H2SALT: Technological Breakthoughts at the Cutting Edge of Underground Hydrogen Storage

The H2SALT project is a strategic initiative co-financed by the Recovery, Transformation and Resilience Plan and the European Union – Next Generation EU, whose main objective is to research and develop innovative technological solutions for the underground storage of hydrogen in salt caverns. This project is essential for moving towards a hydrogen-based economy, a key strategy for the energy future and the decarbonisation of various industrial sectors.

Hydrogen presents the challenge of its low volumetric density, which complicates its efficient storage on a large scale. Currently, underground hydrogen storage technology is not developed at the national or European level, and there are no locations in use for this purpose in Europe. Salt caverns emerge as a promising high capacity, low-cost solution for the efficient, safe and cost-effective mass storage of hydrogen. The project aims to boost the technological maturity (TRL) of this solution to at least TRL 4.

The main objective of H2SALT is to develop an integrated system for hydrogen storage in a salt cavern. This includes structural and gas behaviour analysis in the cavern, the development of tubular products for injection and extraction, the implementation of auxiliary installations for gas treatment, and the definition of a specific business model. In addition, two storage facilities of around 575 GWh are planned in the Cantabrian-Basque basin, after characterising the salt formations on the Iberian Peninsula to identify optimal locations.

To achieve these objectives, the project is structured in five main lines of work: research into the geological structure and behaviour of H2 infrastructures, definition of design parameters and validation of tubular injection and extraction systems, development and validation of designs for gas treatment and preparation, creation of a technical-economic model, and communication and dissemination of results.

H2SALT is the result of the collaboration between a Basque consortium led by TEAM INGENIERÍA Y CONSULTORÍA S.L., and includes TUBACEX TUBOS INOXIDABLES S.A.U. (TTI), TUBOS REUNIDOS GROUP, S.L.U., TAMOIN S.L.U., IBERDROLA CLIENTES S.A.U., BASQUE ENERGY CLUSTER and SIDEREX. It also has the contribution of TECNALIA RESEARCH & INNOVATION and TUBACEX INNOVACIÓN, as well as experts from the Geological and Mining Institute of Spain (IGME) of the CSIC.

Detailed Technological Advances: Milestones in Geological and Materials Studies

The H2SALT project has made significant progress in its lines of research, addressing the technical challenges identified.

Geological studies: Unveiling the potential of the subsoil, one of the first and crucial steps has been the analysis of the data associated with the approximately 800 deep boreholes carried out on the peninsula between 1940 and 2010, samples of which are kept in the IGME’s Lithotheque in Cordoba. This task has made it possible to identify sites with saline levels and to characterise the different salt layers, their thickness and arrangement at depth, as well as other relevant geological parameters.

In the field of characterisation of the salt formations, fundamental composition tests (mineral identification, chemical analysis) and physical properties (dissolution and geomechanical tests) have been carried out on the existing samples. These initial studies are essential to understand the intrinsic characteristics of the salt rock.

Following this characterisation, the focus now turns to hydrogen-salt interaction testing, which involves simulating the most critical storage conditions. Hydrogen permeability studies are being carried out in salt formations using the differential pressure method. After a period of time, the pressure in each of the chambers is measured and the permeability of the sample is determined. Complementarily, the reactivity of hydrogen with the materials in the cavern is investigated by introducing pure hydrogen into a reactor that simulates storage conditions and analysing the impurities formed in the gas extracted at different times using gas chromatography. These studies are vital to predict the behaviour and evolution of the gas over time, including possible leaks or reactions.

The data obtained from these tests are fundamental for developing a characterisation model of the salt formations in different locations in Spain, evaluating their viability for storing hydrogen and their behaviour in contact with these new gases and fluids generated in the cavern.

Materials Research

Ensuring integrity in extreme conditions, materials research in another key area of progress. Knowledge already exists on hydrogen embrittlement mechanisms and their relationship with metallurgical variables and the level of mechanical strength of materials. To further research in this area, H2SALT is developing and validating tubular system designs for hydrogen injection and extraction under cavern conditions.

Representative tube samples have been manufactured at Tubacex and Tubos Reunidos, using different chemical compositions and levels of mechanical strength, including austenitic stainless steel, duplex, nickel-based alloys, and carbon steels. The combination of dimensional ranges between the two companies makes it possible to cover the majority of dimensional and material needs.

The essence of these materials tests lies in testing their most critical state in order to analyse them under the most adverse conditions. To this end, specifically designed laboratory tests are being carried out to simulate the real service conditions of the tubular systems in the salt cavern, including the presence of brine and hydrogen gas flow at high pressure, both inside and outside the system. They are carried out:

• SSRT (Slow Strain Rate Test) in an autoclave containing brine and H2S in solution.
• Electrochemical permeation tests to determine the hydrogen flow through metal surfaces and to estimate the amount of hydrogen trapped.
• Tests under constant load of deformation in an autoclave in the presence of hydrogen to evaluate crack propagation in the material.

These sensitivity and metallographic characterisation studies are essential to select the best performing material and condition, enabling the design of an efficient and safe injection and extraction system throughout its lifetime.

Systems and Business Model Design

The project has defined specifications and requirements for tubular systems, control systems and compressors, as well as for auxiliary hydrogen injection and extraction facilities. Key parameters for hydrogen production plants dedicated to industrial applications have been established. In addition, the conceptual design of a salt cavern has been initiated and work is underway on a technical-economic model (LCOS – Levelized Cost od Storage) for salt caverns, focused on their use as complementary storage for industrial plants using renewable hydrogen.

H2SALT has also defined and implemented a strategic communication plan aimed at strengthening its positioning in the international field of green hydrogen. This plan includes the development of a coherent corporate identity, the creation of its official website (https://h2saltproject.com/) as a central platform for technical and scientific dissemination, as well as the production of a promotional video to reinforce its visibility. In addition, the project has had an active presence at strategic international events, such as REIF Fukushima 2023 and the World Hydrogen Summit & Exhibition Rotterdam 2024, positioning itself as an emerging benchmark in the field of green hydrogen at global level.

The success od H2SALT promises to consolidate underground hydrogen storage as a viable solution, improving the competitiveness of national companies, boosting new lines of business and generating quality employment, contributing to the objectives of decarbonisation and sustainability. This will strengthen Spain´s technological capacity, specially in the Basque Country, to become a benchmark in the renewable hydrogen value chain.