Questions and Answers

Geothermal energy generally refers to the use of heat from the Earth to generate electricity, heating, or cooling energy. Energy from the Earth’s interior is renewable, locally available, and constantly available, meaning it does not fluctuate like wind or solar energy. Geothermal energy is climate-friendly and contributes to the resilience of the energy system.

Three types of geothermal systems can be distinguished:

Near-surface systems (used from a few meters down to 400 m depth):
These are used for heating, cooling, and the seasonal storage of heat from upper soil and rock layers or groundwater. In Germany, such systems are already used in over 480,000 single- or multi-family homes, public institutions, hospitals, schools, and commercial buildings, for example in the form of ground source heat pumps with geothermal probes or collectors. These are connected to heat pumps, which raise the extracted temperatures of just a few degrees (<20°C) to a usable level.

Deep hydrothermal systems (from 400 m depth):
Hot thermal water is pumped from depth to the surface, its heat energy is utilized, and the cooled water is reinjected back underground. Depending on depth and geological conditions, water temperatures can range from 40°C to about 200°C. A suitable site is crucial, requiring freely circulating water in sufficient quantity and temperature. In addition, sufficiently large fractures, fissures, or pore spaces in the rock are needed, ensuring high permeability for thermal water. These conditions are not found everywhere. In Germany, usable thermal water reservoirs are mainly located in the Molasse Basin in southern Bavaria, the Upper Rhine Graben, and the North German Basin, and have already been developed at more than 30 sites.

Deep petrothermal systems / Enhanced Geothermal Systems (EGS) (down to more than 5,000 m depth):
In contrast to hydrothermal geothermal energy petrothermal systems use the heat of deep rock layers with low permeability for thermal water. To utilize the very high temperatures (over 200°C) in these dense rocks, a water circulation system must be created: water is pumped down, heated by the hot rock, and then brought back to the surface. To enable this, the rock must be made more permeable through stimulation techniques. Water is injected under pressure to widen existing fractures and fissures or to create new ones. These “enhanced” geothermal systems are known as “Enhanced Geothermal Systems” or EGS.
The advantage of EGS is that they do not depend on naturally permeable reservoirs that allow economically viable circulation of thermal water. This makes geothermal energy possible in more regions than hydrothermal systems. However, so far there are only a few pilot projects. This is a key focus of research at GeoLaB.

Geothermal energy is a key building block in the global transition toward a climate-neutral energy supply. It plays a crucial role because — unlike wind or solar power — it requires little land, is independent of weather conditions, and offers storage potential. The largest and so far almost untapped energy source lies in the crystalline basement rock. To use this energy source safely and sustainably and to integrate it into heat supply systems, extensive research is essential.

As with any complex field, advancing geothermal energy requires persistence and collaboration among many research teams — much like the development of photovoltaic technology, which became an efficient and widely adopted renewable energy source through decades of continuous research and improvement. Different teams approach the challenges with diverse methods and ideas, and each contributes to creating innovative solutions in the long run.

The GeoLaB research project is part of an internationally connected research landscape, where ongoing exchange of knowledge drives major progress. Germany can take a pioneering role and make important contributions to unlocking the vast energy potential hidden deep within crystalline rock.

Beyond its ecological benefits, large-scale use of geothermal energy also holds economic potential: it can create new jobs, train skilled professionals, and build value chains. In this way, GeoLaB’s research not only supports the heating transition but can also contribute to Germany’s economic development.

Hot crystalline rock is often hidden several kilometers beneath the Earth’s surface and is barely accessible to scientific study. Along the margins of the Upper Rhine Graben, crystalline rock reaches the surface in the Black Forest and the Odenwald. In these regions, the rock can therefore be studied particularly well. In the planned research laboratory, processes that normally take place deep underground can be observed more easily.

The GeoLaB team considers the Tromm region in the Odenwald to be a particularly suitable site from a geoscientific perspective. The infrastructural conditions are good and the political framework is supportive. In addition to these factors, the geoscientific requirements are essential in determining whether the Tromm is the right location for GeoLaB.

Whether the subsurface actually meets the geoscientific requirements for a research laboratory is currently being carefully examined. During the ongoing exploration phase, the subsurface is being investigated through extensive geological, geophysical, and hydrogeological measurements. Based on these findings, a decision will be made as to whether the Tromm is indeed suitable as a research site.

We cannot answer this question yet during GeoLaB’s current exploration phase. The results of all investigations conducted during the exploration phase will be compiled in a scientific site assessment report. The decision on the geological suitability of the Tromm region is planned for late spring 2026. At that point, the course will be set for the next phase, the planning and permitting phase, in which, among other things, the route of the tunnel will be planned and a site for the tunnel entrance will be identified.

GeoLaB is a project of the Helmholtz Association, Germany’s largest research organization. The project is funded with approximately 35 million euros from the Federal Ministry of Research, Technology and Space (BMFTR). Additionally, the Federal Company for Radioactive Waste Disposal (BGE) contributes 15 million euros.

This funding covers the exploration phase and the construction of GeoLaB. Research activities within GeoLaB are project-based and supported by various public funding sources.

In fact, there are already several underground research laboratories in Europe and around the world. The laboratories have different research objectives and pursue these in different types of rock.

Most underground laboratories in Europe are used to research the final storage of radioactive waste. These include well-known underground laboratories such as Grimsel and Mont Terri in Switzerland and Äspö in Sweden. Until recently, there was no specific underground laboratory for geothermal energy. Deep geothermal energy in crystalline rock has so far been developed primarily through research projects such as Soultz-sous-Forêts in France and Utah FORGE. These projects use pilot plants directly in the deep reservoir. However, direct observation of the processes taking place several kilometres underground is only possible to a limited extent. Nevertheless, this is important for improving our understanding.

In order to advance research in Germany and in crystalline rock, an underground laboratory specifically for petrothermal research is needed. Experience from existing and former petrothermal deep geothermal projects further underscores this need for research. This research cannot be carried out in any other laboratory, as the processes important for deep geothermal energy can only be studied under suitable conditions. A specifically designed underground laboratory makes it possible to observe these processes directly underground in the cmplexoty of reality and gain a better understanding of them.

The Bedretto underground laboratory in Switzerland is the first rock laboratory dedicated specifically to geothermal research. However, not all questions can be investigated there. GeoLaB is intended to substantially complement this research and provide new insights – especially for geothermal energy in crystalline bedrock and under geological conditions such as those found in Germany and other parts of Europe.

Research in general thrives on collaboration, exchange and the transfer of findings and knowledge from various projects. The GeoLaB team is in constant contact with teams from other underground laboratories and petrothermal pilot projects worldwide. Research work by several teams in different laboratories also increases the speed of technology development and, most importantly, the safety of a new technology.

The Federal Company for Radioactive Waste Disposal (BGE) is involved in the exploration and construction phases of GeoLaB as a cooperation partner. Its participation aims to gain experience in the development of underground infrastructure. However, BGE’s involvement will end once the research laboratory becomes operational. No nuclear waste repository will be built at the GeoLaB site. The legally regulated site selection process for a final repository is conducted independently of BGE’s fundamental research within GeoLaB.

For more information: BGE classification

The approval process is a multi-stage process within the framework of the Federal Mining Act (BbergG) with step-by-step individual approval. Reviews and approvals are carried out by the Hessian Mining Inspectorate (RP Darmstadt / Department of the Environment Wiesbaden / Department IV/Wi 44 Mining Inspectorate).

On 15 February 2024, KIT was granted the exploration permit for the Tromm permit area.

This is merely the basic right to prospect for a specific raw material in a defined area. The holder of the exploration licence is not yet permitted to take any technical measures. It is linked to a work programme that serves the geological exploration of the permit area.

In July 2024, an operating licence under mining law for the exploration was applied for and approved in september 2024. This approval includes the application for seismic surveys, geophysical investigations such as geo-electrocs, geomagnetics and gravimetry, two exploratory boreholes and hydrogeological observation measurements.

IAs part of the procedure, the Hessian Mining Inspectorate consults specialist authorities and public bodies (including the affected municipalities and nature conservation organisations). The municipalities are entitled to submit a statement. The authorisation procedure includes, among other things, an examination of the operator's reliability and existing expertise, an examination in accordance with water law, immission control law (regarding possible noise and pollution) and nature conservation law. The Hessian Mining Inspectorate prepares and publishes the authorisation notice.

If the assessment for the Tromm site is positive, the planing and approval phase of the GeoLaB project will begin in 2026: extensive planning and necessary detailed investigations of the subsoil are carried out, the documents for the permits to build the tunnel are prepared and submitted to the Hessian Mining Inspectorate. This authority reviews the documents and again involves the affected communities, among others. Construction of the tunnel can only begin once the licences have been granted.

The GeoLaB project offers various information services such as this website and a newsletter. Here we report on the latest news, but also provide background information in the form of reports on the topic of geothermal energy, for example.

We organise public events, such as information evenings or participation in markets, in order to engage with the public. Information on past and current events can be found here.

In addition, GeoLaB regularly offers excursions to the exploration sites (construction site for exploration drilling, measurement campaigns) so that interested citizens can be present on site and ask questions to the project team.

Other formats for different target groups (e.g., students) serve to convey knowledge and foster exchange. For example, at the end of June 2025, school classes were invited to a construction site tour at Tromm.

If the decision on the scientific suitability of the subsurface is positive, the planning and permitting phase of the GeoLaB project will begin (see above). As part of this phase, concrete questions relating to the operation of the rock laboratory and its construction will be critically examined by the permitting authorities. A central aspect of this process is the assessment of suitable sites. In this context, we would like to involve the municipalities, in particular potentially affected local residents, in the implementation process and to provide transparent information on the respective status.

Because transparency and dialogue are important to us, at the beginning of the planning and permitting phase we will explore, in coordination with the permitting authority, the possibilities for involving citizens at an early stage.

In addition, all scientific data collected within the framework of GeoLaB will be handled in accordance with the FAIR principles – meaning that they are findable, accessible, interoperable, and reusable. As is customary in science, however, the data will first undergo quality control before being made available in a transparent, comprehensible, and responsible manner.

For communication, we use a wide range of channels: our website, newsletters, social media presences on Facebook and Instagram, flyers distributed to all households, personal conversations, topic-specific flyers for individual measurement campaigns, as well as information and dialogue events.

Protecting water resources is the highest priority in the GeoLaB project. It is to be ensured that, throughout the entire duration of the project, both the quantity and quality of water resources (groundwater, spring water, and surface waters) in the Tromm region are protected. The responsible authorities also impose very strict requirements. To meet these requirements, comprehensive measurements, models, and controls are necessary. Only in this way can potential impacts be identified at an early stage and countermeasures initiated.

A team from TU Darmstadt is therefore carrying out a comprehensive “hydrogeological monitoring” program involving numerous measurements and investigations. These measurements provide data on water resources, water flows, and water quality in the Tromm region. Over the course of two hydrogeological years, these data will be systematically recorded (autumn 2025 to autumn 2027). Continuous monitoring will follow thereafter. This will document the baseline condition, enable the development of risk-minimization concepts, and allow potential changes to be identified.

TU Darmstadt, as the institution with what is likely the greatest regional expertise in this field, is responsible for data collection and for developing the technical monitoring concept. TU Darmstadt is already beginning this work in order to ensure the best possible basis for evaluation at a later stage. The concept and the data collected up to that point will then be submitted to the competent authorities as part of a permitting process for review and assessment. Decisions on the evaluation of the data and on further steps lie exclusively with the permitting authorities. Neither KIT nor TU Darmstadt makes these decisions.

These activities are planned in coordination with local water utilities, municipal water masters, and forestry offices. Naturally, the collected data will be shared with these stakeholders so that regional water management can also benefit.

Further information on this topic can be found in our flyer.

The construction phase of the research laboratory will temporarily have impacts on local residents. For example, traffic from trucks will increase at times. In coordination with the authorities and municipalities, we will seek solutions that result in the lowest possible impacts for the local population. In principle, the following applies: like any other construction project, the project will comply with all statutory limit values and other requirements.

At present, no site has been determined – neither in Zotzenbach nor anywhere else within the GeoLaB exploration area. As part of the site selection process, precisely these aspects will be taken into account, and these questions will be clarified with great care.

What is already clear, however, is that GeoLaB must be approved by the competent authority, which will carefully review all relevant concerns. Any requirements imposed by the authority will, of course, be fully implemented by GeoLaB. In general, the careful use of resources and minimal intervention in nature and the landscape are central concerns for us.

The long-term impacts of the GeoLaB research laboratory are also part of the planning and permitting process. Since the research laboratory will be located underground and the research activities will also take place there, only minor impacts are expected during the actual research operation. These will be continuously and closely monitored during the operational phase, for example hydrogeologically with regard to water and seismically with regard to ground vibrations.

In contrast, the construction phase of the research laboratory will have temporary visible and perceptible impacts. Construction activities will temporarily affect local residents and the environment. In doing so, all statutory limit values and other requirements will be complied with – as is the case with any other construction project.

Citizens affected by mining damages are entitled to compensation from the mining company that caused the damage or the holder of the underlying mining licence (in this case KIT). This also applies to seismic surveys, exploratory drilling or geophysical measurement campaigns.

Further information:

Lexicon of geothermal energy, Federal Geothermal Energy Association: www.geothermie.de/bibliothek/lexikon-der-geothermie/b/bergschadensvermutung

Federal Mining Act: Laws on the Internet: https://www.gesetze-im-internet.de/englisch_bbergg/index.html

Research in the rock laboratory is intended to continue for as long as possible. The Helmholtz Association, as the responsible research organization, initially commits to maintaining research operations for ten years. However, a longer-term use for research purposes is desirable. Like most underground laboratories, GeoLaB is designed as a long-term scientific experimental space in order to achieve broad and sustainable scientific impact. For example, the Äspö Hard Rock Laboratory (Sweden) has been in operation since 1995, and the Black Forest Observatory (Black Forest; KIT / University of Stuttgart) since 1972.

KIT will assume responsibility for the GeoLaB underground laboratory from the time official approval is granted. Any change in use or any new use can only be implemented within the framework of a new permitting process. If the tunnel is to be decommissioned or transferred at a later point in time, this will be done on the basis of a final operations plan and a future-use plan; as is customary, statements from public-interest bodies will be taken into account. As a research institution, KIT naturally does not pursue profit-oriented objectives in its activities. 

Since June 2024, parts of the area where GeoLaB conducts research are subject to regulations from the general decree of the Bergstraße district for combating African Swine Fever (ASF).

To carry out our measurement campaigns and all related activities, we are in close communication with the General Veterinary Administration of the Bergstraße district. Each measurement campaign and activity is assessed for feasibility. This means that we may need to adjust our campaigns accordingly. The execution of each individual measure must be approved by the Veterinary Office. Only then can the measurement campaigns be conducted in compliance with the rules imposed by the Veterinary Office.