Geothermal technologies in urban centres – opportunities and challenges

Munich, 18 July 2024

The geological structures in Germany show great potential for the use of deep hydrothermal geothermal energy in particular for heat supply. In addition, there are already heating networks in urban centres into which large amounts of energy can be fed. For this reason, geothermal energy in Germany can play a special role in the transition to a climate-neutral heat supply. At acatech am Dienstag on 9 July, experts discussed the use of geothermal energy for heat supply in urban areas, explained the prerequisites and possibilities and discussed the associated challenges and reservations.

In his welcoming address, acatech President Jan Wörner emphasised the importance of security, resilience and sustainability for sovereignty. He emphasised that sovereignty is also linked to security of supply, particularly in terms of energy supply. The term ‘strategic sovereignty’ encompasses the freedom to decide at which level to strive for independence and with whom to cooperate. This is what makes strategic sovereignty so important.

Afterwards, acatech member Rolf Emmermann (founding director and former scientific director and chairman of the board of the Helmholtz Centre Potsdam – GFZ German Research Centre for Geosciences) presented the results of the study ‘Geothermische Technologien in Ballungsräumen. Ein Beitrag zur Wärmewende und zum Klimaschutz’ (in German). The aim of the study is to demonstrate the potential of geothermal energy on the one hand and the possible applications of geothermal utilisation systems on the other.

What is geothermal energy and what types are there?

Geothermal energy is a form of energy that exists in the geological subsurface and is constantly available, explained Rolf Emmermann. It is independent of the seasons and weather conditions and is renewable thanks to sustainable reservoir management. It can be used to provide thermal energy, store heat and cold and to generate electricity. Geothermal energy is divided into near-surface (up to 400 metres), medium-depth (up to around 1,200 metres) and deep systems (from around 1,200 metres). The main challenge is to transport the heat to the surface of the earth so that it can be harvested for direct use. There are three key success factors for this: the most accurate possible knowledge of the subsurface, the drilling technology and the technologies for heat pumps. Considerable progress has been made in all three fields over the past ten years.

Opportunities and potential of geothermal energy

The greatest potential for using geothermal systems lies in urban centres. The demand for thermal energy is high there, the demand density is high and the necessary heat distribution networks are often already in place. In some regions, geothermal energy is already an integral part of heat energy supply planning, and numerous geothermal plants are in operation or being planned throughout Germany.

The greatest proven potential lies in the Upper Rhine Graben, the North German Basin, the Rhine-Ruhr region and the South German Molasse Basin with the greater Munich area, explained Rolf Emmermann. Stadtwerke München has already partially realised its goal of becoming the first major city in Germany to generate all of its district heating from renewable energies – primarily from geothermal energy – by 2040. In addition to the greater Munich area, the Rhine-Ruhr region, the metropolitan region of Berlin, the Hanseatic city of Hamburg, the greater Hanover area and Schwerin are also exemplary regions for geothermal energy in metropolitan areas.

Geothermal energy can increase the resilience, efficiency and cost-effectiveness of the heat supply because

• it is base-load capable,
• as a local form of energy, it guarantees permanent and stable heat supply,
• it can be coupled with other heat generation systems, if necessary, using large or high-temperature heat pumps,
• it can store excess heat seasonally,
• the use of new geophysical exploration methods and innovative drilling technologies increases safety, minimises production costs and reduces the exploration risk, and
• its efficiency can be increased, for example through cascade utilisation (successive utilisation at different temperature levels) and can lead to an increase in operating hours and full-load operation.

How can the potential be utilised economically?

The future development of the geothermal share of total final energy consumption depends on many factors. These include measures to increase efficiency and the future development of price levels. In addition, the willingness to use innovative and complex technologies and to take a holistic approach to larger construction or remodelling projects, including from an energy perspective, will be decisive. The use of geothermal utilisation systems must be planned in good time with the involvement of the approving authorities.

Thomas Hamacher (Geothermal Alliance Bavaria, and Technical University of Munich) put the onus on the authorities. They must clarify where geothermal energy can be used and inform the municipalities so that they can take geothermal energy into account when drawing up their respective heat energy provision plans. Furthermore, it is the task of science and associations to make new findings and information available to all those working in the field of geothermal energy. The Geothermal Alliance Bavaria has drawn up a master plan for the greater Munich area to demonstrate the potential of geothermal energy. Thomas Hamacher´s conclusion: the successes in Bavaria and the Geothermal Alliance Bavaria´s master plan have led to a re-evaluation of geothermal energy.

Christian Pletl (Stadtwerke München (SWM), Development of Regional RE Generation, Head of Geothermal Energy) reported from the field: deep hydrothermal geothermal energy is already a functioning technology with around 20 plants in the greater Munich area. The geothermal plant at Heizkraftwerk Süd is currently Germany’s largest and supplies around 80,000 households with CO2-neutral heat. The expert in energy management and power plant technology reported that planning to include a heat pump and a cooling system is currently under way. The municipal heat energy provision plan for Munich envisages an increase in district heating from the current 30 per cent to 70 per cent – in relation to the total heating requirement. This heat is to be obtained from deep geothermal energy and geothermal heat pumps.

Reservations and economic viability – when is geothermal energy worthwhile?

In the subsequent discussion, the question of general reservations about geothermal energy was answered.

The experts agreed that resistance is greatest where the technology is unknown. In Munich, people are very open-minded and recognise the advantages. Local resistance is primarily due to the expected construction site noise. In principle, slight seismic events could occur – but these could be recognised at an early stage using measuring equipment and thus avoided.

The costs of geothermal utilisation were also asked about. Initially, high investment costs are to be expected, explained Christian Pletl. However, the subsequent low operating costs would justify this. Overall, geothermal energy is comparable to other heating systems in terms of costs.

For electricity generation, on the other hand, geothermal energy plays a subordinate role from an economic point of view. This is due to the efficiency of geothermal plants, which averages around 10 per cent, making electricity generation cost-intensive. However, this utilisation is worth considering as a back-up solution.