... This system uses the thermosiphon principle, Solar vacuum tube is pluged into the bottom of water tank ... is filled inside the solar vacuum tube, Solar vacuum tube transmit solar energy to heat energy,The ... temperature of water inside solar vacuum tube is rising, As the thermosiphon principle, ... Water tank heat insulation layer: 50~60 mm polyurethane foam.5. Stand angle: 15 degree, 20 degree, ...