Energetic and exergetic performance of a novel polygeneration energy system driven by geothermal energy and solar energy for power, hydrogen and domestic hot water

Abstract The present study develops a novel energy system comprising a double-flash based geothermal cycle, a solar-driven cycle, a polymer electrolyte membrane (PEM) system and a waste heat recovery system. The proposed system can be used to generate electricity, produce hydrogen, space heating and prepare domestic hot water, and the solar-driven cycle can be turned off as a double-flash geothermal system when there is no solar radiation and the storage is empty. The unique aspect of the proposed system lies in the coupling relationship between the three turbine units in clear weather. Energy and exergy analyses are carried out to determine the irreversibilities, show the performance of the system and compare it with sole geothermal system. The results show that the proposed system has satisfactory thermodynamic properties. Under the reference conditions, the proposed energy system has a 148.3% (from 6171 kW to 15321 kW) increase in power generation compared with a sole double-flash geothermal system; under the optimal working conditions, the energy efficiency and exergy efficiency of the system can reach 29.6% and 29.2%, respectively. Furthermore, the effect of changing various system parameters on the energy and exergy efficiencies of the entire system and its subsystems were also studied.