In a fully developed hydrogen economy large-scale hydrogen storage is expected to play a crucial role to balance supply and demand of hydrogen, even more so if the hydrogen is produced from renewable energy sources that are usually highly intermittent. To date, the most cost-effective technical solutions identified for storing large quantities of hydrogen is in underground geological formations, in particular in salt caverns and porous reservoirs (e.g. gas depleted field, aquifers), or artificial caverns. While different pilot projects already demonstrate(d) salts caverns as a large-scale hydrogen storage solution, the feasibility of storing hydrogen in porous reservoirs is not yet proven. In particular, the impact of hydrogen-consuming microbial activity needs more research in order to identify the potential risks associated with naturally present microbial communities in reservoirs. It is necessary to identify, characterise and determine site-specific microbial activities across different European sites for specific operational conditions. As well dedicated standards and guidelines are missing, representing a critical gap for the development of a European hydrogen ecosystem. The project results and findings obtained should contribute to overcome these normative gaps.

Artificial caverns for large-scale H2 storage also need more studies and pilots for demonstrating this solution industrially, however they are out of the scope of this project.

Project results are expected to contribute to all the following expected outcomes:

• Generate multidisciplinary knowledge that leads to microbiome-based understanding as needed by the industry and associated actors;
• Make industrially available large-scale hydrogen storage systems that can reduce the cost and improve the efficiency of hydrogen supply across the European landscape;
• Facilitate international collaborations to generate and apply knowledge that can improve underground hydrogen storage operations that contribute to hydrogen sustainability and reduce associated costs;
• Foster sustainable and safe design guidelines for operators of underground storage systems for long-lasting management solutions;
• Contributing to keep European leadership for large-scale hydrogen storage solutions, with particular focus on assessing the potential risks associated with biogeochemical processes.
• Definition of a risk matrix and European guidelines to support SSOs (Storage System Operators) in the identification and management of microbial risk associated with the storage of hydrogen in porous reservoirs;
• Replication of the methodologies developed and demonstrated in the project in sites in other European regions with different subsurface (and operational) characteristics, ensuring an exhaustive coverage of the different European sites’ specifics.

Project results are expected to contribute to the following objectives and KPIs of the Clean Hydrogen JU SRIA:

• Undertake research activities on underground storage to validate the performance in different geologies, to identify better and more cost-effective materials and to encourage improved designs.
• Support the development of Regulations Codes and Standards (RCS) for hydrogen technologies and applications, with the focus on standards, for assessing the risks associated with the storage of hydrogen and microbial activities in porous reservoirs;
• Organising safety, Pre-Normative research (PNR) and RCS workshops;
• Providing inputs for developing Standards, Technical Specifications, or Technical Reports.

Different studies and projects (e.g. HYUSPRE, HYSTORIES) have assessed the feasibility of storing hydrogen in porous media geological formations. However, a comprehensive assessment of the risks (eg. production of certain corrosives compounds and other impurities) associated with the different groups of microorganisms in specific underground formations needs to be studied in detail, considering the boundary conditions specific of each site (e.g., temperature, pressure, pH, rock’s chemical composition, salinity, etc.). Related impact on rock properties (porosity, permeability, mechanical properties) driven for example by dissolution and precipitation mechanisms needs also to be investigated.

To overcome the gaps above and building also on the results of previous studies, projects and analysis, proposals should address the following:

• Taxonomic and functional characterisation of indigenous microbial populations present in the different European porous media geological formations. Relate growth rate and hydrogen-related enzymatic functions to different boundary conditions (e.g. temperature, pressure, rock’s chemical composition, salinity, etc.) should also be considered in the inventory. An interdisciplinary approach is highly recommended. Molecular tools should be applied to profile in terms of microbial taxonomic composition, relative abundances and functional characterisation the indigenous microbial populations present in the different European porous media geological formations (e.g. targeted Polymerase chain reaction (PCR) amplification and high-throughput sequencing of 16S rRNA; analysis of functional genes as molecular biomarker).
• Assess the microbial and geochemical reactions and their interactions between the two to clearly distinguish the reactions of hydrogen (and eventually considering also the impurities due to conversion of depleted natural gas storage to hydrogen storage) within each specific site. The results of the analysis considering multiple geological environments should be reported in order to improve the knowledge regarding the conditions in which reactions take place;
• Development of site-specific bio-chemical modelling. Modelling key microbial activities (i.e., H₂S production, methanogenesis, etc) should allow to understand how physical, chemical, and biological processes are coupled in an underground hydrogen storage;
• Development of standardisable and transferable methodologies for sampling autochthonous microbial populations of underground geological formations, including a reliable system to distinguish possible exogenous contamination;
• Development of laboratory methodologies for the processing and analysis of different types of samples collected from the underground storage sites (e.g. liquids, rocks, drilling mud, etc.). The methodologies developed should be described in sufficient detail to allow reliability and reproducibility of the obtained results among different laboratories;
• Application of the methodologies previously indicated for different sites, assuring an exhaustive coverage of the different European sites’ peculiarities. The methodologies should be applied in different laboratories, considering different site samples. Microbial activity should also be observed during different testing periods, possibly up to six months, and in different batch/reactor operation volumes. Different levels of experiment together with modelling will be necessary to reproduce underground storage conditions and enable upscaling to the reservoir scale.
• Definition of guidelines/protocols to support SSOs in the identification and management of risk associated to the storage of H2 in porous media geological formations, as well as future standardisation activities. The guidelines should also propose a fast-track procedure which allow the SSOs to have a preliminary qualitative assessment of the hydrogen storage feasibility, considering the main relevant factors, as well as assist SSOs in the identification of the optimum storage sites.

In order to ensure an exhaustive coverage of the different European sites’ peculiarities, the consortium should include a large panel of SSOs from different EU Member States, whose operated storage infrastructures represent the variety of EU porous media geological formations. The knowledge and differences in the national underground storage facilities can be very significant, therefore the EU wide coverage should guarantee full usability of results for EU companies.

Building on the results of the previous activities, the proposals should, as relevant, provide recommendations and dissemination for updating and/or development of new standards at the EU and International levels.

Proposals are encouraged to explore synergies with projects within the metrology research programme run under the EURAMET research programmes EMPIR and the European Partnership on Metrology (in particular projects MetroHyVe2, Met4H2 and MefhySto).

For additional elements applicable to all topics please refer to section 2.2.3.2.

Activities are expected to start at TRL 2 and achieve TRL 4 by the end of the project - see General Annex B.

The JU estimates that an EU contribution of maximum EUR 3.00 million would allow these outcomes to be addressed appropriately.

The conditions related to this topic are provided in the chapter 2.2.3.2 of the Clean Hydrogen JU 2024 Annual Work Plan and in the General Annexes to the Horizon Europe Work Programme 2023–2024 which apply mutatis mutandis.