Solar thermal baseload comes on line

In the high desert of southern Spain, not far from Granada, the Mediterranean sun bounces off large arrays of precisely curved mirrors that cover an area as large as 70 soccer fields. These parabolic troughs follow the arc of the sun as it moves across the sky, concentrating the sun’s rays onto pipes filled with a synthetic oil that can be heated to 750 degrees Fahrenheit. That super-heated oil is used to boil water to power steam turbines, or to pump excess heat into vats of salts, turning them a molten, lava-like consistency.

The salts are just fertilizers – a mix of sodium and potassium nitrate – but they represent a significant advance in the decades-old technology of solar thermal power production, which has traditionally used mirrors to heat water or oil to generate electricity-producing steam. Now, engineers can use the molten salts to store the heat from solar radiation many hours after the sun goes down and then release it at will to drive turbines. That means solar thermal power can be used to generate electricity nearly round-the-clock.

The plant in southern Spain, known as Andasol 1, began operating last November and now provides 50 megawatts of power, enough electricity to supply 50,000 to 60,000 homes year-round. Andasol 2 will come online later this summer, with Andasol 3 already under construction. When the entire Andasol complex is completed in 2011, it is expected to generate enough electricity to power 150,000 households – about 600,000 people.

In the face of mounting concern about climate change, developing alternatives to coal and natural gas

Seville
 

Wikimedia
At this 11-megawatt power tower outside Seville, Spain, sunlight reflects off 624 moveable mirrors to heat water pipes atop the 40-story tower, creating steam that drives a turbine.

combustion has taken on a new urgency, and the construction of utility-scale solar thermal power plants in deserts and arid areas is looking like an increasingly promising option. In the United States alone, solar thermal power projects are now being built near fast-growing centers of electricity consumption, such as Las Vegas, Los Angeles, and Phoenix. The first major solar thermal plant to be completed in decades, dubbed Nevada Solar One, started providing 64 megawatts of power to the neon lights of Las Vegas in 2007, although it lacks the latest molten-salt technology. Across the globe, utilities are currently building or planning solar thermal projects in North Africa, Spain, and Australia, among other regions.

Some of the recent claims for solar thermal power have been stunning. Researchers at the German Aerospace Center have estimated that 16,000 square kilometers of solar thermal power plants in North Africa – paired with a new infrastructure of high-voltage, direct-current transmission lines – could provide enough electricity for all of Europe. And scientists have estimated that constructing solar thermal power plants on less than 1 percent of the world’s deserts – an area roughly the size of Austria – could meet the entire world’s energy needs.

Of course, solar thermal has been here before, experiencing a boom in the late 1970s and early 1980s. Its progress then was stalled by collapsing fossil fuel prices, as well as a lack of government support. Today, some critics of the technology fault it for taking up acreage in fragile deserts.

The case for solar thermal power hinges on economics. The sun bathes the Earth with an average of 6 kilowatt-hours of power per square meter over the course of a day, and a concentrated solar power plant like Andasol is the cheapest way to harvest a portion of that. Photovoltaics – semiconductor panels that convert sunlight to electricity – deliver power at roughly 40 cents per kilowatt-hour, while conventional solar thermal power plants can do so for around 13 cents per kilowatt hour, according to the U.S. National Renewable Energy Laboratory. This is only marginally more expensive than the average U.S. price for coal-generated electricity in 2008 of 11 cents per kilowatt hour. The cutting-edge technology of using molten salts to store solar-generated heat is considerably more expensive, but experts expect that price to fall steadily as the technology improves and is mass-produced.

“One of the great things about molten salt technology is that you can get more energy out of the same facility,” says Barbara Lockwood, manager for renewable energy at Arizona Public Services.

Leave a Comment

You must be logged in to post a comment.

This site uses Akismet to reduce spam. Learn how your comment data is processed.