For many people, the notion of ‘range anxiety’ is due to the car not having enough battery to get you where you want to go. But the problem is not necessarily that there isn’t enough charge in your battery, it’s more that you can’t charge your car in time or you have to stop on your way, or your worried that the charger will be broken. But what if you could charge your car without even getting out of it along your journey, and what if you never even had to plug in?
Nikola Tesla
Well, anytime we talk about EVs the story always seems to mention Tesla. And this is no exception, but not in the way you might think. Nikola Tesla was a famous scientist of his day, working in the fields of electrical and mechanical engineering. In modern days, people are much more likely to think of the Californian company of the same name that is really putting it up to the established car makers. But the link to what we’re talking about today goes back to his Tesla coil and the ability to send power wirelessly.
Wireless Charging in a Nutshell
So let’s go back to basics for a moment. What is wireless charging in a nutshell? Well, we suppose you could say that it is a way to charge your car without plugging it in. That may seem like an alien concept, but it is already happening. We’re becoming familiar with wirelessly charging our mobile phones, and this tech will be much more widely used in a few years as newer models get rolled out.
To transmit power wirelessly you need a source and a receiver. The source is going to be a pad on the ground that you drive the car over. But it could also be built into the surface of your garage or the road. The receiver is attached to the underneath of the car. These two must be somewhat aligned for the system to operate.
The source will be a transmitter coil powered by electricity. This coil produces a magnetic field. And here’s the trick. You can place a second coil into that very magnetic field and an electric current will flow. And hey presto, you can use that current in the receiver to charge a battery in your car or phone. It’s this process that we call electromagnetic induction.
But the issue here is that the coils have to be very close together and they have to be almost perfectly aligned. Because the magnetic field has radiated out in all directions there can be a huge amount of loss as only a certain proportion reaches the receiver. This factor is called coupling. In an ideal world, we would have a factor of 1…that is perfect coupling with no losses. But in reality, with current devices like our phones and a lot of the older technology, the factor is something in or around half to two thirds, but that varies wildly.
So what if we came up with a way to be much more precise in that energy transfer. Well, the clever folks over at MIT in the US have come up with some nifty solutions. Let’s now have a look at Magnetic Resonance.
Magnetic Resonance Power Transfer
So, technology for wireless charging is evolving, and there are developments to increase efficiency. One of those is the introduction of Magnetic Resonance. They operate under similar principles but in this case the source and the receiver are tuned to the same resonant frequency. It is this resonance that allows much stronger coupling of the source and receiver. It also allows the distance and alignment of the devices to lengthen out and even reduces the need for them to be perfectly aligned. This is because it allows it to operate in what is more like a tunnel, then simply emitting an omni-directional field.
WiTricity are seeing efficiency of just above 90% from grid to battery. This is a fantastic level of efficiency that is on a par with plugging in. Let’s not forget that there are always losses during charging. Have you ever noticed that when you charge on a public charge point, and the amount of kWh consumed is greater than your actual battery capacity? That’s loss in there.
WiTricity have produced technology, through their roots with MIT, that is being adopted as an industry standard. Thankfully, they are licensing out their patents and technology to a whole array of manufacturers. This will really allow the technology to be taken up at a rapid rate, and avoid issues of compatibility between manufacturers, EV charging companies and various other stakeholders.
Other benefits
Another benefit is that we are seeing the ability for Wireless charging to work in reverse…by that I mean Vehicle to Load or to Grid. One of the issues with V2G is that cars are not always plugged in. If you get home with your battery at 85%, you’re unlikely to plug your car in and make it available for V2G or V2L. But if all you have to do is drive your car to the same spot in your garage or driveway then it is automatically available!
Wireless charging may also be a great addition to autonomous driving. It offers a solution for these vehicles to simply drive over a pad, instead of having to be plugged in by robots at depots or in dedicated charging bays.
The Future
So what are we likely to see in the future? Nobody knows exactly but it looks like there will be a place for wireless charging. We are making consistent gains in efficiency in delivering power. But perhaps the most important is making the technology cost effective. At the moment, it seems to be prohibitively expensive in all cases except for trials and research projects. But it is inevitable that prices will come down as more companies show interest and scale is ramped up.
The use cases will also have a huge impact on how quickly we take up wireless charging. Taxi ranks where cars are queued for a few minutes at a time are a great example. These cars could work nearly 24 hours per day with frequent charges at ranks.
Bus stops might be a great way to electrify cities’ bus fleets. This would allow for smaller batteries, lighter and more efficient buses…and potentially make charging breaks redundant.
But what we also need as a society is to break with the 100 year-old tradition and mentality of ‘filling up’, and instead switching to other forms of what WiTricity dub ‘power snacking’, short burst of charging at intervals.
Summary
We’re really excited for wireless charging, and especially to see how the technology develops over the coming years. It was only 10 years ago that we were looking at the Nissan LEAF picking up just shy of 50kW on DC. Now were talking about charging cars and buses wirelessly as they drive along the road.
Let us know what you think! Do you see a future for wireless charging? Which application do you think is best suited to roll out wireless charging, and are there any easy wins out there for this nascent technology?
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