Making Gas from Prairie Grasses
ROBERT SIEGEL, host:
From NPR News, this is ALL THINGS CONSIDERED. I'm Robert Siegel.
MELISSA BLOCK, host:
And I'm Melissa Block.
The idea of burning grass to fuel your car or heat your home might seem a bit odd, but call grass a biofuel and suddenly it sounds plausible. Scientists are struggling to make biofuels that are cheap enough to compete with fossil fuels such as oil and coal. Growing anxiety over how fossil fuels warm the earth's climate has quickened the pace of research.
NPR's Christopher Joyce reports on some new findings that make grass look more like an energy contender.
CHRISTOPHER JOYCE: Switchgrass, President Bush said in his State of the Union address, could help cure America's addition to oil. That may be the first time the word switchgrass was uttered on the floor of Congress. But the words biomass and biofuels are becoming common. Corn, soybeans and switchgrass are biomass. They can be brewed into biofuel for cars and trucks. That means less imported oil and biofuels don't produce as much carbon dioxide, the gas that's warming the planet, as fossil fuels do.
Trouble is, corn and soybean fuels are expensive. They're also food. So energy experts are looking harder at other sources of biomass like switchgrass. It's a tall prairie perennial that grows fast. An ecologist at the University of Minnesota has been growing it for over ten years.
Professor DAVID TILMAN (University of Minnesota): We actually get more energy from an acre of land growing prairie grasses, mixtures of prairie grasses and converting them into ethanol or into synthetic gas and diesel than you would by growing corn and soybeans and converting them into ethanol or into biodiesel.
JOYCE: What David Tilman did was grow plots of mixed prairie grasses, not just switchgrass but lupine, turkey foot, blazing star, prairie clover - 16 kinds in all. The plots with the most varieties produced the most biomass and the most potential energy - more in some cases than corn and soybeans.
But the multigrass plots did something else. Like all plants, grasses capture and use carbon dioxide out of the air. When a plant or a plant-fuel is burned, the CO2 goes back into the air. That's not good if you're worried about climate change. But Tilman's prairie grasses bury a lot of that CO2 in the soil and in their deep, permanent roots. So a lot of the CO2 stays in the ground after the harvest.
Professor TILMAN: We have discovered a way to make biofuels that by the time the whole life cycle is done and they are combusted, there is actually less carbon dioxide in the atmosphere than there had been before.
JOYCE: The cycle starts again after harvest, with new grass growing from the same roots.
Writing in the journal Science, Tilman calls this carbon negative biofuel, just the opposite of biofuels from corn and soybeans, which are carbon positive, they produce more CO2 than they absorb because it takes more fossil fuel to make them. You need fossil fuel to run farm equipment, to make fertilizer, to make electricity to run fermentation tanks. Prairie grasses need much less help to grow.
Professor TILMAN: They're adapted to the region. They grow with almost no input. We don't have to apply any pesticides. We don't need to use fertilizer. We don't irrigate them. They grow on nutrient poor soils and they are very efficient at converting the resources they do get into energy.
JOYCE: But converting prairie grass into a useable fuel is not easy. Robert Jackson, an ecologist at Duke University who's studied biofuels, says Tilman's findings are encouraging. But the marketplace still rules.
Dr. ROBERT JACKSON (Duke University): Right now biomass is more expensive than traditional fossil fuels and many other renewables, and the only thing that will change that is some sort of carbon tax or carbon trading mechanism. When we pay for carbon, then we change the price structure for that carbon.
JOYCE: The Department of Energy says it costs about five times more to make fuel from grasses than it does to make it from corn. But Jackson notes that prairie grasses do have advantages that could help them compete. Unlike corn, for example, they grow happily on poor, sandy soils. At some point, good places to grow corn will get scarce. That's when grasses may start to look a lot greener.
Christopher Joyce, NPR News.
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