Transportation's Role in Reducing U.S. Greenhouse Gas Emissions ...

Transportations Role in Reducing U.S. Greenhouse Gas Emissions: Volume 2
independent of AER. 27 An average future year efficiency value of 0.255 kWhr/mi is used
in this analysis, following EPRI (2007a).
The PHEV efficiency estimate is then combined with assumed CS mode operating
efficiencies (assumed to provide a 40 percent fuel consumption improvement relative to
base case conventional LDVs in 2030, consistent with future year HEV estimates) in order
to estimate fuel savings and emission reductions for all operation modes. The estimates
account for the relative miles traveled in CD and CS modes, considering the utility factors
associated with PHEV10 and PHEV60 scenarios. The GHG reduction percentages relative
to conventional vehicles are based on GREET outputs for CS (HEV) modes, and EPRI
estimates for the range of electricity generation intensities (EPRI, 2007a). Table 3.2R
summarizes the estimated GHG reductions for PHEV10s and PHEV60s.
Table 3.2I Percent GHG Reduction Range by AER and Time Period
3-48
28
Results for
PHEV40s, which may be considered a “most likely” future technology, would fall in
between these ranges.
Timeframe
CS Mode
(HEV-
Average)
CD Mode
(All AER)
PHEV10
(All Modes)
PHEV60
(All Modes)
Minimum Maximum Minimum Maximum Minimum Maximum
2030 40% 68% 80% 46% 49% 61% 70%
2050 40% 78% 87% 49% 51% 68% 75%
As seen in Table 3.2P, future year PHEVs offer substantial GHG reduction opportunities
beyond conventional vehicles, as well as HEVs. This conclusion is dependent upon a
continual decrease in the GHG intensity associated with electricity production over time,
as modeled by EPRI (2007a). Under these assumptions, the greater the miles traveled in
CD mode, the greater the GHG reduction.
In the absence of substantial improvements in electricity GHG intensity, the potential
GHG reductions for PHEVs become more comparable to HEVs. Figure 3.5 demonstrates
this general finding for a number of different PHEV fuel scenarios (gasoline, diesel,
biomass, fuel cell, etc.) and AERs. As such, under higher GHG intensity conditions,
27 While the increased battery mass associated with higher AER values tends to decrease vehicle
efficiency, this effect is countered by improved electric drive system performance (EPRI, 2007a).
28 Reductions are relative to a fleet average conventional gasoline vehicle (GREET basis). Note that
any advances in HEV efficiency over time are assumed to be approximately equal to
corresponding advances in conventional vehicle efficiency over time. Therefore the percentage
GHG reduction benefits provided by HEVs compared to conventional vehicles are assumed to be
constant across time periods.