How Wirelessly Electric Vehicle Charging Works
Wireless EV charging works in a similar fashion to the way smartphones charge — via magnetic induction. Induction charging works by creating an electromagnetic field in one area, usually via a charged coil of metal, that creates a current in another area close enough to be affected by that field. Because the electromagnetic field creates the current, no cord is necessary to transfer power.
In smartphones, the process works via magnets or pads that the phone must stay in contact with. In electric cars, the same basic concept is used on a larger scale with more power that allows for more space between the charging pad and the vehicle. An inductive charging pad lies on the ground, and the car is parked over it. Cameras inside the car tell the driver when they’re correctly positioned over the charging pad.
Once the car is parked over the pad, the ground pad and the pad attached to the EV generate current. The ground pad is charged with power from the grid, creating an electromagnetic field. The charging pad on the underside of the car resonates at the same magnetic frequency as the pad on the ground, and a current is created to charge the vehicle’s battery. Unlike smartphone charging which requires magnets to be precisely aligned and touching, EV inductive charging has more leeway — the air gap can be inches instead of millimeters.
Where wireless smartphone charging is around 80% efficient with power transfer, wireless EV charging claims to be much better. Tech YouTuber Matt Ferrell in one of his videos spoke with a company that makes wireless EV charging tech called WiTricity. The company’s CEO claims its wireless charging equipment is around 99% efficient. That would be about the same as plugging in at a charging station or at home.
That’s surprising as we’d expect a loss in efficiency due to charging wirelessly rather than plugging in. But other data appears to support this level of charging efficiency. The Rochester Institute of Technology’s Green Technology Accelerator Center partnered with wireless charging company HEVO to conduct a study in which wireless EV charging was 95% efficient in prototype devices. Wireless charging of up to 120kW with 97% efficiency was conducted in 2018 at the Department of Energy’s Oak Ridge National Laboratory (ORNL).
That doesn’t mean we’ll all be charging our Teslas wirelessly tomorrow; the tech is still very much in the testing phase. But WiTricity has already retrofitted multiple EV models with their tech that reportedly works well. Multiple other countries are also testing it and working toward a mass market solution. If improved enough to be rolled out for mass adoption, wireless charging kits for current models would be widely available, and new EVs would have wireless charging capability built in.
That could allow for, as Ferrell talked about in his video, more autonomy for self-driving and self-parking cars. If they could charge themselves via pads built into parking spaces or roads, they wouldn’t really need any human interaction to complete their tasks throughout the day. Eventually, last-mile fleet vehicles, for example, could charge by parking on or driving over wireless charging pads and not need to be plugged in throughout the day, though more improvements in autonomous driving tech are needed before that’s even close to reality.
In addition, Cornell University is already working on wireless charging pads that can be implanted in the roadway and power your car as you drive. Drexel University is also developing wireless charging tech that could be built into roads and be better able to tolerate misalignments between charging pads.
The cost of building that kind of tech into roadways on a wide scale remains to be seen and could get in the way of wireless charging roads becoming mainstream if prohibitively high. The U.S. doesn’t have a great record when it comes to the upkeep of our current roads and bridges, but with Congress recently approving a large infrastructure bill we could, hopefully, see that trend improve.
The Challenges of Wireless EV Charging
One big hurdle to mass-market wireless charging is the expense. At the time of writing, WiTricity says one of their wireless charging stations costs around $700. But calculating true cost is tricky at this point is difficult since the tech is so new. It depends on whether you’re talking about retrofitting a single vehicle or outfitting a whole fleet. It’ll also cost more to add several pads to a large electric bus than to fit a regular EV sedan with wireless charging — up into the thousands, according to The Eco Experts. The bottom line is that, at the time of writing, wireless charging tech will cost significantly more than a wired charging station to install for personal use.
As technology improves and moves toward wider market adoption, that price will hopefully fall. For now, though, it remains more of a costly novelty than a practical solution for a lot of EV drivers. Adding to that is the fact that not much wireless EV charging infrastructure currently exists.
Charging speed is another hurdle. When this tech first started becoming popular a few years ago it only transferred power at around 3.5kW, according to Green Car Reports. At the time of writing, that speed has increased to 11kW, which is enough to add about 34 miles of power to the battery per hour of charging. That’s decently fast, especially if you’ll be parked for a while, but it’s a far cry from the average DC fast charging (DCFC) station.
Some safety challenges will also need to be addressed, such as what would happen if something metal came into contact with the charging pad while it was active. Since an electrical current is running through the pad, a metal object would heat up and could end up causing a fire.
To address that, manufacturers are building fail safes. In Ferrell’s video, WiTricity’s CEO explained that if an object like a metal can or a cat that crawled under the car to try and get warm is detected, the charger would shut off and send a notification to your phone. If a person gets too close to the charging pad, it also shuts off. WiTricity’s website outlines these precautions in a little more detail.
What’s Next for Wireless EV Charging
In development since around 2007, wireless EV charging could finally be coming to the mainstream in the next few years. The Society of Automotive Engineers (SAE) ratified a standard for wireless EV charging in 2020, signaling it can be brought to the mass market. Once manufacturers have tested and developed the technology adequately, we’ll probably start to see wireless charging come standard on electric cars.
It’ll be a while before the infrastructure catches up to this idea and retrofit kits for past models become affordable to the average consumer. But it is a step in an interesting direction.
