Abnormal spots on PV modules near sewage outlets of industrial/ commercial rooftops are a common headache—they’re not just unsightly, but resist rainwashing and harm module performance. What’s the real cause?
These spots aren’t simple dust buildup, but a chain reaction triggered by pollutant deposition. They’re most prevalent on industrial/ commercial rooftops with sewage outlets or towers, where factory exhaust contains metal particles, metal compounds, or acidic/alkaline chemical impurities. These substances have strong heat absorption properties, easily adhering to PV modules and forming spots through repeated circulation.
Impact of Abnormal Spots
Unlike the "dot-like light spots" produced by a single bird dropping or leaf, the light spots formed by pollutants are large, and the covered solar cells are turning into a "planar light spot".
Normally, hot spots from dust or bird droppings can be washed away by rain, but pollutant-induced spots cause permanent module damage. The blocked cells cannot generate electricity properly and instead become "obstacles" in the circuit, consuming the energy of other normal cells and converting it into a large amount of heat, leading to localized overheating or even burnout.
Sustained high temperatures accelerate the aging and yellowing of internal EVA film. Long-term hot spot effects can also cause glass or backsheet delamination, further reducing power generation efficiency and posing safety risks.
Treatment and Prevention Recommendations
(I) Immediate Cleaning Methods
For patches that have not yet caused permanent damage, surface deposits of metal impurities, dust, and other pollutants can be removed manually with a scraper to alleviate localized shading. However, care must be taken to avoid scratching the component glass or coating during operation.
(II) Long-Term Prevention Measures
1.Source Control of Pollution: Increase the height of the exhaust tower or outlet, and install dust filters on the exhaust tower or outlet to filter particulate matter, metal dust, metal compounds, and other pollutants in the exhaust gas, reducing the total amount of pollutants emitted into the air at the source.
2.Optimize Component Installation Layout: During installation, avoid installing photovoltaic components near exhaust outlets or exhaust towers to reduce the probability of pollutants directly depositing on the component surface.
3.Increase Cleaning Frequency: For components that cannot avoid exhaust areas, increase the cleaning frequency, regularly removing surface metal dust, acid and alkali residues, and oil stains to keep the component surface clean and prevent long-term accumulation of pollutants that could cause hot spot effects.
Conclusion
Abnormal spots on PV modules for industrial/commercial rooftop PV are never just "cosmetic issues"—they are core hazards affecting efficiency, lifespan, and returns, essentially caused by the combination of pollutant deposition and hot spot effect. The key to prevention and control lies in "prevention over remediation": installing dust filters at pollution sources, avoiding installing modules in contaminated areas, and regular cleaning are more efficient and cost-effective than addressing spots after they form. Doing these well not only keeps modules free from spot troubles but also ensures stable power generation of the PV system, maximizing the energy value of the rooftop. Incorporate spot prevention into O&M, and let every module continuously generate returns.