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.