German pilot project proves hydrogen can be stored underground in a salt cavern

German pilot project proves hydrogen can be stored underground in a salt cavern

STORAG ETZEL and Gasunie finished filling 2 converted salt caverns at the Etzel gas storage site in Lower Saxony, Germany, with about 90 tonnes of hydrogen in mid March 2026. A salt cavern is an underground space hollowed out of a solid salt deposit, more than 1 kilometer down, and this cavern field has held natural gas for decades. The pilot project, named H2CAST Etzel, set out to answer 1 question, can a cavern built and run for natural gas hold pure hydrogen underground without losing it. That question matters beyond this 1 site, since Germany is planning a national hydrogen pipeline network, and underground storage at this scale had not yet been proven there.

The hydrogen arrives compressed harder than it is ever stored

Hydrogen reached the caverns by truck trailer at pressures of up to 300 bar, a unit that measures how hard a gas is compressed. Once underground it is held at a lower maximum pressure, 170 bar, through a production pipe that runs about 1 kilometer down into the cavern. It took 200 truck trailer loads to complete the fill. In their own announcement of the completion, STORAG ETZEL and Gasunie state that trailer and station availability above 200 bar was severely limited when filling began at the end of 2024, forcing deliveries from as far as 1,000 kilometers away, before market conditions eased enough later on to source hydrogen closer to Etzel.

Following the conversion of the caverns and continuous monitoring of tightness and integrity, another important milestone has been achieved.

Carsten Reekers, project manager at STORAG ETZEL. Source 1.

One supplier accounts for most of the fill

Filling began at the end of 2024, was announced publicly on January 20, 2025, and finished on March 26, 2026, when the project emptied its 200th delivery trailer. An earlier research phase named H2CAST Ready ran from February 2022 through December 2024, funded by the Lower Saxony state ministry for the environment, energy and climate protection, and appears to be the work that led into this fill, though the project does not spell out how the 2 names connect. The German Aerospace Center, an independent research institute and a named partner on that earlier phase, confirms the same 2 cavern count and the same more than 1 kilometer cavern depth, an independent check on the numbers STORAG ETZEL and Gasunie state about their own project.

1 supplier, Plug Power, delivered 44.5 metric tons of hydrogen to the project between April and August 2025 from a plant in Werlte, Germany, using pressurized containers rated at 350 to 380 bar. Plug Power has since signed a new contract for 35 more metric tons. Added together, those 2 figures account for about 88% of the full 90 tonne fill, a MAOWCE calculation, not a figure either company states directly.

Gasunie is confident that together with our employees and partners we will master this next step as a team.

Eddy Kuperus, business development manager hydrogen storage at Gasunie. Source 1.

The next phase of the project is building the above ground equipment needed to purify, compress and measure the hydrogen once it is drawn back out. STORAG ETZEL and Gasunie have already contracted equipment supplier Burckhardt Compression for a high pressure, oil free hydrogen compressor with a digital monitoring system named UP Detect. First tests of that equipment were expected later in 2026, as the plan stood in March 2026, though nothing published since confirms whether they started.