Maximum current handling from PV array

Riley
Riley Registered Users Posts: 67 ✭✭
in PV Installers Forum - NEC, Wiring, Installation #1

I am looking at expanding my PV array to get more power. I have 2 options: a) stay with my current ‘low’ voltage 150V 60A charge controller or b) upgrade the charge controller to a higher voltage 250V 60A charge controller to run high voltage PV run with lower currents (much higher cost and other drawbacks like different vendors and thus lack of integrated SW monitoring).

I have 6AWG PV main conductor from the rooftop down to my mechanical/solar room (so 60A max). There is a 60A PV disconnect breaker on this main 6AWG PV feed line. Note: I can’t add another charge controller due to wiring challenges (I know this would be preferred).

For option a, the total combined currents from the 7 series panel strings are: Imp 60.8A and Isc: 62.63. I know I am pushing this right up to the maximum of my controller and the wiring but I doubt given the age of the panels and less than optimum angles, I’d be hard pressed to 60A. If I did ever get to 60A, I am protected by the 60A breaker.

What do the experts think?

Should I not push the current limits and just install 6 strings (instead of 7 strings) OR go to higher voltage charge controller and run much lower currents?  

Off-grid: XW+6048 / 48V FLA battery bank (428 A/H (Rolls S-550 batteries)) / Conext MPPT 60 150 charge controller / SCP / Insight gateway / 12 - 260W solar panels / Kohler 12KW 12-RES propane genset
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Comments

  • Vic
    Vic Solar Expert Posts: 3,208 ✭✭✭✭
    edited December 2022 #2
    Hi Riley,

    You are correct,  in being concerned about the Isc of the SCC.

    What is the manufacturer and part number of that DC-rated PV input breaker?  Assume that is probably a Schneider.  If you can look for a sticker on one side of that breaker,  it should have a Trip Current specified.  These breakers were often 1 inch wide.

    Many DC breakers for solar systems,  are rated to carry the listed current (like 60 A),  indefinitely,  without tripping.  Otherwise,  that current rating of the breaker would need to be de-rated to 48 Amps maximum Isc (80% of the 60Amps handle rating), or if derating is needed you could look for an 80 Amp DC breaker.

    Which brings up another spec, to consider  --  the maximum DC voltage that this PV input breaker is rated to handle,  especially when thinking about  increasing the PV string voltage  ...

    Later,  Vic
    Off Grid - Two systems -- 4 SW+ 5548 Inverters, Surrette 4KS25 1280 AH X2@48V, 11.1 KW STC PV, 4X MidNite Classic 150 w/ WBjrs, Beta KID on S-530s, MX-60s, MN Bkrs/Boxes.  25 KVA Polyphase Kubota diesel,  Honda Eu6500isa,  Eu3000is-es, Eu2000,  Eu1000 gensets.  Thanks Wind-Sun for this great Forum.
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  • Riley
    Riley Registered Users Posts: 67 ✭✭
    #3
    This is at my summer place so I can't check the breaker now (not there) but I think it's a midnight solar 60A breaker. I was thinking about about changing it to a GFI breaker anyway so I could replace it with a 50A? I didn't understand your comment about derating and looking for a 80A. 

    If I do go to a higher voltage configuration, that breaker will certainly need to be replaced as I assume it's 150VDC. 

    I will make another in the off-grid section about what folks think about mixing brands of gear. I could switch out the CC and go to Midnight Solar classic 250/60. I like having all the same gear from a SW and monitoring standpoint but... 
    Off-grid: XW+6048 / 48V FLA battery bank (428 A/H (Rolls S-550 batteries)) / Conext MPPT 60 150 charge controller / SCP / Insight gateway / 12 - 260W solar panels / Kohler 12KW 12-RES propane genset
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