Improving Low-Load Efficiency of Marine SOFC Powertrains by Means of Efficient Module Hot Standby Operation

Solid oxide fuel cell (SOFC) powertrains can be considered as a promising solution for future zero-emission shipping, yet the decrease in electrical efficiency at low load remains a barrier for full-scale marine adoption. This work provides the first comprehensive quantification of hot standby power demands for marine SOFC modules and evaluates its impact on the multi-modular powertrain efficiency. A thermodynamic process system model of a 112 kW_el rated SOFC module was utilized, including anode recirculation, autothermal pre-reforming in hot standby, heat losses and off-design heat exchanger behavior. Assessing five hot standby heat integration variants, combined fuel-equivalent standby demands ranging from 5.2 to 15.3 kW_chem per module were obtained. The highest-performing configurations are those employing cathode off-gas recirculation, motivating their integration in a multi-modular marine SOFC concept. At the multi-module powertrain level, non-uniform operation strategies, in which individual modules either operate close to their maximum-efficiency point or remain in hot standby, can significantly increase low-load efficiency. At a typical cruise-ship operating point near 15% rated power, efficiencies of up to 55% (LHV to AC) are achieved, compared to only 26% for uniform operation of all modules. The results highlight the importance of incorporating hot standby strategies into future marine SOFC system design.