Which Solar Panel Configuration is Better?

st4rgut

Hi, I'm designing my off grid solar system and want to arrange them as 2S6P. Because of size constraints, the panels must be arranged in a 
3x4 grid. I've sketched out two possible panel arrangements and am wondering whether one is better than the other? The series connections are drawn as a curve between positive and negative terminal and the parallel connections are the long black and red lines. 

Photowhit

Do you not intend t put breakers between each string?
It's a good safety measure and required if you need to meet NEC code.

You will need some extra wires somewhere, I'd just mount them so that the terminal sides are closest together in 2 - 2x3 groups, then brng the groups together;


"B"s represent fuses or breakers for safety/code, stacking will create a bit more resistance than bringing together in a combiner box as is normally done;

st4rgut

Thanks that looks cleaner. Do I need a breaker between panels if I use thick enough wire? Also, why don't you put a breaker between the series connections?

Photowhit

st4rgut said:

Thanks that looks cleaner. Do I need a breaker between panels if I use thick enough wire? Also, why don't you put a breaker between the series connections?

The series connected panels are in essence a single string of cells. So long as the strings are the same there is no problem.
You need the breakers since with 3 or more panels if a panel shorts the other panels can back feed and start a fire in the shorted panel or string.
I suspect you can see that the wire size isn't relevant.

I had a bad time sleeping and was just getting up when I wrote this earlier. If you use 'Y' connectors, you could put inline fuses without having the added resistance of the breakers all in line. Just put the fuse between the panel string and the connector.


You should be cognizant of the wire capacity, you don't want to have a larger currant than the wire can handle. Likely want 10 gauge wire for any connectors...

mike95490

What is your shade pattern ?   If your panels get late afternoon shade (or morning shade) you want to have one string with good illumination (25% harvest), instead of 4 strings only half illuminated ( 0 harvest )

Photowhit

mike95490 said:

What is your shade pattern ?   If your panels get late afternoon shade (or morning shade) you want to have one string with good illumination (25% harvest), instead of 4 strings only half illuminated ( 0 harvest )

Great thought, also snow accumulation. I've got no shading but the snow run down the array as it melts, if I get 10+ inches, I may not try to clear the bottom panels. Mine are wired in pairs across the array.

st4rgut

I get some afternoon shading and am hoping my MPPT controller is smart enough to adjust for that. Thanks for the tip, I will grab me some inline breakers.

mcgivor

Depending on where and when the shading occurs would determine the topography, MPPT controllers are not smart when it comes to shading, any single row of lateral cells on a single panel  can disable the entire string. Should the shading occur late in the afternoon when output is low there is probably little loss, but if during peak noon period that would be a different story, if that were the case then a PWM controller may "out smart" the MPPT