All glass evacuated tubes are the absorbing component of the solar water heater. They absorb solar energy and convert it into energy used for water heating. Each evacuated tube consists of two glass tubes which are made from extremely strong borosilicate glass. The outer tube is transparent, allowing light rays to pass through with minimal reflection. The inner tube is coated with a specially selected coating which features an excellent solar-radiation absorption rate and minimal reflection properties. The top of the two tubes are fused together and the air contained in the space between the two layers of glass is pumped out while exposing the tube to high temperatures. This "evacuation" of the gasses forms a vacuum, which is an important factor in the performance of the evacuated tubes.
Evacuated tube solar collectors still provide an excellent result on a cloudy day. This is because the tubes are able to absorb the energy from infrared rays, which can pass through clouds. Wind and low temperatures also have less effect on the function of the evacuated tubes when comparing them to the flat plate solar collectors. This comes due to the insulating properties of the vacuum.
As the key components of the solar collector, the evacuated tubes have a production that is optimized in geometry and performance.
The tubes are composed of two concentric glass tubes with in each case are half spherically closed on one side and fused together on the other side.
In order to make the solar power usable, the internal glass tube is provided on its external surface with an environmentally friendly, highly selective layer and is thus designed as an absorber.
This coating is thus protected within the vacuum gap. It is an aluminum nitrite sputter layer which is characterized by very low emission and very good absorption.
