Many people ask about how solar heating systems work. There are many aspects to solar thermal heating but here we explain some basic principles.

Basic solar water heating concepts

  1. When the solar panel is hotter than the cylinder (usually by 6-8°C ), the solar electronic controller runs the pump. The pump now pumps antifreeze through the panel where it heats up.  Often a triangle/circle symbol with a pump flashes or spins on the controller screen.
  2. This heated antifreeze is then pumped through the coil in the solar cylinder. The hot antifreeze gives off its heat to the water surrounding the coil in the cylinder. The water in the cylinder heats up as this process continues.
  3. When the solar thermal panel is no longer hotter than the cylinder (usually by 2 – 4°C) the controller switches off the pump.

Solar cylinders in the UK

There are many types of systems and cylinders installed in the UK. However, the vast majority of solar thermal systems use a ‘Twin Coil Cylinder’. For more information on cylinders please visit our cylinders page.

Solar system diagrams

The solar system heats the whole cylinder and the boiler heats the top two thirds of the cylinder if the solar has not sufficiently heated the water. It is critical to the efficiency of the system that the minimum of heat energy is added to ensure the maximum benefit from the solar. For individual controller instructions see the controllers page.

Twin coil solar cylinder
The upper portion of the cylinder is heated by the boiler alone whereas the solar heats the whole cylinder.
Solar Heating diagram
The sun warms up the antifreeze in the panel which is in turn pumps it through lower the coil in the cylinder which heats up the water. The heat rises to the top so the whole cylinder can be heated.