After seeing a video on YouTube about solar can heaters I thought it was fun to build one myself and test it. I had plenty of wood laying around from building my greenhouse so I used the "leftovers," that's why there are different planks on the backside. I deliberately made the container 100 centimeters tall and 50 centimeters wide because plastic plates that go on the front are also sold in those dimensions.
Once I had the box ready it was preparing the aluminum cans that go inside. I drilled extra holes in the top and bottom of the cans for the airflow that must occur inside. I used an extra sturdy can to house the aluminum cans because they crunch and break very easily without support. For the solar heater I used 35 aluminum cans in rows of 7 wide, 5 high.
Next came the paint job. I also screwed 2 additional pieces of wood in place that give some airspace on the top and bottom. Drilled holes in them for the air to move. The cans are also firmly in place and can't go anywhere. I used dull black spray paint. Wanting to be thorough I had to get one more, so the paint cost just under €10. Spraying paint is fairly easy. The paint does has to settle for 24 hours so doing everything takes a couple of days.
Finally, I screwed a plastic plate (2 millimeters thick) on the front. I keep this heater indoors but I suspect for outdoor usage you need a thicker sheet or glass. I drilled a hole through the back to where the upper vacant area is and ran a hose through it.
Results so far are encouraging. I have a simple thermometer on the back that measures the box itself near the exit hose and even after 10-15 minutes sunshine it shoots up to 24-25 Celsius. A few weeks ago on a really good day it got up to 33 Celsius. Maybe inside it's even warmer but I don't have a fancy gizmo at this time for measuring. When you put your hand over the exit hose you can feel the warm air rushing through your fingers. At the very least I can say that it definitely works.