A German engineering professor hopes to transform a coal mine into a giant hydraulic battery in order to facilitate the usage of renewable energy.

Andre Niemann, professor of hydraulic engineering at the University of Duisburg-Essen, believes abandoned mines could be the solution to one of the chief impediments to weather-based forms of renewable energy – how to conveniently store the surplus electricity they generate to counteract the problem of intermittent supply.

Professor Andre Niemann

Professor Andre Niemann

Niemann’s proposal entails converting the tunnels of the Bergwerk Prosper Haniel mine, which is scheduled to go offline following changes to federal policy in 2018, into an vast underground water storage site which can be used in conjunction with an above-ground reservoir to serve as a giant hydraulic battery.

This “pumped storage” system would employ any surplus power generated by renewable energy facilities to pump water from the underground tunnels, located over half a mile beneath the surface of the earth, into the above-ground reservoir. When energy from the hydraulic battery needs to be accessed, the water can simply be drained back into the underground tunnels via the simple action of gravity, generating electricity during the return journey by making passage through turbines.

The proposal dovetails perfectly with Germany’s plans to cut federal subsidies to its coal industry in 2018, which will render the country’s three remaining lignite coal mines, one of which is Prosper Haniel, obsolete.

Prosper Haniel is a highly suitable site for a pumped storage battery, given that it is home to nearly 30 kilometres of underground mining tunnels and situated a mere hour away from western German economic hub of Cologne.

Once it goes offline, the mine’s subterranean passageways could hold approximately 35 million cubic feet of water – an amount roughly equivalent to the volume of the Empire State Building. Niemann estimates that this translates into enough storage capacity to supply the power needs of 410 standard German households.

Similar hydraulic systems have already been successfully deployed elsewhere, in both Germany and the United States. Should Niemann’s proposal be implemented, however, it will mark the first occasion that disused coal mining facilities will have been converted into a pumped storage system.