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Did You know ? 27/07/2021

H2 Underground: Salt Caverns As Hydrogen Storage Solution

While demand and production of hydrogen grow, underground storage appears as a sustainable and big-scale solution.

In the U.S., some 200 kilometers south of Salt Lake City, engineers are working on what will become the world’s largest storage facility for 1,000 megawatts

After decades of being hailed as the energy vector of the future, hydrogen is finally becoming a viable alternative to fossil fuels. A combination of improved technology, lower costs and extended infrastructure has pushed the idea of a hydrogen economy out of think tanks and onto national energy agendas. By 2050, studies suggest that green hydrogen could supply up to 25% of the world’s energy needs.

But with increasing demand also comes a need for greater storage capacity. Hydrogen can be stored physically as either a gas or a liquid. While storage of hydrogen as a gas typically requires high-pressure tanks, an old storage method is gaining traction as demand increases: underground salt caverns.


Salt caverns are artificial cavities in underground salt formations. These are created by drilling into the salt dome, typically 400-1,000 meters below the surface, and injecting the rock with water that dissolves the salt. The resulting brine is extracted, leaving a large cavity where hydrogen can be stored. While there are other methods for large-scale underground storage — such as exhausted oil and gas fields or aquifers (an underground layer of water-bearing permeable rock) — caverns have a number of advantages:


  • Robust As hydrogen has a very low volumetric energy density, the gas is typically compressed before storage. Depending on the depth, salt caverns can be operated with a pressure of up to 200 bar and thus allow for the storage of high volumes of gas.
  • Resilient Salt caverns are impervious to gases and the walls are resilient to reservoir degradation. For example, the first hydrogen cavern was constructed in the UK in 1972 and is still in operation today.
  • Clean Many of today’s applications, such as fuel-cell vehicles, require ultra-pure hydrogen. Salt caverns, which are almost completely hermetic, are very clean and bring a minimum risk of gas contamination by impurities.
  • Affordable Underground caverns remain comparably cheap to construct, with some studies suggesting a ten-fold cost advantage to aboveground tanks. In addition, there is very little exploration work required as many salt structures are already known from previous oil and gas as well as salt exploration.
  • Flexible The salt structures also allow for a lot of flexibility in injection and withdrawal cycles, which means they can even be used to cover daily demand peaks.


  • Lack of research As there is still a limited number of salt caves around the world in use for storing hydrogen, some researchers point to a need for more research of its viability. For example, caverns tend to close up over time, which is accelerated if regularly filled and emptied with gas.
  • Purity One potential issue that can arise is that humidity could be added during the creation of the cavity, which could undermine the purity of the gas.
  • Geographical scarcity The main known drawback of salt caverns is scarcity. While there are currently some 2,000 caverns in North America used to store various energy carriers, most upcoming projects are located in a handful of European countries with large salt deposit, like Germany, the UK, Ireland, France, the Netherlands, and Denmark. Otherwise, most other countries have minor or no deposits at all.


In the U.S., some 200 kilometers south of Salt Lake City, engineers are working on what will become the world’s largest storage facility for 1,000 megawatts of clean power, partly by storing hydrogen in underground salt caverns.

  • The Advanced Clean Energy Storage project, a joint venture between Mitsubishi Power and Magnum Development, will take excess power generated from hydroelectric, geothermal, solar and wind and electrolyse it into hydrogen for storage in the salt caverns, where it can later be used for power, industrial and transport applications.
  • Scheduled for operation by 2025, the first phase will provide 150,000 MWh of renewable power storage capacity — enough to power 150,000 households for one year.
  • The project was recently invited to apply for up to $595 million in loans from the US Department of Energy’s Loans Program Office. 

A government-funded German consortium of more than a 100 companies plans to build a salt cavern in Saxony-Anhalt with about 150,000 MWh of energy from wind power-generated hydrogen.

  • If the project is approved, the Hydrogen Power Storage and Solutions East Germany (HYPOS) could be continental Europe’s first hydrogen storage cavern.
  • More broadly, the project aims to produce green hydrogen on an industrial scale, as well as to build an extensive network of distributor networks and storage stations across Germany to make hydrogen available to all regions.


Spearheaded by ENGIE-subsidiary Storengy, a consortium of French companies have launched the first EU-funded project aiming to demonstrate large-scale underground storage of green hydrogen in salt caverns.

  • With a budget of €13 million, the HyPSTER project (Hydrogen Pilot Storage for large Ecosystem Replication) — a 2021 Innovation Trophy nominee — will take place in the southern French area of Etrez that is already used for natural gas storage in salt caverns.
  • Initially, a renewable-energy powered, 1-MW electrolyser will produce 400 kg of hydrogen per day to be stored, which will eventually be ramped up to 44 tons of total hydrogen storage — enough to meet the daily need of 1,760 fuel-cell buses.

Etrez is a strategic area for green-hydrogen development due to neighboring large-scale projects like the Zero Emission Valley in the Auvergne-Rhône-Alpes region, as well as the construction of hydrogen production and distribution stations in Burgundy-Franche-Comté.

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