Current “hot rock” geothermal projects rely on heat produced by uranium decaying in granite formations. Now a team of geophysicists at the University of Melbourne is proposing a different approach which, they say, has huge potential for power generation in Victoria.
In some places, mineral formations form an insulating blanket which traps a layer of heat relatively close to the Earth’s surface. One of the most effective insulators is carbon, in the form of coal. And brown coal, which has a high proportion of water, is the most effective form of coal.
Victoria has huge deposits of brown coal under which there are areas of rock at temperatures of up to 200°C. In fact, the LaTrobe Valley, in which there is a blanket of brown coal 500 metres thick covering the surface, is regarded as having the best potential in the world for extracting this type of geothermal energy.
The University of Melboune team proposes pumping carbon dioxide down drill holes up to 5 kilometres deep and using the heat in the gas when it returns to the surface to drive turbines. Carbon dioxide is preferred to water because it is lighter and requires less energy to pump.
Another advantage of the LaTrobe Valley is that the area already has an electricity distribution infrastructure for its existing coal-fired power stations.
According to University of Melbourne geoophysics Professor Mike Sandiford, a test plant could be operating in the LaTrobe Valley within four years for an investment of just $100 million.