The commercial design (I won't say its the original as I remember a similar design from the 86 from rodales stocking up 3rd edition, my 77 deluxe edition doesn't have it though):
This fellow (Rich Allen) did a bunch of tests and has a more details on a diy build:
His final conclusions are kind of interesting, looks like you can make it pretty much out of anything as long as there is some metal and decent heat transfer.
Cheap way to get some extra heat in the shop if you get any winter sun anyway. Would be a decent lazy afternoon project
I made something not altogether unlike this quite a few years ago for a solar dehydrator but the above has much better heat transfer than what I used, pretty much like this: http://www.permies.com/t/17891/passi...lar-Dehydrator but I got the plans out rodales "stocking up" book (I have both an older version - which includes many "USDA unsafe" practices (yah yah, test your ph, check your pressure canner temperature.. I can do that) and a new version with some newer processes). My dehydrator build didn't work as well as it should have though because I scaled up the drying area and the collector using dimensional math (1x1x1 dehydrator -> 2x2x2 dehydrator == 1x2 collector -> 2x2 collector) and didn't account for the fact that the drying area should have used cubic math (1x1x1 = 1 cubic foot, 2x2x2 = 8 cubic feet so it needs at least 8x the collector area instead of 2x). The collector part worked fairly well, with even just a black painted box with some old window screen tacked into it (for extra metal to heat up) but was was undersized for the dehydrator box.