Our dependence on foreign oil has researchers and policymakers taking another hard look at weeds and corn stalks as sources of home-grown fuel.
President Bush’s Advanced Energy Initiative, announced last month, calls for research into biofuels from “cellulosic” plant waste, “to displace up to 30 percent of the nation’s current fuel use.” Indeed, in his State of the Union address, the president suggested that one solution to the nation’s “addiction” to oil could be fuel derived from switchgrass, a tall plant native to U.S. prairies. Reinforcing that vision, more than one recent study has suggested that biomass could eventually play a significant role in U.S. transportation energy needs, and do so without adding to the carbon in the atmosphere.
But are these realistic scenarios – or just wishful thinking? The idea of using biomass for energy isn’t new of course. Already, about four billion gallons of ethanol are produced yearly in the United States by fermenting corn and distilling out its energy-rich alcohol. But the amount that can be produced is limited by the land required to grow the corn. What’s more, the process for producing ethanol is inefficient, requiring nearly as much energy to make as is available in the final product.
Advances in genetic engineering, however, now have many experts feeling optimistic about dramatically increasing the amount of biomass that can be harvested from an acre of land, by using microbes to convert leaves and stalks, not just corn, into liquid fuels. They believe this can be done efficiently, too, without exhausting available land and water, and also predict that production costs could be competitive with gasoline.
A recent report by the National Resources Defense Council and researchers at Dartmouth and Princeton projects that by 2050, in part through harvesting both protein and cellulose from corn and switchgrass, existing agricultural land could both supply our food needs and replace gasoline with ethanol.
Unless it’s done carefully, however, deriving fuels from biomass could destroy crop lands through erosion, increase air pollution – and even increase our dependence on fossil fuels. For example, one of the steps in processing biomass, distillation, requires heat. In the short term, inexpensive coal may appear to be a good energy source for this, says John Reilly, associate director for research at MIT’s Joint Program on the Science and Policy of Global Change. But this would cancel out one of the primary benefits of biomass: carbon released by burning biofuels is offset by the carbon captured by growing crops, leading to near-zero total carbon emissions. Using coal for distillation would destroy this balance. In one scenario, Reilly says that “68 percent of the carbon you think you’re saving is actually being emitted through other processes.” Likewise, using gasoline or diesel to transport biomass from widespread farms and other agricultural facilities to processing centers would change the overall carbon equation.
What’s more, models that show biomass supplying a significant amount of the nation’s transportation fuels tend to lean heavily on projections that vehicles will use half as much fuel as they do today, or even less. Without this increase in efficiency, however, there’s not enough land to provide a supply of biomass sufficient to put a dent in the demand for foreign oil.
“High vehicle efficiency is an essential factor for all sustainable transportation scenarios,” says Lee Lynd, engineering and biology professor at Dartmouth and co-author of the NRDC study that said biomass could replace gasoline by 2050. His model assumes two and a half times the current fuel economy for vehicles, as well as sophisticated crop rotations and other land-use decisions to make it possible to supply both food and energy from existing agricultural and pasture lands.
If the past is a guide, such models are extremely optimistic. In fact, although technology has improved fuel efficiency, the average number of miles per gallon for vehicles today is actually less than it was in the late 1980s, according to a recent EPA report. While engines have become better at extracting energy from fuel, cars have also become faster and heavier, cancelling any gains.
Lynd’s optimistic scenario also assumes that the conversion of stalks to ethanol can be done much more efficiently than it is today, by combining existing metabolic pathways from organisms such as fungi and bacteria. A recent white paper from a group of biomass researchers at MIT says that existing pathways will also need to be fine tuned to provide adequate yields. Creating these pathways will depend on continued research, even as less-efficient technologies begin to come online.
Experts look at biomass and see the potential to significantly improve our energy security while helping the environment. Certainly, the vision of vast fields of switchgrass and other crops replacing troubled oil fields in the Middle East is an attractive one. But turning biomass into more than a fuel for niche applications will require a strong R&D effort to bring the technology to fruition.
Image on home page (switchgrass) courtesy of Department of Energy
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