Solar Water Heater (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.

Thermosyphon Systems ::

In this type water flows through the system and when water gets warm it rises as cooler water sinks. The collector is installed below the storage tank so that warm water will rise into the tank. These systems do not involve any pump and are more reliable.