Performance Assessment of a Solar-Geothermal Based Organic Rankine Cycle System Producing Green Hydrogen

Abstract

This study presents a comprehensive thermodynamic (energy and exergy) analysis of a solar-geothermal-based Organic Rankine Cycle (ORC) system integrated with a proton exchange membrane (PEM) electrolyzer for green hydrogen production. The system simultaneously harnesses the continuous heat of a geothermal source and the intermittent solar thermal input to ensure stable hydrogen generation. The effects of key operating parameters (solar radiation intensity, production well temperature, inlet temperature of the PTSC fluid, and ORC and PTSC working fluid types were investigated. The results reveal that higher solar radiation intensities significantly enhance both power generation and hydrogen yield, increasing the hydrogen production rate from 22.9 to 24.3 kg/h and the net electrical output from 4.17 to 4.41 MW. Similarly, increasing the geothermal well temperature from 400 K to 600 K significantly enhances hydrogen production, rising from 15.9 to 45.5 kg/h, and increases the net power output by approximately 185 %. However, the exergy efficiency decreases slightly from 0.26 to 0.17 due to increased irreversibilities at higher temperatures. The optimal working pair was determined to be R134a for the ORC and Therminol VP1 for the PTSC, achieving an electrical efficiency of 9.27 %, exergy efficiency of 25.13 %, and hydrogen production rate of 29.02 kg/h. In addition, the exergy analysis showed that the PTSC (similar to 35 %) and condenser (similar to 24.6 %) are the dominant sources of irreversibility. Finally, the Taguchi optimization identified the optimal configuration (Gb = 3.50 x 10(-4) MW/m(2), T-a = 500 K, T-11 = 600 K, and ORC fluid = R134a) yielding the highest overall efficiency and robust performance under variable operating conditions.