Solar Thermal Water Heating

How do Solar Thermal Water Heating Systems Work?

A solar thermal water heating system uses specialised solar panels known as collectors which collect the heat from the sun and use that to heat the water. The panels are generally fitted to the roof of a building to collect the maximum amount of heat from the sun.

There are two main types of collectors; flat plate collectors or evacuated tubes. These panels heat the water and this is then stored in the home's hot water cylinder.

Most homes in the UK continue to have a boiler or immersion heater as a back up to provide extra hot water if required. To fit a system, you will need to have around five metres square of roof which is sunlit for most of the day and space for an extra, or larger, hot water cylinder.

Flat Plate or Evacuated Tubes?

A flat plate collector is an absorber plate housed behind a glass cover with insulation underneath. It is designed to trap as much heat as possible to prevent losses through convection. Flat plates can either be mounted on top of the roof or integrated into a roof covering. Evacuated tube collectors also have an absorber strip but this is inside a glass tube and surrounded by a heat transfer fluid. They work by using a vaporising process to carry the heat and to ensure the vaporisation occurred they need to be placed at a certain angle.

Evacuated tube collector systems are the more expensive option, however they are generally considered to be more effective in heat transfer and they have a greater surface area to collect the sun's rays. This greater surface area means they can be used on a smaller roof area than a flat plate system.

Benefits of Solar Thermal Heating

Solar thermal heating systems can be used all year round, even in sub zero temperatures, though using these systems in the winter months will probably require the topping up with hot water from conventional systems.

Using these systems should result in a cut in your gas or electricity bills. Savings vary between users but research suggests that typical savings are in the region of fifty five pounds a year for a gas system and eighty pounds a year for an electric water heating system. In addition, householders will also be reducing their carbon footprint. Again reductions vary but are typically between two hundred and five hundred kilograms of carbon dioxide a year.


Installing a thermal water heating system usually costs a little less than five thousand pounds. This figure includes VAT at the five per cent rate. Most systems come with guarantees for between five and ten years and maintenance costs are low.

You may be eligible to earn income from the government's Renewable Heat Incentive scheme if you install one of these systems, full details of which can be found on the energy savings trust website. This scheme allows people to claim retrospectively for installation made from July 2009. Payments to help with installation costs can also be earned from the Renewable Heat Premium Payment Scheme.

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