Economic optimization of modular solid oxide electrolysis system considering degradation and lifetime

The increasing demand for green hydrogen creates an opportunity for highly efficient technologies for hydrogen production such as solid oxide electrolysis. However, degradation introduces uncertainties and additional costs in system design and operation. This study presents an economic analysis of hydrogen production using large-scale solid oxide electrolysis systems, considering the degradation and lifetime of the solid oxide electrolysis stacks. The modularity of the system is factored into equipment sizing, with different heat exchanger materials for inside and outside of the “hot module”. The implications of degradation are examined, with degradation associated costs calculated considering both stack replacement and efficiency drop. Key parameters such as electricity price, heat exchanger size, solid oxide electrolysis stack cost and operating conditions, steam and renewable energy availability, and improved cell technology with lower degradation rates are analyzed for their impact on hydrogen costs. The optimization results indicate that current density of 0.6–0.7 A/cm², with a lifespan of 4–5 years, is optimal for minimizing hydrogen production costs with current technology. The optimal starting conditions are thermoneutral in Potentio-Galvanostatic operation and endothermic in Galvanostatic conditions. For a base scenario assuming an electricity price of 50 €/MWh, the estimated hydrogen cost is 5.3 €/kg, and degradation costs (i.e., stack replacement and efficiency losses) account for 8 % of this value. Various options to achieve cost-effective hydrogen production are proposed in this study. For instance, lower solid oxide electrolysis stack cost, reducing degradation rates, and optimizing stack operating conditions can lower costs significantly by 2 €/kg.