Design reuse of soda cans! They would make a great absorber because they would create a lot of air turbulence and also transfer the heat well because aluminum is so conductive. I am curious how much air is actually flowing through this heater. Ideally, you want to move a lot of air through an air heater to keep it running at a low temperature so you can transfer as much heat as possible to the air flowing through. The opening at the top looks so small! I bet if you would increase the volume of air passing through this collector that you could increase the collector efficiency. I have built my own solar air heater also. Instead of soda cans I used aluminum flashing for the absorber and just added internal fins to create turbulence. Our designs have many similarities. The difference would be that I chose to use a 500cfm fan. It is also hooked up directly to a solar panel but it still moves a lot of air and allows me to transfer a lot of heat from my absorber. I have posted all of the details here: http://practicallyoffthegrid.com/category/solar-a…

Its really good, I have built my own solar air heater also. Instead of soda cans I used aluminum flashing for the absorber and just added internal fins to create turbulence. Thanks for sharing a valuable knowledge about solar heater.