Q4Power Generation Sources
Question
Q.4. Describe principle of operation of solar dryers.
Answer
A solar dryer uses solar-heated air, circulated by natural or forced convection through a drying chamber, to remove moisture from agricultural produce, offering faster and more hygienic drying than open-sun drying.
A solar dryer removes moisture from agricultural, food or other products using solar thermal energy in a controlled manner, as an improvement over traditional open-sun drying. It typically has two main sections: a solar air heater (collector), where ambient air passes over or under a blackened absorber plate under a glass/transparent cover and gets heated by absorbed solar radiation, and a drying chamber, where trays of the product to be dried are placed and the heated air is passed through or over them, carrying away the moisture evaporated from the produce.
In natural-convection (passive) solar dryers, air movement is driven purely by the buoyancy of heated air (chimney effect) without any fan; in forced-convection (active) solar dryers, a small electric or solar-PV-powered fan pushes air through the system, giving faster, more controlled and uniform drying independent of ambient wind conditions.
Because the product is enclosed and shielded from dust, insects, rain and direct UV exposure (unlike open-sun drying), solar dryers produce a more hygienic, higher-quality, faster-dried product with reduced spoilage and nutrient loss, and are widely used for drying fruits, vegetables, spices, fish and grains, particularly benefiting rural and small-scale food processing.