All-glass evacuated solar collector tubes are the key component of solar collector in water heaters, which consist of two glass tubes. The outer tube is made of extremely strong transparent borosilicate glass that is able to resist impact hail up to 25mm in diameter. The inner tube is also made of borosilicate glass, but coated with a special ive coating, which features excellent solar heat absorption and minimal heat reflection properties. The air is evacuated the space between the two glass tubes to form a vacuumed space, which eliminates conductive and convective heat loss. Evacuated solar collector tube could still work efficiently even on cloudy days, because it is able to absorb the energy infrared rays passed through clouds