Green machine: Plug-free electric cars' hidden cost

时间:2017-12-02 08:01:06166网络整理admin

By Helen Knight It’s bad enough forgetting to recharge your mobile phone overnight – the inconvenience is likely to be far worse if you fail to plug in your electric car. Now an array of technologies are being developed to ensure that absent-minded drivers don’t run out of power on the road, but the come with a downside: they risk negating a key environmental benefit of going electric. One potential method to ensure electric cars remain topped up involves a wireless system that charges your car without any thought or effort on the driver’s part. At the Plug-In 2010 conference in San Jose, California, last week Evatran of Wytheville, Virginia, launched a plug-free car charger. To use the device, drivers will simply pull into their garage or charging station and park over a base unit fitted to the floor, and the system will do the rest, says Rebecca Hough, Evatran’s director of marketing. Electric vehicles starting to go on sale over the next few years “will have intelligent control systems that allow the vehicle to request charge when it’s ready”, Hough says. “As long as the vehicle requests charge from our system, our system will automatically begin charging.” The plug-free system is based on induction charging – the technology commonly used to power electric toothbrushes. A coil in the base unit creates an electromagnetic field that interacts with a coil attached to the car, which converts it back into an electric current. The company recognises that the device will require more power from the grid than plug-in recharging systems. It will be about 90 per cent efficient, says Hough. This may be a price worth paying for the greater convenience offered by wireless charging, which Hough says should encourage more drivers to buy electric vehicles. “We believe that our system will eliminate a barrier to electric vehicle adoption and increase the adoption of electrified transportation,” she says. Other companies developing inductive charging systems include WiTricity, a spin-out of the Massachusetts Institute of Technology, while Nissan last year announced that it was looking into wireless charging for its electric vehicles. Earlier this year researchers at KAIST (the Korea Advanced Institute of Science and Technology) in Daejeon, South Korea, demonstrated their Online Electric Vehicle (Olev), which is powered by an electromagnetic field generated by strips buried in the road. Not everyone is convinced that the convenience of wireless charging systems is sufficient compensation for their reduced efficiency. The power lost by these systems in transferring energy could be enough to make electric vehicles and plug-in hybrid electric vehicles less environmentally friendly than conventional cars, says Michael Kintner-Meyer at the Energy and Environment Directorate at the Pacific Northwest National Laboratory in Richland, Washington. If you take into account the energy used to produce the electricity, and compare it with a well-to-wheel analysis of the most efficient diesel-engine cars available today, the difference is already fairly small, says Kintner-Meyer. “It’s on the tipping point. It depends how green your electricity is,” he says. Even a 10 per cent loss in overall efficiency could make electric cars the less environmentally attractive option. “When you compare a highly efficient diesel engine car with an electric car, that 10 per cent may tip the needle,” Kintner-Meyer says. Read previous Green machine columns: A new push for pond scum power, The dream of green cars meets reality, Tackling the plastic menace, Bacteria will keep CO2 safely buried, Recycled batteries boost electric cars, It’s your eco-friendly funeral, Cars could run on sunlight and CO2, Hitting the lights in wasteful offices, Aircon that doesn’t warm the planet. More on these topics: