The direct system is used where the water quality is good (less than 600ppm Total Dissolved Solids/Minerals).

A direct system is where the water to be used in the household (hot water) is heated by means of solar radiation absorption by the vacuum tubes and directly heats the water in the solar water heater.

In the close coupled system the vacuum tubes are in integral part of the storage tank and the heated water in the tubes rises and heats the water in the tank, known as a thermosyphon system. The system operates according to the basic principles of physics.