Over the years I’ve tried about every solar dryer design imaginable. The only common factor in all those attempts was their very limited usefulness here in the humid upper Midwest. None of them could reliably turn food into a non-moldy finished product, unlike the many successful electric models I had built for myself and friends. Some didn’t work at all if not tracked periodically during the day. Others were simply too slow, exposed the food to sunlight, or relied on electric backup at night.
This is our finished solar dryer, 12×4-feet, with 2×2-foot stainless steel screens framed in 2×2-inch cedar, and one of the 4×4 foot heat-generating solar collector panels raised for access. Sunlight shines through the clear glazing, lowering the frequency of the light to make more infrared (heating via the greenhouse effect). Moving inward, it then hits a black-painted aluminum sheet, heating the metal. The back side of the black aluminum re-radiates heat onto the food below, causing the food to heat up and lose moisture while keeping sunlight off the food itself. Moisture given off by the heated food passively flows up the sloped air channels under the food screens. And the galvanized steel roofing, with raised ribs forming the air channels, reflects heat back up toward the food, improving overall efficiency. It’s not the prettiest dryer, not the most compact, and not the cheapest. It simply does what it is intended to do very well by following the rule I always tell people, “You can’t fight physics!”