Solar Food Dryers?

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).

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/

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.

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.

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.....

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    

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.

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

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.

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.

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?