Dynamic Loading for Solid Oxide Stacks Under Limited Actuation

High-temperature solid oxide cells and stacks are increasingly viewed as critical elements for a promising approach to address the intermittency of renewable energy sources, such as wind or solar. Used as electrolyzers, such stacks can harness excess power generated at peak periods, which often do not coincide with peak demand, by producing hydrogen for short- or long-term storage. Used as fuel cell systems, the stored hydrogen can be used to generate clean energy during periods of low renewable generation. The possibility of use as a reversible system further increases the flexibility to deal with the inherent and large variability of renewable sources, as well as the overall economic viability. The power tracking required—for both fuel cell and electrolyzer modes—can lead to thermal fatigue and short lifespans, a challenge that is more acute if used for operation in the reversible mode, due to the significant differences in the thermal profiles of the two configurations. We propose control techniques to develop high-performance controllers for thermal control of the solid oxide stacks, under large variations in the operating conditions. The challenges faced, particularly with respect to actuation and its limitations, differ in the two configurations necessitating a form of gain scheduling in fuel cells and reliance on artificial saturation levels in electrolyzers.