Evacuated Tube Solar Collectors

A solar collector is the engine of any solar heatimng system. Evacuated tube solar collectors are among the most efficient, reliable and cost-effective solar collectors in the market for all weathers, including the northern where freezing temperatures are normally expected. Collectors may be installed in bank arrays for scale-up and can be used for a variety of domestic and commercial heating applications such as residential houses,hotels, apartments, buildings, laundry, libraries, hospitals, etc.

The most popular sizes of evacuated tube solar collectors includes Ø47mm, Ø58mm & Ø70mm tubes. Both Ø47mm and Ø58mm tend to consist of two layers of glasses, and the vacuum between protects the heat from loss. Ø70mm tube tends to be single layer glass where the entire tube is in vacuum. The outer layer of the solar tube usually is borosilicate glass which is very low in iron and allows 98% of light energy to pass through. The absorbing coating found on the inner layer makes the tube differences in efficiency and lifespan. Most common absorbing coating is made from an aluminum and aluminum-nitrogen(Al-N/Al), while the 3 target AIN/AIN-SS/CU tube has an additional copper layer which captures infrared energy and gives a more output, allowing for a much longer lifespan of 20 year or greater.

In an open or direct-flow vacuum tube collector, the potable water is heated directly within the vacuum tubes. Thermosiphon causes the hot water to rise and be replaced by colder water. The hot water is then collected in the top chamber. Heat pipe is the most efficient heat transfer technology available on the solar market today. Instead of water flowing in the center of the vacuum tubes, a hollow copper pipe is inserted through the length of the vacuum tube. This special pipe contains a small amount of special liquid that acts as heat transfer medium. The low pipe pressure drives the fluid to vaporize under lower temperatures (30 C or 86 F) . The vapor rises to a condenser bulb (heat dissipator) where it is cooled back to liquid. Copper heat pipes are used because they can absorb and transfer heat very efficiently with virtually no energy loss. Heat pipe collectors are more efficient than open vacuum tubes but also come at a significantly higher price with the added copper materials.