Wiring from SMA Sunny Boy to (2) SMA Sunny Islands to sub panel

[RDiekmann]

I have a 5kw SMA Sunny boy GTI with 6400w Pv array. We are split phase 120/240v USA ...It is wired all conductors THHN-TNNN 8awg thru schedule 40 one inch conduit 80-90 feet to barn sub panel. Sub panel is rated at 100amp. 30amp DP breaker for PV array in the sub panel. The sub panel is wired to the house panel 350 feet away with 4 AWG conductors in 2 inch schedule 40. 50 amp DP breaker in house panel.

Considering adding two 6048 Sunny Islands at sub panel in barn storage area where panel is located for grid backup. Battery bank would be in ventilated storage area near Islands..

I have downloaded the SMA Sunny Island manual. Under AC connection they state 4 awg. Is this the output connection "grid/gen AC2"?
Incoming for the slave and master would be 8awg from the PV array (Sunny Boy 5kw) which should be AC1.

I've viewed many images of Sunny Island installs and the AC connections look like my 8 awg conductors...
After further reading....
Under the manual 6.2.3 it says "up to 4awg"
6.3.3 says maximum 4awg for grid/generator (AC2)

[bcroe]

Your AC loop might be 800 feet of 4 ga, for a resistance of about 0.2 ohms. With 5KW producing
20A AC at 250V, the voltage drop would be 4V, or about 80W burned up in the feed. At 1.6% of
the total power that could be considered acceptable. I would not want any smaller wire in that
circuit, my AC losses in a 600 foot loop are near 1%. Bruce Roe