What Affects Solar Output

The biggest factors affecting solar output are roof orientation, roof pitch, shading, and local irradiance. Getting these right at the survey stage makes a significant difference to long-term generation.

Roof orientation

South-facing is optimal in the UK and produces roughly 100% of a system's potential output. East and west-facing roofs generate around 80–85%. North-facing is not viable for solar — we will tell you this upfront rather than fit a system that underperforms.

Roof pitch

The ideal pitch for the UK is 30–35 degrees. Flat roofs can be fitted with angled mounting frames. Very steep pitches above 50 degrees reduce generation in summer but improve winter performance slightly.

Shading

Shading is the most damaging factor, particularly with string inverters where one shaded panel can drag down the output of the entire string. On shaded roofs, we recommend microinverters or DC optimisers, which let each panel operate independently.

Temperature

Panels are less efficient at high temperatures than manufacturers' standard test conditions suggest. A bright, cool spring day often outperforms a hot summer day. This is measured by the temperature coefficient — a good panel loses around 0.3–0.4% efficiency per degree Celsius above 25°C.

Panel degradation

New panels degrade 1–3% in the first year (initial LID), then around 0.5% per year after that. A quality panel should still produce at least 80% of its rated output after 25 years. This gradual decline is factored into all our payback projections.