The Optimum Type Of Home For Solar Panels

Fri, 14 Oct 2011 20:45:00 GMT

Not every house has a suitable roof for solar panels, there are several factors that make a home more suitable for a solar photovoltaic system. The main factor is roof direction but other factors can also be important such as roof pitch and shading. We will take a look at the factors that can determine how suitable solar is for your home.

The first and undoubtedly most important factor is roof direction. The orientation of your home can mean the difference between a suitable home and one that would not work very well with solar PV. Many of the same factors are also important for solar thermal panels, these are the panels that are used to heat your water rather then generate electricity. Solar thermal panels are however less prone to temporary shading issues that can more proportionately affect solar PV.

Roof angle and orientation

It is important to point out that whether you have free solar panels or a paid system the angle and orientation of your roof is important. Ideally your roof should face due south but solar panels can work almost as well if they face south west or south east. The further off due south you go the less optimal the conditions would be. This means that if you have a roof that faces east to west rather than north to south it will be far less efficient to install solar panels on. To put this into figures your panels would produce about 20% less electricity compare to ones that face south.

The roof angle or pitch of your roof can also make a difference. In the UK most roofs are at an angle that is suitable for solar, the range for an optimally angled panels are between 30 and 40 degrees. There is a slight variation depending on where you live in the UK, the further north you go the higher the angle should be so in the far north of Scotland a 40 degree slope would be more optimal. In the far south such as the south cost of England a shallower angle would work better, closer to 30 degrees.

With the roof direction and angle you home does not have to have the most optimal configuration for you to benefit from solar. Solar panels will not suddenly stop working because the angle is not perfect or your roof does not face precisely south. As you veer further from the optimal they work less efficiently. For example a roof that is at 20 degrees rather than 30 or 40 will only be 2% less efficient. This means that you home does not have to meet the criteria exactly but it more of a guideline.

Solar panel and shading

Ideally you want to have your roof free of any type of shading or shadows. Although solar panels work in diffuse light a shadow cast on one or more of the panels can greatly reduce the systems effectiveness. Shadows that only appear for a short period are not going to have any significant overall effect; it is the shadowing that occurs for long periods which causes the problems.

If the area of the roof you are planning on having panels installed on has any shading during the day then this may be a potential problem. This could be from chimney stacks, dormers, trees or tall buildings in the locality. If solar panel shading occurs for long periods during the day your systems power output can be significantly reduced. Solar panel shading can be a greater problem during the winter as the sun appears lower on the horizon for longer periods of the day.

Most shading will be obvious such as a tall tree in your garden or neighbours garden casting a shadow on your roof. If you do have any serious type of shade issues it is likely that you will not be able to get free solar panels. If you are considering buying solar panels then the installer should be able to factor in the impact of any shading into their SAP estimates for the systems performance. It means that you will have a better idea if solar really is a good investment for your property.

Considering your suitable roof size for solar

Solar panels are quite large, they can measure up to 2 metres long and 1 metre wide and weigh up to 25 kilos each. This means that you will benefit the most the larger your roof is. There are several reason for this, firstly there are certain fixed costs in a solar system such as the inverter which can account for about £1,000 of the total cost of a solar installation. A single panel can cost around £500 so where a single panel system may cost £1,500 you could double your systems output by adding an extra £500 panel with only a 25% increase in costs. Essentially it means the larger the system the more cost effective it will be.

To get a better idea of how many panels and therefore the size of the system you can fit on your roof take a look at our page on how much roof space is needed for solar panels. The largest sized system that most homeowners install is a 4kWh system which can consist of around 22 panels that would cover an area of over 28 square metres, that is over 300 square feet in old money. The smallest free system is around 10 panels or 1.8kWh which would cover about 13 square metres or 140 square foot of roof space.

With the feed in tariff system which are the government's clean energy cash back grants you get paid the highest rate for a system of up to 4kWh. This means that to get the optimum return from your investment in solar if you are buying solar PV system you should make use of the maximum area of space on your roof up to 300 or so square feet.

So what is the optimum home roof?

Free solar panels

Providers of free solar panel systems are ideally looking for large roofs, this generally means detached or large semi-detached properties. Some installers will install on smaller roofs but given the choice they would go for the large roof. The house has to have a roof aspect that faces between south east through to south west, ideally as close to south facing as possible. There should be no shading at all or only very minor shading.

If you are buying solar panels

Ideally you would want to have the same type of house that free installers are looking for. With paid solar however as you do not have the overheads of the free installation companies you can install a system on a roof that is not optimal and still make a positive financial return. In fact you could in theory install panels on an un-shaded east or west facing wall and still earn enough back through the FIT scheme to cover the cost of the installation at the current FIT rates. This theory is based on achieving a 56% to 58% efficiency but in reality it would be a sensible option for a residential property although there are many commercial buildings with panels attached to external walls rather than roofs.

A final note about flat roofs

A question that is often asked is about solar panels on flat roofs. According to the data on PV performance at different orientations and angles you could achieve 90% efficiency by placing panels horizontally on a flat roof. However it is more economical to place them on an optimally angled frame to ensure the panels are in the optimal position. This is done on commercial flat roof installations. For a large enough and shade free residential flat roof the same system can be used. It is highly unlikely that a free solar company would cater for homes with a flat roof.