Science briefing: New steer on electric cars

By Clive Cookson
Published: May 8 2009 02:48

The drive to grow biofuels for transport has focused on converting crops to ethanol which can be used in internal combustion engines. However, that is the wrong approach, according to a study published on Friday in the journal Science: it is much more efficient to convert biomass to electricity for battery-powered vehicles.
The authors, from the Carnegie Institution at Stanford and the University of California, Merced, calculated that generating electricity, by burning biomass in an efficient power station, delivered 80 per cent more mileage per acre of crops than conversion to ethanol for liquid fuel. It also doubled the greenhouse gas offsets to mitigate climate change.
“It’s a relatively obvious question once you ask it, but nobody had really asked it before,” says Chris Field of the Carnegie Institution.
Bioelectricity was a clear winner over bioethanol, whether the energy came from corn or switchgrass (a new cellulose-based crop).
A car powered by bioelectricity could travel almost 14,000 miles on the net energy from an acre of switchgrass, while a car powered by bioethanol from the same crop would go only 9,000 miles.
“The internal combustion engine just isn’t very efficient, especially when compared with electric vehicles,” says Elliott Campbell, another author. “Even the best ethanol-producing technologies with hybrid vehicles aren’t enough to overcome this.”
Bee shortage not a global crisis Recent declines in honey bee numbers in north America and Europe have prompted widespread concern about an impending crisis, with too few bees to pollinate the crops that depend on them to set fruit. But on a global view, the “pollination crisis” is a myth, an international study has found.
Marcelo Aizen, of Universidad Nacional del Comahue in Argentina, and Lawrence Harder, of Calgary University in Canada, say the world’s stock of honey bees, which has risen by 45 per cent over the past 50 years, continues to increase.
“The honey bee decline observed in the US and in European countries including Britain, which has been attributed in part to parasitic mites and more recently to colony collapse disorder, could be misguiding us to think that this is a global phenomenon,” said Prof Aizen. “We found that is not the case.”
The analysis, which appears in the journal Current Biology, is based on the latest data from the UN Food and Agriculture Organisation. The figures show that the global growth in bee keeping has been driven mainly by demand for honey rather than the need to pollinate crops. Global honey production has doubled since 1961.
Heavy going for bumblebeesZoologists at Britain’s Oxford University have discovered how the honey bee’s heavyweight cousin, the bumblebee, manages to fly. Bumblebees rely on brute force rather than aerodynamic efficiency to stay aloft.
While scientists have become expert at using computers to model insect flight, the Oxford researchers took a more direct approach. “We decided to go back to the insect itself and use smoke, a wind tunnel and high-speed cameras to observe in detail how real bumblebee wings work in free flight,” said Richard Bomphrey.
“We found that bumblebee flight is surprisingly inefficient,” he added. “Aerodynamically speaking it’s as if the insect is ‘split in half’ as not only do its left and right wings flap independently but the airflow around them never joins up to help it slip through the air more easily.”
His Oxford colleague Adrian Thomas called the bumblebee “a tanker-truck”. “Its job is to transport nectar and pollen back to the hive,” he said. “Efficiency is unlikely to be important for that way of life.” The research is published in the journal Experiments in Fluids.
Copyright The Financial Times Limited 2009