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US report finds sky is the limit for geothermal energy beneath us

US Dept. of Energy project estimates geothermal’s untapped potential.

Sonoma Power Plant at The Geysers in California.

With all attention focused on the plummeting prices and soaring popularity of solar and wind, geothermal energy is probably under-appreciated. Sure, you might think, it’s great where you can get it—in, say, Iceland or the Geysers area of California—but those are exceptions, right? Not entirely. Geothermal power sources come in many forms, and they're typically much more subtle than steam shooting out of the ground. In reality, geothermal energy could be a big player in our future mix.

That is made clear by the US Department of Energy’s recently released “GeoVision” report. The report follows similar evaluations of wind, solar, and hydropower energy and leans on information from national labs and other science agencies. It summarizes what we know about the physical resources in the US and also examines the factors that have been limiting geothermal’s deployment. Overall, the report shows that we could do a whole lot more with geothermal energy—both for generating electricity and for heating and cooling—than we currently do.

The highest temperatures are found out West, but these aren't the only places where geothermal techniques can be applied.

There are opportunities to more than double the amount of electricity generated at conventional types of hydrothermal sites, where wells can easily tap into hot water underground. That's economical on the current grid. But the biggest growth potential, according to the report, is in so-called “enhanced geothermal systems.” These involve areas where the temperatures are hot but the bedrock lacks enough fractures and pathways for hot water to circulate freely—or simply lacks the water entirely.

The technology used in natural gas fracking—injecting pressurized fluid underground to form fractures in the rock that released trapped gas into horizontally drilled wells—could be adapted to generate electricity in sites like these. Creating fractures and/or injecting water to get heated by these rocks eventually results in a similar geothermal plant setup, but it takes a lot more engineering than just jamming a straw into a source that's already sending hot water to the surface.

Advancing enhanced geothermal techniques alone could produce 45 gigawatts of electricity by 2050. Add in the more conventional plants, and you’re at 60 gigawatts—26 times more than current geothermal generation. And in a scenario where natural gas prices go up, making geothermal even more competitive, we could double that to 120 gigawatts. That would be fully 16 percent of the total projected 2050 generation in the US.

Additionally, that electricity can be generated around the clock and can even be flexibly ramped up or down, making it an excellent pairing with intermittent forms of renewable energy like wind and solar.

The many flavors of geothermal.

On the heating (and cooling) side, there are two main areas of opportunity. Traditional ground-source heat pumps circulate fluid through loops in the ground to provide cooling in the summer and heating in the winter, and they could be much more widely adopted with minimal effort. The report estimates that installations could increase 14 times over, to 28 million homes by 2050, covering 23 percent of national residential demand. Accounting for limitations in how quickly the market could realistically change brings the number down to 19 million homes—still a massive increase.

There’s even more potential for district heating systems, where a single, large geothermal installation pipes heat to all the buildings in an area. There are only a handful of such systems operating in the US today (Boise, Idaho, has an example), but the report finds more than 17,000 locations where it would make sense, covering heating needs for 45 million homes.

Limited adoption

The report focuses a great deal on the barriers that have so far prevented this eye-popping potential from being realized. Some barriers are indeed technological—those enhanced geothermal systems have yet to reach maturity, for example. Some barriers are simply down to a lack of awareness that things like ground-source heat pumps are already viable options.

But the biggest barriers are financial. Geothermal power plant projects suffer from much higher capital costs (and therefore slower payback times) than other forms of renewable energy. Techniques for placing wells at traditional hydrothermal sites are surprisingly unsuccessful, with many wells failing to produce enough to go into use. With better maps and more advanced site characterization, the misses could be reduced, bringing down costs.

The report also highlights permitting on federal lands as less than smooth. Between awkward overlaps when multiple agencies are involved and backlogs in understaffed departments, it points to approvals that could be consolidated to simplify the process. Streamlining, the report says, could shorten the time it takes to complete a project and reduce the financial risk of starting one. Separately, the constant uncertainty surrounding short-term tax credits for renewable projects also does geothermal no favors.

The 2050 scenarios in the report are based on plausible improvements to these barriers combined with modeling of the economics and operation of the nation’s energy grid. To make the projected numbers a reality, a set of key steps are laid out. Those include the streamlining of permitting, continuing research into the engineering of “enhanced geothermal systems,” improving methods for reducing trial and error at new installations, and outreach to increase awareness of geothermal options.

The other key is maximizing the value of each project. As flexibility is increasingly valued on the grid, compensating geothermal for that value would make it more profitable. There are also a variety of possible industrial uses for heat across the range of ground temperatures—everything from warming greenhouses to aiding cement production. A broader set of applications could help grow the geothermal industry, bringing costs down with scale.

If you’re a geothermal fan and an optimist, the report lays out a tantalizing amount of potential, although it lists plenty of challenges between here and there. In an intro to the report, DOE Geothermal Technologies Office Director Susan Hamm writes, “[T]his report shows us how to move the geothermal dial from what we know exists to what we envision is possible over the next 30 years. The GeoVision analysis takes us beyond a declaration of resource potential by illustrating what is real today and painting a picture of what could be real tomorrow.”

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