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
[MInistry Of Energy In Charge Of Natural Resources, Djibouti]
With a total area of 23,200 km2, the Republic of Djibouti is located in East horn of Africa. It is bordered by Ethiopia in the west and south, Eretria in the north, and Somalia in the southeast. Unique in terms of geodynamics activity, it is situated at the only modern example of continental rifting at an active triple-junction, where two oceanic ridges, Gulf of Aden and Red Sea, meet with East African Rift. This unique geographical area is characterized by the presence of geothermal resources revealed by numerous hot springs and fumaroles found in different parts of the country. One of them, Lake Abhe geothermal field was recently the subject of a complete surface exploration. This is conducted by the scientists of ODDEG and ISOR conjointly with a co-financing of ICEIDA. The objective of this paper is to determine how the medium enthalpy resource in Lake Abhe geothermal field would be best utilized, both technically and commercially. Djibouti possess several medium enthalpy resources for different part of the country and it is situated in a hot arid zone. The backbone of this paper will be how to deal with the hot, arid climate in order to maximize the net power output of the plant. A thermodynamic model was developed using Engineering Equation Solver (EES) to evaluate the performance of ORC geothermal power plants standalone with different cooling system, and an ORC assisted by a parabolic trough solar concentrating collector field. The ACC and hybrid solar-geothermal designs were selected and the NPV and IRR of these designs was modelled to allow an economic comparison. This study estimates a geothermal fluid mass flow of 443 kg/s and temperature of 145.7°C. Under Djiboutian climatic conditions with an average ambient temperature of 30.04°C, the air-cooled condenser basic binary model produces 10924 kWe of gross power output with an auxiliary power consumption of 22.6% of the total gross output power. The fan power represents 51.8% of the parasitic power. For the hybrid solar-geothermal power plant, the net power output is 13865 kWe with 20.6% for the use of the auxiliary components. The hybrid system shows higher power output (up to 21.24% difference) compared to ACC. This study finds the hybrid system to be a better option than individual geothermal system at all ambient temperatures. It is demonstrated that the hybrid is most economically attractive scenario, providing the highest NPV and the fastest payback period of 18 years with the highest IRR of 13%.
|        Topic: Power Generation||Paper Number: 26091|