Roof-mounted solar panels will be able to boost the plug-in hybrid's fuel economy by as much as 10 percent. Power generated by the panels will be used for battery recharging as well as supplying electricity to power windows, lamps, and other accessories.
The issue in the US, as it often does, centers around safety regulations. Specifically, there isn't a lamination process that provides the resin necessary to prevent the glass roof and its photovoltaic cells from shattering, so that presents a problem when it comes to rollover crash-testing in the US.
Still, Toyota executives say they'd like to offer the solar-panel version of the Prius plug-in hybrid in the US eventually. In the meantime, Toyota is preparing to introduce the second-generation version of the Prius Plug-in Hybrid in the US this fall. That model, known as the Prius Prime, will offer as much as 22 miles of all-electric range, and is estimated to get 120 miles per gallon-equivalent when it comes to fuel economy. As for the gas-engine's fuel economy, Toyota is shooting for 52 mpg combined.
As for solar panels on a Prius, the concept isn't exactly new. Way back in 2005, Engadget reported on a Prius that was retrofitted with solar panels that provided enough energy to power the car for about five miles on solar power alone. Like we said, it was 2005. Toyota also offered a solar roof option on the previous-generation Prius; when the car is parked and the cabin air temperature reaches a certain point, a fan powered by a solar panel in the sunroof circulates air to cool it back down.