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

Transportation’s Role in Reducing U.S. Greenhouse Gas Emissions: Volume 2
charging techniques can reduce this time significantly (Burke et al., 2007). Electric
passenger cars are becoming more attractive with the advancement of new battery
technologies that have higher power and energy density than previous prototypes (i.e.,
greater possible acceleration and more range with less battery mass). Currently, nickelmetal
hydride (NiMH) batteries and lithium-ion (Li-ion) batteries are the best options for
BEVs and PHEVs. NiMH dominates the current market, although Li-ion batteries may
gain market share over time, as discussed in Section 3.2.4.
With the advent of California’s Zero Emission Vehicle (ZEV) mandate, an initial attempt
was made to develop BEVs for mass market purchases. However, less than 5,000 BEVs
were produced across a handful of makes and models before the ZEV requirements were
relaxed. For reasons that are still subject to debate, vehicle production was not sustained
in the absence of mandates, ceasing by 2003 in the United States. Today, BEVs are not
available except in niche markets such as neighborhood electric vehicles, with a maximum
speed of 25 mph. (Burke et al., 2007)
Current BEV designs are primarily for LDVs, with estimated ranges typically between 50
and 200 miles between charges (Burke et al., 2007). Like hybrid vehicles, BEVs can
recapture some energy by regenerative braking, which can extend operating range to some
extent. With additional developments in battery technology BEV range is expected to
increase. Beyond a certain point, however, BEV range eventually reaches a point of
diminishing returns, as increased battery weight decreases overall vehicle efficiency.
Increased battery capacity also increases vehicle costs dramatically. For example, doubling
BEV range from 200 to 400 miles might result in battery size and cost increases of 130
percent to compensate for the associated weight increase (Kromer and Heywood, 2007).
Considering these factors, one recent study concluded that an upper bound of about 200
miles between charges was a reasonable limit on commercial BEV range for mainstream
LDVs in the long run (Bandivadekar et al., 2008), although unforeseen technological
advances could change this conclusion.
The electrical energy used to charge a BEV battery can be generated by any source,
including renewable, nuclear, natural gas, coal, and petroleum. As such, the resulting
GHG emissions per mile associated with BEV operation can vary drastically from region to
region and by time of day and year. (See Section 3.2.4 for a discussion of life-cycle GHG
emissions associated with battery charging for PHEV operation.) Some BEV designs
employ on-board chargers, which allow the battery to be charged directly from a standard
120 V wall outlet. Other designs require the purchase of an off-board charging unit.
While the power source for BEVs is readily available, there is a need to develop a publicly
accessible charging infrastructure allowing BEVs to be charged away from users’ homes.
Public access recharging could substantially extend a BEV’s daily range, depending upon
trip lengths and available charge time. As of June 2009 there were 451 charging stations in
the United States, with almost all of these located in California (U.S. DOE, 2009b).
BEVs also will be available for a limited portion of the heavy-duty vehicle segment in the
near future. One opportunity lies with short-haul drayage trucks that move cargo
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