[downx3]

You could use solar water heating as a vector to trap the suns heat in an underground heat store, that you then release at night. How cold does it get?

Edit:

I just tried to find out about night time temperatures. On the wikipedia page 'desert', it suggests it only gets as cold as 0 degrees C. Although I did find a remark that Antarctica was technically a desert.

I just camped out in temperatures below 0 weekend gone, and it wasn't that comfortable, but I was staying under a thin piece of plastic. If I'd have been a bit better prepared it would have been much more bearable.

[dalke]

There are hot deserts and cold deserts. The Gobi has a yearly average temperature of 2.8 °C, with a January average of −26.5 °C and July of 17.5 °C . Red Desert, Wyoming averages -7°C in January.

My relatives in Michigan mentioned that there's a Polar Bear scouting award for camping when it's below 0°F, or -18°C. My own sleeping bag is only rated for -2°C.

[downx3]

I must add then that it was just below 0 degrees C! Don't fancy minus eighteen at all.