Enhanced geothermal system

Based on Wikipedia: Enhanced geothermal system

The Heat Beneath Your Feet

Right now, roughly five kilometers below where you're sitting, rock is hot enough to boil water. This isn't unusual geology—it's everywhere on Earth. The deeper you dig, the hotter it gets, climbing about 25 to 30 degrees Celsius for every kilometer you descend. At ten kilometers down, you're looking at temperatures that would melt plastic.

For over a century, we've known how to turn heat into electricity. And yet this practically unlimited energy source—enough to power human civilization for millions of years—has remained largely untapped. The problem was never the heat. The problem was the plumbing.

The Plumbing Problem

Traditional geothermal power works beautifully, but only in very specific places. You need three things to line up: hot rock, water flowing through that rock, and enough natural cracks and pores to let the water circulate. Think of Iceland, where volcanic activity creates perfect natural radiators. Or The Geysers field in Northern California, where steam shoots straight out of the ground.

These hydrothermal sweet spots are geologically rare. They represent perhaps two percent of the world's geothermal potential. The other ninety-eight percent? Hot, dry, and completely impermeable rock.

This is where enhanced geothermal systems—abbreviated E-G-S—enter the picture. Rather than finding natural underground radiators, you make one yourself.

How You Crack Open the Earth

The core technique is called hydro-shearing, and it's more elegant than it sounds. You drill down into hot granite, then pump water down the well at high pressure. The water doesn't blast new cracks into the rock—that would be hydraulic fracturing, the controversial technique used for oil and gas. Instead, it infiltrates existing microscopic fractures and pries them open wider.

Think about pushing open a heavy door. You're not breaking through a wall; you're using existing hinges. The pressurized water triggers what geologists call shear events—the rock slips along pre-existing weak points, expanding those hairline cracks into pathways wide enough for water to flow through.

Here's the clever part: as long as you keep pumping water through the system, you don't need those fractures to stay open on their own. Unlike oil and gas fracking, there's no need to prop the cracks open with sand or ceramic beads. The continuous water flow does the work.

Once you've created your underground heat exchanger, the process is simple. Cold water goes down one well. It winds through the fractured hot rock, absorbing heat for several minutes or hours. Hot water comes up another well. You extract the heat to spin a turbine, cool the water back down, and send it through again.

It's a closed loop. The same water circulates indefinitely.

Why This Changes Everything

The profound implication of enhanced geothermal is geographic freedom. Traditional geothermal plants cluster around volcanic regions and tectonic boundaries. But EGS works anywhere, because everywhere has hot rock at depth. The only question is how far you need to drill.

The ideal setup is a thick layer of sedimentary rock—three to five kilometers of sandstone or shale—sitting on top of deep granite. The sediments act like a blanket, insulating the heat below. Granite holds heat well and fractures predictably under hydro-shearing.

Modern drilling can reach fifteen kilometers. At that depth, rock temperatures exceed 400 degrees Celsius—hot enough to power the most efficient steam turbines available. And unlike a coal plant or a nuclear reactor, an EGS facility produces power at a constant rate, day and night, regardless of weather. It's what engineers call a baseload resource: always on, always reliable.

A single EGS installation is expected to operate for twenty to thirty years before the rock cools enough to need re-stimulation or relocation.

The Numbers That Matter

In 2006, the Massachusetts Institute of Technology released the most comprehensive analysis of enhanced geothermal potential ever conducted. The findings bordered on staggering.

The total EGS resource in the United States alone, counting rock between three and ten kilometers deep, exceeds 13,000 zettajoules. A zettajoule is a trillion trillion joules—the kind of number you only encounter in discussions of continental energy reserves or stellar physics. For context, the entire United States uses roughly one hundred exajoules of primary energy per year. The EGS resource is about 140,000 times that annual consumption.

Not all of it is extractable with current technology. The MIT report estimated that at least 200 zettajoules were recoverable using existing methods—still two thousand times America's yearly energy budget—with the potential to reach 2,000 zettajoules as drilling and stimulation techniques improved.

The report projected that with $1 billion in research funding spread over fifteen years, the United States could deploy 100 gigawatts of EGS capacity by 2050. For comparison, the entire U.S. nuclear fleet generates about 95 gigawatts.

Cost projections looked promising too: as low as 3.9 cents per kilowatt-hour under optimal conditions. That's competitive with natural gas and cheaper than most new nuclear construction.

Where People Are Actually Trying This

The first serious attempt at enhanced geothermal happened in the high desert of New Mexico. In 1977, Los Alamos National Laboratory completed an EGS reservoir at Fenton Hill, drilling 2.6 kilometers into granitic basement rock heated to 185 degrees Celsius. They called it Hot Dry Rock at the time—the name EGS came later.

The system worked. They circulated water through artificially fractured rock and extracted heat at commercially relevant rates. By 1986, an expanded second reservoir achieved production temperatures of 190 degrees Celsius, delivering thermal output equivalent to about 10 megawatts of electricity.

Then budget cuts ended the project.

The most sustained European effort sits in Soultz-sous-Forêts, a small town in the Alsace region of northeastern France. The EU-funded project connected a 1.5-megawatt demonstration plant to the electrical grid and experimented with triplet well configurations—one injection well feeding two production wells—to optimize heat extraction.

Australia has perhaps the most ambitious project: a 25-megawatt demonstration facility in the Cooper Basin, roughly 1,000 kilometers north of Adelaide. The basin's geology is almost ideal for EGS, with thick insulating sediments over hot granitic basement. Government studies suggest the region could eventually support 5,000 to 10,000 megawatts of generation.

South Korea's Pohang project aimed for 1 megawatt starting in 2010. It would become infamous for other reasons.

The Earthquake Question

On November 15, 2017, a magnitude 5.4 earthquake struck the city of Pohang, injuring dozens and causing over $50 million in damage. It was one of the most damaging earthquakes in modern South Korean history—a country not known for seismic activity.

Investigators traced the likely cause to the Pohang EGS project. All research activities ceased in 2018.

This was not the first time enhanced geothermal triggered noticeable tremors. In Basel, Switzerland, a pilot project caused a magnitude 3.4 earthquake in 2006, alarming residents of the densely populated city. The project was suspended, then permanently canceled.

The phenomenon is called induced seismicity—earth tremors caused by human activity rather than natural tectonic stress. It occurs because EGS relies on deliberately shifting rock along existing fractures. Most of the time, these shifts are tiny—too small to feel at the surface. But occasionally, the injected water can lubricate a larger fault plane, releasing accumulated tectonic stress in a more significant event.

The Geysers field in California, the world's largest geothermal complex, regularly experiences small earthquakes correlated with fluid injection. Most measure below magnitude 3—roughly equivalent to a passing truck—but they demonstrate that pumping water underground is not a seismically neutral activity.

How worried should we be? The Australian government concluded that induced seismicity risks are "low compared to that of natural earthquakes" and manageable through careful monitoring. The consensus among geologists is that EGS-induced tremors are typically small, that sites near major fault lines should be avoided, and that careful pressure management can minimize risk.

But Pohang demonstrated that "typically small" is not "always small." The technology requires geological humility.

The American Push

After decades of intermittent federal interest, enhanced geothermal is experiencing a policy renaissance in the United States.

In 2009, the Department of Energy released $84 million in funding specifically for EGS research, followed by another $80 million from the American Recovery and Reinvestment Act—the Obama-era stimulus package responding to the financial crisis. Multiple demonstration projects received support.

Cornell University launched one of the more interesting initiatives in 2018, planning to heat its Ithaca campus with geothermal energy drawn from two to five kilometers underground. The project received $7.2 million in federal funding and completed a two-mile-deep test borehole in 2022. The system is designed to supply twenty percent of Cornell's heating load—a practical demonstration that EGS can work for institutional-scale district heating, not just electricity generation.

The most aggressive recent commitment came in September 2022, when the Department of Energy announced its Enhanced Geothermal Shot—part of a broader initiative to achieve breakthrough cost reductions in clean energy technologies. The goal: reduce EGS electricity costs by ninety percent, to $45 per megawatt-hour, by 2035.

The Infrastructure Investment and Jobs Act followed with $84 million for four EGS demonstration projects. The Inflation Reduction Act extended tax credits for geothermal development through 2024 and beyond.

Whether this money produces commercial-scale deployment remains to be seen. Enhanced geothermal has promised transformative potential before.

What Makes It Hard

Four factors dominate EGS economics, according to the MIT study.

First: resource temperature. Hotter rock means more energy per unit of water circulated, which means fewer wells and smaller surface plants for the same power output. This is why drilling depth matters—every additional kilometer buys you roughly 30 more degrees.

Second: fluid flow. The artificially fractured reservoir needs to pass water through quickly enough to extract heat efficiently, but slowly enough that the water actually heats up. Getting this balance right requires sophisticated reservoir engineering.

Third: drilling costs. This is the killer. Drilling into crystalline basement rock at depths of five to ten kilometers is expensive, time-consuming, and technologically demanding. Drill bits wear out quickly in hard granite. Wells can cost tens of millions of dollars each. A single EGS installation might need four to six wells.

Fourth: power conversion efficiency. The efficiency of converting thermal energy to electricity depends heavily on temperature differential. A 200-degree resource can't drive turbines as efficiently as a 400-degree resource. Lower temperatures mean more wells, more pumping, more infrastructure.

Drilling costs have historically been the limiting factor. The oil and gas industry has driven tremendous improvements in drilling technology over the past fifty years, but most of that innovation targeted sedimentary rock—softer, more predictable formations. Hard crystalline basement rock remains punishing on equipment.

Recent advances in directional drilling, improved drill bit materials, and even experimental approaches like laser drilling offer hope. If drilling costs drop by half, EGS economics transform.

The Long View

Enhanced geothermal occupies a peculiar position in the clean energy landscape. Unlike solar and wind, it provides constant baseload power. Unlike nuclear, it involves no radioactive materials and can scale from campus heating systems to gigawatt power plants. Unlike fossil fuels, it produces effectively zero operational emissions.

It requires no fuel supply chains, no imported materials, no weather dependence. The resource is effectively infinite on human timescales—the Earth's interior will remain hot long after our sun has burned out.

And yet EGS remains a demonstration technology, perpetually promising, never quite commercial. The geology is universal, but the engineering is hard. The earthquakes at Basel and Pohang spooked investors and policymakers. The drilling costs have proven stubborn.

Still, the numbers are difficult to ignore. Somewhere between 200 and 2,000 zettajoules of extractable energy sits beneath the continental United States alone—more than enough to power civilization for centuries. The heat is there. The water can be pumped. The fractures can be opened.

The question is whether we can learn to crack the earth safely, cheaply, and at scale. The answer may determine how much of the clean energy future comes from below our feet rather than from the sky above.