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SOL

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

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.

Synlight can produce up to 10,000 times the concentration of natural sunlight. Source: DLR

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 convert water into steam by heating, 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.

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.

Solar steam generator from the Institute of Future Fuels. Source: DLR

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.

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

GALACTICA: Test environment for large SOEC modules from the Institute of Engineering Thermodynamics.
Source: DLR