.

Projektinfo – Detailed information on energy research

read short description
subscribe projektinfos

Abandoned mines could be used as underground energy storage and significantly expand the storage capacity in the grid. This can work similar to conventional pumped storage power plants.
© Schluchseewerk AG
Energy storage for power grids
Projektinfo 18/2013

Structure of an underground pumped storage power station.
© EFZN

Suitability of mining regions in Germany
© IGMC
1 / 3

Storing wind energy underground

Pumped storage power plants have been in use for over a hundred years to balance fluctuating electricity loads and to cover peak loads. The energy transition creates additional storage demand with its fluctuating feed-in of wind and solar power into the grid. New sites, however, are scarce. Whether the large differences in the tunnel heights of abandoned mines are usable or not is currently being investigated by an interdisciplinary team of researchers on the basis of two viable locations.

Pumped storage power plants store electricity in the form of potential energy. Using surplus electricity, water is pumped out of a lower reservoir into a higher surface reservoir. With a water turbine, the potential energy can then be converted back into electricity during demand peaks. The efficiency of the overall process is on average about 75 %. The storage capacity is proportional to the usable height difference and the stored water volume.

Nearly 40 above-surface pumped storage power plants with a total output of about 7 GW and a capacity of about 40 GWh are currently in operation in Germany. A further expansion is possible only to a very limited extent because conventional pumped storage power plants rely on suitable terrain profiles. Such locations do exist but environmental impact and significant land use cause acceptance issues for these projects.

arrow
arrow

For this reason, it is appealing to use existing mines as underground storages – an idea that is yet to be implemented anywhere. The main components, the upper and lower reservoirs, the hydroelectric power cavern with the generating set and the electrical systems as well as supply and return lines for electrical power and grid connection are mostly arranged underground. In a hybrid variant, a pond or lake may serve as an upper or lower reservoir. This not only reduces the effort underground but it also increases the drop height of the pumped storage power plant and thus its storage capacity.

The potential in Germany

Mostly hard coal, pitch coal, potash salt, rock salt, ores, spar and shale are or were mined underground in Germany. In total, there are more than 100,000 underground mining structures. However, only a small number of those are suitable for use as underground pumped storage power plants. For example, explosive gases are to be expected in hard coal and pitch coal mines, dissolution and reprecipitation processes in salt mines while mines in loose rock require extensive safety efforts. Exclusion criteria also include toxic or environmentally hazardous materials that could be released. Access to still mineable deposits must also remain secured.

Summarising all restraints, ore mining regions in which suitable mines can be found with a high probability remain viable. In Germany, these include the Erzgebirge, the Siegerland with the Lahn-Dill area and the Harz. Within the framework of the project “Windenergiespeicherung durch Nachnutzung stillgelegter Bergwerke“ (wind energy storage through the reuse of abandoned mines) funded by the German Federal Ministry for the Environment, the scientists at the Clausthal University of Technology and their project partners identified 104 underground mining structures that were either suitable or suitable to a limited extent.

For a rough estimate of the total potential, the researchers made the simplifying assumption that a storage system can be built with an output of 100 MW and a capacity of 400 MWh at each of these locations. This results in a theoretical total output of around 10 GW and a storage capacity of 40 GWh. This would double today‘s installed pumped storage capacity and output in Germany.

Projektinfo 18/2013:
1 / 3

notepad

BINE subscription

Subscribe to publication

Addresses

Project partner
TU Clausthal

Project partner
Voith GmbH

Project partner
OECOS GmbH