Interview with Louis Londe, Technical Director at GeoStock

Hydrogen:
“The need for underground storage is huge to meet global ambitions”

Louis Londe has been working in the field of underground storage since 1990. He is currently technical director at Geostock. He has worked at Andra (Agence Nationale pour la Gestion des Déchets Radioactifs) where he was one of the technical directors of the Cigeo project. 

Why is there so much interest in underground hydrogen storage today?

Until now, hydrogen was mainly stored on the surface, in tanks or spheres, in pressurized or liquefied form at very low temperature (-253°C). This approach was suitable when hydrogen quantities were limited, although it posed a number of technical problems. The use of hydrogen as an energy carrier to decarbonize industry or for mobility implies storing much larger quantities. This will be possible thanks to underground storage, which makes very large volumes available. It is also a safer, more economical and more environmentally friendly approach (smaller footprint) than surface storage.

Is salt cavern storage a mature technology?

We know that salt cavern storage works for all kinds of products, including hydrogen. We are now trying to optimize the models that we have been using until now, for natural gas or for hydrogen. Today there are about 2000 salt caverns for storage. Six of them are or have been storing hydrogen.  The difference between the six existing salt caverns for hydrogen storage and those that we are trying to create today lies in the uses that we will make of the hydrogen. For example, for use in mobility, the hydrogen must be of a much higher quality and purity than the hydrogen used in refineries. The hydrogen will therefore have to be treated at the end. Another example: storing hydrogen to provide electrical energy is likely to involve more frequent injection/withdrawal cycles. 

Will salt cavern storage be preferred in the future?

This storage technique is indeed technically and financially interesting. Germany and France have salt in their subsurface, so they will probably use it. On the other hand, some northern European countries have no salt in their subsurface. Other options will have to be found. It is highly likely that regions with significant underground storage capacity will one day be able to offer services to those with less capacity through interconnected hub systems. But before this happens, each country will need to have its own underground reserves, and those without salt in their subsurface will have to resort to options other than salt caverns.

What are the other options for storing hydrogen?

It is possible to store hydrogen mixed with other gases (mainly methane) in natural porous media, i.e. structures capable of trapping gas molecules such as aquifers. It was in this type of natural porous rock that town gas (a mixture of methane, carbon dioxide and hydrogen) was stored 70 years ago. This is a technique that has been known for a long time. It would then be a matter of gradually increasing the percentage of hydrogen in the mixture as the demand for hydrogen increases. Pure hydrogen can also be stored in this type of tank. It is necessary to ensure that there is a 'cover' over the storage, i.e. an impermeable caprock, such as clay, which will prevent the gas from leaking into the surrounding rocks. 

What is the status of research into aquifer storage?

Geostock is coordinating Hystories, a project involving 17 European countries to study hydrogen storage in aquifers or depleted sites. In the United States, several projects are also being developed. But the Americans do not necessarily go through the pilot stage as in Europe. They are moving faster and the regulations are very favourable to them. They will probably have the first industrial projects.

Is it possible to store hydrogen in cavities created in the rock?

It is possible to store hydrogen in 'hard' rock, for example granite or limestone, in which horizontal galleries or vertical silos are dug. This type of rock cavity is already used to store propane and butane, sealed by groundwater back pressure. As hydrogen must be stored at high pressure, it is necessary to go down deep, to 1000 m or more, where the water table can act as a counter-pressure. Technically, this could be done, but the cost of this type of very deep storage would be astronomical.

When countries cannot use either salt caverns or porous rock storage, what are the alternatives?

For countries like Sweden, which do not have a suitable subsurface, there is one last technique: Lined Rock Cavern (LRC). This involves covering the wall of the rock cavity with a metal membrane to retain the hydrogen. This type of storage is still in the R&D stage. At Geostock, we are currently working on this concept. A pilot cavity of this type containing 100 m3 of hydrogen has just been built in Sweden. The lined mined cavities can be used as storage sites for pure hydrogen, in gaseous form at high pressure and in liquefied form at very low temperature. They can also accommodate ammonia (NH3), a molecule that provides a form in which hydrogen becomes easy to store and transport.

What are the dangers of hydrogen storage?

As with all gas storage projects, the main danger is leakage, which could lead to an explosion. Risk studies are carried out using hazard circles and extreme scenarios to anticipate and control the risks. With underground storage, however, accidents are rarer than with surface storage, because the stored product is far from people and far from oxygen. 

What will be the global storage needs by 2030?

A first analysis can be based on the "hydrogen plans" of the various governments in Europe and around the world, putting them together and playing with the assumptions. If we imagine, for example, that 5% of green hydrogen will be stored underground - which is a low estimate - we will need between 200 and 600 new or converted caverns worldwide by 2030. That's a colossal amount in 8 years! By way of comparison: there are currently 2,000 storage cavities in the world (for gas, oil, petrol, etc.), and it has taken 80 years to reach this value. Hydrogen storage capacities are currently far behind official announcements. The market for the creation or conversion of underground storage cavities for hydrogen is therefore huge.

Interview by Véronique Molénat