TOP 15 homemade DIY solar heaters for water or air

I have described many different types of solar collectors for hot water supply, space heating of a house, pool water heating and other. My 3rd YouTube channel: № 15: This is number 15, and the link to this solar heater is: The heater has a concave mirror and this absorber from evacuated tubes which convert solar energy into heat for hot water supply and space heating of a house. We understand that the sun rays are focused by the concave mirror on the evacuated tubes. In addition, the tubes receive some energy directly from the sun. This type of solar heaters was tested by me. For example, I made several similar solar heaters on the basis of this absorber from a cheap polymer film. The results of their testing have been described by my 3rd Youtube channel, and its link is: № 14: Our number 14 can be made from an old sa