 SOLAR WATER HEATINGWritten by CAT's free information serviceemail: info@cat.org.uk; tel: 0845 3308373 or 01654 705989 Click here to download a printable version of this sheet (2 sides A4, PDF format, 350KB). Solar Water Heating or Solar Electricity? There are two rather different technologies that use roof-mounted panels to collect solar energy. This information sheet is about solar water heating (sometimes called solar thermal) technology; a way to directly heat water for domestic use - e.g. in showers. For information on generating electricity using photovoltaic (PV) solar panels, see our free information sheet on Photovoltaic Solar Power. How does solar water heating work? A solar water heating (SWH) system consists of three major components: one or more solar collectors (tubes or panels, usually mounted on a roof), a pump connected to a controller and a hot water cylinder with two heating coils (twin coil cylinder). The collector uses the solar energy from sunlight to heat a thermal fluid (water with antifreeze). If the fluid in the collector is hotter than the water in the cylinder then the controller activates the pump to pump the fluid through the coil in the cylinder, thus heating water in the cylinder for showers and hot water taps. The second heating coil in the cylinder is connected to a back-up boiler (e.g. gas boiler) to provide hot water when there isn't enough sunshine. Is my home suitable for SWH? Ideally, solar collectors should be south-facing and free of shade, at an angle of between 20 and 50 degrees, but panels facing south-east or south-west will also operate efficiently. The diagram to the right illustrates how performance varies with tilt and orientation. SWH works best on a south-facing roof, but even an east or west facing surface can still produce a good amount of hot water. The SWH system heats water in a cylinder, therefore it is difficult to add solar water heating to a heating system that doesn't have a hot water cylinder (e.g. a 'combi' gas boiler which heats the water on demand when you turn on a hot water tap). Rooftop panels are the most common, but they can also be mounted at ground level. Roof mounted panels are usually a 'permitted development', so you won't need planning permission. Exceptions include National Parks, Areas of Outstanding Natural Beauty, conservation areas and listed buildings. How many panels will I need? As a rule of thumb, you will need about 1 square metre (m2) per person. Of course, this will depend on a number of factors, such as the orientation of your roof, the size of your hot water cylinder - and on how much hot water you use! Collector panels are usually between 2 and 3 square metres, so a typical house often has either one or two of these panels. Which collector type should I chose? There are two types of SWH collectors typically used in the UK: Flat panel and evacuated tube collectors. Both have their strength and weaknesses - for example, evacuated tubes perform better on cold sunny days and flat panels protrude less from the roof - but overall they deliver similar value for money. How much hot water can SWH produce? 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 etc. As this graph illustrates, most of this hot water will be produced in summer. Because solar radiation is much weaker in winter, SWH will not produce enough heat for your hot water in winter, and it will not help with your space heating (radiators). What's the likely cost? A typical SWH system mounted on a house in the UK will cost between £2,500 and £5,000.A big part of this cost is for plumbing and scaffolding, so you can sometimes save money by installing SWH while carrying out repair work - or by integrating SWH in the construction of a new building. Does SWH make financial sense? Yes! The combination of fuel savings and a new government support scheme, the Renewable Heat Incentive (RHI) now means that a typical SWH system in the UK can, over its lifetime, pay back twice its initial cost. Here is an example calculation: The economics of solar water heating A typical UK household uses around 2,500 kWh of energy per year to heat water for showers and hot taps. A solar water heating system that produces 60% of the total hot water thus saves around 1,500 kWh in energy bills. Annual payments and savings: How do I find an installer? To qualify for Renewable Heat Incentive payments you'll need to use installers and equipment accredited under the Microgeneration Certification Scheme (MCS - see link below) You could also check if the installer belongs to a professional body that promotes high standards (see below), and you should always get a few quotes to compare. Further Information Our book Tapping the Sun is an invaluable guide to choosing and installing a solar water heating system, and describes how to choose a system that it right for you, and how it will fit into your plumbing system. Detailed technical advice on the heating options available in your specific circumstances is available through CAT Consultancy. We also offers many residential courses, including one on solar water heating for householders, and another giving professional training to installers. We have many solar water heating systems on display at CAT, so you can have a look around these if you visit us. You can also contact us at CAT's free information service with any further questions. We rely on donations to continue to keep this information service free at point of use. You can support our work by becoming a CAT member or a CAT supporter: Contacts Microgeneration Certification Scheme Energy Saving Trust Trade Associations Solar Trade Association The Institute of Domestic Heating & Environmental Engineers (IDHEE) Association of Plumbing & Heating Contractors Chartered Institute of Plumbing & Heating Engineering
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