Does Car-Mounted Solar Make Sense?

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Even that limited improvement comes at considerable cost. Solar Electrical Vehicles sells its panels for $3,500, whereas NREL could have beefed up its lithium battery to draw another kilowatt-hour from the grid for just $1,000.

Markel notes, however, that Solar Electrical is producing at very low volumes--just two to three systems per day, according to company president Greg Johanson. Economies of scale could sharply lower the system's price. Markel says that optimizing the electronic interface between the solar panel and the hybrid batteries could also boost performance. "The electronics are going to be key," he says. "I know their systems are not designed specifically for the application, so they probably are not the most efficient approach."

The other rooftop solar panel on the market, from Solar Electrical competitor Solatec, operates exactly as Nikkei said that Toyota's would: rather than charging the hybrid-system battery, it charges the lead-acid auxiliary battery that drives the Prius's air conditioner, radio, and other peripherals. Solatec's current system provides just 24 watts and costs $1,650 uninstalled--less than half as much as Solar Electrical's. The lower price and output are both a by-product of the less-powerful thin-film solar cells that the system employs.

Unsatisfied with the visual appeal of the flexible amorphous-silicon panels that the company has been using since 2005, Solatec president Howard Fuller says that the company is now testing a prototype for its next-generation product using printed cells from plastic-photovoltaics developer Konarka Technologies. "Konarka puts out a gorgeous panel," gushes Fuller. "It looks like a couple of racing stripes up there on the roof."

Experts such as Frank and Markel say that building large, stationary solar installations to generate the power to charge electric vehicles will be more cost effective than installing solar onboard. "We want to see sunshine drive the entire society, including our transportation," says Frank. That, he says, will require megawatts of energy. "The ultimate would be to have all shopping centers and industrial parking lots with solar arrays on top. It gives you a little shade and at the same time is charging your car."

Frank says that, even if onboard solar is a marketing gimmick, it could advance the electrification of transportation by advertising the possibility of replacing gasoline with renewable energy. "Whether it's perception or real doesn't matter," he says, "because it creates public awareness."