Solar thermal

Solar thermal systems use free energy from the sun to heat the water in your home. While Solar PV converts sunlight into electricity, Solar thermal converts it directly into heat.

It is one of the most efficient ways to use solar energy, as the conversion of light to heat is more direct than light to electricity.

How it works

  1. Collectors: Solar panels (collectors) are fitted to your roof. These contain a fluid (usually a mix of water and antifreeze).
  2. Absorption: The fluid absorbs heat from the sun.
  3. Transfer: The heated fluid is pumped to a heat exchanger inside your hot water cylinder.
  4. Heating: The heat exchanger transfers the heat to the water stored in your tank.

The system works all year round, though you will need to heat the water further with a boiler or immersion heater during the winter months.

Types of collectors

1. Flat plate collectors

These look similar to solar PV panels. They consist of a dark absorber plate under a glass cover. They are durable and can be integrated into the roof line for a sleek look.

2. Evacuated tube collectors

These consist of a series of glass tubes. They are more efficient than flat plates, especially in colder or overcast conditions, but they are more expensive and have a more distinct, industrial appearance.

Benefits of solar thermal

  • Hot water for free: A well-sized system can provide 50% to 70% of your home’s annual hot water needs.
  • Lower bills: Reduce your gas, oil, or electricity usage for water heating.
  • Compact: You only need a small amount of roof space (typically 2-4 square metres) compared to a full solar PV array.
  • Reliable: Simple technology with few moving parts.

Key considerations

1. Hot water cylinder

You must have a “twin-coil” hot water cylinder. One coil is for your boiler or heat pump, and the other is for the solar thermal system. If you currently have a combi boiler (which has no tank), you will need to install a cylinder to use solar thermal.

2. Roof orientation

A south-facing roof is ideal, but east or west-facing roofs can also work well. The collectors should ideally be tilted at an angle of 20 to 50 degrees.

3. Maintenance

You should have the system checked by a professional every 3-5 years. The main task is checking the concentration and pressure of the antifreeze fluid to ensure the system doesn’t freeze or corrode.

Solar Thermal vs Solar PV: If you have limited roof space and want to reduce your carbon footprint, Solar PV is often chosen because electricity is more versatile than hot water. However, if you have a high hot water demand (e.g. a large family), Solar Thermal can offer a faster payback.

Grants and funding

Solar thermal installations are subject to 0% VAT until March 2027. Some local grant schemes may also be available depending on your region and income level. Check our grants and funding section for more details.