A single shaded panel doesn't just lose its own output — on many systems it drags down the entire string. This is why shading is the most underestimated factor in sizing a rooftop system.
Common sources of rooftop shading
- Water tanks and chimneys — small objects that sweep a wide shadow arc as the sun moves.
- Neighbouring buildings — a wall's shadow can fall differently in winter versus summer.
- Trees — the biggest variable, since they grow and change shape over the system's 25-year life.
- Parapet walls and railings — often ignored, but they block low morning and evening sun.
Even 10–15% shading on one panel in a string can cut that string's output by far more, because of how panels and inverters are wired together. This is also why two rooftops with the same area can produce very different numbers of usable units.
How EPCs catch it before installation
A proper site survey plots the sun's path across the roof through the year and flags shadows hour by hour — not just a single snapshot. Solar 3D Design runs this shadow analysis automatically on the actual rooftop, so the customer's proposal and subsidy numbers hold up after installation, not just on paper.