Geothermal (地热的) power generation is one of our most stable renewable energy resources. Heat generated below the Earth's surface can provide an almost unlimited supply to power and heat homes. And while geothermal electricity only accounts for around one percent of global generation, that is set to at least triple by 2050.
The Geysers in California is the world's largest geothermal electricity complex. It produces enough electricity from its 18 power plants for 725,000 homes, totaling 20 percent of the state's renewable energy. Superheated "dry steam" is channeled from a large sandstone reservoir heated by a large magma chamber (岩浆房) more than four miles beneath the surface.
Heat is captured from its passage through the rock and the heated water converts into electricity. Cooled water is then recycled and pumped back to gather more heat. EGS (enhanced geothermal systems) technologies will open up many more sites for geothermal energy. "You can effectively put a power plant anywhere," said Will Pettit, director of the Geothermal Resources Council. "All you have to do is drill deep enough and you will find hot rock."
Most geothermal plants actually use a flash steam technique, where hot water (at 360F or 180C) is drawn up, passed into lower pressure tanks and flashed into steam to power a turbine (涡轮机). Binary cycle (双元循环) plants are the growth technology because they can operate at lower water temperatures and more diverse geographical locations. They use moderately hot water to heat a secondary fluid with a lower boiling point—as low as 135F—to drive turbines.
Geothermal plants already emit 11 times less carbon dioxide per unit of electricity than the average US coal power plant. They can also operate 24 hours a day to provide a solid base load for homes and businesses.
There are drawbacks too. Seismic activity around drilling wells is a factor. High investment costs are another. But the US government is backing the sector with multi-million dollar funds to push forward advanced EGS research. Geothermal energy is set to play a big part in the low-carbon electricity future.
