Dehydration is a great way to put up food. Second to freezing, it’s the best way to persevere nutrition without adding sugar or salt. And if you use the power of the sun, you won’t need to spend any money on electricity.
In a desert climate you can just put your food out on screened trays. But just a bit of humidity in the air makes this approach risky. Food can spoil before enough moisture is removed. That’s why you should build a solar food dryer.
There are two basic designs for solar food dryers: direct and indirect. Direct dryers are just a box with a piece of glass on the top. Indirect dryers use a box to collect the heat of the sun and then, thanks to the fact that hot air rises, take that heat up into an enclosed box that contains the food you want to dry.
Which design works best? Dennis Scanlin, Coordinator of the Appropriate Technology Program and Professor of Technology at Appalachian State University in Boone, North Carolina has been studying solar food dryer technology for decades. According to Scanlin, indirect drying is the way to go. Scanlin tested three dryers, the Appalachian Solar Food Dryer (an indirect dryer that he invented) against a direct dryer developed by the Brace Research Institute and the Poisson indirect dryer. In an article in Permaculture Activist, “Evaluating Solar Food Dryers: Stocking Up with Solar Power,” Scanlin says,
The Appalachian indirect dryer produced higher temperatures than the other two dryers and also removed more moisture from the tomatoes drying inside each day. In one test, the Appalachian dryer removed 32 oz. (0.95 L) of water during ta day, while the Brace direct dryer removed only 20 oz/ (0.59 L), and the Poisson dryer only 15 oz. (0.44 L). The Appalachian dryer was able to remove as much as 3.73 lb. (1.69 kg) of water in a single sunny day from tomatoes drying inside.
Scanlin also notes that direct dryers degrade the quality of the food and possibly nutritional value due to direct UV exposure.
We built a Appalachian Dryer several years ago and it works great. You do need to remember to bring in the food at night to prevent rehydration and spoilage (for some reason I often flake out and forget to bring in the food). For awhile I had an electric Excalibur Dehydrator on loan and it’s a lot more convenient. But, of course, it uses electricity and makes a lot of noise.
Since I built my Appalachian Dryer Scanlin has decided that it’s not necessary to use insulation. This makes the project even simpler. For just around $200 worth of materials you can easily make an Appalachian Dryer out of plywood nails and screws.
You can find plans for Scanlin’s dryer here.