Energy analysis of a geothermal power plant with thermoelectric energy harvester using waste heat

Abstract

This study investigates the integration of thermoelectric generators (TEGs) into geothermal power plants to harvest energy from the waste heat and possibly, as a result, to increase the electrical energy generation of geothermal power plants. For this purpose, a model of a geothermal power plant-TEG hybrid system has been designed and implemented as an experimental setup. In addition, the optimized layout configuration of TEGs is obtained by using Matlab & Simulink for 48 pieces of the TEGs. A parametric energy analysis is conducted by varying the temperature of the reinjected geothermal brine and the inlet temperature of the cooling water, since TEGs are planned, so they can be employed between the pipelines of the cooling water and the reinjected geothermal brine. The effects that this has on the performance of the organic Rankine cycle (ORC) and the TEGs are then determined. It was found that the power output of the TEGs increases with the rise in temperature of the reinjected geothermal brine, but the net power of the ORC decreases. For the maximum net power output of the ORC, which is 217.6 kW, TEGs are able to produce 43.42 W for the temperature difference of 41.98 degrees C that corresponds to this status. Therefore, TEGs must be used with lower power outputs to achieve more energy production from this hybrid energy system. For the high inlet temperature values of cooling water, the net power of the ORC decreases, and the power output of the TEGs also goes down. TEGs are able to produce 84.29 W for the temperature difference of 60.6 degrees C for the ORC's maximum net power output of 260 kW. Therefore, it is clear that using TEGs in the power plant for low inlet temperature values of cooling water can be considered. In conclusion, this study demonstrates that waste thermal energy in reinjected geothermal brine can be harvested through TEGs, and this energy could be used to feed the electrical equipment of the power plant with low energy consumptions such as lighting, sensors, instrumentation, and control systems. However, TEGs should be used carefully, since they may affect the overall performance of the geothermal power plant.