Underground Hydrogen Storage (UHS) is a promising solution to maximize the use of hydrogen as an energy carrier. This study presents a standardized methodology for assessing UHS quality by introducing the Underground Hydrogen Storage Suitability Index (UHSSI), which integrates three sub-indices: the Caprock Potential Index (CPI), the Reservoir Quality Index (RQI), and the Site Potential Index (SPI). Parameters such as porosity, permeability, lithology, caprock thickness, depth, temperature, and salinity are evaluated and ranked from 0 (unsuitable) to 5 (excellent). The methodology was validated using data from six worldwide sites, including salt caverns and aquifers. Sites like Moss Bluff, Clemens Dome, and Spindletop (USA) scored highly, while Teesside (UK), Lobodice (Czech Republic), and Beynes (France) were classified as unsuitable due to shallow depths and microbial activity. A software tool, the UHSSI Calculator, was developed to automate site evaluations. This approach offers a cost-effective tool for preliminary screening and supports the safer development of UHS.
