Hot Future for Renewable Energy: Deep Geothermal Heat Could Power the Planet for a Billion Years

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Written by Paul Wiseman for Industrial Info Resources (Sugar Land, Texas)--Because the earth's core is hotter than the sun's surface, experts in the geothermal energy field are understandably giddy about its potential to power humanity through the energy transition in a way that is uniquely clean, convenient and reliable.

Surfacing enough heat to power the entire planet, however, presents a huge challenge--and currently deployed technology can't get deep enough to do it. But with significant development, deep geothermal--10 miles deep or more--could be the answer, says Matt Houde, co-founder and project manager for Quaise Energy (Cambridge, Massachusetts). Currently in the research phase, the company hopes to begin drilling its first deep geothermal test well in the first or second quarter of 2024.

Deep Geothermal's Advantages
Unlike current geothermal wells, which must be placed over areas where sufficient heat comes closer to the surface, there's plenty of heat at 10-12 miles deep no matter the location. That means these wells could be drilled near existing gas-fired or coal-fired power plants, to take advantage of in-place powerline grids. That would save millions in infrastructure costs.

Because it's always hot downhole, this is a baseline supply, even more reliable than hydroelectric, which is susceptible to drought. Wind and solar's intermittency issues are well known. The latter two also require huge land allotments and sometimes disturb or kill wildlife. A geothermal plant takes up much less space.

The Challenges
There are two major obstacles to deep geothermal. First is the fact that current drilling machinery and methods can reach only about half the depth needed before the extreme heat and other factors render them useless. More information on deep rock properties will also be required. The second obstacle involves getting the heat to the surface. Here's why.

The most efficient way to collect heat and get it to the surface is by circulating water to and from the source. At 10+ miles down, the good news is that there's plenty of heat--enough to heat water past steam, to a state called hypercritical. At the hypercritical stage, water becomes extremely corrosive, to the point that new cementing methods and pipe coatings must be developed to maintain the flow.

In an email interview, Houde noted that the corrosion issue "has already been addressed for supercritical steam turbines, which are in operation today in new advanced coal power plants, mostly in China/outside the U.S."

Lurking behind all these issues is the cost. Houde said that when currently researched systems are more developed, "We believe we can drill these wells at $1,000/m ($1,000/meter) or $10M-$20M for targeting 500˚C at 10-20 km (kilometers) (6.2-12.4 miles) depth, which can produce power densities approaching 20-50 MWe (megawatts of electricity) per well." That is about five to 10 times higher than is available through shallower wells. Greater capacity will contribute to the deeper wells' economic efficiency by generating more power per dollar spent than is possible from shallower wells.

Said Houde, "At these power densities, we predict we can repower coal plants with geothermal steam at costs below $30/MWh ($30/megawatt-hour). This is highly competitive as a baseline power source compared to wind and solar, and to natural gas prices today." He also feels deep geothermal will compete well with nuclear fusion.

The New Technology vs. Greater Challenges
Drilling down the first few miles is a cinch--oil and gas operators do that daily, and Quaise is counting on the industry to do exactly that as a start. To drill deeper, the company plans to use a microwave technology that has been proven in a Massachusetts Institute of Technology (MIT) lab. In that system a gyrotron, which is a class of high power linear-beam vacuum tubes that generates millimeter-wave electromagnetic waves, will smash the rock into ash, for transport to the surface.

For real-world success, Houde said they must learn more about rock thermal properties and dielectric properties. The latter refers to rock-microwave interactions. Transporting the rocks' ash to the surface over a 10- to-12-mile distance will present further challenges. Stabilizing such a deep borehole must also be addressed.

The Potential
With its small surface footprint, ability to locate virtually anywhere (including in proximity to existing power grids), its low-carbon footprint and its virtually limitless energy supply, deep geothermal offers many advantages, including scalability. Ramping up, once the technology is proven viable, would require drilling thousands of wells worldwide.

In Houde's words, "The oil and gas industry drill tens of thousands of wells per year worldwide, so drilling thousands of deep geothermal wells annually is not out of the question at the economies of scale implicit in the global oil and gas industry."

Industrial Info Resources (IIR) is the leading provider of industrial market intelligence. Since 1983, IIR has provided comprehensive research, news and analysis on the industrial process, manufacturing and energy related industries. IIR's Global Market Intelligence (GMI) helps companies identify and pursue trends across multiple markets with access to real, qualified and validated plant and project opportunities. Across the world, IIR is tracking over 200,000 current and future projects worth $17.8 Trillion (USD).