Carbon-free energy underground storage

Carbon-free energy storage is set to naturally play an increasing role in the energy transformation, contribute to the integration of intermittent renewable energies into energy networks, and reduce greenhouse gas emissions.

The solutions developed and proposed by Geostock for several decades, whether in salt caverns, porous media (aquifers and depleted fields) or in mined caverns, are particularly well adapted to the storage of carbon-free energy:

  • The storage of dihydrogen (H2), usually referred to as “hydrogen”, and its derivatives, ammonia (NH3), methanol (CH3OH), methane (CH4), etc.
  • Compressed air storage
  • Flow batteries (or “Redox/Flow “)
  • Heat storage
  • Underground pumped storage power stations

Hydrogen gas and compressed air storage in salt caverns have been used for several years in commercial applications.

Hydrogen storage

The underground storage of hydrogen can have several applications. Hydrogen can be stored for the purpose of returning electricity to the grid (power-to-power) or for the use of the hydrogen molecule for mobility or for industrial use as a substitute for fossil fuel.

Initially, hydrogen is stored in gaseous form. Hydrogen gas can be stored in a salt cavern, which is a mature technology. But it can also be stored in a porous medium (aquifer or depleted field) or in a lined mined cavern – technologies that are still under technical development or being demonstrated.

Hydrogen underground storage

Geostock is also working on solutions for storing hydrogen in ammonia or liquefied form.


Expected benefits:

  • Green energy storage: zero CO2 emission
  • Storage capacity from 10 GWh to several hundred GWh
  • Combined use (mobility, industry and electricity)
  • Solution for integrating intermittent renewable energies into energy networks

Our services:

  • Consulting, prospective and strategic studies
  • Site selection, investigation and design of underground storage
  • Drilling engineering and construction management services for underground storage
  • Facility operation and maintenance
  • Definition and optimisation of operational cycles, including thermodynamic simulations of hydrogen cavern behaviour
  • Complete management of the hydrogen storage project, from design to construction, including commissioning and start-up

Compressed air storage

Massive storage of compressed-air (CAES) in salt caverns is a competitive technology that can provide services to the power grid, including the integration of intermittent energies and peak consumption period demand. This solution can also be considered in mined caverns and porous media.

Compressed air can be stored either adiabatically (AA-CAES), by recovering and storing heat from air compression and releasing it when the air expands, or isothermally (I-CAES), without heat recovery. In the latter case, an energy source (natural gas or hydrogen) is required to heat the air as it expands to produce electricity.

Compressed air underground storage

Expected benefits:

  • Green energy storage: zero CO2 emissions (adiabatic CAES or isothermal CAES coupled with hydrogen) or low emissions (conventional isothermal CAES)
  • Energy efficiency of about 70% (adiabatic CAES)
  • Relatively low investment
  • Storage capacity of up to 1 GWh
  • Solution to intermittent energy integration and power grid issues

Our services:

  • Consulting, prospective and strategic studies
  • Site selection, investigation and design of underground storage in salt and mined caverns
  • Drilling engineering and construction management services for underground storage
  • Well architecture
  • Definition and optimisation of fast operational cycles
  • Project management, from design to commissioning and start-up

Other carbon-free energy storage solutions

Geostock develops innovative solutions for the underground storage of other carbon-free energies, such as high-capacity redox-flow batteries using salt caverns or mined caverns, underground pumped storage power stations and heat storage. These developments are made through internal R&D, as well as through participation in national and international collaborative research projects.

With almost 60 years of experience in the underground storage of hydrocarbons and more than 10 years of R&D and design studies on the storage of hydrogen and compressed air, Geostock is perfectly able to offer solutions to industrial companies seeking to actively contribute to the energy transition and with massive storage needs of carbon-free energy.

Come tell us about your project

Geostock provides a complete range of services covering the entire life cycle of an underground storage project.

Contact us

Cavité minée – Mined Roeck Cavern
Control room of operated site
Shalapa site operated by Geostock