Solar Dried Foods

I guess I can't say for sure because I haven't built one yet but I'm pretty certain it would NOT be too much if an increase in temp. I'm guessing it wouldn't increase it more than 10 degrees or so at most, but that's just a guess. Personally I would rather look at nicely stained piece than a black box in my yard

Thanks Spencer. I agree, a good sealed wood certainly would be much more pleasant to look at. However, I'm more interested in performance and if painting it black on the outside allows it to do it's job better, I would consider it. Any experienced solar dehydrator builders out there have some insight into exterior color?

Thanks much,
Dan

Ok dan, so my grandfather and my father are musicians and when I was born apparently my dad thought it was appropriate to name me after the group. Could be worse I guess lol. Anyway, I can't imagine that having the wood painted would raise the temp too much. Most, if not all, of the designs I have seen paint the heat collected black anyways. I think the only thing that is bad is direct sunlight, thinking along the lines of a solar cooker, obviously don't want that effect.

Good story on the name. That's something to celebrate! I think I agree that it wouldn't raise temps too much, but I'm wondering if it might even slowing the air movement because there wasn't such a temperature differential from the collection box to the main chamber. Now that I think about that, I think I might just stain and seal the main chamber exterior.

Thanks much, Spencer.

Dan

Hadn't thought about that one Dan. Though it may depend on the design. If the hot air enters from the bottom, then I would think that the already hot air that was in the box is helping to pull air to the top thus increasing flow. If you go with the design that the hot air enters the top (where the humidity draws the air down) wouldn't that be opposing forces?

I think you're probably right. That settles it for me then, it's stain and seal for me. Thanks again, Spencer.

Just a quick thought, of the YouTube videos I have seen where the dehydrator does NOT work, I have noticed that the area of the intake and exhaust are very different in size. I'm wondering if the rocket mass heater info applies here, where the intake and exhaust should have a very similar CSA?

Good question, Spencer, I was wondering the same thing

Would it be feasible to add zeolite to a solar dehydrator?
If the system is working moderately well the zeolite would mostly stay very dry, but when it was very humid out (which hopefully will also be when it's darker and cooler out) then the zeolite would absorb some of the moisture and add heat.
I'm thinking that depending on conditions in your location zeolite could be a nice way to buffer conditions inside the dehydrator.

Dan Grubbs wrote:Thanks Spencer. I agree, a good sealed wood certainly would be much more pleasant to look at. However, I'm more interested in performance and if painting it black on the outside allows it to do it's job better, I would consider it. Any experienced solar dehydrator builders out there have some insight into exterior color?

Thanks much,
Dan

Sounds like you settled this to your satisfaction, but the answer is going to be different in different climates.
Whether it will get "too hot" depends a lot on how hot the climate/weather is to begin with, and on how effective your particular setup is at extracting heat from the sun, and even on what you're trying to dry ("too hot" is different for sourdough starter, herbs, fruits, or meats).

For any solar-gain situation, I would build it and run it for a while first - at least a week in the main season you built it for, or a full year if using it year-round.
Then choose the paint color.

I'm thinking about doing a tower-style, tray-style, or something else - or maybe a side-by-side comparison of the best designs, because I have access to a productive farm where we might eventually want larger volumes for sun-drying.
I haven't built it yet, but one thing I'm considering is ways to shade the sides of the box in too-hot weather, but convert back for better collection in cooler weather. A little roll-down screen (straw, reflective foil like those car sun-screens, or fabric) for the walls or solar collector perhaps, or adjustable angle on the solar collector.

-Erica

we have alot of cloudy days here, ( upper michigan) so when there will be several cloudy days in a row we usually stick them in the sauna over night and for the most part there dry in the morning. the hardest thing i had to solr dry is tomatoes

Does anyone use their solar food dehydrator for a dual purpose? For example, I was thinking of building one that I could take out the racks in the winter time and put in closet rods to dry clothes in for the winter. Do you think it would work?

Sherri Lynn wrote:Does anyone use their solar food dehydrator for a dual purpose?

During the fall, I use my greenhouse as a dehydrator to make raisins. In the spring I use it to start tomatoes.



Six weeks later:


During the spring:

Great idea! Triple purpose! Use my greenhouse to also dry vegetables and put in a clothesline!

Walk Hatfield wrote:We have experimented with about every solar dryer design out there in the past 35 years and came up with our own design back in the mid-1980's that is actually pretty similar to the original posting. But it uses clear glazing and either black cloth or metal over the screen of food. And the roofing is at an angle to improve thermo-syphoning of airflow.

You can see the details on our webite at http://www.GeoPathfinder.com/9473 . That page gets about 150 hits/day, and we do workshops on the design, self-published a booklet about food drying, and do dryer building workshops with groups of folks in our area where we build 10, 4-by-4 foot dryers in a day. Our design was used by the U.N. in a publication they did back in the late '80's since it works well in humid regions, can be modified easily to adapt it to any climate, altitude, or latitude, and it's easy to use found or local materials as long as you stick to the basic physics of the design. It's now used from Alaska to Mexico, at least.

The box-type dryers are all based on adding a solar crutch to an electric box dryer. They work but you have to track the sun, they're slow, they're harder to build, and you can't leave food in them overnight.

We try to keep the direct UV of sunlight off everything but mushrooms. Some varieties, like shiitake, can have 10 times or more their normal vitamin D level if dries gill side up in direct sun. Fruits and veggies all get done in the dark to preserve nutrients and color.

Bob Dahse.

This is five year old post now, but I didn't see any following posts from people who used this design. Has anyone used this and had it work? If it's a working design I could see easily making these from old picture frames and hinging them to the fence so they would be out of the way when not in use. Use decorative tin ceiling tiles for the metal backing and they'd be quite attractive bits of yard decor. But all of that's a no go if they don't actually work.

This is five year old post now, but I didn't see any following posts from people who used this design. Has anyone used this and had it work? If it's a working design I could see easily making these from old picture frames and hinging them to the fence so they would be out of the way when not in use. Use decorative tin ceiling tiles for the metal backing and they'd be quite attractive bits of yard decor. But all of that's a no go if they don't actually work.

I remember seeing that one but I haven't built one yet. I like it, but I have plans of my own design for an indoor/outdoor one. It can be put in front of a sliding glass door and also heats the house.

new link to the solar food drying
This is probably the simplest effective design. Advantage (1) Each tray is heated individually. (2) Smallest storage space of any solar dryer I have seen. (3) Uses radiant heat instead of heating air to heat the food which is then cooled by evaporation. (4) Moist air can either rise or fall depending on the pressure differential and not have to pass through additional trays. (5) You can make as many units as you want but only have to use what you need each time.

Thank you for the shorter link to the plans.

I'm cannibalizing an old 24x24 inch picture frame for the glass on this. Once I have a combination of warm enough dry weather and time I'm going to spray paint some aluminum sheeting and put together my test dryer. Simple is about the limit of my woodworking skills until I buy more woodworking tools (and they're actually a low priority)

I have been playing with greenhouse designs. My thinking is the dehydrator solar panels might make an ideal passive fan for pulling hot air down into earth tubes for heat banking. It won't start working till it has good sun. If the greenhouse is still cool let it vent closed loop inside. If the greenhouse is hot use a wax cylinder to open an over center tumbling block diverter baffle so the air is exhausted out of the build instead of circulated. Either way it is storing the heat in the ground on the way. The flaw I see in this is if the earth tubes start growing fungus of some sort because of condensation then the air couldn't go through the dehydrator. It could still go around a sealed dehydrator though. And if passive is not enough then put a blower fan on the inlet to the earth tubes to boost the pressure and flow through the system. All air going through this system would go into the earth tubes to dump the heat first storing it for night time winter heating. On bright sunny days the greenhouse will need still more venting but let this do the first part of all venting.

I am also working on an earth tube greenhouse design. Among the things my brother in law brought home from the dump for future projects was 8 8' 3" diameter black gas line mains. I plan to use them for the support for my glazing on the south side of my structure dug into the side of a hill. For each support a tube will run from the top of the north wall under the planting beds on the wall and under the floor and connect to the bottom of the support pipe. The pipe heated by the sun will drive air down another earth tube to exit the cooled air at the bottom of the greenhouse. Ihis circulation should reverse at night keeping the air temperature up.

What I had suggested on another post was to use black rocks as heat collectors under a curved glazing so that as the sun traveled from east to west it would heat the rocks on one side then the top and then the other side. The heat stored in the rocks would continue to circulate the air after the sun stopped shining on them extending the drying time.

The only solar dryer I built was an experimental high chair shaped model where the air was heated between the front legs and the shelf box was chest to head height and the air was heated up the back of the chair another 4 feet. The air past horizontally across the trays. The materials were 2x4 and scrap paneling with corrugated cardboard for insulation and plastic wrap for glazing. but it worked.

So if you want to make the radiant dryer discussed above but want to try it out before investing in the glazing try it with the plastic wrap. I have some aluminum baking sheets that I want to paint anyway to stop corrosion, Some drying screens that were left in the barn and a left over sheet of steel roof paneling as used in the illustration, so I am going to try it with the plastic wrap covering the air space on the top of the baking pan setting on top of the drying screen on top of the roofing. If I set it up by the pear tree this fall it will be minimum work and investment.

Hello again, I'm back on the forum after having been locked out of my account for a couple of years. I see on our website stats that lots of folks are linking back to the old posting we did about the radiant-style solar dryer for humid and low-sun climates we designed back in 1985. Thanks to Jason for posting the new link to the GeoPathfinder-dot-com site, and for his comments about what makes the design so effective! It works far better than the box-style air heating driers in humid areas or those at higher latitudes. And it has been built and used worldwide after HomePower magazine and the United Nation's alternative energy publication covered it back in the late 80s. In areas with less humidity, more heat, more solar strength, or for those who strictly dry herbs, the dryer can be "throttled back" in efficiency by simply draping some shade cloth over it. But it's nice to have the full efficiency on a partly cloudy, cool day, when you need to dry something really wet. It's commendable to utilize recycled stuff to build it, and the physical principles that make it work can even be used without having to actually build a dryer (if you have a parked car sitting around with a large window faced south - in the Northern Hemisphere, that is), but the size of the collector is rather important. We've found that here in the upper Midwest a 4-by-4 foot dryer is pretty much the minimum to get veggies reliably dry. Anything smaller north-south doesn't build up quite enough heat at the top of the dryer's slope (works for herbs/greens though), and anything narrower can get east-west crosswinds that suck away the heat too quickly. And be careful with out-gassing plastics affecting your food. The metal collector sheet may keep the gases away from your harvest but I still lean toward hard plastics or glass. Feel free to e-mail us from our site if you can't find answers to other questions about it.

Only thing I didn't have on hand between stuff being saved for a garage sale is the aluminum sheeting. I love the way you've laid it out though and knowing that plastic wrap can substitute for glazing will probably get me out of a pinch in the future.
It's probably going to be sometime next week when I set up the initial test run. If it works during winter I imagine it'll be amazing during summer.

I designed and made this cnc cut dehydrator/children's slide (Slydrator). I figured most suburbanites wouldn't put a food dehydrator in their front yard, but they might put a kids slide......

Anyone looking for stainless steal mesh you can get it from McMaster Carr.

http://www.mcmaster.com/#stainless-steel-mesh/=10uoyrj

Kate Muller wrote:Anyone looking for stainless steal mesh you can get it from McMaster Carr.

http://www.mcmaster.com/#stainless-steel-mesh/=10uoyrj

I've looked there but it seemed expensive. Is it the cheapest option for stainless?

Jason LaVoy wrote:

Kate Muller wrote:Anyone looking for stainless steal mesh you can get it from McMaster Carr.

http://www.mcmaster.com/#stainless-steel-mesh/=10uoyrj

I've looked there but it seemed expensive. Is it the cheapest option for stainless?

I have no idea. I mentor a high school level robotics team and we order hardware from this company all the time. They are the only place that I have seen that carries it but I haven't needed to order any yet.

McMaster, Cambridge Wire Cloth, and Darby Wire Cloth are all fine screen sources if you want a 100-foot roll. We offer type 304, 12-mesh, plain-weave stainless screen in 2-by-2 foot squares from both our website (http://www.geopathfinder.com/Solar-Food-Drying.html , for the cheapest price) and from several E-Bay listings. I've been told that our price is about 1/3 of what could otherwise be found for small quantities. We sell the 2 foot square size to match the 4-foot by 100-foot rolls of screen we buy, and to match the 2-by-2 foot screens used in our radiant solar dryer design. Since 1982 we've been experimenting with various designs, screens, collectors, and mesh sizes to find what works the best in our humid, 45 degree latitude, half-time-cloudy location, but which can be modified to work for many different crops at higher/lower latitudes, altitudes, and temperature.