hours when the solar incidence angle on the solar collector plane is 30°.
The solar-collector array's performance is predicted using hourly climatic data for Godollo in June 2021.A steady-state efficiency equation is used to simulate the collectors 25 : where is η 0 the zero-loss optical efficiency, C 1 and C 2 are heat loss coefficients, and K θ are incident angle modifier (IAM) factors applied to the zero-loss efficiency for the beam and diffuse components of the solar irradiance (G b ), respectively.By assuming that the outlet fluid temperature (T h,o ) is equal to the temperature of the lumped/uniform TES tank (T TES ), Equation ( 1) is solved by: In Table 1, the values of the parameters are given.The solar collector useful heating product (Q u ) is found by using the following equation: where the collector mass flow rate (ṁc ol ), the specific heat capacity of the fluid (c p ) and the temperature levels of the solar collector, inlet (T h,i ) and outlet (T h,o ) are used in Equation (3) for the useful heat production calculation.In this study, the cycle model and parameters used for the thermodynamic analysis of the ORC system are shown in Figure 5. R245fa and R123 were chosen as working fluids according to their properties and the low value of ozone-depleting point (ODP) and global warming potential (GWP), and the details are shown in Table 2.Moreover, both working fluids are suitable for generating energy under 373.15K.According to ASHRAE, R123 has been banned in all European countries regarding ODP and GWP except several Asian countries.Taib et al. 32 did a case study for stakeholders on the usage, prevention, and management of HCFC leaks in ASEAN nations.R123 (one of the HCFCs) was collected from a chiller unit and reclaimed for reuse, eliminating the possibility of inappropriate waste and leakage.At the local level, it is possible to infer that these nations had a common issue of low knowledge, little regulation enforced, less crossministerial cooperation among regulators, no suitable collection and disposal facilities, a lack of financial assistance, and cost competitiveness.The impurity test findings showed that 79.21% of the R123 sample was reclaimable, which might lessen the environmental's negative impact if appropriately recovered.However, in this study, R123 was only used as a performance comparison that the working fluid could optimize.
The first and second law of thermodynamics should be applied to determine the performance of the ORC.The energy equilibrium equation may be used to calculate the quantity of work generated and the heat required by the ORC.The formula for each component are as follows 34 : Process 1-2, turbine (5) The net power output of solar-ORC can be evaluated through the following equation: Meanwhile, the thermal efficiency is as follows: Both the evaporator and condenser are modeled with approach temperature differences of 5 K at the workingfluid output and a heat source temperature equal to that of the TES tank and a cold-sink temperature equal to the highest possible ambient air temperature The evaporator receives a minimum of 5 K of super- heating, while the condenser assumes the working fluid departs in a saturated liquid condition (zero subcooling).The ORC pump (η pump ) and turbine (η turbine ) have isentropic efficiencies of 85% and 85%, respectively.

| TES
All calculations in this work employ a lumped model for the TES vessel, assuming constant temperature and ignoring thermal losses to the environment.When PCMs are used as storage medium, the thermal store is programmed to start each day in a completely discharged (solidified) condition.6][37] Table 3 shows that the material's specific heat capacity, which fluctuates with temperature, determines the TES feature.Differential scanning calorimetry (DSC) may be used to determine the TES material's specific heat capacity.Equation ( 12) is the generic polynomial equation for the specific heat capacity of materials, which is used to calculate the stored thermal energy in Equation ( 13). 38
Assuming that the heat transfer rate during TES device discharging was the same as that of the TESevaporator (Equation 14), the efficiency of the stored thermal energy and the charging-discharging period may be computed using Equations ( 15)- (18).Where τ is the charging/discharging times, m ST is the storage mass (kg), and the CH and DC subscripts reflect charging and discharging operations, respectively.As an evaluation parameter, the dimensionless mass parameter (ζ(T)) of TES material may be utilized for sizing the TES employed for solar thermal.Notably, the organic PCM attributes provided for PCMs represent a typical spectrum of commercially accessible organic aliphatic molecules and inorganic hydrated salt products.Table 4 shows the selected organic PCM materials for this study based on the material's melting temperature and solid-liquid phase according to the T in and T out of evaporator.Mostly, paraffin is a saturated hydrocarbon family, and the longer the length of the hydrocarbon chains, the higher the melting temperature. 43Paraffin is a relatively safe, dependable, low-cost, noncorrosive substance with a low vapor pressure.Nonetheless, some paraffin compounds have unfavorable thermal and chemical characteristics, such as low heat conductivity, flammability, and a significant volume change during the phase shift (solid-liquid) and are incompatible with plastic.Alcohol, fatty acids, and glycols are examples of nonparaffin PCMs.In comparison to paraffin, several nonparaffin compounds are readily synthesized from vegetable and animal oils 44 and have higher melting, crystallization, and heat of fusion temperatures. 45igure 4B shows the location of the TES in the shell and tube-type evaporator.Among the many heat exchangers, the shell-and-tube version has received the most attention.The shell-and-tube type of LHTES is the most oftenused configuration as of its benefits, such as simple design, low cost, low-pressure drop, large heat transfer area, high discharge power, and high efficiency. 491][52] Aside from that, the industry uses shells and tubes 90% of the time.It comprises a shell, a tube, baffles, a front head, a rear head, and a nozzle.The shell diameter ranges from 60 to 2000 mm, the working temperature ranges from 253 to 773 K, and the maximum pressure is 500 bar. 53A suitable shell and tube geometry design considering the TES material and appropriate surface area for optimal heat transmission is required during construction.As a result, the downside of employing a TES-evaporator, particularly when combining shell and tube as one component, is the possibility of solidification or flow obstruction within the tubes.Further research on the TES-evaporator is to use the cascade method.[48] No PCM name Classification T m (K) | 4435 TES with cascaded PCMs considering a specific outlet temperature.It was observed that with an increase in the specific surface area, the effective utilization rate of the system could be improved.It was also found that the effective utilization rate increased with the increase in porosity.Moreover, the cascade method will be suitable for solar ORC applications.Nekoonam and Pourfayaz 55 analyzed selecting the configuration for optimal cascaded in solar thermal applications, and the results show that the cascaded structure stored 14.7% more energy than the average of cases with only one PCM, while the hybridcascaded configuration stored 7.8% more energy than the same cases.

| Exergy analysis
Furthermore, an exergy balance for the ORC system evaluates total energy in terms of the thermodynamic's first and second laws.Exergy balancing may be expressed for a steady state situation where i is the rate of destruction, ṁe x is the exergy of working fluid mass flow, E X ̇in Q and E X ̇out Q are the exergy of heat input and work output, and S ̇gen is the rate of entropy production.Equations ( 19) and ( 20) express the thermomechanical exergy flow. 56 where h 0 and s 0 are specific enthalpy (kJ/kg) and entropy (kJ/kg K) at dead state pressure and temperature (P 0 , T 0 ), which are 0.101325 Mpa (1 atm) and 288 K, respectively, employed in this work.
where ψ system is the exergy efficiency of the whole system can be calculated by Equation (21). 57Ex ̇in is the inlet exergy to the system defined by Equation ( 22), Ex ̇Solar is the maximum useful exergy gained by solar radiation, which T su is the solar's surface temperature (Equation 23), 58 which is assumed 5800 K. 59 Therefore, the exergy destruction for each ORC's component is shown as follows: Process 1-2, turbine Process 2-3, condenser Process 3-4, pump Process 4-1, evaporator where Dpump denote as the destruction of exergy in turbine, condenser, pump, and evaporator, respectively.After determining the exergy flows, the energy input, exergy output, consumed energy, available exergy, and exergy losses may be estimated using the definitions in Table 4.The performance of the components and systems may then be assessed using the parameters specified below., which represents the proportion of exergy that is not destroyed and the fraction of the entire system's available exergy that is associated with a specific component, respectively Table 5.

| RESULT AND DISCUSSION
In this section, a report on the theoretical result of the preliminary design of Solar-ORC parameters, including the ORC cycle performance, and the result of dimensionless TES, will be presented.Figure 6 shows the temperature outlet profile generated by each solar collector for the average time in June.We can see that the three types of collectors produce the same temperature outlet (T h,o ) and heating product (Q u ) trend.The highest temperature outlet is generated at around 9-10 o'clock by EFPC, ETC, and PTC with values of 372, 355, and 365 K, respectively.It is seen that the value of solar irradiance (see Figure 3) from the average climate in June and its very influential in Equation ( 1) compared to the value of ambient temperature.So in the following calculation, the outlet temperature results from the EFPC will be used to be the variable heat source of the solar collector.Meanwhile, at the same peak hours, the value of the heating product (Q u ), the PTC resulted in the highest Q u , around 654.68 kW, followed by EFPC and ETC with values of 632.98 and 480.47 kW, respectively.

| Cycle performance result
Figures 7 and 8 illustrate the comparison of W avg results for each type of solar collector each month using the R245fa and R123 working fluids, respectively.It can be seen in the two figures that the PTC-type solar collector produces the highest W avg each month compared to other T A B L E 5 Exergy rates of each component. 60

Components
Solar collector Evaporator Turbine Condenser Pump

Scheme
Exergy in Exergy out The time profile of solar collector T h,o and Q u for each type of collectors.
F I G U R E 7 Comparison of W avg results of each month by R245fa.
F I G U R E 8 Comparison of W avg results of each month by R123.
types of solar collectors (EFPC, ETC) using either R245fa or R123 working fluid.While, the highest W avg produced in August was 45.5 and 32.33 kWh using PTC for each of the working fluids R245fa and R123, respectively.It is caused by the large Gb in August compared to other months, so it can convert heat into an outlet temperature received by the solar collector.At the same temperature and Gb input, the PTC has a higher potential to generate power compared to EFPC and ETC.The net output power of the waste heat recovery system may be evaluated during the preliminary study.This net output power may be estimated by subtracting the pump power (W pump ) from the turbine power (W turbine ).The overall efficiency of the cycle (η ORC ), which represents the system's net output power (W net ) per input heating power, was another metric used to quantify the performance of waste heat recovery as power production.In this section, we will discuss the performance generated by the solar-ORC system for the average time in June 2021.Figures 9 and 10 show the same trend results in W net and η ORC over time with different fluids.Figure 9 shows that the highest W net generated is at 9-10 o'clock, with values of 45.82 and 28.17 kW for R245fa and R123, respectively.Whereas at the same hour (9-10) in Figure 10, the η ORC of R123 produced a higher value than R245fa with 13% and 12.5%, respectively.This is on account of the value of global solar irradiation (Gb) peaks at 9-10 o'clock, affecting the ORC's W net and η ORC results.At the same time, the enthalpy difference (h) owned by the two working fluids (R245fa and R123) enters the turbine and pump, which affects the amount of W net between both working fluids.

| Sensitivity analysis
A parametric study was performed to investigate the effect of the following variables on the system's electrical output: (1) evaporation pressure and temperature, P 1 , T 1 ; (2) ORC working fluid flow-rate (ṁ wf ); and (3) turbine isentropic efficiency (η isentropic ).The simulation was run for the "daily average" and the system model's EFPC, PTC, and ETC solar collector array variations.In each simulation run, one parameter was changed while the rest remained constant.The goal is to identify significant system parameters and understand their function affecting system performance to maximize overall work production and determine the "maximum power" settings for the daily average condition.
Figure 11 shows the parameters results of the solar ORC involving T 1 , and P 1 .The Solar-ORC's input and output powers depend on the working fluids (R245fa, R123).Figure 11A shows the W turbine -T 1 diagram's output power (turbine power) ranges, whereas Figure 11B shows the W turbine -P 1 diagram's output power (pump power).The results reveal that compared to R245fa, and R123, the working fluid inside the cycle uses less power to run the pump and generates more power from the turbine (at a particular temperature range).The turbine appears to give minimal power in this examination (below 100 kW).][63] Many selection considerations, such as economics, market availability, dependability, maintainability, and other critical technical concerns, must be addressed in small ORC turbine.While, Figure 12A,B show the influence of η isentropic and ṁ the performance result of solar-ORC's W net,daily for each working fluid (R245fa and R123).It can be seen from the two figures that the greater the η isentropic and ṁ wf , the greater the resulting W net , especially from the solar-ORC system, which uses R245fa working fluid.).The outcome allowed us to compare and estimate the amount of TES materials required in the TES system.For example, the value of the (T 1 ) parameter specifies the mass of the TES material necessary to warm and evaporate 1 kg of low-boiling working fluid in the ORC system.The simulated result is shown in Figure 13 for R245fa working fluid, demonstrating that the lower the ζ(T 1 ) value, the less TES material is required to evapourate

| Exergy analysis
Figures 17A and 18A depict the proportionate breakdown of exergy destruction in each component for R245fa and R123, respectively.As predicted, the bulk of the exergy is lost in the solar collector array.This is an unavoidable result of converting solar radiation to enthalpy at a temperature significantly lower than the apparent temperature of the solar as an exergy source for practical reasons.Examining the breakdown of exergy destroyed in the ORC components only (Figures 17B  and 18B) and comparing the exergy efficiencies with those for the nonregenerative ORC system studied in Mago et al. 64 (1) The exergy efficiency of the ORC components in the current study is generally lower; and (2) the relative percentages of exergy destroyed are also different, with the condenser in particular accounting for a significantly greater share of the overall exergy destruction in our study.The former of these results might be attributed to the lower temperature functioning of the system under consideration, as well as the pump and the turbine's low isentropic efficiencies due to their smaller size and positive displacement behavior.
Table 6 details the exergy values of each component resulting from two working fluids (R245fa and R123).The evaporator is the component with the most significant exergy losses, with 3994.7 W for R245fa and 4363.4W for R123.The evaporator's exergy loss mainly results from the irreversibility of heat transfer across a little temperature difference.The substantial exergy loss also reduces the degree of thermodynamic perfection, which is lowest in the evaporator, 62.7% for R245fa and 56.15% for R123.
On the other hand, the evaporator has the most significant effect coefficient, reflecting that the evaporator is the critical component of the analyzed basic ORC.The condenser is the second component that has a more significant impact on Solar-ORC performance.It has the third-highest influence coefficient of 22.8% for R245fa and 20.9% for R123.However, compared to the collector and evaporator, the degree of thermodynamic perfection and energy efficiency is higher.Whole system exergy loss is 9.6-9.8kW, thermodynamic perfection is 69%-70%, and the total exergy efficiencies are 66.7% and 63.7% for both working fluids (R245fa and R123), respectively.
According to the data reported in Table 6, R245fa has greater thermal and energy efficiencies than R123 for the same heat rate available for the evaporator from the solar collector, minimizing overall system exergy losses and enhancing the degree of thermodynamic performance.

| CONCLUSION
The Solar-ORC simulation using climate data in 2021 from Hungary has been carried out with energy and exergy analysis by combining the phase change material in the evaporator.In this study, three types of solar collectors are commonly used with the equation for the efficiency of solar collectors, which will be used for ORC generators using two working fluids (R245fa and R123).The solar collector efficiency equation shows that PTC produces the largest Q u and T 0 with magnitudes of 65.4 Wh and 364.65 K, respectively, compared to EFPC and ETC.With the same solar collector, the largest Wavg was produced in August by R245fa and R123, with 45.5 and 32.3 kW, respectively.However, in this study, the average hours' data profile in June and the EFPC solar collector were chosen as the basis for knowing the resulting Solar-ORC profile.The thermodynamic analysis of solar-ORC shows that the large Wnet and η ORC of the working fluid R245fa produce the most significant values of 45.7 W and 12.6%, respectively, compared with R123.Furthermore, the results of the sensitivity analysis show that the greater the input parameters such as T 1 , P 1 , ṁ, and η isentropic , the greater the W t and W net , daily, which are produced mainly from the Solar-ORC system, which uses R245fa working fluid.
In this study, the use of TES as a heat storage medium has been carried out using the relationship between temperature and dimensionless storage mass parameter (T 1 vs. ζ(T 1 )).There is no fixed size of mechanical and physical properties of the evaporator in this study.So, Figures 12 and 13 can provide engineering assistance to design and construct the effectiveness of the TESevaporator for Solar-ORC.It can be seen from Figure 12 that the trendline of T 1 vs. ζ(T 1 ) is produced by the working fluid R245fa, where the tendency for ζ(T 1 ) will be greater if the value of T 1 is small.Whereas for R123, there is stagnation in the relationship between T 1 versus ζ(T 1 ).
Lastly, to strengthen the analysis results, the exergy analysis was carried out to determine which component has the most significant exergy loss and which produces the greatest exergy efficiency.The analysis results show that the evaporator is the component with the tremendous exergy loss, both R245fa and R123 working fluids, due to insufficient heat transfer from the solar collector to the working fluid.Meanwhile, the total exergy efficiency of R245fa is greater than R123, with 66.7% and 63.7%, respectively.The exergy analysis shows which components should be optimized by design for each component and by cycle with the addition of supporting components.

F I G U R E 2
Average and maximum of monthly solar irradiation in Godollo.F I G U R E 3The average global irradiation and temperature ambient in June.

Figure
Figure 4A depicts the Solar-ORC cycle consisting of a solar collector, water pump, evaporator, turbine, condenser, and pump.Heat transfer occurs in the boiler between hot steam and working fluid or organic fluid with a low boiling temperature, causing the working fluid to change phase into steam vapor, which has sufficient temperature and pressure to turn the turbine and the rotation to be converted into electricity by the generator.Meanwhile, A and B represent the ORC and the water circuits, respectively.In this study, the cycle model and parameters used for the thermodynamic analysis of the ORC system are shown in Figure5.R245fa and R123 were chosen as working fluids according to their properties and the low value of ozone-depleting point (ODP) and global warming potential (GWP), and the details are shown in Table2.Moreover, both working fluids are suitable for generating energy Schematic of the proposed system: (A) solar-ORC, (B) the location of TES_evaporator.HTF, heat transfer fluid; PCM, phase change material.F I G U R E 5 T-s diagram of solar-TES-ORC process represented by R245fa.

F I G U R E 9
The time profile of W net for each working fluids.F I G U R E 10The time profile of η ORC for each working fluids.

Figures 13 and 14
Figures 13 and 14 depict the acquired modeling results for the TES-evaporator.The plots show the modeling results for various working fluids and selected solid materials used as TES materials for adjusting the dimensionless TES material mass parameter ζ(T 1 ) (see Section 2.4) and TES-evaporator temperature at the output (T 1 ) at different working fluids (R245fa and R123).The outcome allowed us to compare and estimate the amount of TES materials required in the TES system.For example, the value of the (T 1 ) parameter specifies the mass of the TES material necessary to warm and evaporate 1 kg of low-boiling working fluid in the ORC system.The simulated result is shown in Figure13for R245fa working fluid, demonstrating that the lower the ζ(T 1 ) value, the less TES material is required to evapourate

F
I G U R E 11 The performance of W turbine for each working fluid: (A) P 1 , (B) T 1 .F I G U R E 12 The result of daily W for each working fluid: (A) ṁ wf , (B) η isentropic .F I G U R E 13 The temperature profile of ζ(T) for each TES material of R254fa.workingfluid inside the ORC system.While Figure14for R123 working fluid shows the value of the dimensionless mass parameter ζ(T 1 ) tends to be constant along the T 1 , rise in the evaporator even though in detail value of ζ(T 1 ) for each TES material shows the same trend with R245fa.Based on Figure13, the acquired values of the ζ(T) parameter vary between 1.43 and 10.98, with the maximum result of ζ(T) = 10.98 achieved for Monel metal as TES material and R245fa as working fluid inside the ORC system at a temperature of 341.3 K. Furthermore, for the same working fluid (R245fa), the TES-evaporator temperature at 369.55 K yields a lower ζ (T) = 1.98 using the organic PCM.Meanwhile, for Figure14, the obtained values of ζ(T) vary between 0.41 and 2.43 at the same temperature range for R123.The highest of ζ(T) is achieved by monel metal with the value of 2.43 at a temperature of 341.3 K.Moreover, the organic PCM results in the lowest of ζ(T) with a value of 0.41 at the TES-evaporator around 369.4 K.It is indicated in the plot that the combination of Monel metal and R245fa has the largest sizing parameter and the combination of R123 and organic PCM has the lowest sizing parameter.The above analysis shows that organic PCM has a low ζ(T) value for both working fluids (R245fa and R123), which means that PCM requires less material to store and transfer heat to the working fluid that requires temperature (358.15-370.15K).Meanwhile, Figures 15 and 16 show the temperature profile of ζ(T) for nine products of organic PCMs for the two working fluids (R245fa and R123), which show the same trend.The greater the TES temperature, the smaller the ζ(T) value.Figures 15 and 16 show that P-bromophenol shows the highest ζ(T) value at 358 K with values of 2.58 and 2.02 for R245fa and R123, respectively.Meanwhile, N-Octacosane showed the lowest ζ(T) value at 370 K of 1.26 and 1.02 for the working fluids R245fa and R123, respectively.However, for R123, the range of values for ζ(T) is lower than that for R245fa.It is caused by the c p value that each organic PCM has and the difference in enthalpies owned by the two working fluids that enter the evaporator.

F
I G U R E 14 The temperature profile of ζ(T) for each TES materials of R123.F I G U R E 15 The temperature profile of ζ(T) for each organic PCM of R245fa.F I G U R E 16 The temperature profile of ζ(T) for each organic PCM of R123.

F
I G U R E 17 Percentage of energy destruction of R245fa: (A) with solar collector, (B) without solar collector.F I G U R E 18 Percentage of exergy destruction of R123: (A) with solar collector, (B) without solar collector.
33rking fluids properties.33 T A B L E 2 The properties of selected TES materials.
T A B L E 3 Exergy performance result of Solar-ORC.