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

Transportations Role in Reducing U.S. Greenhouse Gas Emissions: Volume 2
mode operation is similar to that of HEVs, although in this case most vehicle energy
requirements are met by the electric battery while the ICE just provides intermittent
power boosts for high load events. Blended mode PHEV designs allow smaller, more
cost-effective battery designs while providing most of the benefits of range-extended
vehicles (Elgowainy et al., 2009).
There is in fact a continuum between conventional LDVs which rely solely on IC engines
for power, and fully battery electric vehicles (BEVs – see Section 2.9) which only utilize
battery power. Figure 3.3 illustrates how engine and battery size tradeoffs are
qualitatively associated with different vehicle categorizations. In the figure PHEVs are
classified as “range extenders” which permit a certain amount of all electrical operation.
Most of the literature on the topic defines the low end of range extension to be 10 miles for
PHEVs, or alternatively, defines a PHEV battery capacity to be five kW or greater.
Figure 3.3 Classification of Hybrid Vehicles by Onboard Electrical Power
Fraction of Driving Power (in Percent)
100%
90%
80%
70%
60%
50%
40%
30%
20%
10%
0%
Clear
Classification:
Conventional
Conventional
Source: UCS 2003.
Battery or Motor Size
Vehicle
Classification
Very Unclear
Engine Size
Hybrid
Mild Hybrid Full Hybrid Range Extender
Vehicle Classification by Driving Power Alone
Clear
Classification:
Range Extender
Battery
Electric
A PHEV’s impact on both fuel usage and GHG emissions also depends on the fraction of
travel occurring in the CD mode. Those LDVs that travel relatively short distances each
day may operate in the CD mode most or all of the time, while LDVs that regularly travel
greater distances on a daily basis will operate a good portion of their time in CS mode,
thereby diminishing the relative benefits of the PHEV system compared to standard
HEVs. Figure 3.4 shows the estimated national average “Utility Factor” for LDVs as a
function of AER. As seen in the figure, PHEVs with an AER of 30 miles are estimated to
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