26 July 2013

Germany tests storing electricity in old mines

Underground pumped storage: Scheme: University of Duisburg-Essen
Underground pumped storage: Scheme: University of Duisburg-Essen
Germany's wind and solar power generation is growing fast. However, due to the fluctuation only 40 percent of the generated electricity can be used. Thus, storing electricity is becoming more than important.

Until now there is no solution for this problem. The technology of energy storage by pumped storage plants is known since more than one hundred years. Natural heights were used for it that could cause environmental problems. New storage possibilities are compressed air, battery and hydrogen storage.

One innovative idea has been dreamt up in the Ruhr region: Old mines could be converted into pumped storage hydropower stations that absorb the excess power and then release it when consumers need it, writes Deutschland.de.

German hard coal mining is nearing its end, and in 2018 the last of the mines in the state of North Rhine-Westphalia is scheduled to close down.

Searching for ways of giving the mines a new lease of life, geology professor Ulrich Schreiber at the University of Duisburg-Essen (UDE) came up with the idea of an underground pumped storage hydropower station.

The galleries of the mines, deep in the ground, are used as a reservoir for water. The excess electricity is then used to pump the water up to the surface, where it fills a "topside basin".

If the grid requires electricity, the water simply goes surging down pipes back into the depths - whereby there are turbines fitted into the pipes that generate the electricity.

There are several advantages to the plan. Unlike classic pumped storage hydropower stations, which tend to be located in the hills or mountains, nature does not get touched.

Given a head of some 1,000 meters or more, you can store a relatively large amount of energy - enough to cover electricity supplies for a large city for several hours.

Since the ambient temperature at 1,000 metres underground is 40-45 degrees Celsius, the heated water could also potentially be used for heating purposes.

However, various technical and legal issues need to be clarified before the underground storage system becomes a reality.

Research team is composed of employees of the Department of Energy Systems and Energy management of the Ruhr-University Bochum and the institutes of Geology and Geotechnical Engineering and the Institute for Hydraulic Engineering and Water Resource Management of the University of Duisburg-Essen.

The focus of this study lies in the detection of potentials for different types of underground pumped storage plants. Therefore all geological and geographical conditions, technical and engineering complexity and the costs of storage and energy management aspects are considered.

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