At the moment, though, it takes quite a bit of imagination to picture the lake that’s in the making here in the lunar landscape of the former Cottbus-Nord open-pit mine. Flooding the area began this April. By 2025, the huge pit is planned to have been filled by about 280 million cubic meters (9,9 billion cubic feet) of water. 20 percent will be supplied by rising groundwater and about 80 percent will be taken from the river Spree. The river, though, will only be tapped if it carries enough water, which, so far, has frequently not been the case. With an area of 19 square kilometers (7 square miles) the mammoth, 300-million-euro project will be Germany’s largest artificial lake. Along the edges, like here at the intake structure, the water may be as deep as 30 meters (98 feet) due to the valleys, according to the energy and mining company Leag, the lake’s operator.

© Manuela Mrohs

Construction of a pier in the planned marina district has begun, too. Holger Kech, the lord mayor of Cottbus, has CO2-neutral plans for the new district: “High-rise timber buildings are conceivable there, bicycle paths on photovoltaic panels, connections between local public transportation and autonomous vehicles, district heat from lake water pumps, and more,” he said during a presentation of his ideas for the new district. Residential buildings are planned, and business, tourism and water sports to be attracted to the area. Like here in Cottbus, hopes for a flourishing future are pinned on the legacies of coal mining and raw material extraction around the world. New recreational areas, and tourism along with them, promise to crank up the local economy again and to create jobs. The evolving biotopes are supposed to provide shelter for protected animal and plant species. Last but not least, completely new possible uses for open-pit mines, tailing heaps and brownfields also open up in the wake of energy transition.

The example of the “Neuseenland” (“New Lake District”) in Leipzig shows that such projects aren’t pie in the sky but offer promising prospects. Up until 1990, an area of 200 square kilometers (77 square miles) in the southern part of Leizig was still shaped by the gaping wounds of open-pit mining. Today, the eight lakes that have been created there are an attractive place for water sports, hiking and cycling. In 2017, the Leipzig Neuseenland tourist association recorded some 700,000 overnight stays in the member communities. Consequently, not only Cottbus or the open-pit mines in the Rhineland between Aachen and Cologne would like to copy Leipzig’s success, but coal mines in Australia and Canada are planning similar projects, too.

It’s also conceivable to use such artificial bodies of water as storage lakes for renewable energies. Especially if they had the size of the “Ostsee” lake in Cottbus, says the “Grüne Liga” environmental association and criticizes the fact that this was not done there.

Detlef Schulz, Head of the Electrical Energy Systems department at the University of the German Federal Armed Forces in Hamburg, proposed a totally different idea for the shut-down open-pit brown coal mines a few years ago: since the floors of the residual holes are between 100 and 400 meters (330 and 1,300 feet) below the surrounding surface, they offer a sufficient vertical difference for pumped storage power stations.

Their principle is simple: Whenever the generation of power exceeds demand, the surplus is used to operate pumps that elevate water from a lower basin into a higher one. When electricity is needed again, the water is made to flow back via a turbine. Thus, pumped storage power stations are ideally suited for balancing the fluctuating generation of electricity from wind power and photovoltaic systems. That the technology has not been implemented in open-pit mines so far is due to the fact that the proportion of fluctuating renewable energies was initially small and, for a long time, an end of coal mining not foreseeable, says ETC Energietechnik, the company that has held the patent on the idea since 1998. Now, following the decision to phase out coal and the progressing expansion of renewable energies, this approach might be given a new chance: research scientists from the Wuppertal Institute for Climate, Environment and Energy have calculated that a pumped storage power station in today’s open-pit mines Hambach, Garzweiler and Inden in the Rhineland would have significant technical storage potential of up to 400 gigawatt hours.

This amount of energy could supply some 100,000 four-person households with electricity for one year. Due to the enormous storage capacity, the scientists wrote in their paper published at the beginning of this year, “a more detailed investigation of the technical, environmental and legal feasibility, as well as public acceptance, would be worthwhile.”

Another opportunity to convert a future coal wasteland into an innovative large-scale storage system for wind and solar power was just recently missed when the Prosper-Haniel coal mine in Bottrop was shut down at the end of 2018. It was the last active hard coal mining site in the Ruhr region and, according to the ideas of Hermann-Josef Wagner, Chair of Energy Systems and Energy Economics Mechanical Engineering at Ruhr University Bochum, and André Niemann, Chair of the Institute of Hydraulic Engineering and Water Resources Management at University Duisburg-Essen, was to be converted into the first underground pumped storage power station in the world. In such a project, an artificial lake is created above ground. Instead of a second lake, the lower water reservoir is located deep down underground. The existing system of mining tunnels and shafts, plus the available mining equipment, predestines deactivated mines for such conversions. However, since the shafts at Prosper-Haniel are now progressively being backfilled following the shutdown, the mine is no longer usable as a huge storage system. This has not stopped interest in the project, though, because a large number of suitable mines exist around the world. Particularly Wales and China are showing keen interest in the project, according to Wagner.

© Kreklau/Ruhr Tourismus GmbH

The fact that the plans for pumped storage were not realized doesn’t mean that the former mines in the Ruhr region have remained unused. The dumps that were piled up from the waste removed from the mining tunnels in the Ruhr region have long established themselves as attractive areas for outdoor recreation. Hikers and mountain bikers can be found here just like paragliders. Art installations and observation towers are located alongside nature preserves and wind turbines. “Due to the transformation of the waste dumps into recreational areas and landmarks, the heaps symbolize the completion of the structural change and the unparalleled repurposing and conversion of former industrial wastelands,” says Jan Pass from Ruhr Tourismus GmbH. The same objectives are pursued by the Ostsee project in Cottbus. Work on the lakeshores and in other areas is still pending completion there while the surrounding communities are also avidly planning and building so that marinas, water ski facilities, roads and bicycle paths will be finished on time.

The eastern lakeshore with its two islands, though, will not be developed for buildings, but reserved to fauna and flora, providing a new home to water birds such as bean and white-fronted geese, gray herons, great crested grebes and other species. However, the feathered animals also have to be patient for a while, as only eight percent of the total amount of water has flown into the lake so far. Even so, the loop is closing. Places that once were idylls of nature will, ideally, return to that state in the near future – or provide energy in more sustainable ways.

At the Wolkenberg mountain in the re-cultivated part of the Welzow-Süd open-pit mine near Cottbus, seven ­varieties of grapes are grown, five white and two red, amounting to a total of 26,000 vines in an area of six hectares (15 acres), planted in 2010. The artificial 30 meter (98 feet) high mountain has everything that grapevines love: an eleven-percent slope, a south-southwesterly orientation, a till layer with a thickness of about half a meter (1.5 feet) and a slightly raised pH level of the soil. Only natural precipitation has to be augmented by irrigation. The latter also applies to the slightly smaller vineyard in the former coal mining districts Geiseltal and Meuro. Harvest is planned to begin in early/mid-September and the winegrowers expect 2019 to be a good year.