Chris Gupta of New Media Explorer reports:
This is Mohammed Bah Abba's Pot-in-pot invention. In northern Nigeria, where Mohammed is from, over 90% of the villages have no electricity. His invention, which he won a Rolex Award for (and $100,000), is 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.