I have four 355W solar panels and three 315W solar panels. I have a 40-amp mppt and a 30-amp mppt charge controller with 100V Max PV voltage.

The distance solar panels to charge controllers is around 15 meters and the distance battery to charge controllers around 1.5 meters.

My battery bank system is 24 volt. The solar panel voltage is around 37 volts. They are not connected yet.

Out of the three 315W solar panels, one is pointed south, the other 2 east. he one pointed south is shaded until 9 AM. They are at 16 degree angle. The other four 355W are not yet installed.

The system is in the Caribbean.

I have 8 6-volt batteries in 2 parallel strings.

I need help with the wiring of the solar panels (series or parallel) and also the wire gauge.

Thank you in advance for your help!

The specs for the 315W solar panel are:

 Pmax = 315 W  
 Max voltage = 37.4 V  
 Max current = 8.42 A  
 Open Circuit voltage = 45.5 V  
 Short circuit current = 9.12 A  
 Power tolerance = 0~+6w  
 The maximum fuse rating = 15 A  

The specs for the 355W solar panel are:

 Rating power at stc(Wp) = 355 w  
 Rating power voltage(Vm) = 37.58 V  
 Rating power current(Im) = 9.45 A  
 Open circuit voltage (Voc) = 46.26 V   
 Short circuit current(Isc) = 9.85 A  
  • 1
    what is your actual question? ... it is unknown if you have anything connected ... it is unknown if you are having any problems
    – jsotola
    Sep 7, 2019 at 20:44
  • 1
    How are the panels physically positioned? That is, which angles are they aiming, and which ones are likely to fall into shade together? Sep 7, 2019 at 20:55
  • What voltages are the panels and how far are the distances panels-controller and controller-battery? What is the max voltage input of each controller? Sep 7, 2019 at 20:56
  • 2
    If you have a MPP charge controller, and it appears you do, then you are already getting the maximum power of out of the panels. MPP = Maximum Power Point. To get more power you must increase the INPUT power. One method is to install tracker drives on your panels so that they are always pointing at the sun. This, however, is a fairly expensive upgrade.
    – jwh20
    Sep 7, 2019 at 21:02
  • 1
    Can you please edit into the question the complete specs of both types of solar panels + charge controllers? Without the details from the spec sheets, there's no way to give a definitive answer.
    – Nate S.
    Sep 10, 2019 at 23:35

1 Answer 1


Your panels are 37V yet your controller is 100V max. Since 3 panels is 111V, that means we can only wire 2 panels in series. That also means odd panels will be a problem.

But so far, the odd panel already is, since it has a different facing than the other panels.

The mixed panels are so close in working voltage that they can be paralleled without worry. However that will necessitate fat cables.

To work them in series, will require they be facing the same direction and recieve sun at about the same times. If they are in series, and one is in sun and the other in shade, you will not get much out of that array - whereas if they were in parallel, you would at least have the sun-lit one. However parallel requires fat cable.

So for right now, the two 315W solar panels that face the same way can be placed in series and wired to one of the controllers. The voltage drop calculator says #12 wire will be fine for this purpose with only 2.11% voltage drop. The single 315W panel facing oddly should go on the other controller. This can use #12 but will have 4.22% drop; #10 wire brings this voltage drop into line at 2.55% drop.

When you add the other 4 panels, again the question will be if they can be grouped in pairs, with each member of the pair facing the same way and going in/out of shade at about the same time. If so, they can be placed in series.

Multiple pairs of series-wired panels can then be paralleled together for the cable run back to the panel. Two panel pairs should use #12 for 4.22% drop, or #10 wire for 2.55% voltage drop. Three panel pairs could use #10 wire for 3.83% drop, or #8 wire for 2.52% drop. Or, each panel pair could use its own #12 cable going back to the controller. Your call.

Individual panels should each get their own home-run, as it will not be economical on wire to try to parallel them. Use #12 with 4.22% drop, or #10 for 2.55% drop.

The series pairs of panels should be paralleled onto the larger charge controller. The individual panel(s) should be paralleled onto the smaller one, but no more than 3 panels onto this 30A unit.

  • 1
    I would verify the open voltage potential of the panels, I have seen panels produce well over 2x their rated output causing an inverter failure. Other than this 1 caution this looks like a solid answer based on the information provided.
    – Ed Beal
    Oct 17, 2019 at 9:23

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