Presented as the energy source for a clean future, renewable hydrogen can finally boast to be a viable alternative to fossil energy. Technological solutions are improving in terms of production and consumption, the idea of a hydrogen economy is emancipating from think tanks to become part of national energy programmes. Recent studies confirm that green hydrogen could supply up to 25% of the world’s energy needs by 2050.
However, higher demand also means there is going to be a need for increased storage capacity. Hydrogen can be stored physically using a storage method which has already proven its worth and in which interest is growing as demand is increasing: salt caverns.
HOW DOES IT WORK?
Salt caverns are artificial cavities which are created in geological salt deposits. Future caverns are generally located at a depth of 500 to 1,500 metres. They are three times higher than the Arc de Triomphe. To create such a cavern, it is first necessary to drill into the salt. The second stage consists in injecting water into the salt to dissolve it. The resulting brine (water mixed with salt) is extracted and leaves room for a large, tight cavern where hydrogen can be stored under pressure.
Pros : hydrogen storage in salt caverns has a number of advantages.
- Indispensable chain link: Underground hydrogen storage will enable us to support the development of the renewable hydrogen sector by ensuring security of renewable hydrogen supply for all clients and new clients.
- Flexibility: Salt cavern offer flexibility regarding their injection and withdrawal cycles to respond to the needs of the hydrogen market. Depending on their depth, salt caverns may be operated at pressures up to 200 bars and allowing for large-volume hydrogen storage (from 9 to 6,000 tons).
- Safety: Due to their tightness, salt caverns allow for safe storage of large quantities of hydrogen under pressure. The first hydrogen storage cavern, which was built in the United Kingdom in 1972, is still in service.
- Resilience: There are salt caverns available in France and Europe which could be quickly converted to hydrogen storage. Storengy is the largest storage operator in France and already developing underground H2 storage projects in order to anticipate the sector’s needs and adapt its infrastructure through the HyPSTER and HYGREEN Provence projects.
Cons :
- A concept to be confirmed on an industrial scale: Today, there are 4 hydrogen storage sites in salt caverns existing in the world. These storage facilities are strategic reserves for the use in hydrocarbon refineries. The frequencies and quantities used are low. For energy uses, injection and withdrawal cycles will have to be quicker and offer greater amplitude. Experimental evaluations of the consequences of such more intensive modes of operation will enable us to confirm the concept and viability of future salt cavern hydrogen storage projects.
- Purity of the hydrogen: Another potential problem linked to the operation of a cavern with hydrogen is the development of the composition of hydrogen contained in the cavern. If the hydrogen is expected to absorb moisture (as it is the case for natural gas), it is also possible that bacteriological and chemical reactions take place, thus transforming some of the hydrogen and modifying the overall composition of the gas. Specific treatment to purify the hydrogen at the cavern outlet could thus be necessary (in addition to dehydration).
- Geographical scarcity: The main issue with salt caverns is the relative scarcity of salt deposits. Although there are currently about 2,000 caverns in North America, most of which are used to store different energy vectors, most of the hydrogen projects to come will be located in a handful of European countries which have salt deposits, such as Germany, the Netherlands, Denmark and, to a lesser degree, France, Poland, the United Kingdom…
Upcoming projects and innovations
- 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.
ENGIE EYE
For the year 2050, H2 storage needs reaching 8 TWh have been estimated for France (source: GIE). Within the framework of its 2ß45 Net Zero Carbon strategy, ENGIE ambitions to develop 1 TWh of underground hydrogen storage capacity in salt caverns by the year 2030.
- Storengy, a subsidiary of ENGIE, and its partners, are currently working on the HyPSTER project, the first large-scale underground hydrogen storage demonstrator in salt caverns.
With its 13-million-euro budget the HyPSTER project (“Hydrogen Pilot Storage for large Ecosystem Replication”) has been nominated for the 2021 Innovation Trophies and will be implemented in the region of Etrez, in southern France, which is already known for natural gas storage in salt caverns.
| 
|
A 1-MW electrolyser supplied with renewable energy will produce 400 kg of hydrogen/day to be stored, to finally reach 44 tons of hydrogen to be stored in total – which is enough to fill the tanks of 1,760 fuel cell busses.
Due to its location, Etrez is a strategic area for the development of green hydrogen: the region is located close to large-scale projects such as the Zero Emission Valley in the region of Auvergne-Rhône-Alpes, as well as hydrogen production and distribution to be built in the region of Bourgogne-Franche-Comté.
