Vacuum tubes absorb the sun and convert it into heat that has been used to heat water. Each vacuum tube consists of two glass tubes made of very strong borosilicate glass. The outer tube is transparent, allowing sunlight to pass through with minimal reflectivity. The inner tube is coated with a special coating that has excellent properties for absorbing sunlight with minimal heat loss.
The fusion of the two glass tubes draws out the air in the middle and creates a vacuum, which is the most important factor to achieve the high performance of the vacuum tube.
The vacuum tube is so insulated that the internal temperature of the tube can reach 150 ℃ while the outer tube stays within a few degrees. This means that even in cold weather, the vacuum tube will work.