The geothermal potential of the underground of the Salento peninsula (southern Italy)

The low-enthalpy geothermal energy systems exploit the underground as a heat reservoir, by coupling it with highly efficient heat pumps: in winter, the energy stored in the subsoil can be transferred to the surface to heat buildings, whereas in summer the surplus heat in buildings can be transferred back to the ground providing a cooling action. Despite the high costs for installation, low-enthalpy geothermal systems have high energy efficiency and, therefore, contribute to energy saving, to the use of renewable energy sources, to environmental sustainability (the effects on the hydrogeological cycle are often negligible) and to the reduction in fuel consumption and in gas emissions. In this paper, a simple methodology is proposed to assess the geothermal potential of the underground of the Salento peninsula (southern Italy) at the regional scale, by calculating the equivalent thermal performance of the subsoil, which expresses the thermal power that is potentially extractable and useful to heat or cool a building. Since the possibility of exploiting the underground as a heat reservoir depends on the physical properties and water saturation of rocks, previous detailed studies on the hydrostratigraphic setup of the region are the basis for this analysis of geothermal potential. The equivalent thermal performance depends on the thermal efficiencies of different lithological units, whose ranges of values, for heating only, are provided in literature. For this case study, a stochastic approach has been applied: several combinations of thermal efficiencies were randomly selected from the intervals of reference values for every hydrostratigraphic formation and the corresponding minimum depths below the ground surface that must be reached to get the desired equivalent thermal performance are computed. The results show that the underground of the Salento peninsula has great potentialities for heating of buildings, except for some coastal areas because the saltwater intrusion phenomenon could cause problems for the realization of low-enthalpy geothermal energy systems.