TOKYO — How can Toyota make the world's bestselling green car, the Prius, even greener?
Cover the top with solar panels and run it on sun power.
That's the goal of a trial Toyota is starting this month in Japan. The system generates enough power to drive the Prius PHV for about 35 miles (56 km).
Toyota is running the trial on public roads through February in conjunction with solar cell maker Sharp under a Japanese government-backed initiative called the New Energy and Industrial Technology Development Organization.
Toyota already has a Prius with solar panels. But the technology is offered as a Japan-only option on the Prius PHV, the plug-in variant sold in the U.S. as the Prius Prime.
The new demo car dramatically boosts performance.
Unlike the current system, which charges only while the car is parked, the new version also charges while being driven.
The existing Prius PHV system generates about 180 watts of electricity while the vehicle is parked, enough to power less than 4 miles of battery-only driving. The new system delivers 860 watts, or nearly five times the energy — enough for about 28 miles if the car is charged while parked, or 35 miles if charged while driving.
Some of the gains come through more efficient solar cells. But the new technology also uses many more panels.
The hood, roof and rear window are layered with black solar cells just 0.03 mm thick. Because they are so thin, they can be form-fitted to the Prius' body curves and rear hatch.
A Toyota spokesman said rear visibility is not a problem because the driver can use the side mirrors while driving and the rear-vision video camera when parking or backing up.
Toyota said its test will help it determine how much solar energy will boost the cruising range and fuel efficiency of electrified vehicles.