Theoretical and experimental study of Reversible Solid Oxide Cell (r-SOC) systems for energy storage

A theoretical system model to study different system concepts is presented in this study. An SOC reactor model was developed based on the experimental analysis in pressurized SOFC and SOEC operation mode. An experimental analysis under pressurized conditions was performed on a commercially available Electrolyte Supported Cell (ESC) type 10 layer SOC stack. A simple system model analysis was performed based on this r-SOC reactor. The effect of different system operation parameters such as pressure, temperature, current density and utilization on system performance was analysed. Endothermic operation of an r-SOC stack in SOEC operation mode can lead to higher roundtrip efficiency. Endothermic operation in SOEC mode requires thermal energy supply. A thermal energy storage system to store high temperature heat released during the SOFC operation to supply heat with high exergy content for the endothermic SOEC process was investigated. A system roundtrip efficiency around 55%-60% is achievable with current ESC type r-SOC technology whereas the theoretical limit of roundtrip efficiency for an ideal reactor (no ohmic, activation and diffusion losses) is around 98% for the same operating conditions. Endothermic operation is beneficial and a heat storage concept is an attractive approach for a prototype system.