Geothermal energy
Present situation worldwide and in Switzerland
Geothermal energy is thermal energy stored in the Earth. It is generated by the decay of natural radioisotopes in the rock of the Earth‘s crust and by thermal exchange with deeper layers of the planet. The term “geothermal” originates from the Greek roots “geo” (earth) and “thermos” (hot). Over 99% of the globe’s mass are hotter than 1000° C and only one thousandth – its uppermost 3 km – is cooler than 100° C. Geothermal energy thus provides 24/7 carbon-free energy. Availability is practically unlimited, as radioactive decay inside the Earth produces constant heat.
At a depth of 10-20 meters, earth temperatures in Central Europe are around 12° C. This is the depth up to which temperatures are influenced by the climate. In deeper layers, the geothermal gradient applies, meaning that on average temperatures rise by around 1° C every 33 meters. Hydro-geothermal energy uses natural resources of hot water in the sub-surface. For petro-geothermal energy (hot dry rock geothermal energy), cold water is pumped deep underground. In order to allow the water to circulate, the hot, compact rock is cracked open through high-pressure water injection. The water flowing through these joints in the rock captures the rock’s heat and can be put to different uses depending on depth. Up to 440 meters, shallow geothermal energy is used for heating (heat pumps) and cooling buildings including warm water processing, or as process heat for plant nurseries and swimming pools. Medium-depth geothermal energy (up to 3000 meters and around 100° C) is used to heat entire neighbourhoods, office buildings and industrial sites (district heating). Deep geothermal energy (more than 3000 meters and over 130° C) is used to generate electricity.
Implications for Switzerland
Switzerland has the highest per capita percentage of geothermal probes with heat pumps. The number of new installations has been rising sharply for many years. Around 5% of thermal energy is currently obtained using geothermal probes and heat pumps. No statistics are yet available on the substitution of air conditioners by the use of shallow earth temperatures of around 12° C. To date, deep hydrothermal and petrothermal installations have only been realised in other countries. In Switzerland, projects planned for the years ahead include the following: Haute Sorne, canton/city of Geneva, La Côte, Triengen, Horgen, Avenches. Throughout the world, the technology is still in its infancy. Based on the new Swiss Energy Act, Switzerland is investing heavily in research. Around 80 researchers are currently working at the Grimsel Test Site and the Bedretto Deep Underground Lab. Commercial projects in Basel, St. Gallen and Zurich have not yet proven successful. In Geneva, however, medium-depth boreholes are being drilled to feed into the district heating network. Worldwide, the use of geothermal energy is growing rapidly. This is especially true of deep geothermal energy for electricity generation (e.g. in the US, the Philippines, Indonesia, Mexico or Turkey) and for heat generation (in China, the US, Sweden, Turkey and Japan).