Biofuels compared
The October issue of National Geographic has an in-depth feature on biofuels. We’ve written a fair bit about corn ethanol and biodiesel, but the magazine goes to town with a comparison of various fuels and the crops from which they’re made.
Maybe it’s just our new-found enthusiasm for all things scientific, but among the most interesting parts of the article are statistics that compare the energy balance of fuels. This simple measure weighs the energy value of a refined fuel against the fossil-fuel energy needed to extract it from its original form; corn, wheat or soya beans, for example.
Supporters of corn ethanol as a biofuel had better look away now. The magazine’s figures show that for every unit of fossil-fuel energy used to produce the fuel, it yields just 1.3 units of energy. Its production and use delivers a 22% reduction in greenhouse gases compared to petrol, though, which sounds promising enough.
It’s distinctly lacklustre compared to bioethanol from other sources, though. Brazil may be clearing rainforest to produce “emerald deserts” of sugarcane crop, but the figures suggest that it does at least make a much better fuel. Distilling processes fuelled by waste cane help to reduce the dependence on fossil-fuels, with the cane bioethanol delivering eight times as much energy as it takes to produce, and a 56% reduction in greenhouse gases.
Biodiesel, yielding 2.5 times the fossil-fuel used in its production, doesn’t sound too wonderful, but its production and use creates 68% less greenhouse gases than petrol.
One great hope raised by the article is that of cellulosic ethanol, which could in theory be produced from almost any plant source. Depending on the production method, the magazine says that its energy yield could be as high as 36 times the input, with a 91% reduction in greenhouse gases.
Algae farms are another possibility. The magazine says that bags of the tiny green plants can be used “to siphon carbon dioxide from the smokestack emissions of power plants”. They can also “devour” other pollutants, producing starch for fermentation into ethanol, or oils for producing diesel.
The farms are being trialled in America, but aren’t yet close to being put into widespread commercial use. With China apparently building a new coal-fired power station almost every week, we wonder if it could be time for slime.
IMAGES by Flickr users
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Originally posted 2007-10-23 01:34:00. Republished by Blog Post Promoter
