A solar collector is only of use if it is unshaded for most of the mid day passage of the sun, even in the winter when the sun is very low. This needs carefully checking. The Green Book Live web site gives lists of microgeneration installers and it is worth having a survey done before going ahead.
Installing solar collectors should provide an annual average of about 40% – 50%, maybe even 60%-70% of the domestic hot water for a house based on each person requiring 45 litres per day and allowing about 1 m² of solar collector per person. The government Clean Energy Cashback scheme covers solar hot water. See the Renewable Energy Association for their membership list of suppliers and installers.
Types of panel
There are two main types of solar collector for domestic hot water -
- the flat plate type which is a bit like a huge central heating radiator working in reverse. It has a glazed surface to trap the heat
- the evacuated tube type which is more sophisticated. It has long glass vacuum tubes, a bit like very long thermos flasks which heat an internal liquid which then transfers the heat to the circulating fluid
The evacuated tube types are considerably more efficient than the flat plate because they can even work on overcast days. They are also more compact. However they do cost quite a bit more and a ‘side by side’ research project published by the DTIwas the Department of Trade and Industry but is now the BIS (Department for Business Innovation and Skills) in 2001 compared 8 types of solar collectors of approximately the same cost. It showed that the output for the two types was roughly comparable (table 7.2 on page 36).
Angle of tilt
There is quite an issue around the optimum angle of tilt for collectors and this is to do with whether you have much choice in the matter. Planning consentthe legal basis for being allowed to do some form of development such as building a house. (not to be confused with Building RegulationsThese are the legal regulations which govern how a house is constructed. (not to be confused with Planning Permission which is about whether you are allowed to build the house at all or what it might look like) see Building Regulations) which is all about whether the building is properly constructed). see more on Planning Permissionthe legal basis for being allowed to do some form of development such as building a house. (not to be confused with Building Regulations which is all about whether the building is properly constructed). see more on Planning Permission may be a problem and it may be difficult to find wall or roof space which is near the correct angle. The DTI report mentioned above indicates that the collectors on test were fixed at an angle of 30º to the horizontal because “a tilt of 30º is typical of modern roofs”. This tends to give overheating in summer and not enough in autumn and spring. Especially if you go for a larger collector you may be simply wasting more of your investment in summer through overheat. A rough rule of thumb is that a collector should be at the same angle as the latitude so this suggests something between 50 and 57º, depending where you are in the UK. The REAthe Renewable Energy Association web site states the optimum for a south facing collector is 0.9 multiplied by the latitude + 29°. This gives something between 71 and 77º. Clearly a long way from 30º. The further you go north, and the larger the collector is the more important it becomes to get this calculation right. It is quite common to mount collectors on a steel frame which is then attached to a south facing wall in order to achieve the optimum angle.
If you have roofs facing east and west then it is possible to place a panel on each side to get early morning and late afternoon sun.
Although there are plenty of companies specialising in solar collector installation you may do better using a plumber who is registered with the REA and has experience in this sort of work (although not many do). This is because a plumber is not tied in with one particular set of component parts and may get better deals. Also, if a plumber is already doing work for you elsewhere on the house it may work out cheaper, especially if the solar collector is tied in with work on your heating system. Remember that on an existing house the installation of a solar panel will probably entail scaffolding to one side of the house (or using a cherry picker). This may well cost around £500 so if you have any other roofing work which needs doing it would make sense to include it at the same time.
If you live in a listed building it will need listed building consent and if you are in a conservation area you will need planning permission. Otherwise the planning process is moving towards favouring solar panels providing they fit in visually with the building. Local authorities vary slightly on their guidance and most have an advice page so check your own local council.
Depending on the extra weight on the roof due to the panel you may need to strengthen a section of the roof. Check with your local Building Inspectors department at the council.
Conventional ‘stored’ boiler configuration
There are also other configurations possible. For instance it is possible to arrange it so that if you have a surplus of hot water it can be utilised by the central heating system or stored in an accumulater for use later.
The Renewable Heat Premium Payment scheme is an interim scheme and is part of the Green Deal. It includes one-off payments towards solar thermal panels and is intended to fill the gap until the Renewable Heat Incentive (RHIRenewable Heat Incentive) becomes available