Mining energy
June 10, 2011
If the Ruhrkohle coal company (RAG) has its way, wind turbines could someday dot the top of its many mining waste mounds and hydroelectric pumped-storage stations could be installed in defunct underground shafts, turning former mines into "green batteries."
All the prerequisites exist, according to Walter Eilert, director of renewable energies at RAG. "Three years ago we examined the company's resources," he said. "And we discovered that we had resources in mine water, deep shafts, open surface areas and waste mounds."
Mining companies able to exploit these resources can reduce the so-called "eternity costs" of mining hard coal, Eilert argues. These costs stem, in part, from the need to continue pumping mine water out of shafts after operations have been shut down. RAG, for instance, pumps more than 100 million cubic meters of water out of its mines every year.
Wind conditions similar to North Sea
Initially, the Heine-based company will focus on using its mounds of mining waste, which can reach heights of 70 meters, as a base for wind turbines, according to Eilert. Wind conditions at these heights are similar to those along Germany's North Sea shoreline.
Currently, two wind turbines erected on mining waste mounds in Gelsenkirchen are generating up to 2.5 megawatts of electricity each – enough energy to power more than 10,000 households in the region.
A key challenge for expanding renewable energies is to ensure a constant power load. Electricity generated from solar and wind installations is subject to fluctuations, requiring energy storage facilities.
RAG says it has found a solution. "We aim to store electricity by pumping water into reservoirs," Eilert said. "When demand grows, we allow the water to flow down to turbines that generate electricity."
Two reservoirs needed
The plan is to install turbines in old RAG mines and turn their shafts into hydroelectric pumped-storage stations.
Two reservoirs will be required: one on the earth's surface and one underground. If the wind is particularly strong, surplus wind energy can be used to pump underground water into the surface reservoir. If the wind is low and not meeting demand, water is released from the surface reservoir to flow down a shaft and power electricity-generating turbines.
Pumping mine water from depths as great as 1,000 meters is a task that RAG has mastered for decades. What the company still needs to realize its hydroelectric pumped-storage station concept, however, are large storage tanks to serve as underground reservoirs. It also needs to install turbines and linings in the mine shafts. In cooperation with researchers from the Bochum and Duisburg-Essen universities, RAG aims to complete a feasibility study within three years.
Economical and ecological
After that, the company aims to select mine sites where it can implement the new energy concept in this decade. Two mines in the Ruhr Valley, Auguste Victoria and Prosper-Haniel, as well as one in Ibbenbüren are already shortlisted.
Along the way, RAG intends to secure a global patent for its concept. "So far, all of our research has shown that no one has yet to implement an underground hydroelectric pumped-storage system like the one we have conceived," Eilert said.
According to company calculations, the system will be able to generate about 300 megawatt-hours of electricity. The depth of the mines will play an important role from both an economical and ecological viewpoint. The greater the drop height, the less water is necessary to generate electricity from the turbines.
Equally important, Eilert expects no opposition from environmentalists who are currently trying to block the construction of surface reservoirs in southern Germany. "We don't see hydroelectric pumped-storage stations located below ground having any significant impact on nature, if any impact at all," he said.
Author: Klaus Deuse / jrb
Editor: Sam Edmonds