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Solar Water Heating Factfile
Key points
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A typical solar water heating system in the UK will produce between 40% and 60% of the hot
water a household uses over the course of a year for showers, hot taps etc. (not including
central heating) [1,2].
Most of it will be produced in the summer with some in spring and autumn
Evacuated tube system
Flat plate system
Background Information
Solar energy is captured by a solar collector which consists of:
● an absorber that intercepts and absorbs the solar energy
● a transparent cover that allows solar energy to pass through but reduces heat loss from the
absorber
● a liquid flowing through tubes that absorbs heat and carries it to the tank
● a heat insulating backing to stop the heat escaping.
There has to be a back-up system to provide hot water in weather that isn’t sunny enough (most of
the winter).It is therefore unlikely to be a useful part of a central heating system.
Current use in world and UK
World
 The total installed capacity of solar water heating worldwide was about 180 gigawatts in 2009.
 The largest user of solar water heating is China.
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The European market is growing, although the number of family homes with solar water
heating is low, about 5% in Germany for example.
Cyprus has the highest per person use of solar water heating.
In addition to small collectors, larger collectors are starting to be used for industrial heat and to
contribute to district heating systems [3].
Britain
In the UK, the use of solar water heating has more than tripled since 2008. In 2012, it produced
around 1800 gigawatt-hours of heat [4]. This is equivalent to the hot water each year for around half a
million houses.
Climate change and impact on nature
Solar energy is a renewable resource – it will not run out
The environmental impact of solar water heating schemes in Britain would be very small.
Solar water heating emits no greenhouse gas when generating heat, although some will occur in the
 manufacture,
 installation and
 maintenance
of systems.
The payback time for the energy used in manufacture is estimated at around 1 to 4 years, and
systems may last over 20 years [3].
The greenhouse gas emissions per unit of heat produced are estimated at about
20 grams of CO2 or equivalent greenhouse gas per kilowatt-hour (gCO2e/kWh) [5].
Most systems have little visual impact, as it is easy not to notice them on the roofs of buildings.
Risks
Solar water heating is a very low risk technology. There are some small risks in the manufacture,
installation and maintenance of SWH systems (someone has to get up on a roof), these risks are very
similar to those for photovoltaics panels, and they are estimated as being very low in comparison to
fossil fuel energy [3].
Cost now and in the future
A typical domestic solar water heating in the UK will cost between £2,500 and £5,000, including
installation and the cost of a new twin coil hot water cylinder.
At this cost, the system may produce heat for around
13 pence per kilowatt-hour (assuming 1500 kWh per year for 20 years).
At the moment energy produced by solar water heating is subsidised in the UK through the
Renewable Heat Incentive. [2].
The costs of systems should fall in future as more systems are installed and the cost of individual
components is reduced [3].
Higher building standards mean that SWH is increasingly being installed on new buildings.
This may help to increase familiarity with the technology and reduce the cost.
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World and UK resource
World
The technical potential of solar energy for heating purposes is vast and difficult to assess.
As with solar photovoltaics, the technical potential is greater than current global primary energy use.
The amount we can actually use is mainly limited by the demand for fairly low temperature heat at the
times when solar water heating can supply useful quantities [3].
Britain
 The amount of sunlight received by the UK is not as much as other countries.
 The UK receives much less sunlight in winter compared with summer (about a sixth of the
energy). This makes providing space heating difficult.
 Systems designed to meet around 50-60% of our hot water requirements (not central heating),
would need around two m2 of panel per person [6].
 A family-size system may produce 1500 kWh of heat per year.
Reliability/flexibility
Solar water heating relies on energy from the sun.
This varies from day to day with the weather, and the UK receives much more solar energy in
summer than winter.
Solar water heating can be relied upon to supply a certain amount of energy over a season. Whilst
solar water heating is not a very flexible energy source, storing hot water in well insulated tanks can
smooth out differences in supply between days to some degree.
Extremely well insulated hot water tanks can even be used to store warm water from summer sun for
use in winter [7]. However, the size of tanks required to store large amounts of energy make this
impractical in most cases.
Wales
While it’s true that Wales doesn’t have a brilliant solar resource, solar thermal collectors can make
use of diffuse sunlight, which includes light that makes its way through clouds.
Between 2011 and 2014, 12 accredited companies installed solar water heating systems in Wales
equivalent to 0.134 MW of energy [8] but more systems were probably installed. Many systems were
previously installed but as most of them are installed by individuals on their houses it’s impossible to
have a definite figure.
Case study 1: Solar water heating for a family house in Machynlleth:
http://www.youtube.com/watch?v=iqUN9BykQ_A&list=UUrnnQTkCdAK9rOid_0tL9QQ&index=64
Case study 2: Chirk Castle, near Llangollen, enters solar age:
http://www.nationaltrust.org.uk/article-1356397749561/
References
[1] EIA (2013). Solar Explained: Solar Thermal Collectors. United States Energy Information Administration.
http://www.icax.co.uk/How_IHT_Works.html [accessed 19/2/2014].
[2] CAT (undated). CAT Information service: Solar water heating. Centre for Alternative Technology.
http://info.cat.org.uk/solar-water-heating [accessed 19/2/2014].
[3] IPCC (2011). IPCC Special Report on Renewable Energy Sources and Climate Change Mitigation.
Intergovernmental Panel on Climate Change. http://srren.ipcc-wg3.de/report/ [accessed 21/1/2014].
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[4] DECC (2013). Statistics at DECC. Department for Energy and Climate Change.
https://www.gov.uk/government/organisations/department-of-energy-climate-change/about/statistics [accessed
8/1/2014].
[5] Pehnt, M. (2006). Dynamic life cycle assessment (LCA) of renewable
energy technologies. Renewable Energy, 31 (2006) 55–71.
https://www.ifeu.org/energie/pdf/Environmental%20Impacts%20of%20Distributed%20Power%20Generation.pdf
[accessed 19/2/2014].
[6] Mackay, D. (2013). Sustainable Energy – without the hot air. http://www.withouthotair.com/ [accessed
20/1/2014].
[7] http://www.icax.co.uk/interseasonal_heat_transfer.html [accessed 19/2/2014].
[8]https://rhi.ofgem.gov.uk/Public/ExternalReportDetail.aspx?RP=RHIPublicReport#P7a6eea46addb4aecaaedc
1909123579d_2_oHit0 Accessed 18.12.14
[9] CAT info sheet on Solar Water Heating http://info.cat.org.uk/solar-water-heating
– background information for Energy Trumps cards. Full resource available as free download at
http://learning.cat.org.uk/en/resources
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