SolarPro
Senior Member
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- Austin, TX
Which means that the composite value is not much more than 5% away from either of them.
If the slope of the power versus voltage were 45degrees, that would make a 5% difference. But since the slope of the power curve is close to zero, a 5% change in voltage will not cause anywhere near a 5% difference in power compared to the MPP value.
If there were two strings in the system, then sure the array Vmp would be found roughly in the middle, in between that of the Vmp of the 10- and 11-module string. But this system has three source circuits, which means that the overall array Vmp is going to be weighted toward the Vmp of the 11-module source circuit.
If the slope of the power versus voltage were 45degrees, that would make a 5% difference. But since the slope of the power curve is close to zero, a 5% change in voltage will not cause anywhere near a 5% difference in power compared to the MPP value.
If ifs and buts were candy and nuts, we'd all have a very merry christmas. But if you look at the slope of a power curve between Pmp and Poc, you'll notice that it is not 45?. Power falls off a cliff as you start operating the source circuit above it's Vmp. I understand that a 9% Vmp delta does not extrapolate to a 9% delta in kWh, but it's not 1% either.
And yes, I do understand how unshaded east and west facing source circuits operate on a single MPPT. But those strings have identical I-V curves. Imbalanced strings do not. It doesn't really matter if that imbalance is the result of shading, orientation or a failed module.