Performance and exergy efficiency analysis of renewable energy–integrated high-temperature solid oxide power generation and electrolysis systems

This study evaluates the performance and exergy efficiency of a hybrid energy system integrating a Solid Oxide Fuel Cell (SOFC), Solid Oxide Electrolysis Cell (SOEC), and an Organic Rankine Cycle (ORC) coupled with renewable energy. The system is designed for a 100 kW community load, operating with 5 h of SOEC hydrogen production and 19 h of SOFC power generation. A thermodynamic–electrochemical coupled model is developed to investigate the effects of operating temperature, utilization rates, hydrogen recirculation, and thermal losses (0–5%) on system performance. Results indicate that operating temperature governs system behavior with distinct optimal conditions: SOFC efficiency increases to 59.6% at 1123 K due to reduced polarization losses, whereas SOEC achieves a maximum efficiency of 79% at 1023 K and declines at higher temperatures due to increased thermal compensation demand. Increasing utilization enhances reaction efficiency but reduces exhaust heat availability, limiting ORC contribution to approximately 0.3%. Hydrogen recirculation improves SOFC performance but slightly degrades SOEC efficiency due to higher preheating demand. Thermal losses reduce efficiency by approximately 3.4% in SOFC mode and 2% in SOEC mode, with dominant irreversibility arising from air-side heat exchange in SOFC and water vaporization in SOEC. These results highlight distinct energy-flow mechanisms and emphasize the importance of coordinated thermal management for stable hybrid system operation.