TOKYO -- Toyota has been experimenting with a sun-powered Prius that it hopes will one day require no plugging in.
In a Japanese government-funded demonstration project started in July, Toyota engineers fitted solar panels designed by Sharp to the hood, roof, rear window and spoiler to see how much power the sun can generate.
The electricity from the panels goes directly to the drive battery, so the Prius can charge while moving or when parked.
On a good day, the engineers found that the charge can be sufficient for up to 56 km (35 miles) of travel, more than the 47 km driven a day by the average American, according to a study by the AAA Foundation for Traffic Safety.
But the performance drops off quickly if it is cloudy or even when it is too hot. If used in real-world driving in those conditions, the Prius would have to be plugged in to recharge.
The solar cells are inspired by new ultra-thin solar panels developed for satellites. They are just 0.03 mm (0.11 inches), making them malleable enough to form-fit to the body of a car.
The engineers needed to create a buffer between the car and the cells to protect them, so the actual solar panel modules are closer to 1 cm (0.39 inches).
The trunk of the car is filled with batteries for the solar panels, adding an extra weight of around 80 kg (180 lbs).
Making the entire package lighter and bringing down the extremely high costs are among the biggest challenges for the technology, said Satoshi Shizuka, Toyota's lead engineer on the project, adding that commercialization likely remained "years away."