Large scale underground hydrogen storage is expected to be of key importance to the future fossil-free energy system. It will provide crucial flexibility to overcome imbalances in sustainable hydrogen supply and demand.

Underground storage might lead to impurities in the hydrogen caused by the presence of hydrocarbon components, or by microbiological- and/or geochemical reactions in the cavern which could hamper the hydrogen quality criteria.

Gasunie is currently constructing the first of its kind hydrogen purification pilot plant in the H2CAST Etzel project. Two caverns are filled with 90 tons of hydrogen, the purification pilot plant including compressor reaches finalisation and the test program will start summer 2026. The first test results are expected in 2026, test results will give an insight into the quality of the hydrogen after storage and the efficiency of the treatment processes to bring hydrogen to required quality standards.

The H2CAST pilot project will provide knowledge of importance to possible future repurposing of existing caverns for hydrogen storage. During the operational phase, the facilities will provide insight into the efficiency of the different processes that will serve as input for future design of underground hydrogen storage facilities.