How does underground hydrogen storage work?

1 April, 2024

When we talk about green or renewable hydrogen, we are referring to a versatile energy carrier that enables the storage and transport of energy and makes it available whenever and wherever it is needed. This characteristic makes it a key element that contributes to achieving the European energy supply, decarbonisation and environmental objectives for 2030 and 2050.

Green hydrogen enables the use of surplus electricity generated from renewable sources like solar or wind. Therefore, developing large-scale storage methods is crucial for ensuring energy supply stability during times of peak demand.

Compared to other gases, hydrogen is an element with a lower molecular weight. This makes it very light, as a result the tanks require the right materials in order to prevent leaks, withstand pressure and store it properly, whether in liquid or in gaseous form.

Methods of storing green hydrogen on a large scale need to be developed to support the stability of the energy supply

Features of underground hydrogen storage facilities

Underground storage of hydrogen represents one of the most promising prospects. Similar to the existing practise for natural gas, this method uses large cavities that can hold significant quantities to ensure a supply over longer periods of time. The design and operation of hydrogen storage would be very similar to that of underground natural gas storage. Additionally, leveraging some of the existing infrastructure could present a competitive advantage in terms of both time and cost.

Saline aquifers, mines, or depleted gas and oil fields are especially suitable options due to their capacity and the physical properties that enable the safe and efficient storage of this energy carrier.

When hydrogen is stored underground, a portion of it always remains in the cavity—referred to as “cushion gas”—to maintain the minimum pressure necessary for its stability. The rest of the hydrogen—the “working gas”—can be extracted as needed for its transportation and consumption.

Salt cavities for storing renewable hydrogen

In particular, salt caverns are a very efficient, safe and flexible storage option. These geological formations can hold large volumes. In addition, salt possesses natural sealing properties that counteract possible leaks and reduce the risk of contamination from impurities in the environment. Moreover, both the technical operation of such cavities and their cost are favourable aspects when compared with other alternativ

Another added value of salt caverns is the experience and technical expertise within the industry, as these caverns are similar to the ones currently used for natural gas storage, sharing comparable requirements regarding design, construction, and operational management. The primary differences are found in the compressors and hydrogen conditioning equipment that are installed on the surface

Salt caverns are a very efficient, safe and flexible storage option

Currently, there are more than 300 salt caverns in operation for natural gas storage in Europe, along with several pilot projects in France and Germany aimed at converting some of these into hydrogen storage facilities. According to a study by the International Journal of Hydrogen Energy, Europe has enough salt caverns to store, in theory, up to 84.8 petawatt hours (PWh) of hydrogen-based energy. A petawatt is 1015 watts.

Underground hydrogen storage projects

There are projects for underground hydrogen storage. The development and implementation of such systems will be greatly beneficial in aiding the decarbonisation of the economy:

In the Tees Valley (UK), a master plan has been launched proposing the use of a salt mine to store 1,000 tonnes of renewable hydrogen. This initiative is part of the Tees Valley Hydrogen Innovation Project (TVHIP), which will also feature a 30-kilometre hydrogen pipeline for distribution.

Hydrogen Cavern for Mobility is an underground storage facility for 100% pure hydrogen. It is located at a depth of 1,000 metres in a salt mine near Berlin and will be used to investigate the degree of purity of the hydrogen once it is extracted from the cavern.

-In Spain, two underground hydrogen storage projects have also been designated as Projects of Common Interest (PCIs). These are likely to be salt caverns, one located in Cantabria and the other in the Basque Country. Both are integral to the initial corridors of the Spanish hydrogen network.

The RINGS-H2 project, which has involved companies like Teréga, Storengy, Snam, and Enagás Transporte, used two reactors to replicate the unique subsurface conditions of two distinct storage sites over a six-month trial periodto analyse the effects of injecting hydrogen and biogas into the subsurface.

As renewable energies continue to replace fossil fuels, innovation and research will play a key role in solving challenges such as hydrogen storage. Underground storage of this energy carrier will undoubtedly contribute to the achievement of climate targets and the successful completion of the energy transition.