ALJARAFE PROJECT

First Underground Green Hydrogen Storage Facility in Spain

The global energy system’s transition towards a carbon-free economy has placed green hydrogen at the core of European decarbonization strategies. Its role as an energy carrier is essential for the gradual substitution of fossil fuels and for strengthening energy autonomy.

In this context, Trinity Energy Storage is leading the development of the Aljarafe Project, a pioneering initiative aimed at converting the former natural gas fields of San Juan, Palancares, and La Cerca—located 20 km from Seville—into Spain’s first underground green hydrogen storage facility, with commissioning expected by 2030.

Thanks to its excellent geological conditions for underground storage and its strategic location—adjacent to the future hydrogen backbone and situated in a region with major green hydrogen production projects—the Aljarafe Project stands out as an ideal candidate to become the first operational green hydrogen storage site in Spain.

Located 20 km west of Seville, in proximity to the Andalusian Green H₂ Valley and the future Hydrogen Backbone Network.

From Natural Gas Production to Renewable Energy Storage

The Aljarafe Project entails the conversion of the Marismas C-1 and Rebujena Hydrocarbon Exploitation Concessions into a regulated hydrogen storage concession. The now-depleted reservoirs have a proven storage capacity, supported by five years of injection/withdrawal testing and by technical studies conducted by Geostock and NSAI—both internationally recognized entities in underground storage.

Over the past four years, the project's technical feasibility has been assessed through two R&D initiatives—UNDERGY and UES365—funded by CDTI under the Misiones Ciencia e Innovación programme. These projects have confirmed the excellent geological characteristics of the site for the underground storage of green hydrogen.

This groundwork has enabled Trinity to include Aljarafe in EUH2STARS, the largest European research project on hydrogen storage in depleted fields. The project is demonstrating the technical and economic feasibility of large-scale underground hydrogen storage systems. It is funded with €20 million from the European Union under Horizon Europe 2023 and includes major industrial partners such as RAG, SHELL, and HGS.

Existing Infrastructure, Energy Security, and Industrial Leadership

The existing gas infrastructure remains fully operational and is connected to the transmission network (Palancares Pipeline – F.06). Thanks to funding from the Horizon Europe – EUH2STARS project, basic engineering for the hydrogen storage system and the design of future monitoring networks are currently underway.

The forthcoming inclusion of the Aljarafe Project in the European Union’s list of Projects of Common Interest (PCI) will consolidate its strategic role in ensuring energy supply security and enabling the efficient integration of intermittent renewable energies. Through this, Trinity Energy Storage positions itself as a key operator in the management of resilient and secure energy infrastructure aligned with European climate objectives.

Current gas facilities operated by Trinity in Aljarafe (Seville).

Operational Capacity and Contribution to the Energy System

The Aljarafe Project will make a tangible contribution to the stability and flexibility of the Spanish national energy system. Its operational capacity will enable the storage of green hydrogen during periods of high renewable generation and its release when demand requires it, promoting a dynamic balance between supply and demand. This functionality positions Aljarafe as a key vector for seasonal energy management, providing resilience, efficiency, and structural support to the energy transition.

The Operational Capacity and Storable Energy in the form of Green Hydrogen are in line with ongoing projects in Europe and the United States.

Table. Operational energy storage capacity of the Aljarafe Project (green hydrogen).

A Flagship Project for the Spanish Hydrogen Strategy

The Aljarafe Project represents a strategic opportunity to position Spain as a European leader in green hydrogen storage technologies, contributing decisively to national goals in decarbonization, energy sovereignty, and sustainable industrial development.

Trinity carries out a market consultation to test the support to the Aljarafe project, the first underground hydrogen storage project in depleted gas deposits in Spain

In order to test the support to the Aljarafe project, Trinity Energy Storage SL has carried out an Expression of Interest/Market consultation process. It targeted a diverse range of stakeholders critical to the hydrogen ecosystem, including engineering firms, hydrogen producers and consumers, and industry associations. In total, 27 stakeholders were contacted and invited to participate in the consultation and the main conclusions extracted are highlighted below:

There is notable backing from engineering firms, which have expressed willingness to collaborate on the design and construction phases of this project, as well as other related hydrogen production, consumption, storage, and transport initiatives across Spain. This collaboration underscores the technical feasibility and industry commitment necessary for project advancement.
Support has also been secured from hydrogen producers and consumers, many of whom are currently project promoters. Their involvement reinforces the expectation of both supply and demand for green hydrogen in the medium to long term, providing a solid foundation that justifies the development of storage projects such as Aljarafe, which these stakeholders themselves identify as critical to the hydrogen value chain.
The project benefits from broad support within the academic institutions, associations, and private and public research centers, indicating a strong and ongoing commitment to hydrogen technology development in Spain.

The strong backing from key stakeholders highlighted above is essential for advancing the inclusion of the Aljarafe project in the forthcoming 2026 Ten-Year Network Development Plan (TYNDP). Such endorsement strengthens the project’s position in subsequent European PCI (Projects of Common Interest) processes, which are crucial for securing regulatory support at the EU level.

The prior public market consultations conducted by Enagás and H2MED demonstrate that by 2030—the planned operational year for Aljarafe—there will be established demand, production, and hydrogen corridor infrastructure in Spain, which Aljarafe will be positioned to serve.

Trinity Energy Storage reaffirms its commitment to maintaining and expanding dialogue with industry players, research institutions, and public administrations. This ongoing engagement aims to foster alignment across the hydrogen value chain, ensuring that the project remains responsive to market needs and regulatory developments.

Looking ahead, critical milestones include progressing through the TYNDP inclusion phases, advancing in permitting procedures, and actively participating in the definition of the emerging regulatory frameworks for hydrogen infrastructure. These steps will be pivotal to align project timelines with national and European strategies, positioning Aljarafe as a key asset in Spain’s green hydrogen roadmap.