Solar Shading

Why shading matters more for solar than most people expect

A single shaded panel in a series-wired string doesn’t just reduce its own output - it constrains the entire string. Because the panels are wired in series, the current through all of them is limited by the weakest link. A panel producing 30% of its rated output due to shade forces the other panels in the string to throttle down.

This is the most common and least understood source of underperformance in residential solar systems. A chimney casting a shadow on one panel for two hours each afternoon can reduce total system output by 15–25% during those hours - not just the 5% you might expect from one panel out of twenty.

Types of shading and their severity

Hard shading (opaque objects - chimney, satellite dish, vent pipe): Full shadow on a panel. Most severe. Affects a small area but the impact is disproportionate.

Soft shading (tree canopy, distant hills): Diffuse rather than full shadow. Still reduces output but less severely.

Self-shading (adjacent panel rows in a large array): When rows are spaced too close together, the front row casts a shadow on the row behind at low sun angles (early morning, late afternoon, winter). A good installer calculates the required row spacing for the roof pitch and latitude.

Soiling (dust, bird droppings, pollen): Creates partial shading effects. In dusty areas of Australia - outback, agricultural regions - soiling can reduce output by 5–10% if panels aren’t cleaned periodically.

Design solutions

A competent CEC-accredited installer performs a shading analysis before system design - ideally using a solar pathfinder, shade tool, or 3D modelling software to assess shade at different times of day across all seasons.

For roofs with unavoidable shading, the options are:

1. Avoid placing panels in shaded areas - only install where clear for most of the day
2. Install panel-level optimisers (SolarEdge) - each panel works independently, so shade affects only that panel
3. Use microinverters (Enphase) - same independent operation, plus per-panel monitoring

If a quote doesn’t mention a shading assessment and your roof has any obstructions, ask for one specifically. Under-delivering systems are a common complaint in the solar industry, and shading is frequently the cause.