Evacuated Tubes
Evacuated tubes form an integral component of the Solar Water Heating System. They absorb solar energy and convert it into heat for use in water heating. Evacuated tubes have been in use in Germany, Canada, China and the UK, for many years.
Evacuated tubes are aligned in parallel to form an Evacuated Tube Solar Heater. The angle of mounting depends upon the latitude of your location. 
Efficiency is dependent upon a number of factors, most notably, the level of evacuated radiation (isolation) in your region.
Evacuated Tubes consist of two extremely strong borosilicate glass tubes. The outer tube is transparent thus allowing light rays to pass through with minimal reflection. The inner tube is coated with a special selective coating, which features excellent solar radiation absorption and minimal reflection properties.
The top of the two tubes are fused together. The air contained in the space between the two layers of glass is pumped out, while exposing the tube to high temperatures. This "evacuation" of gasses, forms a vacuum, and as such, there is extremely little heat loss.
Each tube boasts a sealed heat-pipe that extracts heat from the absorber. When liquid comes into contact with the heated absorber, it is vaporised. Heat is then recovered at the top of the tube where the vapour condenses, and the condensed liquid returns by gravity to the absorber. This type of tube is chosen for its reliability, performance and low manufacturing cost.
