Electric and hybrid electric vehicles: A technology assessment based on a two-stage Delphi study Page: 51 of 164
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EV Range (km)
FIGURE 3.2 EV Battery Replacement Cost and Range Associated with the Mean Power
Requirements
hydride battery packs will weigh more (see Table 3.4) because of increases in the mean power
requirements.
Mean power requirements of 66.7, 86.1, and 99.2 kW and mean curb weights of 1,538,
1,351, and 1,222 kg for the three future years were obtained from the basic vehicle characteristics
responses. These numbers translate to 0.043, 0.064, and 0.081 kW/kg, compared with the current
desirable power-to-mass ratio of 0.074 kW/kg (0.045 hp/lb) for the conventional ICE. Cars had
average power-to-mass ratios of 0.053 kW/kg (0.032 hp/lb) in 1981 and 1982 (Heavenrich and
Hellman 1996). Individual models with even lower power-to-mass ratios were acceptable during the
past energy price shocks. For example, the 1982 four-door Chevrolet Chevette equipped with a diesel
engine had a power-to-mass ratio of 0.037 kW/kg (Automotive News 1982). Thus, although future
EVs appear to be underpowered through 2010, their power-to-mass ratios are not unrealistic.
Among the battery technologies that have replacement costs under 10 cents/km, lead-acid
is the least expensive, with very limited range, and lithium-polymer is the most expensive, but with
high range (see Figure 3.2). For a better balance between power and range, a combination battery
pack of lead-acid and lithium-polymer batteries is the best combination. Advances in battery
monitoring technology are predicted to make such mixing and matching of batteries feasible in
portable computing (McCormick 1996). We analyzed hypothetical combination battery packs, in
which both lead-acid and lithium-polymer batteries would power an EV in the year 2020. The cost
objective worked consistently, but power was low. We lowered the power requirement to 85 kW,
assuming that the better speed-torque relationship of an electric motor would not require as high a
power-to-mass ratio as an ICE. The results of the analysis are shown in Figure 3.3. Two curves,
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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/m1/51/: accessed May 7, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.