Solar Panel Cleaning After the Dry Season

The problem

A roof-mounted residential array that had gone through an entire Bay Area dry season without meaningful rain. Every module carried a uniform film of dust and pollen, with scattered bird droppings and leaf debris collected along the lower edge of the array and in the roof valley beside it. Uniform film is easy to miss precisely because it is even — there is no obvious dirty patch to catch the eye from the ground.

How we approached it

Panel glass scratches, and scratches are permanent, so nothing abrasive goes near it. Soft brushes and filtered water, module by module. The filtered water matters: ordinary tap water dries and leaves mineral spotting on the glass, which partly defeats the purpose. Debris was cleared from the array edge and the adjacent roof valley as well, since that is where the next round of buildup starts.

The result

Clean glass across the array — visible in the after photo as sharp reflections of sky and trees where the before shows a flat, dusty surface. End of the dry season is the right time for this, before winter rain does a partial and uneven job of it.