Heat From The Depths

13 October 2022

Over half of all the energy consumed in Germany is used for heating – for instance, for hot water, offices or industrial processes. And 84 percent of this energy is derived from coal, oil and gas. If we are going to achieve the target of making the supply of heat up to 50 percent carbon neutral by 2030, then some things will have to change. Geothermal energy is seen as a promising option here. And yet, little use has been made of heat from the depths – until now.

The potential of thermal water from the depths of the earth is enormous – such, at least, are the findings of a study conducted by the Fraunhofer Institute and the Helmholtz Association. The hydrothermal geothermal process that extracts hot water from depths of between 400 and 5,000 metres would be sufficient on its own to cover about a quarter of Germany’s heating needs, the researchers maintain.

And yet, whereas 90 percent of the heating energy of the volcanic island of Iceland comes out of the earth, the share in the heating mix of geothermal plants in Germany is still decidedly modest. There are currently 42, not including the new plant in the Munich district of Sendling. Taken together they produce just under 360 megawatts of heating energy and 45 megawatts of electricity – less than is produced in the Cologne-Niehl II gas-fired thermal power plant alone.

To exploit the opportunities presented by geothermal energy and achieve the country’s climate targets, thousands of new boreholes will have to be drilled and plants built in the coming years, say the researchers from the Fraunhofer Institute and the Helmholtz Association.

From this October, what are known as vibro trucks will be rolling from Viersen via Düsseldorf to Duisburg, where they will be deployed to chart the geothermal situation of the subsoil. The trucks use vibrating plates to generate vibrations in the soil which spread out into the subsoil as sound waves, which are then in turn reflected differently by different types of stone. Thousands of sensors on the surface intercept these signals. The data thus generated are used by North Rine-Westphalia's Geological Service to generate a two-dimensional sectional view of the subsoil.

In 2021, the state government did manage in this way to fill in some of the blank spaces on the map in the Münsterland – in the process also discovering some promising structures in the strata of stone. Heat suppliers, industrial firms and local authorities can now use these data as the basis for their own investigations. And, thanks to 3D seismology (see box), they can also identify suitable places for geothermal plants.

Last but not least, the acceptance of geothermal projects would have to be underpinned by accompanying measures, industry representatives warn. And these are not equally alive and kicking in all places. Since a geothermal drilling operation has been causing minor earth tremors in Basel since 2008, worries about the potential impacts of the technology persist. Although it must be said that hydrothermal geothermal plants such as those in use in Germany are significantly less exposed to earth tremors. “What’s more, high-risk zones in the subsoil can now be identified more easily and plans adapted accordingly,” says Simon Kremers, whose job at DMT focuses on manmade earthquakes. When geothermal plants are operating, seismic activity in the vicinity is monitored by sensor systems. “The risk of creating noticeable earthquakes is very low, but not zero, of course,” says Mr Kremers.

Which why it is essential to offer local people transparent information and to involve them in the planning process, the geophysicist says. What this might look is demonstrated by a geothermal project in the Breisgau, in which a council of citizens, having grilled various experts, came out with a large majority in favour of the planned plant. Many residents would also like to see the project implemented quickly.

At the moment it can take anything from eight to ten years for hot water to finally start bubbling up out of the earth. Speeding up the planning processes, improving preliminary explorations and standardising the construction of geothermal plants would make it possible to shorten this process by two to three years, says Boris Dombrowski from DMT: “And that’s where we need to head if we want to get the heating transition over and done with as soon as possible.”

And yet, even the very best of preliminary explorations cannot offer a one hundred percent guarantee of success. “Every tenth drilling operation fails – in other words, it doesn’t provide enough water at the required temperature,” explains Boris Dombrowski, deputy head of Geo-Energy & Resources and DMT. And, according to Munich’s public utility company, a single drilling operation costs up to 15 million euro. For local heat suppliers, that kind of loss can spell doom, says geophysicist Mr Dombrowski. Many of them are therefore scared off by the risk.

The German government has for this reason now created a federal fund for efficient heating grids, which has since mid-September been supporting geothermal plants, among other beneficiaries, by funding up to 40 percent of their investment costs. From the point of view of industrial associations, while this is undoubtedly a step in the right direction, the sum total of the available funds is still way too low. Not only that, but state-supported insurance to cover the risk of coming up empty handed, as was originally envisaged by the federal government, is also needed, the associations claim. The point of such insurance would be to compensate for some of the losses in the event of failure. “This move would create a level playing field between geothermal energy and other energy sources. After all, a municipal utility has never yet had to worry about the exploration and extraction of gas or oil as raw materials; all they’ve had to do is purchase them,” says energy expert Mr Dombrowski.