demand and greenhouse gas emissions (measured as equivalent CO2 of all greenhouse gas emissions over the fuel cycle) sooner than the Hydrogen Success case, if cellulosic ethanol comes online by 2010 and grows aggressively thereafter. As with Case 2 (ICEV) efficiency improvements, however, the rate of growth in benefits from biofuels implementation begins to slow toward the end of the analysis period. In 2030-2040, the Hydrogen Success case has the potential to provide greater reductions and, by 2040, delivers two to three times the reductions in oil use and CO2 emissions as the aggressive biofuels scenario.

Chapter 6 also presents the results of several additional cases involving combinations of alternative technologies. Although these scenarios give quantitative results different from those shown here, the qualitative conclusion is similar—that is, alternative technologies can deliver significant oil use and CO2 emission reduction benefits earlier than HFCVs, but the largest sustained longer-term benefits are achieved using hydrogen fuel cell vehicles.


CONCLUSION 14: 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.

BENEFITS OF A PORTFOLIO APPROACH

Based on a comparison of the three scenarios in Figure S.5, the committee concluded that no single approach is likely to deliver both significant midterm and long-term reductions in oil demand and greenhouse gas emissions. Thus, conventional and hybrid vehicle technology, biofuels, and HFCVs should be considered not as competitors over the next few decades, but as part of a portfolio of options with a potential to deliver significant energy security and environmental benefits across a variety of time horizons. Other technologies not analyzed in this study, such as plug-in hybrids, battery electric vehicles, and other types of internal combustion engines, also should be examined as potential candidates for this portfolio. As in other domains, a portfolio of technology options is most likely to improve the chances of success while reducing the risks in the event that any one option fails to deliver on its promise.

Because advanced conventional vehicles, hybrid vehicles, and biofuels can deliver benefits in a shorter time frame, they may be able to more quickly reduce the potential impacts of climate change and reliance on oil imports, while also providing the time needed to further develop and commercialize hydrogen-based fuel cell technologies. Also, should the impacts of climate change or oil shocks mobilize an aggressive policy response, acceleration of HFCVs into the market could provide a path toward a zero-petroleum and potentially low-carbon option that can persist beyond the large, but eventually limited, potential of vehicle efficiency and biofuels alone.

To explore the value of a portfolio approach, the committee constructed Case 4 (Portfolio), which combines all three options of vehicle efficiency, biofuels, and HFCVs (see Chapter 6). Compared to the reference baseline scenario, the results showed that this portfolio of options has the potential to nearly eliminate oil demand from light-duty vehicles by the middle of the century, while reducing greenhouse gas emissions by almost a factor of 10 relative to the assumed baseline case (Figure S.6). Achieving this potential is likely to require a portfolio approach that takes advantage of the synergies among these technologies. For example, many of the technologies needed to improve the fuel economy of conventional vehicles, including weight reduction, improved aerodynamics, lower rolling resistance, and low accessories loads, also will be essential for fuel cell vehicles to reach the

FIGURE S.6 Impact of combining the potential of HFCVs with advanced conventional vehicles, hybrid vehicles, and biofuels in a portfolio approach—Case 4: (Left) annual gasoline use and (right) annual greenhouse gas emissions.



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