Preserve your garden bounty with a solar food drier

solar-food-drier

The [VelaCreations] family lives off the grid, getting the electricity that they actually use from solar and wind power. When they started looking for ways to preserve the fruit and vegetables now coming into harvest the electricity consumption and cost of a food dehydrator made them balk. What they do have plenty of at this time of year is sun and heat, so they built their own solar food drier.

The frame is made of welded square tube. They mention that you will have to alter it if you don’t have welding tools, but building your own MOT welder is just one more fun project to take on. The frame has wood rails to hold the trays of food. It is enclosed with translucent polycarbonate sheets. There is a vent in the top as well as the bottom. As the heat from the sun builds inside, it flows upward, sucking fresh air in the bottom. This carries away moisture from the food and can be regulated by adjusting the size of the bottom vent.

Comments

  1. Matt says:

    Is your dehydrator consuming too much power? Just make an electric arc welder and you will be off the grid in no time!

    • static says:

      portable arc welders where being used before the grid came to rural America. The fuel used to power the welder to construct a metal frame solar powered dehydrator may be the only non-renewable energy it uses in its life time. I suppose the purist could knap a fresh edge on their stone cutting tools to make one entirely of wood

  2. fuzzyfuzzyfungus says:

    Does anybody know if BPA would be released from the polycarbonate in potentially-undesirable-for-food amounts under these conditions?

    I have a great fondness for the stuff as a construction material; but the near-total removal of BPA-containing polycarbonate bottles and epoxy coatings from the consumer market makes me a trifle nervous about putting a sheet of it right above my food and then bombarding it with heat and UV for hours on end.

    Aside from shatter-resistance, would there be anything preventing one from using glass instead?

    • Joshua Short says:

      You might have to cover/frost the glass. The point isn’t light exposure; that may even be detrimental for some things. The keys are airflow and heat. There’s also relative humidity.. you get the idea, though. Keeping these things in mind, you could build using whatever you’re comfortable with / have available.

    • ChalkBored says:

      Glass works fine, it’s just easier to get plastic in a size large enough to use one piece, which is easier to seal.

  3. pod says:

    I don’t think it would be a problem since air in this thing is flowing bottom to top, and it should be circulating fast enough to prevent any possible buildup of toxic compounds

    • Dan says:

      I believe the bpa in drinks bottles is that the plastic degrades and is washed into the directly contacting drink.

      There is no food – window contact so I wouldn’t worry too much.

      That said I’m a little unsure as to what the issue is here. A dehydrator comes as cheap as $50 delivered frm china. There is probably more than $50 of materials in the build. Also the power usage of the one I have is about 90watts, or less. I’ve no idea what solar setup they have, but 90watts isn’t a lot of power.

      This is a great setup, but given the various complexities of drying food for good taste as well as long storage (eg herbs require lower temperatures. Fruits a medium temperature, vegetables quite a high temp) then an electric model would be a much better investment than the materials to build this!

      That said I do like the build. And the end result is clean and neat and deserves kudos.

      • medix says:

        http://en.wikipedia.org/wiki/Sunlight

        At best, you can get about 1kW / m^2 for sunlight

        I’d say that’s pretty good. ;)

        Sure puts 90W to shame in a hurry.

      • medix says:

        You might also want to think about return on investment:

        You spend 50 bucks plus the cost of 90W to operate on a model from China, vs. a one-time investment on materials to build the solar model. Now factor in how often you can use the solar model (average amount of sunlight for your area, seasonal weather, etc) and compare. Would make for an interesting study.. ;)

        • medix says:

          .. also note that 1kW / m^2 is a ‘best estimate’ at zenith.. Actual numbers may vary!

          • Tony says:

            And your efficiency is 10-15%, so there’s your 90 watts.

          • Hurtback says:

            The other item to keep in mind is capacity. This thing appears to be able to have four racks that are 46″x21″. I’m going out on a limb here to assume that the $50 Chinese model does not have that same capacity.

          • dan says:

            No, the Chinese model has six round racks about 18″ diameter. (1526″^2)
            this one has 3864″^2, (though the racks stack on the Chinese one, so there is no reason that you can’t expand of contract the stack of shelves to 12 high to get the same capacity.

            There is still the same argument though,
            1KW/m^2 at ten percent efficiency is 90W, but if the thing is twice as big is 90W enough.
            and you only get that at midday, so for the rest of the day you’re just leaving your fruit and veg (possibly meat) in a bit of a warm box open to insects? certainly ripe for bacteria growth.

            Bear in mind most growing takes well over a day even in a forced air heated drying. this more natural process would take a lot longer.

            Alternatively, and what’s more likely to happen is that the airflow won’t be fast enough and the temperature will rise, (kind of like how dogs die in hot cars), then you’re more cooking than drying food. or you’ll have ideal conditions for bacteria growth in the morning and evening, and temperatures hot enough to “cook” the flavour out of the food that you’re preserving at noon/early afternoon

            In certain areas of the world, out door drying works (and has done for centuries), but (and it’s a big but) that’s dependant on latitude and geography of the landscape and how that affects humidity. (wind flow etc)

            In most areas of the world this would just be a big box that you’ll store fresh food in until it goes mouldy.

            My view on this is the hack is quite cool, and I’d use it for a non-food use (drying hand made paper, or drying wood either to season timber or for burning etc)

            But drying food should be a little more scientific, different foods require different temperatures. for drying, excess heat will spoil some foods, whilst no enough heat will not dry others fast enough so as to encourage bacteria growth.

            If you put the effort into growing the food, you may as well use a decent solution for preserving the flavour as well as the food.

  4. Galane says:

    You’ll also want screens on all the openings to keep flies and other insects out.

  5. BLKMGK says:

    I’m thinking if I put that in my yard every ant for MILES around would come running not to mention bees and a few flies. for my purposes and occasional use the electric model I’ve got is working out okay. A neat project though for sure and certainly capable of more volume than my unit for less power..

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