Perhaps the most important constraint on cellulosic ethanol is geographic. Like corn ethanol, cellulosic ethanol production is limited by the amount of arable land. In May 2006, former CIA Director John Deutch, who's now a chemistry professor at Massachusetts Institute of Technology, wrote a piece for the Wall Street Journal in which he claimed that producing enough ethanol from switch grass (a fast-growing plant that's native to North America) would require vast amounts of acreage. Deutch estimated that producing enough cellulosic ethanol to replace 1 million barrels of oil per day—roughly equivalent to 22 billion gallons of ethanol per year—would require planting 25 million acres of land in switch grass. That's an area about the size of Kentucky, or about 5 percent of the 440 million acres of cropland in the United States.
And all of this assumes that making cellulosic ethanol is even worth doing from an energy standpoint. A peer-reviewed study of alternative automotive fuels to be published this week by Jan Kreider, an engineering professor at the University of Colorado in Boulder, found that like corn ethanol, cellulosic ethanol produces minuscule gains in net new energy. (Other studies have shown both types of ethanol to be net energy losers. Still others claim significant energy gains.) Kreider's paper will be published by the American Society of Mechanical Engineers as part of its 2007 conference on energy sustainability.
Energy requirements aside, "Cellulosic ethanol doesn't have a proven production technology that's economic," Kreider told me Monday. "But even if there were such a technology, there's not enough land, not enough water, and not enough transportation infrastructure to provide the quantity of fuel the Senate is mandating."
So, what about using more ethanol from sugar cane? Well, the United States could, at least in theory, grow more cane. But that wouldn't make much sense, given that Brazil can produce it at far lower cost. And, thanks to pressure from farm-state senators, Congress has effectively limited the use of Brazilian ethanol with its $0.54 per-gallon tariff on foreign ethanol.
The final issue is quantity. Thirty-six billion gallons of ethanol a year sounds like a lot, but it's only 2.34 million barrels per day. And given ethanol's lower heat content—about two-thirds that of gasoline—the effective production would be equivalent to 1.54 million barrels of oil per day. The United States uses nearly 21 million barrels of oil per day, of which 12.54 million barrels are imported. Thus, even if American ethanol producers can miraculously achieve the Senate's goal of 36 billion gallons per year by 2022, they will be producing the equivalent of just 7.4 percent of America's total current oil needs and just 12.2 percent of its imports. That quantity of ethanol will not take America very far toward the oft-repeated goal of energy independence.
Alas, the ethanol craze isn't limited to Congress. Presidential candidate and former Sen. John Edwards, a Democrat, has declared that the United States should be producing 65 billion gallons of ethanol and other biofuels per year by 2025. And every major presidential candidate—including former ethanol heretic John McCain, a Republican—are genuflecting in front of the ethanol altar.
So, don't expect the ethanol binge to stop any time soon. An ethanol-induced hangover is sure to follow.