Reversible solid oxide cell system with thermocline-type thermal energy storage: Numerical and techno-economic analysis

In this study, a novel system − a reversible solid oxide cell system with a thermocline-type thermal energy storage is proposed to address the limits of green hydrogen. This system utilizes a solid oxide cell, operating selectively in both fuel cell and electrolysis modes. In the fuel cell mode, the system produces electricity and an enormous amount of heat that can be stored in thermal energy storage. Conversely, heat stored in the thermal energy storage during electrolysis produces steam and facilitates the electrolysis reaction to produce hydrogen. We conducted a numerical analysis and determined a design of thermocline-type thermal energy storage at representative driving load. Three alternative setups that operated under the same conditions were compared in this study: the reversible solid oxide cell system integrated with thermal energy storage, a stand-alone reversible solid oxide cell system, and a stand-alone solid oxide electrolysis system. The results indicate that the reversible solid oxide cell system with thermal energy storage outperforms the other two setups in terms of system efficiency, water consumption reduction, and greenhouse gas emissions. The proposed system achieves a 27.5 % improvement in efficiency over the solid oxide electrolysis stand-alone system. The study indicated that the proposed system could achieve 0 kg-CO₂-eq/kg-H₂ of greenhouse gas emission, by replacing the natural gas burner with a thermocline-type thermal energy storage. Furthermore, a techno-economic analysis was conducted for all three systems, confirming that the proposed system can reduce a hydrogen production cost from $5.15/kg-H₂ to $3.03/kg-H₂.