Minor amount of shading has a large impact on solar production.

[J.P.M.]

Post #8 the panels are 100% clear all day however it was a partly sunny day. No sun forecast now till next Saturday 1-27.

Thank you. Busy next 1-2 days. Will review/comment ASAP.

Regards,

[Mike 134]

That's what I what I did and that's where the idea of selective (differential) snow coverage from drifting came from.
When was the last snowfall before the photo was taken, how much was it and was it accompanied with any wind that would produce drifting ?
Photo and screenshot in post 1 were taken on 1-19 2 snowstorms 6" on 1-10 and a 2nd on 1-12 another 8" of heavy wet snow some drifting but the 8/12 pitch of the roof helps getting wet snow to slide off. Zero for high temperatures the following days. Later in the week warmed up enough to mechanically remove remaining snow except for what you see in the post #1. That was there at sunrise on 1-19 and remained all day. Saturday allowed me to remove the rest of the snow with some warmer temps and sunshine.
Assuming the photo was taken around mid-day or so, if there is some additional (residual ?) snow on some panels in the morning from drifting (that had mostly melted before the photo was taken) and if the array is equally irradiated throughout the day, the additional snow on the drifted over panels will stay longer than on other panels and so reduce the day long totals for the drift affected panels.

I'd be interested to see any recent day-long totals from the array that starts and closes the day without snow on it.

Post #8 the panels are 100% clear all day however it was a partly sunny day. No sun forecast now till next Saturday 1-27.

[J.P.M.]

If you blew up the photo, you'd see some drifting just at the top of 5, some snow at the bottom of 6, and some drifting upper rh corner of 9. Today (Sunday) they are all 100% clean. supposed to be mostly sunny .

That's what I what I did and that's where the idea of selective (differential) snow coverage from drifting came from.
When was the last snowfall before the photo was taken, how much was it and was it accompanied with any wind that would produce drifting ?

Assuming the photo was taken around mid-day or so, if there is some additional (residual ?) snow on some panels in the morning from drifting (that had mostly melted before the photo was taken) and if the array is equally irradiated throughout the day, the additional snow on the drifted over panels will stay longer than on other panels and so reduce the day long totals for the drift affected panels.

I'd be interested to see any recent day-long totals from the array that starts and closes the day without snow on it.

[Mike 134]

What does the output for those panels (#'s 5,6 & 9) look like on a clear day this time of year compared to the other panels ?

To give an example to your question. All panels free of snow. Had a partly cloudy day today and as you can see the top row of panels are almost all the same. The left side of the bottom row falls off because of some late afternoon tree shading and is more noticeable on partly cloudy days this time of the year.
Screenshot 2024-01-21 at 6.47.48 PM.jpegScreenshot 2024-01-21 at 6.46.57 PM.jpeg

[Rade]

It most certainly does! We finally have had some comprehensive snow fall this past week that covered our panels. The panels on greater slant on the side of the house cleared once the sun warmed them up (note: Don't stand under the panels...). I had to use a snow rake (rubber squeegee on a long pole) to pull the snow pack down. We went from under 2kW of power up to 7.25kW of power during peak daylight.

[Mike 134]

Thank you.

I'm not surprised at the output decrease. anecdotally, my array's output with 2 strings of 8 panels each on a string inverter has each string's output die whenever any late afternoon shade gets to the.

Also, if that photo was taken midday, or even earlier (I suppose/maybe), there may have been (some) snow cover on those particular panels (slightly drifted up maybe ?) earlier in the day that could have melted. I saw a lot of that irregular drifting pattern when I lived in Buffalo.

If you blew up the photo, you'd see some drifting just at the top of 5, some snow at the bottom of 6, and some drifting upper rh corner of 9. Today (Sunday) they are all 100% clean. supposed to be mostly sunny .

[J.P.M.]

Should be within 5% of the rest of the row.

Thank you.

I'm not surprised at the output decrease. anecdotally, my array's output with 2 strings of 8 panels each on a string inverter has each string's output die whenever any late afternoon shade gets to the.

Also, if that photo was taken midday, or even earlier (I suppose/maybe), there may have been (some) snow cover on those particular panels (slightly drifted up maybe ?) earlier in the day that could have melted. I saw a lot of that irregular drifting pattern when I lived in Buffalo.

[Mike 134]

What does the output for those panels (#'s 5,6 & 9) look like on a clear day this time of year compared to the other panels ?

Should be within 5% of the rest of the row.

[J.P.M.]

What does the output for those panels (#'s 5,6 & 9) look like on a clear day this time of year compared to the other panels ?

[scrambler]

I would have thought modern panels should be able to do better than that....

What panel brand and model?
Any optimizers or micro inverters?

[Mike 134]

Checkout the 2 pictures posted with this thread. Very minor amounts of snow left on the top row of the 5th,6th, and 9th panels yet decreased production by 40% ish. Just found it interesting, warmer weather coming soon.