Natural Resources - Geothermal Power Plants

Interview with Willy Gehrer

Why do you consider geothermal energy the wave of the future?

Gehrer: It’s the only energy source that is available around the clock all over the world. It’s almost inexhaustible, can be utilized on a decentralized basis in small units, and operates in a closed cycle, during which it produces no emissions. Given the problems associated with CO₂, this makes it extremely attractive. Anyway, fossil sources will soon be exhausted.

That’s what people were saying 40 years ago.

Gehrer: In those days, for every ten barrels of oil that were used, 40 to 50 barrels of new oil were discovered. Today, that figure is only two barrels. We’re sitting on a virtually inexhaustible supply of geothermal energy, yet choosing to transport oil, gas and coal over thousands of kilometers rather than digging a few kilometers into the earth.

What about the 200 geothermal power plants that are already in operation?

Gehrer: Those plants use hot springs in volcanically active regions as their energy source, whether they be in Italy or in Mexico. Here, ground water with a temperature of about 150 to 200 °C is pumped to the surface and used to produce electricity. Power plants based on this technology already provide some 6,700 MW worldwide. But with another technology, known as the Hot-Dry-Rock process, electricity can now be generated anywhere. The first commercial power plant of this kind is due to go into operation in five years in Basel, Switzerland. It will deliver 30 MW of thermal and 3 MW of electrical power and supply energy to 5,000 households. Based on a 20-year amortization plan, the total cost of generating heat by this means is about 0.02 €/kWh, while for electricity the figure is around 0.12 €/kWh—this is about the same as the cost of energy from a new hydroelectric or wind-driven power plant. I’m convinced that in 20 years geothermal power plants will be delivering 10 % of the total electricity produced worldwide.

How does the Hot-Dry-Rock process work?

Gehrer: Water is forced into the earth at a depth of 4 to 6 km through an injection well. There, it disperses into small cracks and fissures and is heated through contact with the rock, which has a temperature of between 150 and 250 °C. The heated, pressurized water then flows into other wells, which transport it up to a heat exchanger on the surface. The exchanger’s secondary cycle drives a steam turbine with a generator. The cooled water then flows back into the injection well.

Interview coducted by Ulrike Zechbauer