Why Solar Panel Position Matters

In the UK, a south-facing roof produces the most electricity over a year, but east and west-facing roofs work well too, and the pitch of most London roofs is close enough to ideal that it rarely decides whether solar is worth it. Shading usually matters more than either. Here is how direction, angle and shade affect output.

Direction

South-facing panels see the sun for the most hours, so they produce the most over a year.

East and west-facing panels produce less in total, but they spread generation more evenly through the day: east in the morning, west into the late afternoon and evening. For a household that uses most of its electricity in the evening, a west-facing array can match its usage well. An east-west split across both sides of a roof is common and works well.

North-facing roofs produce noticeably less. On a shallow pitch they can still be worthwhile, but they need modelling on a case-by-case basis.

Angle

The sun is high in summer and low in winter. For a fixed array in London, the tilt that maximises year-round output is roughly 35 to 45 degrees, and output falls away only gently either side of it. In practice, most pitched roofs are close enough that panels are fitted flush to the existing slope, which also looks better and keeps wind loading down.

On flat roofs, panels are mounted on frames at a lower angle. A low tilt gives up a little output per panel, but it lets more panels fit without shading each other and keeps the system less exposed to wind. Rules on how far panels may stand above a flat roof are covered in our guide to planning permission for solar in London.

Shading

Shade from chimneys, dormers, trees and neighbouring buildings can reduce output by more than the shaded area suggests. Panels are wired together in strings, and on a traditional string system a shaded panel can hold back the others in its string.

There are ways to manage it: careful string design, panels with half-cut cells that cope better with partial shade, and optimisers or microinverters on the affected panels. The right answer depends on how much shade there is and when it falls, which is why it is assessed at the survey.

What this means for your roof

Very few roofs are perfect, and that is fine. A proper design takes your roof's direction, pitch and shading into account and gives you a generation estimate based on them. Our guide is your roof suitable for solar panels covers the other factors, including roof condition and structure.

If you want to know what your roof could produce, request a solar and battery quotation and we will survey and model it for you.