By Paul Marks, New Scientist, 23 January 2014
Forget the charging cable: breakthroughs in inductive charging for electric vehicles mean drivers just park over a pad in the road to get more juice
I'M ON a bus headed for Bletchley Park, but not to visit the UK's second-world-war codebreaking centre, I'm just along for the ride.
That's because I'm on an electric bus that is one of the first vehicles to use a revolutionary inductive charging technology. Its batteries charge wirelessly when the bus stops to pick up passengers. With no need to plug in to charge, it's a breakthrough that should speed up the widespread adoption of electric vehicles (EV).
Charging an EV is a laborious process. The owner has to find a charging point, connect up their cable and leave the car for some hours. It's inconvenient, and cables can easily get lost or damaged.
Wireless power transfer technology was developed decades ago, but low efficiency meant it was restricted to industrial settings, providing power for robotic vehicles and cranes, for example. That is finally changing.
The wireless system relies on the well-known principle of electromagnetic induction. A magnetic field generated by an alternating current in a primary coil induces a current in a nearby secondary coil. What is new is technology that allows for an energy-transfer efficiency of 90 per cent or higher.
Engineers John Boyes and Grant Covic at the University of Auckland in New Zealand worked out the optimal design for the shape of the coils to minimise energy losses. They also figured out how power can be transferred when the coils are misaligned – so it still functions even if you are terrible at parking. The magnetic field has to be controlled so it stays within a safe limit, otherwise metal carried by passengers, from coins to pacemakers, could heat up.
Two firms – IPT Technology of Efringen-Kirchen in Germany and Qualcomm Halo of London – have licensed the Auckland patents and are developing their own variants.
On 9 January, the UK city of Milton Keynes launched a full-scale electric bus service, plying a 24-kilometre route with eight buses running from the city centre to Bletchley, charged using IPT's pads.
Two of the stops my bus arrives at have power coils embedded in the ground and covered by 3-metre-square toughened pads. Using markings on the road and kerb, the driver aligns the bus, with its pickup coil fitted underneath, over the pad to establish a magnetically coupled link. And that's it: after some wireless authentication to identify the vehicle, the bus's battery pack gets a 120-kilowatt charge for 10 minutes during a built-in timetable stop. The bus still uses diesel, too, but only for its heating system, says John Miles of London-based firm Arup, who is a consultant on the project.
IPT Technology's wireless chargers also supply power to buses on two routes in Genoa and Turin in Italy. After successfully trialling a wirelessly charged Mercedes EV, the firm is planning to expand production of its devices for consumer EVs, says product manager Mathias Wechler.
Qualcomm Halo is developing 3-kilowatt chargers for the Renault Fluence, a four-door family-size car. They are just 25 centimetres square and 2.2 cm deep, with road pads that are 75 cm square and 3.3 cm deep. "In the next two to three years wireless charging will definitely become an option for EVs," says director Joe Barrett.
In a test of the technology's potential, Paul Drayson, a British racing driver and entrepreneur, last October set the world land-speed record for a lightweight EV in a racing car charged by one of Qualcomm Halo's wireless pads. The company's technology will also charge the safety cars in Formula-E – the electric version of Formula 1 which kicks off later this year.
"Charging without the faff of using a cable is a very significant driver of future electric car adoption," says Drayson. Back on my bus, John Loughhead, who directs the UK Energy Research Centre in London, is optimistic. "It doesn't remove all the barriers to widespread EV use. But it certainly chips away at some of them."