STEVE INSKEEP, host:

Here's something as sure as the sunrise. When fuel prices are high, people talk about alternatives, including energy from the sun. They don't often get past talk, but one kind of solar energy is quietly becoming a significant source of electricity in the Southwest.

NPR's Ted Robbins reports.

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TED ROBBINS reporting:

It's well over 100 degrees in the middle of the desert south of Las Vegas, but a construction crew is making it even hotter. They're bolting highly polished, curved glass mirrors to a series of aluminum frames, each as long as a football field. Step in front of one of those mirrors and it's enough to sear your eyeballs.

The crew is fitting together four mirrors all along what's called a solar trough. Gilbert Cohen is managing the project called Nevada Solar One.

Mr. GILBERT COHEN (Project Manager, Nevada Solar One): And when it's completed, it forms a perfect parabola. And when the sun is reflected on a parabola, all the rays are directed to one line.

ROBBINS: And that line gets really, really hot - about 750 degrees. Right at the center where it's hottest is a tube, a closed loop filled once with oil. The hot oil flows around the 400-acre project and into a building where it turns water into steam, which turns a steam turbine, which makes electricity. This is solar thermal power.

Severin Borenstein heads the University of California Energy Institute.

Mr. SEVERIN BORENSTEIN (Director, University of California Energy Institute): The central station solar thermal industry has gotten very little attention and has really not grabbed the imagination of the populace the way solar PV has.

ROBBINS: Solar PV or photovoltaics are what most people think of when they think of solar power - panels on roofs. But compare the output of PV to solar thermal.

The largest PV array in the world in Germany produces 10 megawatts. Nevada Solar One will produce 64 megawatts of electricity; enough to power 40,000 Las Vegas are homes during the hottest part of the day. And it's only the world's third largest solar thermal plant.

Borenstein says PV is great for small-scale uses, highway signs or buildings in remote areas.

Mr. BORENSTEIN: I think for most people, what they care about is cheap, reliable electricity. And then if you make them think a bit more about it, they would like it to be environmentally not too damaging. Generally, they don't want to install stuff in their own backyard or on their own roof; they just want the power company to solve the problem.

ROBBINS: That's exactly what Sierra Pacific Resources is doing. The utility is buying all of Nevada Solar One's output. In part that's because the state is requiring that within the next decade 20 percent of Nevada's power come from renewable sources.

Without that mandate, Sierra Pacific Resources' Tom Fair admits the company probably wouldn't have agreed to buy any kind of solar energy.

Mr. TOM FAIR (Executive for Renewable Energy, Sierra Pacific Resources): You know, frankly, right now they're more expensive than other renewables and can't really compete on the basis of economics alone.

ROBBINS: Again, Severin Borenstein.

Mr. BORENSTEIN: Realistically, conventional energy from coal runs five or six cents a kilowatt hour, from natural gas, maybe seven or eight cents, wind is nine or ten cents, solar is probably 30 cents a kilowatt hour from photovoltaics. Solar thermal is probably about half of that.

ROBBINS: But still far more expensive than fossil fuels. The price difference is partly because the federal government gives bigger subsidies to traditional energy sources.

Scott Sklar, a solar energy consultant, cites the incentives in last year's federal energy bill as just one example.

Mr. SCOTT SKLAR (President, The Stella Group): Twenty-year tax credits for nuclear, 16-year tax credits for natural gas pipelines, and just two-year tax credit extensions for wind and solar and the other renewables.

ROBBINS: Even without other subsidies, two solar thermal plants far larger than the Nevada project are planned for California's deserts. Solar thermal won't work everywhere. It needs light and heat. PV just needs light. Both technologies also need improvements to make them more efficient and economical.

The Department of Energy thinks that'll happen. It says by the end of this decade, electricity from solar thermal may be as cheap as fossil fuel in the Southwest.

Ted Robbins, NPR News.

INSKEEP: If you're burning to know how parabolic solar troughs work, just fire up the computer and illuminate the subject at npr.org.

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