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How Solar Water Heating Works

By: Dr Gareth Evans - Updated: 10 Dec 2012 | comments*Discuss
 
Solar Panels Solar Heating Solar Power

Installing solar panels to heat water offers a relatively cheap way to benefit from solar power, with installations typically costing very considerably less than the alternative approach of generating electricity by photovoltaic systems.

Able to make a major contribution to meeting the hot water demands of an average UK household during the warmer months of the year, solar panels can also be effective for larger-scale solar power projects such as swimming pools.

Solar Heating

The idea behind solar heating is very straightforward. The solar panels themselves – which are water-filled – are designed to collect as much of the heat from the sun as possible and then transfer it to your domestic hot water system.

Most of the commercial versions available are “indirect”, the sun-warmed water travelling through a coil in a hot water tank, heating up the water it contains without ever coming into direct contact with it. Then, once it has given up most of its heat, the cool water returns to the solar panels to begin the process all over again.

This is very similar to the sort of familiar arrangement used by back boilers and wood-burning stoves. Direct systems do exist, in which water from the panels enters the domestic hot supply, but although this kind of approach has some advantages, it is not well-suited for use in areas with hard water.

Solar Installations

According to the Centre for Alternative Technology, based near Machynlleth in Mid-Wales, solar panels should be roughly south-facing to maximise their solar thermal gain and the installation should allow around one square metre of panel surface area per person.

For the average household, this equates to around three or four square metres and a cost estimated at around £3,000 – £5,000 by the UK Low Carbon Buildings Programme, who have grants for householders, communities and other bodies to install this technology.

The panels themselves are most commonly located on the roof-top, since they can accommodate the 20 to 50 degree angle necessary for maximum efficiency, although it is also possible to mount solar panels on frames at ground level.

In addition, it may be necessary to add an additional water cylinder if your current hot-water system is incompatible with your new solar power installation – something any reputable solar heating company will be able to advise you about.

There are two general types of solar panels on offer for water heating – flat plates and evacuated tubes. Of the two, the evacuated tube systems are more efficient, but come at a higher cost – perhaps as much as 70 per cent more than a similar flat plate installation.

Again, it is something that your installer is best placed to help you decide, but as a general rule for most domestic projects, the lower performance of the flat plates can often be compensated for by simply fitting bigger solar panels.

However, for larger installations, such as a swimming pool or similar community facility, the extra cost of evacuated tubes can prove worthwhile in the long run. Much depends on individual circumstances and the intended use, so it is best to seek professional advice if you’re in any doubt.

Energy Savings

Heating water is one of the biggest users of energy in most households – accounting for some 20-25 per cent of our domestic usage according to the Environment Agency. Installing solar panels to heat your water is estimated to be able to provide around a third of your needs – knocking about £50 a year off the average gas-heated home and avoiding over 300 kg of CO2 emissions. Despite the recent hikes in gas prices, the savings are even better for a household heating water by electricity.

Requiring very little in the way of maintenance beyond a yearly check by the owner and a three or five year service by a professional engineer, solar hot water systems are one of the simplest ways to join the renewable energy revolution.

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