The tubes are made from low emissivity borosilicate glass (glass with a very low iron content that has superior durability and heat resistance ) with an all-glass seal and they employ AL/N on AL selective coating , which enables the use of the whole solar energy spectrum to generate heat; this produces greater thermal efficiency in bright sunshine but also produces high efficiency in overcast or diffuse sunlight conditions. Further , the tubes are evacuated and have a barium getter (vacuum indicator) which changes color from silver to white if a tube’s vacuum has been compromised.
An examination of the tubes shows that the outside is actually 2 layers of glass and a vacuum has been created between them. A good way to demonstrate this would be to fill an empty tube with very hot water and notice that it does not even get warm as you hold the tube in your hands. That is because of the “thermos effect” created by having a vacuum between the layers of glass.
Evacuated-tub e solar collectors
Evacuated-tube collectors can achieve extremely high temperatures (170°F to 350°F) , making them more appropriate for cooling applications and commercial and industrial application. The collectors are usually made of parallel rows of transparent glass tubes. Each tube contains a glass outer tube and metal absorber tube attached to a fin. The fin is covered with a coating that absorbs solar energy well , but which inhibits radiative heat loss. Air is removed , or evacuated , from the space between the two glass tubes to form a vacuum , which eliminates conductive and convective heat loss.
Evacuated Tube Solar Water Heater is Efficient
The efficiency of evacuated tube solar water heater is more than 90% , it means that is converts more that 90% of the sunlight hitting its surface to heat that can be used to heat water. The evacuated tube solar water heater is also very cheap to renew. The evacuated tubes are made from ultra strong glass and heat resisted Pyrex with a double wall construction.
The inner tube of the glass is coated on its outer surface with a absorbant coating and on its inner surface with a reflective coating Inside each tube , all the air present is removed making a vacuum and a copper heat pipe is located through the center of the tube. Most of the heat from the sun is absorbed by this sealed heat pipe which contains an anti-freeze type liquid.
As the heat rises , hot vapours from the antifreeze rise up to the top of the heat pipe where its copper connects with a header pipe throught which more antifreeze flows. This hot antifreeze then pumped through pipes inside the hot water tank with the end result that thte water gets hotter and the antifreeze cooler. The antifreeze then continues around the system and back out to the solar water heater to be reheated. The copper at the tip of the heat can reach very height degrees easily heating anwter to around 90 degrees celcius.

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