Geothermal Revisited

Enhanced Geothermal, referred to as hot rocks geothermal, or simply hot rocks, has been studied by MIT, but abandoned in Australia and Switzerland.

Periodically, an attempt is made to resurrect hot rocks for use in generating electricity.

The McClatchy Tribune recently reported on possible hot rocks development in California.

While traditional geothermal is a viable, but very limited energy source that only accounts for 0.4% of U.S. electricity supply, it may be helpful to review how geothermal works and why hot rocks is another pipe dream backed by extreme environmentalists.

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.
Binary Cycle Geothermal Plant - From Geothermal Energy Association
Binary Cycle Geothermal Plant – From Geothermal Energy Association

As the McClatchy Tribune article noted, some existing traditional installations have trouble sustaining the system because the super-heated water supply is gradually depleted. Some geothermal operators have replaced the dwindling supply of water with treated water from sewage treatment plants.

Even though traditional geothermal plants can provide electricity at a reasonable cost, traditional geothermal cannot provide large amounts of electricity because there are too few suitable geothermal resources.

This is why hot rocks is proposed as an alternative.

Theoretically, hot rocks could produce huge amounts of electricity, and a 2006 MIT report gave impetus to the idea of using hot rocks for base load power generation. The MIT report concluded hot rocks was theoretically possible.

However, actual attempts to develop hot rocks have failed.

Groups, such as Greenpeace, have touted hot rocks as a revolutionary method for generating large amounts of electricity.

Unfortunately, the concept has turned into another pipe dream.

Hot rocks entails drilling two wells to depths reaching 10,000 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.

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.

An effort to develop hot rocks in Basel, Switzerland was stopped in 2006, when the project caused a magnitude 3.4 earthquake.

Efforts to develop hot rocks for producing electricity will continue. The Department of Energy (DOE) is funding research into hot rocks. DOE said, “The [$31 million] FORGE initiative is a first-of-its-kind effort to accelerate development of this innovative geothermal technology that could help power our low carbon future.”

Since the United States has ample supplies of natural gas and coal for generating electricity, there is no need to pursue hot rocks, where there is a history of failure, other than to satisfy those who believe fossil fuels cause global warming.

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