The Solar Dryer-Background
The Solar Dryer that we built on the farm of Fayez Taneeb in Tulkarm, Palestine, is based on existing solar dryers in Tamera, Portugal; and on the designs proposed in the book Sechoirs Solaires by Claudia Lorenz-Ladener. More information and background about the first solar dryer in Tamera is available here: http://www.tamera.org/index.php?id=889 .
The basic “tunnel” solar dryer is essentially a table-top greenhouse, with active ventilation provided by electric fans and a dedicated photovoltaic panel. It provides optimal airflow and temperature for drying food; in an environment protected from animals, UV radiation, weather, and contamination. The basic design goal is to maintain, when in sunlight, a constant airflow of about 50 m3 per hour per m2 of surface; and a temperature of between 30C and 50C, the ideal being about 40C. Once constructed, the Solar Dryer is entirely autonomous and “off grid,” and supports both local food autonomy and economic resilience.
Many of these dryers have been built around the world. from the smallest versions of about 2 m2, as proposed by the book mentioned above, up to dryers of 40 m2. The current tunnel-type solar dryer in Tamera is about 18m2.
The design principles are very simple, and many variations are both possible and often desirable. My colleagues in Tamera assured me that for hot, sunny climates, such as Portugal or Israel-Palestine, some changes are appropriate. For example, the designs in the book, developed in central Europe, include leaving the first meter of the dryer empty and painted matte black, to warm incoming air. I was assured that even in the Alentejo, this was not needed to achieve the needed temperatures.
The Solar Dryer in Tulkarm was a result of a combination of these published designs, experience from Tamera, the locally available tools and materials, and the creative impulses of our group. The details will be available in upcoming posts.