Performance Assessment of a Hybrid Fresnel Solar-Geothermal Orc Utilizing Dry Organic Fluids

This study investigates the thermodynamic performance of an organic Rankine cycle (ORC) system driven by hybrid solar and geothermal energy sources. The proposed system utilizes a Fresnel solar collector and a geothermal heat exchanger to supply thermal energy to the ORC, which employs dry organic fluids including butane, pentane, toluene, cyclohexane, and hexane. A comprehensive thermodynamic analysis is conducted, evaluating key performance indicators such as net power generation, exergy irreversibility, energy and exergy efficiencies. The EES (Engineering Equation Solver) program is used for hybrid plant's thermodynamic analysis. The results reveal that butane exhibits the highest exergy efficiency (0.2483) but yields the lowest power output (103.9 kW), while toluene achieves the maximum power generation (112.6 kW) with the lowest exergy destruction (523.5 kW), albeit with modest efficiency values. The performance of the working fluids is further analyzed under varying solar radiation, geothermal source temperatures, and geothermal mass flow rates. As solar irradiation raises from 500 to 1000 W/m2, all fluids show enhanced power generation and energy efficiency, but a corresponding increase in exergy destruction and a decline in exergy efficiency. Similarly, higher geothermal temperatures lead to improved power output and exergy efficiency, while increased geothermal flow rates enhance power generation but reduce both energy and exergy efficiencies due to intensified irreversibilities. Among the tested fluids, pentane offers a favorable balance between energy and exergy efficiency, while toluene excels in power generation. These results highlight the critical influence of working fluid selection on the thermodynamic behavior of hybrid solar-geothermal ORC systems and contribute to the identification of suitable fluids for future low- to medium-temperature renewable power applications.