Strategic Risks in Underground Hydrogen Storage

Abstract Underground hydrogen (H 2 ) storage in salt caverns, aquifers, and depleted gas reservoirs could become a central component of Europe’s transition to a decarbonised energy system. However, subsurface microbial activity may compromise the technical and economic viability by reducing hydrogen purity and volume through consumption and by-product formation. This study presents a multidimensional assessment of microbial risks in underground hydrogen storage, integrating geological classification, expected microbial processes, and techno-economic consequences. Salt caverns, depleted gas fields, and aquifers are compared in terms of microbial activity potential and associated hydrogen losses. The technical analysis is complemented by a review of the policy, economic, and technological context, applying both PESTLE and SWOT frameworks. Results highlight substantial differences in microbial risk and storage performance, with hydrogen losses ranging from