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Wireless Highway Charging While Driving: Calm Your Range Anxiety

New research shows that we’re very close to being able to charge cars, via the road, while they’re moving. So much for having to stop and plug in your plug-in. Now there is just the tiny question of digging up all that pavement.

Backers of electric vehicles talk about building a large infrastructure of charging stations to get around the "range anxiety" issue. But imagine if you never had to stop at all, and you could power your vehicle as it was moving along. That would be better, wouldn’t it? Anxiety free, even.

That’s the vision of researchers at Stanford, who have come up with a "wireless recharging system" that not only removes the range limit issue, but also solves the other major drawback with EVs: that it takes a long time to recharge your battery, even when you can find a station.

The wireless network instead allows drivers to charge as they go, reaching their destination with a battery at least as full as when they started.

The system is outlined in a new paper in the journal Applied Physics Letters (PDF). It is based on "magnetic resonance coupling," which transfers electricity between two copper coils (one under the ground, one in the car) using a magnetic field.

"This concept provides a way that you could transfer that power while you are driving, so the time it takes to charge your vehicle is time you use for driving," says Richard Sassoon, head of Stanford’s Global Climate and Energy Project.

Although car charging is getting quicker, it is still very slow compared to filling up a tank with gas. The Nissan Leaf, for example, which has a range of about 100 miles, takes about 30 minutes to recharge at a "quick-charging station," according to the manufacturer.

The paper sets out a configuration the researchers say would transfer energy with 97% efficiency, taking account of metal obstructions in the road and the vehicle itself. It is similar to technology being developed for home wireless electricity. But the researchers are not yet sure what happens to the other 3%. Probably it is harmless waste heat, though they need to be sure. No one wants to find out in 50 years that our desperate attempt to quell range anxiety ended up giving us cancer.

Then there is the question of actually getting metal coils into all our roads. Sassoon says the technology could be installed with new roads, or as part of retrofits. He sees roads having "wireless power transfer" lanes, like HOV or carpool lanes, which would mean that only some parts of roads would need to be retrofit. And he points out the equipment itself is cheap, even if digging up tarmac might not be.

"We are far away from suggesting that we rip up every road in the country. There’s a lot more research that needs to be done," he says. "But the cost of actually laying down these coils would be relatively cheap. The coils are just pieces of metal."