Mapping the geothermal potential of Italy’s shallow subsoil: a streamlined MILS model approach for extensive datasets

Shallow geothermal energy represents a significant opportunity to reduce energy waste in the heating and cooling sectors. Geothermal maps are a valuable tool for enhancing the exploitation of geothermal resources on a national scale. In this work, we produced maps of Italian shallow geothermal potential for different saturation and groundwater velocity scenarios. For this purpose, we developed a method for quickly computing geothermal potential, based on lithological data and the simplified application of the Moving Infinite Line Source model for heat dispersion. Our approach follows the G.POT methodology proposed by Casasso and Sethi in 2016, but it also incorporates the contribution of groundwater flow, which was not considered in the original G.POT computation. This method enables the computation of geothermal potential from a large amount of input data, given the geological asset, the thermal and hydrogeological properties of the materials that form the subsoil, the initial underground temperature, and the required thermal load. Using this approach, we estimated the geothermal potential related to more than 28.000 sites for which stratigraphic data are available. We gather the stratigraphic logs of every site and compute the geothermal potential for each lithological layer encountered in each log. The derived values have been averaged to obtain the mean potential of the shallow subsoil at a reference depth of approximately 70 m. The final maps are the result of interpolating the point estimates. The different scenarios explore the variability of the geothermal field as it is intrinsically linked to the geological and hydrogeological context. From completely unsaturated to completely saturated conditions, the geothermal potential can increase by a factor that ranges from 4 to 10, depending on the groundwater flow velocity. The regions showing larger increments related to groundwater action are those characterized by sandy or gravelly subsoils, such as Emilia-Romagna, Piedmont, Lombardy, Friuli-Venezia Giulia, and Veneto. The high permeability of these sediments strongly influences their geothermal potential. On the other hand, areas where consolidated rock prevails are less susceptible to variation due to the presence of water in the underground soils, as observed in some regions of Sardinia, Sicily, and Apulia. Both the final maps and selected intermediate results have been published on open-access data platforms managed by Ricerca sul Sistema Energetico - RSE S.p.A, which also host a wide range of other energy-related information to support territorial energy planning.