If you need an easy way to add some juice to an electric car's battery pack, why not just put a solar panel on the roof? It seems like a fairly straightforward idea—yet solar roof panels haven't really taken off for EVs. But Panasonic is still optimistic about this feature.
"Car roofs have the potential to become a new market for solar panels," Shingo Okamoto, Panasonic general manager in charge of solar roof panels, said in a recent interview with Bloomberg.
Panasonic recently launched a revamped solar roof for the Toyota Prius Prime plug-in hybrid in its home market of Japan. Tesla CEO Elon Musk has discussed the possibility of offering a solar roof on the Model 3, potentially creating another major opportunity for Panasonic—Tesla's sole battery supplier and a partner on the automaker's battery "Gigafactory" in Nevada.
The idea of solar roof panels is far from new. Nissan offers a small solar panel for the Leaf, primarily to help power accessories like air conditioning. The Fisker Karma (which recently re-entered production as the Karma Revero) was offered with a full solar roof.
But it's still unclear whether the photovoltaic cells can boost a car's range enough to make them worthwhile. Toyota also offered solar panels on the Prius Plug-In Hybrid, the predecessor to the current Prius Prime. But Toyota says the Prime's Panasonic-supplied solar roof is the first that can supply power to a car's main battery pack. It can harvest enough energy for an additional 1.8 miles to 3.7 miles of driving, depending on weather conditions, Toyota says.
That's not a huge gain, and the amount of extra range drivers actually get could vary widely in the real world. The appearance of shadows can affect the solar cells' ability to harvest sunlight, although Panasonic has tried to compensate for this by changing the design of bypass diodes. It's also worth noting that the optimal position for a solar panel is at an angle, not flat like a car roof.
Thanks to aggressive competition among manufacturers, solar cells are cheaper than ever—but they're still not as cheap as a conventional roof, and also require extra electronics and wiring. If the prices of solar cells continue to drop, solar car roofs may be worthwhile. Even a little extra range helps, after all. Otherwise, the extra cost, weight, and complexity of solar panels may add up to make them not worth the small amount of additional power they provide.