Powering an electric car wirelessly

There’s a number of wireless ways to transfer electric power, either through induction or electromagnetic waves.

Would any of them be useable to transfer a number of kilowatts 6-18 inches through pavement to a vehicle driving at highway speeds?


Please elaborate. I can’t think of any reason to dismiss the idea so definitively.



Oh, sure. And we’ll have personal flying cars, too.
Just because something is “possible”, that doesn’t mean that it’s ever going to be practical. There’s simply no way to send that much power wirelessly without incredible expense, enormous infrastructure, and great danger.

Wireless power transfer over two-meter distance, from the coil on the left to the coil on the right, where it powers a 60W light bulb.


I’ve always thought that if we ever get to plug-in electrics that it might be useful to have an induction charger on the garage floor that you park on top of to charge the car overnight. No muss, no fuss. Of course we’re talking about low power and a distance of only inches, at most.

So what.
It isn’t practical. To do this with automobiles would require Gigawatts of power transfer (just how many cars are on the highway at rush hour?). How much metal would it take for the coils? Are you going to tear up all the roads in the US to do this?
I can light up a fluorescent tube from across the room - that doesn’t mean I can light a stadium the same way efficiently.

Yes, you would tear up all the highways in the US to do this. (But not the local roads.) I can’t see how the infrastructure investment isn’t comparable to a hydrogen distribution network. Besides, highways get torn up all the time for maintenance anyway. Of course if the scheme requires a specialty laser transmitter for every foot of a billion highway-lane-miles, it wouldn’t be reasonable. But if you just need to lay down coils of wire, then that would be very practical.

But anyway… let’s do some math. What would it take for plain-old induction to pass 5 kW given the best-case scenario of just a 2" separation and 2 m^2 of surface area? (Let’s say we’re dealing with super low-riders or some mechanism to get receiver conductors very close to the asphalt.)

Well, let’s see. The US Highways system had a length of 46,837 miles in 2004:http://en.wikipedia.org/wiki/Interstate_Highway_System
If we say that each foot will require 10 lb of copper (think 2 lanes in each direction), than we’re talking about 2.473 billion pounds of copper (not including the amount in each car). The world’s entire copper production in 2006 was around 16 million metric tons: http://investmenttools.com/futures/metals/welcome_to_the_page_about_copper_futures.htm
2.473 billion pounds = 1.121 million metric tons, so I guess there’s enough copper in the world to do this. Even if it requires 10 times the amount of copper, it’s still possible, if you don’t want to make anything else out of copper.
Currently, copper demand exceed production.
So, I guess it’s do-able in the same sense that the Ringworld was do-able…

Beowulf, your argument of “well, if you use… say… 200 lb of copper per foot you could do it. But if you need 2000 lb of copper per foot… in one year… you can’t.” didn’t really go anywhere.

Ok, did some more research: I think the biggest component in a simple transformer-like design would be the cores of the pavement solenoids. You’ll want to make these really, really wide so that the magnetic field at the road’s surface is uniform, still strong a foot off the ground, and is easy to align a moving vehicle with. The copper (or aluminum) winding around these cores would be much more modest in comparison. Luckily, world output of steel is over a billion tons a year, though I guess making all our highways from it wouldn’t be too cheap. Still, for the $1 trillion pricetag of a hydrogen economy, I think it could be afforded.

Now, as for the idiots who’ll bitch about how the high-frequency currents are giving them cancer…

Lets Take this idea a bit further…
Beowulff’s primary argument is the economics of burying lines under every lane of every road in the nation. Why would we need to do that?
[li]If we install WiTricity under garage floors and parking spaces, our cars will be fully charged when we leave the house.[/li][li]Next, we install WiTricity at major intersections, where cars are often stationary, or moving slowly for a brief period of time.[/li][li]Grocery stores and big box stores can install metered charging stalls, for customers to use while shopping. Swipe your debit card, or plug in a few quarters, and the WiTricity starts flowing.[/li][li]When WiTricity enabled cars become more common, we can install it on short stretches of highway, preferably those that are traveled most frequently, and become congested in rush hours. Now when you are stuck in traffic, you will be pulling in much more juice then if you whizzed by at 55. The coils installed in the roads and the batteries in the vehicle would have to be engineered to accept frequent, short, intense charging periods in an efficient way.[/li][/ul]
I don’t think installing coils under every road is a good idea, or even necessary. If cars relied solely on the WiTricity for energy, dirt roads would be useless, off roading would be impossible, and if the power went out we would all be stuck. It might take decades to get every single road converted as well. Thus, batteries are a necessary part of this system. An economically viable implementation of this technology would have to make efficient use of the capabilities of the batteries and the coils.

No one has mentioned this obvious problem, which has kept wireless electrical transmission from being implemented: How do you get people to pay for the electricity they use? With today’s computer technology, wireless networking, and cellular infrastructure, that problem could be solved with software and minimal hardware, installed with the coils.

[ul][li]If we install WiTricity under garage floors and parking spaces, our cars will be fully charged when we leave the house.[/ul][/li][/QUOTE]
But note that a wireless charging system like this under your garage floor would waste about 1/6th of the electricity due to lower efficiency. Would you waste that much electricity just to avoid pushing in one plug when you park your electric car at night?

To compare it to a gasoline car, suppose there were gas pumps that automatically inserted the filler tube and filled up your tank – would you pay 50¢ per gallon more for that?
I remember a time when you had a choice between self-service pumps or a gas station attendant who would pump the gas (and clean your windshield, check the tires, etc.). But you paid more for that gas. The attendants died out, because people were not willing to pay the higher prices. The higher price was about 5% more, less than a third of the waste in your wireless recharger. I don’t think people will accept that much additional cost for wasted electricity.

Isn’t this a strong function of the geometry of the situation? How did you go about calculating the 1/6th value?

What if we don’t try to do it wirelessly? Can we alter the formulation of the tires so that they conduct electricity? Then all you have to do is drive on top of the parallel busbars we would place in the garage floor and in parking lots and at intervals on the highway.

So wait. We’re designing vehicles that are powered by electricity, but not tethered to wires, that receive their power from the surface on which they drive, and consequently, they can’t leave this network?

We already have those. They’re called ‘trains’.

No. I think the idea is to have electric car that would go using batteries on local roads and in the city, but will be powered by wireless/contact devices on highways and recharged in garage. I think that could be solution to limited range of electric cars and actually might work… So, anybody have facts on wireless transmission?

I have a question about WiTricity that I haven’t seen answered (besides what idiot thought that was a good, trustworthy name), does alignment of the coils matter at all? Do you have to carefully aim the thing, or is it very flexible? What, exactly, are the limitations (besides, apparently, 40% efficiency)? And if it’s so simple and wonderful, why hasn’t the world slapped its head, said “doh, why didn’t I think of that,” and start the hype machine rolling? (“omg, it’s better than the IT!”)

For a home base station, I think people Would pay 15% more for the convenience. (It’s one thing to pull up into a gas station, and another to get home and not want to be bothered.) They wouldn’t pay 120%, but 15% I think they would.

More re WiTricity: It seems its efficiency is relatively poor at any sort of distance, but couldn’t the concept be applied to make ordinary induction much more efficient? Ie, you still have huge solenoids in the ground in close proximity, but you could get rid of the iron cores and use a lot less winding?

Re parallel busbars: you couldn’t salt the roads anymore, but ordinary rain should be fine. You’d have to bring the voltage down (say, 24V) and that would put the current very high (400A) which would be pretty difficult to transfer through conductive rubber or metal contacts, but I suppose it’s still feasible. You could also hang stuff overhead at much higher voltage, like with bumper cars. Or, imagine, you could set up a network of overhead wires and create busses with long sticks on their roofs that touch them. Oh, wait, that’s already been done.

That’s kind of where I was going. I like electric trolley cars running on wheels. It has the advantage of having the power generated elsewhere by the cheapest source, but doesn’t have the disadvantages of having to run on tracks like trains. It’s a lot less infrastructure to string new wire overhead if you want to add a spur to your trolley system. Digging up the road to install track is costly and rough on the existing coummuters.

For a home base station, a better design would be a station in the garage, maybe just in front of where the car parks, that can sense when a car pulls in, and automatically line up with it and plug the car in. When you go to start the car, it would automatically unplug also. I could see this being cheaper than a pair of inductors when mass produced, just as convenient, and more efficient.