EVACUATED TUBE COLLECTORS
The Evacuated Tube Collector is made of double layer borosilicate glass tubes evacuated for providing insulation. The outer wall of the inner tube is coated with selective absorbing material. This helps absorption of solar radiation and transfers the heat to the water which flows through the inner tube . These solar collectors comprise of the parallel rows of the glass tubes which are exposed directly to the sunlight. The tubes comprise of the outer glass tube and the metal tube that acts as the absorber of the heat. These solar collectors are used for the commercial applications where maximum amount of heat is to be absorbed and the losses due to radiations have to be reduced.
- Glass tube: The glass tube is formed by fusing two co-axial glass tubes at both the ends. Air between the two glass tubes is evacuated to create vacuum, which works as insulation. Outer surface of inner tube in the evacuated tube collector forms the collector area.
- Absorber coating : Absorber coating is applied on the outer walls of inner tube selectively to absorb the solar radiations to collect energy and to convert light energy into heat energy. The selective absorption coating has absorption co-efficient of 0.94 or more and emissivity of 0.12 or less. The coating should remain intact for the life of the system.
- Gasket : Gasket must have the capability to endure environmental conditions (rain, dust, etc. and in some cases marine environment) and large variations in temperature. In order to achieve these aspects, gasket between the tank and ETC or Manifold and ETC is very crucial for the trouble free performance of the water heating system with ETC. The gasket should be capable of sustaining the temperature and pressure encountered. It should fit tightly above the tube to avoid any leakage. Life of the gasket should be equal to that of the entire system.
Main characteristics of the evacuated tube collector are :
- Capability to endure environmental conditions (rain, dust, etc. and in some cases marine
- Capability to sustain large variations in temperature
- Resistance to leakage from any part of the system
- Stable and durable
- Easy to install
- Efficient in energy conversion