Solar Drying
Removal of undesired moisture from a product using solar energy is known as solar drying. Many agricultural, horticultural and industrial products including chemicals and pharmaceuticals are dried for various purposes like safe storage, easy handling, value addition, further processing and quality improvement.
Solar drying: An eco-friendly concept:
" Solar energy can be used to heat air to temperatures needed for most drying applications. It is environment friendly, freely available and inexhaustible. "
	Solar energy absorbed in a solar air heater provides low grade heat and is good for drying purpose as it meets the requirement of high flow rate with adequate temperature rise.
	The intermittent nature of solar radiation will not affect the drying performance at low temperature. Energy stored in the product will help in removing excess moisture during short off sunshine periods.
	Solar energy in inexhaustible and non-polluting and is available free of cost at site. This saves transportation cost and other related problems associated with conventional fuels.
	The high capital cost of solar dryer can be compensated if the dryer is used for drying multiple products.

Principle of solar drying

Solar dryers make use of air heated through solar energy for drying products. Drying is basically a heat and mass transfer process in which the liquid water from the surface and inside the product is vaporized and the vapour removed by draft. Various factors affecting the drying process are relative humidity, temperature of the drying air, air flow rate and initial and final moisture content of the product. Once the surface moisture has been removed, further drying would depend upon the rate at which moisture from within the product diffuses to the outer surface.

Drying characteristics of some products

Many agricultural and chemical products have been dried using solar hot air dryer at SPRERI. Table below gives a list of such products along with their drying specifications. The main advantages of solar drying have been the retention of original colour and absence of any dirt or impurities. Solar dried products had marked physical difference when compared with same product dried in the traditional methods.