I made a solar heater in 2018, off a non-standard theory of how to make them work well. I used steel cans, not aluminum, that were cut and hooked together into interlocking arcs that face the sun, arranged in a zigzag to increase turbulence above them.
Close up of the cans
My theory is by running air through it slowly, the black cans will make a lot of turbulence, increasing the amount of heat in the air below the glass and above the cans, so the air will be heated up a lot. The cans are steel to be sort of thermal mass to keep the heat production going if the sun goes behind passing small clouds, as it often does here in winter.
On a below freezing sunny day, the input air from the house was 70F degrees, the output was 165F :D
Heat output 165 degrees! Excellent proof of concept!
But there were problems with insulation and the way it connects to the house and it was disconnected and abandoned. With the current heating price increase, I'm upgrading it this fall.
The glass on it is single pane, and the heat is collected right under it, letting a lot go to waste. I have another sheet of glass I'll be adding over it to make it double paned. Hopefully won't have moisture problems in between them, it's pretty steep angled glass though.
The input air wasn't insulated at all. Thin plywood tube connecting to the house with a piece of uninsulated dryer vent. I'll be insulating it all the way down to the heat chamber.
The output air tube was also uninsulated dryer vent, that will be corrected.
The connection to the house didn't work at all. This is a rental, I can't do structural work to do it right. What I had was a thick piece of styrofoam with the two tubes through it stuck into a window. That needs upgrading seriously.
The other problem was it needed a way to control air flow rate and totally stop it when the weather was overcast. I have plans for that too.
With all these flaws, I still had 165 degree output. It was built as a proof of concept test, and I think it passed with flying colors. Hopefully I can make it work even better!
Yes, the concept really works. Free heat. What's not to like?
A few years ago I built something similar. I made a 2x4 frame with a sheet of plywood for the back. Added a piece of foam to insulate the back. The interior had a top & bottom manifold that held stacks of aluminum cans & separated the air into about a dozen columns of cans. I used a knife to cut an X in the bottom of the cans then pushed the material inside the cans a little. The idea was to create turbulence. The top of the cans just had the normal pull top opening. The idea with that was to restrict airflow to allow the air to heat longer. Everything on the interior was painted black. Since it was just an experiment I didn't use glass. Just wrapped it with plastic film left over from a job. It drew outside air & entered the house via the stove exhaust port. I don't recall the exit temp but it was definitely warm. Somewhere around 100' F.
I wonder if there's a way... Well, of course there is - I just need to figure it out. I've been looking for a way to keep my livestock watering systems from freezing. I have a handful of storm windows in their frames, that I picked up for free. Those could work well, for the tops, I've a sheet of corrugated metal I can use for the backs, leftover pvc that could be turned into ducting, some leftover 2x4s from another project that would do well for framing it/them out, and we have a neighbor we could collect beer cans from. So, some flat black paint, some sort of insulating material, and... Hmmmm.... if I ran graduated ducting in such a way that the air would bubble up through the water? The warm aeration ought to keep it from freezing, right?
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I haven't had time to post all the pics etc, but a quick update, I'm getting up to 185 degrees out of it.... and some of my insulation melted!!
Well now.
Guess I need to figure out another way to seal that area!
Could you use that extra output heat as a vent pipe to a greenhouse? Also if you do have a condensation issue maybe you can place it at an angle with a small valve in the bottom to move the water out to where you need it. I don't know if these are feasible or not just spitballing ideas.
Pearl, I feel like the overheating and stagnation are related? More throughput could make it run a bit cooler, but I don't see in this thread a mention of a fan. A DC computer fan wired directly (no battery) to a solar panel (small) might be a simple way to vary the flow based upon the amount of sunshine. It might take some tinkering to find a good balance, maybe using a damper? If you had a fan operating it, then maybe some flap valves would work to seal it when the fan wasn't running, and be blown open when it was. Again, tinkering to get this tuned... but that's the fun part right? The valves might have a damping effect, depending how they were made or weighed.
185*F seems excessive, even without melting stuff. You probably only need 120*-140*F for moving air to feel warm, and not cooling like a draft, and if you weren't there to feel it blowing, any increase in temperature would be welcome.
Without a fan, you might need to increase the stack effect to get more flow? extend the exhaust tube to exit near the ceiling?
Nails are sold by the pound, that makes sense.
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