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[Foxpaw]

I agree with you on the latent heat of fusion there (the phase change thing) but the specific heat capacity of wax isn't all that high, is it? Water seems to me to be the ideal material because of it's extremely high specific heat capacity. However, it is possible that the latent heat of fusion on the wax would be great enough to overcome this.

[Fjord]

Originally Posted by Foxpaw

However, it is possible that the latent heat of fusion on the wax would be great enough to overcome this.

Yep, that's the idea. The other big one is certain salts, like these people make. It's all pretty debatable though. Wax doesn't conduct heat well, so you need lots of surface area. Salts are usually corrosive, or they seperate. And obviously they aren't cheaper than water.

[brpeterson]

I dont know a lot about batteries, but what if you had some nice NiCad or NiMh battery, put that in an insulated container, had a solar panel with a small element to keep the battery warm, and a timer? Any thoughts on that? The set-up would be charged by the car when running. I think that NiMh's can be charged for short times and dont have much of a memory effect, so that may be a good choice, just like the 144v. What do you all think? Any ideas on what kind of timer could be used? Thanks