Electric and hybrid electric vehicles: A technology assessment based on a two-stage Delphi study Page: 13 of 164
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conventional or alternative fuel engine once the energy in the batteries has been depleted.
Alternatively, an HEV may be designed to run exclusively on onboard electricity, generated through
an engine, without ever using energy from the electric grid. Even so, with an adequately large battery
pack, such an HEV could be operated in such a way that morning emissions, which undergo the
longest photochemical reaction, are significantly reduced. The extent of emissions from an HEV will
depend upon its design and the types of fuel and engine used. Many combinations are possible.
Environmental benefits of electric vehicles arise from zero tailpipe emissions, as well as
other more complicated and less obvious emissions changes. EVs represent a potential solution to
urban ozone problems created in part by gasoline- and diesel-powered vehicles. When emissions
from electric power plants are accounted for, electric vehicles not only shift emissions from vehicles
to remote places, they also change the composition and timing of emissions. While nearly
eliminating carbon monoxide and hydrocarbon emissions, their use may also decrease the emissions
of oxides of nitrogen, depending upon the type of power plants supplying electricity (Sperling 1995;
Wang and Santini 1993; Wang et al. 1990). The emissions of two criteria pollutants, sulfur oxides
and particulates, have been estimated to increase on average in the United States, largely due to coal-
fired power plants. However, these increased emissions usually will be at power plants that are
outside the urban areas, and their estimated magnitudes are small compared to the overall emissions
from these two pollutants.
Use of electric vehicles will not simply shift emissions from urban areas to the places where
power plants are located. Significant "per vehicle" reduction in "full fuel cycle" emissions will also
be obtained for most pollutants, sometimes for nearly all pollutants. The latter opportunity occurs
because many urban areas obtain their electricity from hydro-, nuclear-, or natural-gas-powered
generating plants that emit very low quantities of criteria pollutants. Also, most of the electric
vehicles are likely to be recharged at night. Thus, the contribution of sunlight in the chemistry of
pollution formation - especially for ozone - can be reduced drastically. To date, the nature of
these changes has not been carefully studied.
Energy benefits of electric vehicles are in reduced petroleum consumption due to
substitution and increased efficiency of the electric drive systems. Electric drive systems have very
high efficiency, they do not consume energy in idling, and they can be designed to employ
regenerative braking to capture the energy usually lost in braking. These advantages are pronounced
in urban driving involving repeated braking and idling, but relatively small in highway driving. In
urban driving conditions, HEVs also have the potential to be significantly more efficient than
gasoline internal combustion engines (ICEs), even when the HEV engine is fueled by gasoline and
power from the electric grid is not used (Siegel and Mendler 1996). When power both from the
electric grid and the engine is used, the potential to reduce petroleum consumption is significant.
Greenhouse gas benefits of electric vehicles can be highly dependent on the type of primary
energy used in generating electricity. Most of the existing fossil-fuel-burning electricity-generating
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Vyas, A. D.; Ng, H. K.; Santini, D. J. & Anderson, J. L. Electric and hybrid electric vehicles: A technology assessment based on a two-stage Delphi study, report, December 1, 1997; Illinois. (https://digital.library.unt.edu/ark:/67531/metadc708199/m1/13/: accessed May 7, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.