Introduction: Humid Climate Solar Dehydrator

Picture of Humid Climate Solar Dehydrator

This dehydrator is my version of an upper Mid-west design. I adapted it (as recommended) to fit the windows I had on hand, which I also use for my cold-frames. These windows were roughly 32" by 32", which matched nicely with 32" wide galvanized roofing. I couldn't get the wavy kind in my area, only the ribbed, so had to adapt the screen support system accordingly. I used cedar throughout for to withstand weather without coating it with any preservatives or paint. It also makes the frames really light so I can put them on a 4 1/2 foot high shed roof.

Materials (for two dehydrators):

3 1x6 3/4" 6-foot cedar boards (these are fencing boards in my area - I picked for few knots)
1 sheet of 8-foot galvanized ribbed roofing (is enough for 3 dehydrators)
2 yards of 36" aluminum flashing
2 32" x 32" storm windows (or other similar sized glass)
Matte black spray paint
2 yards of 36" aluminum screen
Staples
Galvanized nails (1 1/2")
1" finishing nails for drying screens

Tools:
Jigsaw with metal-cutting blade
Tin snips
Table saw with rip fence to produce frame elements
Stapler

Step 1: A Simpler List of Materials

Picture of A Simpler List of Materials


Two years after initially publishing this Instructable, I found myself conducting a Saturday build of three smaller dehydrators with three friends of mine.  I found 3 windows of the same size at the local Habitat ReStore and worked everything from there.  I also wanted to get the three of them done in less than a day, so I went with materials that simplified things.

For each dehydrator:

1   24"  x 27 3/4"  storm door window
Dehydrator bottom: Aluminum flashing,  white on one side, shiny on the other:  24" x 27 3/4"  (no need to trim ribs)
Heat sink: Aluminum flashing,  black on one side, white on the other:  22" x 26"  (no need to paint)
Nylon screening:  24" x  30"  (easier to work with than aluminum screening)
3  1" x 6" x 6' cedar boards:  one ripped 3 1/2" wide (for top and bottom),  one ripped 4" wide (for the sides),  one ripped into 1" wide pieces (for tray frames).  Once the pieces are cut for the box, rip the remainders into 1" wide pieces.
scrap 2" x 2"  (about 4" - 6" long) for heat sink handle
1 1/4"  galvanized spiral nails  (for making the dehydrator trays)
1/4" staples
8  1 1/2"  deck screws  (to hold the outside box together)

For this size,  the top and bottom were the 27 3/4" sides of the window.  

Because the flashing doesn't have ribs,  you'll have add "risers" to the long sides of the trays using scraps of the 1" wide pieces.  The flashing is much easier to cut than galvanized roofing!   We cut the screening oversize for the trays and found the nylon easier to stretch tight than aluminum screening;  it was also easier to trim once the top pieces were nailed on.

We completed three dehydrators in 4 hours.

Step 2: The Dehydrator in Pieces

Picture of The Dehydrator in Pieces

These are the components of the dehydrator:

1. Glass -- I used the framed pieces from a storm door. This determines the dimensions of your dehydrator. If your glass is 32" by 31", your frame must be 32" by 31".

2. "Heater" - This is left over aluminum flashing I had lying around. It needs cross bars to hold it above the drying screens. Braces on top keep the cross bars from falling off and a handle going over both cross bars on top also adds strength while being useful. It needs to fit inside the frame.

3. Drying screens - I had no access to stainless steel screening, which would have definitely been stronger, so I used aluminum. The screens sit on top of the roofing. I made two for each dehydrator to make loading easier and not overload the screens themselves. Because I used ribbed roofing instead of wavy (which I couldn't find), I had to put risers the thickness of the ribs on at least one side of each screen.

4. Frame with reflector - the dimensions of this are based on the size of your glass. The south end of the frame has a 1" gap above the reflector and the north end has a 1" gap below the glass. This allows air to move rapidly through the dehydrator and carry away moisture from the food you're drying. This is not vital in an arid area, but is essential where there is any humid weather. I have found this design so effective that I've dried greens on cloudy days when there were light showers.

Step 3: Constructing the Frame

Picture of Constructing the Frame

1. Measure your glass. The outside dimensions of the frame must match the edges of your glass.
These directions assume that the north and south sides (N/S) have the same measurement and the east and west side (E/W) have the same measurement.

2. Rip one cedar board to 4" wide. This will be your E/W sides. Cut 2 lengths to the E/W measurement.

3. Rip another cedar board to 3" wide. This will be your N/S sides. Cut 2 lengths to the N/S measurement minus the thickness of your E/W sides. If your N/S measurement is 32" and your board thickness is 3/4", your N/S side will be 30 1/2" long.

4. I put corner braces into this dehydrator. If you're working with a smaller piece of glass, you may not have to. Use the left over piece from ripping the E/W side for these and cut them 4" long. For each E/W side, lay two braces on edge, set the side over them, and nail together.

5. The top is where the glass will lay. The north end of the frame has a top gap of 1" and the south end of the frame has a bottom gap of 1". Nail the north side to the east and west sides (into the brace if you are using them) leaving a top gap. Nail the south side in being sure the gap is on the bottom.

6. Cut the roofing to the glass dimensions. Since I had ribs with flats between them, I had to cut the ribs on the north end and bend those pieces up so I could soundly secure the north end to the frame. Nail the east and west sides of the metal to the frame. There is no nailing done on the south end because of the ventilation gap.

Step 4: Making the "heater"

Picture of Making the "heater"

The heater fits loosely inside the frame (including the braces). The drying screens will have a 3/4" frame, must clear the braces (if you are using them), and the heater needs only radiate to the actual drying surface.

1. Cut the aluminum flashing to size and bend over the corners so you won't cut yourself taking them in and out of the frame.

2. The heater has to float above the screens, so rip 3/4" pieces of cedar and cut to the width of the heater. It will be easiest to do from a new board, though you could use the piece from the making the N/S sides. Cut another ripped piece to the length of the heater to form a handle on its top. Add four braces on top of the cross floats.

3. Spray paint both sides matte black.

Step 5: Make the Screens

Picture of Make the Screens

The screens are constructed of 3/4" cedar and aluminum screening. I made two for each dehydrator so that I could dry two different things at once without them mixing and the narrower size was easier to handle. Because of the ribbing in the roof, I had to add supports for any long edge that would not rest on a rib. These supports are the thickness of the rib.

1. Determine your screen dimensions based on the inside dimensions of your frame (and allow for clearance of braces if you are using them!).

2. Each frame has eight pieces. The strongest way to construct the screen frames is with lapped joints. If the bottom half of the frame has the north/south pieces between the east/west pieces, the top half has the east/west pieces between the north/south pieces. (see photo)

3. Assembly is best done on a workbench top. Lay out the bottom frame, stapling across the butted joints. Cut your screen to the outside dimensions of the frame. Staple it down on one long side, then pull to tighten and staple down the other long side. Staple one short side, then pull to tighten to other short side and staple down. Trim the screening as needed. Secure the top frame to the bottom frame, lapping the joints.

4. Set aside to where nothing with a sharp corner will drop on it, or you may end up with a ripped screen! (Such can be mending with a patch of screening without effecting its ability to dry, but it's a hassle to do.)

Step 6: Assemble the Dryer for Use.

Picture of Assemble the Dryer for Use.

The dryer goes together easily. If I'm carrying it anywhere, I carry the glass separately. Everything else is light enough to sit in the frame.

To load the dehydrator with stuff to dry, remove the glass and heater. I can stand on a stool load greens into the frame when it's on my shed roof. I've also set up the dehydrator on a picnic table and a sunny deck.

Starting with the empty frame:
1. Orient with the bottom ventilation space to the south and the top ventilation space to the north. I usually place a 2x4 under the north side to angle it to the sun when using it on a flat surface.
2. Place the drying frames in the dehydrator. You can load them before or after placement, as it suits you.
3. Place the heater on top, with the cross bars on top of the drying frames.
4. Place the glass on top of the frame.

If your nights are damp, you may want to bring the screens and their contents inside. I've placed mine in my greenhouse at night since it's close at hand and not used in late summer.

I've done May drying of dandelion greens in this. When it's windy, I'll have dried greens in a day. The dehydrator works best between the spring equinox and fall equinox.

Step 7: Using the Dehydrator

[This is an update in September after a summer of drying.]

I used the dehydrator extensively this summer (whenever we had more than one day run of sunshine -- I found that even a day and a half was serviceable.) Here's a list of things I dried:
- dandelion greens
- lambs quarters
- zucchini slices ("veggie chips")
- almond meal
- finishing stop top granola
- pita bread crackers
- oatmeal bread rusk
- cherries
- calendula flowers
- oregano
- garlic chives
- kale
- chard
- turnip greens
- bee balm flowers
- peppermint
- spearmint
- yarrow

The cherries took the longest to dry: 3 days. Everything else dried in a day or day and a half.

I never took anything in since the glass totally covers the frame unit. Dew would settle on the glass, but would not affect the items drying. Even a light shower overnight caused no problems (a good thing, since my area had a lot of rain this summer!).

I put curtain organza on the screen when I dried the almond meal (left over from making almond milk) and finished the granola (ingredients individually toasted then mixed with heated honey and oil). It kept the material from sticking to the screen and the finished product then easily poured into a jar from the cloth layer. Both things dried in less than a day. The organza allowed plenty of air to reach and flow through them.

I just bought The Complete Dehydrator Cookbook and look forward to further drying adventures through October. I may try drying a few "soppy" things like tomato paste on plastic cutting board sheets (available a many a dollar store).

Comments

bobdowser (author)2015-09-19

Hi, Bob Dahse here. Having designed this type of dehydrator with my partner Larisa Walk back in 1985, and now seeing it in use worldwide and with so many variations in materials, it's nice to see it in Instructables. The original plans and much more about the physics behind it, a comparison of glazing choices, instructions on how to tailor it to your climate, latitude, and altitude, and the lowest cost (as far as I know) source for stainless steel screens can be found at:

http://www.geopathfinder.com/Solar-Food-Drying.html

faun108 (author)2011-01-30

Thank you for this inspiring instructable!
I asked myself however if you checked the temperature? I want to build a solar dryer for herbs and most plants should not be dried over 40 degrees celsius. Any expericence or ideas?

amtrudell (author)faun1082011-01-31

Hmmm, I'd heard you shouldn't dry plants over 140 degrees Fahrenheit, which translate to 60 degrees Celsius.

Using this dehydrator in south-eastern Ontario I routinely dry herbs and greens in it. On a day with full sun, a steady breeze from the south, moderate humidity (60 % or less), and air temps higher than 32 deg Celsius, I have had thin leaves begin to brown in the mid-afternoon when I've put them in in the early morning. That's an indication things are too hot. When those conditions occur, I either don't dry or I check things at noon and every couple of hours after that.

This dehydrator is not suitable for a low-humidity, extended high-temp climate (like the desert).

faun108 (author)amtrudell2011-01-31

Thanks for your reply! It´s very much appreciated! I will experiment with it and maybe put a thermometer inside, to get a better idea of the development of temperature.
Best wishes!

jonnyarmony (author)2010-11-25

Hey I was wondering if this model of a dehydrator can be stacked on top of each other. This would be useful, as to not take up so much room.

Also, I didn't see you mention many vegetables that you dehydrate. I imagine that this will work for most, but will it work for carrots, celery, peas?

amtrudell (author)jonnyarmony2011-01-31

A friend of mine made a dehydrator of this design last summer and he was drying all sorts of things with it: onions, carrots, sweet peppers, tomatoes, blueberries, peaches, strawberries.

Check out books on dehydrating from your library or at Amazon. I got one, not so much for the electric dehydrator times, as for recommendations on how to cut up various things and if they should be blanched before drying them.

guy90 (author)2009-08-27

Very informative and useful, thank you for the upload

shilohjim (author)2009-05-24

Is the aluminum screen food safe? I worry about acidic foods reacting with it.

amtrudell (author)shilohjim2009-05-25

Probably not the best for acidic fruits. If you can find stainless steel screen (I've seen expensive US sources for it on the Internet), that is probably the best for everything and would definitely be stronger. My solar drying season is best for vegetables and herbs (non-acidic). Viole fabric (the stuff of sheer curtains) could be put on top of the aluminum screens to prevent or at least mitigate the reaction you worry about. I was thinking of trying that for things like mashed cooked sweet potato patties or winter squash patties. I use viole for juice straining and by chance I left a small bit of rhubarb pulp on it last week, but the bit peeled right off once the viole and it were dry. Also, if you start the drying process with the fruit skin down on the screen, you would certainly minimize any acidic reaction (top of the fruit would be surface dry when you turned it over on the second day or so).

imrobot (author)amtrudell2009-05-26

will this work for meats?

rimar2000 (author)2009-05-22

Very useful work.

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