Off Grid System PV Wiring help of 3 parallel to 2 series (6 panels) or just 8 panels in parallel?

I am going to be getting either six 400 watt LG solar panels (Model #LG400N2W-A5) and the classic sizing tool stated to do 3 parallel and 2 series or I am leaning towards getting 8 Panasonic panels (Model #VBHN330SA17) to wire in parallel. How exactly would I would wire this up and I think I would use a combiner box as well (The MNPV6-MC4-LV for the LG and the MNPV8-MC4 for the Panasonic)? This will be feeding a Classic 150 to 24v battery system and a 4000w inverter (coming soon).

I have done some research and the wiring part is not sinking in. The Series and Parallel for the 6 panels is confusing me. The parallel for the 8 panels seems easy (just wire to the combiner box)...

Any help would be greatly appreciated...

Comments

  • EstragonEstragon Registered Users Posts: 4,478 ✭✭✭✭✭

    How far from array to combiner box, and box to controller?

    Does it get cold (eg <32°f) there?

    Off-grid.  
    Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
    Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
  • EstragonEstragon Registered Users Posts: 4,478 ✭✭✭✭✭
    edited March 2019 #3

    For 2 in series, you hook the + wire on one panel to the - wire on the next. With the 2 joined, you're left with one + and one -. Voltage will be ~ 2 x individual panel voltage. Current (amps) for the string will be ~Imp for a single panel.

    The + wire from each series string goes to a breaker in the box, then to a common positive buss. The - wire goes to a common negative buss in the box.

    From the box, a single (larger) + and - wire go to the controller. Current will be ~Imp x number of strings (so 3x for 3 strings, 8x for 8 panels in parallel).

    Off-grid.  
    Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
    Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
  • bur1196bur1196 Registered Users Posts: 3
    edited March 2019 #4

    Estragon: thank you for getting back to me...Wow, I gotta admit, when you explain it in plain english like that, it makes total sense to me now... so just to reiterate two panels in series and each series hooked to each breaker (creates 3 parallel connections) in the combiner box if I stated that correctly...So if I get the 6 LG Panels, I would only need the MNPV3 and for the 8 Panasonic Panels (I would just wire each panel to its own breaker in the combiner box), I would need the MNPV8-MC4.

    So in your opinion, will the 8 Panasonic Panels in Parallel work fine or would you suggest going to the 6 LG panels in series/parallel?

    As for distance, I will probably go 30 feet from the combiner box to the charge controller (that will be the next step - see what guage wire/etc...)

    I am near Pittsburgh, Pa so it does get cold here (<32°f)...

  • EstragonEstragon Registered Users Posts: 4,478 ✭✭✭✭✭

    How far from the array to combiner box?

    I haven't looked up specs on the panels, but a couple of things to check on each of them:

    1. Voc adjusted for your local record low temp. The 330s in parallel wouldn't be an issue. 400s in strings of 2 wouldn't either. You may be able to do 2 strings of 3, but you'd need to check the cold Voc to be certain it stays under 174v (150v operating + 24v nominal for "hypervoc").

    2. Voltage drop at Imp on each leg (string to box, and combined strings to controller) with wire sizes considered. You can use fewer and smaller wire with bigger (higher voltage) strings. The classic wants ~ 30% headroom on pv voltage over charging voltage, so say 30v x 1.3 = 39v. 400s in strings of 2 or 3 should easily beat that. Single 330s should be checked for Vmp at hot temps (sometimes given in specs as NOCT, or calculated by subtracting Vmp coefficient for 40-45°C cell temp), and accounting for wire loss voltage drop.

    You are correct that you need a bigger box and more breakers for 8 in parallel. If you did 2 strings of 3, you could even get away with just a 'Y' connection and no box at all.

    You mentioned getting a 4kw inverter soon. Before making a final decision on panels, it may be useful to run through overall system needs (battery bank size, expected daily and peak load numbers, any shade issues, full time/year round use vs weekend/summer only).

    Off-grid.  
    Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
    Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
  • bur1196bur1196 Registered Users Posts: 3

    The array to the combiner box will be very close (within a few feet). I plan on putting the combiner box on a post right next to the array and then run the power to the charge controller (max 30 feet)...

    I did do the Midnite Solar Charge Controller String tool and the LG panels of 6 would be fine...Same with the Panasonic 8 panels in parallel...

    The LG Panels are 400W at 40V if I am correct and the Panasonic panels are 330 watts at 58v if I am correct. Is 58V too low for the charge controller (I would be running these all parallel to the combiner box)?

    I actually have a temporary inverter (Spartan Power 3300W) and a 24V lithium battery bank (ten 24V 83A batteries). This is wired like a UPS for the time being...I plan on getting the pre-wired Samlex or Mangum 4000 watt inverters as well as the solar panels soon...Thanks!

    Greg

  • EstragonEstragon Registered Users Posts: 4,478 ✭✭✭✭✭

    58v is fine for a 24v bank. If 40v is hot Vmp, that should be okay too. Lithium charging voltage can be a bit different than 24v nominal lead acid, and have no EQ cycle. It would be good to check for your specific chemistry / pack size.

    Off-grid.  
    Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
    Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
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