Promise Boiling Over  

Kurt Kleiner at Nature has a good summary article on geothermal industry - "Promise Boiling Over" (focusing on Iceland, the US and Australia rather than trying to survey the whole planet like I did in "Geothermia Revisted").

Iceland is famously rich in geothermal energy. The country sits on a geological hot spot that provides enough power to generate one-quarter of its electricity and heat 90% of its homes.

Now, the Icelandic bank Glitnir has decided that the time is ripe to take advantage of geothermal opportunities elsewhere. In September, the bank opened an office in New York to pursue what it boldly predicts will be $40 billion worth of geothermal investment in the United States over the next 20 or so years.

Glitnir's move is one of a growing number of signs that geothermal energy is ready to become a more significant player in world energy production. "If you're a utility, your first choice of renewable energy is geothermal," says Thomas King, managing director of the US Renewables Group investment fund in New York. "It's the cream of the crop."

King's bullishness reflects a growing belief among energy analysts that although the technology hasn't received as much attention as wave or solar power, geothermal companies have outstanding long-term potential. Robert Wilder, chief executive of Californian clean-energy consultancy WilderShares, points to Ormat Technologies, a maker of geothermal plants based in Reno, Nevada, as a sign of the trend: its share price has risen from about $16 a share in April 2005 to $50 this week. Nevertheless, with just 9 gigawatts or so of installed capacity, geothermal energy accounts for only about 0.2% of all electricity produced around the world. In theory, geothermal heat can be found anywhere in the world if you dig deep enough. But in practice, it has only been worth harnessing in regions where water is found in combination with hot, porous rock close to the surface.

For instance, just north of San Francisco, a geothermal field called The Geysers generates 760 megawatts of electric power. The plants there take advantage of a large, naturally occurring underground steam reservoir that can be tapped by drilling relatively shallow wells.

The Geysers are examples of 'dry-steam' power plants: the steam that comes out of the reservoir contains little or no liquid water, and can therefore be routed directly to a turbine to create electricity. However, most plants are of the 'flash-steam' variety. These plants use water that has been heated to about 180 °C, but remains liquid because it is highly pressurized underground. The water is then pumped to the surface. Because the pressure there is lower, most of the water 'flashes' into steam, which can be used to operate a turbine. ...

Even in favourable geological locations, geothermal power has a high capital cost, mainly because it costs a lot to dig the wells. Balancing that are its low fuel costs. Overall, conventional geothermal plants in the United States deliver electricity for between 5 cents and 8 cents per kilowatt-hour: not much more than the average of 4 cents per kilowatt-hour for electricity from a coal-fired power plant.

In Australia, a firm called Geodynamics is trying to develop a new technique that can take advantage of geothermal energy in the absence of a ready-formed reservoir of water. "We believe that our area is probably the best location in the world to make this approach economically viable," says Doone Wyborn, a founder and executive director of Geodynamics in Queensland. The firm plans to use the Cooper Basin, a geological feature of the Australian interior, in which rocks with a temperature of about 270 °C are available quite close to the surface.

Geodynamics aims to drill two wells to a depth of 4.3 kilometres, and to fracture the hot granite in the rocks by pumping down cold water. Once the rock is permeable enough, the system will act as a heat exchanger — water will be pumped down one well, migrate through the rock to the other well, from which it will be extracted and used to generate electricity.

The company plans to have a 50-megawatt power plant in operation by 2010. It estimates the potential capacity of the Cooper Basin at 10,000 megawatts of power, which could be realized by drilling hundreds of wells.

The Geodynamics project is an example of a technology called 'hot-dry-rock' or 'hot-fractured-rock' geothermal. A report by the Massachusetts Institute of Technology (MIT) in Cambridge published in January concluded that this type of 'enhanced' geothermal power generation could greatly enhance our ability to tap geothermal energy. "I feel it's been an ignored option," says Jefferson Tester, the chemical engineer at MIT who headed the panel that wrote the report, The Future of Geothermal Energy. "But I'm very optimistic about the possibility if a lot of things come into place."

Eventually, geothermal energy could be available almost everywhere, the report contends. Deep drilling from any location will eventually hit hot rock. In the United States alone, the report says, the amount of energy available by drilling up to 10 kilometres below the surface is a stunning 13 yottajoules (1024 joules), or 130,000 times the annual energy consumption of the entire country.

Only a fraction of that is economical to exploit. Even so, the report concluded, in the United States alone, enhanced geothermal electrical capacity could reach 100 gigawatts in the next 50 years — enough to fill about 10% of the country's electricity needs.

An important benefit of such systems is their flexibility, Tester says. They could prove to be economical from a very large scale, all the way down to a relatively small, 1-megawatt plant that also provides direct heating to buildings. As in Iceland, this combined heat-and-power approach greatly enhances the economics of geothermal power. But it requires building communities that can make use of the heat. ...

Tester says that geothermal power will make economic sense even without special incentives or restrictions on carbon emissions. As governments move to restrict greenhouse-gas emissions, geothermal power is set to look even better.

King adds that the standards for renewable energy being set by individual states have kicked off a flurry of interest in geothermal power. "It's clean, it's close to zero emissions, and it's baseload power that runs 24 hours a day, 7 days a week. And a well-managed reservoir can keep going practically forever," he says.