The new Toyota Prius plug-in hybrid will gain additional electric driving range with a rooftop solar panel that helps recharge the battery.

Stretching nearly the entire length of the roof, the solar cells can charge the lithium-ion battery pack when the car is parked, and can boost efficiency by as much as 10 percent, though Toyota did not provide specifics.

When the car is being driven, the solar panels also supply power to accessories such as air conditioning, power window and interior lights.

Initially the new technology will be offered only in the Europe and Japan versions, where it is named the Prius PHV.

Koji Toyoshima, chief engineer of the Prius plug-in, told Automotive News that Toyota aims to introduce the panels in the U.S.

The United States roadblock has to do with meeting stringent Federal Motor Vehicle Safety Standards and Regulations.

Toyota hasn’t been unable at this point to laminate the photovoltaic cells in a resin that won’t shatter during a rollover crash, however, the roof panels meet safety standards in Japan and Europe.

SEE MORE: Five Ways Toyota Updated Its 2017 Prius ‘Prime’ Plug-in Hybrid

Toyoshima said engineers are working on a solution so that it can introduce the solar panels to the U.S. version, dubbed the Prius Prime.

“We would like to introduce this, at least in the lifetime of the current model,” the chief engineer said at the car’s Japan debut. “It should be possible to do a lot of charging this way in places like California or Arizona.”

The automaker has been working on solar roof technology for several years, as the Nikkeinewspaper reported the secret development in 2009.

If the solar does panel make it to America, the Prime wouldn’t be the first Prius to boast free electrons from the sun. The third generation Prius had an optional solar roof, but it only powered the ventilation fan when the car was parked.

Automotive News