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The exploitation of solar irradiation in the building sector is a promising way to achieve decarbonization and reduce the operating costs of the building. The potential of solar energy in Greece is high and therefore this idea can lead to excellent results. In this direction, the goal of the present analysis is the detailed investigation of different solar thermal systems for domestic hot water production in the different climate zones of Greece. Four typical cities are studied in order to examine the climate zones A, B, C, and D, while three different solar thermal collectors coupled to insulated storage tanks are studied for every city. The simple flat plate collector, the advanced flat plate collector, and the evacuated tube collector are the selected solar systems for the present work. The climate data and the characteristics of the solar thermal systems follow the Greek Chamber regulations known as "KENAK". The analysis is conducted by following the well-known f-chart method and every design is optimized by using energy and financial criteria. The final design is determined by conducting a multi-objective evaluation methodology. It is notable to state that the collector slope and the collecting area are important parameters of this work, while the study case regards a building with 30 residents. According to the final results, the advanced flat plate collector is the best choice according to the multi-objective evaluation procedure. [ABSTRACT FROM AUTHOR]

In the present investigation, a solar parabolic trough concentrator (PTC) with a linear cavity was examined by using a developed numerical model. More specifically, a V‐shape cavity receiver was studied in this work as a new and alternative design. The use of a cavity in a PTC is a very promising idea because it leads to high efficiency and to low investment cost. Up today, the emphasis in the use of cavities is given in dish concentrators and so there is a need for investigation of cavities also in linear concentrators. Different dimensional and operational parameters of the PTC with a V‐shape cavity were considered. More specifically, the position, aperture area, and the tube diameter of the V‐shape cavity, solar irradiance, inlet temperature level, and mass flow rate were evaluated based on sensitivity analysis. The results revealed that the highest optical performance was attained when the cavity was placed at the PTC focal line. Moreover, it is found that there is an optimum cavity aperture area to determine the greatest thermal efficiency. For the optical errors of 5, 10, 15, 20, and 35 mrad, the optimum cavity aperture wide was calculated at 5, 5, 6, 7, and 8 cm, respectively, with the tracking error to be 0°. The highest thermal performance has found when the collector operates with low inlet temperature, high flow rate, high solar irradiation level, and small cavity tube diameter. [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]

Parabolic trough collector (PTC) is the most mature concentrating technology which is used in a great variety of thermal applications. In this study, the daily performance of a PTC is investigated for all the year period. The module of Eurotrough parabolic trough collector is examined with various storage tanks from 3 m 3 to 15 m 3 and the collector performance is investigated in energetic and exergetic terms. An Input/Output method is applied for the daily evaluation of the solar thermal system, something innovative for concentrating solar collectors. According to the final results, different storage tank volumes lead to similar thermal outputs but to extremely different exergetic outputs because of the high dependence of the mean storage tank temperature with the storage tank volume. For the storage tank of 9 m 3 , the mean thermal efficiencies in December and in June are found to be 37.1% and 68.7% respectively, while the mean exergetic efficiencies 2.0% and 8.5% respectively. Moreover, it is proved that the Input/Output performance method in concentrating collectors has to take into consideration the solar incident angle at solar noon in order high accuracy to be achieved. [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]

Solar-driven technologies for electricity production are very promising technologies for developing sustainable and viable energy units. The objective of this work is the energy and financial investigation of a solar-driven thermoelectric generator system. This system operates without concentrator; it absorbs the incident solar irradiation and it converts it partially to electricity. In this paper, a small module is investigated in details and the analysis is extended for a solar field of 100 m2. A numerical model is developed in Engineering Equation Solver for simulating the solar thermoelectric generator behavior and it is validated using experimental data from the literature. The maximum instantaneous efficiency is found close to 4.5% in the reference operating conditions, while the mean yearly efficiency for the climate conditions of Athens (Greece) is found at 3.2%. The yearly electricity yield is found to be 5414 kWh for a solar potential per area of 1695 kWh/m2. The parametric financial analysis proved that generally, the investment is viable and for a reasonable specific capital system cost of 1000 €/kW the payback period is about 4.5 years and the levelized cost of electricity is around 0.044 €/kWh. • A solar-driven thermoelectric generator is studied in energy and financial terms. • The system is investigated on a yearly basis for the location of Athens in Greece. • The yearly electrical efficiency is found at 3.2% and the electricity production 5414 kWh. • In the main scenario, the levelized cost of electricity is found at 0.0617 €/kWh. • The payback period is found to be about 4.5 years which indicates a viable investment. [ABSTRACT FROM AUTHOR]

The utilization of solar irradiation in the building sector is vital to create sustainable systems. Trigeneration systems are highly efficient systems that usually produce electricity, heating and cooling which are the main energy needs in the buildings. The objective of this work is the energetic and financial investigation of three different solar-driven trigeneration systems that can be applied in buildings with high energy needs (e.g., hospitals or commercial buildings). The parabolic trough solar collector (PTC) is selected to be used because it is the most mature solar concentrating technology. The examined configurations practically are different combinations of organic Rankine cycle (ORC) with heat pumps. System 1 includes a PTC coupled to an ORC which feeds an absorption heat pump machine. System 2 includes a PTC which simultaneously feeds an ORC and absorption machine. System 3 includes a PTC which feeds an ORC and a heat exchanger for heating, while the ORC is fed with and electricity a vapor compression cycle for cooling production. The simple payback period of System 1 is 5.62 years and it is the lowest, with System 2 to have 7.82 years and System 3 to have 8.49 years. The energy efficiency of the three systems is 78.17%, 43.30% and 37.45%, respectively, while the exergy efficiency 15.94%, 13.08% and 12.25%, respectively. System 1 is the best configuration according to energy, exergy and financial analysis. This study is performed with developed thermodynamic models in Engineering Equation Solver and a dynamic model in FORTRAN. [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]

• A nanofluid-based thermal PV coupled a heat pump is investigated. • This system produces space heating and net electricity. • The system is optimized with a multi-objective procedure. • Water/Cu nanofluid leads to 4.80% energy efficiency enhancement. • The heating production is increased by 5.75% with water/Cu nanofluid. The objective of this paper is to investigate a solar assisted heat pump which is driven by nanofluid-based hybrid PV collectors for space-heating and electricity production purposes. The use of nanofluids, as working fluids in the solar collector, enhances both the thermal and electrical performance in order to have higher useful outputs. Practically, the use of nanofluids enhances the heat transfer rates inside the flow and so higher thermal output are produced in the collector and the photovoltaic cell produces higher electricity because it is cooled efficiently by the nanofluids. Water/Cu and water/Al 2 O 3 are found to be the most efficient nanofluids and they are tested in the total system. The system is optimized for steady-state conditions and the optimum design is examined on a daily basis for the pure water case and the nanofluids cases. The optimization procedure is a multi-objective procedure which is conducted using energy, exergy and financial criteria. According to the final results, the use of water/Cu nanofluid is the best case which presents 4.80% higher energy system efficiency and 0.66% higher exergy system efficiency compared to the pure water case. The use of water/Al 2 O 3 leads to an enhancement of 4.34% and 0.19% for energy and exergy efficiency respectively. For the case with water/Cu, the heating production during the winter is found 7423 kWh th and the net electricity production 1068 kWh el. The analysis is performed with a developed thermal/thermodynamic model in Engineering Equation Solver. [ABSTRACT FROM AUTHOR]

Solar energy is an auspicious renewal energy source because of its abundant availability and its flexibility to be converted into heat or into electricity. Concentrated solar power technologies are promising units for producing electricity in large scale applications and parabolic trough solar collector is the most matured technology for these plants. The objective of this paper is to summarize and to discuss the current status of parabolic trough collector commercial power plants around the world and the technological developments in various constituents of such concentrated solar power plants. More specifically, this review includes various developments in the concentrators and receiver tubes in order to enhance both the thermal and the optical efficiencies. Moreover, the different existing and newly developed heat transfer fluids are discussed in this work and the emphasis is given in the discussion of the different operating temperature levels, the storage system and the applications that use different fluids. Furthermore, different tracking options of the parabolic trough solar collector are examined, different storage technologies, as well as various power cycles and their modifications to enhance the overall efficiency of the parabolic trough collector-based power plants are discussed in detail. The final conclusions of this work indicate the recent developments and the future designs of the parabolic trough solar collector power plants. [ABSTRACT FROM AUTHOR]

The present study is a 4E (Energy, Exergy, Economic, and Environmental) analysis of a nanofluid-based parabolic trough collector (PTC) which is conducted with a developed model in MATLAB. MXene (Ti 3 C 2) nanoparticles were added to the silicon oil at weight concentrations of 0.05, 0.08, and 0.1%. The result was the important enhancement of the thermal conductivity of the nanofluid on the rand of 70%–89% for the highest concentration. According to the results, the PTC's optical efficiency was estimated at 79%, while thermal and exergy efficiencies of 74.71% and 22.44% with 0.10 wt% concentration were recorded on July 17, 2019. It is found that the MXene based silicone oil can reduce the system's cost by 0.021 M$ and enhance the energy gained by 1.51% at 0.10 wt% concentration compared to pure oil. Also, the annual CO 2 mitigation from the energy side varies from 2.25 to 2.30-ton CO 2 /year, while the annual environmental gain ranged between 32.73 and 33.28 $/year and 9.065 to 9.102 $/year for the energy and exergy studies respectively. [Display omitted] • A nanofluid-based parabolic trough collector is studied with MXene. • The collector thermal efficiency enhancement is found up to 1.1%. • For the day July 17, 2019, the exergy efficiency was improved from 0.07% to 15.16%. • For energy analysis, the annual CO 2 mitigation varies from 2.26 to 2.30 ton CO 2. • The environmental gain from the energy analysis varies from 32.73 to 33.28 $/year. [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]