Solar Water Heater
A joint venture with the “Pakistan Council of Renewable Energy Technology” (Ministry of Science and Technology) for local production of SOLAR WATER HEATERS with “Sun Shower” trademark.
How It Works
Evacuated Tube Collector System (ETC System)
Working Principle:
ETC System works on a simple principle ‘Black body heat absorption principle’. The principle says, ‘black colour absorbs maximum heat, more than any other colour. Solar water heating systems using vacuum tubes made of borosilicate glass with special coating to absorb the solar energy are called as Evacuated Tube Collector system (ETC Systems).
Vacuum tube, as shown in the sketch, is the main component, which absorbs solar energy. The vacuum tube is an assembly of two concentric, borosilicate glass tubes.
Air between the gap of two glass tubes is evacuated. It results in high level of vacuum, which acts as the best insulation to minimize the heat loss from inner tube. The black coating on the inner tube absorbs the solar energy and transfers it to the water. The water on upper side of Vacuum Tube becomes hot and thus lighter, so it starts moving upwards in the tank. At the same time cold water, which is heavy, comes downward from the tank and is stored at the bottom. The phenomenon is called as natural Thermosyphon circulation, which occurs in every tube.
These systems do not involve any pump and are more reliable.
Evacuated Solar Tube:
All glass evacuated Borosilicate solar tube
High Solar-thermal conversion and low heat loss
Stable advanced selective coating
High level vacuum ensures operation under cold weather
Tube material: Special grade Borosilicate glass
Technical Information
Evacuated tubes are the absorber of the solar water heater. They absorb solar energy converting it into heat for use in water heating. Evacuated tubes have already been used for years in Germany, Canada, China and the UK. There are several types of evacuated tubes in use in the solar industry. Most commonly used collectors are the “twin-glass tube”. This type of tube is chosen for its reliability, performance and low manufacturing cost.
Each evacuated tube consists of two glass tubes 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 special selective coating (Al-N/Al) which features excellent solar radiation absorption 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.
Why a vacuum?
As you would know if you have used a glass-lined thermos flask, a vacuum is an excellent insulator. This is important because once the evacuated tube absorbs the radiation from the sun and converts it to heat, we don’t want to lose it!! The vacuum helps to achieve this. The insulation properties are so good that while the inside of the tube may be 150°C / 304°F, the outer tube is cold to touch. This means that evacuated tube water heaters can perform well even in cold weather.
In order to maintain the vacuum between the two glass layers, a barium getter is used (the same as in television tubes). During manufacture of the evacuated tube, this getter is exposed to high temperatures which causes the bottom of the evacuated tube to be coated with a pure layer of barium. This barium layer actively absorbs any CO, CO2, N2, O2, H2O, and H2 out-gassed from the evacuated tube during storage and operation, thus helping to maintain the vacuum. The barium layer also provides a clear visual indicator of the vacuum status. The silver-coloured barium layer will turn white if the vacuum is ever lost. This makes it easy to determine whether or not a tube is in good condition.
The Getter is located at the bottom of the evacuated tube.
Left Tube = Vacuum Present
Right Tube = Faulty
Evacuated tubes are aligned in parallel, the angle of mounting depends upon the latitude of location.
