Solar drying is in practice since the ancient time for preservation of food and agriculture crops. The objective of most drying processes is to reduce the moisture content of the product to a specified value. Solar dryers used in agriculture for food and crop drying and industrial drying process can be proved to be most useful device from energy conservation point of view. It not only save energy but also save lot of time, occupying less area, improves quality of the product, makes the process more efficient and protects environment also. Solar dryerscircumvent some of the major disadvantages of classical drying; however using merely solar energy for drying application might cause some difficulties that must be overcome. These difficulties can be eliminated-aside from employing heat pumps and to consider a combination between heat pump technology and renewable solar energy. Solar assisted heat pump systems have been studied and used since the last decade in order to increase the quality of products where low temperature and well-controlled drying conditions are needed. Within this paper some investigations and developments on these are reviewed. The review shows that for heat sensitive materials improved quality control, reduced energy consumption, high coefficient of performance and high thermal efficiency of the dryer with solar assisted heat pump dryer can be achieved.
