Photovoltaic plant
Solar power production
Concentrating Solar System
Solar heat production
Power supply
When renewable power is available, the electrolyzer is operated with steam generated from the heat storage system
Power grid
Green hydrogen is used for grid balancing
Thermal Energy Storage System
Solar heat storage and "on-demand" steam generation
Solid Oxide Electrolyser
Green hydrogen production from steam and (renewable) power
Gas grid
Green hydrogen is injected in the gas grid
Chemical industry
Green hydrogen is used as feedstock for ammonia production


The concept of Prometeo is based on the optimization of a Solid Oxide Electrolyser with renewable electricity (from PV, wind or excess grid power) and heat (from Concentrating Solar or Power-to-Heat systems)

The primary heat source is combined with a Thermal Energy Storage (TES) system to supply heat “on-demand”, whenever power is available. Power will be supplied either through a PV plant and/or from the grid during off-peak hours.

The Concentrating Solar plant will collect solar radiation with a Heat Transfer Fluid (HTF, thermal oil) and store the heat in a TES. Depending on the CS technology, the solar heat will be collected and stored up to 400°C (in case of thermal oil) or up to 565°C (in case of a binary Molten Salt mixtures called “Solar Salt”).

Since the SOE requires super-heated steam at a temperature of at least 150°C, the prototype will use a CS technology using mineral thermal oils as HTF up to 310°C. In this case, either linear Fresnel or parabolic Trough collectors can be applied.

The HTF from the CS (or PtH) system may fluctuate in temperature and flow rate. However, during sunny hours the heat will be transferred to the TES system installed in the SOE container. The TES will transfer the heat to the Steam Generator (SG) with the required rate. Therefore, the integrated TES-SG will overcome the fluctuation of renewable heat sources.

End-users will play a key role in Prometeo.
They will provide input for the scaling-up of the prototype to industrial use-cases.

For each use case, the hydrogen production costs will be determined and compared to conventional technologies, such as hydrogen production by steam reforming (for industrial applications), electric batteries (for power storage, grid balancing) and other Power-to-Gas options (gas grid injection).

Chemical industry

Stamicarbon, the Netherlands

The fertilizer industry is one of the largest consumers of fossil fuel. The PROMETEO prototype will be designed to produce renewable hydrogen for the production of “green ammonia”. This aims to reduce the C2 emissions involved in the production of fertilizers.

Gas industry

SNAM, Italy

The gas industry is looking for innovative power-to-gas solutions. The PROMETEO prototype will include downstream requirements for the production of renewable hydrogen to be injected in the gas grid together with methane for different uses.

Energy industry

Capital Energy, Spain

The energy industry needs storage solutions for the efficient use of renewable energy. PROMETEO will be designed for integration in the electricity grid by using substations for buffering peaks of renewable energy.