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Myths About Wireless Charging

Posted to WiTricity in the Grid Professionals Group
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Amy Barzdukas's picture
Chief Marketing Officer WiTricity
  • Member since 2022
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  • Aug 24, 2022
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This item is part of the Electrification of Transportation - August 2022 SPECIAL ISSUE, click here for more

There are many myths surrounding wireless charging for electric vehicles (EVs) – is it real, is it efficient, and does it work? The answer to all three is an unequivocal, “YES!”

Wireless charging is the future. In fact, here’s what’s happening in Korea and China.

Let’s look at some of the myths around wireless charging for EVs and its impact on utilities and the electric grid. And then the realities.

Myth: “It’s not real yet.”

As evidenced by what’s happening in Korea and China, this is clearly not the case. In addition to car manufacturers, fleets around the world are also charging wirelessly. It’s not just an experiment, it’s here. And there are compelling use cases for both personal and commercial application. Check out this Tesla, which charges wirelessly.

Myth: “It would take too long to charge.”

Nope. The wireless charging standard built on WiTricity’s patented solution charges just as quickly as a Level 2 plug-in charger. And since you don’t worry about remembering to plug it in – you simply park and go – it adds peace of mind as well.

Myth: “Plug-in charging is 100% efficient, and wireless, well…”

First, it’s important to understand that plug-in charging is not 100% efficient. Energy loss, primarily in the form of heat, occurs every step of the way from grid to battery. What’s more, regardless of the brand, a plug-in EV charger is made of many components, any one of which may be more or less efficient than similar components in another charger. So, the “efficiency” of the transfer of energy from the grid all the way to battery encompasses a range; a typical Level 2 home charger operates in the range of about 83-94% efficiency grid-to-battery depending on which one you buy.

In the plug-in AC EV charging scenario, much of the heavy lifting is done on the vehicle through the On-Board Charger (OBC) that includes the Rectifier PFC, Inverter, Transformer, and Rectifier – all of which are needed to make the grid power into power that the EV battery can consume. (The unit hanging on the wall is relatively uncomplicated as this video very well explains.)

But with wireless charging, the vehicle doesn’t need an On-Board Charger (OBC), so this helps to reduce the charging complexity on the vehicle. Some of those same switch-mode power operations happen in the wall box as opposed to in the vehicle:

Side Note: Mind the Gap

People ask why doesn’t the “gap” between the ground pad and the vehicle create loss? It seems counterintuitive that space wouldn’t introduce inefficiency. The ground pad and vehicle pad convert the alternating current into the magnetic field that transfers power over the air gap. And, because we use magnetic resonance with specially designed low-loss resonators to transfer power, the loss is very small. In fact, the air gap between the ground and vehicle serves the same safety function as the isolation that occurs for plug-in charging through the isolation transformer (in the OBC between the grid connection and the vehicle). With the highly resonant design of the wireless charger, it’s nearly as efficient as the isolation transformer used for plug-in charging. Wireless charging operates within a narrow band of efficiency (88-93%) that is equivalent to Level 2 plug-in charging, plus you get the added efficiency of not having to spend time plugging and unplugging the vehicle.

In addition, every time you park and charge wirelessly, you’re more likely to be operating in the 20-80% state of charge (SOC) range that the battery likes – and is the most efficient. With plug-in charging, it’s less likely that the 20-80% SOC range will be maintained since drivers tend to forget to plug-in, or don’t bother when they know they have enough battery left for their next journey. In fact, many people plug in once a week, drive all week, and then plug in on the weekend. Not only is this less efficient but it’s harder on the battery. If you’d like a deeper technical dive into magnetic resonance, check out our whitepaper here.

Myth: “It would take too much trouble to get the alignment just right.”

Wireless charging for EVs isn’t like the inductive charging you might use for your toothbrush or phone, where the coils must align perfectly to get a charge. The standard based on WiTricity’s design uses magnetic resonance, which is pretty forgiving. So you just drive up, park, and walk away.

Myth: “Is plugging in really that much of a hassle?”

It’s human nature to find easier, simpler solutions to things that may seem at the time to be “good enough.” (Indoor plumbing anyone?) So a simpler solution with no moving parts means a safer, more reliable charge: no dealing with an armful of squirming toddler while trying to wrangle the cord, nothing to fumble with in inclement weather, nothing to break or get stolen. In commercial applications, those charging cords just get bigger, more unwieldy, and more expensive, where they become tripping hazards to boot.

Myth: “V2G through wireless charging isn’t real.”

WiTricity and Honda demonstrated Wireless charging and V2G in 2017 – and it’s on our product roadmap today.

Myth: “Wireless charging is not as helpful as plug-in charging for utilities looking to assist with EV transformation.”

With Vehicle-to-Grid (V2G) technology enabled, electric vehicles can actually help stabilize the grid by addressing the imbalance between periods of peak demand and peak supply – enabling two-way power flow between the grid and the batteries in an electrified vehicle. For V2G to be dependable, however, the vehicles need to be connected to the charger. Just as wireless charging will simplify connection of vehicles to the grid for charging purposes, it also simplifies connection to the grid for V2G purposes – nobody has to remember to plug in. 

Utilities are working with local governments and fleets to build out the infrastructure to support the electrification of fleets. Now is the time to start future-proofing those investments by anticipating the arrival of wireless charging and the many advantages it brings in safety, reliability, resilience and convenience. Want to learn more? Sign up for the WiTricity newsletter.

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WiTricity
WiTricity is the trailblazer in wireless charging for electric vehicles. Our technology – backed by an extensive patent portfolio – helps accelerate the adoption of EVs by eliminating the hassle of plug-in charging, setting the stage for future autonomy.
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Roger Arnold's picture
Roger Arnold on Aug 25, 2022

Wireless charging through resonant coupling will be a great technology -- if and when cheap ambient temperature superconductors are developed. Until then .. not so much. The resonant circuits for this type of charger inherently involve high currents rushing back and forth between a supercapacitor and an air core inductor. Without superconducting windings, the Q factor of such a resonator will be lousy. Ohmic losses in the coil wires of the air core inductor will be large, even if the copper windings are as heavy as it's feasible to make them. 50% is about the best one can expect for the transfer efficiency at the low frequencies available for this application. It's possible to do better at radio frequencies, but then you run into extreme radio frequency interference problems. Bottom line: low efficiency for wireless charging is a reality, not a myth.

Eric Cohen's picture
Eric Cohen on Sep 15, 2022

Roger, thank you for your comments! We are delighted to see you have done a little research on this topic. We would, however, like to correct some misconceptions and point you to a whitepaper with some basic information for calculating coil-to-coil efficiency for magnetic resonance here: https://witricity.com/wp-content/uploads/2021/11/WiTricity_Highly-Resonant-Wireless-Power-Transfer.pdf and our blog on efficiency here: https://witricity.com/newsroom/blogs/what-is-efficiency-how-do-you-measure-it-and-why-should-you-care/ .

The reality is that superconductors and supercapacitors are not needed to achieve high efficiency. We do use very high-quality factor coils and capacitors (not super-capacitors though); with reasonable current levels, we can avoid excessive losses even with low coupling factors (e.g., k = 10%-30%). The resultant coil-to-coil efficiencies for the system thus vary between about 96%-99% depending on specific operating conditions. You’ll see from our blog that this results in similar efficiencies to plugging-in! Overall, a WPT system is about 90% efficiency on average from AC grid input to DC battery output. All of this occurs at the standardized operating frequency of 85 kHz. If you are interested in learning more, we would be happy to have you talk with one of our experts. Thanks for posting!

Paul Korzeniowski's picture
Paul Korzeniowski on Sep 26, 2022

Interesting  points. If you look at other markets, it is clear that customers prefer the simplicity used with wireless. Also the infrastructure can be less, as long as the vendors clear the technical barriers. While wireless charging may seem a bit of a novel concept, there is a distinct possibility that  it can gain acceptance rapidly.  

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