Shading is one of the most misunderstood parts of solar design. Buyers often assume the effect is proportional — that 10% shade means 10% output loss. In reality, a small amount of shade on the wrong panel can cut output by far more than that. Here's why, and what to do about it.
The basic physics
Solar panels are made of individual cells wired together in series, like Christmas lights. In the simplest configuration, if one cell is shaded, the current flowing through that cell drops — and because they're in series, current through the whole string drops with it.
Modern panels include bypass diodes (typically 3 per panel) that let current route around shaded sections. This limits the damage but doesn't eliminate it. A partial shade can still knock a third of a panel's output to zero.
Then multiply by how panels are wired in strings: if one panel in a string of 10 is partially shaded, the shading can affect the whole string's output, depending on the inverter architecture.
The three types of shading
1. Constant shading
Trees, buildings, chimneys, or other structures that shade the same panels every day around the same hours. Most predictable, most damaging if not designed around.
2. Seasonal shading
Shade that appears only in winter (low sun angle) or only in summer (different shadow angles). Often missed in quick site visits done in one season.
3. Intermittent shading
Moving shadows — passing clouds, flagpoles, distant buildings. Less damaging because it's not consistent but still reduces annual yield.
Design choices that minimise shading impact
Don't install shaded panels at all
Sometimes the right answer is to leave part of the roof empty. An extra 2 panels that produce 30% output because of shade often aren't worth the capital cost. Good design says "no" to the obviously bad positions.
String layout matters
Panels that are likely to be shaded together should be on the same string. Mixing shaded and unshaded panels in one string is the worst of both worlds.
Microinverters or power optimizers
These are per-panel or per-pair devices that isolate shading effects to the shaded panel itself. A 10% shaded panel produces 10% less. Panels next to it are unaffected. Adds cost, but on a heavily shaded roof, it can add 15–25% to annual production.
Microinverters add roughly 10–20% to hardware cost. They're worth it when the roof has significant partial shading, complex geometry requiring panels at different orientations, or when per-panel monitoring would help identify issues. On a clean, unshaded roof, string inverters are still the better economic choice.
Clear the shading source if possible
Sometimes the best fix isn't a design workaround — it's trimming the tree. A good designer will tell you honestly when this applies and when it doesn't (protected trees, neighbour's property, etc.).
How to evaluate shading during design
A serious installer will do a shading analysis before designing the system. This typically involves:
- Site visit at roughly solar noon, ideally in multiple seasons or with digital tools that simulate seasonal sun paths.
- Sun-path diagrams showing shading patterns through the year at your location.
- Modelled annual production that accounts for the specific shading identified.
"We had a quick look at your roof and it should be fine" is not a shading analysis.
Small shading, big impact — the takeaway
If someone tells you a little shading doesn't matter, they're either being careless or selling. Modern systems can handle shading well, but only with design choices made specifically for that site. Ask to see the shading model before you commit.