[poultrygeist]

I think the power you'd get from a solar panel or even a car battery, wouldn't be enough to kick out any real heat.

they seem to be used more for low power lighting which is in the region of a few watts.
You'd need hundreds of watts to keep anywhere warm.

Unless it's for frost protection in a small space only.

Rob

[jaap]

I probably needed Poultrygeist to tell me it is not possible to take this idea further! I have now found a link which explains about a heat storage system which makes real sense, I will investigate more....
check out:
http://www.reuk.co.uk/Solar-Greenhouse-Heat-Sink.htm

But you might be right, it might not get me further then frost protection.