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Beneath our feet is an almost limitless source of energy, but while a few lucky locations have geothermal heat close to the surface, the rest of the world will need to dig a lot deeper. The challenge is how to get deep enough.
Iceland, home to more than 200 volcanoes and dozens of natural hot springs, is one of the few countries where tapping into this energy isn’t hard. Dotted around the country are steaming pools of water, heated by the geothermal fires that burn just below the crust. Iceland now heats 85% of its houses with this geothermal energy, while 25% of the country’s electricity also comes from power stations that harness this heat from underground. It’s an appealing prospect – an almost limitless supply of energy waiting to be tapped.
But geothermal energy offers an essentially inexhaustible green energy source across the planet. And it’s “always on”, unlike wind or solar power, since the heat is continually emitted from the Earth’s molten core and the decay of naturally occurring radioactive elements in our planet’s crust. Indeed, the Earth emits such enormous amounts of energy as it cools that the heat lost into space each year is enough to meet the world’s total energy demands many times over.
The challenge is tapping into that energy. Currently, only 32 countries in the world have geothermal power plants in operation. There are fewer than 700 power plants around the world, generating around 97 Terawatt hours (TWh) in 2023 between them. That is less than half the amount of electricity generated by solar in the US alone and far short of estimates for the potential contribution that geothermal could make to the global energy mix. Some estimate that geothermal could contribute around 800-1400TWh of electricity annually by the middle of the century with a further 3,300-3800TWh per year of heat.
“The Earth itself has the potential to address a variety of hurdles in the transition to a clean energy future,” argued Amanda Kolker, geothermal programme manager at the National Renewable Energy Laboratory (NREL) in the US, when releasing a report on the potential of geothermal energy in 2023.
One reason geothermal is not more widespread is the high upfront investment needed to extract that energy. But physically reaching it has also been beyond us so far.
For other parts of the world to enjoy a part of this geothermal bonanza of clean energy, we need to drill deeper to reach the temperatures needed to generate electricity or provide large-scale heating for nearby neighbourhoods.
Tapping into the heat emitted by the Earth is relatively easy in places such as Iceland where it is close to the surface. Drill down far enough, though, and it is possible to reach a point where water temperatures surpass 374C (705F) at pressures above 220 bars (one bar being average pressure on the Earth’s surface at sea level). This is where water enters an energy-intense state known as supercritical, where it exists in a form that is neither liquid or gas. The hotter and more pressurized it is, the greater energy it contains.
In fact, a single superhot geothermal well could produce five to 10 times the energy that commercial geothermal wells produce today, according to the NREL.
The deepest hole ever dug by humans dates back to the Cold War, when there was a race between the superpowers to drill as far into the Earth’s crust as possible. The Soviets managed to plough their way through 7.6 miles (12.2km) of rock – creating the Kola Superdeep Borehole, on the Kola Peninsula, high in the Arctic Circle. It took them almost 20 years to reach that depth and it remains the deepest humans have managed to delve into the Earth.
Quaise Energy, a spin-off from the Massachusetts Institute of Technology (MIT), is turning to new types of drills and drilling techniques to bore some of the deepest holes ever created in the hope of bringing geothermal energy to parts of the world that never thought it was possible.
Quaise Energy is experimenting with millimetre-wave directed energy beams that vaporise even the hardest rock. It focuses high-powered beams of radiation similar to microwaves but at a higher frequency onto a segment of rock, heating it up to 3,000C (5,432F) so that it melts and vaporises. By directing the beam so it bores through the rock, holes can be created without the debris and friction created by traditional drilling techniques.
Millimetre-wave drilling is a process that can operate largely independent of depth. And millimetre-wave energy can also transmit through dirty, dusty environments.
GA Drilling, a Slovakia-based company, is exploring a different high-energy drill technology to bore into the Earth’s crust. It is using a pulse plasma drill, based on very short high energy electric discharges that disintegrate rock without causing it to melt. This avoids creating any viscous molten rock, which can be difficult to remove and can stop drill bits penetrating further.
Slovakia-based GA Drilling, meanwhile, is exploring a different high-energy drill technology to bore into the Earth’s crust. It is using a pulse plasma drill, based on very short high energy electric discharges that disintegrate rock without causing it to melt. This avoids creating any viscous molten rock, which can be difficult to remove and can stop drill bits penetrating further.
For its part, the NREL has turned to AI to analyze complex subterranean environments to try to find the best places to drill for supercritical water, as well as helping to predict and detect faults with drills before they cause major issues.
