Thermodynamic analysis of a solar-enhanced geothermal hybrid power plant using CO2 as working fluid

CO2-based Enhanced Geothermal Systems (EGS) and closed-loop supercritical CO2 Brayton cycles for solar thermal systems are both currently being developed for environmentally-friendly power plant systems. However, the recompressor needed in closed-loop supercritical CO2 Brayton cycles operates at high temperature and pressure with attendant higher manufacture and maintain cost. Here a solar thermal-EGS hybrid system is proposed where the geothermal power plant provides the base-load electrical power while the solar system increases the system capacity factor by generating additional electric power during peak demand hours. The two stand-alone systems and the hybrid system were modeled to predict the system efficiencies. It is found that comparison with the stand-alone CO2-EGS and CO2-solar thermal systems, the hybrid system has equal or even higher efficiency than the efficiency of the sum of two separate systems. Moreover, the operating pressure can be decreased and the recompression compressor can be removed in the hybrid system which reduces costs of the system installation and maintenance.