Based on an Energieschweiz podcast by Podcastschmiede, Emilia Minardi and Lucia Vasella

Summary of the Interview:

1. Fundamentals of geothermal energy

• Definition: Geothermal energy (earth’s heat) refers to the heat stored underground (in rock, gravel, sand and groundwater). It originates partly from solar radiation in the upper layers and partly from the Earth’s geological history in deeper zones.

• Temperature profile: In Switzerland, a constant temperature of around 10 °C prevails from a depth of 15 metres. Thereafter, the temperature rises by around 3 °C for every 100 metres of depth (e.g. 40 °C at 1,000 m; over 130 °C at 4,000 m).

• Advantages: It is independent of weather and season and provides a reliable source of energy. Furthermore, it has a very minimal impact on the landscape at the surface.

2. Near-surface geothermal energy (up to a few hundred metres deep)

• Applications: Mainly geothermal probes (vertical boreholes with U-tubes acting as heat exchangers) or groundwater heat pumps, which extract stable temperatures from the ground or groundwater. A heat pump raises this temperature to heat buildings efficiently.

• Heat storage: A new and important trend is the storage of surplus summer waste heat (e.g. from building cooling systems or waste-to-energy plants) underground, so that it can be retrieved in winter.

• Current situation: Switzerland is one of the world’s leading countries in the implementation of near-surface geothermal energy.

3. Deep geothermal energy (industrial and large-scale projects)

• Hydrothermal geothermal energy: Utilisation of natural, hot deep groundwater (thermal water from depths of 500 to over 2,000 metres) for district heating networks, industry or – from approx. 100 °C – for electricity generation.

• Petrothermal geothermal energy (EGS / Enhanced Geothermal Systems): Independent of natural thermal water deposits. Injecting water under high pressure creates or widens fractures in deep, hot rock. Cold water is fed down through a borehole, heated within the artificial fracture system, and extracted via a second borehole.

• Dealing with seismic activity: The tremors that occurred during earlier deep drilling operations (Basel in 2006, St. Gallen in 2013) provided a wealth of data. Today, the seismic risk is managed through a better understanding of the subsurface, precise monitoring and strict threshold limits.

4. Haute-Sorne pilot project:

• Project type and classification: The project in Haute-Sorne (Canton of Jura) is described as a ‘flagship project’ for Switzerland. It is a pilot project in the field of deep geothermal energy, more specifically what is known as petrothermal geothermal energy (also known as EGS or Enhanced Geothermal Systems).

• Technology and objective: The main objective is technology transfer, to demonstrate that this EGS technology – which has already been successfully demonstrated in other countries such as the USA – also works under the geological conditions in Switzerland. This method involves injecting water under high pressure to create an artificial fracture system within deep, hot rock, allowing water to circulate within it and transport geothermal heat to the surface. Ultimately, the plant is expected to supply electricity to around 6,000 households.

• Current status: The project is being implemented step by step and in phases. So far, an initial borehole has been sunk, and a test injection and a test stimulation have been carried out. According to expert Christian Minnig, the evaluation was positive (“all lights are showing bright green”), and no unforeseen difficulties were encountered. A decision (“go-ahead”) is currently awaited for the next phase, in which the second borehole is to be drilled.

• Safety approach: After each individual step, work is paused for analysis. This is also a response to experiences from previous deep drilling operations (such as in Basel in 2006 or St. Gallen in 2013), which triggered seismic tremors. Thanks to the knowledge gained over the years, improved understanding of the subsurface, monitoring systems and clear thresholds for a potential suspension of operations, the seismic risk associated with the project in Haute-Sorne is to be managed safely.

5. Future prospects and potential in Switzerland

• Potential by 2050: According to estimates by the Swiss Geothermal Association, geothermal energy could meet a quarter of the country’s heating requirements by 2050. The target for electricity generation is two terawatt-hours per year.

• Challenges: Deep geothermal energy is still in its infancy in Switzerland. There is a need for better underground exploration campaigns, the development of a domestic industry, and adjustments to the regulatory framework by the cantons that own the subsoil.

6. Information for homeowners

• Feasibility assessment: You can check whether a geothermal probe or groundwater utilisation is eligible for authorisation at your own property via cantonal geo-portals (suitability maps) or the website www.kann-ich-bohren.ch.

• Cost-effectiveness: Although the initial investment is high, the system pays for itself in the long term due to very low running costs. To calculate the costs, please refer to the online heating cost calculator (in German, French and Italian).

• Subsidies: Cantons and municipalities offer financial support for the switch, which can be viewed via the platform www.energiefranken.ch (in German, French and Italian)