Fusion tech is set to unlock near-limitless ultra-deep geothermal energy

The heat beneath our feet

Everyone knows the Earth's core is hot, but maybe the scale of it still has the power to surprise. Temperatures in the iron center of the core are estimated to be around 5,200 °C (9,392 °F), generated by heat from radioactive elements decaying combining with heat that still remains from the very formation of the planet – an event of cataclysmic violence when a swirling cloud of gas and dust was crushed into a ball by its own gravity.

Where there's access to heat, there's harvestable geothermal energy. And there's so much heat below the Earth's surface, according to Paul Woskov, a senior fusion research engineer at MIT, that tapping just 0.1 percent of it could supply the entire world's energy needs for more than 20 million years.

The problem is access. Where subterranean heat sources naturally occur close to the surface, easily accessible and close enough to a relevant power grid for economically viable transmission, geothermal becomes a rare example of totally reliable, round-the-clock green power generation. The Sun stops shining, the wind stops blowing, but the rock's always hot. Of course, these conditions are fairly rare, and as a result, geothermal currently supplies only around 0.3 percent of global energy consumption.

The deepest holes in human history are not deep enough

If we could drill deep enough, we could put geothermal power stations just about anywhere we wanted them. But that's harder than it sounds. The Earth's crust varies in thickness between about 5-75 km (3-47 miles), with the thinnest parts tending to be way out in the deep ocean.

The deepest hole humanity has ever managed to drill is the Kola Superdeep Borehole. This Russian project near the Norwegian border struck out in 1970, aiming to puncture the crust right down to the mantle, and one of its bore holes reached a vertical depth of 12,289 m (40,318 ft) in 1989, before the team decided it was unfeasible to go any deeper, and ran out of money.

At that depth, the Kola team members expected the temperature to be somewhere around 100 °C (212 °F), but in reality they found it was closer to 180 °C (356 °F). The rock was less dense and more porous than expected, and these factors combined with the elevated heat to create nightmare drilling conditions. The Kola site has fallen into complete disrepair, and this "entrance to hell," a pinnacle (or perhaps nadir) of human achievement, is now an anonymous, welded-shut hole.

Germany spent the equivalent of more than a quarter of a billion euro on its own version in the late 80s, but the German Continental Deep Drilling Program, or KTB borehole, only got to 9,101 meters (29,859 ft) before terminating. Again, the temperature rose far earlier than expected, and the KTB team was also surprised to find that the rock at this depth was not solid, and large amounts of fluid and gas were pouring into the bore hole to complicate the effort further.

These temperatures were hot enough to thwart the drilling process, but not hot enough to make a good geothermal energy business out of. So while these projects and others have been invaluable scientific resources, new technologies are needed to unlock the geothermal potential under our feet.

Direct Energy drilling: A path forward

Where conditions become too difficult for physical drill bits to operate, researchers have been testing the capabilities of directed energy beams to heat, melt, fracture and even vaporize basement rock in a process called spallation, before the drill head even touches it. You can see the effect of spallation on tough rock in the GIF below from Petra's "Swifty" boring robot, although Petra's not revealing what exactly is used to create that heat.

Military experiments in the late 90s showed promising results indicating that laser-assisted drilling could get through rock 10-100 times faster than conventional drilling, and you can bet this was of great interest to oil and gas companies.

A direct-energy drilling process, wrote Impact Technologies president Kenneth Oglesby in a 2014 MIT report for the US DOE's Geothermal Technologies Program, would offer some huge advantages: "1) no mechanical systems in the wellbore that could wear out or break, 2) no temperature limit, 3) equal ease penetrating any rock hardness, and 4) potential for replacing the need for casing/cementing by a durable vitrified liner."

That last point is interesting – a direct-energy drill would effectively cauterize the rock it cut through, melting the bore shaft as it goes and vitrifying it into a glassy layer that would seal out fluids, gases and other contaminants that have caused problems in previous ultra-deep drilling projects.

But lasers, wrote Oglesby, don't cut the mustard. "The deepest rock penetration achieved to date with lasers has been only 30 cm (11.8 in). There are fundamental physics and technological reasons for that lack of laser drilling progress. First, the rock extraction particle flow is incompatible with short wavelength energy which is scattered and absorbed [by dust and particulate clouds] before contacting the desired rock surface. Second, laser technology is deficient in energy, efficiency, and is too expensive."

Enter the gyrotron, and millimeter-wave energy beams

The solution, it seems, might come from the world of nuclear fusion. In order to replicate the conditions that smash atoms together at the heart of the Sun, and thus release the safest and cleanest form of nuclear energy, fusion researchers need to generate staggering amounts of heat. We're talking in the range of a sustained 150 million degrees, in the case of the ITER project. Fusion research has been the beneficiary of billions of dollars in international government funding, and thus it's accelerated progress and commercialization in other areas that might not otherwise have had a budget.

One example is the gyrotron, a piece of equipment originally developed in Soviet Russia in the mid-1960s. Gyrotrons generate electromagnetic waves in the millimeter-wave part of the spectrum, with wavelengths shorter than microwaves, but longer than visible or infra-red light. In the early 1970s, researchers working on tokamak designs for fusion reactors discovered these millimeter waves were an excellent way to substantially heat up plasma, and over the last 50 years, gyrotron development has made impressive progress on the back of fusion research and DOE funding.

Indeed, gyrotrons capable of generating continuous energy beams over a megawatt in power are now becoming available, and that's amazing news for deep drillers. "The scientific basis, technical feasibility, and economic potential of directed energy millimeter wave rock drilling at frequencies of 30 to 300 GHz are strong," wrote Ogilvy. "It avoids Rayleigh scattering and can couple/transfer energy to a rock surface 10¹²X more efficiently than laser sources in the presence of a small particle extraction plume. Continuous megawatt power millimeter-waves can also be efficiently (>90 percent) guided to great distances (>10 km) using a variety of modes and waveguide (pipes) systems, including the potential of using smooth bore coiled and jointed/ joined tubing."

"Thermodynamic calculations," he continued, "suggest a penetration rate of 70 meters/hour (230 ft/hour) is possible in 5 cm (1.97 in) bores with a 1-MW gyrotron that couples to the rock with 100 percent efficiency. Use of lower- or higher-powered sources (e.g. 100 kW to 2 MW) would allow changes in bore size and/or penetration rate."

That would be a huge boost to traditional oil and gas drilling projects – but, barring too many further surprises, it should also significantly change the equation for ultra-deep drilling, making it possible and profitable to get deep enough into the crust to unlock some of the Earth's immense geothermal energy potential.

Quaise: Commercializing ultra-deep, supercritical geothermal power

In 2018, MIT's Plasma Science and Fusion Center spun out a business called Quaise, specifically focused on ultra-deep geothermal using hybrid systems that combine traditional rotary drilling with gyrotron-powered millimeter-wave technology, while pumping in argon as a purge gas to clean and cool the bore while firing rock particles back up to the surface and out of the way.

The company has raised some US$63 million to date, comprising $18 million in seed funding, $5 million in grants, and $40 million in a Series A financing round closed earlier this month.

Quaise plans to drill holes up to 20 km (12.4 miles) deep, significantly deeper than the Kola Superdeep Borehole – but where the Kola team took nearly 20 years to reach their limit, Quaise expects its gyrotron-enhanced process to take just 100 days. And that's assuming a 1-MW gyrotron.

At these depths, Quaise expects to find temperatures around 500 °C (932 °F), which is well past the point where geothermal energy takes a massive leap in efficiency.

"Water is a supercritical fluid at pressures above 22 MPa and temperatures higher than 374 °C (705 °F)," said Quaise. "A power plant that uses supercritical water as the working fluid can extract up to 10 times more useful energy from each drop when compared to non-supercritical plants. Aiming for supercritical conditions is key to attaining power densities consistent with fossil fuels."

Quaise is working on full-scale, field-deployable demonstration machines, which it says will begin operating in 2024. It plans to have its first "super-hot enhanced geothermal system" rated to 100 megawatts in operation by 2026.

The next step is commercial genius: Quaise plans to take advantage of existing infrastructure like coal-fired power plants, which will eventually be mothballed as emissions restrictions become ever tighter. These facilities already have enormous capacities to convert steam into electricity, as well as established commercial operators and experienced workforces, and they come conveniently pre-connected to the power grid. Quaise will simply replace their current fossil fuel heat sources with enough supercritical geothermal energy to keep the turbines spinning indefinitely without ever needing another lump of coal or puff of methane.

Quaise expects to re-power its first fossil-fired plant in 2028, and then go on to refine and replicate the process all over the world, since the heat should be available absolutely anywhere on Earth with this drilling technology. There are somewhere upwards of 8,500 coal-fired power plants around the world, totaling over 2,000 gigawatts of capacity, and they'll all have to find something else to do by 2050, so the opportunity is clearly mammoth.

"We need a massive amount of carbon-free energy in the coming decades," said Mark Cupta, Managing Director at Prelude Ventures, one of the key Series A investors in the company. "Quaise Energy offers one of the most resource-efficient and nearly infinitely scalable solutions to power our planet. It is the perfect complement to our current renewable solutions, allowing us to reach baseload sustainable power in a not so distant future."

We don't need to tell New Atlas readers how massive a shift this could be for baseline clean energy and the process of decarbonization. Indeed, if this technology works as expected (and the crust doesn't find new ways to fight back against our intrusions), and the economics stack up, this new use for gyrotrons could ironically end up putting fusion reactors out of a job.

Importantly, it'll take up almost no space on the surface, in contrast to industrial-scale solar and wind. It'll also precipitate a global geopolitical shift, since every country will have equal access to its own virtually inexhaustible energy source, and it sure will be nice when big countries don't have to "liberate" the populations of smaller ones to gain access to energy resources.

Check out a short video below.

Source: Quaise Energy