Transient Operating Strategies for Multi-MW Solid Oxide Electrolysis Systems Promoting Power-Following Operation

Kurzfassung

Operating electrolysis processes with renewable energies allows to efficiently store and distribute the energy independent of grid connections as well as avoiding curtailment due to the grid’s load-frequency control. High temperature electrolysis reactors based on Solid Oxide Electrolysis Cells (SOEC) can operate at the highest efficiency, compared to other electrolysis technologies, which makes SOECs an attractive technology. However, the inherent volatility of renewables requires transient operation of the electrolysis process and SOEC reactors are commonly regarded as unsuited or even incapable of frequently switching operating points. This contribution tries to give an answer on the question of how volatile renewables like offshore wind energy can be integrated into an SOEC process and how the SOEC reactors can be operated transiently. A modular plant design is considered and relevant operating points for a single module are introduced including standby operation. Based on that, operating and control strategies for switching between the identified operating points are developed by means of transient system simulations with an in-house developed and validated model. The strategies are analysed in terms of switching time and how they may affect the stacks' lifetime considering the resulting temperature gradients. Subsequently, the strategies for modular operation are applied for the plant configuration to showcase power following of a wind profile. In addition, the influence of the number of individually controllable modules and their operational range on the power following capability is shown.