Organic Rankine Cycle Utilization for Green Hydrogen Production in Geothermal Power Plants: Review

Abstract

The global shift towards renewable energy necessitates solutions for intermittency and energy storage. This review comprehensively examines the integration of Organic Rankine Cycle (ORC) technology in geothermal power plants for sustainable green hydrogen production. Geothermal energy provides a stable, base-load heat source, which the ORC effectively converts into electricity to power water electrolysis, overcoming the variability of other renewables like solar and wind. The analysis highlights that the choice of organic working fluid (e.g., R245fa, R123, Isobutane) is critical for system performance, hydrogen production rate, and economic feasibility. Furthermore, advanced ORC configurations (e.g., regenerative, dual-pressure) generally yield higher efficiency and power output, albeit with increased complexity and cost. The temperature and flow rate of the geothermal fluid are identified as paramount factors, where higher temperatures typically increase hydrogen output and reduce costs, though an optimal balance must be found to avoid escalating operational expenses. A key strategy for improving economic performance is utilizing waste geothermal heat to preheat water for electrolysis, significantly reducing its electrical energy demand. Thermoeconomic assessments indicate that this integrated approach can be economically competitive, with reported hydrogen production costs ranging from approximately 1.1 to 4.2 USD/kg H₂ and attractive payback periods. In conclusion, coupling geothermal-powered ORC systems with electrolyzers represents a promising and synergistic pathway for producing green hydrogen, enhancing the viability of geothermal plants and contributing to the clean energy landscape.