The recent rapid deployment of renewable energy has had an unexpected effect: a renewed view of subsurface engineering’s importance. High shares of variable energy generation heighten the need for large-scale, long-duration storage solutions, many of which rely directly on geological reservoirs. Several technologies are currently under development or early deployment, including Compressed Air Energy Storage, Underground Thermal Energy Storage, subsurface flow-battery concepts, and Power-to-Gas systems involving hydrogen storage in salt caverns, depleted reservoirs or aquifers. Their levels of technological maturity vary widely, as do their site selection constraints, optimal operating conditions and geological requirements.

This presentation will provide a comparative overview of these major subsurface energy storage options, emphasizing their respective storage mechanisms, feasibility conditions, and screening criteria. A detailed focus will then be placed on Underground Hydrogen Storage (UHS) in salt caverns, one of the most promising options for seasonal balancing due to its high energy storage density and the favourable properties of salt formations. Building on this context, the second part of the webinar will present the ongoing work of my Master’s research, which aims to develop a structured and reproducible site-selection methodology for UHS. The case study focuses on the Magdalen Islands (Québec, Canada), where salt diapirs offer a rare geological opportunity for local, long-duration storage of green hydrogen produced from wind power. Updated results from the geological, hydrogeological and technical suitability analysis will be shared, along with the multi-criteria evaluation framework used to map and rank prospective storage zones.