Sizing of a solar–geothermal hybrid power plant in remote island electrical network

Abstract The rapid increase of world energy demand over the past decades has led to an extensive exploitation of the planet’s natural resources. Given that the population growth will continue for the next decades, there is an urgent need for a switch to Renewable Energy Sources (RES). One of the promising solutions to the energy problem is the geothermal energy which consists of stored energy in the earth in the form of water or steam at high pressure and temperature. Countries located in seismic zones possess a high geothermal potential due to their position at destructive and constructive plate margins. Greece is one of the countries with a remarkable potential in geothermal energy of medium and high enthalpy fields. Interest in the exploitation of geothermal fields for electricity generation is mainly focused on non-interconnected Greek islands, where energy is produced from oil-based generators with high energy cost and low-quality electricity, mainly during the summer months which is a period of high energy demand. In this respect, the present study investigates the possibility of combining a geothermal power plant with a concentrated solar array to provide energy to an autonomous island grid. Since the productivity of geothermal fields is gradually decreasing over the years, the combination of solar with geothermal energy source aims to the extension of the productive lifetime of the field, achieved by reheating the geothermal fluid during reinjection to the injection well. The thermal energy, generated by concentrated solar collectors, increases the temperature of the geothermal brine and reduces the energy degradation of the field. In this study, the energy efficiency of different reheat values are studied in order to achieve the combination of a geothermal power plant and a concentrated solar field that can meet specific targets for lifetime energy production. According to the results, the proposed installation can merely contribute to the energy autonomy of the island grid during periods of low demand and provide energy security in periods of high energy consumption.