Soiling

Definition

Soiling is a thin or thick layer that builds up on the panel glass over time and, after irradiance, is one of the most important factors affecting a plant's performance. The layer can spread evenly across the panel or collect along the lower edge where rainwater runs off.

Signs in the imagery

In the RGB image it shows as a dulled panel surface, a change in tone, or a dark band along the lower edge. Even soiling leaves no clear trace in the thermal image. Heavy edge soiling, however, can heat the bottom row of cells and become visible in the thermal image.

Possible causes

• Dust and sand, especially in dry periods
• Nearby farmland, dirt roads, quarries or industrial sites
• Pollen and leaves
• Low tilt and little rain, so the dirt does not wash off

Effect on production and safety

As less light reaches the cells, production falls gradually, and the loss accumulates for as long as the soiling lasts. Uneven soiling creates mismatch between cells and can switch the bypass diodes in. Heavy edge soiling can lead to permanent hot cells over time.

Recommended action

Plan cleaning according to the distribution of soiling across the plant, giving priority to the most affected rows over the whole site. Follow the cleaning method and water quality recommended by the panel manufacturer. At the flight after cleaning, compare the difference using the same panel records.