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How much difference in output do you expect to see in each individual panel in your array? I know there can be variation due to soiling, shading, temperature, manufacturing tolerance, etc. The majority of my panels are within 1-2 W of output from each other when none are shaded. However, I have two that - at the peak of the day - can be typically 5 W lower output than the median, and one that can be 9W higher at the same time. These are 250W panels, so basically at the very peak output range from 205W to 220W simultaneously. At some other times in the day though, they can all be within a watt or two of each other, particularly at dusk and dawn when they all are getting only indirect ambient light exposure.
Interestingly, the three outlier panels are all in one horizontal row in landscape. The big difference is where they are in in proximity to the roof planes. All 16 panels are south-facing, 19 deg slope, and mounted about 5 inches off the asphalt roof. The two low performers are just below a Dutch gable, meaning there is a vertical gable wall about a foot past and above them. I know the framing of the Dutch gable also extends vertically into the attic below, potentially blocking hot attic air from rising to the higher parts of the attic. The bedrooms below get the most sun and are the hottest in the summer typically. The high performer panel is just adjacent, but to the side of the Dutch gable - meaning the roof plane turns 90 deg at a roof hip just beyond it, so it has much less warm roof surrounding it.
The other difference is morning shade, the high performance panel takes an hour longer to come out from tree shading than the lowest performance, same for the surrounding roof area heating up.
I've blown off any leaves, and also hosed down mild dust buildup on the panels. I haven't gone up to scrub them down, but they don't look to have much soiling. (In fact as an experiment I did squeegee with distilled water a couple of other ones down that I could reach with a small ladder, there was no improvement in output compared to ones next to them that I merely hosed down.)
Interestingly, the three outlier panels are all in one horizontal row in landscape. The big difference is where they are in in proximity to the roof planes. All 16 panels are south-facing, 19 deg slope, and mounted about 5 inches off the asphalt roof. The two low performers are just below a Dutch gable, meaning there is a vertical gable wall about a foot past and above them. I know the framing of the Dutch gable also extends vertically into the attic below, potentially blocking hot attic air from rising to the higher parts of the attic. The bedrooms below get the most sun and are the hottest in the summer typically. The high performer panel is just adjacent, but to the side of the Dutch gable - meaning the roof plane turns 90 deg at a roof hip just beyond it, so it has much less warm roof surrounding it.
The other difference is morning shade, the high performance panel takes an hour longer to come out from tree shading than the lowest performance, same for the surrounding roof area heating up.
I've blown off any leaves, and also hosed down mild dust buildup on the panels. I haven't gone up to scrub them down, but they don't look to have much soiling. (In fact as an experiment I did squeegee with distilled water a couple of other ones down that I could reach with a small ladder, there was no improvement in output compared to ones next to them that I merely hosed down.)
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