Sunshine day: Solar panels are the latest trend as cars go for the green

The Fisker Karma's solar panel covers the roof of the luxury plug-in car. (Kiichiro Sato / Associated Press)

Even as skies are gray this winter, automakers are looking to sunnier times -- not just for more sales, but also to power solar cells going on new cars.

Toyota recently announced that the next-generation Prius will have an optional solar panel that powers an electric fan. The fan activates to cool the cabin when the car is parked and the interior temperature rises.

Fisker Automotive, a start-up based in Irvine, Calif., goes further. The luxury hybrid shown at the North American International Auto Show in Detroit has a large solar panel that supplies extra juice to the battery.

But don't expect to start passing up gas pumps just yet. "Banish any thought that you are really running your car on solar energy," says Bradley Berman, publisher of HybridCars.com. "There simply isn't enough area on the roof of the car that faces and receives the sun's rays hitting it."

Adding a big solar array can stretch mileage up to 10 percent, says Dan Sherwood, president of 3Prong Power of Berkeley, Calif., which specializes in giving Priuses longer electric-only range.

Where solar panels are showing up:

Toyota Prius. (Kiichiro Sato / Associated Press)

Toyota Prius
The cabin fan is powered by a pair of solar panels embedded in a moonroof. Price of the option is yet to be set, says spokesman Bill Kwong. Also included in the option package for the new Prius, due in late spring, will be a remote-control switch for the air conditioner to cool down the car when it has been parked on hot days.

Fisker Karma
The $87,000 plug-in hybrid -- Fisker's first production model, due out later this year -- will have a 5-foot by 4-foot solar panel.

It can add only about 5 all-electric miles a week if the car is parked in the sun all the time, says Fisker's Russell Datz, so the feature is as much about bragging rights as utility. "It fits in with the whole theme of the car," Datz says. "It's a 'green' car in a market where there are no 'green' cars."

Audi A8. (Kiichiro Sato / Associated Press)

Audi A8
While the focus is on hybrids, some conventional cars have quietly used the solar fan idea for a while. The system on Audi's A8 sedan can make a big difference in cabin temperature, says spokesman Jeff Kuhlman.