Panel Configuration for BEST battery charging?

[Ddow]

Because of physical constraints my new upgraded system I think will be limited to 8 200W panels, might be able to use 8 12V 250W Panels. Old system is 12V, new system could be 12 24 or 48. Thinking since everything is going to be replaced I should try to go to higher voltage since 1 of the 2 ox 4 panel strings will have an increased run of 30’ for total run of 60+’. But I do already have large wire in most of the present system (1 x 4 panel 12V 4p) these are a being replaced.

Because of physical constraints there will be 2 strings - 4 panels each separated by maybe 30’, and another 30’ to the controller. Can/should you run all 8 panels as Parallel? Combine at some point and run to one MPPT? Or keep separate and use two controllers?

Then which one of these Panel options is the better choice in terms of gaining Max Charging potential to the batteries. Or is there a better option to run 2 x 4 panel strings of 200W panels? Seems like 66A at 24V should be my choice if you can run them all “Parallel”?

8 200W 24V Pan. 8p
24V Bat
1600W / 24V = 66A 24V

8 250W 12V Pan. 4s4p
24V Bat
1000W / 24 = 41A 24V

8 200W 24V Pan. 2 strings 4s
48V Bat
400W ? / 48 = 8A. 48V

I understand that these numbers also will be derated and have Voc involved eventually in order to get the correct MPPT and actual input numbers.

Thanks for any suggestions or clarification.

 

[sunshine_eggo]

Rather than try to recommend something specific, these are guidelines to follow:

PV Array Vmp should be at least 1.5X system voltage.

PV Array Voc should NEVER exceed MPPT ratings using NEC guidelines

Higher voltage is preferred for longer runs.

If shading or even partial shading is an issue, parallel should be favored over series, but better yet, the source of shade should be moved or destroyed.

 

[Mattb4]

Best to not think of panels as being 12v , 24v and such, work with their actual rating for Voc and Vmp. For instance, if a panel has a Voc of 23vDC and your SCC allows up to a Voc of 150vDC from PV, you could wire 6 in series for 138Voc. That gives you a small amount of headroom against cool temperature but likely not enough in a frigid climate region. Better would be 5 max in series for 115Voc.

I find it best to start with your SCC ratings and than figure out the best combination of panels to fit within them. For instance if you get a high PV voltage SCC it may not only have a Voc number like 450Voc, but it may have a Vmin (minimum voltage) and a Vsu (Start up voltage) to plan for.

Some RV style 200w panels will have the same voltage for Voc as RV 100w panels. This allows you to match them to hook in parallel or even in series ( I prefer to parallel 2-100 to get same voltage and matching amperage as a 200w).

 

[Ddow]

I see your point

So if these are my options I would guess the first one is the better way to go?

“12V 250W”
Voc. 22.8V
Imp 13.2
Voc 4s4p = 91.2V 48V Bat
Imp = 52.8A

“24V 200W”
Voc. 45.4 V
Imp. 5.32 A
Voc 4s2p = 90.8V 48V Bat
Imp. = 10.64A

Shouldn’t be hard to find a MPPT to fit this?

 

[sunshine_eggo]

PV Array Voc should NEVER exceed MPPT ratings using NEC guidelines

Controllers are sized by Voc, not Vmp, and you must allow overhead for cold temperature voltage increase.

Option 1 will require a 150V/80A controller. 16 250W panels = 4000W. 4000W/48V = 83A

Option 2 will require a 250V/30A controller as 4S will be 181.6V not 90.8V. 8 200W panels = 1600W. 1600W/48V = 33A

MPPT are rated by OUTPUT current.