The present invention relates to a process of storing energy through the conversion of thermal energy and subsequent power generation by means of a gas turbine set with compressor, expander and power generator, with at least one and with a second low-temperature reservoir, and a high-temperature reservoir with bulk material as the heat storage medium, the electric energy is stored in the form of high-temperature heat above the turbine outlet temperature in a thermal reservoir, that during the power generation phase a compressed gas from the compressor is heated in a low-temperature reservoir to a temperature near the turbine outlet temperature and subsequently heated in a high-temperature reservoir with stored heat from electric power to a temperature level of at least the turbine inlet temperature, and that the ratio between the bed height in flow direction and the mean particle diameter of the bulk material in the high-temperature reservoir is at least 10.