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Solar dryer is another technology to harness the solar energy that is used to dry fruits, vegetables, and crops for preservation. Solar dryers are of two types: direct and indirect. In direct solar dryers, the substance that is to be dehydrated is exposed to the sunlight in a vast field. Indirect solar dryers consist of an insulated box coated inside with a black absorption surface, an air inlet and an air outlet, and a single- or double-glazed glass.

A solar dryer works on the principle of the density differential.

The inlet air hole is at the lower side for the entrance of the cold air and the outlet air is at the upper side of the opposite wall. The sunlight coming through the glazing keeps the inner environment warm, which dehydrates the substance. The cold air takes the hot air enriched with moisture content from the box and, because of the difference in the density, the air is ventilated through the hot air outlet.