Question 18kpv Solar main with Grid back-up

Forgive me if I'm not posting in the correct place.  I am looking to install an EG4 18kpv system with solar pv as the main source of power but want to tie to the grid as a back-up to the pv. I do not want to backfeed the grid, only use it to charge batteries or run critical loads in low production periods.  I've looked through the EG4 wiring diagrams and I'm unsure of the proper set up for this.  Any help or a point in the right direction would be greatly appreciated!