Almost two billion people live without a reliable source of electricity, but they may not have to live without refrigeration.

In a simple, rugged twist on the gas-fired refrigerator, a prototype gadget uses heat from fire to create a cheap source of cooling.

The cylindrical device, 10 centimeters in diameter and 20 centimeters long, has a chamber on each end – one made of steel and the other of aluminum. The chambers are separated by a ceramic insulator fitted with two valves.

To charge the unit, a user places its steel side on a fire for 30 minutes. A liquid coolant in the steel chamber turns into gas and passes through a one-way valve into the aluminum chamber. After removing the device from the fire, the user lets it sit to allow the gas to condense, then inverts it and slides the aluminum end into a 38-liter ceramic food-storage pot.

The coolant chills the food by absorbing heat and moving as a gas through the second valve – which opens when the device is inverted – back to the steel chamber.

The device can keep food cooled to 4 degrees C for 24 hours.

A prototype was demonstrated in 2005 by an industrial designer, William Crawford, at London’s Royal College of Art. He says it could be built for as little as $18 per unit.