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

Transportations Role in Reducing U.S. Greenhouse Gas Emissions: Volume 2
Cobenefits
Although PHEVs may not offer dramatic benefits with respect to life-cycle GHG emissions
relative to HEVs, they do provide an opportunity to significantly lessen the U.S.
dependence on petroleum, as well as the potential for reduced air pollution attributed to
mobile sources in urban areas (Kammen et al., 2008). Based on the assumed utility factors,
we assume a PHEV10 will reduce gasoline consumption by 23 percent, and a PHEV60 by
75 percent for a national average vehicle. The broad penetration of PHEVs into the LDV
market offers by far the largest potential for reduced gasoline consumption of any LDV
strategy evaluated in this section; only BEVs and fuel cell vehicles (Section 2.8 and
2.9) have the potential for greater reductions in LDV gasoline consumption.
In addition to the substantial fuel savings and associated energy security benefits
associated with PHEV use, sizable reductions in other pollutants may be realized.
However, PHEVs (and BEVs) present unique air quality considerations due to the split
location of emissions between stationary source power plants and mobile on-road
vehicles. On-road vehicles are subject to manufacturer emission certification
requirements, although actual end-use emissions can vary in both their grams per-mile
emission rates, as well as their total mass emissions, depending upon driver behavior,
maintenance levels, and total miles traveled. On the other hand, electric power plants are
subject to firm emissions caps, enforced by stringent monitoring requirements. In
addition, these emission caps are independent of electricity demand, so if demand
increases, emission intensity must decrease in order to meet the specified emission
limits. 34 The specific caps on NOx, SOx, and mercury emissions decrease over time, which
will further reduce their associated emission rates per kWh.
Because PHEVs can operate for limited ranges without creating create point-of-use
emissions and powerplants are often located in rural areas, their use can reduce air quality
problems in densely populated areas. On all-electric mode PHEVs also operate very
quietly and can reduce noise pollution. Another possible cobenefit of widespread use of
PHEV charging systems would come from the use of smart chargers. These chargers
could be remotely signaled to alter charge rates to perform load frequency control for the
grid power system. This could result in more efficient grid electric generation if
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widespread use was achieved. Finally, some of the battery technology advancement
34 Reliance on electricity generation for charging PHEVs and BEVs also changes the spatial
distribution of emissions, which can in turn have significant (usually favorable) impacts on ozone
formation and pollutant deposition patterns. See EPRI (2007b) for a detailed analysis of national
air quality impacts, as well as water impacts, associated with different vehicle charging scenarios.
35 Off-peak charging of large numbers of PHEVs using smart charges that communicate directly
with the grid will permit improved voltage and frequency regulation as well as some improved
management of “spinning reserves” at the system level. Fine tuning of PHEV charging times and
intensities is particularly helpful for the integration of renewable into the power grid, given the
variability of wind and solar power inputs (EPRI, 2009).
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