Hot rocks and high hopes  

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The Economist has a look at developments in the world of geothermal power - Hot rocks and high hopes.

OVER the course of the next ten years a company called Geodynamics, based in Queensland, Australia, is planning to drill as many as 90 wells, each 4,500-5,000 metres deep, in the Cooper Basin, a desert region in South Australia with large energy reserves. But the company is not drilling for oil or gas. It is looking for an energy source that is far cleaner and more abundant than any fossil fuel: heat emanating from hot rocks deep beneath the Earth’s surface, a promising emerging form of geothermal energy.

Conventional geothermal power exploits naturally occurring pockets of steam or hot water, close to the Earth’s surface, to generate electricity. (Heat from the water is used to boil a fluid and drive a steam turbine connected to a generator.) Because such conditions are rare, the majority of today’s geothermal power plants are located in rift zones or volcanically active parts of the world. In Iceland, around one-quarter of the country’s electricity is produced by geothermal power stations; at the Svartsengi power station, the naturally occurring hot water also flows into a lagoon, which is a popular (and photogenic) bathing spot.

Geothermal power stations can also be found along the “Ring of Fire” around the Pacific, in Indonesia, the Philippines and on America’s west coast. Conventional geothermal power stations worldwide have a total capacity of 10.7 gigawatts (GW) and will generate 67.2 gigawatt hours (GWh) of energy this year—enough to supply power to more than 52.5m people in 24 countries, according to America’s Geothermal Energy Association.

Engineered geothermal systems (EGS) are based on a related principle, but they work even in parts of the world that are not volcanically active, by drilling thousands of metres underground to mimic the design of natural steam or hot-water reservoirs. Wells are bored and pathways are created inside hot rocks, into which cold water is injected. The water heats up as it circulates and is then brought back to the surface, where the heat is extracted to generate electricity. Because the Earth gets hotter the deeper you drill, EGS could expand the reach of geothermal power enormously and provide access to a virtually inexhaustible energy resource.

“The beauty of the concept is that if it works, it can work anywhere in the world,” says Subir Sanyal, president of GeothermEx, a consultancy based in California. According to “The Future of Geothermal Energy”, a report issued by the Massachusetts Institute of Technology (MIT) in 2007, the thermal energy available in America in rocks 3-10km (1.9-6.2 miles) beneath the Earth’s surface is nearly 140,000 times greater than its annual energy consumption. Conservative estimates suggest just 2% of that energy could be tapped by EGS in practice, but even that would be far more than is needed to supply all of America’s electricity. Tapping it will, however, require both technical and economic hurdles to be overcome.

At the moment only a few EGS plants exist worldwide, including a pilot plant in Soultz, France, and a small commercial plant in Landau, Germany. But Geodynamics and other companies around the world are hoping to change that. Over the next decade Geodynamics plans to build ten 50 megawatt (MW) power stations in Cooper Basin, and that may just be the beginning. According to Doone Wyborn, the company’s chief scientist, the area’s resources could support hundreds of power stations with a total generating capacity of up to 12.5GW—more than all the geothermal power stations now operating worldwide. There are also plans for new EGS projects in America, Britain, France and Germany. Those in the field have high hopes for future expansion: the International Geothermal Association predicts that there will be 160GW of geothermal capacity installed worldwide by 2050, about half of which will be EGS. ...

But man-made earthquakes are not unique to EGS; they also occur as a result of oil-and-gas drilling, and damming and mining operations. The question is whether they can be controlled. Ernie Majer, a seismologist and deputy director of the Earth Sciences Division at Lawrence Berkeley National Laboratory, who is working on refining EGS seismicity guidelines for America’s Department of Energy, believes they can. “With proper study and implementation, you can guarantee that there won’t be big ones,” says Dr Majer, who sees small quakes as a nuisance rather than a danger. Still, many in the industry agree that EGS should be developed in remote areas first, rather than in densely populated cities such as Basel.

And the risks associated with EGS must be balanced against the drawbacks of other energy technologies, such as fossil fuels, which produce carbon-dioxide emissions and occasional oil spills, and nuclear power, which produces radioactive waste. Wind power, meanwhile, is criticised for causing noise pollution, killing birds and despoiling landscapes. The real question, in the end, is what people are ready to put up with in return for a secure energy supply. “It’s a trade-off,” says Dr Majer. “You have benefits and hazards. There’s no perfect technology.”

Whether EGS can overcome the obstacles it currently faces, and go on to play an important role in the world’s renewable-energy portfolio, should become clear in the next decade. “The well failure has set us back,” acknowledges Dr Wyborn of Geodynamics. But he is certainly not giving up. According to the MIT report, the first 100MW of installed EGS capacity should be the most difficult and costly to achieve, but after that it should get easier and cheaper. Scarcer and more expensive oil would certainly help. “There are thousands of wells being drilled for oil across the world every year,” says Dr Wyborn. “I imagine that in a couple of decades all of those drilling rigs that are now redundant, because we’ve run out of oil, will be drilling geothermal wells instead.”

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