Solar Thermal

Hot water generation from solar panels

Most of the hot water demand for a household in summer can be produced by a solar thermal system.  The main components of a solar thermal system are:


  • Collector – this may be a flat panel or evacuated tubes
  • Controller – this may be separate or combined with a pump
  • Hot Water Cylinder
  • Expansion Tank


Flat panel collectors are more robust and look similar to Velux windows.  Evacuated tube collectors will produce hot water at a higher temperature.  A smaller roof area is required for a solar thermal system than for a solar PV system.  A solar PV system might have 12 to 16 panels, but a solar thermal system with flat plate collectors might only require 2 panels.


The fluid heated by the solar panels is normally kept in a closed loop and is partly anti-freeze to avoid it freezing in winter.   A hot water cylinder is required to store the heat generated.  When the solar panel is hotter than the water in the cylinder, the controller turns on the pump and fluid from the solar panel flows through the coil in the cylinder, heating the water.


A back-up heating system is required for space heating and when there is not enough sunshine for water heating.  This system is normally a regular gas boiler.  There may be problems if this is a combination boiler as it may not be designed to cope with the incoming water being pre-heated.


It is possible to claim the Renewable Heat Incentive for solar thermal systems on Domestic and Non Domestic properties.

Evacuated Tube Collectors