Research into the electrothermal energy storage system (ETES) has been ongoing for five years now, with some €29 million invested to date. Siemens Gamesa and Hamburg Energie are partners in the project, together with Hamburg University of Technology (TUHH), which is responsible for the accompanying research activities. Volcanic rock serves as a storage medium: a blower heats the heaped rock to 750 °C. The excess green electricity can thereby be stored in the stones as heat. When demand peaks, the ETES utilizes a steam turbine to re-electrify the stored energy.

The plant currently converts wind power into heat that can be stored for a week. The up to 30 megawatt hours (MWh) of energy that the plant can thereby generate currently supply 1,500 households in Hamburg. The plant has a potential of up to 130 MWh – enough to supply 12,000 households. The costs for storing one kilowatt hour are less than 10 cents, and are therefore extremely low. Decommissioned coal-fired power plants would be an ideal location for this technology, since many of the required components, such as turbines, generators, and a grid connection, are already available there.