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bennelson 09-22-09 10:12 AM

Ben's DIY Solar Food Dryer
Hi everyone!

This summer, my wife and I joined a CSA - Community Supported Argiculture.

Basically, you "buy-in" for a share of whatever a farmer grows during the season. The trouble with that is you may end up with a whole bunch of who-knows-what that you can't possibly eat at once.

Wouldn't it be nice to be able to preserve some of that for the winter without canning or buying a (energy-gulping) freezer?

So, I tried building my own solar food dehydrator.

I had a few misc parts around, and figured I could build one out of junk for basically no cost.

First, I built a box out of foamcore and scrap 2x4s, then added glass to the top and plexiglass to the front.

I had two 12V DC computer fans that I attached to holes on the back top of the dryer.

Those run to a spare 12V battery from my electric car project. That battery gets charged up by a 15-watt PV panel.

Thus, the sun can shine in during the day and help dry, and the fans can run 24-hours a day, but still be solar powered. There are three holes cut in the bottom front of the dryer to allow in air, which are covered by a bit of screen to keep the bugs out.

Inside the box, I have 1x2's screwed to the side to support the screens. Those are recycled modern window screens which have been well washed.

Food is prepared by washing/peeling/slicing and getting laid out, single layer, on a screen. The screen goes inside and the fans pull air through it for a couple days.

So far, I have done tomatoes, basil, apples, pears, and peppers.
Tomatoes can stick to the screen. The basil got amazingly dry. Apples were good, but the pears almost turn into candy.

Here's a tomato after a few days in the drier. It gets sweeter, and is great in salads and pastas. (No I didn't Photoshop the clouds...just good exposure on the camera.)

Last night, I cored, peeled, and sliced about half a 5-gallon bucket of apples. After all that work, it came to about a screen and a half of slices.

I found that the apples were small enough that I could slice an entire apple at a time with my hard-boiled egg slicer, although it didn't cut as clean as a knife.

You can also see all these photos on Flickr by clicking the following link:
solar dryer dehydrator construction - a set on Flickr

Daox 09-22-09 10:45 AM

Very cool Ben!

So, how well does it work so far Ben? Are you happy with it?

I always thought it was kinda wasteful to have a food dehydrator that runs a heating element and fan all day! There has to be a better way, and this looks like it.

bennelson 09-22-09 11:19 AM

It works pretty well overall.

It's fairly sloppy construction, so the door on the front doesn't fit as tight as I would like it to. I didn't have a door latch around, so I just ran a couple of drywall screws threw to hold the door shut.

Ideally, I would add weather-stripping around the door and a nice tight latch, so that it is easy to open and close, but seals up and still keeps the animals out.

I painted the inside bottom of the box black, as that was plywood. I didn't bother to paint the foamcore. Also the screens are basically black, and fill up so much of the inside of the dryer, I don't think the walls of the box suck up much solar energy - it just hits the screens instead.

In one of the photos, you can see a larger piece of plexiglass over the top of the whole unit. This protects the edges of the foamcore from rain, and helps cover up the fan holes in the back.

It's actually raining out right now - about the first rain in a month - I am not sure how well I can dry things out when it's wet!

bennelson 09-25-09 08:49 AM

It's still raining out!

Ok, well RIGHT now, it's just really cold and cloudy. We hadn't had any rain in a month, and then we get rain rain rain, wet, and cold.

Not exactly the best thing for a solar dryer.
Even though the fans only pull a tiny amperage, the battery is slowly wearing down, as the PV panel has made essentially NO electricity for the last three days. It wasn't even fully charged when I started!

I hope for sun, rather than having to break down and plug in a battery charger. Even then, my house is on a renewable energy program, where all my electricity comes over the grid from wind and other renewable sources.

Daox 09-25-09 09:24 AM

Is the dehydrator even doing anything with the high humidity?

Ryland 09-25-09 11:58 AM

This is the style that we have at my parents house.


we built it about 15 years ago and it works really well, because the food is kept in the dark it holds it's color and nutrition and the larger area lets things dry quickly.

bennelson 09-25-09 01:40 PM

I just checked the dryer.

Even though we have had all the rain and humidity, the apples ARE still drying out, but not at the rate I would expect with better weather.

I think all they would need right now is just ONE DAY of sunlight and NON-100% humidity.

My big concern with all the rain is a chance of any mold forming on the apples due to the humidity before they dry.

It was just unfortunate that I just started a big batch right when the bad weather hit.

I still have 3 gallons of Asian Pears, which are SO GOOD dried, but I need some better weather and peeling and chopping time first.

Daox 09-04-13 11:16 AM

Hey Ben, have you used your dehydrator since the last update to this thread? Any suggestions / changes you would incorporate if you made a new one? I'm thinking about making one and am looking for suggestions and info.

The you posted Ryland is really interesting too. How long does it take to dry a 'batch' of stuff in one of those dryers?

bennelson 09-04-13 12:26 PM

I took that dehydrator apart. I only used it for one season. It was really a creative recycling project.

The walls of the box were foam-core, which really isn't an outdoor-rated material.

I guess that if I were to do it again, I'd build from scratch using some materials that would let me store the dryer outdoors year-round. Sheet aluminum would be good. Otherwise, the type of sheet-metal used in HVAC might work well. Something like cedar might be good too.

Direct solar heat drying is great, but doesn't work at night or cloudy days. I liked the combination of direct solar and moving air from solar-powered fans.

jbarb2903 10-25-14 03:40 AM

Amazing idea - we have gone the extra step and rendered ours so it fits in with the exterior of our home as we keep it on that patio!Pro Rendering Sydney

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