Feasibility study for implementation of a solar-geothermal hybrid plant based on an organic rankine cycle in Lake Abhe geothermal area, with a particular hot arid climate, Djibouti

Abstract

Lake Abhe, situated in southwestern part of Djibouti, is one of promising geothermal field and was recently the subject of a complete surface exploration. Djibouti possesses several medium-enthalpy resources distributed in different parts of the country and it is located in a hot arid climatic zone. This particular climate makes it necessary to find new ways in modelling common geothermal power plants. The objective here is to determine how the medium-enthalpy resource in Lake Abhe geothermal field would be best utilized, both technically and commercially. The backbone of this paper will be how to deal with the hot arid climate in order to improve the efficiency of the power plant. A thermodynamic model was developed using Engineering Equation Solver (EES) to evaluate the performance of ORC geothermal power plants standalone, and an ORC assisted by a parabolic trough solar concentrating collector field. Based on the results obtained in this study, the solargeothermal hybrid scheme increases the power generation compared with geothermal-only power plants. Results of the basic model of the binary power plant with an air cooled condenser and hybrid modelling are presented. With a geothermal fluid mass flow of 443 kg/s and temperature of 145.7°C and under Djiboutian climatic conditions with an average ambient temperature of 31°C, two models have been proposed. The air cooled condenser basic binary model produces 11 706 kWe of gross power output with an auxiliary power consumption of 24.5% of the total gross output power where the fan power represents 58.5% of the latter. The cycle efficiency is 12%. For the hybrid solar-geothermal power plant, the net power output is 14 778 kWe where 23% go for the use of the auxiliary components. The hybrid outperforms the basic binary plant by 26.24%.