Efficiency analysis of a novel reversible solid oxide cell system with the secondary utilization of the stack off-gas: A model-based study

Abstract

Systems with reversible solid oxide cells (rSOCs) can potentially overcome the spatio-temporal mismatch between intermittent generation from renewables and continuous electricity demand by operating bi-directionally. Achieving high energy conversion efficiency is one of the critical design objectives for a typical rSOC system. However, only a few papers discuss the effect of parameters and system processes on efficiency, and thermal management designs considering gas flow rates of the fuel and air loops are not yet seen. This work presents a novel rSOC-based system that employs a heat recovery unit for absorbing thermal energy as parasitic power gain and a water-gas heat exchanger instead of the electric evaporator to utilize the stack off-gas secondarily. Modeling and efficiency analysis of such a system is performed using a physically finite element method-based rSOC stack model coupled with extra auxiliary component models. Results indicate that efficiencies of 92%, 71.1%, and 62.4% can be achieved at 1,023 K and 1.23 bar in electrolysis, discharge, and the round-trip, respectively. The parasitic gain can significantly improve system efficiency and output performance and reduce the power loss in regulating the temperature uniformity of the stack with increased airflow. The outcomes can serve as guidelines for the thermal management design of real rSOC systems and control strategies optimization.