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Power plants constitute the main sources of electricity production, and the calculation of their efficiency is a critical factor that is needed in energy studies. The efficiency improvement of power plants through the optimization of the cycle is a critical means of reducing fuel consumption and leading to more sustainable designs. The goal of the present work is the development of semi-empirical models for estimating the thermodynamic efficiency of power cycles. The developed model uses only the lower and the high operating temperature levels, which makes it flexible and easily applicable. The final expression is found by using the literature data for different power cycles, named as: organic Rankine cycles, water-steam Rankine cycles, gas turbines, combined cycles and Stirling engines. According to the results, the real operation of the different cases was found to be a bit lower compared to the respective endoreversible cycle. Specifically, the present global model indicates that the thermodynamic efficiency is a function of the temperature ratio (low cycle temperature to high cycle temperature). The suggested equation can be exploited as a quick and accurate tool for calculating the thermodynamic efficiency of power plants by using the operating temperature levels. Moreover, separate equations are provided for all of the examined thermodynamic cycles. [ABSTRACT FROM AUTHOR]

The focus of the current study is on a cogeneration unit designed to produce both electricity and hydrogen, which is made up of a parabolic trough collectors' field associated with a storage tank, a recuperative organic Rankine cycle module, and a proton exchange membrane water electrolyzer. The latter system operates using electricity generated by the organic Rankine cycle to produce hydrogen, which can subsequently be used as either a fuel or a storage medium for seasonal storage. The study begins with a thermodynamic investigation under both steady-state and dynamic conditions. The solar field is simulated using the Engineering Equation Solver, while the organic Rankine cycle and the electrolyzer are modeled in Aspen Plus. The analysis extends to economic and environmental evaluations, along with an optimization procedure based on techno-economic criteria. Regarding the optimum design case, the annual net electricity yield is determined at 333.8 MWh, the yearly hydrogen production amount is equal to 6236.6 kg, while the yearly energy efficiency is calculated at 14.9% and the yearly exergy efficiency at 15.9%. Finally, the economic investigation indicates the net present value is about 645,555 €, while the system contributes to saving 198.1 tn CO2-eq during the yearly operation. [Display omitted] • A solar-driven electricity and hydrogen cogeneration unit is investigated. • Thermodynamic, economic, and environmental aspects are examined. • The net electricity production is found at 333.8 MWh per year. • The hydrogen production amount is determined at 6236.6 kg per year. • The investment NPV is 645,555 €, while it saves 198.1 tn CO2-eq per year. [ABSTRACT FROM AUTHOR]

The purpose of this simulation study is the examination of a solar-driven power cycle that is driven by collectors with evacuated tubes. The power cycle is an organic Rankine cycle (ORC) that works with cyclopentane. The novelty of the cycle is the use of reheating in order to enhance its thermodynamic efficiency, while the cycle also has a recuperator. Moreover, the cycle is compared with the conventional ORC in order to determine the performance enhancement with the examined idea. The analysis is done with a developed program in Engineering Equation Solver and both in steady-state and transient conditions for a typical year. The analysis was conducted in terms of energy and economic performance. According to an optimization procedure for maximizing the net present values of the investment, it is found that the novel design leads to a net present value of 68 k€, a simple payback of 10 years, and a yearly energy efficiency of 7.0%, while the respective values for the conventional ORC are 44 k€, 10.8 years, and 5.1% for its optimal design according to the net present values maximization. Thus, it is obvious that the suggested design increases both energy and financial performance, compared to the usual design. [ABSTRACT FROM AUTHOR]

The objective of this study is the investigation of a cogeneration system for heating and electricity production, which is driven by solar dish concentrators. There is an organic Rankine cycle (ORC) driven by the solar field and produces electricity with its turbine and heating from its condenser. The solar field includes 100 m2 of solar dish concentrators with spiral absorber and an insulated storage tank of 4 m3 storage volume. The system is examined parametrically for different pressure levels in the turbine inlet and superheating degree. The system exergy efficiency is maximized for a superheating of 30 K and a maximum pressure equal to 70% of the toluene critical pressure. In this case, the system produces 12.41 kW electricity, 28.55 kW heating, while the energy efficiency is 51.20%, and the exergy efficiency is 20.69%. Moreover, the system is examined for a typical sunny day, and it is found that the electricity production is 125.6 kWh, the heating production 288.86 kWh, the energy efficiency 48.96%, and the exergy efficiency 19.77%. In the end, the simple payback period of the examined system is found at 6.28 years, which is a good value. [ABSTRACT FROM AUTHOR]

The goal of the present paper is the investigation of a solar desalination system with an organic Rankine cycle system for power and freshwater production. This system is an environmentally friendly technology that is able to utilize solar energy properly in a novel cogeneration application. A parabolic trough concentrator with a smooth and corrugated receiver was employed as the heat source of the desalination system. A humidifier–dehumidifier desalination technology was used for producing freshwater. The electricity is produced by an organic Rankine cycle which is fed both by the solar field and by the hot brine. The present analysis is performed by using a detailed numerical model which is validated by experimental literature data. Based on the final results, the corrugated tube has a maximum performance of 66.59%, and it is more efficient than the smooth tube with 63.11%. The average freshwater productions were estimated equal to 13.09 kg hr−1 and 12.71 kg hr−1 for the corrugated and smooth tubes, respectively. The maximum net work production is found at 7.57 kW with R113, while the less efficient working fluid is R134a. It was found that the application of the developed desalination system leads to the production of high amounts of fresh water and a significant reduction of the equivalent CO2 emissions. [ABSTRACT FROM AUTHOR]

• A novel Carnot Battery system with double waste heat source exploitation is studied. • Organic Rankine cycle, high-temperature heat pump and latent storage are used. • Parametric analysis and optimization are performed in steady-state conditions. • For the benchmark scenario, the roundtrip efficiency of 64 % was calculated. • Performance enhancements up to 174 % compared to ambient source unit were found. Carnot batteries are critical technologies for increasing the penetration of renewable energy sources because they enable suitable energy storage for long-term periods. The achievement of a high round-trip efficiency is an important point that determines the sustainability of the Carnot batteries. In this direction, the present work comes to investigate a Carnot battery with latent storage that exploits properly a waste heat stream. The examined unit includes a high-temperature heat pump, an organic Rankine cycle, a latent storage system and the proper heat exchanger for the waste heat stream exploitation. The novelty of the studied idea lies in the exploitation of the waste heat stream in two ways. Specifically, the waste heat stream feeds firstly the latent storage system with heat, and secondary it feeds the evaporator of the heat pump with heat input for enhancing the heat pump's coefficient of performance. This design makes it possible to achieve high round-trip efficiency values and also to exploit properly a waste heat stream. For the benchmark scenario with 100 kW electricity input, 350 kW waste heat input at 200 °C and 160 °C storage temperature, the round-trip efficiency was found at 64 %, the system's energy efficiency at 14.2 %, the system's exergy efficiency at 36.7 % and the produced electricity at 64 kW. [ABSTRACT FROM AUTHOR]

Summary: The objective of this work is the investigation of an alternative refrigeration system, which combines a supermarket CO2 booster system with an organic Rankine cycle. The waste heat after the high‐pressure compressor is used in order to feed the organic Rankine cycle for electricity production. The working fluid in the organic Rankine cycle is selected to be the octamethyltrisiloxane (MDM), which has a low global warming potential, and so all the used working fluids in the system are environmentally friendly. The system is studied in the transcritical region for ambient temperatures from 27°C to 40°C. In every case, the system is optimized in order to minimize the overall electricity demand. According to the final results, the system coefficient of performance (COP) can be enhanced from 4.83% to 7.60%, while the electricity consumption can be reduced from 4.60% to 7.03% compared with the conventional booster system. Higher enhancements are found in cases with higher ambient temperatures. Furthermore, a preliminary financial study indicates that the examined idea is viable with the simple payback period to be 5.45 years. The present study is conducted by using a homemade model written in Engineering Equation Solver. The objective of this work is the investigation of an alternative refrigeration system, which combines a supermarket CO2 booster system with an organic Rankine cycle. According to the final results, the system coefficient of performance (COP) can be enhanced from 4.83% to 7.60%, while the electricity consumption can be reduced from 4.60% to 7.03% compared with the conventional booster system. Furthermore, a preliminary financial study indicates that the examined idea is viable with the simple payback period to be 5.45 years. [ABSTRACT FROM AUTHOR]

Summary: The objective of this work is the investigation of a novel solar‐driven cogeneration system, which combines both flat plate collectors (FPCs) and evacuated tube collectors (ETCs). This system includes an organic Rankine cycle in order to produce electricity and heat exchangers in order to produce useful heating at 50°C, which is a usual temperature level for domestic applications. The combination of FPCs and ETCs aims to reduce the investment cost and so to design a cost‐effective solar‐driven cogeneration system. The FPCs are located before the ETCs in order to work at lower temperature levels and the ETC at higher temperature levels, a design which provides optimum compatibility between temperature levels and solar thermal efficiency values. The system is examined energetically, exergetically, and financially. The power production is selected at 5 kW, while the heating production is studied from 5 kW up to 35 kW. According to the final results, it is found that in the typical case of 20‐kW heating production, the simple payback period of the system is around 11 years, while the energy and exergy efficiency at 16% and 4%, respectively. The analysis is conducted with a developed model in Engineering Equation Solver under steady‐state conditions. [ABSTRACT FROM AUTHOR]

The main objective of this work is to investigate the utilization of nanofluids in the solar field in order to achieve higher system performance. An Organic Rankine Cycle (ORC) driven by solar parabolic trough collectors (PTCs) is the examined system. Four different nanoparticles are examined (Al 2 O 3 , CuO, TiO 2 and Cu) in the base fluid (Syltherm 800), as well as the pure thermal oil is examined as working fluid. The examined ORC is a regenerative cycle and four organic fluids are also tested (toluene, MDM, cyclohexane and n-pentane). In every combination between the organic fluid in ORC and working fluid (nanofluid) in the solar field, an optimization procedure is followed. The concentration of every nanoparticle and the pressure ratio (pressure in the turbine inlet to critical pressure) are the optimization parameters. According to the final results, toluene is the best organic fluid and CuO is the most suitable nanoparticle. The combination of these two working fluids leads to 167.05 kW electricity production and to 20.11% system efficiency with concentration 4.16%. The enhancement by the use of nanofluids is found up to 1.75% compared to the respective case with pure thermal oil and this result indicates that the use of them is able to improve the performance of solar driven ORCs. For the other nanoparticles and Toluene in the ORC, Cu, Al 2 O 3 and TiO 2 lead to 166.18 kW, 165.72 kW and 165.60 kW electricity productions respectively with optimum concentrations 3.98%, 2.51% and 2.57% respectively. [ABSTRACT FROM AUTHOR]

The objective of this work was to optimize and to evaluate a solar-driven trigeneration system which operates with nanofluid-based parabolic trough collectors. The trigeneration system includes an organic Rankine cycle (ORC) and an absorption heat pump operating with LiBr-H2O which is powered by the rejected heat of the ORC. Toluene, n-octane, Octamethyltrisiloxane (MDM) and cyclohexane are the examined working fluids in the ORC. The use of CuO and Al2O3 nanoparticles in the Syltherm 800 (base fluid) is investigated in the solar field loop. The analysis is performed with Engineering Equation Solver (EES) under steady state conditions in order to give the emphasis in the exergetic optimization of the system. Except for the different working fluid investigation, the system is optimized by examining three basic operating parameters in all the cases. The pressure in the turbine inlet, the temperature in the ORC condenser and the nanofluid concentration are the optimization variables. According to the final results, the combination of toluene in the ORC with the CuO nanofluid is the optimum choice. The global maximum exergetic efficiency is 24.66% with pressure ratio is equal to 0.7605, heat rejection temperature 113.7 °C and CuO concentration 4.35%. [ABSTRACT FROM AUTHOR]

The use of solar thermal energy for electricity production is a clean and sustainable way to cover the increasing energy needs of our society. The most mature technology for capturing solar energy in high temperature levels is the parabolic trough collectors (PTC). In this study, an Organic Rankine Cycle (ORC) coupled with PTC is analyzed parametrically in order to be optimized financially and energetically. The first step is the thermodynamic investigation of the ORC by using various working fluids. The second step is the energetic and financial investigation of the total system which includes the solar field, the storage tank and the ORC module. By testing many combinations of collecting areas and storage tank volumes, finally cyclohexane proved to be the most suitable working fluid for producing 1 MW el with PTC. Specifically, in the optimum situation a solar field of 25,000 m 2 with storage tank of about 300 m 3 leads to a payback period of 9 years and to an internal rate of return (IRR) equal to 13.46%. Moreover, an economic comparison for different commercial collectors is presented, with Eurotrough ET-150 being the financially optimum solution for this case study. [ABSTRACT FROM AUTHOR]

• A solar-assisted pumped storage system with flat plate collectors is studied. • The novelty is based on the use of the solar thermal field for boosting the heat pump. • The solar-assisted system is compared in detail with an ambient source system. • The global optimum system presents a 68.48% power to power recovery ratio. • The simple payback period is around 7.8 years with 150 m2 collecting area. The objective of this work is the investigation of a solar-assisted pumped thermal energy storage system. The examined unit includes a solar field with flat plate collectors, a high-temperature heat pump, a latent storage system and an organic Rankine cycle. This system is fed by electricity from any renewable energy source (e.g., wind turbines or photovoltaic panels), and so the compressor of the heat pump is driven. The heat pump is fed with low-temperature heat from flat plate collectors, and it rejects heat of medium temperature to a latent storage system. The next step is exploiting the stored heat from an organic Rankine cycle for power production when there is a need for using electricity. The studied system is a "heat and power to power" system and can lead to high power recovery ratios. The analysis was conducted with a developed mathematical program in Engineering Equation Solver, and it was validated with numerical results from the literature. The optimum storage temperature has been found at 150 °C and the optimum temperature in the evaporator of the heat pump at 75 °C. In this case, the electricity recovery ratio (or power to power ratio) is found at 68.48%, the organic Rankine cycle efficiency at 18.45%, and the heat pump coefficient of performance at 3.704, while the collecting area is 150 m2. The use of a similar system without solar collectors but with the ambient as the heat source leads only to a 32.14% power recovery ratio. So, the specific gain of the used collecting area is 35.17 W/m2 which is an important amount of electricity. In the global optimum case, the simple payback period of the solar field investment is found to be at 7.8 years, which is a reasonable value and proves the financial viability of the examined idea. Moreover, this work proves that providing heat input of a relatively high temperature in the heat pump of the pumped thermal energy storage system is an excellent choice for recovering higher amounts of electricity. [ABSTRACT FROM AUTHOR]

This article presents a simulation study which focuses on the thermodynamic analysis of a solar-driven trigeneration system for heating, cooling, and electricity production. The system uses parabolic trough collectors operating with Therminol VP-1 for feeding an organic Rankine cycle operating with toluene and an absorption heat pump operating with a LiBr–H2O working pair. The collecting area is selected at 100 m2 and the storage tank at 4 m3. The system is studied parametrically in order to examine the impact of various parameters on the system energy efficiency, system exergy efficiency, electricity production, heating production, and cooling production in the simple payback period of the investment. The examined parameters are the following: solar beam irradiation level, solar beam irradiation angle, superheating degree in the turbine inlet, pressure level in the turbine inlet, heat source temperature level, generator temperature level, and the heat input in the generator. For the nominal case of a 15 kW generator input, the electricity production is 6.3 kW, the heating production 11.5 kW, and the cooling production 10.7 kW. The system energy efficiency is 40.7%, while the system exergy efficiency is 12.7%. The financial investigation of the investment proved that it is viable with the simple payback period to be 8.1 years in the nominal case and it can be reduced to 7.8 years with an optimization procedure. Lastly, it has to be said that the examined system is found to be a viable configuration which is an ideal choice for application in the building sector. The analysis was conducted under steady-state conditions with a model developed using Engineering Equation Solver (EES). [ABSTRACT FROM AUTHOR]

This work investigated a trigeneration system for the building sector. Biomass is the utilized energy source which feeds an organic Rankine cycle for electricity production. Heating is extracted from the power cycle, especially with the proper heat exchanger after the turbine. A vapor compression heat pump is used for cooling production, and it is fed by work power from the turbine shaft. The total configuration was examined parametrically by investigating different superheating cases, pressure levels, and ambient temperatures. The analysis was energetic and financial for the climate conditions of Athens, Greece. For the case with a nominal cooling load of 10 kW, the system's yearly energy and exergy efficiencies were 48.68% and 24.86% respectively. The payback period was 5.02 years, the net present value was €118,000, and the internal rate of return was 21.57%. The yearly electrical, heating, and cooling production were 99.39, 91.17, and 22.67 MWh respectively, whereas the biomass energy input was 438 MWh on a yearly basis. [ABSTRACT FROM AUTHOR]

The exploitation of low-grade heat sources that are available from existing thermal systems processes consists a promising concept for the production of energy. In this research, the integration of an Organic Rankine Cycle (ORC) unit on a supermarket transcritical CO 2 refrigeration system with ejectors is investigated, which is supplied with low-grade heat by the common discharge of the compressors. The optimization analysis proves that for different combinations of CO 2 temperature and pressure in the ORC evaporator, as well as for different ORC condensation temperatures, there is a different optimum ORC evaporation temperature that leads to the highest energy production. Concerning the annual performance analysis conducted for the city of Athens, Greece, operation with isopentane is found to provide the greatest energy production with 10.36 MWh annually, which corresponds to a 3.69% reduction in the refrigeration system's energy consumption. For operation under the ambient temperature of 40 °C, the corresponding reduction of the refrigeration system consumption due to the presence of ORC is 7.54%. Finally, the financial analysis reveals that toluene is the most advantageous solution, leading to a payback period of 3.9 years, with a net present value by the end of the project's lifetime equal to 34.32 k€. • Integration of an Organic Rankine Cycle to a transcritical CO 2 refrigeration system. • Optimization analysis of the system for operation with different working fluids. • Energetic and financial investigation for the case of Athens, Greece. • Isopentane leads to annual production of 10.36 MWh with 3.69% energy savings. • The lowest payback period is 3.9 years and it is achieved for operation with Toluene. [ABSTRACT FROM AUTHOR]

Waste heat recovery is an effective way to reuse waste energy in order to produce useful energy products. This technique aids in the reduction of CO 2 emissions and to create sustainable and efficient systems. The objective of the present review paper is to summarize and to discuss the studies about waste heat recovery with the organic Rankine cycle (ORC). The ORC is a usual choice in waste heat recovery technologies because this cycle can operate with low, medium, and high-temperature heat source and so this cycle presents high flexibility and compatibility with waste heat. The novelty of this work is based on the investigation of different aspects of the examined technology and also the investigation of the cogeneration systems, which are based on the waste heat recovery with ORC. The results of this work indicate that the exploitation of waste heat is an attractive way to produce electricity efficiently. The cogeneration with waste heat is also an alternative design with promising results because it can lead to high overall efficiencies and optimal utilization of waste energy. [ABSTRACT FROM AUTHOR]

Highlights • A solar organic Rankine Cycle was considered using dish collector as the heat source. • The performance of three cavity receivers was modeled and compared. • A hemispherical cavity receiver was experimentally investigated. • Alumina/thermal oil was investigated as the solar working fluid. • The system was evaluated at different sizes and concentrations of nanoparticles. Abstract The objective of this work is the investigation of a solar-driven organic Rankine cycle with nanofluid-based solar dish concentrator. Three different cavity receivers are tested with the alumina/oil nanofluid in order to determine the most effective choice. More specifically, the examined cavities are hemispherical, cubical, and cylindrical, while the organic Rankine cycle is a non-regenerated system with superheating, R601 working fluid and heat rejection temperature at 310 K. The analysis is perfumed using the first and the second thermodynamic laws. The organic Rankine cycle is investigated for different pressure in the turbine inlet and different nanoparticle concentrations are also studied. According to the results, the thermal performance of the cavity and the electricity production are improved by decreasing alumina nanoparticle size, and by increasing the nanofluid concentration. Moreover, the optimum pressure in the turbine inlet was found at 2 MPa. Finally, the hemispherical cavity receiver has been found to be the best choice with cubical to be the second one and the cylindrical to be the less effective choice. [ABSTRACT FROM AUTHOR]

The organic Rankine cycle (ORC) is an effective technology for power generation from temperatures of up to 400 °C and for capacities of up to 10 MW el. The use of solar irradiation for driving an ORC is a promising renewable energy-based technology due to the high compatibility between the operating temperatures of solar thermal collector technologies and the temperature needs of the cycle. The objective of this review paper is to present and discuss the operation principles of solar-ORC technology and the wide range of solar-ORC systems that have been studied in the literature. Various solar thermal technologies that can drive the ORC are investigated, such as the flat plate collector, evacuated tube collector, compound parabolic collector, parabolic trough collector, linear Fresnel reflectors, dish concentrators and solar towers. Both simulation studies and experimental investigations are included in the study. Hybrid systems and different thermal storage techniques are also examined in detail. Moreover, systems with ORC which produce many useful outputs such as cooling, heating and fresh water are studied because they present high sustainability indexes. The limitations of the technology are also highlighted, along with critical suggestions aimed at steering future research in this field. The final conclusions indicate that the development of trigeneration and polygeneration systems with ORC sub-systems is a promising avenue, not only for the future development of solar-ORC technology but also for the development of renewable and sustainable energy systems in a broader context. • Solar driven organic Rankine cycles are summarized and discussed in detail. • Concentrating and non-concentrating solar thermal systems are included. • Parabolic trough collector is the best solar technology for power production. • The use of solar organic Rankine cycles in polygeneration is a promising idea. • There is a need for conducting future experimental studies in a great scale. [ABSTRACT FROM AUTHOR]

• A parabolic trough collector with a linear V-Shape cavity receiver was studied. • The V-Shape cavity receiver was coupled with an organic Rankine cycle system. • The solar organic Rankine cycle system was evaluated exergetically and financially. • The optimum turbine inlet temperature is 592 K and the optimum pressure 6 MPa. • The simple payback period was found close to 6.01 years for the large scale setup. In this research, a parabolic trough concentrator with linear V-Shape cavity receiver was studied as the heat source of an organic Rankine cycle system. The solar organic Rankine cycle system was evaluated under exergy and economic analyses. Thermal oil was used as the solar working fluid, and ethanol was used as the organic working fluid under different turbine inlet temperatures and turbine inlet pressure. The influence of different operational parameters, including solar radiation, mass flow rate, and inlet temperature of solar working fluid was investigated on the performance of the solar organic Rankine cycle system. It was found that exergy gain and exergy efficiency of the solar system improved with increasing solar radiation, increasing inlet temperature, and decreasing the flow rate of the solar working fluid. The highest organic Rankine cycle efficiency and total efficiency were found to be 35%, and 25% at turbine inlet temperature of 592 K and turbine inlet pressure of 6 MPa, respectively. Finally, the lowest levelized cost of electricity, and the lowest payback period were calculated equal to 0.0716 (€/kWh), and 8.79 (years) for the optimum condition of the developed solar organic Rankine cycle system, respectively. The present study is beneficial for improving the performance of the solar organic Rankine cycle systems with parabolic trough concentrators in a simple and convenient way and the development of solar thermal technologies. [ABSTRACT FROM AUTHOR]