Radiative Cooling in the Sub-Saharan Desert

A new way of lowering temperatures without using electricity has recently been developed. Iterrae, a French company, has discovered a way of using radiative cooling, a phenomenon that takes place at night, when the Earth is cooled by the 0 K temperatures that can be found in outer space. A "Sahel granary", designed to keep grain cool, was constructed in Burkina Faso with the support of the UN and the World Bank. Radiative cooling is particularly perceptible on dry and clear night as air humidity acts as an insulant and the infrared radiation can transfer low temperatures more readily. In those conditions, the radiation can be absorbed by a black body, in this case black anodized aluminium. With outdoor temperatures of 28° C it is possible to obtain an indoor temperature of 10-15°C in a 100m3 volume and on a 130m2 surface area, the equivalent of 30-80 W/m2. This system could be very useful for the storage of harvests and food in poorer, desert areas lacking power networks. However, in order to shave off the effect of temperature peaks, Y. and P. Fayet, who invented the system, use expanded graphite filled with a phase-change material (PCM) such as an alkane or paraffin, in order to store the cooling energy gathered at night. This innovative system has a huge potential for free, environmentally friendly cooling in developing areas, but is still very costly to implement at this stage.