An energy storage device for storing energy including: a high-temperature regenerator containing a storage material and a working gas as heat transfer medium for the purpose of exchanging heat between the storage material and the traversing working gas, a closed charging circuit for the working gas, including a first compressor, a first expander, a first recuperator having a first and a second heat exchange duct, the high-temperature regenerator and a pre-heater, wherein the first compressor is coupled to the first expander by a shaft, a discharging circuit for the working gas, and including a switch that selectively connects the high-temperature regenerator to either the charging circuit or the discharging circuit, such that the circuit containing the high-temperature regenerator forms a closed circuit.