Orientation and tilt

Your roof should ideally face due south at a pitched angle of around 30° from the horizontal to give the best overall annual performance. Installations at any pitch and facing anywhere to the south of due east and due west are feasible, although output and income will be reduced. Installation is not recommended on roofs facing north.

This table shows the percentage of the ideal annual output you will get for a system with a different orientation and tilt.

Seasonal performance

The chart below shows a typical seasonal spread of energy generation for a system of 2.9kWp facing south. The winter months generate significantly less electricity compared to the summer months.

Site location

The amount of electricity generated by a solar PV system can also vary depending on where you live. Northern areas receive slightly less energy from the sun over the year. For example, a 1kWp system will generate less electricity in Northern Scotland than it would in Cornwall. However, solar electricity is still worthwhile – the differences aren’t substantial.

Shape of roof area

Solar PV arrays are made up of modules of about 1.5 square metres which allows most available roof shapes to be accommodated. Typical UK installations are around 15 to 25 square metres. For example, a 2.9kWp system could comprise 15 panels taking up an area of 20 square metres and will generate roughly 2,450kWh per annum.

Shading

All the modules are connected, so any shading on a single module will affect the performance of the whole array. A system can tolerate some shading early or late in the day without much reduction of overall output but it should not be shaded between 10am and 4pm. Nearby trees, chimneys, TV aerials and vent pipes are all common causes of shading and should be accounted for before any installation.

Solar electricity doesn’t necessarily require direct sunlight and can still generate electricity on cloudy days. You could get as much as a third of the energy on a cloudy day as you would get on a sunny day at the same time of year.

Structure and Building Regulations

When installing a solar hot water system building regulations will apply. This is in part to ensure that your property can support additional load, both internally and on the roof.
Before proceeding with the installation, you must check with your Local Authority Building Control officer that all proposed work is compliant with current building regulations.
Please note that there may be additional costs associated with building control notification.