. "6 Hydrogen and Alternative Technologies for Reduction of U.S. Oil Use and CO2 Emissions." Transitions to Alternative Transportation Technologies--A Focus on Hydrogen. Washington, DC: The National Academies Press, 2008.
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Transitions to Alternative Transportation Technologies — A Focus on Hydrogen
TABLE 6.7 Assumed Greenhouse Gas Emissions per Unit of Fuel Consumed
Greenhouse Gas Content of Fuels(g CO2 equivalent/MJ fuel used LHV basis)
90 (AEO 2007 projections to 2030 show this staying approximately constant)
Hydrogen from on-site reformation
100 (TIAX, 2007)
Hydrogen from coal with CCS, pipeline delivery
16 (92% CO2 capture rate, assuming U.S. electricity mix)
0 (100% CO2 capture rate, assuming zero-carbon electricity is used for CO2 compression) (adapted from Ruether et al., 2005). Coal mining, transport, and plant and mine construction emissions are estimated to be about 3.8 g CO2 eq/MJ H2, but this is counterbalanced by GHG savings of about 4.3 g CO2 eq/MJ, due to exported electricity from the plant)
Hydrogen from biomass, pipeline delivery
10 (TIAX, 2007)
Hydrogen from electrolysis using zero-carbon electricity (wind, hydro, solar)
Ethanol from corn
70 (22% reduction relative to gasoline)
Ethanol from cellulose
13 (85% reduction relative to gasoline)
SOURCES: Ruether et al. (2005); TIAX (2007).
2025 is likely to be very low carbon in these scenarios (70 percent biomass hydrogen or coal hydrogen with CCS).
Case 1 (Hydrogen Success)
Figure 6.15 estimates gasoline consumption for the Hydrogen Success case and the reference case. Oil displacement is about 0.8 percent in 2020, rising to 24 percent in 2035 and 69 percent in 2050. Although it takes several decades for hydrogen’s impact to be seen, beyond 2025 it enables growing reductions in both greenhouse gas emissions per year and annual oil use. Hydrogen may be important to achieve long-term stabilization goals requiring deep cuts in carbon or oil use. Figures 6.15 and 6.16 show a dip in the reference case after about 2020. This occurs even though the increase in fuel economy of new cars levels off because the entire on-road fleet fuel economy increases as new efficient vehicles replace older vehicles.
FIGURE 6.14 Greenhouse gas emissions from hydrogen supply over time.
FIGURE 6.15 Case 1 gasoline consumption relative to the reference case.
FIGURE 6.16 Case 1 greenhouse gas emissions relative to the reference case.
Greenhouse Gas Reductions
Figure 6.16 shows the committee’s estimate of the reductions in greenhouse gas emissions for Case 1 (Hydrogen Success) relative to a reference case, where no hydrogen technologies are introduced. Greenhouse gas emissions per