As part of my research I read about "downdraft" dehydrators, which seems somewhat counterintuitive to me as the air has to follow a more circuitous path, but apparently works well. This design has the benefit of lower overall height. The idea here is that the chimney part attached to the side heats up and sucks the air out through the solar collector.
The advantage that I see with starting with a pre-built rack like you have is that it's already on wheels and so it would be easy to move around. So raising it, or radically altering it in any way that makes it less mobile would be losing the best thing you've got going for you. Keep it mobile.
What if you were to simply make a hole somewhere at the bottom of the cabinet for your air intake, and add a vent at the top where the warm moist air would escape. Get an 8' length of 6 inch black plastic pipe (ABS) or a metal stove pipe (also black). The black color would be a heat sink/solar collector. Find an inexpensive solar powered fan that would fit into intake end of your 6" black pipe, and it would push air through the pipe and up into your dehydrator.
As the wind blows, it would turn the vent and pull air through your dryer. I'd buy a good one with ball bearings -- something that turns easily and moves a lot of air.
That's all it would take.
Because the fan is solar, when the sun is out, it would be pushing air through the pipe and past your drying food. And the vent would turn on its own with just a little bit of breeze.
The whole thing would disassemble in about 2 minutes, if that, and you could roll it into storage. Basically, it would be two pieces --- the drying rack and the black feed pipe. You could easily glue the little solar powered fan right into the end of your pipe.
"The rule of no realm is mine. But all worthy things that are in peril as the world now stands, these are my care. And for my part, I shall not wholly fail in my task if anything that passes through this night can still grow fairer or bear fruit and flower again in days to come. For I too am a steward. Did you not know?" Gandolf
There are 18 slots for 18"x26" racks, so there is potential to dry a lot of product at once.
Seems like a very useful basis for a dehydrator. That someone gave it to you for free is good news.
When you've settled on a design and built your dehydrator using it, why not take a couple pics of it and post them with the story of building the thing? We've got a good thread on those sorts of repurposing projects here: https://permies.com/t/12412/projects Dale Hidgins started the thread, and it's titled "My re-use projects--- and yours as well" Your project would be a great addition.
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Location: Penticton, BC. USDA Zone 6b, 300 mm annual precipitation