In the transition toward decarbonized energy systems, hydrogen technologies are emerging as key enablers. Solid oxide electrolysis cells (SOECs) offer the highest efficiencies among electrolyser technologies. However, their perceived thermal constraints have limited their consideration for transient operation and, consequently, for the integration of fluctuating renewable electricity in both off-grid and grid-connected applications. This study challenges that perception by demonstrating the potential and feasibility of SOEC systems to provide grid-relevant ancillary services while enabling direct integration with renewable energy sources.

Our research presents three major advancements in grid-integrated and off-grid SOEC operation, exploring and demonstrating the capability of SOECs to provide ancillary grid services, including fault ride-through (FRT) as well as frequency and voltage control. First, we introduce and validate an advanced operating strategy for dynamic SOEC operation. Pulsed operation using pulse-width modulation (PWM), switching the stack current between open-circuit and nominal operation, decouples electrical loading from the system’s thermal response. This enables rapid changes in power consumption while limiting temperature variations and thermal gradients. Experiments conducted on a multi-stack SOEC system, pressurized up to 25 bar and integrated into a complete Power-to-X (PtX) process, demonstrate rapid modulation of the duty cycle over a range of 10-100 %, resulting in fast changes in average power consumption with only small temperature variations. The results demonstrate a dynamic range comparable to proton exchange membrane (PEM) electrolysers without compromising stack integrity, substantially increasing the potential of SOEC systems to provide grid-balancing services. Second, simulation-based analysis of LV-FRT scenarios shows that SOEC systems can tolerate severe faults, recover rapidly and contribute to grid stability when operated under appropriate control strategies. Third, for off-grid applications, we investigate the potential of reversible SOEC operation in fuel cell mode to provide backup power for standalone, renewable-driven electrolysis plants. This is particularly relevant when coupled with power-to-X (PtX) processes – such as Fischer-Tropsch, methanol, methane, or ammonia synthesis – which require continuous power supply. An extended simulation study, based on a validated multi-stack module model and a plant design, optimized for efficient SOEC operation, quantifies the achievable backup power output in fuel cell mode.

Overall, the results demonstrate that SOEC systems can evolve from steady-state hydrogen producers to flexible, multi-functional assets that actively support grid stability and renewable energy integration.