Co-optimization of park-level electricity-heat-hydrogen integrated energy systems with reversible solid oxide cells

Reversible solid oxide cells (rSOCs) enable bidirectional energy conversion in integrated energy systems; however, their system-level value under diverse renewable conditions remains unclear. This study develops a mixed-integer nonlinear programming (MINLP) framework for joint capacity planning and hourly dispatch of a park-level electricity-heat-hydrogen system. A semi-empirical rSOC model incorporates mode-switching, thermal dynamics, and operation-dependent lifetime degradation. The framework is applied to Xiamen, Chengdu, and Jiuquan, together with a with/without-rSOC comparison for Xiamen. Results show that renewable availability strongly influences system configuration and rSOC operation. Jiuquan achieves the lowest total annual cost (27.28 million CNY) through abundant renewables and frequent electrolysis operation, whereas Chengdu relies more heavily on grid electricity and fuel-cell operation. In Xiamen, rSOC integration reduces total annual cost and grid electricity purchases by 10.87% and 18.30%, respectively, while increasing renewable generation by 47.55% and renewable utilization from 86.94% to 92.29%. These results demonstrate the economic value of rSOC-enabled multi-energy coupling under region-specific renewable conditions.