SERIES: Wind Energy

Storing renewable energy in stones

2 March 2021
Series on wind energy (6): Pilot project in Hamburg highlights volcanic rock’s ability to store electricity

Wind power and photovoltaics have all kinds of advantages as outlined in the previous articles in this series. However, volatility remains a big issue as this leads to fluctuating output. The solution lies in storage. Siemens Gamesa is presently testing a particularly innovative variant in downtown Hamburg.

Thermal battery with 1,000 tons of volcanic rock 

A huge insulated pile of stones is heated with excess electricity at Trimet Aluminium SE in Altenwerder. This gigantic battery stores excess electricity temporarily thanks to a gargantuan hot-air dryer which heats the stones to 600 degrees Celsius. The well-insulated stones store the heat - or 30 megawatt hours of electricity - for several days. When electricity is needed, the heat is extracted and its steam is used to drive a turbine, which in turn drives a 1.5-megawatt generator. The plant then produces electricity for up to 24 hours and can supply 1,500 households or charge around 50 electric cars.

Charging the thermal battery takes about six hours and the temperature loss is only about 15 degrees Celsius. The test facility is about the size of an Olympic swimming pool. The concrete structure is 22 metres in length, eleven metres in width, eleven metres in height and contains around 1,000 tonnes of volcanic rock.

Electricity, heat, electricity energy storage

Last year saw the creation of the Future Energy System (FES). The partner Hamburg Energie GmbH is testing the storage system on the market. Renewable energies are available in large quantities with plenty of wind and sun, often far more than the electricity grids can transport at present. Storage facilities serve to buffer periods of low production, e.g. when there is a lull and darkness. Many storage technologies offer limited capacities or are too expensive. For this reason, Siemens Gamesa is developing particularly cost-effective storage technology as part of a project funded by the German Ministry of Economics and Energy.

New lease of life for shut coal-fired power plants

Apart from Hamburg Energie, the Institute for Technical Thermodynamics at the Hamburg University of Technology is also involved in the storage concept. The TU Hamburg is researching the thermodynamic principles of the bulk material technology used. One of the researchers' ideas is to convert decommissioned coal-fired power stations into environment-friendly electricity storage facilities for obvious reasons namely the availability of the entire infrastructure.

A guest article by Daniel Hautmann, freelance scientific journalist and author.

Sources and further information



    Mankind has used wind power for thousands of years. Wind power is now more important than ever amid ongoing climate change and the conversion of energy to renewable energy sources. Daniel Hauptmann’s book shows other possibilities of harnessing wind power, when the power of inventors and investors are added on a large scale. The author goes far beyond the usual perspective of wind power for generating electricity and gives other fascinating examples - from cargo ships and wind-powered racing cars to floating wind turbines. The author highlights the technical facts and the environmental impact of each exampleDaniel Hautmann: Windkraft neu gedacht. Erstaunliche Beispiele für die Nutzung einer unerschöpflichen Ressource, Hanser Verlag, Munich 2020, 229 pages, hardcover edition EUR 39.99, EUR 31.99. 


    Daniel Hautmann, 45, has been writing about technology, energy and the environment for around 20 years. He is a trained industrial mechanic, editor of trade journals and specializes in regenerative energies, especially wind power. He has competed with a world champion windsurfer and flew headfirst in a glider with the European aerobatics champion. His texts have been published in Brand Eins, Technology Review and the Süddeutsche Zeitung, among others. He occasionally presents radio shows, produces podcasts and writes books.


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