ASwiss power company is in a race with a firm in Australia to be the first to generate power commercially by boiling water in the rock five kilometres underground.

But when tremors started cracking walls and bathroom tiles in Basel, a Swiss city on the Rhine, the engineers knew they had a problem.

The 3.4 magnitude tremor on the evening of Dec. 8 was no ordinary act of nature: It had been accidentally triggered by engineers drilling deep into the Earth's crust to tap its inner heat and thus break new ground — literally — in the search for new sources of energy.

Basel was wrecked by an earthquake in 1365, and no tremor, man-made or other, is taken lightly. After more, slightly smaller tremors followed, Basel authorities told Geopower Basel to put its project on hold.

On paper, the Basel project looks fairly straightforward: Drill down, shoot cold water into the shaft and bring it up again superheated and capable of generating enough power through a steam turbine to meet the electricity needs of 10,000 households and heat 2,700 homes.

Scientists say this geothermal energy, clean, quiet and virtually inexhaustible, could fill the world's annual needs 250,000 times over with nearly zero impact on the climate or the environment.

A study released this year by the Massachusetts Institute of Technology said if 40 per cent of the heat under the United States could be tapped, it would meet demand 56,000 times over. It said an investment of $800 million to $1 billion US could produce more than 100 gigawatts of electricity by 2050, equalling the combined output of all 104 nuclear power plants in the U.S.

"The resource base for geothermal is enormous," Prof. Jefferson Tester, the study's lead author, said.

Humans have used heat from the earth for thousands of years. The ancient Romans drew on hot springs for bathing and heating their homes. Geothermal energy is in use in 24 countries, including the U.S. But those sources — geysers and hot springs — are close to the surface.

Hot dry rock technology, also called "enhanced geothermal systems" or EGS, involves drilling to where the layers of granite are close to 200 C. The equipment is similar to that used for oil, but needs to go much deeper, and the hole must be wider to accommodate the water cycle.

Aeneas Wanner, a Swiss expert, said that if you imagine Earth as an egg, "a bore hole would only scratch the shell of the egg a little bit."

Hot rock geothermal energy could operate 24 hours a day and doesn't depend on sun or wind. But it's decades away from serious rivalry with existing energy sources.

Andthere are drawbacks — not just earthquakes but cost. A so-called hot rock well five kilometres deep in the United States would cost $7 million to $8 million US, according to the MIT study. The average cost of drilling an oil well in the U.S. in 2004 was $1.44 million, according to the U.S. Energy Information Administration.

Tremor troubles

In Basel, water was pumped down the injection well in the test phase in December, and as expected, it heated toaround 200 Cas it seeped through the layers of rock below.

But that's where the water remains for the time being; it caused the rock layers to slip, causing the tremors and rumbles that spooked the townspeople.

Geopower Basel, had forecast some rock slippage. In fact, it said the location on top of a fault line — the upper Rhine trench — was an advantage because it meant the heat was closer to the Earth's surface.

But with $51 million already spent, drilling stopped and the official launch date was moved back from 2009 to 2012.

The rival project near the southern Australian town of Innamincka faces more benign geological conditions and less population. Its target date for operations is now two years ahead of Basel's, aiming to produce 40 megawatts of electricity by the end of 2010, enough to supply over 30,000 households.