“The trick in all this to work is to paint the empty cans in black and use polycarbonate or double-glazed glass panels in the design.
With a project like this you can have almost free heat for a garage…”
I might add that you can experiment with the layout of the cans.
Try laying them out sideways or standing up and see what layout will give you the most exposure (collection) area.
DIY 1: http://blog.hemmings.com/index.php/2007/04/26/almost-free-garage-heat-just-drink-a-lot-of-soda/
DIY 2: http://www.goodshomedesign.com/diy-solar-panel-out-of-pop-cans/
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