This is part of IEEE Spectrum's SPECIAL REPORT: WINNERS & LOSERS 2009, The Year's Best and Worst of Technology.
A new kind of geothermal system in Australia’s desert holds great promise for clean electricity generation.
Four kilometers down below the orange earth of Australia’s Cooper Basin lies some of the hottest nonvolcanic rock in the world—rock that the geothermal industry had never seriously considered using to make electricity. But next month Geodynamics, an eight-year-old company based in Milton, Queensland, will prove otherwise when it turns on its 1â¿¿megawatt pilot plant here. The company has done more to harness this unconventional form of geothermal energy than anyone else in the world.
Geodynamics picked a place in the middle of Australia with a smattering of trees, a mostly dry riverbed, and a town with a population of about 14. Even in the best circumstances, building a geothermal power plant is a risky endeavor: drilling costs money, and divining what’s going on in the depths of the Earth is still something of a black art. Here, geothermal companies must clear yet another hurdle. The world’s 10 000-MW collection of geothermal power plants exploits existing underground reservoirs of water and steam. Australia’s geoscientists, by contrast, must create their own.
This very experimental technology is known as an engineered geothermal system, or EGS. If it works—and the finances and expertise at Geodynamics’ disposal suggest that it will—heat from deep under the outback could contribute a few gigawatts of clean round-the-clock power, up to 20 percent of Australia’s capacity today. And if it works here, many other countries will want to give it a whirl.
In the last few years, the concept of geothermal energy has undergone a dramatic reshaping to include a broad range of geological conditions not normally deemed useful. In the United States, for example, EGS could potentially contribute as much as 100 000 MW of electricity in the next 50 years, according to an MIT report released in 2006. Today conventional geothermal capacity in the United States amounts to about 3000 MW, less than half of a percent of the country’s total electric capacity. In famously geothermal Iceland it comes to 450 MW—about one-fourth of the island’s total. Australia’s use of geothermal heat is basically nil.
If the three dozen geothermal ventures now trolling the Australian continent are any indication, that situation is about to change. But there’s a catch. Only a couple of EGS projects have ever produced power, and those are in Germany and France, where the rock is considerably more pliant than Australia’s granite underpinnings. That hasn’t stopped Geodynamics, whose managing director, Gerry Grove-White, contends that the system he is shepherding into existence is the first with real commercial promise. ”None of those hold the prospects of ours, with our massive [geological] resource and much higher temperatures,” says Grove-White, a power engineer and former executive at Tata Power, India’s largest private utility. The reasons for his optimism have everything to do with the unique conditions into which Geodynamics has plunged itself.
Today virtually all geothermal systems are in volcanic regions, near the boundaries of tectonic plates. When two plates heave into each other, one tends to buckle under the other, creating openings in the mantle through which magma can seep up, heating the rock above. Mining the underground heat, however, requires a carrier. Today’s systems rely on rainwater, which collects in fractures in the crust and drips several kilometers down, pooling in cracks and porous rock. A geothermal company drills a well, builds a power plant above it, and starts pumping water. The water comes to the surface and explodes into steam, which turns a turbine, which drives a generator, producing electricity. The hotter the rock and the larger the buried reservoir of water, the better the system should perform.
Now eliminate from that picture much of the water and shrink the fractures where the water pools to millimeter-wide slivers. Move the system to the middle of a desert, 500 kilometers from the closest grid connection. Those are the circumstances that Geodynamics chose to face in the Cooper Basin.
Australia’s granite is a natural nuclear pile, warmed by the decay of uranium, thorium, and potassium isotopes. The result is some of the hottest nonvolcanic rock in the world, with temperatures in the range of 200 to 300 C not uncommon a few kilometers below the surface.
Geodynamics was offered a rare glimpse of the deep Earth and its temperatures thanks to an Australian oil and gas company called Santos, which has been drilling its way through the Cooper Basin for decades. Where it didn’t find fossil fuels, Santos did uncover remarkably hot granite, and its abandoned wells have served as windows into the underground. ”In our case, figuring out where to drill was easy. We went right alongside wells that Santos had drilled in the past,” says Grove-White.
Geodynamics’ first big stroke of luck came early, when it drilled a well and hit hot water that seemed to be trapped in place rather than leaking down into harder-to-reach crevices. ”Nobody had ever realized that such conditions existed—an environment a long way away from volcanoes and full of high-temperature waters,” says geoscientist Doone Wyborn, who is Geodynamics’ executive director.
Granite generally fractures horizontally in this geological environment, so the lack of downward cracks wasn’t a complete surprise; even so, more water seemed to be pooling than anyone had anticipated. The discovery made all the difference, because it meant that water injected into the ground would stay there to soak up heat rather than trickling uselessly away. Even better, such water-holding conditions might well apply in much of the rest of the continent, whose geological conditions are more uniform than just about anywhere else.