ENERGY ALTERNATIVES: RENEWABLE
ENERGY AND ENERGY CONSERVATION
TECHNOLOGIES
(b) Solar Dryers :
Of all the direct uses of solar energy, sun drying of crops
is perhaps the most ancient and widespread. Traditionally,
drying is done by spreading the products on the ground in the
open and exposing them to the sun. However, at the same time,
they are exposed to bad weather and insects. In order to
reduce the risk resulting from such hazards, solar dryers
have been designed, built and used extensively. The earlier
units were based on the "greenhouse effect". They reduced the
drying time, enhanced the quality of the products, and were
found particularly useful for products harvested in the wet
seasons. Solar dryers have also been used for timber and wood
drying. Generally,the principle of the solar dryer is to heat
air in a suitable solar collector and circulate it by natural
or forced means through the product to be dried. The solar
collector or air heater, as it is normally called, may be
external to or form an integral part of the dryer. Solar
dryers are particularly suited to small homesteads and
villages in developing countries, where they can play an
important role in crop preservation. As an added incentive,
the technology involved in the construction and operation of
a typical dryer is simple enough to be universally applied.
One attraction of solar dryers is that several designs can be
built by using mostly locally available materials. Further
research is required, however, with regard to materials
particularly, to ensure that the units last for more than ten
years. Perhaps, the main inhibitions to the use of solar
dryers have to do with lack of information and the
acceptability of dried products. The latter factor is of
great importance when the products are cash crops.