1.color paint steel material,unpressurized 2.ISO,CCC,CE,5years warranty,OEM ... of stand:18°,20°,38°,45°Working Principle:There is water in the vacuum tubes and free to flow into tanks ... . When the water in the tubes is heated by the sun's rays ... firstly, this makes water in the tubes lighter. Therefore, the cold water in the tank move downwards and hotter ...