Geothermal systems

When it comes to climate neutrality, most of the attention goes to renewable electric­ity generation. “However, the key to the energy transition is actually the heating transition,” Prof. Rolf Bracke, director of Fraunhofer IEG points out. After all, generating heat for the industry sector, district heating and buildings takes up 56 percent of annual final energy consump­tion. By contrast, generating electricity only takes 14 percent of the primary en­ergy. “If we want to be climate-neutral, we have to generate heat from renewable sources. Solar thermal systems will re­main a niche option due to the amount of space they take up. And there isn’t much room left for expansion in term of biomass either – we can only burn as much wood as we can regrow here in Germany. That just leaves geothermal heating,” says Prof. Bracke. The demand for space and hot wa­ter heating in buildings alone represents 31 percent of Germany’s final energy con­sumption. Although shallow geothermal energy is used in a significant proportion of new residential construction projects, with percentages well into the double-dig­it range, and medium-depth geothermal energy supplies many local heat networks in districts, there are few large-scale projects focusing on deep geothermal energy – because the effort involved is far greater. Instead of drilling a hundred meters down as for shallow geothermal energy, deep geothermal energy requires drilling down some thousands of meters, where the water reaches temperatures of 100 to 150 degrees Celsius and only remains in liquid form due to the high pressure. The amount of heat generated by deep geothermal systems would be enough to supply existing district heating networks. This is particularly important in densely developed cities, where it is not possible for every house to tap into shal­low geothermal energy. Deep geothermal energy is also a good option for industrial processes, greenhouses, bakeries and paper manufacturers, as they need more energy than residential buildings.

“Deep geothermal energy could supply industrial process temperatures of up to 180 degrees, in combination with large heating pumps, for example – that corre­sponds to up to a third of the total indus­trial demand for heat,” says Prof. Bracke. It’s a combination that Fraunhofer IEG is exploring as well. The research team is working with the Fraunhofer Institute for Environmental, Safety and Energy Technology UMSICHT to develop a plan for switching a Hagen-based paper factory’s heat-intensive paper man­ufacturing process to a deep geothermal system, complete with a large heating pump. Bio-gas will also be used to supple­ment any shortfall. “While the upfront costs of a deep geothermal system are much higher than systems that burn fossil fuels to generate heat, the operating costs only amount to 20 to 25 percent of the fossil systems. So, depending on the location, deep drilling will pay for itself in five to 15 years,” explains Prof. Bracke. That’s why RWE Power AG is considering a deep drill­ing operation. In conjunction with Fraun­hofer IEG, it is developing a geothermal power plant that could supply the Aachen region with renewable heat from 2029. It’s an important date, because the last RWE lignite power plant, which supplies Aachen’s district heating network, is due to shut down that year. The municipal utilities companies in Düsseldorf and Duisburg, as well as the Düsseldorf airport are also working with Fraunhofer IEG in the field of geothermal heating networks.

Fraunhofer IEG is adopting an entire­ly unique approach in the Ruhr region, which is essentially built on a labyrinth of coal mines. “In Bochum, we intend to use the mines for seasonal heat storage, for industrial waste heat for example. We’re currently building a demonstrator in the form of a large concentrated solar power plant, which we’re using to heat the 20 de­gree mine water up to 70 degrees. Then, when needed, it can be raised to the district heating temperature of 110 degrees using a large heating pump. This approach, whe­reby we make use of easily available heat, could become the key to the heating tran­sition for metropolitan areas on the Rhine and in the Ruhr region,” says Prof. Bracke hopefully. The large heat pump from Fraun­hofer IEG is set for installation in 2022.

Meanwhile, the Fraunhofer Institute for Energy Economics and Energy System Technology IEE is campaign­ing for low-temperature networks. Instead of running at 90 to 120 degrees Celsius, these run at just 40 to 50 degrees. In collaboration with the German Energy Efficiency Association for Heating, Cool­ing and CHP (“Energieeffizienzverband für Wärme, Kälte und KWK”) and various European research partners, Fraunhofer IEE has produced a reference manual showing how these networks could be implemented under a wide range of dif­ferent conditions. “These low-temperature networks offer many advantages,” says Dr. Dietrich Schmidt, head of department at Fraunhofer IEE. “At these temperature ranges, usable waste heat and geothermal heat would be available in much greater quantities. What’s more, heat pumps and solar thermal systems are much more efficient at lower temperatures.” It also reduces the strain on existing pipes and minimizes transport losses. Across Europe as a whole, the potential savings amount to a total of 14 billion euros a year. If you set yourself high targets, then clear­ly, you must search for solutions in every nook and cranny — not only looking to the heavens for sun and wind, but also down below, deep within the earth.