Geothermal energy, the effort to tap the earth’s “renewable” internal heat, is often touted as the most promising potential source for clean, green energy — only this week, the White House was bragging about its investments in geothermal generation. Team Obama may not have noticed, but geotherm has had a rough few months.
First off, Al Gore went on The Tonight Show in November, telling Conan O’Brien and his nighttime audience:
People think about geothermal energy — when they think about it at all — in terms of the hot water bubbling up in some places, but two kilometers or so down in most places there are these incredibly hot rocks, ’cause the interior of the earth is extremely hot, several million degrees.
Unfortunately, as an army of critics immediately pointed out, Gore was exaggerating once again. Temperatures at the earth’s core, as far as we know, are only about 6–8,000 degrees Celsius.
This is still pretty hot, in fact hotter than the surface of the sun (5,000 degrees Celsius). So while Gore had his numbers wrong, he was correct in that there is plenty of energy down there. Less than a month later, however, a 30-year, $60 million effort to tap geothermal energy outside Basel, Switzerland, finally ended. The reason? Drilling down two miles and then fracturing rock in order to inject water was causing earthquakes. Indeed, Markus O. Haring, the former oilman who long headed the project, is now on trial in Switzerland on criminal charges of causing $9 million in property damage.
The very next day, AltaRock, a California company that was the flagship of the Obama administration’s efforts to develop geothermal energy, announced it was canceling an almost identical project in northern California for the same earth-shaking reason. AltaRock had already received a $6 million grant from the Department of Energy and an additional $30 million from Silicon Valley investors Google, Khosla Ventures, and Kleiner Perkins Caufield & Byers (a firm in which Gore is a full partner), but residents of the surrounding area expressed jubilation — their houses had been wracked by tremors several times.
And so, as with other forms of “renewable” energy, making geothermal work in practice turns out to be difficult. Yet does this mean we should abandon our efforts to tap the earth’s heat? Not at all. In fact, when properly understood, it will become clear that we already tap this “terrestrial energy” at more than 100 major sites around the country. We should build more of them.
The heat of the earth — as currently understood — comes from two sources. The first is the residue of collisions that occurred at the earth’s formation. As the solar system condensed out of a spiraling dust cloud, the earth and the other planets aggregated from larger and larger chunks of material. In the later stages, these segments became nearly planet-sized. The frictional heat generated by these cosmic collisions still reverberates throughout the earth today.
The second source of the earth’s heat is incredibly small. It is the uranium and thorium atoms that make up only 8–10 parts per million of the earth’s substance. At least half the earth’s heat and perhaps as much as 90 percent (no one is entirely sure) comes from the radioactive breakdown of these two elements.
How can we access this terrestrial heat — our only source of energy that does not come from the sun? One way is to bring water in close contact with it in order to produce steam to generate electricity. This occurs naturally with fumaroles and geysers, which occur where hot magma from the earth’s core comes in contact with groundwater. Unfortunately, these intrusions occur in only a few places, mostly on volcanic islands and along earthquake faults. Iceland gets 13 percent of its electricity from geothermal, Hawaii 20 percent, and California 6 percent. But such sites are few and far between.
Everywhere else, it is necessary to drill deep into the earth. Three to five miles down, the rock must be fractured so that water can be injected to produce steam. This is what is setting off the earthquakes. The whole process also poses enormous engineering problems. Can the steam be raised several miles to the earth’s surface, or will the power plants have to be built deep underground?
There is, however, another option. Why not mine the uranium and thorium directly, and then concentrate them in a controlled environment? Their steady breakdown can even be accelerated slightly into a chain reaction. The intense heat that results — around 600 degrees Celsius — is nowhere near the earth’s internal temperature, but it’s hot enough to boil water to produce the desired electricity.
This, of course, is what we do in a nuclear reactor. The technology has been known for decades. We once built such plants widely but have since largely abandoned the effort. Other countries have picked the technology, however, and there are now 55 reactors under construction in Asia and Europe, with more to come in the Middle East.
As our crude efforts to tap geothermal energy begin to run into difficulties, it might be worth reconsidering this much more elegant solution. Nuclear and geothermal are, after all, only two different methods of tapping terrestrial energy.
– William Tucker is author of Terrestrial Energy: How Nuclear Power Will Lead the Green Revolution and End America’s Long Energy Odyssey.