I think solar panels have pretty low amperage output (I'm not a solar expert) but maybe we could use this while driving around, using the suggested power supply, then switch it to solar power when the car is sitting with the engine off?
Maybe a panel would be enough to maintain a slightly lower temperature while we're at work?

http://www.electronickits.com/kit/complete/peltier/ck500.pdf

Make sure you read the whole article.
This seems to be right up our alley.

But there is no information on how long the project shown takes to cool down the air mass in the cooler.

Kind of funny though how the Aussies' used almost exactly the same size 'Esky/Cooler" as Compugeek!