I run them both and they are both acceptable, but question is which layout is cost effective or efficient?
I do not know how 6 in a string can be acceptable to SUNNY DESIGN, REGARDLESS of your ambient Temperature. I am
hmy: confused.
6 x 31.1 Vmpp per module = 186.6 V!! That is less than the minimum of 200V for the Inverter. And that is at room Temperature, which it never will be. And the V will go way down as modules will be 40 deg F hotter than even ambient T.
I don't think this system would even turn on.
On the other end: 12 modules x 37.8 Voc = 453.6 V.
MAx V allowable for this specific Inverter is only 500 V!! Not 600. as
PW Dickerson very aptly pointed out.
That means that 500 / 453.6 = 1.10 cold T adjustment factor is the highest you can go.
Accordingly, the coldest T allowable is 32 F. RECORD lowest cold.
(per NEC Table 690.7)
If it can
ever get colder, that is a problem. As
GGUNN pointed out: it will void your warranty.
You need a SMA HFUS if you expect colder ambient Temp.'s. That'll allow 600 Vdc. max.
I don't see 6 as acceptable ever.
Nor 12, as good design, unless you are in Coastal CA, Florida, etc........