More than ten years of research and field testing has resulted in the development of a solar
tunnel dryer well suited to medium sized farms or small cooperatives. The non-patented
design was developed at the University of Hohenheim, Germany [21], and has been
duplicated successfully throughout the world. A key to this success has been the adaptation
of the dryer design to the local climate and manufacturing possibilities in multiple countries.
By 2003 over 1,000 Hohenheim type solar dryers were in use in 60 countries [22]. Over half
of these dryers were manufactured in the country of use; the rest were supplied by Innotech,
a German corporation manufacturing prototypes of the dryers. Innotech supplies the dryers
in kit form for roughly 5,500 US$ (2000), for use in locations where manufacturing has not yet
been established. Innotech also offers a consultancy for quality assurance and marketing of
dried products for export to industrial countries.[
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.