I think I just figured out a good DIY panel thats cheap
 

I've been trying to find a way to build a water based panel thats cheap and made with common free items. I kinda gave up and was looking at going air over water.

See this thread here;
https://ecorenovator.org/forum/showthread.php?t=7083

I started to look again at finding a water based design and thought of one. Basically it would look like a soda can air heater panel. The soda cans would be sealed together with silicone and have a 1/4"ish hole in the domed bottom, right in the center.

Basically, the cans are stacked vertically, top can is sealed to a common manifold as is the bottom can. As the water enters the first can, it pools a small amount of water in the bottom of the can. It then pools a small amount on the top of that next can as it enters and then again pools a small amount of water at the bottom of the next can in line and continues from there.

The top and bottom shape allows for some water to pool and collect heat. The sides are the radiator fin collecting the solar heat. Heat is transferred to the water at the tops and bottoms of the cans.

Tubes painted black of course. I have not come up with an manifold material yet. I'm thinking maybe aluminum rain gutter might work. Most good silicones are rated for 400F and sticks to cans very well. Only a small hole is needs to be drilled to each soda can with the tab removed so construction should be easy. Unistrut works very well for lining up cans while gluing FYI

Thoughts anyone?

Rain Gutter down spout could work if there was coolant in the mix to prevent rusting.

I made an air heater this way. I found if you drill the hole in the bottom off to one side, then stack them so hole is on the opposite side from the flip top hole, it gives better heat transfer. I'm not sure if that would matter with water. But I am really anxious to see if this works. Keep us posted.

I have almost all the materials already. What I don't have is time since I'm starting a business. I don't know if it will happen this year now.

It occurred to me that the can seal to the manifolds will have to be very tight, otherwise water vapor will get into the unit and condense on the glass.

I'm thinking down spout manifolds but the upper manifold would have a copper pipe inside with holes and maybe small nozzles directing the coolant into the top of the cans. The top manifold would surround the pipe and keep moisture contained.