Solar Water Heating - Some Questions Answered

Sustainability in our homes is as much about the energy we use when we live in them, as it is about the way in which our homes are built.  Efficient water heating systems are something to consider when making our homes more energy efficient, and can be installed in both sustainably built homes and existing ‘modern’ homes.

Exploding the myths

Solar water heating seems to be one of those peculiar things that most people seem to have heard about but few know very much about it (except that they think it costs thousands of pounds, and only works in summer). Having said that, there are those who know of someone else who has had it for years and will say that it works very well. It is true that solar water heating has been around for years – it is as we say, a ‘mature’ technology.  This means that the focus of manufacturers is on the production of equipment rather than on its development. Some solar systems have been installed for 20 – 30 years and have been saving energy all that time. Systems installed today will probably go on working for 25 years or more with little or no maintenance.

How does it work?

Solar collectors (either the glass tube or flat plate variety) are fixed to a roof which receives a reasonable amount of sunshine. Roofs facing south east or south west are still suitable. If you have a thatched cottage the collectors can be mounted on frames on the ground. A new hot water cylinder with a second ‘solar coil’ is usually required. Well insulated connecting pipes and a pump are also installed. Most systems have a separate circuit with anti-freeze fluid in the collectors. The heated fluid is pumped round the circuit and the heat is transferred to the cool water at the bottom of the cylinder. A boiler is still required to provide back-up energy when there is insufficient sunshine.

How much energy does it capture?

A good solar system will capture anything between 50 and 70 % of the energy required to heat your water, averaged across the year. During hot spells in summer people find that they can switch off their boilers as the solar system provides all their hot water. Solar collectors work by absorbing either direct sunshine or diffuse radiation on overcast days. They also work on clear days in winter if the sun is shining. On cold cloudy days there is little solar energy available to be collected. Beware of any companies who appear to claim to offer more, either that they are more effective or don’t need sunshine to work!
 
Which collectors are best?
Some people say that the evacuated glass tube collectors are best because they are more efficient (which they are but only slightly in the case of heating domestic hot water). Others prefer the flat plates. The fact is that there are advantages and disadvantages to all collectors. Evacuated glass tubes are permeable to various gasses and over time they become less effective. Flat plates collectors may go green with age more than the tubes. Certainly the manufacturer’s guarantee period for flat plate collectors is at least twice that of the evacuated tube collectors.
 
How much do systems cost?
A typical system which has two collectors and a new twin-coil cylinder and is suitable for the average house should cost in the region of £3,000 - £4,000 depending on the access requirements to the roof, and how long the job actually takes. A good installation should take between 2 and 3 days, otherwise the quality of work may be inadequate.
 
Can it also heat my house?
Solar collectors capture energy from the sun. There is much less sun power in winter when you want energy input into the central heating. However, in spring and autumn and on bright days in winter solar energy can make an appreciable contribution to the heating of a house, particularly if that house is well insulated and if the house is fitted with under floor heating. If you are considering a new house, or a reasonable extension to your existing house, plan into the design a THERMAL STORE. A thermal store can take in heat energy from solar collectors, a wood burning stove or wood pellet boiler, or ground source heat pump, and distribute it around the heating system. The lower temperature required for under floor heating makes this a very attractive combination with solar energy.
 
A final word
Beware of being “sold to” by unscrupulous companies,- there are a lot out there. Shop locally,- always get a quote and take time to think it over. You are making a big commitment; NEVER sign anything when someone visits you.

By Andrew Baldrey of Sarum Solar, in connection with DCRS

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