Solar PV

Irradiation levels and generation predictions

The amount of radiation available is predictable: location, orientation and pitch of modules dictates the output. Panels facing south will generate the most electricity. Modules generate electricity from light, even through cloud cover. UK irradiation is similar to that of northern Germany, where PV systems are deployed in much larger quantities

Irradiation levels and generation predictions


Central to the planning of a solar PV system is the ability to accurately predict how much electricity can be generated over the long term investment period. While the UK’s unreliable weather may suggest that prediction is likely to be difficult, when averaged over a year the figures are very reliable.

The location, orientation and pitch of PV system modules influence its achievable yield. Taking these factors into account at the design stage allows for accurate performance and financial modelling.


The closer the orientation of the PV modules is to south, the higher the total generation as the modules will be exposed to stronger radiation through the entire arc of the sun, whether or not there is cloud cover. Daily irradiation levels will differ according to location, while the optimum angle for the modules varies the further away from the equator they are located.

An easterly-orientated array will generate most of its electricity in the morning, while a westerly-facing array will generate more in the afternoon. This can be an important distinction, depending on the site’s electricity demand through the day.

The pitch of the roof or mounting system also plays a part – if there is a steep pitch this will compromise electricity generation in summer, when the sun is high in the sky, but will improve its performance with a low winter sun. A shallow pitch will perform better in summer but not as well in the winter as the sun’s light will be hitting the panels at a shallow angle.