The abundant but expensive energy source that's under your feet

To go faster and deeper will require advances in drilling technologies.

Companies are developing drilling equipment that is more stable when breaking through hard rock at high temperatures.

Some firms are even aiming to penetrate rock without using standard drills.

Quaise, a company with roots at the Massachusetts Institute of Technology (MIT), is using a technology called millimetre wave drilling. The frequency is similar to that of microwaves.

Quaise's application involves "sending electromagnetic waves in the microwave millimetre wave spectrum to essentially melt and vaporise through the rock," explains Harry Kelso, Quaise's communications manager.

Traditional geothermal energy clusters around hotspots on the earth's surface where very hot rocks can be easily accessed.

"Millimetre wave drilling really enables you to access super-hot geothermal just about anywhere in the world," says Kelso.

While Quaise is planning to use some conventional drilling at the project site it's developing in Oregon, Kelso says that conventional drills start to break down more quickly when it reaches very hard rock.

Replacing drill bits increases the cost and time of drilling.

In Quaise's case, Kelso says, "millimetre wave drilling is really what changes that because we're not using a physical drill bit."

Other companies are also working on advanced drilling technology, such as projectiles that move several times faster than the speed of sound.

Another crucial resource in the process is water. While some types of next-generation geothermal could create risks of water contamination or overconsumption, careful design can avoid this problem.

Initially Quaise's system requires a lot of water, but according to Kelso, once the water is in the system it is continually circulated over the super-hot rocks.

"We're essentially just recycling the water over and over," he says.

Quaise is continuing to raise funds, with the aim of its Oregon project being up and running by 2030.

Like other early versions of geothermal systems, it's an expensive project to get up and running.

"The economics are somewhat challenging," Kelso admits. "Geothermal today is still more expensive because you are not getting as much power out of the well as you would if you were using that well for fossil fuel."

But Quaise hopes that by targeting very high temperatures, of between 300C and 500C, the economics will improve.

While the higher end of that temperature range is ambitious, it's a case of the-hotter-the-better.

"It allows you to get 10 times more energy per well from geothermal, which changes the economics and the power potential of geothermal," according to Kelso.