A comprehensive 4E assessment of geothermal-assisted hydrogen production via an ORC–PEM integrated system: Comparative evaluation of conventional and low-GWP working fluids

In this study, a geothermal-assisted Organic Rankine Cycle (ORC)–Proton Exchange Membrane (PEM) electrolyzer system is comprehensively investigated for green hydrogen production. A total of 4,775 operational data points obtained from a geothermal power plant were used to model and evaluate the proposed system. Six ORC working fluids, namely R134a, R290, R227ea, R1234yf, R1234ze(E), and R1243zf, were comparatively assessed from thermodynamic, economic, and environmental perspectives. The results showed that the selection of the working fluid significantly affects the overall system performance. Among the investigated fluids, R227ea provided the highest thermodynamic performance, with a net electricity production of 44.66 kW, hydrogen production rate of 3.17 × 10⁻⁴ kg/s, energy efficiency of 4.036%, and exergy efficiency of 1.812%. In comparison, R1234yf showed the best performance among the low-GWP alternative fluids, achieving 40.94 kW of net power output, 2.904 × 10⁻⁴ kg/s of hydrogen production, 3.701% energy efficiency, and 1.662% exergy efficiency. From an economic perspective, the lowest levelized hydrogen cost was obtained with R1243zf as 1.364 USD/kg, whereas the shortest payback period was achieved with R227ea as 7.4 years. In addition, R227ea yielded the highest annual income of 63,383 USD and the highest CO₂ emission reduction of 82.10 tons/year. The Sustainability Index values varied between 1.012 and 1.018 for the investigated fluids. Overall, the findings indicate that R227ea offers the best thermodynamic and environmental performance, while R1234yf represents a promising low-GWP alternative for geothermal-assisted green hydrogen production. The results also demonstrate that working-fluid selection should be performed through an integrated thermodynamic, economic, and environmental assessment rather than relying on a single performance criterion.