In the coming months, an unnamed manufacturer will bring an electric car to market that offers wireless charging from WiTricity, Alex Gruzen, the company’s chief executive, tells IEEE Spectrum.
Unnamed, yes, but not utterly unguessable. Among the companies that have demonstrated wireless charging are BMW and Hyundai. And, though there are other wireless charging companies out there—Qualcomm, for example—Hyundai has explicitly named WiTricity as the supplier of the system it showed on its new Kona EV last week at the International Geneva Motor Show. Other companies known to be working with WiTricity include Honda, Nissan, and Toyota.
Magnetic resonance was developed at MIT in the early 2000s. It works by establishing a kind of duet between an oscillating magnetic field in a pizza-box-size charger on the floor and a receiver mounted under the car.
The charger and receiver are tuned to resonate, which is why little energy goes astray, making transmission as efficient as you’d get from a cable.
"There’s often a misconception that somehow plugging in is 100 percent efficient," Gruzen says. "But a plug-in is from just 88 to 94 percent efficient; WiTricity's wireless system runs at 90 to 93 percent.”
The resonance also gives you a certain leeway in aligning the car and the charging plate. The vertical clearance can be as little as 10 centimeters (4 inches) for a sports car, and as much as 25 cm for an SUV. The left-to-right positioning need be only within 10 cm of dead center. The fore-and-aft error—which is easier for a driver to control—is 7.5 cm.
Drivers shouldn’t take long to get the hang of parking close enough to the charger on the first try. That ease of use is the entire point.
“About 70 percent of plug-in [hybrid] customers never bother to plug in,” Gruzen says. “They don’t want to deal with cables. And broad, mainstream consumer behavior does not change, as it might with the 1 percent who are early adopters. I plug in every day—I’m a career-long tech early adopter—and let me tell you, it’s a pain in the ass.”
So wireless charging for EVs isn’t just a trick; it’s a marketing necessity. And for it to catch on, it’ll have to be affordable.
Gruzen says that in early, low-volume production the cost difference between the wireless system and the conventional plugged-in one could be in the US $800 range. That’s for a complete set—for the receiver on the car, the transmitting pad, and the charging unit that connects to it. And, if the product hits true mass-production levels, the cost difference to the carmaker could come to just a few hundred dollars.
I ask him why anyone would want a slow charger at a parking spot when he can have access to fast-charging stations, such as the ones that Tesla’s building. He says there simply won’t be enough grid capacity to supply power to enough fast-charging stations once EVs throng the roads.
“Fast chargers? It’ll be like the gas lines of the 70s, queuing up for your spot,” he says. “We want people to be able to start their day with a full battery charge, and when they park at work, it starts charging again, without any intervention or work. Real plugging in is something you do only when you’re in transit and you need a range extender.”
Editor’s note: This story was updated on 25 April 2018; the price information was clarified.