Solar Thermal

As the name suggests, solar panels use the sun’s natural power to provide energy efficient hot water for the home. Switching to a renewable energy source like solar heating can result in significant savings, both in CO2 and energy bills. The technology is simple, effective and entirely sustainable which is good for the environment – both now and in the future.

Flat plate on-roof collector panels are mounted on top of roof tiles or slates, and are therefore most suited to providing solar heating to existing properties, whereas in-roof collector panels are perfect for integrating solar heating into new-build properties as they are built into the roof structure. Evacuated tube collectors offer premium solar heating performance in cloudy conditions and complete flexibility as they can be mounted on any surface, including facades and flat roofs.

How Solar Heating Works

A solar heating system consists of three main elements:

  • Solar panels or collectors
  • Hydraulic pump station and controller
  • Solar cylinder
  • Solar water heating (known as solar thermal) systems capture the free heat from the sun and use it to heat up water for use in the home.

It’s a simple process:

  • Panels on your roof absorb heat from the sun – they are known as the collector
  • The water in the panels heats up
  • This hot water is pumped through a coil in your cylinder
  • Which transfers the heat to the water in the cylinder


Effectiveness of Solar Heating

The ideal situation for solar panels is facing due south, although they are effective facing anywhere between south east and south west. As a rule of thumb you need between 1 and 2 m2 of collector (solar panels) per person living in the house.

During the summer months, an on-roof solar heating system can generate as much as 100% of the hot water required for an average household; even on dull days some hot water can be produced. In the winter, up to 30% can be generated, with the remainder being provided either by a conventional boiler or electric immersion heater. On average, a well-designed solar heating system will generate around 50-60% of the annual domestic hot water demand – while also substantially reducing carbon emissions.

The reality will depend on a variety of factors:

  • How much interest you take in how the system works and adapt to make the most of the free hot water (ie having showers in the evening rather than the morning). The sun isn’t as reliable as a timer clock.
  • The size of your cylinder. Many cylinders only hold enough water for a day’s supply of hot water, so a day or two of cloud and rain will mean you have to turn on the boiler or immersion heater.
  • How you program your back up heating. If your control panel does not allow you to program the hot water and central heating separately, you may not get the maximum benefit from the solar panels when the heating is turned on. By only boosting the hot water once the sun has gone down, you maximise opportunity for solar heating.
  • Adequate insulation of both cylinder and pipes carrying hot water.
  • Allowing hot water temperature to vary. If you do not need high temperatures all the time, you will have less need for back-up heating. You will also reduce heat loss. However, it is important to make sure your cylinder reaches more than 60 degrees centigrade at least once a week to avoid risk of Legionella.


What Type of Solar Thermal Panel Is Best?

There are two types of solar thermal panel: flat plate panels and evacuated tubes.

Flat Plate Panels

Flat plate panels consist of an absorber plate in an insulated metal box. The top of the box is glass or plastic, to let the sun’s energy through, while the insulation minimises the heat loss. Lots of thin tubes carry water through the absorber plate heating the water up as it passes through.

Evacuated Tubes

Instead of a plate, evacuated tube collectors have glass tubes containing metal absorber tubes, through which water is pumped. Each tube is a vacuum (the air is ‘evacuated’ hence the name), which will minimise heat loss.

What Does Solar Thermal Cost?

The cost of installing a domestic solar thermal panel system will depend on the type and quality of the panels, whether you need scaffolding, and how easy it is to integrate into your existing plumbing system.

As a rough guide, average systems are likely to cost between £4,000 and £7,000.

One off capital grants of £300 are available from the Renewable Heat Premium Payments scheme until 31 March 2013 (unless the money runs out before then). You apply for this through the Energy Saving Trust.

Panels are available for DIY installation, but buying them this way means that you have to pay the full rate of VAT (instead of the 5 per cent rate) and, more significantly, won’t be eligible for the renewable heat incentive, if it is introduced. Well installed, and properly-used, solar hot water systems will provide around 60 per cent of the hot water a home needs.

Planning Permission For Solar Panels

Solar panels are generally considered ‘permitted development’ in England and Wales as long as they do not protrude more than 200mm from the wall or above the roof slope; and are not higher than the highest part of the roof.

They are permitted in a conservation area as long as the panels are not installed on a wall that fronts a highway. However, if you live in a listed building you will have to apply for planning permission. Up-to-date advice is available on the government’s planning portal.

Stand alone solar is permitted development as long as it is less than 4m high, more than five meters from the boundary, and the surface area of the panels does not exceed nine square meters; or any dimension of its array does not exceed three meters. In a conservation area, it must not be nearer to the highway than it is to the dwelling. If it is in the grounds of a listed building you will need to apply for planning permission.