Opportunities for large-scale energy storage in geological formations in mainland Portugal

Abstract

This article presents the first assessment conducted in Portugal to identify geological formations suitable for large-scale energy storage for the following technologies: Underground Natural Gas Storage, Underground Hydrogen Storage, Compressed Air Energy Storage (CAES), Underground Pumped Hydro Storage and Underground Thermal Energy Storage. The identification of geological formations focused on aquifers, salt formations, engineered rock caverns and abandoned mines. Public access geological information was collected, compiled in a database and spatially referenced in a GIS environment. The GIS and database were cross-checked with the criteria for selecting geological reservoirs and with existing or forecasted spatial, environmental and social constraints to define those reservoirs worth studying at the local scale. The outcome is a first screening of sites that need to be studied at the local scale. In total forty-six prospective reservoirs were identified, seventeen in salt formations, twelve in existing or planned caverns in salt domes, eleven in igneous host-rocks, one excavated cavern in igneous rocks and six in saline aquifers. Abandoned mines other than salt mines were not included, since a detailed analysis of the status of the mines was beyond the scope of the project. The technology with the largest potential for application the Portuguese reservoirs seems to be CAES.