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Experiments in Dust Failures


There's not much to maintain in a PV system. Keeping the PV surfaces clean and and replacing occasional failed components is about the extent of it.


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".
Equipment Failures 

There were several failures with the Xantrex inverters, but only one since the upgrade to Sunny Boys. The link on the left leads to the failure log pages.


Declination Adjustments  One routine maintenance task is the changing of elevation angle. I perform this about a month after the autumnal equinox and about a month before the vernal equinox. It takes about an hour.