Solar water heating

This gives you a broad introduction to the topic of solar water heating, but for more detailed guidance please go to our solar thermal guidance page.

Improved insulation levels in British buildings have reduced the amount of energy required to heat occupied space. As a result, generation of hot water is taking up a higher proportion of our energy consumption and solar panels are increasingly being adopted to address this aspect of our contribution to global warming.

Once solar heating is installed it is almost entirely maintenance free and a 4m² array will provide half of an average family’s hot water needs for the year. Normally used to supplement a conventional water heating system, solar panels will cut the amount of heating fuel used by between 40% and 60% - which is about 1,500 kilowatt hours (kWh) per year, according to the Solar Trade Association.

Flat plate
There are two main types of system:Flat plate collectors consist of a metal sheet embedded in an insulated box covered by glass or clear plastic. The solar energy absorbed by the sheet is trapped by the glazing above and insulation behind the panel. The heat energy is then transferred via circulating copper pipes containing a mixture of water and glycol and through a heat exchanger in the hot water cylinder.

On average, this ‘indirect’ approach will convert about 50% of the energy received into useful heat. 

Tubes
Evacuated tube collectors are generally considered to be about 20% more efficient because of their ability to capture energy from low levels of sunlight. Being cylindrical, they have a 180 degree absorbing surface facing the sun for most of the day whereas flat plates are only in an ideal absorbing position for a short period.

The cost of installing a solar hot water system ranges between £2,500 and £4,000 dependent on the size of the system – grants are available from the DTI’s Low Carbon Buildings Programme as they are for most renewable type technologies. 

A typical domestic installation in the UK would have a panel area between 3 and 4m² when using flat panels and about 2m2 with evacuated tubes. The storage cylinder will typically have capacity for between 200 and 300 litres depending on usage patterns in the building.

Issues to consider:

The solar installation must be carefully integrated with any existing heating system to provide the full benefits to the end user – only fully trained and experienced heating engineers should be employed to carry this out.

The position of the installation is important both from an aesthetic and performance point-of-view – is the user happy to have solar panels on their roof?
Planning permission is still required in many areas although this restriction may soon be relaxed.

Anti-freeze must be applied to the collector loop to avoid the system freezing in cold weather 

These systems do also have the potential to provide low temperature space heating as well as hot water via a triple coil cylinder. Solar thermal collectors feeding underfloor heating, in particular, is becoming more common across continental Europe and may eventually make an appearance in the UK.