All of the following are examples of soiling except which?

• A. shade
• B. dust
• C. bird droppings
• D. dirt

Answer: (A)

Soiling means deposits on a surface that block or scatter sunlight and reduce performance. Dust, dirt, and bird droppings are classic examples because they accumulate on a surface and lower light reaching the cells. Shade isn’t a cleaning or deposition issue; it’s caused by something blocking the light from reaching the surface, like a nearby object or a cloud, so it lowers irradiance without being a surface contaminant. Therefore shade is the exception, while dust, dirt, and bird droppings are all examples of soiling.