Another milestone reached

After the successful completion of the conversion and leak tests with hydrogen of two caverns in 2024, STORAG ETZEL began storing the first quantities of a total of 90 tons of hydrogen at the turn of the year. The storage is part of the research and development project "H2CAST Etzel", which is developing the technical implementation of hydrogen storage in salt caverns. "This marks another milestone in the conversion of existing caverns for hydrogen storage in Etzel," says Carsten Reekers, project manager of the research and development project "H2CAST Etzel".

The gaseous hydrogen, delivered by truck trailers at a pressure of 300 bar, displaces the brine from the caverns when stored via the cavern head and borehole piping suitable for hydrogen. The brine is transported away via the STORAG ETZEL brine plant.

"After expected teething problems in the procurement of hydrogen - you can see that the hydrogen market is still in its infancy - now, as of the end of January, several tons are safely stored underground at a maximum pressure of 170 bar," Reekers continued. "We are proud of what we have achieved so far and have now shown that the existing facilities in the Etzel cavern field are suitable for hydrogen storage. Our specialist colleagues in the gas operation have the process steps for hydrogen filling well under control."

STORAG Etzel is continuously pursuing its hydrogen storage strategy. The Etzel caverns are scalable and flexible, meaning that existing underground gas and oil storage facilities can be quickly converted for the use of hydrogen. "We'll be ready to go when the H2 market is," says Reekers.

In 2025, STORAG Etzel and its project partners still have a number of challenging milestones ahead of them in the H2CAST project. The focus will then be on the construction and commissioning of the hydrogen purification plants. Different processes and their efficiency are to be tested. Preparations for this are already underway. "We are very confident that we will also succeed in this step as a team effort with our employees and partners," Reekers continues. "It is an advantage that we can operate and maintain the plants with specialist staff from our existing organization. Our decades of experience in underground storage helps us here," Reekers concludes.

Due to the lack of an H2 pipeline connection, the hydrogen still has to be delivered to Etzel by truck. Up to three truckloads of hydrogen per week will arrive in Etzel until the summer. A total of around 200 truck trailer loads are required to fill the roof area of the caverns with hydrogen. As early as the beginning of 2024, small quantities of hydrogen were introduced into the caverns under maximum gas pressure as part of upstream tests to demonstrate the hydrogen-tightness of the caverns and drilling equipment. In the future, the Etzel site will be supplied with hydrogen by pipeline after being connected to the already approved H2 "core network".

The storage of hydrogen has been approved by the supervisory authority, the State Office for Mining, Energy and Geology (LBEG).

About H ₂ CAST Etzel

The H2CAST Etzel project aims to demonstrate the feasibility of large-volume underground storage of hydrogen and to prove the suitability of the salt caverns in Etzel for hydrogen storage. The operational operation of hydrogen storage is being tested and will serve to establish a hydrogen industry in Germany and Europe. H2CAST stands for " H2 CAvern Storage T ransition ", i.e. the conversion of the existing large-volume caverns and technical facilities in Etzel for the future storage of hydrogen as a building block of a renewable and thus ecologically sustainable energy system.

The project is funded by the State of Lower Saxony and the Federal Ministry for Economic Affairs and Climate Protection (BMWK).

Review: Technical progress of work at H ₂ CAST so far

The H2CAST project envisaged that a so-called production pipe would be installed in one of the access boreholes of the caverns, through which hydrogen would be stored and discharged. A sealing element, a so-called "packer", at the lower end of the production pipe seals these welded pipes from the outer pipe cemented to the rock.

In between, an annular space a few centimeters wide, comparable to a double-walled tank, was created over the hydrogen production pipework that runs to a depth of about 1 km. This annular space is filled with a liquid and forms a two-barrier system against the surrounding rock. A special monitoring system can collect and measure even very small amounts of hydrogen in the annular space, should it diffuse through the seals.

New cavern head was built

At the end of the borehole, a further developed cavern head from Hartmann Valves, manufactured in Lower Saxony, was installed, which has additional monitoring options.

installation of a brine pendulum train

Another pipe string has been installed in the production pipe tour as a brine pendulum string with a smaller diameter. This can now be used to bring brine displaced during the initial filling of the cavern with hydrogen to the surface. A special feature is that this process can also be reversed in the H2CAST project. This means that brine from the cavern field can be pumped back into the caverns until they are almost completely filled with brine again. The displaced hydrogen is transferred to one of the two caverns, which acts as a "hydrogen pipeline" in this operating mode. By pumping in or conveying brine, the usable storage volume (working gas volume) for hydrogen can be continuously varied and the hydrogen gas remaining in the cavern to maintain the support pressure, the so-called "cushion gas", can be minimized. In the subsequent test operation, this can be used, among other things, to test different pressure levels in the cavern, as can be expected in the future hydrogen economy, and H2 purification.

Proven and safe technology from natural gas storage is used

The components largely rely on suitable technology that is already available on the market and has proven itself in the storage of natural gas over decades. The individual elements are tested here in real operation with hydrogen; they were previously examined in the laboratory by specialists under artificial hydrogen loading for their H2 compatibility.

Goals of the later H ₂ demonstration operation

The H2CAST demonstration operation is intended to demonstrate long-term suitability under real operating conditions. "In particular, we want to show that the existing systems in the Etzel cavern field are suitable for hydrogen storage without the need to develop new components. This makes enormous economic sense in a Germany-wide market ramp-up, without any restrictions on system safety," says Carsten Reekers, head of the H2CAST joint project.

Praise for the project partners

STORAG ETZEL would like to express its sincere thanks to H2CAST’s partner companies and institutions, whose hard work and commitment have enabled them to successfully achieve the project goals through teamwork.

Further schedule of work

Following filling with the first tranche of around 45 tonnes of hydrogen, the caverns will be pressurised with the second tranche of 45 tonnes, bringing the total to 90 tonnes of hydrogen, up to the highest permissible pressure. Construction of an above-ground test facility will begin in spring. This is expected to enable gas storage operations from winter 2025, including the work steps of compression, gas drying and cleaning, pressure control and quantity and quality measurement.

Project results are published

The Etzel site is to be "H2-ready" by 2026. Subsequently, the research results and technical standards of the H2CAST Etzel flagship project, funded by the state of Lower Saxony and the federal government, will be made available to other hydrogen cavern sites in the region, thus serving as a "blueprint" for the conversion of caverns for future hydrogen storage in Germany.

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