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Solar Food Dryers?

 
Posts: 257
Location: Nicoya, Costa Rica
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Hey, thanks for replying, and sorry for the confusion. The solar collector is only the top slide of that triangular greenhouse thing. Whatever you see painted of a brick color. There is actually a black-painted sheet of corrugated zinc roofing 2" below the transparent panel. The hot air gets inside the chamber from a slot on the top left (looking from standing in front of the door), which is the same size as the screened opening at the bottom of the slide. Yes, there was a wall made of cardboard I made to remedy a mistake made by the guy who helped me make it; then it fell in (you can see it at the bottom of the greenhouse thing inside), but I saw it wasn't affecting the operation much. The chimney is a faux wall on the right-hand side, however, I didn't have enough wood (all the material was donated and on a budget), so I made a half wall that turned into a chimney pipe that I painted black and moved back to the sunny side for a passive solar chimney effect. I am keeping the dehydrator under my solar panel rack to protect it from the rain and excessive sun. I am aware that all my changes jeopardized the top-draft design. Someone told me top-draft is not indicated for the Tropics anyway. Thing is, when the sun is not shining, all activity stops, while I was of the impression that some draft would go on by inertia.
I still like the top draft, because it allows me to have a fan pointing down. A fan at the bottom might get dripped on by my pineapples.
 
Sergio Santoro
Posts: 257
Location: Nicoya, Costa Rica
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Here is the rear of the monster.
IMG_1639.jpg
[Thumbnail for IMG_1639.jpg]
 
Sergio Santoro
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Location: Nicoya, Costa Rica
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Even if I were to replicate the same model, or make the actual one true to the design, I need advice on the material. The transparent sheets are all cracked under the sun, starting from the screws (with washers). The silicone thing is all brittle and air and bugs come in from everywhere. I also couldn't find a bug-proof way to seal the door. I think I used some fridge door rubber thing. I could use polycarbonate for the transparent panels, but wouldn't a smooth surface reflect part of the light-heat?
 
gardener
Posts: 2989
Location: Southern alps, on the French side of the french /italian border 5000ft high Southern alpine climate.
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Just bumped into this.

Sergio, if you want walk in. Why not try to adapt a solar kiln?

https://www.google.fr/search?q=solar+kiln&safe=off&rlz=1T4SAVJ_enFR550FR551&prmd=ivnsp&tbm=isch&tbo=u&source=univ&sa=X&ved=0CBQQsARqFQoTCLfNyKWfxscCFUu1FAodb3YH9Q

I can't find the old virginia tech solar kiln plan. But there's plenty about.
 
pollinator
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Location: Longbranch, WA
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I don't know if this material is available there but it is common here, glass sliding doors. In the tropics you do not need the slope on the solar collector. The sun comes up and shines on the East side of the solar collector then shies down on the top then shines on the west side as it sets. Therefor if you make your solar collector rectangular with g;ass on the east, top, and west. Fill it with layers of stones with metal roof sheets in between so that the air has to circulate back and forth through the stones. The stones will get heated during the day and if you cover it with a blanket at night the heat will continue to circulate.
 
Sergio Santoro
Posts: 257
Location: Nicoya, Costa Rica
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I just took a look at the solar kiln, and it seems like an interesting alternative. I'll read about it later.

Hans, what do you mean with "not on a slope"? That the solar collector can be horizontal, or vertical? I'd imagine horizontal, like a glass coffin.
 
Hans Quistorff
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"like a glass coffin." Yes that would be a good description.
 
Posts: 78
Location: Eastern Cape,South Africa Zone Cfb, Annual rainfall 570mm,
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Hi, If anyone near Henley on Thames ,UK would like a DIY solar dehydrator to tinker with I have one going as I am leaving the UK soon. There are photos on the new topic I created in food preservation.
 
Sarah Joubert
Posts: 78
Location: Eastern Cape,South Africa Zone Cfb, Annual rainfall 570mm,
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Sorry, that's where I am now! I meant under regional: Europe
 
Posts: 24
Location: Port Lavaca, Texas
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Would it be possible to use a Fresnel lens aimed at a black pot for instance incorporated into a solar dryer to boost inside temps? Maybe add a solar powered exhaust vent in case it got to hot?
I remember we used to use the cracker jacks magnifying lens to burn stuff when we were kids
 
Posts: 204
Location: South of Winona, Minnesota
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Larisa Walk wrote: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).



I'm quoting my old post as it seems relevant to where this topic has meandered. I think most folks are over-thinking or over-engineering the concept of a solar food dryer. Our design has been drying hundreds of pounds of fruits and veggies for us for over 30 years. We've been teaching about this design for over 20 years and as a result it is being used world-wide, some for commercial use. Complicated heating collectors, fans, boxes, etc. are absolutely unnecessary and are a waste of time/money/resources. Here's the current link to our webpage at GeoPathfinder.
 
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Location: North Carolina
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I know this isn't what you asked for but I was myself thinking about building a solar food dehydrator and then I realized that I already have a huge one, it's my attic. I plan to build some simple racks that can be hung up in there and do my drying. Just don't forget that the stuff is up there. Maybe an option for you I don't know.
 
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If you are in a warm enough climate you may not need solar panels. Even just an old window or glass door or piece of acrylic attached to a wood box on  an angle fitted with screens for drying  the produce may be all you need. Here is a DIY  picture. http://gardenclub.homedepot.com/build-a-dehydrator/

Also I've seen hanging  screened dehydrators on Amazon that look like bird cages with 3 trays inside for less than $50.
 
pollinator
Posts: 323
Location: Poland, zone 6, CfB
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Here is my "monster"

It consists of movable beer can solar collector, that can be connected anywhere I need and a "cabinet" with shelves for stuff I want to dry.



Shelves are just wooden frames with aluminium mesh. Area of shelves is 4 square meters.



For herbs, it usually takes half a day of a good sun to dry



This is a prototype I was testing to see if it works, so the cabinet is covered just with cardboard, but since it works great, I will replace cardboard with plywood soon.

Temperatures in the cabinet diifer, close to the inlet from beer can solar collector are approximately 30-35 degrees Celsius more than air temperature, while at the outlet just 15-20 degrees more, so you can choose your drying temperature by using different shelves.

It is possibe to get much higher temperatures by connecting collector directly to the cabinet, without tubes, but then it is more difficult to follow the sun, and temperatures can get up to 55-60 degrees Celsius higher than air temperature, which is in case of many herbs not beneficial.
 
Posts: 103
Location: Australia, Now zone 10a, costal, sandy, windy and temperate.
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Matt Smith wrote:

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




The above link doesn't work... Try this one.

http://www.news.appstate.edu/2009/07/09/solar-food-dryers-designed-at-appalachian-preserve-food-worldwide/

 
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I just stack window screens on my front porch in the sun.   Air flow and mild heat cause food to dry; I also want to keep the bugs out.

So, first screen goes down with no food; second screen is placed at an angle on top of the first and food is placed to dry; place a third screen square on top of the second to keep the bugs out.  Fourth screen is off center from the 3rd and food goes on; 5th screen is square on the 4th to keep bugs out. Off-centering creates space for airflow through the screens.

If I'm drying herbs and don't want the sun to bleach out the color, I'll place a lightweight dark cloth over the final screen.   On a long summer day, dill will dry in 1 day, apple slices take 2-3 days.  I dry all my culinary and medicinal herbs, apples and pears.  I haven't had a problem with ants or bugs getting in.

The whole thing is light-weight, easy to move and store.  I don't use aluminum screens because some food is acid;  I think that the screens are nylon.  I've also experimented with placing a glass window on top of the stack and it does warm up faster.
 
steward
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Location: Sunshine Coast, BC
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Bonnie; I love the simplicity of your system. We humans sometimes tend to make things a little more complicated than they need to be, I think. Okay, off to find some window screens . . .
 
pollinator
Posts: 254
Location: Central Texas (Georgetown)
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Mark Vander Meer tells me I have figured it out.

Also, Mark supplied a neat PDF for us created by the Little Colorado River Plateau Resource Conservation and Development Area, Inc.

Lucas McIver has been involved with Mark's structure (to what degree I don't know).
20170521_131326.jpg
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Solar Dehydrator - Air Movement
Filename: Solar-Chimney-Dehydrator.pdf
Description: PDF supplied by Mark
File size: 1 megabytes
SOLARDEHYDRATOR_XXB02_pic01.jpg
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Model similar to Mark's structure and PDF's structure
 
Davin Hoyt
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Posts: 254
Location: Central Texas (Georgetown)
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Paul asked me to innovate:

1.) The air entering the system needs to come from a dry place.

2.) The air leaving the system needs a boost.

(We argued)

(I agreed to make a model of a structure that incorporated his ideas, but have the opportunity to switch back to Mark's structure)

I was semi-successful in coming up with a design.

Here is the hybrid with leaders to explain the functionality option 1 and functionality option 2.
SOLARDEHYDRATOR_01_pic03.jpg
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Solar Dehydrator Model - Hybrid
 
Hans Quistorff
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Posts: 986
Location: Longbranch, WA
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I was semi-successful in coming up with a design.

Here is the hybrid with leaders to explain the functionality option 1 and functionality option 2.


I think you are beginning to get the concept but getting the exit air through the incoming air on the front would cause to much restriction.
My prototype did not have a roof so I was able to extend the exit air wall above the top of the cabinet with glazing on the front of the extended portion which gave the needed boost.
In your modified design you continued the exiting air across the top of the cabinet it would pick up some boost from the heat absorbed by the top of the cabinet then it could turn vertical with glazing on the front to the roof and exit under the roof so rain can not enter.
One of my previous suggestions was to use black rocks in the triangle between the cabinet and glazing instead of collector plates. The rocks will store heat so that the circulation will continue for a time after solar collection stops.
 
Davin Hoyt
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Hans Quistorff wrote:

I was semi-successful in coming up with a design.

Here is the hybrid with leaders to explain the functionality option 1 and functionality option 2.


I think you are beginning to get the concept but getting the exit air through the incoming air on the front would cause to much restriction.
My prototype did not have a roof so I was able to extend the exit air wall above the top of the cabinet with glazing on the front of the extended portion which gave the needed boost.
In your modified design you continued the exiting air across the top of the cabinet it would pick up some boost from the heat absorbed by the top of the cabinet then it could turn vertical with glazing on the front to the roof and exit under the roof so rain can not enter.
One of my previous suggestions was to use black rocks in the triangle between the cabinet and glazing instead of collector plates. The rocks will store heat so that the circulation will continue for a time after solar collection stops.



I believe you are saying that my hybrid model could have:

1) a chimney (back false wall extending upward past dehydrator cabinet ceiling).

2) air draw at exit of chimney (front plane of chimney being glass/transparent material).

3) more heat applied to air entering dehydrator cabinet (front portion of cabinet ceiling replaced by glass plane).

Note: These modifications would require corrugated roof modifications.

Thanks Hans!!
 
Hans Quistorff
pollinator
Posts: 986
Location: Longbranch, WA
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What I am proposing does not require any roof modifications. To make sure we are referring to the same things  I will refer to the captions in illustration #1.
Where it reads "air exits dehydrator cabinet at bottom" into hollow back wall insulated on the outside.
Where it reads "Air exits" at the top of the wall change the wording to 'air turns and crosses top of cabinet in hollow ceiling insulated on top'. show hollow ceiling like you did back wall.
Show tromb wall illustrated like solar collector up to the rafters. Move the "Air exits system" wording to the front with arrow pointing to under the rafters.
Below "Air enters system" wording change ceiling to cabinet and add triangular space can be filled with rocks which dry early morning air and when heated during the day continue air circulation into the evening.

I believe those simple changes Would be enough to make a very efficient system.  Insulation can be as inexpensive as repurposed plastic corrugated advertising signs or as simple as using foil backed foam panels for the outside wall and ceiling.  Because mine was not exposed to rain I just used corrugated paper box material for the exterior.  My goal was cross flow of air instead of down flow so I place air entry holes between each tray level front and back of the cabinet. My solar collector was vertical with the cabinet starting three feet up and was a three foot cube. The trombe wall was another three feet. This put the cabinet where loading and unloading the trays was easy. With cross flow spacing of pieces to be dried could be closer than with down flow.
 
Larisa Walk
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I'm always amazed at the complexities people get their minds into when dealing with something as simple as food dehydration. Want a solar food dryer really cheap and already built? Look outside. See that motor vehicle parked in the sun? It gets hot. Now face the biggest window toward the sun (S in the N hemisphere, N in the southern). Prop up a screened tray of uniformly thinly-sliced food so that it sits in the sunlight shining through that window. Place some black cloth over the food to block nutrient-sapping light and to generate heat that radiates down onto the food and creates some air convection. Crack open a couple of windows about an inch. You now have a very effective solar food dryer, even for highly humid areas. You can see a purpose-built design using this principle, tested worldwide since 1985, at this site: http://geopathfinder.com/Solar-Food-Drying.html.

The biggest problem with stacking up trays in a box, emulating an electric dehydrator, is that you have to fight physics. With an electric dryer, if it doesn't work terribly well you simply leave it run constantly and let the meter spin. Humidity is concentrated, airflow and heating must be greatly increased, and the whole thing requires tight seals, big collectors, and optimized air paths. Using indirect radiant heating is much simpler, much more effective, and easier to build. I know I'll never convince a die hard box fan to think outside the box, and I know that the box designs just seem so obviously right, but sometimes the mentally obvious choice isn't what's supported by actual food drying experience in the real world.
 
pollinator
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Larisa Walk wrote:.... Want a solar food dryer really cheap and already built? Look outside. See that motor vehicle parked in the sun? It gets hot. Now face the biggest window toward the sun (S in the N hemisphere, N in the southern). Prop up a screened tray of uniformly thinly-sliced food so that it sits in the sunlight shining through that window. Place some black cloth over the food to block nutrient-sapping light and to generate heat that radiates down onto the food and creates some air convection. Crack open a couple of windows about an inch. You now have a very effective solar food dryer, even for highly humid areas. You can see a purpose-built design using this principle, tested worldwide since 1985, at this site: http://geopathfinder.com/Solar-Food-Drying.html.....


Larisa, I think you're right and that works fine ... but what if you do not have such a 'vehicle'? My bicycle does not have windows ...
I do have a living-room window facing south-east (sun all morning until about 3.30 PM during summer). Maybe I could use that for drying fruits (and mushrooms)? I still have some time to figure that out before my trees produce the needed amount of fruits    
 
Mother Tree
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The boys have just made me a very basic dryer.  At this time of year it works very well, and it gives us a chance to test things out and design another one to suit our needs for the rest of the year.  Maybe a bigger, more upright one with more shelves and a 'chimney' that won't cause panic if a rain cloud appears.  We're enjoying having the see-through door on this one, but when the novelty has worn off we'd probably be quite happy with wooden door.



There were a couple of design flaws on this one.  It really needs a handle that doesn't heat up in the sun.  And we need a way to stop the door opening too far and damaging itself while I have both hands in use maneuvering the trays in and out. There are also plans to add some kind of closable lid in case it rains.
 
Larisa Walk
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Inge Leonora-den Ouden wrote:

Larisa Walk wrote:.... Want a solar food dryer really cheap and already built? Look outside. See that motor vehicle parked in the sun? It gets hot. Now face the biggest window toward the sun (S in the N hemisphere, N in the southern). Prop up a screened tray of uniformly thinly-sliced food so that it sits in the sunlight shining through that window. Place some black cloth over the food to block nutrient-sapping light and to generate heat that radiates down onto the food and creates some air convection. Crack open a couple of windows about an inch. You now have a very effective solar food dryer, even for highly humid areas. You can see a purpose-built design using this principle, tested worldwide since 1985, at this site: http://geopathfinder.com/Solar-Food-Drying.html.....


Larisa, I think you're right and that works fine ... but what if you do not have such a 'vehicle'? My bicycle does not have windows ...
I do have a living-room window facing south-east (sun all morning until about 3.30 PM during summer). Maybe I could use that for drying fruits (and mushrooms)? I still have some time to figure that out before my trees produce the needed amount of fruits    



Good for you to be one of those without a car. It's not the most ideal setup anyway, just something that most people are stuck with. A greenhouse will also do the trick but house windows don't heat up the space enough for drying fruits but may work OK for mushrooms. Some folks have built our dryer and made the black heat collector removable and use the glazing covers in early spring for cold frame covers. Flexibility can be designed in when building from scratch.
 
Larisa Walk
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Burra Maluca wrote:The boys have just made me a very basic dryer.  At this time of year it works very well, and it gives us a chance to test things out and design another one to suit our needs for the rest of the year.  Maybe a bigger, more upright one with more shelves and a 'chimney' that won't cause panic if a rain cloud appears.  We're enjoying having the see-through door on this one, but when the novelty has worn off we'd probably be quite happy with wooden door.



There were a couple of design flaws on this one.  It really needs a handle that doesn't heat up in the sun.  And we need a way to stop the door opening too far and damaging itself while I have both hands in use maneuvering the trays in and out. There are also plans to add some kind of closable lid in case it rains.



The main problem with this type of design is that the food is exposed to sunlight, which "bleaches" out the color and related nutrients. The only time that UV sunlight is desired is when drying mushrooms. Exposure of the gill/pore side of the mushroom to sunlight increases vitamin D levels dramatically. The mushrooms need to be in direct sunlight however, not behind glazing. Read more about this at http://www.fungi.com/blog/items/place-mushrooms-in-sunlight-to-get-your-vitamin-d.html.
 
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I dry leaves more than anything else, and since we live in an arid climate, the drying rack my husband made works great.
My main problem is drying fruits. I end up drying them in an electric dehydrator. The cherries have a burnt flavor unless they are dried in a dehydrator that keeps the temp low enough while allowing good air circulation. Can a solar dehydrator do this?
 
Burra Maluca
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Larisa Walk wrote:The biggest problem with stacking up trays in a box, emulating an electric dehydrator, is that you have to fight physics.



Not necessarily.  Mine has mesh top and bottom so the air can flow up or down, whichever way it wants, and moist air can't pool anywhere.  Essentially, it's just a way to keep the flies off stuff as it's drying.  And I think it takes far less material to build a box-shaped one than one where all the trays are laid out side by side.  

I think the important thing is to be able to see all the options and choose which one suits your own climate and available facilities.  For me, a car with the window open wouldn't keep the flies off, which is all I really want.  Assuming I had a car available for the purpose.  A box seems more do-able.
 
Larisa Walk
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William Bronson wrote:
I intend to build mine to the dimensions of commercial kitchen sheet pans. There are perforated pans of these dimensions that I'll use for my trays.
They are aluminium,which would be a nonstarter for some,but works fine for me in this application.



I've looked into the idea of the commercial sheet pans. Aluminum would be OK if you're doing non-acid veggies. Not so great for acidic fruit. I think a highly perforated stainless steel tray would be the ultimate in durability and ease of cleaning, but haven't yet found anything that meets the criteria and is within price range of the screen.
 
Larisa Walk
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Burra Maluca wrote:

Larisa Walk wrote:The biggest problem with stacking up trays in a box, emulating an electric dehydrator, is that you have to fight physics.



Not necessarily.  Mine has mesh top and bottom so the air can flow up or down, whichever way it wants, and moist air can't pool anywhere.  Essentially, it's just a way to keep the flies off stuff as it's drying.  And I think it takes far less material to build a box-shaped one than one where all the trays are laid out side by side.  

I think the important thing is to be able to see all the options and choose which one suits your own climate and available facilities.  For me, a car with the window open wouldn't keep the flies off, which is all I really want.  Assuming I had a car available for the purpose.  A box seems more do-able.



In the car scenario, the dark/black cloth keeps insects off the food. It's a good option for those adverse to building something, whether for lack of funds or skills.  An acquaintance of ours dried food in her car while at work, checking in on it at lunchtime. The food was prepped in the morning and set up on the trays when she parked her car. Another fellow we knew had an old junker that he towed into place to face the sun and he used it all summer. The point is that you can often "make do" with whatever is at hand. In the midwest, in our experience, the humidity is only overcome reliably with the non-stacked tray design. All other solar dryers have failed to deliver here without backup electric crutches, unless conditions are perfect (hardly happens especially when you need/want it). We depend on solar drying for a significant portion of our food preservation for the year. Other than raisins, we don't buy any fruits or veggies which, as vegans, are a primary part of what we're eating daily.
 
Richard Gorny
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A tiny solar panel (size of a A5 paper sheet) and recycled fan from old PC makes wonders to speed up drying process. A small portable solar panel and a portable fan are very versatile by the way and have so many uses that I consider them valuable pieces of homestead hardware.
 
Larisa Walk
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Liz Hoxie wrote:I dry leaves more than anything else, and since we live in an arid climate, the drying rack my husband made works great.
My main problem is drying fruits. I end up drying them in an electric dehydrator. The cherries have a burnt flavor unless they are dried in a dehydrator that keeps the temp low enough while allowing good air circulation. Can a solar dehydrator do this?



Our solar dryer can do a fine job on fruits, including watermelon (with a few tricks). In an equatorial or arid climate our design may need some tweaks to keep a highly sweet fruit, like cherries, from caramelizing. If your conditions are always no clouds and no humidity, you can use a less efficient paint on the collector plate, such as brown or dark blue. I prefer to keep options open and would do some partial shading, with screen or shade cloth over the glazing to reduce the heat, leaving the paint black. That way you still have the option of using the dryer at full strength when you need it, like when first putting a load of very wet food on the trays. As the initial high moisture level reduces, less heat is needed and then is when to do the shading. All of this requires some experimentation on the user's part as there isn't a thermostat on any solar food dryer, at least not one that is home built, simple, and inexpensive. Thickness of pieces also affects results with thinner slices more likely to caramelize. BTW, one year, even in Minnesota, we had some tomatoes get scorched on a hot summer day. I thought they were a write off. But it turned out that the flavor was comparable to oven roasted tomatoes. I threw those dried tomatoes into dishes with canned tomatoes and the flavor was really enhanced. Now we try to intentionally replicate the conditions on at least some of the tomatoes that we dry.
 
Davin Hoyt
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Location: Central Texas (Georgetown)
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My last visit to Wheaton Labs was for the ATC of 2017.
While there, I documented the solar dehydrator that Tim Barker and Rob Griffin built during the ATC of 2016.
I have found the time to bring that forward. :)



Digital Market Link: https://permies.com/t/86785f35/Solar-Dehydrator-Plans-Hot-Aussie


 
Davin Hoyt
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Hi Everyone,

The University of Georgia contacted me wanting to build a solar dehydrator based on the plans at the digital market:
https://permies.com/t/solar-dehydrator?f=35

This is what they came up with...
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Solar Dehydrator on trailer at University of Georgia.
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Solar Dehydrator on trailer at University of Georgia.
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Solar Dehydrator on trailer at University of Georgia.
 
Time is the best teacher, but unfortunately, it kills all of its students - Robin Williams. tiny ad:
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