Power-to-Gas-to-Power technologies offer strong potentials for energy markets with highly stochastic energy production from renewable sources, such as wind and PV. Increasing efficiencies and cost effectiveness are key issues in state of the art reversible solid oxide electrolyzes systems and still a major challenge. Using a reversible SOE system (rSOE), instead of two separate units that operate alternately for gas or power production, promises to be a very cost effective solution. The rSOEC system can switch between these two operation modes, which results in a more compact system that can be operated almost full time. Additionally, the system can be highly efficient operated with a whole range of different fuels, which increases the technologies flexibility and usability.

This multiuse and multifuel character of rSOE systems leads to very particular challenges in the development. A feasible concept has to combine all necessary BoP components and control mechanisms allowing all modes of operation, while keeping efficiencies and cost effectiveness. One particular challenge for the system design is heat management. A method was developed that promises best possible use of heat recirculation in all modes, while being minimal in design and regulation requirements. For the first time dynamic simulations for all operating conditions e.g. start-up, shut-down, stand-by and mode-switching processes, including all relevant mass and energy flows are currently developed. This strongly supports the system development by making them more effective, since iterative development circles and thus development time and hardware costs are reduced.

The project “Hydrocell” (2013-2016) demonstrated the usability of these simulation methods. A Proof-of-Concept SOEC system has been developed and tested with electricity to H₂ (LHV) conversion efficiencies above 80%_el.

Within the current project “AuRora”, various system designs for a fully autonomous rSOE system were identified. The concepts are switchable between H₂O electrolysis, H₂0+CO₂ co-electrolysis with system integrated catalytic methanation and multifuel SOFC operation. System concepts are developed with conversion efficiencies above 80%_el* for H₂ production and CH₄ production. Based on the simulation results, including CFD, a 1kW_elProof-of-Concept will be realized on the testrig in 2017.

Within the presentation, the theoretical background, different rSOE systems designs, optimized operation conditions, as well as measurements performed in the project “Hydrocell” and “AuRora” will be explained. This includes steam-electrolysis, H₂O + CO₂ co-electrolysis with system integrated catalytic methanation, SOFC operation with H₂, as well as multifuel operation with system integrated fuel reformation.

* based on LHV energy content