At 05:32 PM 11/13/2007, Michael Elliott wrote...
>So, how important is the difference between 160 or 300 Watts of power
>going to the headlights when compared to 100,000 watts moving the van?

The point is valid, but some math is missing.

The useful BTU capacity of gasoline is reduced by the fact that engines
are very much less than 100% efficient, and there are also drivetrain
losses before any energy is used to move the car.

20% efficiency is in the ballpark, so we're talking about 20K Watts
actually being used. An A/C Vanagon has a maximum output of 67 HP, or
49 KW, and would  cruise at some fraction of that (1/3?) , so all of
those figures seem to be reasonable.

140 Watts of 12V power from the alternator is more than that from the
engine, because alternators, too, are not 100% efficient. 55% is a
reasonable ballpark, to that 140 W of DC takes ~250W of engine power.

250W / 20KW = 1.25%

If a Vanagon gets 20 MPG, then the savings would be about the same as
getting an extra 1/4 MPG.