DEAR CAR TALK: Is it technologically feasible to utilize a flat solar glass panel over (or as part of) a car roof in order to extend the driving range of battery-powered cars on sunny days?

House roof solar panels are raised and angled to catch the sunlight, but this obviously would not work in an automotive situation because drag coefficient would be increased, thereby resulting in severely diminished economy.

I seem to recall that a few years ago, Toyota used solar sunroofs to power an interior fan to ventilate hot interiors in some Prius models while they were parked.

Could this technology be adapted in some way to recharge electric vehicle batteries so that driving range would be increased and dependency on plug-in recharging decreased in certain situations? – Michael

RAY: Not until solar panels get a lot more efficient and cover a lot more of the car’s surface area, Michael. They just can’t produce enough power yet to make a meaningful difference.

You need to provide something like 36,000 watts to power a 50-horsepower electric motor (that’s less than most electric car motors, by the way – the Chevy Bolt’s motor, for example, produces up to 200 horsepower). A typical solar panel, on the other hand, produces about 300 watts.

So, if you were willing to park out in the desert for, like, 10 days, you might be able to fully charge up your EV with one panel. But by then your dashboard would be cracked and melted. Not to mention the Snickers bars in your glove box.

I mean, you’re right that any extra power you add to the battery extends its range. It’s just not clear, when you factor in the energy output and the cost of the panel, that it makes economic sense yet.

Pretty soon, car panels themselves – roofs, hoods, trunks – will be able to be coated with a solar collection film. That will multiply the potential collection area. And over time, solar collectors themselves will get more efficient and be able to produce more energy.

And if cars, and batteries, get lighter, that would help, too. So would autonomous cars, which could move around when “parked” to “catch the sun.” Kind of like kids on spring break.

But we’re not there yet, Michael. Write back to me in five years, and I’ll update you on the progress.

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