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System Advisor Model (SAM)

Shading effects on PV - How do I get reverse diode voltage

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Dimitrij
Topic Author

26 Jan 2017 16:04 #5108 by Dimitrij

Shading effects on PV - How do I get reverse diode voltage was created by Dimitrij

Hello everybody,

I use some approaches from SAM to build my own model for bifacial power plants. In "SAM Photovoltaic Model Technical Reference" the approach of Chris Deline "A simplified model of uniform shading in large photovoltaic arrays", 2013 is used for calculating shading effects on a PV module. For this the value of "reverse voltage of the (bypass) diode" of the PV module is needed.

Now my question is: where do I get this value from? Some datasheets I checked don't provide this information. I also couldn't find where this value is entered in SAM.

Thank you very much for your support.

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pgilman

26 Jan 2017 23:42 #5109 by pgilman

Replied by pgilman on topic Shading effects on PV - How do I get reverse diode voltage

Dear Dimitrij,

In the Deline article, they assume Vd = 0.5, and reference a paper by Bishop (1988) for the reverse-bias cell behavior.

For the non-linear self-shading option, SAM assumes that each module has 3 bypass diodes. The diode voltages are not inputs to the model.

Best regards,
Paul.

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Dimitrij
Topic Author

27 Jan 2017 11:19 #5110 by Dimitrij

Replied by Dimitrij on topic Shading effects on PV - How do I get reverse diode voltage

Dear Paul,

thank you very much for your quick reply!
Unfortunately I am a mechanical engineer, not an electrical one, so I have only basic knowledge about diodes.

Did I understand you correctly that Vd=0.5 V is used in SAM for the bypass diode as a constant value which does not depend on the choosen module type?
I found a datasheet from the bypass diode "SM 74611" from Texas Instruments, which is used in PV modules. There they indicate the maximum reverse voltage as 30V, which is a completely different magnitude (attached file, page 1).

Kind regards
Dimitrij

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pgilman

27 Jan 2017 22:40 #5111 by pgilman

Replied by pgilman on topic Shading effects on PV - How do I get reverse diode voltage

Dear Dimitrij,

I think there is a difference between bypass and blocking diodes in the array circuit between modules, and the bypass diodes in the module circuit between individual solar cells in the module.

Best regards,
Paul.

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