I/V-curve problems in Module Layout

[Anna_Sweden]

I am writing a guide about shadings on PV-systems, hence I am really interested in the “Module layout” with the possibility to view I/V-curves.

I have created a string with six 200 W modules, 60 cells, 3 bypass-diodes, connected in series to an inverter with one MPPT. I have also created a really near shading which, most of the day, is almost covering the lowest row in three of the modules. This should result in two MPPs: one with the three shaded modules included and one without them when the bypass-diodes are taking over. This is not the case. Instead I get various results during the day, even though the shadow is almost completely constant, for example:

11.45: full production, 1 MPP.

12.00: 2 MPPs - one with a really low current and one with approximatly half the full voltage.

12.15: full production, 1 MPP.

I think the result at 12 is the correct one, the others are not. Why is this the case? Can I do anything about it?

Anna

[André Mermoud]

I don't see well your configuration, the shading objects and the disposition of the modules.

I find rather strange that you have a shade at 12:00 and no shade at 11:45 or 12:15: please have a look on the shade drawings.

Perhaps you have a rather thin shading object, and the shades don't affect the corners of the submodules, which are taken as reference for the shading evaluation in the Module Layout part.

[Anna_Sweden]

Thanks for your quick reply! I did not realize I can attach images, but maybe that will make it easier to understand.

11.45:

11.45 Shadow

 

12.00:

[Anna_Sweden]

12.00:

 

12.15:

[Anna_Sweden]

So you see the shadow is almost constant but the IV-curve is varying a lot. This is continuing all day, not just around noon.

Do you know why?

Is there anywhere I can read about the IV-curve algorithm to understand it better? I am really curious about your sentence "the shades don't affect the corners of the submodules, which are taken as reference for the shading evaluation in the Module Layout part".

Anna