I do not have strong credentials to address this group, but there is
an issue on my mind that may be worth discussing here. Probably we
can all agree on the following points: (1) HEVs with small traction
batteries (Toyota, Honda, etc.) substantially reduce gasoline
consumption and CO2 emission. (2) PHEVs (such as are under active
consideration here) would provide an additional substantial
improvement. (3) For the moment at least, suitable traction
batteries are expensive and of limited availability.

My assumptions are that: (1) conventional ICE-only vehicles achieve
30 mpg, (2) HEVs with their modern transmissions, electronic control
systems, and a "unit traction battery" achieve 50 mpg, and (3) PHEVs
with similar systems and a number of "unit traction batteries"
achieve 150 mpg in their overall driving cycle. These values are
chosen to make a particular point, and are not meant to be definitive.

If vehicles travel 12,000 miles/year and gasoline casts $2.50/gallon,
each HEV saves 160 gallons of gasoline, 3200 pounds CO2 emissions,
and $400, compared to the ICE vehicle. Each PHEV saves the same
amounts, compared to the HEV. But, finally making my point, it does
not do so with one additional "unit traction battery". The PHEV
requires several additional betteries. Experts here would know
better than I, but I suppose that the number would be at least three
additional.

Based on the initial assumption that such batteries are in limited
supply, I argue that they will do more to reduce gasoline consumption
and CO2 production if deployed singly in HEVs, rather than multiply
in a correspondingly smaller number of PHEVs.

I do not argue this to oppose active research into PHEVs, advanced
battery technology, or anything of the sort. I fully appreciate that
PHEVs operating in polluted urban environments would offer important
advantages compared to HEVs. Rather, that HEVs appear at present to
be more efficient in reducing fuel consumption and CO2 emission, per
battery, than PHEVs would be.

Ideally, HEVs will be manufactured as rapidly as possible, AND be
designed with the potential to be converted into PHEVs when the cost
and supply bottlenecks of suitable batteries eases.

To simplify matters, I have ignored related issues of the cost and
potential CO2 emissions of the "external" electricity required for
PHEVs, and any difficulty in externally recharging the batteries.
My point is that HEVs appear to be a more "battery-efficient" way to
go, even without considering those issues.

DAS