FIGURE 4.17 GHG emissions for cases combining ICEV Efficiency Case and PHEV or HFCV vehicles at the Maximum Practical penetration rate with the EPRI/NRDC grid mix.

FIGURE 4.17 GHG emissions for cases combining ICEV Efficiency Case and PHEV or HFCV vehicles at the Maximum Practical penetration rate with the EPRI/NRDC grid mix.

depend on using lower carbon primary sources for electricity and hydrogen (see Appendix C).

For the first Portfolio Case, Figures 4.18 and 4.19 combine PHEVs at the Maximum Practical penetration rate with the Efficiency Case for the two grid mixes. For the EIA grid mix, there is very little difference in GHG emissions between the Efficiency Case, where no PHEVs are introduced, and the PHEV-10 and PHEV-40 cases. The benefit of PHEVs appears only when a lower carbon grid (the EPRI/NRDC grid mix) is used. This highlights the importance of low-carbon electricity for gaining the potential benefits of PHEVs. The HFCV case has significantly lower GHG emissions than either of the PHEV cases for a similar level of energy supply decarbonization. That is, well-to-tank carbon emissions for supplying hydrogen can be reduced by about two-thirds by 2050 (as in the 2008 Hydrogen Report), resulting in greater CO2 reduction than when the electricity carbon emissions (g CO2/kWh) are reduced by two-thirds by 2050 (as in the EPRI/NRDC grid case). This is true because HFCVs are somewhat more efficient than PHEVs on an energy per mile basis.16

Finally, the committee estimated GHG emissions for cases that combine efficiency, biofuels, and PHEVs or HFCVs for the two grid mixes (Figures 4.20 and 4.21). Again, the importance of a low-carbon grid is apparent for the PHEVs; the GHG emissions reduction in 2050 is about 55 percent for efficiency + biofuels, 59 percent (71 percent) for efficiency + biofuels + PHEV-10s (PHEV-40s), and 80 percent for efficiency + biofuels + HFCVs. With the

FIGURE 4.18 GHG emissions for cases combining ICEV Efficiency Case and PHEV or HFCV vehicles at the Maximum Practical penetration rate with the EIA grid mix.

FIGURE 4.18 GHG emissions for cases combining ICEV Efficiency Case and PHEV or HFCV vehicles at the Maximum Practical penetration rate with the EIA grid mix.

FIGURE 4.19 GHG emissions for cases combining the ICEV Efficiency Case and PHEV or HFCV vehicles for the EPRI/NRDC grid mix.

FIGURE 4.19 GHG emissions for cases combining the ICEV Efficiency Case and PHEV or HFCV vehicles for the EPRI/NRDC grid mix.

FIGURE 4.20 GHG emissions for scenarios combining ICEV Efficiency Case, Biofuels Case, and PHEVs or HFCVs for the EIA grid mix.

FIGURE 4.20 GHG emissions for scenarios combining ICEV Efficiency Case, Biofuels Case, and PHEVs or HFCVs for the EIA grid mix.

16

Furthermore, the facilities to generate hydrogen from coal or natural gas will be new and use a process that can be adapted relatively easily to carbon capture. Retrofitting an existing pulverized coal electric plant (about 50 percent of current U.S. generating capacity) with carbon capture will be very expensive.



The National Academies | 500 Fifth St. N.W. | Washington, D.C. 20001
Copyright © National Academy of Sciences. All rights reserved.
Terms of Use and Privacy Statement