Hot water rises and fills tank with hot water.

The tank has to be higher than the collector .

The tank can be in the roof if it can be higher than the collector and there is space in side .

When temperature of the geyser drops the electrical element will kick in  - some systems have a timer/controller and some just work like a normal geyser   - if the temp drops below a certain temperature the element comes on . 

This often is a simpler system and less expensive but not cosmetically appealing.

These can overheat if hot water not drawn off .

THERMOSYPHON 150Ltr/20HP(47mm)

THERMOSYPHON 200Ltr/30HP(47mm)

THERMOSYPHON 300Ltr/30HP(47mm)