North facing panels do better on cloudy days than south facing. Weird.

[millsan1]

I have some north facing panels in my config. Pretty shallow pitch on the roof, so almost flat, probably 15 degrees.

Anyway, they are there to capture summer sun, mid day. Obviously they don't produce much half of the year.

But an interesting thing I have seen is that on cloudy, overcast days, where there is no direct light, those panels out perform the south facing panels I have. Anyone smarter than me know why?

 

[BKY2003]

Does all the panels have diodes?

 

[millsan1]

All the same panels

 

[kommando]

Diffusion of the light, they will out perform more upright south facing panels as the clouds bounce the light around in all different directions.

 

[SeaGal]

For same type and number of panels, I would have expected them all to perform the same on a bright but cloudy day. That's what my 15 degree E-W panels do. I don't see why N facing would be better than the S facing - is this regularly observable or a one off?

All I can think is that the reflection from clouds from N is brighter than reflection from clouds from the south - maybe because the sun is hitting the water particles at a more direct angle?

I notice that that my West facing panels generate more power in the morning on a bright overcast day than on a clear day, but that is more logical.

 

[SeaGal]

they will out perform more upright south facing panels

I was assuming both N and S are angled at 15 degrees

 

[BKY2003]

Do you happen to have your MPPT as individual?

 

[SparkyJJO]

My guess is because of being flatter more than the direction.

 

[millsan1]

For same type and number of panels, I would have expected them all to perform the same on a bright but cloudy day. That's what my 15 degree E-W panels do. I don't see why N facing would be better than the S facing - is this regularly observable or a one off?

All I can think is that the reflection from clouds from N is brighter than reflection from clouds from the south - maybe because the sun is hitting the water particles at a more direct angle?

I notice that that my West facing panels generate more power in the morning on a bright overcast day than on a clear day, but that is more logical.

Regular observation. It's not a huge difference, but def a difference, especially when compared to a sunny day, where the S arrays obviously perform much better.

 

[millsan1]

Do you happen to have your MPPT as individual?

Yes, strings are on their own MPPT

 

[timselectric]

The flatter panels have access to more reflected sky.

 

[SeaGal]

The flatter panels have access to more reflected sky.

But aren't the S facing panels also at 15 degrees?

 

[millsan1]

But aren't the S facing panels also at 15 degrees?

No, S facing are at 40 ish

 

[SeaGal]

Ah! OK - makes total sense then, more reflected light captured by flatter panels.

 

[Kiwi2000]

I would guess that they see more of the sky on a diffuse cloudy day. How steep are the S panels? Are there more trees or buildings on the south side?

 

[teal95]

I have a commercially installed 8 kW ground mount system facing south at the preferred angle for my latitude (~40) and a 20kW system I installed on my barn roof (4/12 pitch facing east and west). On sunny days roof makes ~2x ground mount. When it's overcast roof makes ~3x what ground mount makes. It would be more but I have some shading issues on the roof.

 

[millsan1]

I would guess that they see more of the sky on a diffuse cloudy day. How steep are the S panels? Are there more trees or buildings on the south side?

40 ish

no particular issues with shading or whatever.

 

[Kiwi2000]

40 ish

no particular issues with shading or whatever.

Then I would say the 15 degree north panels see more sky on a diffuse cloudy day.