CO₂-neutral fuels | Hydrogen as energy carrier


Efficient production of green hydrogen through solar heat-assisted solid oxide cell electrolysis

Duration: 1.1.2020 – 30.6.2024

In the SOL research project, researchers from the DLR Institutes of Future Fuels and of Engineering Thermodynamics are investigating the coupling of concentrated sunlight with a solid oxide electrolysis cell (SOEC). The resulting new process is so interesting because it could produce green hydrogen or synthesis gas with the highest efficiencies on a multi-megawatt scale. Especially for industries with high CO2 emissions, such as the fuel, steel and cement industries, the process could be an interesting option to reduce CO2 emissions.

Solid oxide cell electrolysis (SOEC) saves about 15 percent electrical energy

In water electrolysis, electrical energy splits water into its elements hydrogen and oxygen. Among the electrolysis technologies, the solid oxide electrolyzer cell (SOEC) has the potential for the highest efficiency. Compared to the already established electrolysis processes, such as alkaline electrolysis (AEL) and proton exchange membrane electrolysis (PEMEL), about 15 percent of the energy to be supplied electrically can be saved. This is due, on the one hand, to the high operating temperature of the SOEC of 700 to 1000 degrees Celsius, at which the reaction can take place faster than at lower temperatures. The high temperatures, water is used as steam, which is split into oxygen and hydrogen directly in the SOEC. Part of the total energy required for the energy-intensive splitting of the hydrogen from the water can also be supplied by thermal processes by evaporating water.

At DLR's Synlight research facility, the world's largest facility for experiments with artificial sunlight, researchers use concentrated sunlight to generate water vapour for a SOEC module. To do this, they irradiate a solar radiation receiver with a subset of Synlight's total of 121 high-power lamps, which can be coupled with a solid oxide cell electrolysis (SOEC) unit. Water is evaporated and superheated in the solar radiation receiver. Under real conditions, the SOEC module would now convert the steam into hydrogen and oxygen. The researchers in Jülich only simulate this process step virtually. The Institute of Engineering Thermodynamics uses the results of the tests in Synlight for the experimental investigation of a SOEC unit at DLR Stuttgart.

SOEC module: Pure water electrolysis and co-electrolysis

In addition to pure water electrolysis, the SOEC can also perform so-called co-electrolysis, a simultaneous electrolysis of water and carbon dioxide. The synthesis gas produced is a necessary base material for synthetic hydrocarbons, such as fuels and basic chemicals.

Potential for further uses goes beyond pure hydrogen production

Due to the low technology readiness level (TRL) of SOEC, it is not yet possible to combine solar thermal energy with SOEC technology on an industrial scale. The researchers want to use the results and experience from the SOL project to demonstrate in a follow-up project that a solar thermal plant can be coupled with a solid oxide electrolyser with more than 50 electrical kilowatts (kWel). They are developing system concepts for this in the first phase of SOL. These will be verified and improved in the course of the project by data obtained from the experiments taking place at Synlight.

Test environment for large SOEC modules from the Institute of Engineering Thermodynamics

The work in the SOL project is a preparatory step towards energy plants on an electrical megawatt scale that can produce hydrogen or syngas.


Solar Heat Supported Solid Oxide Cell Electrolysis (SOL)

Project Duration

1.1.2020 - 30.6.2024

Project participants

  • Institute of Future Fuels
  • Institute of Engineering Thermodynamics


Basic funding of the DLR


Nathalie Monnerie

Head of Department
German Aerospace Center (DLR)
Institute of Future Fuels
Evaluation of solar production processes
Linder Höhe, 51147 Köln-Porz

Dr.-Ing. Marc Heddrich

German Aerospace Center (DLR)
Institute of Engineering Thermodynamics
Pfaffenwaldring 38-40, 70569 Stuttgart