A Nigerian teacher and Ashoka fellow, Mohammed Bah Abba has invented an earthenware refrigeration system for preserving perishables in arid climates. Because the system preserves food, families that have used them have seen a drop in disease and an increase in income. The pot-in-pot is simple, affordable, and made from local materials, and so can be introduced throughout Nigeria and West Africa.
One clay pot is filled with wet sand, which must be kept moist. Into this sand bed is placed a second smaller pot, which is then covered with a damp cloth. The water in the sand evaporates, causing a drop in temperature, and cooling the inner pot.