The heat miles beneath our feet-deep geothermal energy-could provide more than enough clean, renewable energy to meet world demand as we transition away from fossil fuels, according to a presenter at the inaugural TEDX Boston Planetary Stewardship Event held November 13-14.

Timed to align with the United Nations' Climate Change Conference, the TEDX Boston event was "designed to spotlight actionable ideas for human activity to achieve a sustainable relationship with the planet's natural systems," according to the event's web site.

Great Potential
"The total energy content of the heat stored underground exceeds our annual energy demand as a planet by a factor of a billion. So tapping into a fraction of that is more than enough to meet our energy needs for the foreseeable future," said Matt Houde, one of 100 speakers at the TEDX Boston event. Houde is co-founder and project manager at Quaise Energy.

Today, however, we can't drill deep enough to unlock that energy. "If we can get to ten miles down, we can start to find economic temperatures everywhere. And if we go even deeper, we can get to temperatures where water [pumped to the site] becomes supercritical," a steam-like phase that will allow "a step change improvement in the power production per well and so cheapen the cost of energy," Houde said.

The deepest hole that's been drilled to date, the Kola borehole, went 7.6 miles down. It took 20 years to complete because conventional equipment like mechanical drill bits can't withstand the conditions at those depths. They break down. "And the truth is, we'll need hundreds if not thousands of Kola boreholes if we want to scale geothermal to the capacity that's needed," Houde said.

Enter Quaise, which "is developing technology to blast rock with microwaves to potentially drill the deepest holes on Earth. And no, I'm not stealing a plot device from Star Trek. This technology is real and has been proven in [an MIT] lab," said Houde, who went on to describe the Quaise approach in more detail, the challenges involved, and progress to date.

Many Benefits
First, however, Houde addressed the many benefits of deep geothermal energy in general. These include being available 24/7, which "can help balance out the intermittent flows of wind and [solar]." Deep geothermal plants will also have a "minimal surface footprint"-they won't need much land. Houde illustrated this with an artist's rendition of a future rig next to truck shipping containers.

Finally, Houde said, geothermal is "the perfect energy source to take advantage of the largest workforce in the world, the oil and gas industry." That industry has "11 million jobs in the US alone, and a skill set that is exactly what's needed for geothermal to rapidly scale."

Drilling with Microwaves
Quaise is working to replace conventional drill bits with millimeter wave energy (cousins to the microwaves many of us cook with). Those millimeter waves literally melt then vaporize the rock to create ever-deeper holes.

The general technique was developed at MIT over the last 15 years. In the lab there scientists demonstrated that millimeter waves could indeed drill a hole in basalt. Further, the gyrotron machine that produces the millimeter wave energy is not new. It's been used for some 70 years in research toward nuclear fusion as an energy source.

The Quaise technique also takes advantage of the conventional drilling technologies developed by the oil and gas industry. The company will use these to drill down through surface layers (what they were optimized for) to basement rock (which millimeter waves can easily power through). Houde explained that millimeter waves "are ideal for the hard, hot, crystalline rock deep down that conventional drilling struggles with." They are not as efficient in the softer rock closer to the surface, but "those are the same formations that conventional drilling excels at." Hence the company's hybrid approach to the problem.

Challenges Remain
There are still several challenges that must be solved to scale the Quaise technology. These include some fundamental science, such as a better understanding of rock properties at great depths. Further, "we need to advance the supply chain for gyrotrons" and the waveguides that carry their energy downhole, Houde said. That equipment is currently optimized for specialized one-off projects in fusion research. For deep geothermal applications, they must be produced in quantity and be robust and reliable in a field environment.

There are also engineering challenges that must be addressed. "Chief among them," said Houde, "how do we ensure full removal of the ash [created by the process] and transport that ash up the borehole over long distances?"

Progress to Date
In the lab at MIT, engineers demonstrated the technology by drilling a hole in basalt with a 1:1 aspect ratio (two inches deep by two inches in diameter). Quaise has extended the MIT results by scaling up the power density of the microwave beam as well as the depth of the hole by a factor of ten to achieve a 10:1 aspect ratio. In parallel, the company is building the first field-deployable prototype millimeter-wave drilling rigs.

"Our current plan is to drill the first holes in the field in the next few years," Houde said. "And while we continue to advance the technology to drill deeper, we will also explore our first commercial geothermal projects in shallower settings."

Related Links
Quaise Energy
Powering The World in the 21st Century at Energy-Daily.com

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