Natural Circulation System

As shown in the diagram, by gravity flow, water from the cold water tank enters the solar tank at point A and fills it up. The cold water from the solar tank in turn flows via point B in the bottom header pipe of the absorber and into the copper tubes at point C, until all the absorber tubes and the header at the top of the absorber are full.

When the sun rises to a certain level, its energy, which falls on the absorber fins and tubes, begins heating the water contained therein. The heated water being lighter than the cold water rises and via the top header pipe (point D) of the absorber, flows into the top of the solar tank through point E. The more cold water from the solar flows into the absorber tubes, gets heated and rises to the top, and so on. This process is called as 'Thermosyphon Process'. This process continues until the temperature of the water in the solar tank and the absorber equalizes. Now the solar tank is full of hot water.

(Note:- Average temperature is 60 degree centigrade at the end of 7-8 hours of bright sunshine.)

Further when the hot water is drawn from the solar tank outlet (point F) to the utilities point, cold water enters into the solar tank and takes its place at point A, thus lowering the overall temperature of the hot temperature between the water in the solar tank and the absorber tubes, the thermosyphon process starts once again, as explained earlier.

The diagram also shows the back up electrical heater (to be used during cloudy days) and the sacrificial anode rod in the solar tank to prevent galvanic corrosion (but not scale formation), if the hardness of the water quality is less than 140 ppm, thereby ensuring effective working for longer time.