The transformation of grapes into raisins started in the Middle East in ancient times. They were later traded in the Mediterranean Sea by the Phoenicians, Romans and Greeks. Nowadays, raisins
have a large applicability in a wide range of products such as breakfast cereals, dairy, bakery and confectionery products and nutritional bars. They may be produced in tunnel dehydrators or
by using solar energy, which are the most applied methods worldwide. Producing raisins using solar energy is a contribution to the increasing society demand on renewable energies for a sustainable world. There are two methods of using solar energy for crop drying: sun and solar drying. Sun drying comprehends the direct exposure of products to the sun. The products are placed on the ground in the open air and their temperature is raised by direct absorption of incident radiation. In solar drying, the solar energy is captured by some process to rise the temperature of the drying air (Fuller, 1993) and air flows through the product by
natural or forced convection (Ratti and Mujumdar, 1996). In general, both methods involve high labour costs and solar drying also requires a higher equipment investment. Nevertheless, solar
drying has some advantages: it is more hygienic, because products are protected from dust, insects and rodents, and products spoilage by moulds is prevented, since products are also protected from the rain