Enhancing geothermal ORC power generation with SOFC: A comprehensive parametric study on thermodynamic performance

Abstract

Geothermal energy is a promising renewable energy source due to its abundant global reserves. However, most geothermal resources are of low grade, severely restricting their power generation capacity and efficiency. In this study, the geothermal organic Rankine cycle power generation system is combined with a solid oxide fuel cell-gas turbine system to improve the overall power supply and heat utilization efficiency. The heat source and cycle temperature are upgraded using high-temperature solid oxide fuel cell waste gas, and the combined system’s efficiency is further improved through cascade heat utilization. Electrochemical-thermodynamic models are developed for the proposed system, and energy-exergy analysis is carried out. The effects of fuel cell current density, operating temperature and geothermal grade on the combined system’s performance are comprehensively analyzed. Compared to the standalone geothermal system, the energy efficiency and output power of the organic Rankine cycle increase by 8.11% and 7.95% respectively in the baseline case. Under the lowest geothermal temperature condition, the cycle output power is improved by 22.64%. The net power of the combined system can vary from 358 kW to 846 kW by adjusting the fuel cell current density from 1000 A m−2 to 8000 A m−2, demonstrating a flexible power supply capability. The optimal solid oxide fuel cell operating temperature is 1023.15 K, resulting in the highest system overall energy efficiency of 14.85%. The presented work provides essential guidelines for improving geothermal power generation performance and designing applicable combined systems.