What’s the Best Solar Food Dryer?

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Appalachian Food Dryer. Image: Mother Earth News.

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.

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Brace Direct Food Dryer. Image: FAO.

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.

The Poistk Dryer

The Poisson Indirect Dryer. Image: Mother Earth News.

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.

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Our Appalachian Food Dryer, badly in need of a paint job.

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.

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13 Comments

  1. Years ago I discovered the cage match between Updraft dryers, like the Appalachian dryer in the first photo, and Downdraft dryers, where the collector panel is attached at the TOP of the drying chamber.

    At that time it was not resolved which was a better design, but a recent internet search unearthed the opinion that Downdraft dryers are better in cooler climates, and even for slightly overcast days. They work more by creating airflow and worry less about high heat. So, if that sounds like your climate (as it is for me), you might want to check out the Downdraft design.

  2. I will note that the version of dryer you are recommending is not appropriate for the very humid portions of the midwest without as much solar heating during the day as you might get further south.

    There is a design for those of us in the more humid mid-west that works much better (I’ve tried the first and second models which both molded my food and the smaller model that I now use). The smaller one uses sheet metal with a tray on top and shade cloth for your food and either plastic or glass topping it. the heat is more directly pulled out of the box much faster with a much smaller amount of food being dried per heating area. The cost to build each box is fairly cheap, ribbed sheet metal and left over glass and trim work with a bit of black cloth and black paint on certain parts. I would recommend that over a design that has way too much food in a space for our weather conditions here in the midwest.

    This is one of those caveats – it really depends upon your insolation, humidity, etc. Be careful.

  3. Pingback: What's the Best Solar Food Dryer? | Root Simple | kimblesfood.org

  4. My nine-tray Excalibur does not make much noise at all. I wonder if something was wrong with the one you borrowed.

    I cannot imagine how any solar dehydrator would work here. However, I know people do dry outdoors on sheets and screens.

    When I was a vendor at a craft show, I found a woman selling dried apples and bought a quart bag of them. I ate out of that bag all day, but left half for the next day. The next day, I just started eating non-stop, not looking, just eating. One time as I put my hand in the bag, I just happened to look in the bag. There were about the same volume of maggots as apples.

    When I took them back to the woman, she said she was sorry and gave my money back, offering to give me another bag. Her husband said she did not put a batch in the oven to kill the eggs. So, there may be a final step in the oven.

    • I meant to say the woman dried her food outdoors and froze the apples in quart bags until she put them in her booth. According to her husband, she put them in the oven to kill eggs. Most of the solar dehydrators are not tight enough to keep flies out. After my experience, I wonder how people with solar dehydrators keep insects out. I know ants will be drawn to food, as well as flies.

  5. I was reading one of your blogs from back in 2008, and it was about the plans for your Solar Dehydrator. You indicated that the plans for the Appalacian food dehydrator you guys bought was divided into two issues, and therefore you gave two links. Those article links are not functioning at all. Do you happen to still have the plans, or are the ones link to Mother Earth News in this blog the same.
    Thanks, Sisu

    • Thanks for mentioning this. I need to update that old post. I’d go with the new article in Mother Earth News. It’s got all the plans as well as the designer’s new ideas about the dehydrator.

  6. We built an Appalachian solar dehydrator several years ago and dubbed it “The Dehydrinator” (copying someone else who had built one). It takes up a lot of room in the garage during the rainy season, but I can dry the heck out of very large quantities of fruits, veggies, herbs, and flowers, so I think it’s worth the space. The one planned modification is replacing the fixed screen at the bottom (intake) with a hinged version. When something falls off or through the drying screens, it ends up at the bottom of the collection box and as designed, there is no easy way to get it out. Also, I’d caution folks in this climate to worry about burning food as it really can get that hot!

  7. I’ve seen versions of this before. I’ve mulled over the idea of making one strictly for heat and venting it into a window during the cold months here.

  8. Do we know anything about plywood and off-gassing relative to temperature? Would that be of any concern in an application like this? Also, I’d be curious to hear others’ input re: if putting baffles in to make the airflow serpentine (it wouldn’t make a greater surface area but might increase the time it takes for the air to get to the top & thereby increase temp & rate flow?) could allow for making the collector area length shorter. The massive size of this thing seems to be a drawback.

  9. food wast is very rampant in agriculture producer, if the food left after harvesting is collector dryad and stored, it could feed half the world population.

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