Leondavibe

Only things i can think is 
The panels are divided over 3 inverters ie 3phases 
 
Each inverter can only feed it's panels to said phase
 
ie lets say pv
phase 1 4kw 
Phase 2 3kw 
Phase 3 3kw
 
So if load is 5kw on phase1
And 4.5kw on phase 2 
 
It would have to assist from grid on those phases
 
The 3 phases are 3 seperate rails solar from the one rail can't reach the other rails
 
The last phases output goes to waste if no load on that phase
Unless if you set the items to work only from batteries to then refill batteries when load is less 
Or if batteries are pooled and thus if the items are set to only use batteries the last phase can push into batteries and the first two phases can assist from the batteries pulling the power the last phase is pushing into the batteries