Vacuum Solar Tubes - how they work

The question very often arises as to how evacuated tube solar panels work compared to the flat panel solar option.

While the flat panel option can be explained in a very simplistic way, the vacuum tube solar panels are a little more complicated and require a more technical explanation. I’m not going to attempt to cover all the technicalities here but I will try to outline a basic explanation:

The vacuum tube solar panels contain evacuated glass tubes which act individually to heat up solar absorbers which subsequently heats the fluid system in the manifold that in turn is circulated through the domestic hot water tank where the transfer of heat takes place from the fluid to the domestic water. The system of transfering the heat from the solar panels to the domestic hot water system is the same for both types of panel, it is themethod by which the heat is harvested from the sun that differs.

Each individual tube consists of two glass tubes made from strong borosilicate glass. The outer tube is transparent, allowing sunlight rays to pass through with minimal reflection. The inner tube is coated with anabsorbant AL-N/AL coating layer that is greyish in colour and features excellent solar radiation absorption and minimal reflection properties. The space between the two glass layers is evacuated and this vacuum creates a perfect thermal insulation minimises the heat loss of the collector.

There is a copper pipe inside the coated glass tube with a small amount of a heat conducting fluid. When heated, this fluid is converted from liquid to gas and naturally moves to the top of the tube where it transfers the heat to the solar fluid in the manifold. The gas then condenses back into a liquid, and flows down the inside of the tube. This process continuously repeats itself  within each vacuum tube.