Indirect solar dryers

As the name suggests, indirect solar dryers do not have the sun shining directly on the drying food, but rather in a separate collector area.  The heated air then moves from the collector to the drying chamber via thermal draft caused by rising air.  The design we have been using is based on plans from Appalachian State University but modified to reflect local materials.

To date, experience is suggesting that managing the air flow is critical to the performance of the dryer.  Some of the attempts tried to simplify to upper outlet, and those proved susceptible to wind speed and direction--in certain conditions the draft was stopped.  That led to a lot of trial and error experimentation with controlling the ventilation.  You will notice that in the header photo above the inlet vents were completely blocked for a "stagnation" test--this looks at what happens when the air flow is completely stopped.

So far, this dryer has not performed as well as the direct dryer.  But since it can dry food without exposing it to the sun, we are continuing to work to improve it for situations where protecting the food from direct sun.