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Storing electricity under the sea: a reality! The H2-O project represents an alternative to electricity storage.

Type Non-profit project
Founded 2020
Company Size 1
Member Type
Headquarters 75007 Paris, France
Social network


The H2-O project represents an alternative to electricity storage. The aim is to compensate for the intermittency of renewable energies. by storing and producing offshore green electricity from green hydrogen. Surpluses from renewable energies such as wind, photovoltaic or even nuclear power, while waiting for these surpluses, will be converted into green hydrogen through an electrolyser immersed in the sea at great depths. The green hydrogen released will then be stored in very large-capacity tanks, themselves immersed in the immediate vicinity of the electrolyser. This stored hydrogen, under pressure at sea, in very cheap concrete tanks will then be transformed locally into green electricity via a fuel cell or a hydrogen turbine coupled to a generator. The green electricity thus produced will be redistributed via the same network according to needs and peak hours. H2-O has a triple objective: 1 - To improve the productivity of the complete cycle by 30%. - Sea water, one of the raw materials for hydrogen, is available in abundance on site, free of charge and requires no pumping, transport or pressurisation (+2%). The efficiency (+3%) of electrolysis is favoured by the water pressure (20 bars at minus 200 metres). The very energy-intensive phases of compression, decompression (+15%) to reach 700 bars or liquefaction (+35%) of the stored hydrogen are therefore also eliminated; the pressure will depend on the depth of the installations and will be perfectly constant (20 bars at a depth of 200 metres). The conversion of hydrogen into electricity via a fuel cell or a hydrogen turbine coupled to a generator will be done in the immediate vicinity of the tanks in order to optimise efficiency and minimise line losses (+2%). The transport of electricity over long distances remains simpler, safer, faster and more economical than that of hydrogen at equal power, especially if the underwater cable linking the offshore wind turbine to the shore is reused. 16.000 m3 of hydrogen stored at a depth of 200 metres would allow the production of one gigawatt whatever the hour. 2 - Designing very large-capacity tanks. The construction of these concrete tanks lined with a polymer liner will make it possible to considerably reduce their prices and increase their volumes. Submerged tanks are not subject to any pressure other than the Archimedes' thrust since they are open to the outside (principle of an inverted bell). The volume of the tanks is therefore not limited, unlike pressurised hydrogen tanks made of carbon fibres or isothermal tanks for liquid hydrogen at -163°C. Safety against the risk of explosion and fire will therefore be enhanced by the immersion and constant temperature of the tanks (17.5° at a depth of 200 metres). 3 - Respect the environment: - The immersion of the tanks will eliminate all visual pollution. The rockfill of the reservoirs, intended to compensate for the Archimedes' thrust, should favour the development of underwater fauna and flora (reserve effect, reef effect) and allow a solid anchoring of the floating wind turbines. The co-produced oxygen could also be used for the production of chlorine, salt, soda and their derivatives, as well as on site in fish farms for the oxygenation of the aquatic environment which favours fish growth. The production, storage and instantaneous conversion of green hydrogen into green electricity should make it possible to reduce greenhouse gas emissions, compensate for the intermittency of renewable energies and store large quantities of "green electricity" offshore at a low cost. 4 - The consortium Given the scale of the project, it seems necessary to create a consortium that can bring together the technical skills and financial capacities of several companies: "". (H2-O: symbolizes the Offshore Separation of Hydrogen and Oxygen from Water). Philippe Géraudel
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Headquarters 75007 Paris, France

SDG’s of application

The Sustainable Development Goals are a call to action to end poverty, protect the planet and ensure peace and prosperity everywhere.
Clean water and sanitation
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Affordable and clean energy
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Industry, innovation and infrastructure
SDG 9 icon
SDG 11
Sustainable cities and communities
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SDG 12
Responsible consumption and production
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