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I ran a simulation with a centralized inverter and DC optimizers. in the loss diagram, the mismatch loss (modules and strings) is close to 0%. that is fine. I ran a similar simulation with string inverters instead and still DC optimizers. in the loss diagram, the mismatch loss (modules and strings) is higher than 3%, as if there is still a module mismatch ... I don't understand why? Could you help me? thanks

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  • 1 year later...


When one or several cells are shaded, the whole sub-module becomes reverse-biased, the by-pass diode is activated above the current corresponding to the residual power of the diffuse part.

This results in a quite different situation as the previous one: the true Pmpp maximum is decreased in voltage (voltage of each sub-module, plus the diode reverse voltage), but the current remains the same Impp.

When you have one only string, the Vmpp of the string is reduced but the Impp current is identical for all modules, so that the Pmpp of the string remains the sum of the Pmpp of all modules.

However the voltage of this Pmpp may be (often) below the voltage threshold (VmppMin) of the inverter.

With several strings in parallel on a single MPP input, this reduced Vmpp induces a severe mismatch.

As a consequence the optimizers don't have anything to recover with partial shadings on a single string.

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