Wireless Chargers Puff Up Their Green Credentials

By Priya Ganapati

Saving energy usually involves a lengthy checklist: turning off the lights, turning down the heater, changing the light bulbs. But what if you could increase efficiency and convenience at the same time?

This eco–couch potato's dream is about to come true, say the supporters of new wireless power technologies, which they say can eliminate inconvenient power cables and ugly "wall warts," while sipping electricity efficiently and sparingly.

"Everybody's mouth drops when we show our products," says Ron Ferber, CEO of Powermat. "You could have wireless chargers anywhere in your kitchen, hidden in your walls, and can charge multiple devices at high power."

There's just one problem: Until now, wireless chargers (like those used in many electric toothbrushes) have been less efficient than plugged-in power sources, not more. And the companies working on next-gen wireless power have done nothing to substantiate their claims of greater efficiency.

One thing is clear: Charging gadgets wirelessly is a growing trend. Startups such as Powermat, WiTriCity and WildCharge are trying to free users from being tied to their chargers. Palm showed off a wireless charger for its new Pre phone at the Consumer Electronics Show earlier this year. And even Intel has been working on a wireless-charger research project for the past two years.

Unlike the monolithic, plugged-in wall charger, wireless chargers for electronic devices promise to make it easy to separate the gadgets from their power sources. The chargers come in two parts: a charging surface that can be plugged discreetly into a power outlet, and a receiver that goes on the back of the device you want to charge. The charging surface conducts the power through those receivers to the electronic devices that are dropped onto it. This combination allows for the charging surface to be hidden — sometimes as far away as another room — creating the illusion of gadgets that recharge themselves.

"It is the wave of the future," says Sara Bradford, principal analyst at research and consulting firm Frost & Sullivan.

Wireless chargers broadly use two principles familiar to those who took high-school physics: electromagnetic induction and magnetic resonance.

Electromagnetic induction is one of the fundamental principles of physics. It describes how an electric current passing through a coil of wire creates a magnetic field. Place a second coil of wire in that magnetic field, and either move that coil or change the electric current in the first. This induces a current in the second wire. Electricity has been effectively transfered from one wire to the other, paving the way for wireless transmission.

In the case of magnetic resonance, two coils tuned to the same frequency exchange energy strongly and can do so over longer distances than with simple magnetic induction.

These ideas aren't new. Physicist Nikola Tesla offered theories on wireless power transmission in the late 1800s. But concerns about power efficiency and loss have kept the products from going mainstream.

"The power and efficiency of these devices has been quite low," says Bradford. "They capture only about 60 percent of the power to begin with and then convert it to DC, so there's a significant loss to deal with."

Compare that to cellphone-battery chargers today, which boast an average efficiency of at least 80 percent, says Chris Calwell, director of policy and research at Ecos Consulting, a firm that helps companies reduce their energy use.

To better understand how that's possible, consider how efficiency is measured in a traditional, plugged-in battery-charging system. Each system consists of three parts. The first is a power conversion unit that takes the high-voltage AC current from the wall and converts it to low-voltage DC for the gadget — where efficiencies can be as high as 80 percent.

The second step is the battery-charging circuitry, where losses are very little, says Calwell. Finally, the battery's own efficiency is a measure of how much output it delivers relative to the amount of power put into it. Overall efficiency is measured by taking the efficiency of each part of the system into account: Multiply the three percentages, and you might come up with a lower number than you'd expect.

In case of wireless chargers, proponents claim they are no less inefficient than their plugged-in peers.

"People's intuition is that wireless powers must lose a lot of energy," says Josh Smith, an Intel researcher. "But the discrepancy is not as big as your intuition may suggest."

Take those claims with a grain of salt, says Calwell. There are no standard energy ratings for wireless chargers yet, and no independent tests have been run on the chargers.

The startups behind the wireless chargers are keeping their cards close to their chest. Instead of offering details on how efficiency is being measured, the companies would rather use platitudes on having the right technology to extract greater efficiency despite cutting the cord.

Powermat's Ferber, whose wireless-charging products made their debut at CES starts answering questions about the energy efficiency of his products by saying, "I could tell you, but I would have to kill you."

Press for details, and he says, "We are using multiple technologies today to eliminate the biggest issues with wireless charges related to slow charging and low efficiency."

If that strikes you as banal or secretive, it is clearly the idea. All Ferber will say is his products offer "more than 90 percent efficiency".

Ecos' Calwell is skeptical about that statement. "I am dubious of that kind of efficiency claims," he says. Without any details of how the efficiency is being calculated, the 90 percent figure doesn't mean much, agrees Frost & Sullivan's Bradford.

Eric Giler, CEO of WiTriCity, a startup spun out of MIT's engineering school, is more circumspect in his claims. Giler says his company's wireless chargers can rival their plugged-in counterparts, though so far his wireless chargers have shown power of efficiency just about 50 percent. (In contrast to Calwell, Giler says plugged-in chargers he's tested are less than 50 percent efficient.)

WiTriCity's selling point, though, is the convenience. The company uses highly coupled magnetic resonance to create wireless chargers that can power cellphones and notebooks over a distance of up to 7 feet. "You will never have to reach into your pocket or purse to find the charger or even a charging mat again," says Giler.

Researchers at Intel have also been working to create a viable wireless charger. At the company's Seattle Lab, researchers have been working on a project called Wireless Resonant Energy Link or WREL (pronounced whirl).

"We have been focusing it on the products that are most important to Intel, basically laptop computers," says Smith.

At its conference for developers last year, Intel demonstrated wireless transfer of 60 watts of power at 75 percent efficiency over a distance of less than 5 feet.

These wireless efficiency claims may seem all right, except they are probably just one part of the overall system. What companies may be touting is just the transmitter-to-receiver efficiency, says Calwell.

"If you add up all the other parts," he says, such as the AC-to-DC converter and the battery itself, "then there is very likely to be significant degradation." That's a more serious problem for a wireless system whose transmission efficiency is only 60 or 75 percent than it is for a wired system where transmission can be as efficient as 80 or 90 percent.

Wireless-charger makers, meanwhile, are pressing their green credentials. Their chargers, they say, cuts standby power losses — the power drawn by the charger even when there is no battery attached. Also, the ability to charge multiple devices through one charging station means the technology potentially eliminates losses from having many different chargers plugged in.

"That's ultimately what we see as our No. 1 benefit," says Powermat's Ferber. "If you are into energy conservation and the green movement, there are obviously significant efficiencies you have here."

Calwell is more skeptical of these claims. "There are laws of physics that can't be changed," he says.

There's only one way to settle the debate. It is time for wireless charger makers to come clean with their efficiency metrics. Only then will we be able to tell whether this technology truly lets gadget lovers have convenience and eco-friendliness at the same time.

Photo: Intel Wireless Power Demo/Intel