20 kW Wireless Car Charging At 90% Efficiency Achieved

APR 5 2016 BY MARK KANE 42

Department of Energy’s Oak Ridge National Laboratory has developed a 20 kW wireless charging system for electric cars, that has achieved 90% efficiency (and up to 95% from motor input to the vehicle battery according to a recent video put out by the lab) .

Oak Ridge National Laboratory's 20-kilowatt wireless charging system features 90 percent efficiency.

Oak Ridge National Laboratory’s 20-kilowatt wireless charging system features 90 percent efficiency.

20 kW is around three times more than the typical on-board charging capability today,  and according to ORNL it’s also the highest wireless rate for passenger cars at the moment.

For the project ORNL used Toyota RAV4 EV.

“This ability can help accelerate the adoption and convenience of electric vehicles. Industry partners from Toyota, Cisco Systems, Evatran, and Clemson University International Center for Automotive Research contributed to the technology development demonstrated today at ORNL.”

“ORNL’s power electronics team achieved this world’s first 20-kilowatt wireless charging system for passenger cars by developing a unique architecture that included an ORNL-built inverter, isolation transformer, vehicle-side electronics and coupling technologies in less than three years. For the demonstration, researchers integrated the single-converter system into an electric Toyota RAV4 equipped with an additional 10-kilowatt hour battery.”

Madhu Chinthavali, ORNL Power Electronics Team lead said:

“We have made tremendous progress from the lab proof-of-concept experiments a few years ago. We have set a path forward that started with solid engineering, design, scale-up and integration into several Toyota vehicles. We now have a technology that is moving closer to being ready for the market.”



The next goal for the team is a 50 kW version, although personally we’d like to see some research effort into making the 20 kW/95% efficient version commercially available soon.

Whether or not it is safe to be around a charging device that loses 10% of the energy transfer (which would be up to 2 kW at 20 kW), ORNL thinks yes:

“As the researchers advance their system to higher power levels, one of their chief considerations is safety.

“The high-frequency magnetic fields employed in power transfer across a large air gap are focused and shielded,” Chinthavali said. “This means that magnetic fringe fields decrease rapidly to levels well below limits set by international standards, including inside the vehicle, to ensure personal safety.””

More on the project:

“Convenience and simplicity are at the heart of the ORNL system, which places a strong emphasis on radio communications in the power regulation feedback channel augmented by software control algorithms. The result is minimization of vehicle on-board complexity as ORNL and partners pursue the long-range goal of connected vehicles, wireless communications and in-motion charging. While the team’s initial focus has been static, or motionless, wireless charging, the researchers also evaluated and demonstrated the system’s dynamic charging capabilities.

Energy Efficiency and Renewable Energy’s Vehicle Technologies Office provided funding for this competitively-selected project as part of a broad portfolio in support of DOE’s EV Everywhere Grand Challenge, which aims to make plug-in electric vehicles as affordable to own and operate as today’s gasoline-powered vehicles by 2022.

“Wireless power transfer is a paradigm shift in electric vehicle charging that offers the consumer an autonomous, safe, efficient and convenient option to plug-in charging,” said David Smith, vehicle systems program manager. “The technology demonstrated today is a stepping stone toward electrified roadways where vehicles could charge on the go.”

Toyota provided several vehicles for the research, including RAV4s, a Scion and a Plug-in Prius.

Other members of the ORNL project team are current staff members Steven Campbell, Paul Chambon, Omer Onar, Burak Ozpineci, Larry Seiber, Lixin Tang, Cliff White and Randy Wiles as well as retired staff members Curt Ayers, Chester Coomer and John Miller. The research and demonstration took place at ORNL’s National Transportation Research Center, a DOE User Facility.

UT-Battelle manages ORNL for the DOE’s Office of Science. The Office of Science is the single largest supporter of basic research in the physical sciences in the United States, and is working to address some of the most pressing challenges of our time. For more information, please visit http://science.energy.gov/.”

source: ORNL

Categories: Charging

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42 Comments on "20 kW Wireless Car Charging At 90% Efficiency Achieved"

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Put one of these at every traffic light, parking spot etc. and life will be getting better


Realistically I believe what flmark said below about taxis using them is where wireless charging will be the most useful in plublic.


90% efficient = 10% losses. 10% of a Tesla 90D battery = 9kwh = running a large toaster for 4 and a half hours in your garage every time you charge. Sheer waste.

Paul Stoller

That’s roughly the same charging efficiency of the current corded chargers, yes it is a waste but it’s not a different situation that we are currently seeing with most corded chargers.


I don’t think so. Just the transmission is wireless instead of a cable. You still need the actual charger, so those 10% losses are added ON TOP of the other losses.

Paul Stoller

Okay, that makes sense, I was thinking they were giving the efficiency of using the system overall including the charging losses.

That being said if they can get this up to 95% efficiency paired with a high efficiency charger you should be in the same ball park as some of the less efficient corded charging systems. And at that point I think the convenience factor for some use cases would make it worth the loss.


Wrong!, since the currant coming out of the vehicule adapter is already DC, the power goes streight tru the power module of the car, to the battery. No additionnal losses exept the one from the wireless system itself.
And who the hell would use wireless to recharge a completely drained 90KwH battery EVERYDAY?!? Who drins his MS battery everyday here?
I have been using my Plugless System for 2 years now and there aint no way i’m going to go back to a plug, not even for my future M3.
Keep in mind that most people only travel 30 miles a day, thats usually under 10Kw a day and 10% of that is only 1Kw, a nickel’s worth of electricity. I’m not loosing any sleep over that. cheers!


How lazy of you!!
And that 5cent/kwhr isn’t svailable with US average at $.12/kwhr.
Personally if one want automatic it is simple enough to get an automatic plug/arm that slides into a slot, cone, etc to plug in or a Tesla Snake at a fraction of the price.


Driverguy01 said:

“…since the currant coming out of the vehicule adapter is already DC, the power goes streight tru the power module of the car, to the battery. No additionnal losses exept the one from the wireless system itself.”

Hmmm, doesn’t converting household AC to the DC the EV needs for direct DC charging involve transformer losses? Losses typically between 8-15%?

And yes, the 10% (or more) wireless charging losses will be on top of the transformer losses.

I don’t think wireless charging can ignore the Second Law of Thermodynamics.


The transformer for a proper wireless system is the wireless coil system. The fact that power is transferred through the air gives the proper isolation from the utility. There is no additional transformer for a proper wireless system and you can charge direct to battery.

Plugless power systems by Evatran (partner in this system) create DC but not controlled enough to be direct to battery. They send the DC into the onboard charger which converts the voltage further for charging the battery. Any wireless charger worth using will be direct to batter and have a PFC front end. Plugless power has neither and therefore has a power factor of 0.7 or so.

MTN Ranger

There can be quite a variablity in the efficiency. Anywhere from 5% to 15% less than a wired L2. See my post below.


I don’t think it takes 90kWh to charge a Tesla P90D. Isn’t there some buffer in there.


That’s one way to heat your garage in the winter!


..and have warm toast too boot.


Or overheat the pack in summer killing it.

MTN Ranger

That’s not hugely different than the 88% average that Plugless Power gets. Idaho National Laboratory testing in 2013 found the system had a power delivery efficiency between 84%-90%, compared to 95%-99% for corded charging systems, depending on the alignment of the Adapter and Pad, the separation gap, and the rate of power transfer in use (kW).



Thanks for that info and the source you gave Matthew! It’s great to have facts like that for us all to see.


Just glad to hear that DOE is strongly pursuing it, as charge-everywhere is easily digestible information to the masses – park-and-fill in the utopian (near?) future, meaning a soccer-duty vehicle has ~80%-ish charge effortlessly and continuously, once widely available. The V2G possibilities have utilities interested at the manual-plug level, imagine at the ‘if it’s parked and charging, it can be tapped’ level.
I can dream.. my utility isn’t one of the famously ‘bad’ ones that get so many responses, so I’m all for ‘let’s Not build another turbine’ voluntary savings/Control programs. shiny.


10% is not a small amount.


Convenience is worth something.


That is 10% on top of what you are already losing to rectify from AC to DC PLUS the loss from transforming from AC to another via a transformer. So it could add up to 25%. I know that the price if electricity is low and if you have your own solar system then adding 25 to 30% more is not a big deal. A solar watt plus storage is under a dollar now. But I still think that it is not much to do. A plug in is more efficient. Or maybe a robot. The Model S parks itself in the garage so making a small robot to plug it in is simpler.


Escalators exist and yet are not needed.
Remotes for TV’s, etc, exist, and yet are not needed.
Automatic door openers exist and are not needed.
Automatic door locks exist and are not needed.
I could go on all day.

All those things are convience, and use energy.

If you so concerned about energy waste, get on a bike, and never drive and EV.


I’m skeptical. What exactly is 90%?

Since it’s going over the air, it would need to be AC, and probably higher frequency than 60Hz. Just the electronics (upconvert, then rectify) on either end could end up being 90% (81% total). If they achieved that to be 90% (95%/95%), that’s realistic, though I’m skeptical.

If they’re talking about over the air being 90%, that’s more believable. But consider that 10% leakage from 20kW system is twice that of microwave oven, and you can see the problem. Even 95% has radiation power of a microwave oven. Would FCC allow this, especially for widespread use?

To achieve 90% overall from wall outlet to battery, and assuming even distribution, they’d need 96.5% on each leg; unequal distribution would need some being even higher efficiency. I’m highly skeptical of the claim.

Mark Smolinski

I have my DVR & other electronics on power strips so I can drive a stake through the heart of all my energy vampires. A few watts here and a few watts there…& in case of the DVR, about a hundred wasted watts killed off. Being too lazy to plug in my car would negate all my vampire efforts many times over. Plugless charging has a place where vehicles idle like taxi stands or bus depots…but I hope it does not become the norm in the average home garage.

The far right nut jobs, several years back, said electric cars would/should not succeed because no one wanted to be bothered plugging in. For the sake of vampire killing efforts everywhere, I hope to God that we are not all that lazy.


Gasoline cars will fail because people do not want to be bothered with going to a filling station and filling up. 😉



Personally, I’m not interested since the waste bothers me and plugging in is pretty damn simple.

But if this helps bring more people to EVs, I’m all for it!

Bill Howland

Some people with RH find it very difficult to insert, or remove a cord connector.

Wireless charging is a godsend for these people and the (up to) 90% efficiency is acceptibly high enough.


I am not sure how often this happens but corded charging stations are subject to their cords being cut off by people who are looking for scrap metal to sell. There is a conference center in Gastonia, NC that had eight L2 stations and someone cut all of the cords off.

Bill Howland

I have no idea what ‘motor input’ is, …. I suspect they don’t either.

Most charging systems have no rotating parts.

(My Roadster did use the AC motor as the main part of the charging circuit, but it is stationary during charging).

(Up to) 90% efficiency isn’t so bad. Now if they can keep the current draw from being as ‘ratty’ as the current 3.0 kw models, then that would definitely be an improvement.

Bill Howland

I assume the block diagram was a ‘simplified’ diagram…

To meet Euro standards, they’d need to get the apparent PF up to over .99, which is a routine job, although it would add to the cost of final unit.

Doing that alone would decrease the customer’s power supply requirement, and save installation costs.


True Bill, but as far as i know, very few supplyers apply an extra charge because of the PF so, it’s really a non issue for the vast majority of us.
On my install, the only difference is the 30 amp breaker instead of the 20 needed for a ususal install. If Evatran was to make the same system with a PF of .99, i would imagine a few hundreds dollar more would be added to the system’s cost.
Sometimes, you have to pick your battles.
Always good to hear from you bill. 🙂

Bill Howland

Thanks Driverguy01.. Yeah things are progressing..

The rattiness I complain about on your 3 kw unit is acceptible because no one is complaining about it, as they would at higher power levels.

Is there somewhere I can get objective (as in a testing laboratory results, etc) of the new “Tesla” plugless design (i.e. 6 kw model)?

I’m curious as to how its performance compares with the current 3 kw model.

These things work, and for people with Arthritis they are a godsend.

Or for people whose spouses constantly forget to plug it in.


My understanding of efficiency measurement done by the DOE for plug in appliance is power drawn from the wall versus what’s being left in the battery.
So it’s all losses count.
I’m not sure that it is what 90% wireless efficiency mean.

Anthony Fiti

Yeah, count me as one of the folks who’d rather see 20kW at 95%+ rather than 50kW at 90%.

I’d be happy with 10kW at 95%+, since 10kW charging is enough to refill a Tesla battery in 8 hours (overnight).


Two contacts on a speed bump under the car touching two contact on flex springs under the car are 100% efficient and can go much higher than 20 KW. Security can be provided electronically and communication by bluetooth. Wireless is non sense when simple contacts are cheaper and more efficient.


I’ve advocated a similar solution, not a speed bump but a flat scissor jack mechanism to carry the charge connectors from floor to chassis. The elevating portion could easily be on a tray with positioning screw drives in two axises so you wouldn’t even have to be very careful to park directly over the charger interface.


Apparently the Model S in summon mode is able of excellent accuracy, so that doesn’t seem to be a problem anymore. Specific details of contacts coming together can be examined more precisely and what you mention is a possibility but if it is possible to keep the ground contacts simple static ones than almost every parking place can be equipped on the cheap. The car would either have enough accuracy to be right above the contacts or the contacts would have very large size (hand palm size one foot apart) which is my preferred solution, or an appropriate mechanism for example the one you mention would be on the car contacts. In any case the car contacts would somehow at least be protected by a movable cover and come down somewhat to get to the ones on top of the speed bumper. That would be about 4 inch down.

It is really too bad I don’t have the possibility to work on this myself because I would love to do it.


A scissor jack has the distinct advantage of using the vehicle’s weight to maintain whatever degree of pressure is necessary for excellent contact that may be needed for extremely high charge rates.

I’ve worked with high voltage contacts, and the insertion and removal forces, and spring pressures can get quite high.


Sure 10% seems like a lot to some but in one year it’ll cost me $50 more so about 14 cents a day extra in electricity costs… IMO Well worth it especially if it can be combined with the summon feature. I don’t like the cable and I’ll probably invest in one of those plugless systems or tick the option if Tesla offers it. It’s a cool system even for residential. With all the solar energy produced, so what if you waste 10% of it? Depends how your electricity is produced…


Glad to see they’re already planning for a 50 kW version, but they need to scale this up a lot more than that.

Will wireless charging be able to handle the superfast charging rates needed for tomorrow’s EVs? Will they be able to handle the current needed to charge a 300+ mile EV in 10 minutes or less? Or would that require an impossibly large pickup loop in the car?

I’d love to hear from someone with an informed opinion on this subject.


The 300 miles in 10 minutes mean a power of around 700 KW. Unless we make a serious breakthrough in superconductor at room temperature, there is not much hope to have enough with a pancake sized devise under the car. Super high power is one more reason, with 100% efficiency and lower cost, to go the secured conductor’s route. They allow low speed charging in a garage or at a parking place and very fast charge, megawatt level in a dedicated supercharger location that can have extra systems for even more secured operation while sending higher power at higher voltage.


Most of the losses in a wireless system are in the coils and air gap. This puts a lot of heat into the coils. Without active cooling, the power level will be limited. The info that has been released about this system is very limited. For all we know, it only ran at 20kW for 0.1 seconds. It never said whether or not they ran continuously at 20kW.

Note, with supercharger, all power conversion is done in an outside cabinet with liquid cooling.