Historical Review and Recent Trends in Solar Drying Systems

The application of solar drying technology in agricultural area to preserve vegetables, fruits, and other crops has proved to be practical, economical, and eco-friendly. In this communication, a comprehensive review of the various designs, details of construction, and operational principles of many practically realized designs of solar energy drying systems is presented. Solar drying system is used to dry crops extensively in many countries. It improves the quality of product, minimizes waste, and employs renewable energy sources. However, availability of suitable information is missing in many of the countries where solar drying systems are most needed. Such systems are available in varied range of sizes and designs and are used for drying various foods and agricultural products. At present, there are various types of dryers that are available to suit the needs of farmers, food, and grain distributors. Therefore, the selection of dryers for a particular situation is largely based on what is available and the types of dryers currently used are widely based on available circumstances. A synthesis view of classification of solar energy dryers is presented. Two groups of solar energy dryers can be identified, viz., passive or natural-circulation solar energy dryers and active or forced convection solar energy dryers. The appropriateness of each design type for application by farmers in developing countries is discussed. Some recent developments in solar drying technology are also discussed.