three solar food dehydrators

[Paul Wheaton]

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.

YouTube

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[Cheribelle]

Very interesting. The third one almost has me hooked.

[Cyngbaeld]

Do you know where the plans might be for those?

[am1too]

Hey that's neat. I just picked up the glass. Now all I need is the screen. That should be very easy to make. I don't understand the down draft very well but understand that heat rises easy enough.

[SolarGary]

Hi Paul,
Great video.

It might be worth adding a layer or two of black window screen in the collector part of the dryers to improve the efficiency and airflow in the collector. Scott and I did some testing of solar air heating collectors over this past winter and found that adding two layers of black window screen to the collector doubled the heat output over an empty black box style collector -- all the numbers here:
http://www.builditsolar.com/Experime...ting/Index.htm
The screen has to be placed such that the air has to flow through the screen to get out of the collector -- that is, inlet on one side of the screen and outlet on the other side. I don't see why it would not have the same sort of effect on a dryer?

Not that it really makes any difference, but adding water vapor to air actually makes it lighter. I guess the reason that 2nd dryer works is that the air is cooling (which makes it sink) rather than the fact that its picking up water vapor?

Gary

[ryanthomas]

My experience with solar dehydrators is that they only work well when the air is below about 60% relative humidity. That's probably most of the time in Montana, but people in the south may end up with moldy fruit before they get dry fruit. Places where there's a mix of humid and dry days, you just have to wait for a few days of low humidity. All of my experience is with the first type shown in the video, so maybe the downdraft types would work better.

[jwal10]

I have a smaller version of the 3rd dryer, works very well. I also use the solar collector to heat my cabin. A solar chimney on the south wall of my cabin draws the warm air from the solar heater, through the dryer, and up to a collection box at the top of the solar chimney. It is then distributed to registers near the floor of the living area. The dryer is built right into the south wall of the cabin. A plenum at the bottom of the dryer feeds directly under the floor of the cabin to the solar chimney and is opened when heat is needed. When the heat is not needed in the house it is closed and the air is vented through the dryer. The smell is wonderful when drying many things, tomatoes and basil....heavenly. Onions, leeks and garlic, not so much so it is closed for those things. Works well as our clothes dryer during the winter too....James

[Kevingr]

I made the mistake of showing these to my wife. Now she wants one. They look pretty cool though, be a nice way to deal with all of our apples from the apple trees every year.

[Paul Wheaton]

I have another video of a fella that made something similar out of an old upright freezer:

YouTube

[am1too]

Originally Posted by ryanthomas

My experience with solar dehydrators is that they only work well when the air is below about 60% relative humidity. That's probably most of the time in Montana, but people in the south may end up with moldy fruit before they get dry fruit. Places where there's a mix of humid and dry days, you just have to wait for a few days of low humidity. All of my experience is with the first type shown in the video, so maybe the downdraft types would work better.

Are you talking about all day and night or just the day time humidity? The humidity can go way down here especially in the afternoon but really climbs at night. It can be 65 % at 8 Am and 60 by 10 AM and 40 by noon till say dusk and then it climbs back to 70 and even 80.

So can these thing by shut down or regulated in some way? I did catch something about a by pass but not sure it was related to the food dehydrators. It would be a nice thing to build into a house as it could do double duty as described in the utube vids. Interesting.

I didn't quite catch the black screen idea and didn't see it in anything.

[ryanthomas]

I'm sure you could add a door and close it at night. The draw probably wouldn't be much at night anyway. The only way to know if it will work well is to try it.

[am1too]

Originally Posted by ryanthomas

I'm sure you could add a door and close it at night. The draw probably wouldn't be much at night anyway. The only way to know if it will work well is to try it.

So would that have an effect on the mold problem? Does any one have an idea how hot these dyrers get?

Would having a door effect the interior temp? None of the ones I saw appeared to have any insulation.

I guess one could install some kind of heat for the night.

[Fae]

I asked my DH to build me a solar dehydrator several years ago but thankfully, I realized it would not work in lower Alabama. I bet I could grow a lot of mold though.

[kvr28]

I built one this weekend, I'm pretty stoked to try it out

[ryanthomas]

Originally Posted by am1too

So would that have an effect on the mold problem? Does any one have an idea how hot these dyrers get?

Would having a door effect the interior temp? None of the ones I saw appeared to have any insulation.

I guess one could install some kind of heat for the night.

I really don't know if it would help the mold problem. It probably would, as long as you can dry the food in a few days or less. The temperatures can get up over 150 degrees, but I think the food is better if it is dried cooler. Dry air flow around 100 degrees is enough to dehydrate. I don't think they're going to do much at night, since the sun is what creates the draft. I would just start experimenting with small batches to figure out what works with your climate.

[am1too]

Originally Posted by kvr28

I built one this weekend, I'm pretty stoked to try it out

Say you wouldn't have more pics or details would you? I'm interested in what you used for screen, the top vent and interior. I have some black plastic screen used as window screen on about 20 large window screens in allum frames.

What are the outside dementions?

I recently picked up the sheet glass and messed up. I could have gotten enough to build a small green house. Any way the glass is 35 inches wide and 7 ft long. Tempered too.

[wildolive]

What material did you use for the trays? (the material the food is on)

[Windy in Kansas]

Neat. I thought we'd be talking old Buick station wagon here.

[Sanza]

very nice kvr!

[Alice In TX/MO]

It says in the video to use stainless steel screen.