麻豆传媒

ELECTRIC cars have several advantages over gas guzzlers, but having to plug them in every day isn鈥檛 one of them. The good news is that you may not need to 鈥� all electric cars could soon come with wireless chargers.

鈥淚 won鈥檛 buy a car I have to plug in again,鈥� says engineer Olaf Simon, who organised a trial of wireless charging in Berlin, Germany. 鈥淲ireless charging is so convenient.鈥�

In fact, this type of charging may offer more than just greater convenience, it could be the technology we need to transform the way we get around. With a wireless charger under every parking space, drivers would only need to worry about charging on long journeys. One day, even that problem may be gone: it could be possible for electric cars to charge wirelessly as they drive.

Magnet power

Surprisingly, home wireless charging is nearly as fast and as energy efficient as plugging in. All the firms developing wireless charging for vehicles say that less than 10 per cent of the electricity is lost during transfer. Plug-in chargers lose around 5 per cent, so there is actually little difference.

For charging during stopovers on long trips, drivers will want to use rapid chargers that supply more than 100 kilowatt-hours. It makes more sense to plug into these, says Graeme Davison, who led Qualcomm鈥檚 efforts to develop wireless charging for electric vehicles up to 2018. Wireless systems can supply this much electrical energy, but it makes the systems much more expensive.

The basic principle behind wireless charging is simple. An alternating current is fed through a coil in a pad beneath the vehicle, generating a changing magnetic field. A second coil within the vehicle is designed to resonate with this field, inducing an alternating current that is converted into a direct current that charges the battery. The systems can also work in reverse, allowing electric vehicles to supply electricity back to the grid.

鈥淗ome wireless charging is nearly as fast and as energy efficient as plugging in鈥�

Magnetic resonance charging, as it is known, works even if the coils are up to 25 centimetres apart 鈥� unlike the inductive charging mats for gadgets such as phones, which require there to be near-contact.

This air gap does have a downside: the magnetic field in this space can induce currents in metal objects and living tissue, which can cause them to heat up. In theory, if someone threw a cigarette packet under a charging car, the foil might heat up enough to catch fire.

There are two solutions. One is to have a large receiving pad in the car, spreading the magnetic flux over a wider area and keeping it within safe limits.

But some firms are making this pad as small as possible to save space. In this case, the solution is to have built-in metal and motion detectors, so the charging process is shut off if, say, a child crawls under a car.

Simon doesn鈥檛 favour this approach. 鈥淚t鈥檚 safe, but it鈥檚 not reliable,鈥� he says. If something gets under your car, the next morning you will find it hasn鈥檛 charged.

This isn鈥檛 an issue with the charging pads already on sale, which are designed to be placed on the floor in people鈥檚 garages. But if you rely on street parking, as more than a third of households in the UK do, it might be a problem.

The best solution is to have wireless chargers installed under every public parking space, including those on the sides of roads, and for any electric vehicle to be able to use them. This would be much more preferable to having cables and plug-in points littering the pavement. Indeed, on narrow city streets, there is simply no room.

Charging up

Thankfully, companies have been working on common standards from the start. And this process should become easier now the two largest players are about to merge. On 11 February, Witricity announced it was acquiring Qualcomm鈥檚 wireless charging division.

A government-funded trial in Berlin tested wireless charging from real, outdoor parking spaces. It showed that different firms鈥� systems can all work together, losing little more than 10 per cent of energy during transfer at most. The cars and parking spaces are still being used a year after the trial finished, says Simon, who works for German manufacturing firm SEW-Eurodrive. 鈥淣obody wants to stop.鈥�

But putting wireless chargers everywhere isn鈥檛 going to be cheap. The first wireless charging option to go on sale from a car manufacturer, BMW, costs around 鈧�3000. Ground pads suitable for public parking spaces would cost even more as they need to be far more robust, says Simon. Then there is the cost of embedding them in the ground and hooking them up to the electricity supply.

It isn鈥檛 a showstopper, though. 鈥淭he costs will come down over time,鈥� says Phil Hack of UK Power Networks, part of a team looking at the feasibility of installing wireless chargers in taxi ranks and in the depots of delivery firms.

Companies with large fleets of electric vehicles might be the first to install lots of outdoor charging pads, says Hack. When a delivery vehicle returns to a depot, it is frequently moved around for cleaning and loading, so being able to charge it without having to plug it in each time would be a big advantage, he says.

鈥淓lectric buses that charge wirelessly as they drive have been running in South Korea since 2010鈥�

Car park owners will be key players too, says Davison. For instance, shopping centres might want to install wireless chargers to attract people with electric cars (see box).

Another idea is allowing homeowners to lease the parking space in the road outside their property from the local government, giving them exclusive access to a space fitted with a wireless charger. Money from the scheme could be used to fund further installations. Once every space has wireless charging, streets could revert to non-exclusive parking.

If that happens, the next step might be to place wireless chargers under main roads. Electric buses that get power wirelessly as they drive have been running in South Korea since 2010. But these buses have specialised systems that only work on particular short routes and have a top speed of just 60 kilometres per hour.

To push the idea further, Davison鈥檚 former team at Qualcomm recently built chargers into a 150-metre section of road in France. This proved that a car could get enough energy to power its engine and charge its battery while travelling at 100 kilometres an hour.

Crucially, the car was fitted with the same kind of receiving pad used for stationary charging. So if roads are ever electrified, any cars with standard wireless charging should be able to take advantage.

Qualcomm has shelved the work for now as it currently costs too much to outfit a whole road. But when most cars are electric, this approach would make more sense.

So could the widespread availability of wireless charging change the way we drive and encourage more people to buy electric cars? Davison, perhaps surprisingly given his role in developing the technology, makes no big claims. Wireless charging is just another convenient feature, like electric windows, he says, but a desirable one. 鈥淲hen you鈥檝e had it, you really miss it when you don鈥檛 have it any more.鈥�