Solar Dehydrator

by Daisy

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I have been researching solar dehydrators and there is a cardboard and duct tape one making the rounds on the internet that seems like an inexpensive starter model. I may make a “real” one later, one that won’t melt if it rains, but in the meantime this one should allow me to experiment with the concept a little. Here’s what I’ll need:

  • 2 cardboard boxes
  • clear plastic wrap, plexiglass, or glass
  • duct tape
  • black paint, black plastic, or black paper

One box needs to have tall sides and be squarish and the other needs to be long and more rectangular. So I guess I’m off to the home of the best free boxes: the liquor store. While I’m there I might as well get some brandy for that recipe for vanilla extract I have been looking at for a while. I have a vanilla bean that isn’t getting any younger.

Day 1:

None of the boxes was long and skinny like I’m supposed to have for the solar collector, so I grafted two similar size boxes together with duct tape and cut off the “top”. I also added another layer of cardboard on all sides to improve the insulation factor a little bit:
Then I attached the solar collector part at an angle to a nice, square box with more duct tape and cardboard from cutting apart one of the other boxes:

I cut holes in the bottom and top of the collector and into the drying box for through ventilation:

. . . and glued black construction paper to the bottom of the solar collector box and covered the collector with plain old plastic wrap. Not very durable, but it will have to do for a start.

The whole thing rests on a third box. I made a shelf out of scrap cardboard to increase the surface area inside the drying box for drying things. A cloth will drape over the top of the drying box to keep bugs and things out while in use.

The sun is going down so I will have to wait until tomorrow to test it out.

Day 2:

11 a.m. The sun has been up for a while and I put a thermometer inside the box to see what temps we can generate inside. It is 90 degrees ambient temperature and 108 degrees inside the box. Doesn’t seem nearly hot enough to me. I will adjust the angle of the box to get the most sun and put one tomato out there and see how it goes.

11:30 a.m. It is up to about 130 degrees. Better, but is it good enough? I will keep checking the temperature and the tomato.

12:00 p.m. 145 degrees. Cut surface of tomato skinning over a little.

2:00 p.m. 150 degrees. We have had a few clouds today, but it has been mostly sunny with a high of 98 degrees.

7:00 p.m. 95 degrees. The tomato is somewhat wrinkly around the cut edges and a thick skin has formed on the cut surface, but this tomato is far from dried after 8 hours in the box.

Not what I had hoped. Is this the best the cardboard solar dehydrator can do?

What may have gone wrong:

  1. Solar collector too deep and narrow.
  2. Construction paper not dark enough and sides of collector not blackened.
  3. Inadequate insulation.
  4. Plastic wrap too reflective and not insulating.
  5. Not enough sun.
  6. Need to calculate the angle of the sun to adjust the angle of the collector.
  7. Tomato on solid surface instead of a screen.
  8. Need several days to dry–but what to do with the fruit overnight? Will it spoil before it dries?
  9. ???

I will try another tomato on the next very sunny day and see if I get another result. I may also try to build a solar collector with a wider surface area and completely black out the inside. I don’t want to give up on this because I think it is a worthwhile project and I believe it is do-able. I just need the right design and the right procedures for usage. So far my only expense has been duct tape and plastic wrap, so I don’t feel like I have wasted my resources.

Perhaps the climate here is too humid for the kind of 1-day dehydrating I was hoping for.

Back to the drawing board and, for the time being, back to the old oven with my tomatoes.



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{ 4 comments… read them below or add one }

Kate May 18, 2011 at 9:14 pm

I also made this dehydrator! I’m using it now. It took 3 days for my mango slices to dry. I’m drying tomatoes now. Again, it is a bit slow. I painted my chute with black paint instead of using construction paper. Also, I lined my dehydration box with mylar. I don’t have a thermometer, but I can feel the warm air coming in….

I would love to hear if you made any changes and gotten better results! I’m a missionary living on the equator. It should work here!

Tomato Lady May 19, 2011 at 7:21 am

Kate–Never made any mods, I think my problem was my distance from the equator. Yours sounds like it’s doing just fine!

Julia @ January 2, 2013 at 12:38 am

New subscriber — just browsing. I also made this in Iowa — didn’t have spectacular luck. Still want a dehydrator that is solar powered, and I’m thinking that it’s not the distance from the equator, but the materials used. If I try again, I’ll let you know.

Daisy January 2, 2013 at 10:00 am

Julia–Yep. It’s so humid here. I don’t know if it would ever work in our climate.

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