An important feature contributing to consistent quality is the use of
photovoltaic powered fans for fo
rced convection. The controlled drying process results in
high-quality. The acceptable load for the dryer ranges from 1.5 kg/m²
for medicinal herbs to
25 kg/m² for rice or coffee. For a standard dryer with a 20 m² drying area, this corresponds to
30 to 500 kg per batch
Some dryers made in Thailand are equipped with a gas powered air-heating unit to allow
drying during the six-month rainy season. In contrast, Turkish weather is dry enough to allow
the all-solar dryers to operate well with twice the standard drying area. Local manufacture of
the Turkish models allowed a total installation cost of less than 1000 US$ in 1997, resulting
in a payback period of only one year. The models used in Thailand were more expensive due
to the gas-powered back-up heating unit.