Response of schist bedrock to a thermal pulse

Abstract : The Solargeotherm project is assessing the possibility of using vertical geothermal probes drilled into a schist bedrock for storing the thermal energy produced by solar panels and later releasing it. A thermal pulse was delivered through one of the geothermal probes in order to characterize the stratified thermophysical properties of the schist bedrock (thermal conductivity, volumetric heat capacity). The relaxation phase (cooling) was interpreted by a 1D instantaneous infinite line source type analytical solution. The temperature rise in the borehole (arrival of the thermal pulse) is too complex for an analytical interpretation, because of its highly transient character and the dynamic thermal interactions between the down leg and up leg of the U-shaped probe. A numerical 3D modelling was therefore carried out. Numerical results of the modelling are in good agreement with observations.