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for this one, please visit the site as they have a lot of pictures and more into and a lot of helpful comments....
they've also included a pdf that I've attached
but the jest of it all....
I started with some 2x4s and plywood to build a simple box. I’m no carpenter, but I learned that if it’s wobbly, just add more nails.
Sealed the box using adhesive caulk, just to keep any heated air from escaping the box.
drill holes into the bottoms of the cans except for the bottom row drill holes into the sides
Stack the cans with liberal doses of adhesive caulk. Give them enough time to dry.
Once they’re dry, I painted each column with black BBQ paint. Black to best absorb the sun’s heat, BBQ paint to keep from flaking off the cans. At the top, I drilled an outlet hole. I left an inch or two of space between the tops of the columns and the top of the box to permit air to flow out of the columns.
I drilled the outlet hole based on the diameter of some wet-dry vacuum hose I picked up, about 1-1/2 inches in diameter.
Then started to caulk the columns in place. At the bottom, you can see the inlet hole I drilled. At about this point, I realized that a better place for the inlet would have been through the plywood at the bases of each column. In this location, the air can simply pass over the cans (there’s about 1/2 to 3/4 of an inch between the cans and the upper edge of the 2×4 frame) and not really pick up that much heat. If I were to relocate the inlet, it would force all the air to pass through the cans and pick up the absorbed heat. Next time.
Caulked a clear plexiglas cover on the front and sat the furnace out in the sun for a full day over the weekend to see how it would work.
source: How to Build a Solar Heating Panel with Soda Cans