The Vacuum Tube is the key component in a solar thermal vacuum tube system.

The tube is similar to a conventional Dewar flask and consists of two borosilicate glass (“Pyrex”) tubes sealed together.
"Pyrex" glass has long been recognised for its high resistance to chemical and thermal shock.

The outer side of the inner tube is coated with layers of composite selective absorption materials, using a sputtering process.
The inner surface is silvered to give a highly reflective mirror finish.
The annular space between the outer and inner tubes is evacuated to avoid heat loss in conduction and convection.

The technology of the film coating and its application are the primary factors that determine the effective function of a tube and its efficiency

As it is pumped through the manifold the liquid in the circuit is heated from the energy generated within the vacuum tube, and as it then passes through the coil transfers this heat into the body of water in the cylinder, gradually heating it up.

Recent improvements to the technology are resulting in even better utilisation of solar energy for a quicker response   -  on a recent installation, a full 170 litre cylinder was up to 45°C throughout within 3 hours of start-up.