Work is expected to start next January on a large-scale geothermal project in Geneva that could provide natural heat and energy for thousands of homes.
Despite the failure of the ambitious Deep Heat Mining project in Basel, which was put on hold in 2007 after drilling work triggered a series of small earthquakes, several other Swiss cantons have declared an interest in geothermal power.
The SFr200 million ($173 million) Geneva project, initiated by the local power company Services Industriels de Genève (SIG), with support from the Federal Energy Office and cantonal energy department, is currently awaiting final approval from its executive board.
If all goes to plan, by 2020 over ten thousand new homes in Thônex, southeast of Geneva, will be provided with natural heat and electricity, explained SIG's geothermal project leader.
"Ideally we aim to provide the entire new district with geothermal power," Damien Sidler told swissinfo on Tuesday.
The advantage of the Thônex site is that the local authorities already carried out exploratory drilling to a depth of 2,700 metres in the 1990s. The project was later shelved for economic reasons, but modern technological advances and a thirst for renewable energies has reinvigorated interest.
Although the existing well is currently blocked 1,115 metres below ground level, SIG is certain that it can make use of the site and fit a large heat pump. Engineers will also search for other larger, deeper pockets of hot underground water nearby the well. Work is due to begin on January 20.
If this is successful, drilling will begin in 2010 on a second borehole – 3,500-4,000 metres deep – and then a third, to create a circuit between the wells. Hot water can then be pumped and re-injected underground after it has cooled down.
But the most ambitious part of the project should begin in 2020: a 5,000-to-6,000-metre-deep borehole.
Rather than exploiting hot water found in underground layers of soil, engineers will drill deep down through layers of rock, then inject water to capture the extreme heat before it is forced out of a second borehole.
Back at the surface, the hot water – at a temperature of 160-200 degrees Celsius - runs a steam turbine that is coupled with a generator. This principle is similar to the Basel project.
"But the seismic risks in Geneva are much lower than in Basel," said Sidler, adding that the project would rely on expert advise from Basel engineers, who continue to carry out tests on their site.
Despite the problems encountered in Basel, other cantons too are cautiously moving ahead with large geothermal projects.
The city of St Gallen has the most ambitious plans. The local authorities hope to be able to heat around one-third of the city's homes with hot water, which can reach temperatures of 170 degrees Celsius beneath the eastern Swiss city.
But unlike Basel, where the rock is fractured, at St Gallen the steaming water is found in layers of soft permeable sandstone and can be extracted using long-distance heat pumps. A feasibility study is due to be presented next spring. If all goes to plan, local residents will then have the final word on a SFr120 million credit.
But Nicolas Deichmann, expert at the Swiss Seismology Service, has raised some question marks.
"The project may also be accompanied by some small seismic movements," he told the Bern-based Bund newspaper on Monday.
The Zurich city parliament should also decide this week on a SFr20 million credit for a geothermal project. But the city's local power company remains cautious.
During rebuilding work to Triemli Hospital, test drilling will begin to a depth of 3,200 metres to examine the potential of such a project. If successful, the future hospital and several nearby apartments could be heated and have air-conditioning running on naturally heated underground water by 2010.
Other smaller projects are also being considered at Lavey-les-Bains in canton Vaud and at Brig in canton Valais, which both enjoy underground thermal waters.
Meanwhile in Basel, the Deep Heat Mining project is still suspended following a series of tremors that took place from December 2006 onwards after a test geothermal project for heating and power generation got underway in the city.
The tremors were strong enough to cause cracks in buildings. Several thousand claims for damage were filed with insurers and total costs for the damage are expected to exceed SFr7 million.
The cantonal government will make a decision whether to pursue the project after it receives a risk analysis at the end of 2009.
swissinfo, Simon Bradley in Geneva
Total energy consumption in Switzerland was 890,440 terajoules (TJ) or 247,344 gigawatt hours (GWh) in 2005.
Geothermal installations accounted for slightly more than 11 GWh in the same period, according to the Swiss Society for Geothermal Energy.
In comparison, hydropower plants (about 57% of domestic electricity supply) produce around 35,300 GWh annually.
Geothermal power is energy generated by heat stored in the earth, or the collection of absorbed heat derived from underground, in the atmosphere and oceans.
Prince Piero Ginori Conti tested the first geothermal generator on July 4, 1904, at the Lardello dry steam field in Italy.
The largest group of geothermal power plants in the world is located at The Geysers, a geothermal field in California, United States.
As of 2008, geothermal power supplies less than 1 per cent of the world's energy.
Experts at the Massachusetts Institute of Technology claim that the United States can kick its addiction to fossil fuels by drilling more wells to tap the Earth's heat.
Switzerland has some 50,000 small geothermal facilities providing heat and energy to houses, apartments, offices and hotels – the highest density of geothermal installations in the world. But there are no geothermal power plants.
In Switzerland there are no volcanoes and the geology is extremely varied so you have to drill down to 5,000 metres to find major sources of heat.
In 2008, the Federal Energy Office invested SFr1.5 million in geothermal power, or 12 per cent of the renewable energy budget.