Installation with solar controller (SR500)

How thermosyphon solar systems work
Thermosyphon systems in their typical configuration do not have pumps and other controls. They are based on the natural convection principle: hot water rises and cold water sinks. In the case of thermosyphon systems: as the potable water (or a antifreeze fluid, in colder climates) entered into the collector it warms and rises to the top of the collector and to the tank, where it is stored (that’s the reason why tanks are always above the collector).

Thermosyphon Systems & Advantages
Thermosyphon systems are cheap, and since there are no pumps or controls they are reliable systems without technical or maintenance problems.
Relatively to the batch ICS systems, thermosyphon systems allow a much higher flexibility: since the hot water is stored in a well-insulated tank - instead of being kept in the collector itself, like in batch systems – it can be used many hours after, without the problem of nighttime losses

Thermosyphon Systems & Limitations
The big disadvantage or limitation of thermosyphon systems is that they depend deeply on air temperatures. To be more precise, they will stop working if temperatures drop below the freezing point and stay there for long. In that case the system needs to be drained or warmed. To overcome this limitation, in cold climates, some manufacturers equip their thermosyphon systems with small circulating pumps - pumps that are turned on in very cold weather conditions to move water and to prevent the one in the collector from freezing. Only in this case, thermosyphon systems are truly an all-climate solution.