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Understanding Mismatch Detailed Conputation.


psmith
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I am a newbie on this . I was trying to understand few things on detailed computation of mismatch (Loss section that uses RMS of Voc and Isc).

As I am seeing the help section , the IV curves are based on single diode model that has following parameters :

I = Current supplied by the module [A].- Unknown

V = Voltage at the terminals of the module [V].- Unknown

IphRef = Photocurrent [A]

IoRef = diode inverse saturation current [A]

Rs = Series resistance [ohm].

Rsh = Shunt resistance [ohm].

Gamma= Diode quality factor, theoretically between 1 and 2, often less

q = Charge of the electron = 1.602·E-19 Coulomb

k = Bolzmann's constant = 1.381 E-23 J/K.

Ncs = Number of cells in series.

Tc = Effective temperature of the cells [Kelvin]

As I understand we get IV curves from this equation .Now looking at the detailed computation, It uses RMS values of Voc and Isc and obtains statistical sample of Voc and Isc . It then uses them in generating IV curves after aligning Voc and Isc (summing etc) . But, As I see the single diode equation has these two parameters as unknown that is calculated from the photocurrent IphRef. I am not able to relate this part . How we are generating the new IV curves from the statistical sample . Are we using this same single diode equation to generate IV curves here or some more info is there? Or I am interpreting things incorrectly ??

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  • 4 months later...

The Mismatch between PV modules in an array is a rather rough calculation, based on a statistical distributions of the parameters.

The phenomenon is mainly related to the mix of different I/V curves, by calculating the addition of currents (in series) and then voltages (strings in parallel).

This is not really sensitive on the exact I/V curve of each PV module, so that we may avoid recalculating the I/V curve from the one-diode model for each module.

The shape of each I/V curve will be very similar for all the concerned modules. Therefore this tool uses the basic I/V curve of the reference module, and performs a "scaling" if the voltage and the current according to the individual Voc and Isc of each module.

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