high quality reasonable price beautiful design Manufacture Non-pressurized solar water heater.1,vacuum tube length:47/1500mm,58/18002, ... .Working principle:1,The high quality vacuum tubes ansorb the solar ultraviolet ray;then heat the cold water in the vacuum ... ,and the cold water sink to bottom,then heat by solar collector.so the whole system is always circulatingcontinuously.3,The electromagnetism ...