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How much does shading reduce solar panel output?

Short answer

MCS installers use a sun-path chart with 84 segments. Each segment blocked by trees or buildings on your southern horizon knocks 1% off the estimate. Eleven segments gives a 0.89 shade factor. Close objects such as chimneys and vents count far more: the same object within 10 m can cut the factor to about 0.60.

Last checked 24 September 2026 · 1 source

In more detail

  • SF = 1 − 0.01 × segments (MCS 032:2025 Appendix A, formerly MGD 005).
  • Near shade (≤10 m): draw a circle of radius = object height; count all segments inside.
  • The installer must give you the sun-path diagram if SF < 1; MCS says its method is within 10% for most systems.
  • Optimisers/microinverters or separate MPPTs can reduce shading losses; MCS's simple method doesn't credit them. Separate SF per MPPT allowed.

The facts, dated

  1. 01
    MCS sun-path chart segments / value each — 84 / 0.01

    standard · UK · checked 24 September 2026 · MCS

  2. 02
    MCS worked example far shade: 11 segments — 0.89 SF

    standard · UK · checked 24 September 2026 · MCS

  3. 03
    MCS worked example near shade (<10 m): 40 segments — 0.60 SF

    standard · UK · checked 24 September 2026 · MCS

What we saw in the field

No field evidence in the brief quantifies shading. Customer 2's garage array on a separate string, and the MPPT-per-roof designs described, are consistent with MCS allowing a separate SF per MPPT.

Sources

Last checked: 24 September 2026