H2SALT Project: Underground hydrogen storage in salt caverns

The H2SALT project, in which Iberdrola Clientes — a company forming part of Iberdrola España — is participating, was completed on 1 March 2026 after more than three years of activity, establishing itself as a key initiative for the development of underground hydrogen storage in Spain.

Launched in 2023, H2SALT's main objective was to study the feasibility of hydrogen storage in salt caverns, one of the most efficient and cost-effective alternatives for storing large volumes of hydrogen and facilitating its subsequent distribution. This technology is strategic for driving the energy transition, as it enables better integration of renewable energy and promotes the decarbonisation of key industrial sectors.

Throughout the project the team addressed technical challenges associated with underground hydrogen storage such as the behaviour of the gas in contact with geological formations, the leak-tightness and safety of the cavern, hydrogen permeation and the embrittlement of materials and components. Key milestones achieved include the structural and behavioural analysis of the gas within the cavern; the study of the sensitivity of materials to embrittlement under high-pressure conditions in the presence of hydrogen, brine and gases associated with cavern operations; and progress on the technological solutions required for injection, extraction and control systems as well as auxiliary facilities.

Within this framework the company has focused its efforts on developing a business model for salt cavern storage, concluding that its viability depends on shared use amongst several hydrogen plants to optimise capacity. The model is geared towards the efficient allocation of storage and its coordinated operation with hydrogen production by an electrolyser.