Monday, April 9, 2012

Vacuum tube solar UV collectors

The evacuated tube solar collector works by absorbing solar energy in the form of UV rays and converting it into thermal energy. An evacuated tube solar collector contains a number of evacuated tubes. Each evacuated tube is responsible for independently absorbing the sun's radiation that reaches it. Evacuated tube solar collectors work more efficiently in mid morning and mid afternoon. For places with freezing climates, evacuated solar collectors are able to maintain a temperature in the range of 75ºC to 175ºC. Their operation is not affected by rising or falling temperatures. This property makes these solar heaters ideal for places with cold climate.
The UV rays are absorbed by an absorbing film which lies in between the 2 layers of glass on the inside layer. This special absorbing film absorbs more than 92% of the UV rays that incident the tube.

The heat is transferred by conduction to a copper fin inside the inner layer of glass. A heat pipe that is inserted into the fin absorbs this heat and transfers it to the copper header at the top of the collector. The heat pipe is a thin copper tube which contains a small amount of liquid, typically glycol. 
The glycol inside the tubing runs past the copper ends of the solar UV collectors and is heated to 200-300°C.
The heat then passes through a heat exchanger and is transferred to the hot water storage tanks.

An evacuated tube is made up of 2 layers of strong borosilicate glass that are joined together. There is a vacuum in between the 2 layers of glass. This layer of vacuum prevents the heat from escaping the tube once it is gathered. Because of that vacuum tube collectors outperform in efficiency any other solar collector on the market.   

Other advantages of the vacuum tube collectors - passive solar tracking. Due to the round shape, 
vacuum tube solar collectors work more efficiently in mid morning and mid afternoon.

They are light, and because tubes are inserted in the rack, snow falls between the tubes, thus making it suitable for conditions with snowfall. What little is left, still gathers UV even through the thin layer snow, although in smaller amount.


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