A solar tube consists of two glass tubes made from extremely strong borosilicate glass. The outer tube is transparent allowing light rays to pass through with minimum reflection.

The inner tube is coated with special selective coating which has excellent solar radiation absorption and minimal reflection properties.

The top of the 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 space between the two glasses form a vacuum which is an important factor in the performance of the solar tube.

In order to maintain the vacuum between the two glass layers a Barium Getter is used. During manufacture of the solar tube this getter is exposed to high temperatures which causes the bottom of the vacuum 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 Solar Tube during storage and operation thus helping to maintain the vacuum.

Principle of Operation
This glass tube is placed at an inclination of Degrees of Latitude plus 8 degrees. If the installation is in the Northern Hemisphere then this glass tube will face South. Similarly if the installation is in the Southern Hemisphere the tube will face North.

The incident solar radiation falling on the tube passes through the outer transparent tube and will strike the inner coated tube. This inner coated tube acts like a black body and absorbs most of the incident solar radiation and is heated up in the process. The vacuum in between the two glass tubes will prevent the heat energy entrapped from being dissipated as there is no medium available for dissipation.

The absorbed heat energy is then passed on to the cold water flowing into the glass tube and thereby heating it up.

What is a Heat Pipe?
In larger systems (which do not operate under the principle of thermo siphon) where the tank and the collector are separate heat pipes are used to enhance the performance of the system.

This heat pipe is inserted into the vacuum/evacuated tube. This heat pipe is made of pure copper (99.9 % purity). In this heat pipe a thermic fluid / distilled water is placed.

Principle of Operation
On absorbing the incident solar radiation, the vacuum tube gets heated up, which in turn heats up the heat pipe. The thermic fluid/distilled water on being heated up forms steam and rises up. This steam then passes on the latent heat of steam to the medium (in our case water) which is required to be heated . By passing off its latent heat the steam condenses and forms a liquid. This liquid then comes down to the bottom of the pipe and the process is repeated.

The distilled water / thermic fluid inside the heat pipes boils and evaporates much faster due to the presence of vacuum.

Suggested Uses of the Solar Water Heater

1. For Bathing Purposes - The water from the Solar Water Heater can be used directly for bathing purposes during winter or during cold days.
2. For Preheating Water for Cooking - For cooking purposes water can be pre heated by using the solar water heater, this reduces cooking gas bills drastically.
3. For Making Tea / Coffee - The water from the Solar Water Heater may be sufficiently hot to directly make tea or coffee reducing electricity or gas bills.
4. For General Purpose Cleaning - Hot Water from the Solar Water Heater can be used to
   • Clean toilets
   • Wash dishes
   • Wash clothes
   • Clean Floors etc.
5. Sterilization - Very useful in hospitals for sterilization uses, specially in the maternity ward.
6. Process Industries - For pre heating boiler water.

	Download Solar Water Heating Manual 1
	Download Solar Water Heating Manual 2