This is part of IEEE Spectrum’s special report: Winners & Losers VII
Of all the possible biofuel crops that can be grown in the United States, perhaps the most attractive is Panicum virgatum, otherwise known as switchgrass. A hardy perennial native to North America, it needs little fertilizer and water, and pests don’t seem to like it much. So it holds out the shimmering promise of one day producing vast quantities of fuel in “carbon neutral” fashion, absorbing as much carbon dioxide in growth as it releases when burned.
Compared with sugarcane or corn, though, switchgrass is tricky to use, because it provides cellulose—the natural polymer that gives plants their rigidity—rather than simple sugars. So you need to do some elaborate processing, first to break down the cellulose and then to ferment the resulting sugary brew so that it turns into ethanol, which can be served neat or blended with gasoline. As yet, nobody has succeeded in producing switchgrass ethanol on a commercial scale, and the economics of doing so remain fuzzy.
One company that believes it’s on the verge of success is DuPont Danisco Cellulosic Ethanol (DDCE), based in Itasca, Ill. Founded in May 2008 by DuPont and Danisco, DDCE has just completed a pilot ethanol plant in Vonore, Tenn., which is slated to open officially in a few months. The facility, built in partnership with the University of Tennessee, will be able to produce almost a million liters (250 000 gallons) of ethanol per year from either switchgrass or corncobs. DDCE then plans to build a much larger plant in Tennessee with a capacity of nearly 60 million L a year. Meanwhile, it’s taking advantage of more than US $70 million in state support to enlist farmers to start growing the grass now. The company is thus positioning itself on the cutting edge of a new “grassoline”-based economy.
“We’re doing scale-up and commercialization,” says Vonnie Estes, vice president of commercial development and marketing for DDCE. “Once we get it up and going, it’ll be competitive with gasoline—I have no doubt.”
Perhaps she should have doubts. Here’s one: Will it be possible to transform the half billion or so cars and trucks in the United States so that they can use more homegrown ethanol and less gasoline? Even Estes sees that hurdle. “That’s one of the big issues—creating the market,” she says.
But even if a market does emerge and DDCE’s production process proves highly profitable, this technology can’t be considered a winner. Why? Because it will fail to satisfy the main premise for adopting it in the first place: to benefit the environment. A simple thought experiment sheds light on the dark side of grassoline.
Suppose you replaced all the gasoline the United States now uses with switchgrass-derived ethanol. How much land would that take? The United States consumes 522 billion L of gasoline a year. Because of the difference in energy density, you need about 1.5 L of ethanol to replace a liter of gasoline. So the yearly requirement for ethanol would be about 780 billion L. A hectare of switchgrass can supply about 4700 L of ethanol a year, so the United States would need to devote roughly 170 million hectares (420 million acres) to it.