The project would be a world first – putting a pumped-storage hydroelectricity plant into an old mine, thus avoiding potential planning objections.
As Germany seeks ways to make renewable energy more reliable, one of the major questions is how to store energy generated by solar on sunny, or by wind turbines on blustery days.
Pumped-storage hydroelectricity plants work by using power from solar or wind turbine sources to pump water from one tank to another above it. When the sun goes in or the wind stops blowing and electricity is needed, the water from the top is released to the bottom tank – pushing through turbines as it goes and generating power.
Marko Schmidt, an industrial engineer for the Energy Research Centre of Lower Saxony (EFZN), has carried out a study on building such a plant in the abandoned Wiemannsbucht mine shaft in Bad Grund, a town in the western Harz mountains which he said could be done for up to €200 million.
Several potential pitfalls remain – including as-yet unfound investors – but he says the plant could stimulate the economy and provide urgent energy relief to the region.
“The Harz is one of the most outstanding regions where an underground pumped-storage plant is possible,” Schmidt told news agency DAPD.
A total of six such projects have been proposed for the West Harz region. The storage capacity of the proposed plant in Bad Grund is 400 megawatt hours - enough to provide more than 40,000 households with electricity for a whole day.
While the proposed plant would store energy generated by local wind turbines, future larger projects could also be used as storage for offshore wind power from the North Sea.
Above-ground storage plants, already in use throughout Germany, act as energy reservoirs to overcome intermittent energy shortages common with renewable sources such as wind.
The new subterranean proposal in the Harz would make use of elevation differences between old tunnel crossings in the mines, which can be as deep as 900 metres.
For Schmidt, the underground plant idea's attraction lies in its minimal impact on the landscape. He said he did not expect Harz residents to protest its construction as they had previously opposed wind turbines and above-ground power lines.
Policy makers have yet to throw their full support behind the project, one of 16 proposals to stimulate the economy of the Harz region, but their rhetoric is optimistic.
The government of Lower Saxony supports the project and is following it with “interest and excitement,” said a spokeswoman for the Ministry of Economic Affairs.
Pending legal approval, the plant could be built in between three and five years, providing the region with up to 150 new jobs, while the plant's daily operations would employ up to seven people.
Wolf-Rüdiger Canders, professor of electrical machinery at the Braunschweig University of Technology, believes in the project and said it was “not unrealistic” that investors would be found.