The increased use of renewable energies creates the problem of permanent availability. The availability of photovoltaic electricity in Europe is around 1000 hours per year, around twice as much in the case of wind. To be able to guarantee security of supply, appropriate storage capacities are required. Siemens Gamesa has built the first fully-fledged electrothermal energy storage system. 1000 tons of stone are heated by means of renewable energy and thanks to the energy storage system, 130 MWh can be stored. When necessary, it is converted into electricity by a steam turbine, so around 3000 households can be supplied for 24 hours.