Mohammed Bah Abba made a really cool invention, which won a Rolex Award of $100,000 –a refrigerator than runs without electricity. Here's how it works. You take a smaller pot and put it inside a larger pot. Fill the space in between them with wet sand, and cover the top with a wet cloth. When the water evaporates, it pulls the heat out with it, making the inside cold. It's a natural, cheap, easy-to-make refrigerator.
Evaporative fridges are a relatively well-tested, proven, low-tech approach to cooling. They can cool produce, food and beverages at about 15-20 C below ambient temperatures. They are most appropriate in hot, dry (not humid) climates
http://www.off-grid.net/2008/05/24/low-energy-refrigeration/
