AN AMBITIOUS project to extract geothermal energy from hot rocks was launched in the UK this week. Can it avoid the same fate as recent high-profile and potentially dangerous failed attempts elsewhere in the world?
The plan is to build a 3-megawatt commercial geothermal energy plant to power the in Cornwall, and the nearby community. A pilot project will test a technique to extract heat from hot dry rocks at a depth of about 3.5 kilometres.
The technology involved has yet to prove itself to be reliable or safe. A Swiss geothermal project in Basel (pictured), was closed down in December 2006 after its construction that shook the town. A similar project in the Cooper Basin, South Australia, was suspended last month after the main borehole carrying water from the surface to the deep rocks mysteriously sprang a leak. An investigation is currently under way to find the cause. There is only one commercial hot dry rock project in successful operation, in Landau, Germany.
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Traditional geothermal energy plants extract water from naturally heated underground reservoirs. Hot dry rock projects search for geological conditions where the temperature of the rock exceeds about 150 掳C. A borehole is drilled and water injected at high pressure, causing any small cracks in the rock to expand, creating a capillary network. Fresh water is then pumped down one hole to the capillary network, where it boils to steam. The steam is extracted via a second hole and used to drive a steam turbine, or for heating.
Creating the capillary network is where dangers may lie. Inducing immense pressures on an area of rock that is already under great stress can have unpredictable consequences. In Basel, geologists expected small earthquakes but predicted they would be less than magnitude 2. The biggest quake was magnitude 3.5. 鈥淣ormally that鈥檚 not going to cause any damage,鈥� says Roger Musson of the British Geological Survey, 鈥渂ut when you get that at a shallow depth, it can produce quite strong shaking in the local area.鈥�
of the Swiss Seismological Service, Zurich, who investigated the Basel earthquakes, points out that hot rock geothermal energy is a fledgling industry. 鈥淭ampering with the Earth鈥檚 interior always brings with it some risks and some hazards,鈥� he says. 鈥淚 would caution not to delude ourselves that we are at a stage where we can call these projects commercially viable and routine.鈥�
The Basel team made some fundamental errors, claims Roy Baria, technical director of , the company contracted to dig the Cornwall site: 鈥淭hey stimulated a region that is naturally very seismically active. The site in Basel is under compression stress, whereas the site in Cornwall is under tension. The situation is completely different in the UK.鈥�