How super-hot rocks miles under the earth's surface could provide limitless clean energy

The future of clean, renewable energy is underneath our feet. Quite literally.

The core of the earth is very hot — somewhere between 7,952 degrees and 10,800 degrees Fahrenheit at the very center. If we can drill down from the surface into what's called superhot rock, then we could access the heat of the earth and turn it into a massive source of zero-carbon, always available energy.

A new report out Friday from the Clean Air Task Force, a non-profit climate organization, finds that this category of clean, baseload superhot rock energy has the potential to be cost-competitive with other zero-carbon technologies — while also, very critically, having a small land footprint.

The Clean Air Task Force commissioned a non-profit geothermal organization, the Hot Rock Energy Research Organization, and an international clean energy consultancy, LucidCatalyst, to estimate the levelized cost of commercial-scale superhot rock electricity. They determined that it could eventually cost between $20 and $35 per megawatt hour, which is competitive with what energy from natural gas plants costs today.

This is not reality yet. Currently, there are no superhot rock geothermal energy systems operating and delivering energy, Bruce Hill, the chief geoscientist at Clean Air Task Force and the author of the report, told CNBC. But money is flowing into research projects and companies that are working to develop the technology.

The report posits that superhot rock energy can be commercialized in the 2030s, and argues that its unique set of features — it's a clean source of inexhaustible baseload energy with a small footprint — make the investment worthwhile.

"It will take public and private investment similar to those being allocated to nuclear, carbon capture, and hydrogen fuels," Hill told CNBC. "Geothermal programs receive far less funding from Congress and the U.S. Department of Energy than these other programs. Superhot rock geothermal isn't even in the decarbonization debate — but given a decade or two of aggressive investment it could be producing baseload power — local, energy dense, clean-firm (baseload) and competitive," from a price perspective.

While energy from superhot rocks is not being used now, geothermal energy is being used in a few places where super-hot temperatures exist close to the surface of the earth. Currently, about 16 gigawatts of power come from geothermal globally, according to CATF — that's less than 0.2% of the world's total. For comparison, there is 2,100 terawatts of capacity for coal energy globally and 1 terawatt of capacity for energy generated from photovoltaics, or solar panels.

But accessing superhot rock energy involves tapping into hotter, dry rock — which is everywhere, but sometimes far beneath the surface.

The deepest borehole ever drilled in the earth went down almost 8 miles in the Kola Peninsula of Russia in the 1970s, but the rock there was not nearly as hot as 752 degrees Fahrenheit — the minimum required for this type of energy. (Rock starts melting at between 1,112 and 1,832 degrees Fahrenheit, so the functional window for superhot rock geothermal is roughly between 752 and 1022 degrees Fahrenheit, Hill said.)

How far you have to drill to get to 752 degrees depends on where you are. On the edges of the tectonic plate boundaries or near recent volcanic activity, it might be two miles down, Hill told CNBC, but in the middle of a continent you might have to go down 12 miles.

Water would be pumped down into the hole and returned to the earth in a super-heated state known as "supercritical,", which has the properties of gas and liquid at the same time. That supercritical water would then be directed to power generators.

Conventional geothermal energy systems "have a very small but measurable carbon footprint," Hill told CNBC. That is why the Hellisheiði ON Power plant in Iceland has a Carbfix crarbon capture plant attached to it. A superhot rock energy system would have some carbon emissions associated with the construction of the plants, but "because the working fluid, water, is injected into dry rock there are no such hydrothermal related carbon dioxide emissions," Hill said.

Iceland is a leader in investigating superhot rock geothermal energy with its Iceland Deep Drilling Project. A test there suggests one well could produce 36 megawatts of energy, which is five to ten times more than the typical three to five megawatts of energy a conventional geothermal well could generate.

Iceland is well suited to study geothermal energy because of it's located where the American and Eurasian crustal plates are pulling apart from each other.

"We are replenished with constant supplies of magma energy to feed our geothermal systems," Guðmundur Ó. Friðleifsson, who served as a coordinator and principal investigator in the IDDP effort for over 20 years, told CNBC. "Magma energy is also at relatively shallow depths and relatively easily accessed, and Icelanders by nature are explorers of Celtic and Norse origin who love to sail into or out to the unknown," Friðleifsson said.

Beyond Iceland, Italy, Japan, New Zealand and the United States are leaders in superhot rock geothermal, according to Friðleifsson. Other areas on the edges of tectonic plates, including Central America, Indonesia, Kenya and the Philippines, also have some development.

For superhot rock geothermal energy to be commercialized and deployed broadly will require new technology, including rapid ultra-deep drilling methods, heat-resistant well materials and tools, and ways to develop deep-heat reservoirs in hot dry rock.

These are not insignificant, but they are "engineering challenges, not needed scientific breakthroughs," the CATF report says.

For example, drilling into hard crystalline rock takes a long time with current rotation drill techniques and the drill bits have to be replaced frequently. One potential solution is using energy instead of a mechanical drill.

Quaise Energy is develoing such a drill, building on research from Paul Woskov at MIT. The Quaise drill is being tested at Oak Ridge National Laboratory, according to CATF.

"The solution to drilling is to replace the mechanical grinding process with a pure energy-matter interaction. Sufficient energy intensity will always melt-vaporize rock without need for physical tools," Woskov told CNBC.

"Directed energy drilling has been considered since the laser was invented in the 1960s, but so far unsuccessfully because the infrared wavelengths are scattered in a drilling environment, the laser sources are of too low average power, and lasers sources are not efficient. We now have gyrotron sources since the 1990s that operate at millimeter-wavelengths that are more robust in a drilling environment, more powerful, and more efficient."

So far, private investment in the superhot rock space is "very small," according to Hill. CATF didn't have an exact number, but they estimate it's in the hundreds of millions of dollars at the most, and this includes investments by the Newberry Geothermal Energy consortium for work done 10 or 15 years ago, Hill said.

But it's getting easier to raise money in the space, according to Carlos Araque, the CEO of Quaise, which has raised $75 million so far, including $70 million in venture capital.

"The first 10 [million] took a lot longer than the other 65 because it was done in the 2018-20 period; things accelerated significantly in the 2021-22 period probably pushed by many investors realizing the need for new tech in this space," Araque told CNBC. "Investors are increasingly aware that we need to invest now on the technologies that will enable full decarbonization towards 2050."

Investor Vinod Khosla, the first backer of Quaise, recently talked to CNBC about his belief in backing potentially revolutionary technologies to fight climate change, and pointed to super hot rock geothermal as an example.

"A superhot rock well, like 500 degrees, will produce 10 times the power of a 200-degree well. And that's what we need," Khosla told CNBC. "If we can drill deep enough we can get to those temperatures — many, many — all of Western United States could be powered with just geothermal wells, because there's geothermal everywhere if you go 15 kilometers, 10 miles deep."

The CATF report said that big tech companies, and their associated deep pockets, could have "an important role" in funding the early development and commercialization of superhot rock energy by buying power purchase agreements or investment dollars to power "rapidly expanding energy intensive operations like data centers," the report said.

Indeed, Microsoft President Brad Smith spoke in Seattle about how vital it is for Microsoft to expand access to clean sources of energy to be able to continue to expand its business.

Oil and gas companies could use their resources to help spur development in the superhot rock industry, the CATF report said. "Drilling deep into the Earth to produce energy is the oil and gas industry's core expertise, which provided innovations that drove a rapid transformation of shale fossil energy resources previously considered impossible."

The government is also chipping in. The U.S. Department of Energy also has up to $20 million available in funding to develop better and faster geothermal drilling. Also, President Biden's Bipartisan Infrastructure Law allocates $84 million for the U.S. Department of Energy's Geothermal Technologies Office to build four pilot demonstration sites of what it calls enhanced geothermal systems, including superhot rock geothermal. Similarly, the Department of Energy recently announced Enhanced Geothermal Shot in an effort to reduce the cost of enhanced geothermal systems by 90%, to $45 per megawatt hour, by 2035.