1, Vacuum tube is consists of two layer of glass tubes
2, ISO900:2000, CE certificate;
3, 0.91 transmittance of outer tube.

4, The outer tube is made of extremely strong transparent quartz sand which can resist impact from hail up to 25mm in diameter.

5, The inner tube is also made of quartz sand, but it is coated with a special selective coating with strong heat absorption and lowest heat loss.

6, The air is evacuated from the space between the two glass tubes to form a vacuum, so it  eliminates heat loss.

7, This why the tubes are able to absorb the energy from infrared rays which can pass through clouds.

8, So it also can operate in low temperature and low sunlight medium.