While corn-grain ethanol and biodiesel are the only biofuels to have been produced in commercial quantities in the U.S. to date, the study committee found much greater potential in biofuels made from lignocellulosic biomass -- which includes crop residues like wheat straw, switchgrass, whole trees, and wood waste. This "drop-in" fuel is designed to be a direct replacement for gasoline and could lead to large reductions in both petroleum use and greenhouse gas emissions; it can also be introduced without major changes in fuel delivery infrastructure or vehicles. The report finds that sufficient lignocellulosic biomass could be produced by 2050 to meet the goal of an 80 percent reduction in petroleum use when combined with highly efficient vehicles.
Vehicles powered by electricity will not emit any greenhouse gases, but the production of electricity and the additional load on the electric power grid are factors that must be considered. To the extent that fossil resources are used to generate electricity, the report says that the successful implementation of carbon capture and storage will be essential. These vehicles also rely on batteries, which are projected to drop steeply in price. However, the report says that limited range and long recharge times are likely to limit the use of all-electric vehicles mainly to local driving. Advanced battery technologies under development all face serious technical challenges.
When hydrogen is used as a fuel cell in electric vehicles, the only vehicle emission is water. However, varying amounts of greenhouse gases are emitted during hydrogen production, and the low-greenhouse gas methods of making hydrogen are more expensive and will need further development to become competitive. Hydrogen fuel cell vehicles could become less costly than the advanced internal combustion engine vehicles of 2050. Fuel cell vehicles are not subject to the limitations
|Contact: Lorin Hancock|
National Academy of Sciences