|| I worry a
lot about dirty glass. Most of the literature claims that normal
rainfall is adequate to keep the panels clean.
We don't get much rain here, but there is a lot of dust, and
many birds. I've had a problem with birds roosting on the upper edge of
the panels, and their flyovers cause some trouble. I visit the array
several times weekly and remove two or three bird blemishes.
Finally I performed an experiment to quantify the effect of dust. It was a little subjective but meaningful results were
The bird roosting problem was solved by stretching a slack wire a few
inches north of the upper panel edges. But the flyover blemishes
and dust accumulation will always be maintenance issues.
I'm troubled by the potential for power loss caused by surface
contaminants. Each sub array in the system consists of 24 panels (864 individual cells)
are series-wired. If a small area of one cell is shaded by an
opaque bird dropping the entire sub array photocurrent is
correspondingly reduced. If the shadowed area is large the cell
becomes a load instead of a source, and suffers a polarity reversal. This condition usually causes no permanent damage, but
the power delivered by the entire string suffers many times the loss of
the impaired cell's contribution.
I fretted about this, and finally found some documentation
to support my concerns. This site contains lots of valuable
information, and demonstrates how an impairment of 75% of a single
cell's surface can reduce the entire module power by 70%. So the
moral of this story is "keep the birds away".