http://www.economist.com/business/displaystory.cfm?story_id=10727996The power of concentration
Feb 21st 2008
ON FEBRUARY 22nd, at an event featuring film stars, astronauts and technology gurus, Acciona, a Spanish conglomerate, is due to inaugurate a new power plant a few miles from Las Vegas. In fact, the plant has been running since last June. But the technology it uses, known as “concentrating solar power” (CSP), is hot right now, as the Hollywood luminaries might put it.
Acciona's new plant, called “Nevada Solar One”, can generate up to 64 megawatts (MW)—enough, it says, to power more than 14,000 homes. The Solar Energy Industries Association (SEIA) says that more CSP plants, with a total capacity of 4,000MW, are in the pipeline and have signed contracts to sell their future output. An 11MW plant opened in Spain last year (pictured). New Energy Finance, a research firm, estimates that 2,000MW of capacity is in the works in Europe.
As their name suggests, CSP plants generate electricity by concentrating the sun's rays, usually to boil water. The resulting steam drives turbines similar to those found at power plants that run on coal or natural gas. There are several different designs. The Nevada plant uses long curved mirrors, called parabolic troughs, to focus light on a tube of fluid running just above them. The Spanish plant uses a forest of smaller mirrors to focus light on a tower in their midst. Other concepts involve long flat mirrors and devices resembling satellite dishes.
Solar power, of course, does not produce climate-changing greenhouse gases. But it also excites utilities because it generates the most power just when it is needed: on hot, sunny days when people turn on air conditioners. And CSP provides a way around the main drawbacks of solar power from photovoltaic cells. Unlike them, it does not involve expensive silicon wafers. And some designs provide power round the clock, not just when the sun is shining, by storing energy in the form of molten salt.
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