One secret of good research – whether to advance basic science or to apply in business or public policy – is to challenge a common assumption by asking a question others have not thought of.
That is what Chris Field and colleagues at the Carnegie Institution at Stanford in California did in a study of biofuels for transport, published today in the journal Science.
Everyone is used to driving cars powered by liquid fuels such as petrol and diesel. And in the US the drive to grow biofuels for vehicles has focused on converting crops to ethanol which can be used in internal combustion engines.
However, that turns out to the wrong approach, according to the study (carried out with the University of California, Merced). It is actually much more efficient to convert biomass to electricity for battery-powered vehicles.
The authors calculated that burning biomass to generate electricity in a power station delivered 80 per cent more mileage per acre of crops than converting it to ethanol for liquid fuel. It also doubled the greenhouse gas offsets to mitigate climate change.
Asking whether bioelectricity or bioethanol is a more efficient use of crops and land is “a relatively obvious question once you ask it, but nobody had really asked it before,” says Field.
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.”