DESCRIPTION

Solar water heating systems use the energy from the sun to heat water,
most commonly in the UK for hot water needs. The systems use a heat
collector, generally mounted on the roof in which a fluid is heated by the
sun. This fluid is used to heat up water that is stored in either a separate
hot water cylinder or a twin coil hot water cylinder inside the building.
The systems work very successfully in all parts of the UK, as they can
work in diffuse light conditions.

There are two types of collectors used for solar water heating applications

- flat plate collectors and evacuated tube collectors. The flat plate
collector is the predominant type used in domestic systems as they tend
to be cheaper. Evacuated tube collectors are generally more expensive
due to a more complex manufacturing process (to achieve the vacuum)
but manufacturers generally claim better winter performance.

WHERE CAN SOLAR WATER HEATING SYSTEMS BE USED?

Ideally the collectors should be mounted on a south-facing roof, although
south-east/south-west will also function successfully, at an elevation of
between 10 and 60°. The panels can be bolted onto the roof or
integrated into the roof with lead flashings. They look similar to rooflights.
Solar water heating systems are suitable for any building type that
has sufficient year round hot water needs (ideally during the day) and a
suitable south-facing roof of sufficient size. This technology is
particularly suitable for low-density housing developments. Retail units or
offices with canteens and washrooms and/or showers may also have a
suitable demand for hot water.

Where possible, solar water heating systems should be placed on roof
areas not visible to the road or sight line of other buildings. Some
systems can be integrated flush to the roof. The systems are no more
intrusive than a roof light (window in the roof) when roof integrated.

COST RANGES

Domestic installation

Costs are in the range £2,500 to £4,000 for a fully installed individual flat
plate standard household system (4m2). Discounts, starting at 10%, are
likely to be available for bulk purchases. These will need to be negotiated
with suppliers and will depend on the size of the order.

Costs are in the range £2,850 to £3,500 for a fully installed individual
evacuated tube standard household system (4m2). Discounts, starting at
10%, are likely to be available for bulk purchases. These will need to be
negotiated with suppliers and will depend on the size of the order.

Commercial systems

There can be a large variation in the costs of installation labour, pipework,
fittings etc for commercial systems that depend on site-specific
issues. Probably the most important issues are the relative locations of
the solar collectors and the hot water storage (obviously the closer
together they are the shorter the pipe-runs), the degree of complication
in running the pipe-runs from the collectors to the hot water storage (i.e.
is there an obvious route for the pipes) and the ease (and costs) of
establishing safe working access on the roof area where the collectors are
to be mounted. The interface between the solar suppliers/installers and
the main contractor can also be a significant factor in determining cost
(where the main contractors can add a significant fee for their role in coordinating works).
Large system costs (for installed systems) based on flat plate solar
collectors start at around £700 per square metre but can be higher due to
factors such as those listed above.

See section 4.6 for details on available grants.

OUTPUT RANGES

Domestic systems

A 4m² collection area will provide between 50% and 70% of a typical
home’s hot water requirements depending on the quantity of hot water
required and the timing of that requirement. The percentage can be
increased if:

• Hot water is drawn off during the day, allowing more water to be
heated up in the afternoon

• Low flow showers and spray taps are fitted so that less hot water
is required

• Showers are taken instead of baths.

The system is particularly beneficial for dwellings where residents are at
home using hot water during the day, for example, young families or the
elderly. Savings from solar water heating are difficult to predict and will in
practice depend on how much water the occupants use and at what times
they use it.

The Energy Efficiency Commitment Scheme bases savings from solar
water heating on an average figure of 454kWh/year saving per m2 of flat
plate collector or 582kWh/yr per m2 for an evacuated tube system.
Assuming a 4m2 system this would provide a saving in energy use of
1,816kWh/year and 2,328kWh/year respectively for the two systems, 34
to 44% of an average modern house space and water heating demand.

Commercial systems

The same Energy Efficiency Commitment Scheme base savings can be
applied for commercial systems; an average figure of 454kWh/year saving
per m2 of flat plate collector.

TECHNICAL FEASIBILITY ISSUES

• Systems should be in locations that will be unshaded at all times of
day if possible. Gable roofs, chimneys, trees and other buildings in the
vicinity should be identified as potentially shading the modules. They
may cause the performance of the system to drop in the early morning
or late afternoon.

• The optimum elevation and angle for a solar water heating system will
depend on when the hot water is required - for example, midday or
early evening.

• There needs to be space for a preheat cylinder in or close to the
roof space.

• The potential for vandalism should be assessed if the system can be
seen from the ground or if it is accessible due to raised pavements or
other buildings. Sometimes it is necessary to cover panels with heavy
duty perspex to protect them from flying objects.

• Solar water heating systems are most commonly fitted with standard
boilers, rather than combination boilers due to the requirement for a
hot water tank. However, there are a number of manufacturers that
make combination boilers specifically designed to take preheated
water from solar water systems.

MAINTENANCE REQUIREMENTS

Solar water heating is a comparatively simple system and so could be
installed by any suitably trained plumber but it is recommended to use
approved installers such as those registered for the Clear Skies funding
scheme (see Links to existing suppliers lists) or the Solar for London and
sunrise schemes.

The occupiers of the building with a solar thermal system should plan to
undertake an annual maintenance check, ensuring that the collector
surface is clean, there is no corrosion, sensors and fixings are properly in
place etc.

ADDITIONAL BENEFITS OF TECHNOLOGY

Savings in fuel bills for an average family of 2 adults and 2 children using
a standard 4m2 household system could be:

• Where the solar water heating is supporting a gas heating system,
based on a cost of 1.5p/kWh for gas, approximately £27.24 (flat
plate) or £34.92 (evacuated tube) per year.

• Where the solar water heating is supporting an electric heating
system, based on a cost of 6.38p/kWh for electricity, the cost saving
would be approximately £115.86 (flat plate) or £148.53 (evacuated
tube) per year.

PLANNING AND LEGISLATIVE ISSUES

The planning authority will assess what visual impact, if any, solar water
heating systems would have on the local amenity. Systems can be
designed so visual impact is minimised. For example, some systems can
be integrated flush to the roof and when this occurs they are no more
intrusive than a roof light (window in the roof). This is most cost effective
when the system is part of a new build development rather than when
being retrofitted on an existing building.

For new developments, which must apply for planning permission
anyway, the planning authority’s assessment will normally be part of the
larger assessment of the whole development proposal.

Some solar water heating systems have been granted permission in
conservation areas as they can be very discreet, looking similar to roof
lights. An example is an English Heritage case study of a solar thermal
system integrated into the roof of a development consisting of a three-storey
office building, 2 houses and 3 flats in a conservation area;

www.english-heritage.org.uk/filestore/policy/pdf/context_p6-19.pdf.

Retrofit

Planning permission for retrofit has been covered here as it is being interpreted differently in different areas. For retrofitting onto existing buildings, it is permissible to make certain types of minor alterations to properties without having to apply for planning permission. These are called
permitted development rights. If the property is located in a Conservation Area, however, planning permission may be required for these types of work that are regarded as Permitted Development in other areas. This is because the council may have removed some of the Permitted
Development Rights by issuing an Article 4 Direction. Article 4 Directions are made when the character of an area of acknowledged importance would be threatened if inappropriate alterations were made. This means that you are required to submit a planning application for work that normally does not require permission.

The London Plan states that ‘energy efficient measures and renewable energy technology should not be precluded in areas of heritage, but should be designed sensitively’. Planners need to
consider what aspect of an area or a building is being conserved, as well as whether the panel can be seen from outside the site. Particular opportunities on roofs in sensitive areas are likely to be rear slopes or centre valleys, where they would not disrupt the overall architectural
interest of the building. English Heritage have advised that each case would need to be judged on its own merits. There are likely to be locations within most conservation areas where careful siting would not damage character.

LINKS TO SOURCES OF MORE DETAILED TECHNICAL INFORMATION

• Companion Guide to PPS 22: The technical annexes, available at
www.odpm.gov.uk/planning.

• Solar Trade Association, The National Energy Centre, Davy Avenue,
Knowlhill, Milton Keynes, MK5 8NG, T: 01908 442290,
F: 0870 0529194, E:enquiries@solartradeassociation.org.uk
W: www.solartradeassociation.org.uk.

• Solar for London,Sustainable Energy Action Ltd, 42 Braganza Street,
London SE17 3RJ, T: 0207 820 3156 (Solar for London Hotline),
F: 0207 582 4888, E: info@solarforlondon.org,
W: www.solarforlondon.org.

• sunrise, Creative Environmental Networks, 8th Floor, Ambassador
House, Brigstock Road, Thornton Heath, Surrey, CR7 7JG,
T: 020 8683 6683, F: 020 8683 6601,
E: info@greenenergycentre.org.uk , W: www.cen.org.uk.

FAQS

How do you connect solar water heating in a block of flats and who gets
the benefit?

In a small block of flats, each flat can have its own individual system of
solar panels and hot water storage cylinder and pipework. Where a
communal solar hot water system is envisaged, this can feed into a
communal heating system giving benefit to all tenants via reduced overall
heating costs. Alternatively, a standalone communal solar hot water
system can supply hot water to tenants individually via a heat meter, so
that their consumption can be monitored and they can be charged
individually, at an appropriate rate.

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