The Solar Tunnel-Dryer


Since its development at the University of Hohenheim many years ago, the Solar Tunnel-Dryer has proved itself many times over. It is used in many countries to preserve food through dehydration. It is used by fishermen in Bangladesh to dry fish, by famers in Togo for bananas, for spices in China, etc. Through the training that took place during the Global Campus, Solar Tunnel-Dryers were also introduced into the Peace Community of San José de Apartadó, where they are used to dry Cacao. The Tunnel-Dryer is weatherproof; short rainfalls are therefore not a problem.


Solar Dryer


One half of the floor of the Tunnel-Dryer is painted black, and serves as the “collector.” Here solar radiation is transformed into heat. The air is heated and thus has a lowered relative humidity. A fan then blows the air across the goods to be dried, where it absorbs moisture. The food to be dried will cover the floor in its half of the Tunnel-Dryer, so here the floor does not need to be painted black. The sunlight which falls on this drying area helps vaporize moisture in the food. Because the fan (in the far triangular end of the Tunnel-Dryer in the photo) is powered by a photovoltaic (PV) module, the interior temperature can be kept quite constant. More intense sunshine will quickly cause the interior temperature to rise in the dryer. The fan then has to provide a higher air flow, to prevent the interior from becoming too hot. Because the PV-module is delivering maximum power, the fan is running at its maximum speed. When the sunshine is weak, the PV module delivers less current and the fan turns more slowly. The air remains in the dryer for a longer time, and has more time to be heated.
Advantages of the Solar Tunnel-Dryer:
Insects such as wasps and fruit flies are prevented from entering, and cannot contaminate fruit. In dusty climates, less dust is able to accumulate on the goods being dried. Brief rainfall does not lower the quality of the results. In the case of temperate latitudes, higher humidity, or lower air temperatures, food will be dried more quickly than via open air drying.
For a detailed guide to construction, please visit:
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The Tunnel-Dryer in Tamera was built under the guidance of Alec Gagneux. Since that time it has dried many fruits and vegetables—an important element in the processing of seasonal overproduction from the gardens.


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