My very unscientific experience has been this (keep in mind this is usyally 80 degrees or above weather):  1 battery lasts 24 to 36 hours. I have the fridge set on 5 and usually have the freezer full of ice pops for the kids too.   I have 2 group 42 deep cycles so I can usually camp for a regular or 3 day weekend just on batteries. I have 80 watts of solar. Cheap panels from eBay, probably $130 for the 30 watt and $170 for the 50 watt.   If it's sunny, and I rotate the panels with the sun, I can go indefinielty on solar.  As soon as it's cloudy the panels are worthless and the batteries start to drain.  Having 150 watts of solar would probably be best.
 
Sooo, on a long sunny trip my beer is 100% cooled by solar power. That is technology at it's pinnacle.
 
Bryan
 
> Date: Wed, 20 Oct 2010 08:03:37 -0600
> From: jones@COLORADO.EDU
> Subject: Power consumption & recharging with Vitrifrigo
> To: vanagon@GERRY.VANAGON.COM
> 
> I ran a test on power consumption of the Vitrifrigo
> and measured the alternator's capacity for recharging.
> Then I looked at solar PV capabilities today to decide
> if solar was right for the way I camp. This information
> might be of use to others, so I put it up:
> 
> http://jones.colorado.edu/VW/Vitrifrigo/VitrifrigoBatteryTest.txt
> 
> http://jones.colorado.edu/VW/ChargingAuxBatteries.txt
> 
> One other factoid: a Vitri tech specialist pointed out that
> the fridge needs certain power. Power = V x A. If the
> wiring to the fridge limits V, then A will be higher than
> their spec. Yes, I confirmed this with my initial wiring. ;-)
> 
> Richard