Soiling Losses
Soiling losses in solar PV systems are the reduction in energy production caused by the accumulation of dust, pollen, bird droppings, pollution particles, and other contaminants on the front surface of solar panels. These deposits block incoming light, reducing the irradiance that reaches the active solar cells and lowering power output.
Soiling is a natural consequence of outdoor panel exposure and is one of the key contributors to the performance ratio gap between theoretical and actual production.
Typical Soiling Loss Rates
Soiling losses vary dramatically by location:
- Rainy climates (Pacific Northwest, UK): 1–2%/year (rain provides frequent self-cleaning)
- Humid, moderate rainfall (Southeast US, Central Europe): 2–4%/year
- Semi-arid (California, Southwest US): 3–6%/year
- Arid desert (Middle East, North Africa, Atacama): 5–20%+ without cleaning
- Agricultural areas (pollen season): Up to 10–15% during peak pollen periods
Self-Cleaning and Maintenance
Rainfall: Rain is the most effective free cleaning agent for solar panels. Panels installed at tilt angles ≥5° allow rain to wash off most soiling. Flat panels accumulate more soiling because rain doesn't run off effectively.
Manual cleaning: For high-soiling sites, periodic panel cleaning improves performance. Cleaning frequency and method (dry brush, low-pressure water, deionized water) should be balanced against labor cost and water cost.
Anti-soiling coatings: Some panels now include hydrophobic anti-soiling coatings that repel dust and are activated by dew or light rain. These coatings can reduce soiling accumulation by 20–40%.
For SolarScope analysis in high-soiling environments, apply a soiling factor of 0.92–0.95 to production estimates.