The most common applications for solar thermal systems are -

-  Domestic Hot Water

-  Swimming Pools 

The following diagram shows a conventional solar collector installation, including its associated components, for a domestic hot water system.

The same components are used in a swimming pool installation, except that the hot water cylinder is replaced by a stainless steel heat exchanger specifically designed for these applications.

System Operation

The electronic controller monitors the water temperature in both the collector and cylinder.
When the temperature within the collector manifold is some 5ºC greater than the cylinder, the pump is switched on to circulate the solar heated water through to the solar coil in the cylinder.
When the water in the cylinder is hotter than in the collector, the pump is switched off.

In cold weather, as the temperature in the collector reduces towards zero, the controller will switch the pump on to prevent freezing.
The liquid in the pipe circuit also contains a small amount of glycol as an additional precaution against freezing.

To enable the pump to work efficiently, the liquid in the pipe circuit is pressurised to 2 / 3 bar.
As the temperature of the liquid in the pipe circuit increases, its volume increases slightly  -  this volume change is absorbed by the expansion tank.

The lower coil of the dual coil hot water cylinder, which is connected to the solar collector, is manufactured from heavy-duty finned copper piping to maximise its heat transfer capability, while the cylinder itself will normally have a 75mm thick insulation coating to minimise heat losses.

The remaining components within the system are straightforward conventional plumbing items in every-day use around the world.