The Pot-in-pot refrigerator

The Pot-in-pot refrigerator is a easy to built, zero energy cooling solution.
All you need is two clay pots of different diameter, sand, water and some cloth.
A link on Mohammed Bah Abba who brought this solution to my attention.
And a wikipedia link on the subject.
1st Important note: It works only in dry climate – the more humid the air – the lesser it cools.
2nd Important note: It is not zero engergy – you just don´t electricity.

How to build a pot-in-pot refrigerator