HDR stands for hot dry rocks (also known as HFR - hot fractured...

HDR stands for hot dry rocks (also known as HFR - hot fractured rocks). It differs from conventional geothermal in that the water that circulates to generate power isn't found there in the first instance - its pumped down. That means it can be exploited in many more locations (such as Australia). It is a relatively new field which has been enabled by advances in drilling and fracturing techniques from the oil and gas industry. Thats why competitors (such as the nuclear lobby) like to describe it as "unproven". In reality all the pieces of the puzzle have been proven but no-one has yet put them together. Shouldn't be too long now - the resource is enormous and is being actively explored all over the world, though Australia has some of the best potential.