Like many of you, I suspect, we’ve got a few too many tomatoes at this time of the year. One of our favorite ways to preserve our modest harvest is with our solar dehydrator. There’s nothing like the taste of sun dried tomatoes, but unless you live in a very dry desert climate like Phoenix, Arizona you can’t just set fruit out in the sun and expect it to do anything but go moldy. In most places in the world, including here in Los Angeles, the relative humidity is too high to dry things out in the sun. Solar dehydrators work by increasing air flow to dry out the food. The one we built uses a clever strategy to get air moving without the use of electric fans such as you’d find in your typical store bought electric dehydrator.
Our solar dehydrator is constructed out of plywood and consists of a heat collector containing a black metal screen housed in a box with a clear plastic top. This screen heats up on a sunny day and feeds hot air into a wooden box above it. Vents at the bottom and the top of the contraption create an upward airflow through natural convection (hot air rises). You put the food on screen covered trays in the upper box. With sliced tomatoes it takes about two full days of drying and you have to take the food indoors at night to prevent mold from growing (a minor inconvenience). We built our dehydrator several years ago and have used it each season for tomatoes, figs and for making dried zucchini chips.
You can find plans for this “Appalachian Dehydrator”, designed by Appalachian State University’s Appropriate Technology Program, in the February/March 1997 issue of Home Power Magazine. The February/March 1999 issue of Home Power features a refinement of this plan, but we just built the original design and it works fine. The original plans and improvements to those plans are split between two articles: Issue #57 and Issue #69. You need to download and read through both before building this dehydrator. . Alternatively, the always excellent Build it Solar website has a whole bunch of solar dehydrator designs, including a nice cardboard version. And while you’re in the library there’s also a book by Eben Fodor, The Solar Food Dryer.
As an added bonus to the tinkerers out there, take almost any of these designs, remove the top box, stick it in a window and you’ve got a passive solar room heater.