Technology
All-glass evacuated solar collector tube
Evacuated tubes are made from glass, typically ultra-strong and heat resistant Pyrex with a double-wall construction. The glass on the inner tube is coated on its outer surface with an absorbance coating, and on its inner surface with a reflective coating. Inside each tube all air is removed, forming a vacuum, and a copper heat pipe runs through the centre of the tubes. Most of the infra-red radiation (i.e heat) from the sun is absorbed by this sealed heat pipe, which contains an antifreeze-type liquid.
As the temperature rises, hot vapours from the antifreeze rise up to the top of the heat pipe, where its copper tip connects with a header pipe through which more antifreeze flows. This hot antifreeze is then pumped through pipes inside the hot water tank with the end result that the water gets hotter and the antifreeze cooler. The antifreeze then continues its journey around the system and back out to the solar water heater to be reheated.
The copper at the tip of the heat tube can reach well over 200℃, easily heating water to 90℃ on hot days and to 60℃ even in the winter. This simple system is completely sealed and needs minimal maintenance over its 20-year-plus lifespan.
The advantage of using evacuated tubes is that they will work even during the coldest winter months, unlike the old style flat plate solar collectors. The vacuum prevents the heat tube from being cooled too much by the ambient temperature, which can be well below freezing, and so winter sun can easily heat water to over 60℃ even in the depths of the coldest season. Even if it is very cloudy and very cold, enough sunlight gets through to keep the tubes well above freezing, and so they will be still be pre-heating the water, which can then be heated further by a standard immersion heater or gas burner, reducing the cost of heating the water.
The evacuated solar collector tubes we use contain many advanced technologies. It uses high boron-silicon 3.3 super-hard glass (the king of glass) and a high-quality solar collection compound absorption coating, giving the solar collector tube even higher absorption, lower reflectance rate and faster and stronger solar collection ability, a world leading technology.
Specifications:
Configuration: Two concentric boron- silicon glass tubes
Coating and technology: Graded AI-N/AI selective surface by sputtering
Solar absorptance: 0.88-0.94
Emittance(°C): 0.08-0.04
Vacuum jacket pressure: <5x103 Pa
Stagnation temperature: Over 230 °C
Impact resistance: Withstand hailstones of 25mm in diameter
Strength(tested pressure): 0.6 Pa
