Road works. Inconsiderate drivers. Congestion. Today’s drivers have their fair share of stress already. But now there is a new malaise for the modern motorist: range anxiety.
That is the term given to drivers of electric cars that are struck by the sudden fear that their vehicle does not have enough charge to reach its destination. Most of us have experienced that sinking feeling when the little orange indicator light comes on to tell us we are low on petrol, but there is not a gas station in sight. Imagine that, combined with the feeling that you get when your cellphone starts beeping because the battery is low, and you are nowhere near a plug. That gets you close to the feeling of range anxiety.
It is an interesting phenomenon, particularly when you begin to look at how many of us actually use our cars. According to the US Bureau of Transportation Studies, 78% of drivers do less than 40 miles (65km) a day – a trivial distance for many of today’s electric cars. In fact, the poster child of electric cars – the Tesla – has a range of 300 miles (485km) using some batteries.
According to, Dr Richard Sassoon, of Stanford University, there are “three main reasons” that many of us choose the internal combustion engine over its cleaner, quieter alternative.
“One is the short range that an electric vehicle can travel between charges, and that’s based on the size of the battery,” he said. “The second is the lack of a sufficient charging infrastructure, and the third is that even if you can charge, it takes a long time to charge – several hours. That means you’re going to have to take a break in your trip in order to charge your vehicle.”
Researchers and firms are trying to tackle all of these problems. Firms, such as Better Place, have started building battery “switching stations” that allow drivers to pull in and swap their batteries as easily as filling up with gas, whilst countless researchers are developing more efficient batteries.
But Dr Sasson believes there may be another answer: recharging roads.
Engineers in his lab are developing a way to wirelessly charge electric cars from magnetic coils embedded into the road. The car would pick up the power via another coil, meaning – in theory – that you would never have to make a charging stop again.
The system works using a technique called “magnetic resonance coupling”. You can think about resonance as the phenomenon that allows an opera singer to smash a glass using only the power of their voice. In that case, when the singer hits a note that has the same resonant frequency as the glass, they couple and energy begins to build up in the glass, eventually causing it to smash.
Instead of using acoustic resonance, the Stanford team use the resonance of electromagnetic waves. A coil in the road that is connected to a power line is made to vibrate with the same resonance frequency as the coil on the bottom of the car, allowing energy to flow between them.
Traffic charge
It builds on pioneering work done at MIT in 2006 which showed the technique could be used in stationary situations, to power televisions and other gadgets. The Stanford system now claims to have upped the efficiency dramatically. They have come up with designs of coil that allow 97% efficient transmission of power over a distance of about 2m (6ft). Using models, they estimate they can transfer up to 10kW of power.
