Thermophysical and chemical analysis of gneiss rock as low cost candidate material for thermal energy storage in concentrated solar power plants

A packed bed of rocks with air as heat transfer fluid can be considered as a cost effective storage system, as it enhances the dispatchability of the concentrated solar power plant at lower costs. However, the identification of suitable rocks to be used as a storage medium requires a prior experimental characterization, since the studies published about the behaviour of rocks at high temperatures are scarce in literature. This work aims to investigate the potential of gneiss rock as a candidate storage material in solar power plants. Thus, thermal stability of two varieties of gneiss rock has been studied at temperatures up to 1000 °C during heating and cooling by thermogravimetric and differential thermal analyzer (TG/DTA). The influence of temperature on specific heat capacity, thermal diffusivity and thermal conductivity has been analyzed. Furthermore, the chemical composition and crystalline phases have been identified by X-ray fluorescence and X-ray diffraction, respectively. The obtained results proved the potential of this type of rocks in terms of high thermal capacities, high density and good thermal stability up to 550 °C.