Gardening has become my new hobby since I found a nice place to reside in. My housemate loves gardening, too, and organises our backyard a bit more systematically than I do with my own patch in front of a warehouse.
Last year we had more tomatoes than we could eat, and the herbs from the front yard might be harvested much more if I had a decent option to dry them. When I saw clips for building solar dryer, I got hooked on the idea, as it utilises some clever principles, and needs to energy input.
A solar dryer consists of a well insulated heating element, a drying compartment and a chimney as air outlet. The heating element consists of stacks of connected cans, painted black and fitted into a small box with a glass or perspex pane. The suns heats the cans, which hopefully start air convection inside, the heated air rises, holes in the bottom allow cold air to be sucked in. The heating element connects to the top of the drying compartment.
If there's material to dry, the warm air sucks the moisture out of it, gets heavier and sinks to the bottom. The outlet on the bottom connects to a chimney on the back, where the temperature differential should allow it to rise again, permitting constant airflow through the drying section.
I found some window panes today, potentially the most expensive part when bought instead of reused. In a household which loves a drink or to, empty cans will naturally accumulate, which means all I need to find/source is some timber and some MDF maybe.
My first draft for the can stack is pretty simple, I removed the bottoms of the cans, made little winglets with a tin snip on the top, used duct tape to keep it together and spray painted the lot in black. I can fit 6, maybe even 7 of those stacks behind the pane, and luckily the height fits 6 can on top of each other nicely.
At the moment, the first stack bakes in the noon sun. I want to test whether duct tape suffices a tight, durable seal. Besides heat, there will be no physical stresses once the heating element is put together.
However, if the tape comes loose after a while, it would mean disassembling a box potentially tightly sealed with silicone to fix it.
While the first stack is constructed a bit sloppy, the air gains about 10-12ª celsius while passing through it. No idea whether this will increase or decrease when I have 6 or 7 of them in parallel, or how much this depends on the outside temperature.
I'm a bit torn whether I want to have a go at the downward draft design, which might need the chimney part going quite far up to pull the moist air out. Which means I have to continue building this thing to figure out whether adding moisture to air will facilitate the airflow. Doh.
