Solar Food Dryers?

This is a DEHYDRATING KITCHEN CABINET!

I don't know if this exact model would move air well. I wanted to get a rough idea of what this would look like.

The idea was to merge my latest solar dehydrator plans with the exterior wall of a kitchen, to allow for easy interior access to the dehydrating cabinet and contents.

These are units: A solar collector unit, and a dehydration cabinet unit.
I wanted to design the two pieces/units.... but I don't know if air will move through them well.
Not weather protected!

Modular design makes sense Second collector on top to draw air out should be effective. To clarify the design, is the exit side drawing air from the bottom of the cabinet?

Hans Quistorff wrote:To clarify the design, is the exit side drawing air from the bottom of the cabinet?

Yes. There is a false wall on the north side of the cabinet.

Here is the one I made.
I would like to make a room sized one later.

Hello...is there anybody out there?  I’m considering building a dry food system for next season. To stack functions it would be nice if the warm air could heat the home when it’s not in use as a dryer. One far fetched idea I had years ago was to run a long cloche up a hill, a clear tunnel going up the hill to a dryer or a home. It seems a lot of draft might get going. I’ve thought about a long sloped greenhouse also and what that could be used for. I also wanted to turn a entire house into a draft inducer for natural ventilation and heating.

Jeremy Baker wrote:Hello...is there anybody out there?  I’m considering building a dry food system for next season. To stack functions it would be nice if the warm air could heat the home when it’s not in use as a dryer. One far fetched idea I had years ago was to run a long cloche up a hill, a clear tunnel going up the hill to a dryer or a home. It seems a lot of draft might get going. I’ve thought about a long sloped greenhouse also and what that could be used for. I also wanted to turn a entire house into a draft inducer for natural ventilation and heating.

Those are workable ideas. In fact if a greenhouse is too hot for plants in the summer use it as a dehydrator.

If you have a solar heated tube running up the hill and buried earth cooled tube running down the hill, at night the circulation will reverse. the tube exposed to the sky will cool the air by radiating heat out causing the air to fall and the ground will warm the air causing it to rise. Thus some drying could occur at night as well as during the day.

Which climate and season do you want to dry food in?

I live in such a dry climate that inside a sunny window in September and October is sufficient for drying food. Actually, in early September a sunny window is too hot, and foods high in sugar, such as fruit or tomatoes, burn. October is perfect here for a sunny window, or other seasons outside in a well ventilated spot such as on my flat roof. I got a little tent meant for keeping flies off an infant outdoors, and it works great for drying food. I just put trays and plates in it, consolidating them when the food is half-dry, and adding more every couple of days. If you are in a damp climate then yes, heating the air to reduce its relative humidity and using some system to increase the air flow are needed, and your idea could work.

About using the hot air for heating a house, I think it might be slightly helpful, but generally hot air doesn't make nearly as comfortable a heating system as direct passive solar gain and heat storage. But of course that's not possible in all locations.

I happened upon several hundred square feet of structural insulated panels and a bunch of insulated polycarbonate, and had no good place to store the panels.  So I built a solar kiln, loosely based on Virginia Tech's plans. I made changes to capitalize on upward air movement so I may be able to use it without the solar power function in certain seasons. I have yet to dry a batch of wood in it, but we are currently running our first test using it as a large batch solar dehydrator.  Nearby Wichita is an aviation capitol, so there are lots of surplus metals.  I can get stainless steel mesh by the yard in 48inch widths, so I can affordable make several hundred square feet of drying racks for not too much.  Questions/opinions welcome . . .

Nice build.  Does your part of Kansas get much in the way of humidity?  Have you or others (Virginia Tech?) had a chance to test it in very humid climates?  We end up battling both molds from low drying potential and extended drying times.....and additionally, bugs that may fancy what's being dried before it reaches suitable dehydration.  I find that both the molds and bugs can be reduced by getting the air temperature high enough to reduce their growth or comfort level, but not so high that it's cooking the item within.  I like the idea that yours is sort of a 'walk-in' type set-up with the flexibility for wood and veggie/fruit drying.

It is pretty humid here in certain seasons.  This time of summer is dry, but spring and early summer tends damp.  Virginia Tech designed the system to work through humid seasons of sub-tropical climates, I believe.

[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?
 

I think air gaps are ok.  Its the moving air that carries away the moisture as the food dries so I wouldn't worry about air gaps from your rough cut stuff.  You can use mop head string to seal the gaps if you want installed as you put the boards together, but again its the moving air that carries away the moisture, and besides, who said the air has to follow yours or anyone else's prescribed path.  We are talking about drying food here not  super insulating and sealing a leeds certified greenie home.

Just char the interior with a propane torch.   Build your box and char the thing.  Keep some water handy in case you catch it on fire to douse the flames.  The char, as we know, is non-toxic and absorbs odor, but mostly it absorbs heat.  I would stay away from ALL the paints and the silicone; they cost too much in too many ways, but mainly by contamination.  

We used to dry on tables made with 1x4s with hardware cloth to put the food on and covered with cheese cloth.  No issues, stupid easy, and cheap.  Apples dried in 2 days, squash in 2 days, roasted peeled green chilis in 2 days.  I don't recall flies being an issue, but when you grow up on a farm they are just part of everyday life, like scraping cow dung off your boot.  The only thing we didn't try drying are tomatoes.  Some sites say that high acid foods like tomatoes are corrosive to the zinc coating,  which is an elemental mineral we all need, so does it really matter if it does?  Hmmm... then again maybe not.

Has anyone built a solar dehydrator on top of a propane grill base? My propane grill rusted out around the flame deflector and burners but I'm thinking the base would be good repurposed to make a mobile solar dehydrator.

Larisa Walk wrote:

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.

Hi Larisa,
where can i find plans/design of your food dryer?  the url with geopathfinder doesn't work for me.

Thanks!

We're "retired" somewhat and are no longer maintaining our website. But you can find most of its content on the Wayback Archive here: https://web.archive.org/web/20180117013247/http://www.geopathfinder.com/Solar-Food-Drying.html
You can message me through this site if you have any questions.

A comparison between the giant solar food dehydrators at Wheaton Labs:

Anonymous wrote: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! 

OLD THREAD; Adding This For Future Visibility:

https://aurorasolar.com/blog/storing-solar-energy-everything-you-need-to-know/

(On storing solar energy for cloudy days)