I believe the ac couple limit for “any” Growatt would be less than or equal to the output capability of the Growatt grid forming inverter. Give the Growatt white paper I link below a read. It for the SPF but I believe it is applicable to all Growatt ac couple capable inverters- I have found it’s description of how their ac coupling works is spot on for the MIN-US inverters. Specifically, page 4 “In the application of micro-grid without grid input, the AC output of the SPF 3000-6000T HVM-G2 inverter can serve as a voltage source to connect grid-tied inverters and loads. In this scenario, the power of the grid-tied inverter must be less than or equal to the power of the SPF inverter.”
blob:
https://community.growatt.com/562792fe-efef-4a14-8172-4730007a7b06
Link doesn’t work, go to link below and search for “
AC_Coupling_frequency_shifting_technology_of_SPF_3000-600”
Growatt
community.growatt.com