Abstract :
Drying of medicinal herbs should take place as soon as possible after harvesting; otherwise insects and fungi, which thrive in most
conditions, render them unusable. Conventional drying methods such as open sun drying and conventional-fuel dryers are not suitable;
since they may yield a less quality product and/or may increase the drying cost and/or time. Moreover, they may not be reliable and
environmentally safe. Therefore, the trend is toward using controlled-nonconventional drying methods, to improve the quality of the
product to be dried and at the same time to decrease the drying cost and time. These methods use renewable energy sources for their
operation, which are highly recommendable. This work proposes and develops a new controlled drying method; which uses a solar collector
and a bio-gas fuel to heat the drying air, and a stand-alone photovoltaic (PV) system to feed the electrical load of the dryer. The
designed control technique ensures correct and continuous operation of the dryer’s subsystems. Also, this work presents the dynamic
modeling for the different components in the solar thermal system, which is responsible for heating the drying air. The results indicate
the high effectiveness of the drying method.
2008 Published by Elsevier Ltd.
