Solar charging with some shade
I'm facing west today, so I'm getting a pretty good shadow on one of six series-connected panels. Panels are all around 135w @ 12v. Shade is on the far-left panel - about half of it: No...
Forum Discussion
I have/had? a glimmer but need clarification, if available :)
A. the claim is the lowest current panel (the shaded one) drags down the current for the string, including the Imp from the string.
B. the other claim is that the shaded panel has lower voltage so that reduces the total voltage of the string (and so its wattage) but the current remains the same.
How can both be correct?
Now in the OP photo of the controller it shows Imp of 7.3 and Vmp of 77.8 with the shading. Imp of a 135w panel is about 7.6, so let's ASSume the insolation at the time is a little less than STC, and allowed for an Imp of 7.3 and that was what it would be even with no shading. (claim B)
How can the Imp be so high at 7.3 if the shaded panel's current is cut back and that has lowered the array current to that? (claim A)
Vmp at 77.8 is way low compared with say 6 x 17.6 Vmp = 106v at STC, so the array wattage is much reduced for sure, but the claim is that is that 77.8 is the Vmp the controller has selected based on whatever.
If the Vmp "knee" on the IV curve for the prevailing insolation is that low, so is the insolation low (lower curve on the graph, knee farther to the left), but then how can the Imp still be way up there at 7.3 (out of 7.6) as on the upper insolation curve near STC?
If I had a string and an MPPT controller that displayed Imp (not all do) I would like to run a test where I shaded one panel somewhat and watched Imp to see what it did.
A. the claim is the lowest current panel (the shaded one) drags down the current for the string, including the Imp from the string.
B. the other claim is that the shaded panel has lower voltage so that reduces the total voltage of the string (and so its wattage) but the current remains the same.
How can both be correct?
Now in the OP photo of the controller it shows Imp of 7.3 and Vmp of 77.8 with the shading. Imp of a 135w panel is about 7.6, so let's ASSume the insolation at the time is a little less than STC, and allowed for an Imp of 7.3 and that was what it would be even with no shading. (claim B)
How can the Imp be so high at 7.3 if the shaded panel's current is cut back and that has lowered the array current to that? (claim A)
Vmp at 77.8 is way low compared with say 6 x 17.6 Vmp = 106v at STC, so the array wattage is much reduced for sure, but the claim is that is that 77.8 is the Vmp the controller has selected based on whatever.
If the Vmp "knee" on the IV curve for the prevailing insolation is that low, so is the insolation low (lower curve on the graph, knee farther to the left), but then how can the Imp still be way up there at 7.3 (out of 7.6) as on the upper insolation curve near STC?
If I had a string and an MPPT controller that displayed Imp (not all do) I would like to run a test where I shaded one panel somewhat and watched Imp to see what it did.
