Hydrogen has one characteristic that cannot be ignored: this ultralight gas (approximately 11 times lighter than the air we breathe) occupies a much larger volume than the other gases under normal atmospheric pressure. Indeed, to store 1 kg of hydrogen, you need a volume of about 11 m3. Given that this quantity can allow a hydrogen powered vehicle to travel 100 km, it is easy to see why storing it in its natural form is so complicated. We therefore need considerable technical resources to be brought into play to increase its density and reduce the size of storage facilities. These days, hydrogen can be compressed to 700 bar pressure, or 350 bar for transport.
A number of methods for hydrogen storage in the form of gas at high pressure are possible:
in tanks or cylinders allowing hydrogen to be transported by lorry,
in service stations and storage tanks on hydrogen vehicles, where it will then be used to supply a hydrogen fuel cell, allowing the generation of electricity,
in massive underground storage facilities.
It is also possible to store hydrogen in liquid form, cooling it to a very low temperature. The liquefaction of hydrogen reduces its volume further. However, this more expensive and complex method is only used today for specific uses such as the storage of liquid hydrogen in rocket fuel tanks.
In addition, studies are also under way on the transport and storage of hydrogen in the form of ammonia.
Hydrogen can be used to store electricity, helping to compensate for the overproduction of renewable energy (solar, wind etc.) at certain times and its inadequacy at others. Indeed, the production of solar or wind power is reliant on natural elements and therefore cannot be dispatched according to consumption. It is therefore necessary to be able to store the surplus electricity when production is higher than consumption. Since electricity cannot be stored in large quantities over a long period, the solution is to convert it into hydrogen.
Thus the Power-to-Gas process, which we have been studying for a number of years as part of the Jupiter 1000 project with GRTgaz, consists in producing hydrogen by the electrolysis of water, from renewable electricity. It is then possible to store the hydrogen, to inject it into the gas transport grid, or convert it into synthetic methane by reacting it with CO2. This Power-to-Gas chain can thus be used as a response to the problems of modularity, high fluctuation and storage of renewable electricity. This is an essential component when building multi-energy grids.
First of all, we are developing a Power-to-Power project, allowing the bulk storage of hydrogen in a salt cavern. Its principle:
To produce hydrogen by electrolysis using surplus electricity,
the hydrogen is stored in a geological storage space,
that stored energy is then returned when the grid needs it.
This HyGéo pilot project is being run by us in partnership with Hydrogène de France (HDF) and the Bureau de Recherches Géologiques et Minières (French Geological and Mining Research Bureau, BRGM) to develop solutions for the large scale storage of hydrogen for multiple applications.
This project is also in line with the Multiannual Energy Plan (MEP), with its encouragement to examine the benefit of re-using salt caverns for storing hydrogen. HyGéo has been certificated by Pôle Avenia, the only French competitive cluster for the underground energy sector.
Furthermore, in our desire to be proactive and offer solutions to the problems of hydrogen storage, we are committed to the RINGS project. That process, in partnership with the University of Pau and the Pays d’Adour, is aimed at studying what impact the integration of hydrogen will have on our aquifer storage infrastructures.