Wireless Power: Beyond Charging Mats and Solar Panels


After years of hope (and no little amount of hype), wireless power is finally getting into consumer hands. However, the technology that is showing up on trade show floors and store shelves is a far cry from the truly disruptive promise of wireless power.

As we cram more computing power into our mobile phones and use them to deliver the web, take photos and shoot video (as well as talk), a key limitation has become the battery. Anyone who has experienced a three-hour battery life after surfing on a Wi-Fi network knows first-hand that battery life can impede the enjoyment of a full-featured mobile device.

And that problem is the one that wireless power will one day solve. Not through the slew of charging mats that will be on offer over the holidays, but using the type of over-the-air power that Intel and WiTricity are trying to develop. Before we get all excited about the idea of a battery-less future, it’s worth talking about the different flavors of wireless power that exist.

Technology Landscape

  • Inductive: There are two types of inductive wireless power on offer. One is promoted by the Wireless Power Consortium and relies on delivering power through magnetic contacts between the device that needs power and a charging mat. The other, promoted by Intel and WiTricity, relies on magnetic resonance and hopes to one day transfer without requiring device contact, although it still needs an electric connection from a wall outlet or a battery. Delivering power via contact is about 70 percent efficient, but delivering it over the air becomes less efficient the further apart the two magnets that are generating the power get.
  • Conductive: This is the old-school type of wireless power that uses the contact between two metal plates to charge something. It’s fairly efficient, but its usefulness is limited by the plate-to-plate contact and the fact that it still needs an electric current.
  • Solar Photovoltaics: Right now, solar panels aren’t a great source of wireless power for mobile devices because the surface area for a solar panel is small, solar panels aren’t very efficient at generated power, and people don’t typically keep their phones out in the sunlight.
  • Kinetic Power: We’ve written about M2E Power’s charger that converts the motion generated by a person walking into usable power for a mobile phone. However, it takes about 6 hours of walking time to create enough power for 30 minutes of talk time. For some that will work, but for many that’s just not enough.

Current Market Players

Nikola Tesla identified the how to deliver wireless power using magnetic induction back in 1891, and the Consumer Electronics Show both this year and last was full of cord-free demos. But it wasn’t until earlier this month that Powermat, a joint venture between HoMedics (yeah, the company that makes all those massagers, water purifiers and personal spa gear) and Powermat Inc. of Israel, introduced a $99 charging mat available at Best Buy and Target. The mat clicks with your iPod touch, BlackBerry or iPhone using a special sleeve ($30-40 per device) charges them up, saving you a few outlets and avoiding the irritation of plugging in your micro USB cable.

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  1. Stacey Higginbotham Monday, October 26, 2009

    Excellent points on Micro USB. I considered mentioning the standard, especially since it will allow people to consolidate charging much as these mats do, but I was trying to stick with wireless.

  2. Pedro Hernandez Monday, October 26, 2009

    Good points about Micro USB. In the near term, handset makers will still ship their phones with wall warts (or at the very least the cables), so while complexity will be eliminated, you’ll still end up with a kitchen drawer full of the stuff. Or worse, they end up generating more e-waste.

    Though we’re trained to plug in our devices, like Katie mentioned, I bet many consumers are willing to be retrained to cut the cord if the efficiency kinks and pricing premiums are worked out.

  3. This was an informative story, so thanks for that.

    But the story is lacking because it doesn’t deal with the two most important developments in mobile device charging that are currently underway — and which stand to impede the progress of wireless power:

    1) You simply cannot have the wireless power discussion without factoring in the global agreement among handset vendors to standardize on Micro B USB charging tips by 2010-2012. Most major handset vendors (including holdout Apple) have now agreed to converge around this port on their devices. This will create massive momentum, reduce ‘tip complexity’, allow ‘shared chargers’, enable you to charge from a friend’s device, and also save money for the device makers who can choose to NOT include a charger with every device.

    2) The Micro B USB standardization work was also driven by EU regulators as a push towards more Green wall warts. The new breed of AC Adapters with Micro USB tips will feature technology to avoid the “vampire draw” of power when the mobile device is fully charged or disconnected. Compare this to the non-green entropic power usage of wireless power.

    Put together, this means Micro USB will beat wireless power on Bill of Materials, power efficiency, environmental friendliness, compatibility, OEM adoption, and availability. Tough act to follow! I’m not writing wireless power off completely, but as you wrote, it’s niche.

  4. Stacey Higginbotham Friday, October 23, 2009

    You guys are right to focus on the efficiency of the charge, which is why folks are trying to use this for smaller devices rather than cars. The Wireless Power Consortium believes that induction can deliver efficiencies between 50 percent and 70 percent, meanwhile over the air power has been demonstrated to be 45 percent efficient with the coils 2 meters apart, but that efficiency falls off rapidly with the distance.

  5. Josie Garthwaite Friday, October 23, 2009

    Juicing up via a wireless charging mat might be a better experience for drivers, but only if the problem of energy loss that James mentions can be solved. Otherwise it would make fast charging for EVs — which Nissan, at least, considers critically important for charge points in places like shopping malls and along major roadways (http://earth2tech.com/2009/08/17/5-misconceptions-about-electric-car-charging/) — an even bigger challenge than it already is.

    Speed may not be the top priority for charging up at home or at the workplace, but even in those situations losing the plug doesn’t seem worth the price of prolonging the charge time.

  6. James Kendrick Friday, October 23, 2009

    As it’s been told to me, the problem with wireless charging for phones and other gadgets is the amount of energy that is lost with today’s technology. The Dell engineers told me that induction charging like that used in the Latitude Z notebook you mentioned typically loses 50% of the energy, resulting in long charge cycles. They were particularly proud that in the Z charging they were able to convert “more than 70%” of the energy for the charge.

    That’s a problem that current technology doesn’t seem able to address yet, and that’s the rub IMHO.

  7. Katie Fehrenbacher Friday, October 23, 2009

    This is a really interesting post that digs into the specifics of the wireless power standards, which I didn’t know much about before. But I think a really large – and largely unmentioned in this post – market is wireless power for electric vehicles. Consumers are already trained to plug in their gadgets/phones etc, but don’t have the same mindset when it comes to cars. Driving into a garage and over a wireless charging mat would be such a better experience than crawling on hands and knees in your garage and plugging in the vehicle. Clearly EVs and plug-in hybrids are a very small market right now, but some think itll make up between 5 and 10% of worldwide car sales by 2020. I could even envision a car maker incorporating wireless power into its car and marketing the vehicle without the plug-in language. Check out Josie’s post on car makers already looking into this: http://earth2tech.com/2009/07/22/wireless-charging-making-the-leap-from-gadgets-to-cars/

    Also, more proof that wireless power of the kinetic kind will be very difficult to figure out and will take a lot of money. RIP M2E: http://earth2tech.com/2009/07/24/fire-sale-motionetics-grabs-m2e-powers-assets/

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