A deconstruction and quantification strategy for the reversible efficiency of solid oxide cell systems in an entire cycle

Abstract

High-temperature solid oxide cell (SOC) technology is a promising solution for peak shaving and valley filling in intermittent renewable energy microgrids due to its high efficiency and reversibility. Energy conversion is typically done in units of one charge/discharge cycle; however, a precise definition of the SOC system efficiency in continuous switching cycles has not yet been found, particularly lacking unrestricted quantification of reversible efficiency and mode scheduling optimization. This paper proposes, for the first time, the concept of generalized reversible efficiency (GRT) for SOC systems, along with a novel deconstruction and quantification strategy to solve the optimal GRT of such systems over an entire cycle. Specifically, the switching efficiency analysis is based on an energy-flow model of the reversible SOC system, which incorporates a secondary heat recovery process. An algorithmic strategy consisting of an improved decomposition-based multi-objective differential evolution algorithm is designed to optimize GRT under multiple constraints. Results indicate that GRT can be converted into cycle P2G2P (Power to Gas to Power) in any direction. The global maximum GRT is around 60.4%, occurring at the lower point of the medium capacity (denoted as $\gamma$, $\gamma$≈ 160). The optimal GRT decreases with increasing $\gamma$, exhibits a trade-off with the discharge efficiency, and is affected by thermal dissipation and internal energy losses, especially during discharge.