19 – SOLAR DRIERS

Publisher Summary This chapter discusses the wide variety of solar driers. Natural open-air driers are very simple constructions. The material to be dried is placed outdoors on a tray, a rack, or the floor, and is dried by ambient sunshine and wind. Some of these driers can have a fixed or movable roof to protect the crop against rain. In direct solar driers, the material to be dried is placed in a transparent enclosure of glass or plastic. The sun heats the material to be dried and the enclosure causes a heat buildup because of the greenhouse effect. Sometimes ventilation through the enclosure is introduced through vents or chimneys. Hybrid systems are solar driers in which another energy source, such as a fossil or biomass fuel or electricity is used to supplement solar energy in the drying process. Open-air coffee drying is employed worldwide mainly on small-scale holdings as it is generally regarded as the cheapest method of drying coffee beans. During the day, the beans are exposed to the sun, whereas at night and during rainy periods, the trays containing the beans are covered over.