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Drilling for heat: The future of geothermal

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States across the country are making pledges and taking action to move toward 100% clean energy. Wind and solar energy occupy the spotlight – justifiably given their rapid growth, plummeting costs, and enormous potential. But there may be another important piece of the puzzle just under our feet.

Geothermal literally means heat from the earth, and geothermal energy has been used commercially to produce heat and electricity for decades, and used practically – for bathing, cooking and so on – for millenia.

Today, new developments create the potential for an expanded role for geothermal in a clean energy future, something I learned during a recent webinar sponsored by the National Renewable Energy Laboratory.

There are several ways to take advantage of geothermal energy. The main method, conventional geothermal, uses pockets of hot pressurized water near the surface (about 1.2-2.5 miles down) to produce heat or electricity: pumping the water up, extracting the heat and then reinjecting the cooled water. Conventional geothermal is well-established (producing 17 terawatt-hours of electricity in 2020), always on, and low- or no-carbon, but it is geographically limited to areas with bodies of hot, pressurized water, which are rare and difficult to find.

Enhanced geothermal (EG) is the industry’s answer to this problem. Enhanced geothermal uses the advanced drilling and rock-fracturing technology of the oil and gas industry to extract the energy from hot, deep (about 2.5 miles down), non-porous rock without the environmental pollution that comes from fracking for fossil fuels. Water is injected into one well, forced through fractured passages in hot rock, and pumped out of another well so that the heat can be extracted. Enhanced geothermal is the likely next step for the industry, but still faces some engineering hurdles (such as the difficulty of drilling into very hot, very hard rock).

The industry is also looking beyond enhanced geothermal and to producing energy from what is known as “supercritical” water. Supercritical water forms when water is heated to hotter than 374º C and is subjected to immense pressure (greater than 217 times atmospheric pressure).1 Drilling wells into regions that contain supercritical water for geothermal energy would allow a well to produce many times more energy than a typical geothermal well, albeit with many engineering and technical difficulties still to be solved, including the increased risk of micro- earthquakes.

Finally, there are also companies working on closed-loop geothermal systems. Closed loop systems work like giant ground source heat pumps, but operate at much higher temperatures and go further underground (they are likely to go at least 1.5 miles down versus tens of meters for ground-source heat pumps). They circulate liquid through closed pipes and wells, allowing it to pick up heat by conduction, and use the temperature differential between the vertical wells rather than a pump to move the liquid. These systems could, in theory, have almost no above-ground footprint, work at shallower depths than EG systems (1.5 miles vs. about 2.5 miles) and have minimal environmental impact, while also being able to ramp up or down without having to curtail energy, since the fluid can absorb more and more heat as it sits.

These technologies have the potential to be especially valuable in the transition to a 100% renewable energy system. Geothermal energy is flexible and can be used directly for heating, to produce electricity, and even for cooling (with a geothermal heat pump). And because the temperature of the earth is relatively constant, it can be available whenever we need it.

I was able to get a better picture of the industry’s view of its future at NREL’s NextGen Geo webinar, which I attended on March 31. Speakers working on different aspects of geothermal discussed how geothermal is likely to grow, why now is the right time for geothermal, and some new and intriguing possibilities that could make geothermal even more useful.

The first big takeaway came from Jamie Beard, the director of the Geothermal Entrepreneurship Organization. She said that the oil and gas industry and the geothermal industry are essentially the same in terms of skills, processes and technology. The major difference is that the geothermal industry is drilling for heat, not hydrocarbons. As the oil and gas industry declines due to competition from renewable energy and the need to decarbonize the energy system, geothermal may be able to repurpose oil and gas industry assets to support a transition to a more sustainable system.

The second big takeaway was that the growth of the geothermal energy industry seems to be picking up speed. There were nine power purchase agreements for geothermal energy signed between November 2019 and September 2020. According to Tim Latimer, the CEO of Fervo Energy, there are innovations coming out of projects like Utah FORGE, there’s interest in geothermal from state and federal governments, and new ideas are bubbling up for how to use geothermal facilities to co-produce valuable minerals. Jamie Beard also noted that many oil and gas associations and companies have formed groups to investigate geothermal.

The last big takeaway came from Alex Grant, Principal at Jade Cove Partners. He identified geothermal brine – the industry term for the hot water with dissolved minerals used to generate electricity in a geothermal system – as a potential source of low-cost, low-carbon lithium. Lithium is one of the main materials used in modern batteries, and so is an important resource to help decarbonize transportation (with electric vehicles), the electricity system (with battery storage) and to maintain modern technology. There are no companies currently producing geothermal lithium, but three commercial-scale projects are in development.

The speakers at NextGen Geo believe that the industry is poised to become a major source of energy around the world. If their predictions bear out, geothermal could become one of the main sources of low-cost, low-carbon heat and electricity for the world, joining solar and wind as one of the main components of a 100% renewable-powered society.

A geothermal power plant in The Geysers Complex, California. Photo credit: U.S. Department of Energy via Flickr.

 

 

  1. Supercritical water requires pressure above 22 megapascal. Atmospheric pressure is about one-tenth of a megapascal.↩︎