TRANSIENT OPERATING STRATEGIES FOR SOLAR HEAT SUPPORTED SOLID OXIDE ELECTROLYSIS SYSTEMS FOR HYDROGEN PRODUCTION

Abstract

Considering the transformation of the energy system, there are two main challenges. First, efficient and cost competitive long-term energy storage on a large scale. Second, making renewable energy accessible for hard-to-electrify sectors like transport and heavy industry. Converting renewable electricity into green hydrogen in Solid Oxide Electrolysis Cells (SOEC) is considered a viable solution for both challenges. Besides the high efficiency, SOEC offer the possibility to supply part of the energy demand by industrial waste heat or by renewable sources, such as solar thermal energy. The SOEC technology itself is mature but the integration within large systems and coupling with up- and downstream processes still requires research to be done on the SOEC's transient behaviour as well as identifying safe and efficient operating strategies. In this contribution, a solar-SOEC coupled system concept is introduced and analysed for its capability to cope with typical fluctuations in solar irradiance. The main focus is laid on the transient behaviour of the SOEC reactor during variation of different operating parameters, namely current, feed gas temperature and reactant conversion. Results show that the current variation has the strongest effect on the stacks’ temperature, yielding relevant temperature gradients, especially in endothermic operation. Whereas by increasing the reactant conversion during endothermic operation, it was possible to reduce thermal stress in the stacks, while increasing the hydrogen output as well as the system's efficiency. It is presented how these effects can be combined and utilized for the development of control and operating strategies that aim at improving system performance. This will be exemplary illustrated for improving system performance during a period of overcast and thus reduced heat supply.