Reverse IV Characteristics

[Viktor K]

Hi all,

First time posting on here. I'm curious about the reverse IV characteristics listed on pvlib, specifically on the page for the singlediode.bishop88 function (https://pvlib-python.readthedocs.io/en/stable/reference/generated/pvlib.singlediode.bishop88.html) and the page describing power loss due to partial shading (https://pvlib-python.readthedocs.io/en/stable/gallery/shading/plot_partial_module_shading_simple.html).

On the bishop88 page, the default reverse breakdown voltage is -5.5V, whereas the shading page uses -15V and mentions that a normal c-Si cell "can get to -10 to -20V in reverse bias". I'm wondering why -5.5V was chosen as a default (I don't see this in the bishop88 paper), and where the -10 to -20V range comes from? Similarly with the other breakdown factors.

And in general does anybody have advice on where to find more info on the reverse IV for different module types? I cannot seem to find good references even for common Si modules. The bishop88 paper cites a few sources but my general feeling is that the reverse breakdown is 1) difficult to study and 2) avoided in real devices, so the literature isn't clear (at least for me). I imagine module manufacturers would know the most about their module/cell reverse IVs but I haven't come across this info in datasheets.

Thanks in advance for your time!

Viktor

[Mark Campanelli]

Hi Viktor,

  First, welcome to the forum.

  My suspicion is that the -5.5V is more appropriate for SunPower’s (now Maxeon’s) interdigitated back contact cells, whereas -10 to -20 V is more typical of “standard” x-Si cells. My understanding is that, independent from the protective bypass diodes, the -5.5 gives less power loss from, say, a single shaded cell in a module string. However, driving a cell in reverse bias is not without other consequences, such as heating, but I am not an expert here.

  Unfortunately, I cannot provide any good advice as to how to get good estimates of the model parameters you need. I also have never seen a sensitivity analysis that might suggest which ones you should spend more time and money on to estimate. (I’d be delighted to know if you find one.) I think some people have actually covered single cells, taken I-V curves of a module, and then tried to fit the breakdown and bypass-diode parameters by fitting those curves. That said, it would be much nicer (and cheaper) if manufactures just shared accurate estimates 🙂.

Mark Campanelli

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Intelligent Measurement Systems LLC

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[Kenneth J. Sauer]

I would also recommend searching online for:

"type a" "type b" solar photovoltaic pv cells reverse bias

Namely, look into the difference b/w Type A & Type B solar PV cells.
It's often discussed in regards to partial shading &
hot-spots/hot-spot testing.

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