Reversible SOC system development, operation and energy system (grid) integration

Reversible solid oxide systems are expected to play a major role in future seasonal/periodical energy storage methods. Previous FCH JU projects[[https://www.clean-hydrogen.europa.eu/projects-repository_en]] such as BALANCE, SElySOs, ECO and NewSOC have explored some of the most promising proposals with respect to systems, materials and process chains that are suitable when using a reversible solid oxide system. In BALANCE the concept of rSOC was the highlight and activities focussed on rSOC operation and implementation. The projects REFLEX and SWITCH also include rSOC at the core of their systems. In REFLEX, hydrogen is generated locally and re-used by the same system. The system can be operated in island mode or in electricity grid connected, no connection is made to the gas grid. SWITCH focuses on the continuous supply of hydrogen for industrial or mobility use. The rSOC at the heart of the systems provides the arbitrage of using either electricity or methane as source of hydrogen, according to the best available source at any moment. The SWITCH system can operate on methane from the gas grid although reinjecting hydrogen back into the grid is not foreseen at any moment. Moreover, other projects dealing with monitoring, diagnostics and control for SOC have provided a reference framework for the implementation of solutions that are able to guarantee optimal operation and durability of stack and BoP (Balance of Plant).

The current rSOC stacks/systems lack clear performance specifications when used on blends of natural gas and hydrogen. Therefore, still a large gap needs to be filled both at the system and cell/stack level that call for further research. Learnings and findings from the above projects should form the base for the investigations proposed in this topic.

The scope of this topic is to design and develop a reversible solid oxide system of at least 5 kWe in fuel cell mode and capable of absorbing at least 15 kWe in electrolysis mode. The solution developed should be validated in a relevant environment. Continuous operation of at least 3 months should also be demonstrated.

The reversible solid oxide system (rSOC) should be designed and developed to allow for:

• Full compatibility with the existing natural gas grid of today and the hydrogen grid of tomorrow in addition to the electricity grid. This will in turn contribute to achieving to the following major objectives i) transition from natural gas to hydrogen as an energy vector ii) decentralised energy production, iii) balancing the high variability of electric energy from renewables and iv) energy security;
• Connection to both the gas grid and the electricity grid. The gas for FC Mode operation will be taken from the gas grid and the hydrogen produced from EL Mode operation (with or without processing) will be fed back to the gas grid;
• Reinjection of gas/hydrogen into the gas grid. In the case of reinjection as hydrogen, local concentration monitoring and mixing with natural gas (diluting it) is of essence. The alternative option of performing co-electrolysis raises the challenge of collecting and storing CO₂ of sufficient purity for co-electrolysis operation. This can potentially be coupled to the storage of oxygen produced in the electrolysis mode. Proposals can adopt any of these approaches;

Addressing the issues above will help promoting a prosumer hydrogen-based stationary sector.

Proposals should address the following at the system level:

• A rSOC system capable of generating at least 5 kW_e in fuel cell mode and capable of absorbing at least 15 kW_e in electrolysis mode needs to be developed, in line with the KPIs mentioned in the expected outcomes;
• The concepts used in developing the system should allow scalability to higher powers not only by adding individual stacks but also by increasing the stack power;
• The system should be able to operate not only with 100% hydrogen as fuel but also with mixtures of hydrogen and natural gas in Fuel Cell mode. In Electrolysis mode the system should be able to operate either in steam electrolysis or co-electrolysis mode, depending on the best possible approach leading to compatibility with the gas grid;
• A functioning prototype of the system should be validated in a relevant environment. A mix of hardware and hardware in the loop components can be chosen, to demonstrate how the system would work when deployed in the real world. A set of suitable algorithms and logics should also be implemented in order to monitor, diagnose and control the system for optimal operation in both modes and during switching. Safe operating strategies and appropriate design maps for system operation should be addressed. Electrical load following in electrolysis mode is quite critical; hence, performance with respect to load following should be quantified in a suitable manner;
• The reversible solid oxide system should have a common set of BoP (Balance of Plant) for both modes of operation. This is to ensure that the CAPEX cost stays low. The downstream gas/chemical processing system is a separate system of its own and is not part of the rSOC system which is to be developed and tested.

Proposals should address the following at cell & stack level:

• On the cell level, either commercially available cells may be used, or electro-catalytic materials can be specifically engineered keeping reversible operation in mind. The cells should perform up to the current standards or higher and should meet the KPIs given above. The same should be replicated on the short stack and full stack levels. The cell should be able to operate at a current density of at least 1.5 A/cm² or higher in both modes of operation. Transient time during switching between modes should be quantified and kept low for practical operations;
• Appropriate State of health monitoring methods and monitoring tools should be developed and implemented which can predict performance degradation when cell is operated the two modes EL (with steam electrolysis and/or co-electrolysis) and FC (with several combinations of feeding mixtures);

These methods and tools should be translated for use on stack level and implemented on the full system.

Proposals should also demonstrate how the solution developed would allow to create a synergy between the gas transmission system operator and electric transmission system operator. In addition proposals should develop and propose early business models targeting at energy companies including gas and power utilities.

Activities developing test protocols and procedures for the performance and durability assessment of electrolysers and fuel cell components proposals should foresee a collaboration mechanism with JRC (see section 2.2.4.3 ""Collaboration with JRC""), in order to support EU-wide harmonisation. Test activities should adopt the already published EU harmonised testing protocols[[https://www.clean-hydrogen.europa.eu/knowledge-management/collaboration-jrc-0_en]] to benchmark performance and quantify progress at programme level.

Activities are expected to start at TRL 3 and achieve TRL 5 by the end of the project.

The conditions related to this topic are provided in the chapter 2.2.3.2 of the Clean Hydrogen JU 2022 Annual Work Plan and in the General Annexes to the Horizon Europe Work Programme 2021–2022 which apply mutatis mutandis.