Mohammed Bah Abba is from northern Nigerian. He won the 2001 Rolex Awards for Enterprise for his invention of a simple cooling system that can help preserve food in rural areas where there is no electricity. Eggplants stay fresh for 27 days, instead of the usual three. Tomatoes and peppers last for up to three weeks. The Pot-in-Pot system works by putting a smaller clay pot inside a larger one. The two are separated by constantly moist sand. Evaporation causes a cooling affect in the inner pot.
At a recent SEED workshop in Malaysia we decided to try this for ourselves. We also replicated the experiment later with different pots.