October 15, 2020

An Experiment With Solar Dehydrating

Something I researched early on was solar dehydrators. I have my Excalibur, which I love, but being able to dry foods with just the sun always interested me. What I learned from my early research was that solar dehydrators have limited usefulness in areas of high humidity.

Most of our weather comes up off the Gulf of Mexico, which means most of our weather includes a high level of humidity. That's not always the case, but humid days outnumber dry ones and changes in our humidity are unpredictable. The other problem is that our sunny summer days often turn cloudy by mid-afternoon. More than once I've had to take a solar started dinner and finish it on the stove. Between those two factors, I've not been inclined to invest the time and money to either make or buy a solar dehydrator.

My solar oven is a Sun Oven. The other day, I recalled the solar cooking webinar I hosted several years ago for that brand's manufacturer. (Does anyone remember that? It's still available online, here.) I remembered that one of the things discussed was how to use the oven as a solar food dehydrator. The technique is different from using it for cooking, so I knew there would be a learning curve. Before the remnants of hurricane Delta blew through, we had a week of day-long sunshine; perfect weather to give this a try.

I chose something inexpensive for my experiment, onions. My first go-round was not successful; I cooked the onions rather than dehydrate them. But we still ate them and I learned from that experience. My second try turned out much better.

I started with two pounds of whole onions.

Three things turn the Sun Oven into a solar dehydrator. The first is the optional baking/dehydrating rack. Parchment paper keeps the food from falling through the wire.

The second is to set the oven lid on top of the lid latches. To use as a cooker, the latches hold the oven door firmly in place, allowing it to do its moist heat magic. Leaving the lid ajar allows moisture to escape.

The third difference, is to offset the direction the oven is facing, so that it is not pointed directly at the sun. The holes in the door handle enable tracking of the sun to maintain baking temperatures.

By offsetting the direction of the oven to the east, the temperature can be kept at a lower dehydrating temperature. The recommended adjustment is about six inches, and I soon figured out how to adjust it to keep the oven temp in the dehydration range.

Sun Oven in dehydrator mode. 

With my electric dehydrator, I can just set it and forget it. Using the Sun Oven required frequent checking and adjusting. I learned to rotate the trays and remove onions as they became dry enough.

It took three full days to dry the first batch of onions. Final yield for two pounds of fresh onions was about ¾  of a quart jar dry.

My solar dried onions.

The main disadvantage is that the Sun Oven doesn't hold much. I had five trays-worth of sliced onions, but only have four trays. But I combined trays as the onions shriveled, and added a new tray of fresh as room allowed. I'm not on a time schedule, so it really doesn't matter unless humid or cloudy days push in!

So! After this success, I found a DIY solar dehydrator that is claimed to work even in humid weather. It's at this website. It would still be a huge project to acquire materials and build, but I'm no longer assuming that solar dehydrating isn't feasible for me. Maybe someday?


Rosalea said...

Very interesting Leigh. Mother Earth News has a plan for a solar dehydrator that I would love to build. The humidity could be a problem here as well, as summers seem to be more and more that way.

Cockeyed Jo said...

Leigh, to combat humidity in ours we installed a stronger fan than the two computer fans. We watch the weather also and load it full of vegies we want to dehydrate when the humidity is less than 75%.

We do attend to it quite frequently turning items at least twice during the process to promote even drying. Yes, it's quite different than the set and go electric models.

Ours is big enough to do several large loads at once with 8 trays 16"x24." Herbs dry within a da, other veggies (blanched) about a day and a half, fruits and whether whole or sliced three days at most.

Toirdhealbheach Beucail said...

Leigh, at Old Home we had a nice dry climate, so making things like sun dried tomatoes (my favorites!) was not a big deal. We, like you, suffer from the humidity.

This is an interesting device I will have to explore - have to pay such careful attention will only work if I were to do something like, say, work from home.

Ed said...

We get most of our weather from the Rockies and great plains which explains why most of the time it is dry and also why when we get the occasional summer storm that blows humid air up from the south we darn near melt.

Seeing the picture of your solar oven with a cat sitting in the background begs the question, how many times has a cat leaped over the shields onto your oven?

Leigh said...

Rosalea, there seem to be quite a few styles for solar dehydrators. At that link that I gave (this one) there's a comparison chart of several styles (just scroll down a bit). The Mother Earth dryer is one of those being compared, so you might find the chart of interest. They claim theirs works in humid areas, so I plan to do a little research on plan reviews.

Jo, I've seen quite a few with added fans, which is an option. Of course, that has to be powered, another consideration. I think you're right that they all require at least some turning of food items. I usually turn things in my electric dehydrator, although mostly to keep it from sticking to the tray!

TB, yes, that's a consideration too. My solar oven dehydration experiment required frequent monitoring. The Walk Radiant Dryer (at that link) is intriguing because it claims it works on humid or partly cloudy days and requires no tracking. Maybe the key is "radiant" drying.

Ed, ha! Never! Although I have caught same cat napping on top of electric dehydrator when it was out on the back porch. (Although it wasn't on at the time. :)

www.self-sufficientsam.blogspot.com said...

Sounds like a lot of work to me! LOL!

Leigh said...

Sam, it's work now for convenience later!

Cockeyed Jo said...

Leigh, HELLO, the fans are solar powered. LOL We did a science experiment and wired the solar panels from those $1 solar path lights together for power to run the fans. It works fine.

wyomingheart said...

Very interesting, Leigh! We dry a bean that’s called a shuckey bean. It is dehydrated because the green bean is snapped and the white bean inside needs to be dried as well. The easiest way we have found to dry them is on a screen and put on the dash board of the truck. Of course, it must be a sunny day, but it only takes about 6 hours to do a large screen full, and it keeps the kitchen cool ;)! We are very interested in building a solar oven next summer, so thanks for the link! Get a great week-end!

Goatldi said...

My first experience with dehydration was with large cookie sheets (restaurant quality) fairly heavy . I put cooling racks that one uses for cookies and such on top and placed the product on them and covered with those large plastic craft sheets one could purchase at fabric stores that folks cut up in various shapes and stitched. Such as Kleenex box holder etc.

Put it all on our patio roof which was flat and lower to the ground than the roof itself. And walked away . Had great success especially with tomatoes to use in my chèvre. Then we could afford a purchased dehydrator.

I am hoping for some successful tomato endeavors again this coming vegetable garden season. So much fun to be back at it!

Leigh said...

Wyomingheart, dehydrating is nice for small amounts, Your idea of using the cab of your truck is pretty clever!

Goatldi, another clever idea! What kind of humidity do you have?

Susan said...

It's always a good idea to have a natural-powered backup for the things we need. I have a solar oven on my wish list!

Leigh said...

Susan, I agree, as does (I imagine) anyone who's had their power knocked out for several days or weeks. I really like my solar oven. Food tastes so good cooked in it. For my cloudy day back-up, I'm working on a rocket stove cooker and haybox cooker combo. One of these days I'll be able to share about that.

Renee Nefe said...

oooh! I'm glad that is working out for you...having a supply of dehydrated veggies will be awesome... especially if the veggies came from your garden. :D Did the onions smell yummy while they were drying?

Leigh said...

Renee, a successful experiment is always exciting! I mostly use my dehydrated veggies in soups and stews; just toss a handful into the pot.

I didn't really notice how the onions smelled as they dried, I suppose because it was outside. But I know onions in the electric dehydrator smell very good.

Nancy In Boise said...

Interesting and that solar dryer on that website is huge! I wonder if you could just build a lightweight frame with netting or something I'm covered with some screening?

Leigh said...

Nancy, good question. Their dehydrator is big! I think the smallest units they show are 4x4 feet, so that's 16 square feet. I haven't read all of their information thoroughly, so I don't know how small it could be made and still utilize the principles. On the other hand, if I were to lay out all the trays of my Excalibur into a square, it would come to almost 8 square feet. I've often lamented that that's not enough space, so I suppose a 4x4 solar dehydrator like that would be a good size for someone like me. The real question is where to store it when not in use!