Thermodynamic and economic multi-objective optimization of geothermal and solar combined power system

• Developed a dual-pressure ORC for high-altitude solar–geothermal hybrid power. • Synergistic solar–geothermal heat input enhanced thermal efficiency. • NSGA-II identified Pareto-optimal trade-offs between efficiency and cost. • DP-ORC with R1233zd(E) reaches 13.18% thermal efficiency. • Minimum LCOE is 0.162 $/kWh under optimized settings. To address the challenge of effectively utilizing Tibet’s abundant solar and geothermal resources for local power supply, this study proposes a novel geothermal-solar dual-pressure organic Rankine cycle (DP-ORC) system tailored for high-altitude applications. The research aims to investigate how key thermodynamic parameters-namely low- and high-pressure evaporation pressures and superheat-affect both energy conversion efficiency and economic feasibility of the system. Six environmentally friendly pure working fluids (e.g., R1233zd(E), R600) are evaluated through detailed parametric analysis. A multi-objective optimization using NSGA-II is conducted with system thermal efficiency and levelized cost of electricity (LCOE) as competing objectives. The results demonstrate that increasing both low- and high-pressure evaporation pressures significantly improves net power output and system efficiency, while lower superheat enhances exergy performance. Among all candidates, R1233zd(E) exhibits the best overall trade-off, achieving a thermal efficiency of 13.18% and the lowest LCOE of 0.162 $/kWh. Component-level cost and exergy analysis further reveal that the condenser contributes 52.72% of total system irreversibility, and solar collectors account for 42.3% of the capital cost. This work provides a systematic framework for the thermo-economic optimization of hybrid renewable systems in resource-rich but infrastructure-limited regions, demonstrating the superior performance of R1233zd(E) in balancing efficiency and cost.