Agricultural and other products have been dried by the sun and wind in the open air for thousands of years. In industrialised regions and sectors, open air-drying has now been largely replaced by mechanised dryers, with boilers to heat incoming air, and fans to force it through at a high rate. Mechanised drying is faster than open-air drying and uses much less land giving a better quality product. But the equipment is expensive and requires substantial quantities of fuel or electricity to operate.
Solar drying refers to methods of using the sun's energy for drying, but excludes open air sun drying. The justification for solar dryers is that they may be more effective than sun drying, but have lower operating costs than mechanised dryers. A number of designs are proven technically and while are yet in widespread use, there is still optimism about their potential. The choice between alternative types of solar dryer will depend on local requirements and in particular on the scale of operation.
