Dynamic modeling and parameter analysis study on reversible solid oxide cells during mode switching transient processes

Reversible solid-oxide cells (SOCs) are a promising technology for mitigating the fluctuation of power from renewable sources. Mode switching between electrolysis and fuel cells occurs frequently and is necessary for an SOC stack. Herein, a dynamic SOC-stack model was developed and validated against experimental data. Subsequently, we extensively studied the stack temperature (Ts), voltage (Vs), and reversible efficiency (ηre) with different designing and operating parameters, including stack heat capacity (Cs), inlet hydrogen fraction (xH), stack operational pressure (p), inlet work medium temperature (Tin), current density (I), and mode switching frequency (f). For an actual SOC plant, the stack may work in a nearly adiabatic environment. Our calculation results show that with xH increasing from 0.2 to 0.6, the variation in ΔTs decreases by 25%, Vs increases by 10%, and ηre increases by 2.9%. With fourfold increasing in CS and p, ΔTs decreases by 75% and 25% and ηre increases by 0.47% and 1.8%, respectively, whereas, Vs is nearly unaffected. ΔTs and ΔVs almost proportionally increase with I. In relation to Tin or f, ΔTs is unaffected, ΔVs decreases, and ηre slightly increases. Overall, this work identified the most critical stack designing and operating factors affecting the transient behavior of an SOC stack during mode switching processes. The results can serve as guidelines for SOC-stack design and operation-strategy optimization.