OT: Hybrid cars

[Oleg Goldshmidt]

Oleg Goldshmidt <pub at goldshmidt.org> writes:

> Even if your car is a plug-in there are things to consider. Take a new
> Prius with an extended Li-ion battery with capacity of 4.4kWh. I pay
> ILS0.54/kWh at home, so at 80% efficiency a full charge will set you
> back about 3 shekels. At ILS8/l this is about 0.375l of 95 octane
> petrol. Thus, if you buy petrol instead of charging the battery, at
> 15km/l you will drive about 5.5km instead of 25km for the same money. A
> clear win for Prius. However, consider this: a Prius plug-in is *at
> least* ILS180K on the Toyota site, whereas a Corolla starts at
> ILS124K. That's 56,000 difference, equivalent to 7000l of 95 octane
> petrol (at 8 shekels/l). Let's download PDF catalogs with fuel
> consumption data from the site. To cover the 7000l of fuel equivalent of
> the price difference between a plug-in Prius (25.6km/l) and a Corolla
> (17.9km/l) you need to decide whether or not you believe the 25.6km/l
> figure (cf. [2] below). If you do, you'll break even after ~420,000km
> [7000/(1/17.9-1/25.6)]. Convert into years for yourself.

I suppose it is generally clear, but a limiting case is always
instructive.

Assume you buy a plug-in Prius and you *never* drive more than
25km/day. Also assume that you drive exctly 25km/day for 364 days a year
(excluding Yom Kippur), no faster than 45km/h, and fully recharge every
night. Therefore, you drive only on battery, and your fuel consumption
is 0. Assume also that you work for Hevrat Hahashmal and the electricity
is free. This is, obviously, the best possible case for a plug-in
hybrid.

Your "null hypothesis" is a car that gives you 17.9km/l (a petrol Toyota
Corolla or equvalent), that costs 56K less, the difference equivalent to
7000l of 95 petrol at today's high prices. At this level of fuel
consumption you need to drive 125,300km in your Prius to justify the
price difference. Since you drive 9100km/yr (25*364) it will take you
almost 14 years to break even. Again, this does not take into account
the TCO, or the interest that your 56K would earn over 14 years if
invested, or anything but the purchase price difference.

I cheated, of course: the 17.9km/l is a mixed city/highway number. For a
fair comparison under the assumptions above we need to take the city
consumption for the Corolla as well. A quick google yields a value of
9.6km/l for a 1.8L Corolla - that is almost twice as bad as the mix
value. We get 67,200km, or just under 7.5 years to justify a plug-in
Prius under our assumed - and extremely beneficial - conditions.

Please note that none of the above should be misconstrued as any kind of
put-down for Prius or hybrid cars in general - they are just overpriced
(IMHO). Plug in the real quotes for your own estimates, of course.
   
-- 
Oleg Goldshmidt | pub at goldshmidt.org