With alternative fuels increasingly important in the U.S. energy future, a team of researchers in California set out to answer a critical question: Which is a more efficient use of land—turning biomass crops into power for an electric vehicle, or turning them into ethanol to power a more conventional combustion engine?
What is the most efficient use of biofuels crops? Using crops to make ethanol produces less transportation and greenhouse gas offsets than converting the crops to electricity for electric vehicles. [Image courtesy of McDade and Campbell / UC Merced]View the full-size image 
The answer, reported in the 8 May issue of Science, is that biomass crops provide more "miles per acre" of cropland when converted into electricity than into ethanol.
Biomass crops, such as corn or switchgrass, are a potentially promising source of power for sustainable transportation. One option is to chemically convert biomass into ethanol, which could then replace or supplement conventional gasoline. Another possibility is to burn biomass to generate electricity for an electric vehicle.
A limited amount of land is available for growing biofuel crops, however, without impacting food prices or greenhouse gas emissions.
Elliot Campbell of the University of California, Merced, and colleagues have now estimated the demands on land use that these two approaches would make.
The researchers calculated that vehicles powered by bioelectricity would travel more miles, with respect to the area of cropland needed to produce the biofuel stock, than vehicles fueled by ethanol.
This difference held up when comparing a variety of vehicle types, feedstocks and energy conversion technologies, primarily due to the greater efficiency of electric engines over internal combustion engines.
Bioelectricity also offers more possibilities for reducing greenhouse gas emissions through measures such as carbon capture and sequestration, which could be implemented at biomass power stations but not for individual internal combustion vehicles, according to the authors.
Ultimately, decisions about which way to use biofuel crops also will need to consider a variety of other factors, such as impacts on regional water resources, battery toxicity and recycling, and economic constraints. But, the authors write in their study that their results do suggest that "alternative bioenergy pathways have large differences in how efficiently they use the limited available land to maximize transportation and climate benefits."