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‘Hot Rocks’ Advanced Geothermal: A Reality Check

By Donn Dears -- November 3, 2015

“The potential for traditional geothermal power plants is limited by the scarcity of areas in the United States where geothermal energy is available, and by the diminishing supply of water as the geothermal resources age. In California, waste water has been used to augment the natural supply of water.”

Electricity has been produced successfully from geothermal sources for decades. The first successful geothermal power plant dates at least from 1911 in Larderello, Italy.

Today, in the United States, there are successful geothermal power plants in California and in Nevada.

The potential for traditional geothermal power plants is limited by the scarcity of areas in the United States where geothermal energy is present, much less commercial, and by the diminishing supplies as geothermal resources age. In California, waste water has been used to augment the natural supply of water.

Traditional geothermal uses three methods for generating electricity:

  • The direct steam method uses high-temperature steam as it emerges from the earth to drive a turbine generator. These are the most cost-effective plants, but sites with steam are rare.
  • Most conventional geothermal systems draw high-temperature brine (above 400 °F) from the earth, and injects it into a low-pressure chamber where the super-heated water flashes into steam. The steam is used to drive a turbine generator.
  • For low-temperature resources, binary cycle systems are used. Moderate temperature geothermal fluid is passed through a heat exchanger, where the heat is transferred to a fluid such as iso-butane which vaporizes. The vaporized fluid then drives a turbine generator.

Hot rocks have been touted as a revolutionary method for generating electricity.The industry refers to hot rocks as enhanced geothermal systems (EGS). An MIT report in 2006 said that EGS could produce most, if not all of the electricity needs of the United States.

Basic description of hot rocks: While Khosla’s investment has garnered media attention in hot rocks, hot rocks is nothing new.It should be noted that an attempt at hot rock development in Basle, Switzerland in 2006 was halted when the “hydro-shearing” produced earthquakes exceeding 3 on the Richter scale. Hot rocks is like any other fantasy that’s based on some theoretical premise.

The best scams always have a thread of truth around which to wrap the story used to lure the naive. Some things to keep in mind to check the hyperbole.

  • Like other fantasies, hot rocks is likely to be trumped by reality, and taxpayer subsidies will go the way of Solyndra’s.
  • The Department of Energy has reportedly thrown over $100 million into the development of hot rocks, with every indication that this taxpayer money will have been wasted. According to a 2005 report by Reuters, the Australian government also proposed spending A$500 million on PACE, acceerated geothermal hot rock development.
  • Geodynamics Limited in Australia has attempted to develop such installations since before 2003, and have drilled wells to depths of 14,500 feet. Subsequently, the wells have been abandoned, with various excuses given for the failure of the projects to produce electricity on a sustained basis.
  • Hot rocks entails drilling two wells to depths reaching 8,000 feet or more, where there are high-temperature rock formations. Fracturing techniques are used to open fractures in the rocks between the two wells. Water is injected down one well where it is converted to steam as it travels through the fractures in the hot rocks. The steam rises to the surface through the second well and is used to drive a turbine generator.
  • Radical environmentalists, such as Greenpeace in its R[e]volution report, made similar claims. The R[e]volution reports refer to heat-exchange surfaces (HDR technology) rather than EGS.
  • The media has picked up on the fact that hot rocks requires the fracturing of rocks several thousand feet below the surface to allow water to flow into the high-temperature rock formations. The media likens this to fracking, though the industry likes to refer to this practice as hydro-shearing.
  • Hot rocks recently became newsworthy again when Khosla Ventures invested in AltaRock Energy, a company attempting to develop hot rocks.
  • An alternative to these traditional geothermal plants is the concept of hot rocks.

Source: Binary Cycle Geothermal Plant – From Geothermal Energy Association


In the 19th century, William Stanley Jevons recognized geothermal was a limited energy source given technological constraints (The Coal Question, p. 120–21):

The internal heat of the earth … presents an immense store of force, but, being manifested only in the hot-spring, the volcano, or the warm mine, it is evidently not available.

He appears to be about as correct today as when he penned these words in 1865.

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