Potencial de la geotèrmia de baixa entalpia combinada amb energia fotovoltaica

Abstract

Renewable energies represent a sustainable solution to the increasing global energy demand. In the range of the renewable energies, one of them is geothermal energy, which it is one of the most efficient renewable energies since it has no problem with climate intermittence, but it is less applied in practice due its high initial investment cost. Low-enthalpy geothermal energy uses the subsoil as thermal energy storage, and it can provide heat from the subsoil inside home during winter season and infiltrate heat in the subsoil cooling the home in summer. This system, as uses the ground as a source of thermal exchange, requires that the body rock that acts as storage has the following characteristics: high permeability, high thermal conductivities and low thermal capacities, moreover it should be isolated or semi isolated for prevent the heat to dissipate. The geothermal system uses heat pumps with are nowadays developed with better “Coefficiencent of performance” (COP). This means using minimal electrical energy to produce heat in a very efficient way. In this paper, a system of two integrated renewable energies it is used: low-enthalpy geothermal energy, that covers the demand for thermal energy and photovoltaic solar energy, which covers the electrical demand. Thus, the energy to drive the geothermal heat pump is also renewable, since it comes from the photovoltaic. The installation of the combined system is framed in Catalonia, in the town of Sant Gregori, Girona, which sits on a pliocene river terrace, where the big-grained water-saturated sandstones form a good thermal storage for using of low-enthalpy geothermal technique. The database of two months of operation of the renewable system allow to compare this renewable installation with the old non-renewable system, that worked during one year in that building and was based on electricity from the network and natural gas. The change of the installation entails a great initial investment of 27.900€. But periodically, with analysis of invoices, an economical and energetical reduction is observed. Economically, the new combined renewable system provides a monthly savings of 140,61€ and 1.710€ per year, thus, the investment recovery will be at 16,3 years. Energetically, 55,59% of the electric cost is reduced. It was consumed 11,71 kW/day average with the old system, to 4,66 kW/day that is consumed now, and 100% (total) reduction in natural gas consumption. The combined renewable system has environmental benefits, since being a self-service system, the low energy consumption required by the electricity grid would be equivalent to cataloging the Building as “Near Zero Energy Building” (nZEB), to an energy classification type “A” and zero emission of CO2