Coal pit to wind farm: Energy giant to fast-track energy makeover for old mine sites

German energy giant RWE is beginning to investigate the possibility developing wind power on former opencast coal mines much earlier than has been previously possible.

The soils of an opencast mine are often unstable for many years after their closure, needing several years to settle before they can be cultivated.

Moreover, with modern wind turbines weighing as much as 6,500 tonnes, it can take up to 15 years before opencast mines can be built on.

However, on the initiative of RWE, experts from the Ruhr University Bochum and engineering firm Jörss-Blunck-Ordemann (JBO) will investigate the possibility of accelerating the timeframe to allow wind farms to be built on closed opencast mines much earlier than previously.

The research project will receive funding of over €680,000 from Germany’s Federal Ministry for Economic Affairs and Climate Protection.

“Together, we want to push ahead with the expansion of wind power and also use more difficult locations for this purpose,” said Christian Vogt, responsible for developing wind farms at RWE.

“We are thus very pleased that the Federal Ministry for Economic Affairs and Climate Protection is supporting our project, thereby helping to examine to what extent and under what conditions the use of freshly recultivated areas is possible.

“In the Rhenish mining area alone, we want to build 500 megawatts of additional renewables capacities by 2030 to advance the energy transition.”

The researchers will be working on the Inden opencast mine for a period of three years where they will select the most complex possible subsoil for their studies. Gravel and sand weighing as much as a wind turbine and its foundation will then be piled up on a circular area with the radius of a wind turbine.

Measuring devices will then be used to record any geomechanical changes and computer calculations based on the recorded data and accompanying geotechnical laboratory investigations will be carried out to model the settlement of the subsoil.

These measurements will not just take into account the deadweight of the wind turbine, but also the effect of wind loads on the ground around an active turbine.

“We are confident that we can reliably assess the suitability of sites on freshly recultivated areas using computer simulations, which we want to confirm using the test fill in Inden,” said Torsten Wichtmann, professor of soil mechanics, foundation engineering, and environmental geotechnics at Ruhr University Bochum.

“This innovative project combines our many years of expertise on wind turbine foundations and soil mechanics issues in the recultivation of former opencast mines.”