Hot dry rock geothermal energy

Hot-Dry-Rock (HDR) is a type of geothermal power production that utilises the very high temperatures that can be found in rocks just a few kilometres below ground. This is done by pumping high pressure water down a bore hole into the heat zone. The water travels through fractures of the rock, capturing the heat of the rock until it is forced out of a second bore hole as very hot water, which is converted into electricity using either a steam turbine or a binary power plant system. All of the water, now cooled off, is injected back into the ground to heat up again. Hot dry rock is the end point for a range of technology for mining heat from the earth that ranges from

natural geothermal systems where there are already cracks or pore spaces filled with water hot enough to generate power through
systems where there are some cracks and connected pore spaces to
rocks where there are little to no cracks or connected pore spaces.

When natural cracks and pores will not allow for economic flow rates, the permeability can be "enhanced" or stimulated by pumping cold water or water with acids and chemicals through the ground. These artificially created geothermal systems are called Enhanced Geothermal Systems, or EGS. There are HDR and EGS systems currently being developed and tested in France, Australia, Japan, the U.S. and Switzerland. The biggest HDR project is currently installed in Australia.

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