Illustration: Jason Lee

Making ethanol from crops has considerable, and growing, allure. As an energy source, bioderived ethanol is renewable, and its by-products are biodegradable. And, most important, to the extent that the ethanol takes the place of gasoline, it economizes on imported oil and can reduce greenhouse gas emissions.

Many countries are promoting use of the fuel, but so far Brazil is the ethanol exemplar. The alcohol accounts for about 20 percent of the fuel burned by automobiles there. About 70 percent of new cars sold in Brazil are flex-fuel vehicles that can run on a blend of biofuel and gasoline, and the country’s ethanol exports to Japan, Sweden, and other countries are expected to double during the next five years to more than US $1.3 billion [see “The Omnivorous Engine,” in this issue].

Even the United States—where ethanol is made from corn rather than sugarcane, a relatively expensive and inefficient process—is experiencing an ethanol boom. Besides the 100 ethanol plants already operating, at least 40 more are under construction, and another 100 or so are planned.

Some of those projects make more sense than others. Among the least sensible is a facility near Richardton, N.D., that was scheduled to open last month. The Red Trail Energy plant, which is fueled by lignite, a dirty and inefficient type of coal, is scheduled to produce 50 million gallons of ethanol per year. Mick Miller, Red Trail’s chief executive, points out that the plant would comply with all relevant air pollution regulations. But carbon dioxide is not regulated in the United States, and per unit of energy used, the plant’s CO₂ emissions will be high.

The ethanol picture doesn’t have to look like that. In fact, the good news is that most new ethanol plants using up-to-date technology will help reduce oil imports and cut greenhouse gas emissions somewhat. But there’s ethanol, and then there’s ethanol. In today’s hothouse political climate, some weird projects have taken root along with essentially sound ones.

Making ethanol requires energy to drive biochemical conversion processes. First a corn mash or slurry is cooked and enzymes are added to transform starch to sugar, and then yeast is added to ferment the sugar into ethanol.

Traditionally, most ethanol factories have been relatively small mills, in which corn is crushed and processed. Such “dry mills” typically produce 50 million to 75 million gallons of ethanol per year and are fueled mainly by natural gas. Larger plants producing upwards of 100 million gallons per year are more commonly “wet mills,” where the corn is processed as a slurry. Wet mills typically rely on coal. But during the current construction boom, dry mills are being made larger, and more of them will also burn coal—about a quarter of the 40 under construction, by one estimate.

The growing reliance on coal is not, on the face of it, such an odd thing. Coal has been cheap relative to natural gas in recent years, and most ethanol plants are being built in parts of the country that rely heavily on coal for electricity anyway. The pursuit of energy independence, too, makes it tempting to use domestic coal to make an alternative fuel that will replace imported oil. But per joule of heat produced, coal releases two to three times as much carbon dioxide as natural gas, and that makes coal-generated ethanol a dubious way of reconciling energy and environmental imperatives.

Besides using coal to fuel the production plant, a lot of energy is used to fertilize and irrigate the corn, and further, the corn may also have to be transported a long way to the facility. On average, about 40 percent of the energy needed to make ethanol goes into growing the corn and about 20 percent is needed to transport it, with the production plant accounting for the other 40 percent. But, of course, the energy costs and emissions associated with farming and transportation can be much higher than average.

According to Nathanael Greene, an ethanol specialist with the Natural Resources Defense Council (NRDC), in New York City, coal-produced ethanol shipped a long way to its final destination and derived from corn grown with techniques that release a lot of carbon dioxide from the soil can actually have “carbon impacts that might be worse than gasoline’s.”

Something like that scenario is found at the Red Trail Energy plant. Red Trail has assured North Dakota farmers that much of the 18 ­million bushels of corn needed each year will be bought locally, and Miller, its CEO, told IEEE Spectrum that all of it, in fact, will be bought locally. But earlier statements by the company suggest that at least some corn will be brought in by train or truck from other states. Doug Koplow, an expert on ethanol subsidies with Earth Track, in Cambridge, Mass., points out that because of the ethanol plant construction boom, even in corn-rich states like Iowa, corn may be shipped in from out of state to keep new plants running.

Coincidentally, the Red Trail plant’s inputs, outputs, and balances have been modeled by a team at the University of California at Berkeley. The work is part of what Berkeley’s Energy and Resources Group calls the ERG Biofuels Analysis Meta-Model (EBAMM).