Design and control of high temperature electrolyser systems fed with renewable energies

Abstract : Power-to-Gas could become an attractive solution for renewable electricity storage, provided that affordable electrolysers are able to operate efficiently under intermittent conditions. This work aims to assess the technical feasibility of operating intermittently a Solid Oxide Electrolysis Cell (SOEC) system around 1073 K. Realistic unfavourable conditions are considered, consisting in a standalone system operated with no external heat source and integrating hydrogen compression to 3 MPa. Two challenges are tackled in this work: i) the system power load range, limited to 60-100% due to thermal gradients, is extended via efficient control strategies, ii) procedures are defined to minimise the impact of the intermittency on the lifetime. First, a modular control strategy is proposed, consisting in the use of several SOEC units which are either operated in a tolerable power load range, or switched off. The system power load range is hence extended to 15-100% in the case of four units. A complementary control strategy, consisting in internal electrical heating, enables to extend the load range by reducing thermal gradients, but it may decrease the lifetime. Thus, it is applied to only one unit for it to follow the load curve and extend the system power load range to 3-100%. Secondly, 1800 on-off electric cycles are applied to an SOEC with no degradation increase, which shows that repeated start/stops do not decrease the lifetime. Start-up, standby and shut-down procedures are also defined. Finally, two case studies of Wind-SOEC and Solar-SOEC systems operated over one year show that, with the implemented control strategies, the SOEC system stores the applied power with an average efficiency of 91% vs. HHV, while units operate under tolerable conditions apart from one unit which follows the load curve and may have a decreased lifetime.
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Floriane Petipas. Design and control of high temperature electrolyser systems fed with renewable energies. Other. Ecole Nationale Supérieure des Mines de Paris, 2013. English. ⟨NNT : 2013ENMP0015⟩. ⟨pastel-00873645v2⟩

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