Abstract
Modular solid oxide fuel cell systems can support partial maintenance during power generation. Existing capacity assessments may overlook reserve withdrawal when a maintained stack leaves its healthy-reserve role. A maintenance service capacity criterion is proposed to account for normal-output reduction and reserve withdrawal. First, normal, maintenance, and healthy-reserve role responses are characterized under uniform and nonuniform hydrogen supply. Second, output reduction and reserve withdrawal are combined into a maintenance-induced capacity loss. Then, object-exchange relations, conditions for identity-independent capacity, and guaranteed and selectable service-window boundaries are derived. Finally, simultaneous responses test composability, and analytical extensions examine general multi-stack maintenance sets. The results show that maintaining A rather than B gives normalized capacity differences of 0.0493 and 0.0891 under 45:55 and 40:60 hydrogen supply, respectively. In the four-stack analytical extension, object selection raises the maintainable count from two to three at the same resource budget. The criterion links maintenance planning to the output available throughout the required service interval.