HEVO units are comparable to Level 2 charging plug-in stations used by EV fleets, which typically take eight to 12 hours per day to charge, according to Stahl. "We can charge up to three times faster than many wireless competitors at up to three times the distance," he said.
"Regardless of battery capacity, these figures remain the same," Stahl said in an email reply to Computerworld.
WiTricity's charging technology offers up to 25kW, with the company's systems for passenger cars outputting from 3.3kW to 6 kW while systems for fleets and small buses are in the 10kW to 25kW range.
WiTricity claims it takes the same amount of time to charge a vehicle wirelessly as it would plugging it in, which in a passenger car with a dead battery is nominally four hours.
However, one emerging technology is fast-charging systems, which offer a high-voltage DC charge instead of a slower AC charge. With a fast charging station, a vehicle can be fully charged in as little as 20 minutes, according to Hayfield. "This could be a major step toward EVs becoming generally equivalent to (gas-powered) vehicles when it comes to refueling," Hayfield said.
One fast-charging standard designed for electric vehicles is CHAdeMO. The major proponents of the technology are Japanese automakers, including Toyota, Nissan, Mitsubishi, and Japanese industrial giants such as Fuji Heavy Industries Ltd. and Tokyo Electric Power Co. to name a few.
Worldwide adoption
According to IHS Automotive, there are as many as 2,445 CHAdeMO fast chargers in operation and more than 57,000 CHAdeMO-compatible EVs around the world, which accounts for 80% of all EVs on the road. The highest concentration of EVs comes from Japan in the form of the Nissan Leaf, Mitsubishi i-MiEv and Honda Fit EV among others.
Hayfield pointed out that fast charging and wireless charging are two distinctly different technologies.
"Beyond the longer charge time with wireless... there are many other factors which make its adoption a long term trend," Hayfield said of wireless charging.
Among the obstacles that wireless charging must overcome is that it's currently not in production; it must be added aftermarket. Also, the magnetic coil charging system adds weight and cost the the vehicle, Hayfield said.
"Public trials are really only just beginning now. There are safety and interference issues that must be tested in the real world," she added.
Additionally, while wireless charging is supposed to add a level of convenience for EV owners, "plugging in is not a major problem for most," Hayfield said.
Efficiency is key, size matters
Another drawback to wireless charging is power loss. Transferring electricity through the air between two copper coils means some power will dissipate.
HEVO's wireless charging devices have a power transfer efficiency of more than 85% at 12 inches of separation, according to Stahl.
Eric Giler, WiTricity's CEO, said anything under 90% end-to-end efficiency should not be acceptable.
"Think about it. If you're transferring 10,000 watts, and if you're at 85% efficiency, you're continually wasting 1,500 watts of electricity. Even at 90%, you're still wasting 1,000 watts. That's a lot of energy to waste," he said.
HEVO's Power Station technology comes in three parts: a power transmitter - a coil that can be embedded in the pavement or an object; a receiver in a vehicle and a smartphone app. The app can be used to find wireless charging parking spaces, and can also tell the driver when the vehicle is aligned properly for charging.
HEVO's Power Station transmits at 220-volts with up to 10 kilowatts of power for charging a vehicle. The larger the copper coil, the more power that can be transferred.
WiTricity, originally a research project at MIT, was formed in 2007 after scientists demonstrated they could use two copper coils to create a magnetic field and power a 60-watt light bulb wirelessly. To date, the company has garnered more than $40 million in venture capital funding, the last round being led by Toyota.