Orthogonal Experimental Optimization and Economic Evaluation of a Coupled Multi-Parameter Simulation for a Concentrating Solar–Geothermal Energy Storage System

[Objective] This study employs numerical simulation methods and orthogonal experiments to conduct preliminary a priori research on a novel concentrated solar power-geothermal long-duration energy storage system (GEO-CSP), aiming to comprehensively evaluate system parameter performance and economic viability. The system utilizes concentrated solar power to heat a working fluid to high temperatures, then injects the thermal energy into underground reservoirs via injection wells to enhance the thermal storage capacity of the formation. [Methods] A multi-software coupled simulation approach was adopted: SG-Tower software calculated the solar collector field's heat collection performance via ray tracing; COMSOL multiphysics models simulated heat-flow coupled heat transfer in underground reservoirs, analyzing the effects of storage temperature, injection flow rate, and reservoir characteristics on thermal storage efficiency; MATLAB/Simulink constructed a two-stage flash power generation model and simulated the power generation process. [Results] Based on analysis of 27 sets of orthogonal experimental designs, results indicate that under optimal operating conditions (e.g., injection temperature of 350°C and injection flow rate of 100 m3 h?1), geothermal storage efficiency can reach 0.936 and power generation efficiency can reach 0.335. Parameter sensitivity analysis reveals that injection temperature and injection flow rate are the primary controlling factors affecting system performance (contribution rates of 78.3% and 14.0%, respectively). Under typical operating conditions, a reservoir thickness of approximately 100 meters balances heat exchange efficiency and heat loss, optimizing overall system performance. Economic analysis indicates that in depleted oil and gas reservoir conversion scenarios, the investment payback period is reduced to less than 5 years, with cumulative net profits for a single well pair reaching 31.5367 million yuan over a 30-year lifecycle. [Conclusion] This a priori study provides a theoretical basis for parameter optimization and engineering applications of solar-geothermal coupled energy storage and power generation systems, holding significant importance for advancing the development of long-duration renewable energy storage technologies.