Optimal coupling of solar and geothermal energy sources for driving an organic Rankine cycle

The present study concerns the design and simulation of a hybrid Organic Rankine cycle (ORC) powered by solar and geothermal energy. The system is designed for maximized geothermal source utilization through partial evaporation. A dynamic simulation is performed considering the climate conditions of Athens, Greece, and hexane as the working medium in the system. The hybrid ORC is evaluated for four medium-grade geothermal water temperatures, 100 °C, 120 °C, 140 °C, and 160 °C, and six solar collecting areas from 100 to 600 m 2 and its performance is compared with the corresponding standalone solar and geothermal systems. The results show that the hybrid system achieves higher annual electricity production across the majority of examined cases, with a maximum increase of 8.1% over the separate systems, and a lower Levelized Cost of Energy (LCOE), ranging from 0.037 €/kWh to 0.119 €/kWh. A multi-criteria analysis is also conducted to identify the optimal solar collecting area for each geothermal source by minimizing the distance to the ideal solution on a Pareto front defined by two objectives: maximum electricity production and minimum LCOE. The findings highlight that source hybridization under a careful design is a solution of high potential for the development of effective and sustainable units for electricity generation.