Sunshine will cover your daily commute

Startups, and even major automakers, are turning their cars into mobile solar arrays. Hyundai’s 2019 Sonata (the solar version) uses an expansive roof-top solar panel to extend its electric range by 800 miles extra per year, assuming at least six hours of daily sunshine. And startup Sono Motors of Germany—reporting €214 million ($235 million at current exchange rates) in paid pre-orders—and Dutch firm LightyearOne both promise electric cars that charge themselves with their own photovoltaic panels.

Major R&D efforts are underway. The market research firm IDTechEx found that patent activity for solar vehicles has quadrupled in recent years, with nearly 1,000 intellectual property claims for solar-powered cars worldwide in 2016 and 2017.

It predicts the number of vehicles running on solar alone will rise from zero today to many thousands within the next decade. Most of this activity is in China: 71% of solar car patent applications have originated there, mirroring the electrification of China’s car market, the world’s largest, accounting for more than half of global EV sales.

But physicists (and economists) argue that slapping solar panels on your car is not the most efficient way to procure electrons. Nor will it get you very far. For one thing, turning a vehicle’s body panels into power plants is pricey compared to buying solar power from the grid, even amortized over the life of the car, according to Jeremy Michalek, a professor of mechanical engineering at Carnegie Mellon University and director of its Vehicle Electrification Group. Nor are cars’ photovoltaic cells particularly efficient or well-positioned to capture sunlight. Even a best-case scenario would see less than 25% of solar energy converted into electricity. Under ideal conditions, that might boost a car’s range by 25 miles each day (still above the typical commuting distance in US cities of less than 16 miles; pdf).

But buying a car or truck has never relied much on reason to seal the deal. As carmakers have long known, identity, symbolism, and “hedonic attributes,” what economists call the irrational pleasure of driving a car, dictate many of our decisions. With solar panels poised to give us just enough juice to cut the charging cord and drive off into the sunset, we may be willing to pay the price. Just don’t go too far after dark.