Los Angeles is one of the best solar markets in the United States — 284 average sunny days per year, high electricity rates that make every kilowatt-hour of solar output financially significant, and a growing residential and commercial installation base that now numbers in the hundreds of thousands of systems across Los Angeles County. It is also one of the worst markets in the United States for solar panel soiling. The city’s seven-plus-month dry season — from April through October — produces a continuous, unrinsed accumulation of mineral scale, smog particulate, coastal salt aerosol, and bird guano on every horizontal and south-facing solar panel surface in the city. Research from the National Renewable Energy Laboratory, the California Energy Commission, and independent inverter data studies documents output losses of 15 to 30 percent for Los Angeles solar panels operating through a full dry season without professional cleaning — with panels carrying bird guano deposits experiencing cell-level shading losses of 30 to 40 percent at the affected cells. This guide breaks down exactly where those numbers come from, what each contamination type does to the panel’s output, and what real inverter data shows before and after a professional clean.

01 How Each Contamination Type Affects Solar Panel Output — and By How Much

Not all soiling on Los Angeles solar panels produces the same output loss. The mechanism of loss differs by contamination type — and understanding the mechanism is what allows a property manager or homeowner to correctly interpret their inverter data and prioritise cleaning urgency. Here are the four primary contamination types found on Los Angeles solar panels, ranked by output impact severity.

02 Real Inverter Data — Before and After Professional Cleaning in Los Angeles

The output loss from soiling is not theoretical — it appears directly in inverter monitoring data as a measurable, progressive decline in daily kWh production that correlates with the dry season’s accumulation timeline. The following comparison table represents the output data pattern documented on Los Angeles residential solar installations serviced by Skyworks Unlimited — showing the measured daily kWh difference between the pre-clean soiled state and the post-clean restored condition at different system sizes and contamination scenarios.

The guano row above illustrates the most important data point in the table: a single bird guano deposit on one cell of an 8 kW system reduced daily peak output from 33 kWh to 19 kWh — a 42 percent loss — because the bypass diode in the affected cell string forced the entire string into bypass mode to protect the shaded cell from thermal damage. Removing that single deposit restored full string output in the next morning’s inverter log. This is the bypass diode hotspot effect, and it explains why even partial panel cleaning that removes guano deposits produces output gains disproportionate to the area of panel surface cleaned.

03 Why Los Angeles Is the Highest-Impact Solar Soiling Market in the US