Study: Bioelectricity bests biofuels on miles per acre

May 8, 2009 11:57 AM PDT
Study: Bioelectricity bests biofuels on miles per acre
by Martin LaMonica Font size Print E-mail Share 32 comments Yahoo! BuzzGrowing plants to make electricity is a more efficient and environmentally sound way to power vehicles than biofuels, according to a study meant to spark a debate over energy policy.

The study's authors modeled how far different classes of cars could go based on the available energy from a unit of land and found that bioelectricity--burning biomass to make electricity--far outperforms ethanol.

The paper, published on Thursday in Science, found that bioelectricity delivered 81 percent more distance per unit area of crop land than ethanol. Greenhouse gas emissions per area of land were 100 percent less than cellulosic ethanol. (Click here for PDF of results.)

In one example, they found that a small truck powered by bioelectricity could travel almost 15,000 miles compared with 8,000 comparable miles for an internal combustion equivalent.

(Credit: UC Merced)Making electricity from biomass, such as switchgrass, is made by burning the plants to make steam to turn an electricity turbine. That electricity could be used to charge up a plug-in electric car.

The starting point for the study is that there's a limit to the amount of land available for transportation energy without affecting food prices and impacting greenhouse gas emissions. The Environmental Protection Agency earlier this week proposed measuring greenhouse gases from biofuels to include changes in land use, a decision fiercely opposed by the ethanol industry.

"Our hope is just to bring this general point to the forefront: Maybe we should be thinking about how efficiently we use our land, and not just about what's the best way to do ethanol," study lead author Elliott Campbell, an engineering professor at the University of California at Merced, told MSNBC.

The study did a lifecycle analysis that accounts for both the energy produced by each technology--ethanol versus bioelectricity--and the amount of energy consumed in the production of vehicles. Working on the side of electricity was the fact that electric powertrains are far more efficient than internal combustion engines, Campbell said in a statement.

Liquid fuels have one clear advantage over electric vehicles in that refueling is far faster. Also, internal combustion engine cars can be converted relatively cheaply--estimated at about $100--to run both gasoline and ethanol.

"If the goal is to have more of those gallons come from renewable sources rather than imported oil, fuels like ethanol are the only technologies that are having an impact today," Matt Hartwig, a representative for the Renewable Fuels Association, an ethanol trade association, told Scientific American.

Although bioelectricity used in a plug-in vehicle was a clear winner over ethanol in terms of efficiency and greenhouse gases, the study's authors said they intended to open up a debate rather than make specific policy recommendations.

"We found that converting biomass to electricity rather than ethanol makes the most sense for two policy-relevant issues: transportation and climate," said co-author Chris Field, director of the Department of Global Ecology at the Carnegie Institution. "But we also need to compare these options for other issues like water consumption, air pollution, and economic costs."

From what I have read switchgrass grows wild on the prairie and requires no additional watering, or fertilizers. WIRED magazine has a good article on switchgrass, and its potential as a biofuel.

switchgrass for ethanol

In January, USDA researchers completed a five-year evaluation of another biofuel feedstock with the potential to make a serious dent in US petroleum usage. In the largest study to date, switchgrass has been shown to produce 540% more energy than was used to grow, harvest, and process it into cellulosic ethanol, while reducing greenhouse-gas (GHG) emissions by 94% when compared to gasoline.
USDA geneticist Ken Vogel commented that the study demonstrates switchgrass’s potential to be a major renewable biofuel that reduces GHGs and could “potentially displace 30 percent of current U.S. petroleum consumption.”

Key points from the study include:

Researchers don’t expect switchgrass to replace corn fields, but see crop development occurring on marginal, highly-erodible lands.
Ethanol yields on marginal land averaged 300 gallons per acre (corn-grain ethanol produces 350 gallons per acre).
Biomass left over after converting switchgrass into cellulosic ethanol could be used to provide energy for the distilling and biorefinery processes, further adding to the fuel’s net energy balance. Comparatively, corn-grain ethanol typically uses natural gas or other power sources for processing.
Experimental switchgrass strains currently undergoing testing could potentially produce 50% higher yields than those found in this study.
Six cellulosic ethanol refineries are currently being constructed in the US, with partial funding from the DOE.
For comparison: soybean-based biodiesel offers about a 320% energy return, and grain-based ethanol produces about 125% more energy than it uses. Neither of these have the potential to displace more than a small fraction of US petroleum usage.

The study was conducted by researchers at the University of Nebraska-Lincoln and took place in North and South Dakota, and Nebraska.