Solar Thermal Systems

Solar Thermal technology generates hot water from daylight and is one of the most cost-effective forms of renewable energy in the UK. Solar Thermal Panels can help to reduce hot water bills and can be used in conjunction with other renewable technologies, such as Solar PV, biomass and Ground Source Heat Pumps.


  1. Domestic Water Heating
  2. Commercial Water Heating
  3. Domestic space heating
  4. Under-floor heating
  5. Heating of swimming pools


Installing a Solar Thermal System brings a range of financial and environmental benefits, including:

  • Reduction of CO2 emissions.
  • Use of a free energy source (the sun) reduces use of fossil fuels - coal, gas, oil.
  • Consumers enjoy more independence from utility companies.
  • Advantages over other renewable energy technologies - well suited to the urban environment and silent.
  • Immediate and substantial saving on hot water bills.
  • Extended boiler life.
  • A good return on investment.
  • Adds value to the property.
  • Renewable Heat Incentive Payments/Tariff.

On-roof System

In-roof System

Typical System Componants

  • Solar collector (panel)
  • Hot water store (usually twin coil tank)
  • Flow and return pipes (solar primary)
  • Heat exchange fluid
  • Means of circulation and control
  • Means of coping with temperature fluctuations from -15°c to 250°c
  • Means of control of the legionella bacteria
  • Delivery of the hot water to the outlets

How It Works

In its simplest form a solar thermal system works as follows; solar panels (known as collectors) absorb as much of the sun's heat as possible. These panels contain liquid, which once heated travels to a coil in the hot water cylinder and transfers heat to the water store. So over a period of time a full tank of hot water is created. The time period depends on the intensity of the sun, the size and efficiency of the collectors and the size of the hot water tank.

Back-up Heat

As can be seen in the diagram, the tank has a separate heat exchange coil, which can be used to provide a supplementary heating when solar energy is not available or is inadequate.

Hot Water Cylinder

Solar Thermal Array - Larger System

In-roof Array above Conservatory

Flat Plate Collectors

Flat plate collectors are similar to a velux roof window and consist of fluid filled metal "envelope" with a selective black coating that greatly improves absorption of solar energy. This is housed in a glazed, insulated box. The collector is mounted usually on a roof and connected to the hot water system of the building in a similar way to a conventional boiler, using insulated pipework that feeds a coil in the hot water cylinder. During new build they can be roof integrated prior to tiling so as to minimise impact.

Water is circulated either by thermo-syphon or, more commonly using a circulating pump. The pump is controlled in such a way that when the temperature of the collector is lower than the temperature in the hot water system (known as hysterisis) the pump is switched off. Flat plate collectors need to be protected against frost. This is achieved by the addition of antifreeze to the heating circuit, or by arranging the system such that the collector drains down when the pump is switched off.

A typical 4 person family home would require 3-5m² of panel.

Evacuated Tube Collectors

Evacuated tube collectors consist of around 20 vacuum tubes typically around 100mm in diameter and 2 metres in length. They mount onto the roof plane on a framework. Each tube is fitted with a heat transfer fluid, the upper ends of which are connected to a manifold heat exchanger that is connected to the primary circuit of the building.

Evacuated Tube Collectors are more efficient than Flat Plate Collectors. Typically 3m² of Flat Plate is equal to 2m² of Evacuated tube. Although more expensive to buy, evacuated tube can be less time consuming to install and are less position sensitive as the tubes can be rotated in their housing to attract maximum amounts of solar energy. They also have the advantage of being suitable for fitting to outside walls.