I would think all that variation would have some effect on MPPT logic... somehow... not sure how.
My interest in it being somewhat piqued, I tried a different experiment a bit ago. We have grey overcast with some sleet coming down. I know spring is around the corner - just haven't seen it yet.
I wired the roof array into the single Classic 150 thru its disconnect breaker. So I can shut off either the roof array, or the shop array while watching the screen on the Classic.
Very poor output, as would be expected in these conditions - 526 watts and the Classic is running the arrays at 87 volts in the poor light. This is 100 watts/kW installed capacity.
Shutting off the breaker for the house roof array causes it to drop to 352 watts output and the Vmp does not change. This figures out to an output of about 94 watts/kW installed capacity. Turning the roof array back on makes it come up to 525 - about the same as before. Shutting off the shop array makes it drop to 143 watts and the Vmp showed 88. This figures out to an output of 95 watts/kW installed capacity for the 1.5 kW east/west roof array. Turn everything back on and it came up to 530 watts and 87 Vmp, so no basic change from all three readings with everything on.
So if I add those figure up for the individual outputs; 143 + 352 = 495 watts. This is vs ~525 with everything on. That's a 6% boost today with the grey sky and some precipitation coming down. Not the same as the ~13% that I measured yesterday with what I call "Cloud Shine", but still get more power with the entire works on one controller.
The other thing I noticed yesterday is that with the whole works on one controller I was still making 68 watts after the sun had set for the day! If I turned off even breaker in a combiner the Classic would go to zero output and not come back. Flip that breaker back on and it went to 68 watts with the sun below the horizon. LOL!
I don't know what the explanation is, but I am concluding there is some sort of "boost" from connecting multiple arrays together as one big unit. On the perfect day I will get less power by doing this because the Classic can only handle about 4.8 kW on a 48V system, so it's going to amp-limit itself and "waste" part of the array. But the thing is, on those days I don't need the power because the bank is floating by 2:00 in the afternoon anyway. I want to optimize output on the less than perfect day because that's when we need the power the most.
The Classic's power measurement to the batteries is very accurate - in the neighborhood of +/- 1% with the type of shunt they use in there. So I'm satisfied that it's not erroneous readings. I'm going to leave it all on one Classic for now and shut off the individual breakers from time to time over the next few days in various conditions and write down what I get. If it proves out that I can get even 6% more on the bad day, it's worth it to take the "hit" on the good day simply because on the good day the controllers would have the whole works throttled back in Float anyway.
I'm thinking it has something to do with the arrays being combined, being able to collect more available light, and sending it down one pipe, eliminating the losses in an additional MPPT controller. But that's just my theory on it.
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Chris