Solar Food Dryers?

Anyone got plans for a durable one (not the plastic sheeting kind - I tried that with no success)? I've got plenty of sun, so I see no need to buy a $200 high quality electrical dryer.

I don't have any plans, but I don't think you need them. should be easy enough to rig something up.

I think it would be a good idea to separate the food you're drying from the solar collector so your food isn't degraded by the sunlight (unless your drying shiitake mushrooms). so make a solar air heater that leads to a dark box with the trays of food. maybe something along the lines of the soda can heater mentioned in the alternative energy thread for the heater. folks have used old refrigerators and upright freezers as the dark box portion. a small box made of plywood could work, too, if you don't need refrigerator-sized capacity.

some folks put a chimney in the top of the refrigerator and feed the hot air in at the bottom. other folks reverse that. both designs work.

I once checked out some really great books from the library that had ideas and building plans for solar dehydrators. Maybe you want to check with your library?

Here's one we made. Works really well, as long as the sun is shining. Does not work at all on cloudy days.

Raisins made with fall harvested grapes took a month to dry because of intermittent rain clouds...but they did eventually dry!

I use it to dry seeds, herbs, roots. We dried almost a gallon of cherries in June, a couple gallons of sliced apples in September. Tried to make fruit leather by spreading apple butter on a ghee-smeared screen...the thicker parts peeled off but the thinner parts had to be soaked off the screen. Next time!

marina i have to say ive seen that pic before but it inspires me every time. i had a similar design setup in my head but yours is awesome. are there no problems with drying in the summer? we get no clouds or rain from like june to october. i was thinking of adding a possible smoker assembly at the bottom of mine so when it gets too cold, or its not sunny i can use it to smoke jerky, hot peppers, or anything else. i also had the idea of having on a rotating platform, so it can either move with some sort of mechanical action through the day or an electric motor. i plan on building it this spring i hope i have time to.

If you want a solar food dryer that doesn't expose the food to direct sunlight (although you should dry all mushrooms exposed to sunlight as their vitamin D content is dramatically increased), works on partially sunny days (depending on what you're drying), does not require any high tech crutches, and has worked in the humid upper Midwest for over 25 years, check out our design at http://www.geopathfinder.com/9473.html

The dryers built in a stacked tray, cabinet format that mimics an electric dryer but utilizing a solar collector to provide the heat, do not work as well because all the moisture is being pushed up through several trays of food. Since the sun is not providing energy 24/7 on any dryer, you need to make optimum use of the energy available during the day. However, complicating the design with fans or having to track the sun's path violates the K.I.S.S. approach that we take to design (keep it simple, stupid).

soil - it dries things really well in the summer, average temperature is between 100 and 110. We accidentally burned tomatoes with it one year....that was sad, but it was 110 ambient temp that day, so maybe that had something to do with it.

The trays up at the top actually dry faster, contrary to what you might think (with moisture moving upward thru the trays). I think the box being black helps heat the air in there even without the solar collector doing it's thing, and the top portion of the cabinet is hotter, thus drying things up top faster.

I think incorporating a smoker is a really good idea. I hope you have the time too!

I'd love to figure out a design for a dual solar/wood dehydrator so that raisins in the fall (when we have intermittent cloudy days) don't take quite so dang long to finish.

Here are a couple from this thread:

And really old school:

And a video:

http://www.youtube.com/watch?v=5U1JgAkW-xY

I am currently building a dryer much like marinajade's. Like most of my projects, overthought overbuilt. My collector panel is on a pivot so that I can adjust the angle per month. The whole thing is on a frame and will have wheels so I can relocate it with my garden tractor. The design also incorporates a port to accept ducted smoke from my big green egg. There are a few issues that I am still concerned about though...

1. I want the added benefit of the box being black but the thought of paint is unappealing. Was thinking maybe a homemade concoction of black walnut stain?

2. Because I am using roughcut lumber I expect in time to develop small gaps as the wood dries. I could use food grade silicone but would rather not. Maybe cotton and wax chinking?

3. for optimal drying how hot shout it be?

three solar dehydrators.

The first solar dehydrator is shown by robert and marina at dell artimus farm. The solar heat comes from a heated panel at the bottom, and there is a black chimney at the top that creates a draw. They use a stainless steel screen. The dryer is a year and a half old. They have dried beans, flowers, cherries, grapes (raisins), kale, walnuts and apples. They tried some tomatoes, but those ended up as pig food.

Matt at feral farm shows a "down draft solar dehydrator." The solar heat enters at the top and then goes down. Because as it gathers moisture, the solar heated air gets heavier. He has nettles in there.

Mark Vander Meer, of wildland conservation service in Missoula, Montana shows off his solar food dehydrator still loaded with dried plums. Those plums have been in there all fall, winter and most of the spring. He talks about trying to dry fruit with electric food dehydrators and how expensive that was. This solar dehydrator also uses the down draft technique. He says plums take three days and apples take a day and a half.

These are all passive systems. There are no fans.

Do you have any schematics for how to build that last one? That seems really interesting! I would love to try building one of those before my berries start fruiting!

We made a solar dehydrator like Mark VanDeMeer's but with the high humidity we have almost year round here in Florida it just does not work...we finally caved and bought an electric dehydrator...it was an expensive one but costs less than .07 cents per hour to run and is pretty effecient.

On the downdraft ones,the entrance opening should be the same area as the exaust opening I believe.Sinking air in the actual chamber is a result of both gaining moisture and cooling.

Hi, this is Marina, I rejoined finally.

The tough thing is getting it to be airtight. I think that's why it's probably smart to chop a hole in an old fridge or something, then you only have the one junction to worry about sealing, whereas when you build a box you have to be concerned about every single crack. Ours could be waaaaaay tighter, that's the main criticism I have. But it works just fine for our needs.

Then again we live in a very hot and dry climate, we can dry things just by leaving them on the counter......but the thing we built is faster, cleaner, and keeps the flies off your fruit while it dries (that's another big important reason to seal up cracks - fruit fly maggots hatching out of food in the winter would be a real bummer).

1. I want the added benefit of the box being black but the thought of paint is unappealing. Was thinking maybe a homemade concoction of black walnut stain?

That sounds cool! Um.....what about soot rubbed into the wood? might be messy if you tough it later though....

2. Because I am using roughcut lumber I expect in time to develop small gaps as the wood dries. I could use food grade silicone but would rather not. Maybe cotton and wax chinking?

We used rolled up wool blanket pieces, mostly cause we had a lot of little scraps left over from another project, and the thickness of the fabric helps fill in wide gaps. I'd be concerned about wax getting too soft in the heat. Like i just said, this is a challenging aspect of these contraptions.

3. for optimal drying how hot shout it be?

We've had a thermometer in several parts of ours. It gets really really hot here in the summer, and on a 110 degree day the top trays get up towards 125-130, the bottom trays are more like 110-115. I think electric dryers stay below 120. Some people are concerned with their food being exposed to temps more than 110 or even lower.....when the air temperature outside exceeds that I don't know how you'd go about drying food and keeping it cool enough to meet raw foodist standards. Luckily, we do not care.

thomas wrote:
1. I want the added benefit of the box being black but the thought of paint is unappealing. Was thinking maybe a homemade concoction of black walnut stain?

dellartemis wrote:
That sounds cool! Um.....what about soot rubbed into the wood? might be messy if you tough it later though....

First off, I am very impressed by all these designs, much more sophisticated than the cardboard chimney we built last year to demonstrate the concept.

I have no improvements on these designs.
But I've been interested in color and paints for a while, so I thought I'd chip in on that aspect.

1) Paint anyway. First off, for most of us, high-temp paints should work just fine. Set up the system and run it for a few hot days with no food, until there is no odor of off-gassing paint, and then start drying your food. You can use stoveblack (charcoal or soot mixed into your choice of grease) or modern Rustoleum enamel-type paints that are designed for the temperatures your dehydrator might reach. Any paint is likely to offgas less than black plastic.

2) DIY non-toxic paint: Check with your local hardware store on ingredients in ordinary paint if you want minimal VOC (offgassing) content. If needed you can get a few squirts of a straight black pigment from the hardware store or an art supplier. (Bone black or ivory black are forms of charcoal, Mars black is an iron oxide, neither is particularly toxic as paint pigments go).
You can mix the pigment yourself with a water-based binder such as milk casien or egg yolk and water. Or, go for a natural, non-toxic, but smelly oil paint with food-grade linseed oil (AKA flaxseed oil). Linseed oil will take at least a week to dry, more in cool weather or with low airflow, so plan to set it out a while before adding food. Warning: I was taught that charcoal pigment can keep linseed oil paints from curing properly, they might stay tacky.

A couple other non-toxic options for black color on wood:
3) Ink or pencil: The soot idea is not bad, you could also use graphite. Both are used as pigments e.g. for India Ink, and I believe you can get food-grade soy-based black ink also.
Paints could be more of a fire risk, where inks might not be as problematic. Water-based inks or paints will be much quicker, but may be harder to make permanent or very dark.
Any of the above will be flammable, and oil-based paints may increase the flammability of your wood.

Non-Flammable and Minimal Offgassing:

4) Cast-Iron Black: How about the blackness of a cast-iron skillet? You could use a flat sheet of steel or iron, doesn't have to be very thick (panels from an old appliance might work, if you can expose a non-enameled side). Sand or burn off any paint/enamel, oil with any food-grade oil such as you would use for seasoning cast iron, and heat if needed over a fire.

5) Pyro / Blackbody solution:
Take any metal panel, heat it over an open fire, until you have enough soot deposited on it to increase its heat absorbtion.

6) Inert Rocks: You could also consider using any naturally black material, like local stone, a thin layer of black sand, or dark sandpaper.

You folks are a wealth of info. So a few updates on the build.

The pivot for the collector is done and will allow the collector panel to rotate from 40 to 80 degrees. With a small modification I can get it to 32 but since I wont be drying anything in december I may not. Have experienced less than expected shrinkage with the rough saw wood so far. I love the idea of using old wool for chinking. After seeing the down draft styles I am tinkering with a slight modification that will allow my plenum to operate in both air flow set ups. Be interesting to test. Since mime will also be a cold smoke chamber I tested it with smoke from the Big green egg, worked well and the thing smells fastastic hickory smoked. Now if the kids would sleep later so I can make some progress. next up collector,wheels,tractor connection and racks.

I just bought milk paint from the realmilkpaint company....Just mix with water and paint. It took 2 coats to get a good black for me, now I Just have to test. As far as ease of use, it was fantastic, it dries really quick though. I was painting out in the sun in the morning and when I put down some paint you could see it evaporating off. This was during the second coat because the surface was so hot. Ill report back.

well now for the old school redneck way to do it.

ive never used anything but a elec. dehydrator. but my ex-wifes grandparents used to tell us about drying apples in the rear window of an old un usable car. them old cars had huge back windows. theyd lay the apples up in the back window. keep the windows rolled up. this built up the heat and kept the bees and wasps off the apples. i cant image there was any air flow. but i guess the sheer heat of it all would dry the fruit. i never saw it done. just what i was told

Do the downdraft designs actually drop moisture at the bottom? And if so, how does the solar chimney still have enough pull? I can't wrap my head around it and I'm not interested enough to actually purchase a design.

It's been surprisingly hard to find a drawing of a downdraft design on the internet.

Yes. http://tinyurl.com/79vxwsy

Hope this is helpful.

Dusty
http://farm-dreams.com

Well, I looked at it but it's not a downdraft system in the same way as the ones in Paul's video. Those have a solar chimney that pulls the air through. I'm trying to figure out if the solar chimney draws even the moist air out or if moisture tends to collect below the food racks.

Hi I was wondering about the dehydrators on the youtube video. We would like to build one like the last one, my question is this, I live in michigan, will this work for me? also i saw a bit of mention to it being used as a smoker. Is there a place here or where ever that has good solid info on drying meats this way? It would be along the lines as using a cold smoke house correct ?, where the smoke enters from the outside, rather than being cooked? I think these are fabulous!

Somehow my old post has become thomas hatfield.. been away awhile. so some progress.

sealed everything from the outside with food grade silicone. Using batten board allowed me to seal the edge of the batten, so the stuff is 1" away from the inside. Also in similiar thinking once everything was caulked from the outside I painted regular exterior paint. Walmart had dark green oops paint for $7.50. The inside is still rough sawn wood. I thing the thickness of the wood will keep any nasty gases or chemicals on the outside. The positive internal pressure created by the heat/smoke should help also. Shingled it with "soda" can shingles I cut awhile back. Its slow going because I got TOO much going on. Maybe another month or so. The thing is supper heavy and though the wheels work fine I think bigger is better. The pivot was very difficult and time consuming to make, if adjusting the panel by month makes a huge difference it may be worth it. If not it was just an exercise in complex cutting,fitting and problem solving. I will try to get some pics up then its nicer outside.

Your ideas look new and fresh here, I just read about it in article and here you are implementing it. I am also working on my solar calculator when it will finished , I will post pics of my set ups.

Here's mine, simple and easy to build: http://www.velacreations.com/solarfooddryer.html

Check out "Appalachian" solar dehydrators, free plans pdf, tested and true, have made and used two of them, wore one out!! Easy to build and cheap to boot.
http://tec.appstate.edu/sites/default/files/HPImprovingSolarFoodDryers.pdf

Tim Meyer wrote:Check out "Appalachian" solar dehydrators, free plans pdf, tested and true, have made and used two of them, wore one out!! Easy to build and cheap to boot.
http://tec.appstate.edu/sites/default/files/HPImprovingSolarFoodDryers.pdf

Weren't the various downdraft designs essentially an improvement on the type shown in this link, as the warm air doesn't have to fight itself to exit the unit?

Im trying a downdraft type where its just a basic box with an open bottom. The food sits on a screen towards the top, and right above that I have alluminum sheet metal painted black and it is sealed to a piece of glass. There is about 2 inches between the black plate and the glass, the size is about 24 x 30. I put a thermometer in there during the sunny days, granted its only March but its been in the 60's and 70's here. I can't seem to get the temperature very high in there. I thought the downdraft type relies more on radient heat on the product not heating the air. Any ideas why mine isnt heating up very much?

Does anyone know where to find or purchase downdraft solar dehydrator plans?
I would like to build mine out of metal. I got the idea from "D acres" video on youtube. They built a separate compartment in their dehydrator where they can have a small smoldering fire. That way In the cooler month's in the fall or on cloudy days they have a way to get the extra warmth.
With hearing the responses from others it sounds like having a way to extend the months I can use the dehydrator is a valuable gain for the future.
The other aspects I would like is for it to be somewhat portable and have wheels on the bottom, an adjustable collector panel, and stacked shelf formation - so plans that have roughly these aspects would be useful to me.
Thanks
Laura (CT)