Saturday science subject: Fueling cars with grass

A hot topic in the U.S. presidential primaries is energy independence, and domestically produced, corn-based ethanol is often cited as a viable alternative to foreign oil. However, as the Scientific American reports, a much more pedestrian plant could prove to be a better source of fuel than corn.

The plant in question is switchgrass, a.k.a. Panicum virgatum, a perennial grass that often naturally grows on the borders of crops. The U.S. Department of Agriculture worked with farmers to evaluate the grass' potential for biofuel, and it found that the plant could be far more energy-efficient to grow than corn:

But yields from a grass that only needs to be planted once would deliver an average of 13.1 megajoules of energy as ethanol for every megajoule of petroleum consumed—in the form of nitrogen fertilizers or diesel for tractors—growing them. "It's a prediction because right now there are no biorefineries built that handle cellulosic material" like that which switchgrass provides, Vogel notes. "We're pretty confident the ethanol yield is pretty close." This means that switchgrass ethanol delivers 540 percent of the energy used to produce it, compared with just roughly 25 percent more energy returned by corn-based ethanol according to the most optimistic studies.

The U.S. Department of Energy (DOE) is partially funding the construction of six such cellulosic biorefineries, estimated to cost a total of $1.2 billion. The first to be built will be the Range Fuels Biorefinery in Soperton, Ga., which will process wood waste from the timber industry into biofuels and chemicals. The DOE is providing an initial $50 million to start construction.

Better yet, USDA plant scientist Ken Vogel and his team found that switchgrass stores enough carbon in its roots to offset 94% of the greenhouse gases generated to both cultivate it and burn the resulting ethanol as fuel.

There is one downside. The Scientific American quotes Energy Secretary Samuel Bodman as saying switchgrass requires a more complex refinery process than corn. Nonetheless, Bodman says it's "worth the investment" to develop the process because cellulosic ethanol "contains more net energy and emits significantly fewer greenhouse gases than ethanol made from corn." The U.S. Department of Energy is already co-funding the construction of six refineries designed to produce cellulosic ethanol, the first of which will be built in Soperton, Georgia.

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