The term "geothermal energy" refers to energy stored in the form of heat in solid formations beneath the earth's surface, which has primarily been formed from the decay of naturally occurring radioactive elements. The temperature is constant all year round from a depth of approximately 15 metres below the surface. In Switzerland, the temperature at a depth of 5,000 metres is around 200° C. This heat can be utilised with the aid of a variety of methods:

As a rule, vertical geothermal sensors, ground-water springs, geothermal structures such as foundation piles, trenches, tunnel water, etc., are utilised in combination with a heat pump for heating – and in some cases for cooling – purposes.

Switzerland is currently world leader when it comes to the utilisation of geothermal sensors. No other country in the world has so many in place in proportion to its surface area!

Sources of hot water below the earth's surface (aquifers) can be tapped by drilling, and energy can be obtained from dry rock layers with the aid of enhanced geothermal systems technology. At temperatures above 100° C, these energy sources can be used for electricity production, while the residual heat can be utilised for heating purposes.

At present, no electricity is produced in Switzerland from geothermal sources. However, the Deep Mining project in Basel plans to construct a facility capable of producing 3 MW of electricity and 20 MW of thermal output, which will be capable of supplying around 10,000 households with electricity and 2,700 households with heat. The preparatory work on this pilot project was already commenced in 1996 on the initiative of, and with the support of, the Swiss Federal Office of Energy. The unexpectedly strong tremors that were triggered by the construction of the power plant at the end of 2006, however, underscored the fact that this technology is still very much in the research stage, and that a great deal of research still needs to be carried out in the areas of reservoir stimulation and induced seismic activity.

The potential for geothermal electricity production in Switzerland is very high, but considerable uncertainties continue to exist with respect to costs and feasibility. Nonetheless, the outlook for this inexhaustible, clean and uninterrupted energy source is very promising: it is CO2-free, delivers a constant energy supply and requires little space. Experts anticipate that by 2030 a dozen or so power plants will be in operation with a combined output of around 800 GWh. Over the long term it is conceivable that geothermal power plants will meet a significant proportion of Switzerland's electricity demand.

Research and development

The SFOE's Geothermal energy research programme focuses on two priorities: combined heat and power production from enhanced geothermal systems (see above), and the heating and cooling of large-scale systems with geothermal energy.

Large commercial and services buildings often require as much energy for cooling purposes as they do for heating, and geothermal energy can meet both these requirements. In winter, with the aid of geothermal probes or geostructures, heat is fed into the building via heat pumps. In summer, with the aid of a free cooling process, surplus heat is removed from the building and fed underground where it is stored for heating purposes. The SFOE is supporting the development of tools for designing and optimising these complex systems, as well as for assessing their degree of success.