A small shadow across one corner of a panel can cut output far more than its size suggests. Understanding how strings and bypass diodes work explains why — and what can be done about it.
Why small shade = big loss
Panels in a string are wired in series, so current flows through the weakest link. A shaded cell restricts current for the whole string — and since the inverter tracks the whole array's optimum point, output can fall much further than the shaded area alone.
Bypass diodes: the safety valve
Every panel has bypass diodes that route current around a heavily shaded section. They prevent hot-spot damage, but the shaded panel still contributes little. If a diode has failed, the panel behaves as fully shaded even in full sun — a common, invisible loss.
Common shading sources
- Water tanks, pipes and parapet walls
- Trees and neighbouring buildings (worse in winter when shadows are long)
- Other rows of panels on ground-mount systems
- TV antennas, cables and even bird droppings
What to do about it
- Map shadows across the day, especially in the morning and afternoon
- Trim branches before they grow into the array's path
- Rearrange strings so shaded panels sit on separate MPPTs
- Consider panel-level optimisers for unavoidable partial shade
- Fix failed bypass diodes — detected during string-wise testing
Frequently asked questions
Will shading of one panel stop the whole system?
Not usually — modern inverters and bypass diodes keep the system running at reduced output. But one badly shaded or faulty panel can drag a whole string's production down significantly.
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