Hot Rocks Resurrected

Hot Rocks Resurrected

A writer for the WSJ interviewed a professor at the University of Texas, and then wrote a glowing article about the prospect of unlimited supplies of electricity from, what is referred to, as enhanced geothermal systems, better known as hot rocks.

There are, of course, variations on geothermal systems. Some are in use today around the world, taking advantage of the heat from the Earth’s interior that produces steam and hot brine near the surface.

An area in California, known as the geysers, is where the preponderance of geothermal energy is used in the United States for generating electricity.

The hot rocks proposal is different, in that it requires drilling thousands of feet into the Earth to reach areas where hot rocks are found in abundance. 

The concept of hot rocks has been around for decades. The Sierra Club made a big fuss over hot rocks nearly twenty years ago.

My first article covering hot rocks was in 2010. It described geothermal energy and attempts in Australia for developing hot rocks.

The article provided a description of geothermal energy. Quoting from the article:

Hot rocks entails drilling two wells to depths reaching over 10,000 feet 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 would be converted to steam as it travels through the fractures in the hot rocks. The steam would rise to the surface through the second well and be used to drive a turbine generator.

Traditional geothermal uses three methods for generating electricity.

  1. 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.
  2. Most conventional geothermal systems inject high-temperature brine (above 400 °F) from the earth into a low-pressure chamber where the super-heated water, often contaminated with salts and silica, flashes directly into steam, and where the steam then drives a turbine generator.
  3. 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

The WSJ writer should have looked deeper into what he had been told.

Here is a quote from his article:

“There is huge upside to digging down miles and injecting water into underground reservoirs—think radiators—and then the heated water is pushed back out to generate steam and electricity. It’s carbon-free—clean, green and mostly unseen.”

While theoretically possible to produce unlimited quantities of electricity from hot rocks, it’s easier said than done.

In 2003, Geodynamics Limited, in Australia, attempted to develop hot rocks, but the efforts failed. The company drilled wells to a depth of 14,500 feet, but couldn’t sustain the production of steam.

In 2006, an effort was made in Basle, Switzerland to develop hot rocks, but it was stopped when there were earthquakes.

While earthquakes shouldn’t be a major problem, they can’t be dismissed out of hand.

Governments have thrown money at Hot Rocks in hopes of proving it can be made to work.

The Department of Energy reportedly threw $100 million into the unsuccessful development of hot rocks in Nevada. According to a 2005 report by Reuters, the Australian government also proposed spending A$500 million on a hot rocks project.

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.

Experience derived from fracking and the drilling of horizontal wells may help generate more steam or hot brine, but that steam or hot brine still has to be brought to the surface for use in steam turbines. (There is another proposal for a closed loop system to obtain  a constant flow of hot water and brine, but that has separate challenges.)

The idea for hot rocks has resurfaced, and there will be efforts to prove it works. 

VOX recently announced, “Geothermal energy is poised for a big breakout.” The VOX article described all the same advantages and prospects the WSJ writer did.

The Union of Concerned Scientists has also tossed the old chestnut into the mix: 

Hot rocks for generating an endless supply of electricity.”

Hot rocks needs to be seen in the context of historic evidence, and the writer should have presented a more balanced description of hot rocks. Thus far:

  • Exploratory hot rock wells have failed.
  • Millions of dollars have been spent on other attempts to prove hot rocks work.

Will improved fracking make a difference? Time will tell. But the idea that we will have abundant electricity from hot rocks by 2030, or even 2040, as suggested in the WSJ article, is pure conjecture.

As for the WSJ? It needs an objective, energy editor to ensure that reporters and writers provide balanced, factual information. 

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8 Replies to “Hot Rocks Resurrected”

  1. If I may, I would like to add to your excellent and concise writeup. US DOE funded projects in the western US utilized geothermal steam so hot it required expensive very high temperature alloy steels. The geothermal fluid/steam was so full of salts and other contaminants that the various types of heat exchangers tested had plugged and corroded at a very high rate, making the whole process economically uncompetitive and with poor availability. This seems to be a trend with renewable energy options.

  2. Whether a “hot rocks” energy source is viable depends on the amount of energy in the source (rock temperature and volume) and the rate that energy is to be withdrawn. Rocks contain a finite amount of energy as heat and that heat moves rather slowly through them. Fracking may increase the rate heat can be withdrawn, but other limits to removing that heat remain. It would require a very hot and very large expanse of hot rock to generate a significant power source on the scale of commercial power plants. And what would be the cost of installing that infrastructure??

  3. Back in 1982, I was the only chemist in the small geothermal group at EPRI. I advised against EPRI helping to fund the Los Alamos Hot Dry Rock project. At high temperatures, rock-water interactions can’t be controlled. Some water runs away (you don’t get it back). Meta stable silicates precipitate in the water you do get back. These problems are built into the rock-water interactions.

    Our geothernal group had too little money to waste it on the Hot Dry Rock project.

    • Thanks for your comments that provide additional information based on knowledge and first hand experience.
      It will be interesting to see how new hot rock projects evolve. The WSJ reporter seemed enthusiastic, based on limited information from a biased source.

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