Deep geothermal energy to tap huge heat potentials

Around 56 percent of Germany's energy needs are met by the heating sector. However, only 15 percent of this is based on renewable energy sources. In a joint roadmap, researchers from the Fraunhofer-Gesellschaft and the Helmholtz Association have taken a look at deep geothermal energy in order to sound out how much potential for a sustainable heat supply could be contained here. The researchers conclude that more than a quarter of the annual heat demand, i.e. over 300 TWh, can be covered by deep geothermal energy, and also provide recommendations for action on how this goal could be achieved.

The study focuses on hydrothermal reservoirs, i.e. thermal water-bearing rock strata at depths of between 400 and 5,000 meters with a water temperature of up to about 180 degrees Celsius. Rolf Bracke, head of the Fraunhofer Institute for Energy Infrastructures and Geothermal Energy (IEG) and co-editor of the roadmap, puts the usable energy potential from these sources at 220 to 430 TWh per year.

"There is enough energy underground, and the low-hanging fruit of deep geothermal energy should be tapped as soon as possible," said Bracke, who emphasized that decarbonization of the heating sector in Germany would not be possible without geothermal energy. On the positive side, he said, regions with high geothermal potential, such as the southern German Molasse Basin in the Munich area, the Upper Rhine Graben, the North German Basin and the Rhine-Ruhr region, also generally have a high population density with a corresponding demand for heat.

Of the 80 million or so inhabitants in this country, around three quarters live in urban structures, and since a large proportion of cities are equipped with district heating networks, the transformation of the municipal heating network with the aid of geothermal energy is particularly suitable here. "This is where interconnected heating systems will be expanded in the future, and this is where geothermal can play a big role." The sustainable expansion of geothermal energy is therefore an investment in cities, he said. One sees a demand of 170 TWh/a for deep geothermal energy in the municipal sector.

But the study also sees great potential of 130 TWh/a for industrial process heat for sectors that operate at a temperature level that can be represented by geothermal energy - equivalent to a quarter of industrial heat demand. Geothermal energy is also said to play a significant role as a heat storage system. Here, more than 500 TWh/a could flow in, and the storage facilities would have to be designed in such a way that they could be integrated into the heating networks.

Currently, Bracke said, there are 42 deep geothermal plants in operation in Germany, with 360 MW of thermal capacity and 45 MW of electrical capacity. "The plants have been operating successfully for many years, are integrated into municipal systems, and operate at 25 to 30 euros/MWh at competitive generation costs." But scaling up still needs to happen quickly, he said.

The study assumes that an expansion of installed capacity from less than 400 MW today to 70 GW will be required. It recommends expanding by 100 TWh annually by 2030 and 300 TWh by 2040/45. Three-digit billion sums come into play here: "We need to make investment decisions quickly that are in the order of 2 to 2.5 billion euros per GW of installed capacity."

Quickly, he said, technology also still needs to get on track to meet the target. "If we want to expand 300 TWh per year in the future, then the leap from more manufacturing-based production of the plants to industrial capacity must also come." New and better drilling methods would need to be established in the market in the coming years, he added, along with more competition in borehole and high-temperature heat pumps and the integration of storage. And with a view to the new German government, the roadmap relies on clear expansion targets for geothermal energy now being formulated and these also being underpinned by appropriate regulatory measures.

The roadmap considers it important to limit the economic risks, such as exploration of deep geothermal energy, for small and medium-sized enterprises such as municipal utilities. To this end, financial instruments are needed to balance risks between municipalities in the form of state insurance or funds that participate financially in projects. In addition, he said, the federal government should increase funding for efficient heating networks to more than 1 billion euros, and the states should set up a nationwide geophysical exploration program to reduce the discovery risk for municipalities. According to Bracke, about 100 deep wells are needed for every GW of installed capacity.

Currently, the geothermal industry employs about 20,000 people in this country (as of 2016). Annual sales are around 1.3 billion euros. A ramp-up of geothermal energy would bring numerous new jobs, Bracke said. "You can assume 5 to 10 full-time jobs per MW of installed capacity."