All-glass evacuated tube :
Consists of two glass tubes which are fused together at one end. The inner tube
is coated with a selective surface that absorbs solar energy well but inhibits
radiative heat loss.
The air is withdrawn ("evacuated") from the space between the two glass tubes to
form a vacuum, which eliminates conductive and convective heat loss.
These tubes perform very well in overcast conditions as well as low
temperatures. Because the tube is 100% glass, the problem with loss of vacuum
due to a broken seal is greatly minimized. Glass-glass solar tubes may be used
in a number of different ways, including direct flow or heat pipe configuration.

Technical data table
      Model tapeTG47 TG58
      Length1500mm 1800
      Outer tube diameter47mm 58mm
      Inner tube diameter37mm 47mm
      Glass thickness1.6mm 1.6mm
      Thermal expansion3.3x10-63.3x10-6
      MaterialBorosilicate Glass 3.3 Borosilicate Glass 3.3
      Absorptive CoatingAL/N/AL AL/N/AL
      Absorption coefficient>92% >92%
      Emission coefficient<8% <8%
      VacuumP<5x10-2Pa P<5x10-2Pa
      Stagnation Temperature>200>200
      Net weight 2.1KG