Impressive natural phenomena thousands of metres below the earth

Hot subterranean water is to be expected in the kind of karstified limestone that lies deep below large areas of north-western Europe. Limestone contains the necessary cavities. Over millions of years, water flowing into and infiltrating such crevices gradually wears away the limestone and creates cavities. The water there already has a temperature of over 50 degrees and, at a depth of four kilometres, it can reach as high as 130 degrees. Hot water from a depth of up to 3.6 kilometres is already being sourced from carboniferous limestone in Belgium and the Netherlands and used to run successful geothermal plants. The DGE-ROLLOUT project will benefit from the very valuable experience and insights of that initiative.

The underground strata of North-Rhine Westphalia include karstifiable carboniferous rocks (limestone and dolomite rocks) in three different stratigraphic sections and thus at three different depth levels. Limestone lies in the chalk layer at a depth of about 2.5 kilometres, while carboniferous limestone and resedimented carbonates lie within the carbon layer at a depth of about five kilometres, and Devonian reef limestone lies at a depth of up to six kilometres.

Practical, safe, clean – and socially desirable

Hydrothermal, fracking-free geothermal energy must be technically safe and clean for both people and the environment. Not only that, it must also be economically sensible, politically and socially desirable and legally permissible. The DGE-ROLLOUT project pools the transnational expertise of various institutions and companies, including the state Geological Survey institutes of North-Rhine Westphalia, Belgium, France, the Netherlands and Ireland, as well as research institutes, network organisations, companies working in the field of gas and oil exploration/supply and energy utilities. The project is divided into three work packages:

1) Charting and networking, led by the Belgian Geological Survey

• Creation of a common, transnational knowledge base
• Investigation and depiction of the deep geothermal potential in a 3D atlas
• Investigation and depiction of heating demands and customer types
• Compilation and comparison of various stages of development, and regional differences in infrastructure and internal processes, amongst other things
• Clarification of the legal and financial issues
• Development of an online network of all key information to do with planning and production of hydrothermal/geothermal energy

2) Support for decision-making and exploration, led by Energie Beheer Nederland B.V.

• Risk minimisation during exploration work for deep geothermal projects to facilitate economic, public and political decision-making
• Creation of practical application and decision-making aids for investors and end users
• Development of a standardised exploration method for complex geological conditions

3) Enhancing the performance of geothermal plants, led by the Flemish Institute for Technological Research

• Increasing the performance capability of geothermal plants to achieve further carbon reduction through more knowledge of the hydrothermal reservoir and improved heat storage

Heating networks – including those in the coal mining district – play a huge role

Performance improvements will be carried out under real conditions in Balmatt (Belgium), Bochum (International Geothermal Centre, GZB), at the Technical University of Darmstadt and in Weisweiler (RWE Power). The facilities exemplify a range of questions:

Balmatt is the first geothermal facility in the project area to recover water with a temperature high enough to generate electricity. Bochum is a geothermal location with heat storage opportunities in a decommissioned hard coal mine. Darmstadt has been designed to test the storage of seasonal heating surpluses. Weisweiler is a conventional lignite-fired power plant where the inclusion of geothermal production is being explored.

All four plants are linked to existing heating networks – something of particular interest to the “coal region” of NRW, with its many power plants. The Weisweiler lignite power station still supplies its customers with district heating generated using lignite. A few years from now, clean, climate-friendly heat from the earth could be converted into district heating. The deep geothermal potential here is highly promising. Studies and analyses will show whether, and how, deep geothermal energy can be the heat source of the future.