Evaluating the Performance and Efficiency of Hydrogen Carriers for the SOEC/SOFC System with Thermodynamic Methods

The present study investigates the performance and efficiency of a solid oxide fuel cell (SOFC) and solid oxide electrolysis cell (SOEC) hybrid system integrated with intermittent renewable energy. Solar energy is adopted as the renewable energy input, and system behavior is evaluated under hydrogen and ammonia as primary fuels and energy storage media. The effects of different fuel sources on power generation and electrolysis efficiency are analyzed to assess their impact on the integration of renewable energy with the SOFC/SOEC system. For the SOFC system operating with ammonia as the fuel, at a fuel utilization rate of 70% and a current density of 3000 A m − 2 , the net output power at 873, 923, 973, and 1023 K is 7.41, 8.72, 9.87, and 11.00 kW, respectively, with corresponding system efficiencies of 15.76%, 27.82%, 42.00%, and 58.53%. When hydrogen is used as the fuel under the same conditions, the net output power increases to 7.56, 8.82, 9.93, and 11.30 kW, with system efficiencies of 35.48%, 41.38%, 46.55%, and 53.00%. For the SOEC system with a current density of 3000 A m − 2 and a steam utilization rate of 70%, the ammonia production system requires input powers of 28.99 kW (873 K), 25.11 kW (923 K), 23.12 kW (973 K), and 21.26 kW (1023 K), achieving system efficiencies of 45.39%, 52.41%, 57.13%, and 61.90%, respectively. Under the same operating conditions, the hydrogen production system requires 2.36, 2.59, 2.84, and 3.32 kW less input power than the ammonia system at 873, 923, 973, and 1023 K, respectively, resulting in electrolysis efficiencies higher by 11.13%, 14.57%, 17.68%, and 22.17%. These results indicate that the hydrogen production system exhibits superior efficiency and lower power demand compared to the ammonia production system under identical operating conditions.