A Modest Proposal
Iceland turns geothermal energy into electricity in two ways: Venting 600°F steam from a mile underground through a turbine, and a more energetic method that pulls 390° water from deep wells and heats surface water, making steam to drive turbines. Harnessing a natural supply of supercritical water — water that's three times as hot and under enormous pressure — and turning it into electricity would be like switching from diesel to jet fuel. "If we succeed, we expect to increase power output by 5 to 10 times [above what a typical well can produce]," Fridleifsson says.
To appreciate the benefits of free supercritical water, it helps to understand that most coal plants and nuclear power plants make supercritical water before generating electricity. The plants transfer heat energy — produced by burning coal or by the radioactive decay of isotopes — to water in a pressurized tank to bring it to a supercritical state. The process allows the water to maintain the high-energy intermolecular hydrogen bonds of a liquid, yet flow through pipes with near-zero resistance like a gas. It then runs through heat exchangers to create even more steam, which drives turbines to make electricity.
The IDDP well will dip two and a half miles belowground into a pocket of water heated to 1,100° by a bubble of magma. Water normally exists as steam at this temperature, but the immense pressure of the rock above holds the water in a near-liquid state. Once the water squirts to the surface, it will retain nearly all the energy that heated and compressed it. It is virtually certain that engineers will have to redesign existing heat exchangers to handle the water's heat and potentially corrosive chemistry, but a plant running on naturally occurring supercritical water could churn out up to 500 megawatts, on par with a small nuclear reactor and half of what a large coal plant produces. Unlike these, though, the IDDP's zero-emissions power source will last as long as the Earth's core continues to heat rainwater.
Iceland's geothermal efforts are currently operating at 20 percent capacity. If it exploited the island's full reserves in only the conventional way, it could produce 20 terawatt-hours of electricity per year — about the same as three nuclear reactors. Tap into other supercritical reserves, or drill deeper into existing wells, and Iceland's electric output could be five times that of the U.S., the world's largest producer of geothermal electricity; Iceland is only the size of Kentucky.
In 2000, Fridleifsson recruited Wilfred Elders, a professor emeritus of geology at the University of California at Riverside, from retirement to co-lead the IDDP. Geological studies revealed that supercritical water does indeed flow under Iceland, and the six-mile-wide Krafla caldera was the place to go after it. They realized that all they have to do is tap the stuff — and hope that it doesn't destroy the drilling equipment in the process.
Five amazing, clean technologies that will set us free, in this month's energy-focused issue. Also: how to build a better bomb detector, the robotic toys that are raising your children, a human catapult, the world's smallest arcade, and much more.