Long the “perpetual also-ran of renewable energy,” geothermal could be about to have its day, provided it solves a number of engineering challenges and one big PR problem, writes Vox’s David Roberts.
Offering a deep-dive primer on geothermal technology, Roberts begins by laying out the full promise of the heat produced by the Earth’s molten core.
“Just 0.1% of the heat content of Earth could supply humanity’s total energy needs for two million years,” he writes, citing an estimate by the U.S. Advanced Research Projects Agency–Energy (ARPA-E). “There’s enough energy in the Earth’s crust, just a few miles down, to power all of human civilization for generations to come. All we have to do is tap into it.”
But, he adds, therein lies the rub.
The first problem: while a fortunate few jurisdictions (think: Iceland) possess a bounty of high-quality geothermal resources, those lucky few typically know that they have them, as “giant reservoirs of pressurized hot water often reveal themselves on the surface through fumaroles or hot springs.” As for the rest of the world, “exploration and characterization of new fields is expensive and uncertain,” keeping this most conventional and established form of geothermal energy “a niche solution, difficult to standardize and scale.”
The solution for that is enhanced geothermal systems (EGS), which use high-pressure water injection, similar to fracking, to release hot water from rock. A “magisterial” 2019 GeoVision study from the U.S. Department of Energy found such a project feasible, writes Roberts, with “strong public and investor interest, real market demand (thanks to ambitious state renewable energy goals), and a flood of new technologies borrowed from the oil and gas industry.”
But the method still has steep engineering challenges, “especially as targets gets deeper and drier”, as well as a PR problem—that is, the fracking part. Even though the more controversial aspects of natural gas fracking do not pertain to enhanced geothermal processes, “there are whole U.S. states and countries where [fracking] is banned,” Roberts notes.
But, should such challenges be overcome, “the prize is almost unthinkably large,” he adds. The GeoVision study estimated that, “assuming an average well depth of 4.3 miles and a minimum rock temperature of 150°C,” geothermal in the U.S. could produce “at least 5,157 GW of electric capacity—around five times the nation’s current installed capacity.” He points to figures from the Department of Energy estimating that America’s enhanced geothermal resources are “theoretically sufficient to heat every U.S. home and commercial building for at least 8,500 years.”
Technologies still in the conceptual stage could also overcome current technical challenges while spurring an enormous leap in performance: “super-hot-rock geothermal,” for example, could deliver 10 times the power of the standard variety.
“You could get more power out of three wells on a 400°C project than you can out of 42 EGS wells at 200°C, using less fluid and a fraction of the physical footprint,” writes Roberts. “Experience to date shows that the hotter geothermal gets, the more competitive its power price, to the point that super-hot EGS could be the cheapest baseload energy available.”
Another in-development technology, called advanced geothermal systems (AGS), uses no fracking, but rather circulates fluids through a closed-loop system of wells. A key benefit: a small surface footprint with little in the way of aboveground infrastructure, once initial drilling is complete.
Even more importantly, AGS has the potential to provide both “always-on” and dispatchable power, with the ability to “ramp up and down almost instantaneously to complement variable wind and solar energy.”
But AGS remains at the start-up stage, with companies like Eavor and Fervo Energy still working on challenges like preventing drilling equipment from melting as it descends to the temperatures necessary for AGS to be economically viable. Eavor is currently drilling at 70°C.
Despite the difficulties perfecting the technology, interest is growing, says Roberts. “It made waves when, a few months ago, the ‘Frack King’—Mukul Sharma, an oil and gas engineer at UT Austin who has been key in the development of hydraulic fracturing—launched a new EGS venture called Geothermix.”
Similar incursions that leverage the core strengths of the fossil industry will continue, Roberts predicts, along with deeper investments from that same sector.
“What’s likely is that oil and gas majors will eventually start buying up geothermal start-ups,” he writes. “Investments in geothermal would give them a way to shelter part of their portfolio from the brutal oil market.”