| Experiments
in Dust |
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
obtained.
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)
that
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".
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