How Does Solar Thermal Work?

By Katie Anderson on July 29th, 2011

A solar water heating system consists of solar panels, a pump station, a twin coil cylinder, a solar cylinder and a boiler.

Also known as solar thermal, the system uses the solar panels – sometimes referred to as collectors – which are installed on rooftops to gather energy from the sun to provide a home with hot water all year round.

Aside from using the energy from the sun to heat water, a solar thermal system can also be used to generate central heating.

Using solar thermal panels can cut your water heating bill by up to £85 per year, and will provide around one third of your hot water. Investing in solar thermal can help cut CO2 emissions by approximately 580kg, depending on which fuel you are using.

Systems cost approximately £5,000 (inc. VAT).

How does it work?

1. The roof mounted solar panels are made up of cells which contain a liquid.
2. The liquid absorbs solar radiation (energy) which heats the fluid.
3. The solar panels are connected to a hot water cylinder via pipes.
4. When the liquid has reached the desired temperature, the pump station begins to circulate the hot fluid down into the twin coil cylinder.
5. The hot fluid enters the twin coil cylinder and heats the water held inside.
6. A sensor monitors the temperature of the water until it becomes ready for use within the home.
7. If the water within the hot water cylinder doesn’t reach 60C, or the set temperature, the boiler will fire up to supplement the system.

Solar thermal terminology

  • Solar water heating panels – there are two types of panels; evacuated tubes and flat plate collectors. Flat plate collectors are either integrated into the roof or fixed onto the roof tiles.
  • Pump station – the pump circulates water or heat transfer fluid (water or water mixed with antifreeze) around the system.
  • Twin coil cylinder – used in place of a traditional single-coil cylinder, the upper coil is used to connect to the traditional boiler-heated circuit, whilst the bottom coil is connect to the solar circuit.
  • Solar controller – it uses sensors to monitor heat differences between the collector and the water in the tank, and will switch the pump on and off accordingly.
  • Boiler – works by topping up the heat and makes the water hotter. Consequently you’ll still have hot water when solar energy is unavailable, for example during the winter months.
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