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Highly efficient hydrogen production using solid oxide electrolysis integrated with renewable heat and power

SOE technology on cell, stack and system levels has been developed in various FCH 2 JU projects such as SOPHIA, Eco, SelySos and HELMETH52. Additionally, scale-up of high temperature electrolysers into the MW industrial-scale with integration of the waste heat in the process has already started (projects GrinHy and GrinHy 2.0).

Thermal integration of heat into SOE by using solar heat from Concentrated Solar Plants (CSP) or from power-to-heat (PtH) systems has only been a subject in the project SOPHIA so far. It was demonstrated that coupling of a SOE with CSP power plant can reduce the electricity demand of the SOE from the grid to less than 5% of the annual operating time, and can achieve a higher energetic efficiency and sustainability index compared to a photovoltaic system.

In a wider context, the project should couple high-temperature electrolysis with solar heat or power-to-heat sources at different levels from stack box to multi-kW scale and larger system level to investigate operational behaviour in detail. This should result in the identification and provision of practical technical solutions resulting from the specific operating conditions given by the coupling with intermittent RES for electric power and heat.
The project should cover the following topics:

  • Build-up of a stack box and a system with power capacity higher than 20kWel, including a SOE system, a solar steam source, or other renewable heat sources;
  • Investigation of the dynamics of the heat and electricity supply and the reactions of the SOE, under typical cycling conditions (e.g. day-night). System design should focus on solutions to maintain the SOE core warm during night. The sensitivity of SOE towards steam temperature variations caused by solar radiation volatility and / or upon dynamic operation should be investigated. A strategy should be formulated for buffering the fluctuation of heat and electricity and safe operation regimes for the SOE core also by modifying SOE stack and/or module design;
  • The specific operating conditions for the proposed solution should be specified (e.g. steam temperature) and determined versus the specific technology scale (e.g. number of stacks) clarifying the upscaling potential and conditions;
  • Perform a concept design study for a heat Integrated SOE system scale-up towards units of 100 MWel with heat supply from a large-scale renewable heat source such as a CSP plant and electricity from renewables.

TRL at start of the project: 3 and TRL at the end of the project: 5.

Any safety-related event that may occur during execution of the project shall be reported to the European Commission's Joint Research Centre (JRC) dedicated mailbox , which manages the European hydrogen safety reference database, HIAD and the Hydrogen Event and Lessons LEarNed database, HELLEN.

Activities developing test protocols and procedures for the performance and durability assessment of fuel cell or electrolyser components should foresee a collaboration mechanism with JRC (see section 3.2.B ""Collaboration with JRC""), in order to support EU-wide harmonisation. Test activities should adopt the already published FCH 2 JU harmonized testing protocols to benchmark performance and quantify progress at programme level.

The FCH 2 JU considers that proposals requesting a contribution from the EU of EUR 2.5 million would allow this specific challenge to be addressed appropriately. Nonetheless, this does not preclude submission and selection of proposals requesting other amounts.

Expected duration: 4 years

Increasing penetration of intermittent Renewable Energy Sources (RES) on the grid requires large energy storage capacity. According to the analysis of CertifHy [51], EU´s demand for hydrogen in 2030 will reach 10 million tonnes, of which 17.3 % should be produced by renewable sources to fulfil the goals for the energy transition. A large share of this green hydrogen will be produced by electrolysis in areas of low electricity prices associated to renewable power from photovoltaic or wind. High-temperature steam electrolysis exhibits the highest electrical efficiency among existing water electrolysis technologies for hydrogen production with the potential of further enhancing efficiency when high-temperature heat is used for supplying steam. Therefore, it has also the potential for producing renewable hydrogen very cost –efficiently.

Solid Oxide Electrolysis (SOE) technology has already been developed to TRL 7 including the coupling with industrial waste heat. Most of the applications rely on steady state operation of the SOE process. However, in the cases where the electrolyser is placed in the area of inexpensive electricity generation, e.g. by photovoltaics, such heat is not available all the time or not available at all. The obvious conclusion is to consider renewable heat since concentrated solar power systems are available at medium – big scales, economic and efficient in areas where photovoltaic electricity is inexpensive.

The challenge is to leverage the SOE´s efficiency by integrating renewable heat to produce renewable hydrogen with the highest efficiency among all water electrolysis technologies. As a result, renewable hydrogen will be efficiently produced in large amounts at places where both solar heat and renewable power are available. A specific challenge is given by the need of optimising the coupling of high-temperature steam electrolysis with two intermittent sources: renewable electricity and high temperature solar heat.

Dedicated solar steam generators with steam storage and handling are necessary to buffer the intermittent nature of solar heat and avoid thermal cycling of the SOE in variable operation. Furthermore, an optimized heat integrated system concept is necessary. Still due to the dynamic operation during start up and shut down cycles, steam temperatures will vary. This will demand for a SOE core technology robust enough to cope with temperature transients and gradients. This requires detailed investigation of operational models optimized for such a combination. The focus is on performance and durability of SOE in a relevant testing environment, given the fluctuations of renewable energy sources. The challenge includes understanding how fluctuating operating conditions affect the SOE core, the identification of operational strategies that are safe for the SOE, and which implications are expected on system efficiency and economics considering the production of hydrogen.


Integration of renewable heat will lower the cost of hydrogen produced by high-temperature solid oxide electrolysers at places without cheap steam sources. It will support the deployment of hydrogen use for lowering the carbon footprint. The project should therefore have the following impacts:

  • Demonstrate ≥ 98% availability and the production of hydrogen by operation of > 1,000 h with production loss < 1.2%/kh;
  • The SOE with renewable heat integration shall demonstrate electrical efficiency ≥ 85% based on LHV and specific energy consumption of <39 kWh/kg H2 in a market-representative relevant environment;
  • Make SOE technology a suitable path for cheap green hydrogen production in places where both renewable heat and electricity are available and without a waste steam supply (e.g. from industry);
  • Efficient operation strategy of SOE coupled with two RES (electricity and heat) for facilitating RES integration in the grid and grid balancing.

The successful achievement of the project should:

  • Set the ground for efficient concepts of hydrogen production from renewable sources directed to sector coupling between electric and gas grids, involving SOE;
  • Unlock new market opportunities that shall act as an additional driver for scaling-up the European SOE technology and contribute to further reduce CAPEX;
  • It is expected that the deployment of RES, particularly solar thermal solutions, will leverage from the results of the project.

The conditions related to this topic are provided in the chapter 3.3 of the FCH2 JU 2020 Annual Work Plan and in the General Annexes to the Horizon 2020 Work Programme 2018– 2020 which apply mutatis mutandis.