The invention relates to a system and a method for storing electrical energy which are based on a closed thermodynamic cycle. They make it possible to store electrical energy in a very efficient, cost-effective, and safe manner. No environmentally hazardous or expensive materials are required. The system comprises a compressor, a turbine, and two packed-bed storage units which are operated at different temperature levels.
In order to load the packed-bed storage units, the cycle is operated as a counterclockwise heat pump process. In this process, the heat generated at the outlet of the compressor is expanded at a high temperature level into a first packed-bed storage unit and stored therein. The “cold” produced during the subsequent expansion of the gaseous working medium in a turbine is stored in a second packed-bed storage unit. This requires mechanical energy which is provided by an electrical machine. In order to discharge the energy storage system, the cycle is operated in reverse (i.e., as a clockwise cycle). Before entering the compressor, the working medium is cooled with the cold stored in the second packed-bed storage unit and, after compression, absorbs the heat from the high-temperature packed-bed storage system. The hot working medium at high pressure is expanded by means of the turbine and thus energy is generated.