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Geothermal energy: the heat is on in St. Gallen!

The future site of Switzerland’s first geothermal power plant. (in new window)

The future site of Switzerland’s first geothermal power plant.© City of St. Gallen

These vehicles were used to carry out the seismic survey. (in new window)

These vehicles were used to carry out the seismic survey.© City of St. Gallen

How the hydrothermal system works. (in new window)

How the hydrothermal system works.© City of St. Gallen

In November 2010, after a series of feasibility studies and seismic surveys, an overwhelming majority of the St. Gallen electorate greenlighted plans to build Switzerland’s first ever geothermal power plant in the city. The deep drilling work will begin in January 2012 and, if all goes according to schedule, the green power plant will be operational by autumn 2014.

St. Gallen’s geothermal project

The site of the first geothermal power plant in Switzerland will be the city of St. Gallen. It is hoped that the project will pave the way for the attainment of the ambitious goals that the city has set itself in its long-term energy master plan (Energiekonzept 2050):  

  • to cut the consumption of energy, the use of fossil fuels and CO2 emissions;
  • to ensure a heat supply that is produced from locally available resources;
  • to reduce dependency on individual energy suppliers, both domestic and foreign;
  • to create jobs in the region.

Harnessing geothermal power is just one of many measures that will help the city of St. Gallen to improve its green credentials by 2050.

What prompted such a move?

In 2007 St. Gallen’s heating bill totalled more than CHF 120 million. 90% of this energy was generated from fossil fuels (oil and gas). A feasibility study found that selected parts of the city were potential geothermal hot spots. Subsequent seismic surveys were carried out in and around St. Gallen to generate a picture of the rock layers deep below the city. Seismic vibrators mounted on special trucks injected low-frequency vibrations into small test bore holes. The resulting sound waves, which varied depending on the type of rock that the vibrations bounced off, were recorded using ultra-sensitive equipment (geophone). The results of the data evaluation showed that water as hot as 170 degrees Celsius could be tapped at 4000-5000 metres beneath the district of Au, making it the ideal site for deep drilling and ultimately a geothermal power plant.

The management team worked on the project further before putting it to a local referendum in November 2010. The project was resoundingly passed, with over 80% of the local electorate voting in favour of the plans.

How does geothermal power work?

In hydrothermal systems two holes are drilled to a depth of around 4500 metres. The first is used to draw up the warm water, the second to pump cold water back down into the rock to begin the heating process all over again. On the surface, the two holes are practically side by side, yet underground they are 1200 metres apart. This stops the hot water being cooled by the cold water being fed back down the pipes. The hot water, which is over 100 degrees Celsius, can then be used to generate electricity, while any residual power is used for heating purposes.

Could an earthquake strike St. Gallen?

The city of Basel also looked into using geothermal power from 5000 metres below ground. Unlike St. Gallen, the bedrock in Basel is not permeable. This meant that vast amounts of water had to be injected at high pressure into the rock (“petrothermal system”). A second hole then served as an artificial water circulation system to bring the geothermal energy to the surface. This simulation, which was conducted in winter 2006/2007, caused a series of tremors that could be felt above ground and caused millions of francs worth of damage. A subsequent risk assessment found that the earthquake-prone bedrock of the city did not lend itself to the extraction of deep geothermal power.

In contrast, the naturally aquiferous rock in St. Gallen is drilled open and the hot water deep below is brought to the surface, thus mitigating the seismic risk which is already much lower than that of Basel.

The canton of Thurgau is currently carrying out a series of test drillings. In one of its villages, Schlattingen, an innovative vegetable grower would like to make his contribution to a more ecologically friendly environment by heating his greenhouses with geothermal power.

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