Bird Droppings on Solar Panels: How Much Production Loss?
Bird droppings cause more solar production loss than general dust, sometimes by a factor of 10. Here's the data and what to do about it.
Most homeowners think bird droppings are mostly an aesthetic problem. They're not. Droppings cause concentrated 'hard shading' on a single cell, which can disable an entire panel, and sometimes an entire string, out of proportion to how much surface they cover.
Hard shade vs. soft shade
Dirt and debris can block sunlight, but the effect varies with the amount of buildup, panel tilt, rainfall, shading, and equipment condition. We don't have a verified typical loss figure for San Diego homes. Compare monitoring data under similar weather conditions before and after cleaning rather than expecting a fixed percentage gain.
Why this is worse than it sounds
Dirt and debris can block sunlight, but the effect varies with the amount of buildup, panel tilt, rainfall, shading, and equipment condition. We don't have a verified typical loss figure for San Diego homes. Compare monitoring data under similar weather conditions before and after cleaning rather than expecting a fixed percentage gain.
What to do about it
Schedule cleaning more frequently if you have heavy bird activity. Don't try to clean droppings yourself with a garden hose, dried droppings need to be softened with deionized water and lifted with a soft brush, not blasted off. Aggressive hose pressure can micro-scratch the anti-reflective coating where the dropping was.