Once touted as an environmental and economic cure-all, corn ethanol has had a rough year. The collapse in grain and oil prices, preceded by overinvestment in refineries over the past few years, badly hurt ethanol producers. Meanwhile, environmentalists have steadily chipped away at ethanol's green credentials. Far from being better for the planet than gasoline, many scientists now argue that ethanol actually has a sizable carbon footprint, because when farmers in the U.S. use their land to grow corn for fuel rather than food, farmers in the developing world end up cutting down more forests to pick up the slack.
Now a new study makes the case that ethanol isn't even the greenest way to use biomass as a fuel. In an article published in the May 8 issue of Science, researchers from the Carnegie Institution, Stanford University and the University of California-Merced (UCM) used life-cycle analysis which takes into account the entire impact of a biofuel from field to vehicle to show that converting biomass to electricity (to power electric cars) produces 80% more transportation energy than turning it into ethanol (to power a flex-fuel car), with a carbon footprint that is half as small. (Bioelectricity is created the same way fossil fuelgenerated electricity is: Biomass is usually burned to generate heat, turning water to steam and driving an electrical generator.)
For every acre of land planted with an energy crop like corn or switchgrass turning that biomass into electricity gives you more "miles per acre" than converting it to liquid ethanol, which is how biomass is used today, according to the study. A small SUV powered by bioelectricity could travel nearly 14,000 miles on the energy produced by an acre of switchgrass, while an ethanol-powered SUV could go only 9,000 miles. "It looks like converting biomass to electricity, instead of using it to make ethanol, makes the most sense for both transport and the climate," says Elliott Campbell, an environmental engineer at UCM and lead author of the study.
On carbon, too, bioelectricity was a winner. On average, the carbon offset from using bioelectricity is 100% bigger than the offset for using ethanol. (Even though biomass releases carbon when it is burned, just like oil, when new plants are growing they absorb carbon dioxide from the atmosphere, reducing the overall carbon footprint.) "It's simply the case that bioelectricity is just a lot more efficient than using ethanol, in most ways," says Campbell.
But the Science study doesn't take into account other impacts that bioelectricity might have compared to ethanol, like water consumption or air pollution. Growing biomass, even on marginal agricultural land, does require water, as does making electricity. There's a bigger problem electric cars still remain few and far between, while there are already millions of U.S. vehicles on the road that can run on an ethanol blend. Creating the sort of infrastructure that can support electric cars on a mass scale won't be cheap, and it's not a cost that Campbell and his colleagues included in their study. "There's a lot more we have to look at on biomass," says Campbell.
Still, the ethanol industry's days may be numbered. Ethanol wouldn't exist but for government subsidies, yet in the 2007 energy bill, Congress ruled that to be eligible for support, corn ethanol has to emit 20% less climate pollution than gasoline. If you include the indirect land-use effects of ethanol the increase in deforestation caused by using land to grow fuel it's unlikely to hit that target. On May 5, the Environmental Protection Agency (EPA) released a proposed rule that would take into account indirect land-use effects when judging just how green corn ethanol is. Unless the rule is changed the powerful corn lobby will be working hard to make that happen corn ethanol might not meet Congress's requirements, which could spell the end of subsidies. So, if there's any future in biofuels, it looks like it might have to be bioelectric.