Biofuels offer the potential to reduce oil imports because they can replace a fraction of the liquid fuels needed for U.S. light-duty vehicle transportation. They can also reduce CO2 emissions because they use carbon that was captured by plants in their last growth cycle, not carbon stored during previous millennia, and the repeated growth cycles recapture the CO2 emitted during combustion of the fuel. Biofuels from different sources will have a different impact on oil imports and on net CO2 emissions.

Grain ethanol has a 20 to 25 percent energy gain over the fossil fuel inputs used for its production and, on average, reduces CO2 emissions by 18 to 25 percent over the use of gasoline on an energy-equivalent basis. Grain ethanol production is fully commercial but is constrained by grain availability because it competes with the use of grains for food and animal feed.

Much more biomass is available from non-grain sources. The technology for cellulosic ethanol has not yet been demonstrated for commercial production. It should be significantly better than grain ethanol with respect to CO2 emission reductions because plant lignin and other plant residues can be used to supply the needed manufacturing process heat, reducing the use of fossil fuels. The key issues for cellulosic ethanol are commercial readiness, economics, and sustainability of biomass production including maintenance or improvement of soil productivity.

Biomass gasification is technically feasible, and many components have been commercially demonstrated. If the CO2 produced in gasification were captured and sequestered, biomass gasification would have a negative CO2 emissions balance. Economics will be the primary issue with biomass gasification, as it is with cellulosic ethanol, but it currently appears to be more competitive and closer to commercial reality. For a given amount of biomass, the thermochemical routes will produce roughly the same amount of biofuels on an energy-equivalent basis as the biochemical routes. A potential route to biofuels is through the use of algae, either as a source of cellulose or as a means to produce hydrocarbons. These routes have yet to be demonstrated above the pilot scale.

Biodiesel production from plant and animal oils is fully commercial, and the technology is considered mature. The production cost is mainly in the plant oil cost and remains uncompetitively high.

Therefore, biofuels offer significant potential to reduce CO2 emissions from oil use by the U.S. light-duty vehicle fleet. The extent of these reductions is highly dependent on the biofuel source. Grain-based ethanol and biodiesel are severely limited by grain availability and cost. Non-grain biomass offers a large new source of biofuels, but cellulosic ethanol technology is not commercially ready and gasification routes to biofuels require commercial demonstration. Either or both of these routes could greatly expand biofuels production. However, their availability and commercial tim States will be able to meet the biofuels target of 35 billion gallons per year by 2017.


CONCLUSION: The committee’s analysis indicates that at least two alternatives to HFCVs—advanced conventional vehicles and biofuels—have the potential to provide significant reductions in projected oil imports and CO2emissions. However, the rate of growth of benefits from each of these two measures slows after two or three decades, while the growth rate of projected benefits from fuel cell vehicles is still increasing. The deepest cuts in oil use and CO2emissions after about 2040 would come from hydrogen. See Chapter 6.


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