In early July, various print and online media announced that Toyota would offer a rooftop solar panel as an option on the next generation Prius due in 2010. Some hybrid fans got excited about the possibility of on-board solar energy generation, while solar power and automotive experts cast the news aside as fluff. The experts understand that there’s a mismatch between the amount of solar power that can be delivered and how that energy might actually be used by the Prius.

Some journalists and hybrid fans initially speculated that a Prius solar roof could extend the car’s electric range or radically boost miles per gallon. After all, solar-powered cars have achieved remarkable results, especially in competitions like the 21-year-old World Solar Challenge. However, cars that run solely on the sun are specialized units, super lightweight with very expensive optimized solar equipment—and typically not featuring any consumer features. Some don’t even have brakes. By contrast, the Prius solar panel will more likely be limited to running a small ventilation fan while the car is parked. That was the function of the solar panels embedded in the glass sunroof of the 1992 Mazda 929. (There literally is nothing new under the sun.)

Aftermarket kits from companies like Solar Electric Vehicles have allowed individuals to emulate a factory-installed solar panels. The cost of the kits can range from $30 to $4,000, depending on the amount of voltage produced. The biggest users of automotive solar panels are RV owners, who have the largest space on which to deploy them and thus can produce the most power. But even with the most expensive system, the power is typically channeled into running accessories like laptops and other electronic gadgets.