In the drive to create green energy, hot rock energy is a serious competitor for the more well known wind and solar power. Hot rock energy is a vast, environmentally friendly, economical energy source. As this diagram above shows, it is very simple. Water is injected into a borehole and circulated through a "heat exchanger" of hot cracked rock several kilometres below the surface. The water is heated through contact with the rock and is then returned to the surface through another borehole where it is used to generate electricity. The water is then re-injected into the first borehole to be reheated and used again.
The energy source is granite bedrock up to four kilometres beneath the surface of the earth, where the slow decay of potassium, thorium and uranium generates temperatures as high as 300 degrees.
Australia is home to all of the world's six listed hot fractured rock geothermal energy companies. As the thermal map below shows, Australia has a significant number of locations with thermal activity well up into the 300deg range.
Estimates by the Centre for International Economics are that Australia has enough geothermal energy to meet electricity consumption for 450 years.