The history of modern deep geothermal energy use in Bavaria

In 1998, Erding was the first geothermal plant in Bavaria to supply households with heat in an environmentally friendly way. In 1983, an exploration well could not find the targeted oil. Instead, thermal water was found at around 65°C. The city of Erding decided in 1986 to take over the well from the oil company and to use the heat from below. Since then, 29 other geothermal projects have followed in Bavaria. This makes the Molasse Basin the hotspot for geothermal use in Germany. The installed deep geothermal capacity in Bavaria is currently around 325 MWth and 40 MWel. This corresponds to over 90% of the thermal or almost 80% of the electrical capacity installed throughout Germany. A total of 30 deep geothermal energy projects were implemented in Bavaria between 1998 and 2021. Of these, 24 systems are currently in operation, one project is in the construction phase (as of November 2021). The projects are 15 heat-only plants, eight combined power and heat systems and one power-only plant for which heat extraction is planned in the future.

Therme Erding, fed from a 2300 m deep borehole (source: Therme Erding).

The Bavarian Molasse Basin

There are three suitable regions for hydrothermal geothermal use in Germany. Underground layers containing aquifers with a temperature of more than 65 °C, which allow direct use for heating purposes, can be found in the Upper Rhine Graben, the North German Basin and the Molasse Basin.

The subsoil of the Bavarian Molasse Basin contains the so-called Malm. This layer is located at the surface (Franconian Mountains) north of the Danube and dips towards the south, so that it lays about 3000 meters deep under the metropolitan area of Munich and deepens towards the Alps to 5000-6000 meters depth. The so-called Malm reservoir is characterized by a fractured karst aquifer with generally high flow rates and can reach a thickness of up to 600 meters. Due to its depth in the southern part of the Bavarian Molasse Basin, the groundwater found there has favorable temperatures for geothermal use. South of Munich, it is even hot enough (>100°C) to produce electricity in addition to heat extraction. Local changes in reservoir characteristics lead to spatial differences in the success of drilling. This implicates that depending on the location in the Molasse basin not every project could be successfully implemented in the past.

Location of the Molasse Basin in Germany (modified after GeotIS: Geothermal Potentials. Agemar, T., Alten, J., Ganz., B, Kuder J., Kühne, K., Schumacher, S. & Schulz, R. (2014): The Geothermal Information System for Germany – GeotIS – ZDGG Vol. 165 Issue 2, 129-144).
Schematic representation of the subsurface from the Danube to the Alps (Source: Geothermie-Allianz Bayern)

Geothermal Potential in Bavaria

Around 30 % of Bavaria’s CO2-emissions are emitted by the building sector, the majority of which is due to the supply of hot water and space heating. In order to become climate-neutral in Bavaria by 2040, the capacities for renewable energy generation must be further expanded.

Geothermal heat pumps are technically well developed and have their strength particularly in sparsely populated areas, which account for around 50% of the total heat demand in Bavaria.

Deep geothermal energy is particularly suitable for the energy-efficient central heating networks in urban centers, since the systems only require a little space and produce quietly. The heat supply through deep geothermal is one of the most climate-friendly renewable energies with a high CO2 avoidance potential.

The calculated technical potential of hydrothermal deep geothermal energy for temperatures >80°C corresponds to 7655 MWth. Estimates by the Geothermal Alliance Bavaria show that this could theoretically cover up to 40% of the heating demand of entire Bavaria. In order to cover the heat demand of the southern Bavarian cities in the area of ​​the Molasse Basin, more than 800 production and injection wells (over 400 doublets) would be necessary in addition to the current projects.

If the base load (35% of the heat demand) is to be covered, 16% of the identified district heating demand in Bavaria could be provided by deep geothermal energy. This could save almost 2 million tons of CO2 equivalent per year. For example, if you want to cover 70% of the heat requirement, up to 6 million tons of CO2 equivalents can be saved each year. In terms of specific greenhouse gas emissions, deep geothermal energy has the best net avoidance factor of all renewable heating technologies.

Greater workload of a deep geothermal system leads to an increase in profitability. In addition, the energy contained in the thermal water can be depleted down to a low temperature. Therefore, cascading use in industry and agriculture and cooling applications represent an attractive opportunity to contribute to greater utilization and profits of geothermal projects and the decarbonization of agricultural and industrial processes.

Deep geothermal potential in the Bavarian Molasse Basin. The performance has been divided into approximately 8 km² clusters, each containing a (hypothetical) geothermal doublet. Areas with a high degree of uncertainty are gray shaded, areas in which unsuccessful projects are located were excluded. The temperature limit was set to <80°C. (Source: Geothermal Alliance Bavaria)

Challenges in Expansion Dynamics

The development of geothermal plants (drilling, power plant, district heating network etc.) is characterized by high initial investment costs and a long depreciation period. This fact keeps away many municipalities from the technology.

The exploration risk for future geothermal wells and thus the basic prerequisite for the economic success of deep geothermal energy can be predicted comparatively well in the Molasse Basin. However, there are significant local differences in terms of exploration risks. Lowest risk is expected is the area of Munich, south of Munich and in the eastern Molasse, where there are already a large number of successful wells.

In order to use the potential in northern Bavaria, which has no thermal water-bearing aquifers in suitable depths, and in the low-permeability rocks of the Molasse Basin, further research in the field of EGS (Enhanced Geothermal Systems) must be carried out. For a profound assessment of the deep geothermal potential outside the Molasse Basin, some basic scientific questions are still unanswered and require investigation whether the necessary geological conditions for economic use are given.

In the past, microseismic events have occurred in the vicinity of certain geothermal projects. These weak earth movements are thought to be caused by pressure and temperature changes as cool water is reinjected. By adapting the operation, however, perceptible earth movements can be minimized or even prevented entirely.

So far the seismic events in the Molasse Basin have not reached the level that could damage buildings under the existing building standard. Nevertheless, the slight earth movements were perceptible and partly audible through a loud noise. In some cases, this has led to significant insecurity among the population.

Figures and Facts on the Expansion of Geothermal Energy in Bavaria

Geothermal energy already makes an important contribution to sustainable energy supply in Germany, and particularly in Bavaria.

A nationwide overview of the current status of geothermal energy use is provided by the regularly updated statistics “Geothermal Energy in Figures” published by the German Geothermal Association. They present, among other things, the number of installations as well as the installed thermal and electrical capacities. In addition, the Energy Atlas Bavaria provides detailed, state-specific information on the use and potential of geothermal energy in the Free State of Bavaria. Together, these sources offer a sound and up-to-date data basis for assessing the significance of geothermal energy.

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