Enhanced or "hot rock" geothermal power production usually works by pumping water into fissures in hot rocks deep underground, A shaft is drilled into the fissures and some ot the resulting super-heated water comes to the surface where it is used to drive a turbine.

One problem with this technique is the amount of water needed since much of it remains underground.

In 2000, a Los Alamos National Laboratory physicist, Donald Brown, proposed replacing water with supercritical carbon dioxide, a pressurized form that is part gas, part liquid. Subsequent modelling at the Lawrence Berkeley laboratory has shown that using carbon dioxide would produce 50% more heat than using water because the carbon dioxide will flow more freely than water through cracks in the rock.

As well as being more efficient, using carbon dioxide would sequester much of the gas.

A Salt Lake City-based geothermal developer, GreenFire Energy, has now announced plans to build a two-megawatt carbon dioxide-based demonstration plant near the Arizona-New Mexico border. The company proposes to commence drilling in 2010 and says that the location could yield enough heat to generate up to 800 megawatts of power and, in the process, could absorb much of the carbon dioxide generated by the six large coal-fired power plants in the region.

(Adapted from sources including Technology Review)