Panasonic is ready to take the lead offering solar panels embedded into mass-produced electric car roofs.

The Japanese electronics giant started this move in February partnering with Toyota by adding its 180-watt array of solar cells into the roof of new Prius Prime plug-in hybrids. Battery range is increased through this passive technology that Prius Prime buyers can choose as an option.

“That means you get about 10 percent of annual mileage from solar just by letting your car sit,” said Shingo Okamoto, the general manager at Panasonic overseeing the project, in an interview in Tokyo.

Panasonic, with its role supplying solar roofs to the strong-selling Prius Prime and through its partnership with Tesla, could be well positioned in this newly emerging feature. It taps into the need to bring extended range to plug-in vehicles – and the fascination many consumers have with clean technology perks like having solar panels on their home and their electric car.

“Car roofs have the potential to become a new market for solar panels,” Okamoto said. “We made history in the auto industry and in the solar industry with the sun powering mass-produced cars for the first time in the world.”

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Toyota engineers are well known for bringing efficient technologies to the Prius hybrid and plug-in hybrid family including regenerative braking and lightweight materials. These have added to miles per gallon and range, and solar panels add to the energy the Prius Prime can tap into.

“We are aware that the panels are supplying only a small amount of electricity,” said Shoichi Kaneko, chief engineer for the Prius. “But this system is still a breakthrough as we are making use of the energy we would be wasting otherwise. By filling all available space with cells, it is possible to extend the range easily to 10 kilometers (6.21 miles).”

Panasonic engineers have done their share of testing out the solar cells to see how energy is stored under varying conditions. They’d already gained a lot of experience crafting solar panels for houses.

It’s certainly different than a residential rooftop, with the curving contour of a car’s top. There’s also vibration occurring while driving the car, unpredictable appearance of shadows, and very limited space available on the car’s roof.

Okamoto said the Panasonic team was able to adjust the way bypass diodes are configured inside the car’s solar panels. That’s given the panels more of a smooth flow of electricity.

Automakers like Toyota can work with Panasonic to adjust their rooftop design to add more space for solar cells, extending the range.

Toyota did give this technology a try with a limited release back in 2009. It had less capacity with the ability to produce only 56 watts of power, and it could only charge the Prius’ ventilation systems.

Tesla CEO Elon Musk has shown interest in placing solar panels, which he tweeted about in November. The upcoming Model 3 may come with a solar roof, Musk said.

Panasonic and Tesla are hard at work on making battery packs for the Model 3. They’re also working together, and with Tesla’s SolarCity subsidiary, to produce home solar rooftop panels. The team has been working to make home roof tiles embedded with solar panels in various styles popular across the U.S.

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Other companies are exploring interest in solar roofs customized for electric cars.

Nissan offers a small solar panel option for its Leaf electric cars, providing extra power to systems such as the air conditioners and radios. Hanergy Holding Group unveiled four concept solar cars last year, but they’re still in the pre-production phase.

In August, the Karma Revero plug-in hybrid luxury sports car was launched with solar cells embedded in the rooftop. The designers said it has a solar roof providing more of the power than the previous Fisker Karma’s solar panel.

Toyota is finding interest in the solar roof option. At the end of April, the company said it had sold 1,350 units in Japan equipped with solar panels. That made for nearly 9 percent of the total since the option was added, the company said.

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