How to calculate Amps for strings of bifacial panels?

[ddxv]

I am trying to calculate the max amps for breakers and for wire guage estimates, but I realized the way I was calculating it for bifacial lead to some questions.

First, is it correct to calculate max amps leaving panels as watts/voltage? While this makes sense for the rated 440W, for the bifacial total of 550W it no longer aligns with the other way of Strings * Max Power Amps.


Amps = number of strings * (rated 440W / VMPP)

Strings	Series	Count	VMPP	VOC	Volts From Panels	Max VOC	Watts	Max Watts	Total Amps
2	8	16	34.71	41.51	277.68	402	440	7040	25.35

Amps = number of strings * (bifacial max watts at 550W / VMPP)

Strings	Series	Count	VMPP	VOC	Volts From Panels	Max VOC	Watts	Max Watts	Total Amps
2	8	16	34.71	41.51	277.68	402	550	8800	31.69

Amps = number of strings * Max Short Circuit Amps

Strings	Series	Count	Max Power Amps	Short Circuit Amps	Strings * Max Power Amps = Amps
2	8	16	12.68	12.88	25.36

So if I am selecting a breaker, would it be the red or green for each string?

12.68 * 1.25 = 15.85
vs
15.85 * 1.25 = 19.81


And would this also hold true for estimating the total amount leaving the combiner box for 2 strings:
25.36 vs 31.69


Panel specs if I'm missing anything:

https://signaturesolar.com/product_images/DNA_440w_BF10_Datasheet.pdf

 

[eppich8479]

Instead of "amps leaving" i think you should say,"amps that can be supplied"

Im not an electrician, but volts are all that matters. Except, your wire needs to be rated for the amps you intend to use, plus like 25%

 

[Brucey]

I multiply VOC 41.51A by Isc 12.88A and get 535W.

Two parallel strings you'd be looking at around 26A.

Some bifacial spec sheets I've seen show the increased amps for the bifacial output tiers.

 

[ddxv]

I multiply VOC 41.51A by Isc 12.88A and get 535W.

Two parallel strings you'd be looking at around 26A.

Some bifacial spec sheets I've seen show the increased amps for the bifacial output tiers.

For the breakers in a combiner box then I'd want to multiply by 1.25 right? So the 12.68 x 1.25 = 15.85A. That could maybe work with 15A breakers but to be safe I should upsize to a 20A breaker?

So in this example, the combiner box should have 2x 20A breakers and the wire leaving rated for 40A.

 

[Brucey]

For the breakers in a combiner box then I'd want to multiply by 1.25 right? So the 12.68 x 1.25 = 15.85A. That could maybe work with 15A breakers but to be safe I should upsize to a 20A breaker?

So in this example, the combiner box should have 2x 20A breakers and the wire leaving rated for 40A.

I don't believe you need to derate if using fully rated breakers like the Midnite mnepv series.

I would go with two mnepv20 breakers in an midnite mnpv3 or 6 combiner box. mnpv6 is nice because you can split the bus bar if you want to add another pair of strings to another controller/mppt.

 

[ddxv]

Thanks, that sounds good.