Geothermal Energy: Hot Dry Rock (HDR) - The Habanero

Hot Dry Rock (HDR) geothermal energy or heat mining has recently been recognized as a new resource according to Irena Knethl's article on alternative energy technology in Australia in the Yemen Times.

Hot Dry Rock technology is capable of generating low cost, base-load power on a large scale.

In Australia the US $5.4m experimental basin represents the largest known geothermal resource in the world and has the potential to supply thousands of megawatts of low cost power. Known resources have the energy equivalent of 50 billion barrels of oil according to the article.

Hot Dry Rock (HDR) does not depend on new technology. It relies on extracting heat from particularly hot granite at depths of less than 5 km (approximately 3 miles) from the surface
The heat is extracted by means of circulating water from a deep surface well, through an engineered underground heat exchanger, with the hot water returning to the surface through the second well.

HDR geothermal electricity should be distinguished from conventional geothermal electricity, such as the power plants installed in the hot spring regions. Conventional geothermal energy is generated from naturally occurring hot water and steam in rocks near volcanic centres. This form of electricity production is well established in many countries. Conventional geothermal power stations are generally limited in size and are often linked to emissions of volcanic gases and toxic elements.

HDR geothermal energy generations differ from its conventional cousin below ground. It relies on artificially creating an underground heat exchanger to extract heat from high temperature locks by circulating water. It uses existing technologies, equipment and skills that were developed for the oil and geothermal power generation industries. The simplest HDR plant consists of one injection well and two production wells. Water from the injection well flows through the underground heat exchanger developed within the hot rocks. The superheated water is brought to the surface under pressure and used to boil an organic liquid. The water cooled by the process is the re-injected into the underground heat exchanger in a closed loop, to extract more heat. The vapour goes through a turbine to generate electricity.

It is thought that a small number of locations around the world have the right conditions for cost effective production of HDR electricity.

Such power plans can only work where there are special geological conditions and very hot granite rock. This rock has to be no deeper than five kilometres as that is the current depth that oil-drilling equipment can comfortably reach. The granite has to be covered by a three kilometre thick blanket of insulating rocks so that the heat does not escape to the surface.

The pilot well has been named “The Habanero”, after the world’s hottest chilli. Outside of volcanic areas, these rocks are the hottest in the world. Hot dry rock geothermal electricity production in Australia will be the deepest and the hottest well ever drilled on mainland Australia and also first deep geothermal well.

It is expected that HDR geothermal will become an important energy source in the next ten years.


Additional Diagram

The article also contains an intriguing snippet about a new wave power "air bag" developed in Australia:

A revolutionary system of extracting energy from ocean waves has been invented in Australia. It uses an underwater air bag coupled to underwater compartments that circulate air. The system is anchored to the sea floor, does not protrude above the waterline, and encourages marine life in the same way as an artificial reef. It uses a flexible air-filled membrane, which moves up and down as waves pass overhead. During compression, a valve opens and air is stored in a lower compartment. While existing wave energy devices use only part of each wave's energy, this new system achieves greater efficiency by focusing more of the wave energy on the device.

A prototype unit exposed to an 80 m wave front has the potential to produce 1.5 megawatts of electricity, which mean a production capacity of 13 million kilowatt hours per year – equating to enough electricity supply 770 to 1.026 homes.

Official Webpage of the Hot Dry Rock (HDR) Project

Yemen Times article on Hot Dry Rock technology plus the wave power air bag and solar tower