EDIT: Oct 31/06 by metrompg: split these posts from the thread Alternator v. no alternator - 10% gain @ 70 km/h , since there is some potentially good info in here.
If you want some cheep solar panels visit your local VW dealer and ask for the panels that come with the new cars - they throw them away - suction cup mount to the windshield and put out 200-250ma - I have a stack of them. I also inquired yesterday on pricing for the SunPower cells and panels. $9 per cell quantity 50 pricing was what I got a few years ago and each cell puts out 3 watts 5.5 amps peak sun at .65 volts. You need high efficiency when you want to power up a car electrical system since sunlight surface it minimal.
Also note that not all cig plugs are connected to the battery when the key is off so charging there will not do much other than power up any accessories that are connected to the same circuit with the output of the panel, which under no load can reach 24 volts POOF! Both my Scion and 94Geo are on/off with the key.
JanGeo 
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