Bad Penny

Bad Penny

It may not be fair to categorize Hot Rocks as a bad penny, since research and development is frequently worthwhile, but it keeps turning up as a solution to the world’s energy needs.

Hot Rocks was first tried in Australia by Geodynamics Limited in the early 2000s, and failed at least twice. The Geodynamics website is no longer available.

In Hot Rocks, two parallel wells are drilled to a depth of 14,000 feet to reach magma, or hot rocks, where the rocks are fractured so that water can be injected down one well to generate steam from the hot rocks, and then rise in the parallel well to be used in a geothermal power plant.

Hot Rocks was hyped by environmental groups as a revolutionary method for generating all the world’s electricity.

Geothermal Drilling, the new term for Hot Rocks, has recently been tried in Iceland. Drilling was again done to around 14,000 feet in an effort to generate supercritical steam for use in a geothermal power plant.

The Iceland Deep Drilling Project (IDDP) was designed to produce steam at high temperatures to increase the efficiency of Iceland’s geothermal generating system.

Iceland generates more than one-quarter of its electricity using geothermal power from conventional geothermal sources.

Conventional geothermal uses three methods to generate 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 naturally flowing steam are rare.
  • Most conventional geothermal systems inject high-temperature brine (above 400°F) from the earth into a low-pressure chamber where the super-heated water flashes directly into steam, which then drives 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

Drilling to reach Hot Rocks could result in producing super-critical steam that would improve the efficiency of a geothermal power plant.

Power Magazine reported that an initial attempt in 2009, in Iceland, was successful and reached the magma at a relative shallow depth of 6,000 feet. Unfortunately, the site had to be abandoned three years later, in 2012, due to failure of the well casing.

The possibility of Hot Rocks as a worldwide method for generating electricity remains the objective of the group pursuing this technology.

While the original efforts in Australia weren’t limited to volcanic zones, the group now pursing Hot Rocks is targeting volcanic areas where reaching the magma might be easier to do.

Rather than revolutionizing geothermal production of electricity, the new approach limits its potential use to volcanic locations: Many of which are already making use of geothermal energy.

Obviously, Iceland is a unique case with its huge geothermal resources, so whether its efforts are applicable elsewhere remains an unanswered question.

The renewables community persists in extolling the virtues of Hot Rocks as demonstrated by this quote from Wikipedia,

“Hot dry rock (HDR) is by far the most abundant source of geothermal energy available to mankind.”

Hot Rocks keeps turning up like a bad penny, and may yet evolve to be useful for limited applications, but not as a revolutionary, worldwide method for generating electricity to eliminate fossil fuels.


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One Reply to “Bad Penny”

  1. Donn,

    This is a much older idea. Los Alamos National Lab is near a caldera in New Mexico, and started a Hot Dry Rock project in the 70s. This project was closed down in the mid-90s.

    When I was in the EPRI geothermal group in the early 80s, our group decided not to join the LANL project. LANL only wanted a token amount of our money, as I recall. They wanted our endorsement more than our money.

    The problem was that we were pretty sure Hot Dry Rock would not work. Basically, most geothermal waters have had geologic time scales to equilibrate with their surrounding hot rock. Newly pumped-in water, meeting hot rock, tends to dissolve minerals, precipitate metastable minerals, and basically become a big mess. This doesn’t happen much with fracking because people don’t look for high-temperature rocks to frack. Also, frackers add sand and chemicals to fracking water, but these additions don’t work as well at high temperatures.

    My knowledge is out of date and I admit it. But, IMHO, this Hot Rock plan is also out of date, no matter often it is proposed.