An evacuated tube collector works in much the same way as thermos bottles. The evacuated tube collector consists of multiple large glass tubes that surround smaller glass tubes.
More specifically, each outer glass tube consists of a vacuum that surrounds an inner glass tube. Each inner glass tube is covered in an absorbent coating and contains within it a copper sheet that encircles the smaller fluid tubes found at the center.
Vacuum reduces convection & conduction
The tubes are made of clear borosilicate glass, which maximizes the amount of sunlight that can pass through. The sunlight is then absorbed by the coating covering the inner glass tubes. It is important that the air between the inner and outer tubes be “evacuated,” thus sealing the two tubes together and creating a vacuum. This vacuum serves as an insulator, trapping heat between the inner and outer glass tubes, and is the reason for the evacuated tube collector's unparalleled efficiency.
Depending on the region in which you live, there may be disadvantages to using an evacuated tube collector. Evacuated tube collectors prove to be more economical in colder areas or in places that receive below-average lighting. If you live in the Sunbelt, flat panel collectors tend to be more cost-effective. While there are some disadvantages to using an evacuated tube collector, there are actually more advantages from choosing an evacuated tube over a flat plate collector. Thanks to their excellent insulation, evacuated tube collectors perform just as well in cloudy or cold conditions as they do in full sunlight.
Evacuated Tube Collector Or Flat Plate Collector?
While evacuated tube collectors are generally more expensive than flat plate collectors, their lifespan makes them worth the extra money. Plus, since the vacuum prevents the inner tube from dirt or oxidization, companies usually provide generous warranties on evacuated tube collectors. Not only are these collectors more aesthetically pleasing, but they are also much easier to install than their flat plate counterparts.
The evacuated tube collector may be more expensive, but it is ideally suited for areas where large volumes of heat can be put to use (i.e. space heating or industrial process heating). As the evacuated tube collector is more efficient than the flat plate collector, it is also an attractive solution for houses where only a small part of the roof is available for collector installation.
Conversely, if the solar water heating system is used for pure water heating instead of space heating, a flat plate collector system is generally a better option, because an evacuated tube collector would be too costly as a lot of the generated heat cannot be put to use.