Integrating water and energy sustainability: A poly-generation system for desalination, zero liquid discharge, and green fuel

This study presents the design and analysis of an integrated, geothermal-powered system that simultaneously produces electricity, clean water, and green hydrogen. The system addresses global concerns over energy security and resource scarcity by fully utilizing a 180 °C geothermal source in a closed-loop manner. The geothermal fluid first drives a primary Organic Rankine Cycle for power generation. The residual heat is then directed to a Zero Liquid Discharge desalination unit to produce freshwater and recover salts. This purified water, along with a portion of the generated electricity, is fed into a Proton Exchange Membrane electrolyzer for high-purity hydrogen production. A secondary Organic Rankine Cycle further recovers remaining geothermal energy to boost efficiency. Thermodynamic and economic modeling reveal the system can generate significant outputs: approximately 2.7 MW of net electricity, 112.1 m³ /day of freshwater, and 218.1 kg/day of hydrogen. The thermodynamic model yields an overall system efficiency of 14.6% under base case operating conditions. Key factors influencing performance include the ZLD heat-source temperature, turbine pressures, and flow density of electrolyzer. Optimization of key parameters demonstrates the potential to elevate this efficiency to 16.8%. With an estimated investment of 3.69 MM$, the system is projected to achieve payback in under two years. By operating entirely on renewable geothermal energy and incorporating a fully closed-loop water cycle through Zero Liquid Discharge technology, this poly-generation system offers a sustainable, economically viable, and environmentally benign solution for the co-production of essential utilities. • Cascaded ORC design for efficient low-enthalpy geothermal utilization. • Direct coupling of ZLD desalinated water to PEM hydrogen production. • Integrated production of electricity, freshwater, and green hydrogen. • Rapid economic return (∼1.37 years payback). • Supports net-zero water and energy goals and resource circularity.