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Visitors take a look at Hyundai Sonata Hybrid equipped with solar panels during a press preview at the Seoul Motor Show on March 28, 2019.

JUNG YEON-JE/AFP/Getty Images

It seems like a bright idea. Cars drive outside. The sun is outside. So combine the two and let the sun charge electric cars as they drive through solar panels.

But, so far, there haven’t been many production electric vehicles or hybrids that have used them. Hyundai is offering a solar panel on its hybrid Sonata in Korea and Toyota has a demonstration Prius hybrid that uses solar panels on the hood and roof. But right now in Canada, no vehicles come with standard solar panels.

The 2017-19 Karma Revero, a plug-in hybrid electric vehicle (PHEV) that started at $130,000, came standard with a roof-mounted solar panel. The standard solar roof was scrapped when the car was redesigned for 2020, although the company says you can order one as an option.

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The 2019-19 Karma Revero came standard with a roof-mounted solar panel.

MARK BLINCH/Reuters

Even Tesla, which sells solar panels for houses, doesn’t offer a solar roof on any of its vehicles.

We’ve had solar calculators and solar-powered lights for decades, so why can’t we have solar-powered cars in our driveways?

“The answer is that solar cells simply don’t produce enough power,” says William Dunford, a University of British Columbia professor of engineering who advises the university’s solar-car club. “If you have sunny days or you don’t travel very much, you may be able to get away with it, but it isn’t going to work for most people, especially in Canada.”

Green or gimmick?

Dunford says the solar panels the Revero had added about 1.6 kilometres to 4.8 km of extra battery range a day, “depending on the conditions.”

That’s barely enough for a trip to the grocery store – and you’d only get that much if you were sitting parked outside on a sunny day.

“The area on car hoods and roofs is too small to generate the level of power necessary to significantly add to an EV's range,” says Derek May, senior project manager of transportation at Pollution Probe, a national environmental non-profit. “Costs are currently too high to justify the added range to a typical EV.”

Panels could also add “thousands” to the cost of a car, Dunford says.

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The idea of solar-powered cars isn’t new. There’s been a World Solar Challenge, a 3,000 km race through Australia’s Outback, since 1987. This year, a Belgian team won after the Dutch team’s car caught fire 250 km from the finish line.

But those cars are slathered in solar panels. And they’re driving in a sunny country.

Right now, the best solar panels only convert about 20 per cent of the sunlight they absorb into electrical energy, May says.

Panels are expected to get better in the next five to 10 years, but you would still need a lot of them to fully charge a vehicle.

“I did the calculation once in a thermodynamics class – even a 100-per-cent efficient solar panel on a car roof wouldn’t be able to power a car for normal operations,” says Jonn Axsen, director of Simon Fraser University’s Sustainable Transportation Action Research Team.

While it’s possible to also cover a car’s hood, trunk and sides in solar panels, it “would look a bit odd,” UBC’s Dunford says.

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“And because angles are different all over the car, the power is never going to be optimum,” Dunford says. “The best way to extract energy is to have a panel pointed directly at the sun.”

Sunnier future?

Hyundai says it’s working on transparent solar panels that would give extra power to cars with gas engines, helping them pollute less. A Dutch startup, Lightyear, is working on a €150,000 ($220,000) car that it claims could get about 12 km of range an hour from its solar panels.

But, at least for now, it makes more sense to generate solar energy on your home’s roof instead of your car’s.

Not only do you get more energy, but you can also sell any you don’t use back to the grid to make money.

“Solar panels are much better on building roofs or in an open field – there’s more area to capture sunlight,” Axsen says.

Have a driving question? Send it to globedrive@globeandmail.com. Canada’s a big place, so let us know where you are so we can find the answer for your city and province.

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