Does shading kill my solar panel output?

Shade is the #1 enemy of solar output — and almost always underestimated. A branch, a chimney or a neighbouring building blocking 10% of a panel can kill 60% of a whole string's production. Here's why.

Why a small shadow does so much damage

In a series string, current is set by the weakest panel. If shading drops one panel to 30% output, the other 11 are forced to produce at 30% too. Like a traffic jam: the slowest car sets everyone's speed.

Real numbers

• Spot shade on 1 cell of a panel: -8 to -15% on that panel
• Constant partial shade on 1 panel in a string: -20 to -40% on the whole string
• Chimney shade across 2-3 panels: -50% across the whole array during shade

How to mitigate shading

• Microinverters: each panel runs independently, shade doesn't bleed
• Power optimizers (SolarEdge, Tigo): DC-DC per panel avoids the string effect
• Bypass diodes: built into every modern panel, cut losses by 20-30%
• Smart layout: place panels outside the shadow cone between 10am and 3pm
• Annual tree pruning

Shading study: demand it before buying

Serious installers use HelioScope, PVsyst or Aurora to simulate shading hour by hour for a year. Demand that report. If they refuse or do it 'by eye', change installers.

To understand wiring see series vs parallel panels and compare architectures in microinverters vs string inverter.