The pot-in-pot refrigerator or zeer pot is an invention which cools food without electricity. It's a new invention revolutionalizing food storage for sellers in African countries and elsewhere.
It was invented by Mohammed Bah Abba, a Nigerian teacher from a family of pot-makers. It is so simple and clever.
You insert a clay pot within a larger clay pot and add wet sand between them. The evaporation process lowers temperature of inner pot. So food vendors can keep food preserved and cool in markets throughout the world without electricity.
guavas can be kept for 20 days, compared to just two without. The evaporation of the outer liquid draws heat from the inner pot. The temperature in inner pot can be 10 degrees or more lower than outside. It works best with a slight breeze, and with lower humidity.