Technology

The vacuum tube envelope

The low iron, highly transparent special glass of the tube is transmissive through for the entire spectrum of solar radiation up to UVB radiation and is therefore even suitable for the conversion of the energy from UV radiation into heat. The tube is provided with an anti reflex coating based on nano particles. This increases the average transmission ratio to 96% , prevents weathering and additionally strengthens the glass through the sealing of microscopic cracks.

Hail impact resistance

NARVA vacuum tubes excel through their excellent resistance to hail impact. They were tested by the TÜV-Rheinland Group using the ice cube test in compliance with DIN EN 12975-2:2006. In a further test procedure, the impact induced bending of completely drained collector tubes was tested in compliance with the norm draft prEN 12975-2:2004. In the test, a 150 gram steel ball was allowed to perpendicularly fall 10 times onto the glass tubes. The results of the test were that all samples resisted a falling height of 40 cm. 75% of the samples resisted a falling height of 60 cm.

Vacuum technology

The knowledge of the latest evacuation processes is used under consideration of the sorption kinetic behaviour patterns of the tubes to be evacuated. The manufacturer's many years of experience with vacuum-sealed glass-metal connections is a guarantee for long-term quality. The tubes contain a "getter" material which keeps the vacuum stable throughout the entire service life.

Glass-metal connection

A new glass-metal connection was developed and patented for the NARVA vacuum tubes: The absorber tube passes through a robust and resilient metal cap made of a special alloy that is tightly fused externally to the glass tube. This new glass-metal connection is able to withstand shearing and vibratory forces caused by wind load, expansion and cavitation impacts to an extraordinary degree as the construction bending moment, which is transferred from the absorption tube, is taken on by the metal and essentially puts no stress on the glass. Moreover, the metal cap has very low thermal conductivity which minimises heat loss and in that way significantly lowers the temperature change of the glass such that even the sprinkling of cold water in the stagnation state does not lead to damage.

Absorber

State-of-the-art highly selective absorption materials based on titanium oxide nitride are used in NARVA vacuum tubes.

Architectural integration

NARVA vacuum tubes are offered in three different standard lengths and thereby offer flexibility as a design element for facades, balcony balustrades, pergola etc.

Exploitation of electricity substituting fields of application

NARVA vacuum tubes deliver high operating temperatures that increase the efficiency of thermally driven ad- or absorption machines. At present, 135 million electrically driven compression cooling machines are sold worldwide that, especially in times of stronger solar radiation, cause electricity networks to break down with increasing regularity. The use of thermally driven air conditioners can help to reduce peak loads on the electricity network.

Comparison: Effectiveness of various collectors

s-power systems offer clear advantages in comparison to the flat collectors and the Sydney vacuum tube collectors: