Yes kitestrings, you have the basics.
Our Mini Grid that we create here, has absolutely no connection to the main utilities Grid.
The 'OzInverter' creates our MINI GRID for all our buildings etc, and its a Pure Sine Wave, for us its 50HZ, and a 236vac.
So The GTI is connected to our Mini Grid and its internal settings allow the power voltage its creating to push above the normal Mini Grid voltage. If you have normal appliances operating from the Mini Grid then they have first choice of the GTI created Power.
No appliances running or the GTI is creating more than you are using then the 'Ozinverter' because it has a 'H Bridge' design, allows the AC voltage to flow backwards through the 'OzInverter' and create DC voltage at about 60VDC that then charges the batteries. Somebody boils a kettle of water on the Mini Grid, then the GTI created AC power is diverted.
We have 11kW, 5off, GTI's working and connected into our Mini Grid, some of the GTI's internal settings i have altered so they shut down if there AC output voltage rises to high as the full 11kW is not required.
I have 3 other type of methods so the batteries do not get overcharged.
Three methods of controlling the back charging from GTI's is possible for 'AC Coupling'.
A. Use the Internal codes/settings in the GTI's to sequential shut down when a specified ac output voltage is reached. This works reasonably well with my system as some installations GTI,s are up to 400 meters away from the ‘OzInverter’ and batteries, and the batteries do push back slightly, but this depends on the cable voltage sag.
B. Use dc voltage comparators circuit to shut down the GTI ac side with a relay when the DC battery voltage rises above a charging rate voltage. But you will need to run a data cable to all your installations, and again allow for voltage sag.
C. Use PWM dc controllers that are connected directly to the 48vdc battery bank. These Diversion controllers, (Morningstar Tristar PWM at about 200 Euros each), will regulate the charging and any excess power when the batteries are full and will dump/divert to other permanently connected sources, ie, Air Heaters 2kW each or Hot water heaters, underfloor electric heating, etc, etc.
The above are a cost effective and very reliable system.
A is used most, and C is my guaranteed safety system. Where i do not have access to the GTI internals, then i use B.
For a 19kW PV Array I prefer using 2off 1.7kW & 4off 2.5kW GTI's for 14kW, and using DC Charge controllers for the 5kW as these can gently finish charging that precious 48vdc battery bank.
NOTE, I have not used a HF, High Frequency GTI, because second hand old heavy toroidal types are easily obtainable and very cheap, plus you get to use the GTI internal MPPT . 'Oztules' and others have experimented with HF types and do not find any real difficulties.
NOTE. Its best to use GTI’s at a max output of 2.5kW as above this the GTI tends to surge on a long cable connection.
Its real simple when you really look at it.
And its cheap by using second hand GTI's. You don't need all those expensive MPPT DC charge controllers. You dont need all that thick DC cable. And very importantly your batteries are normally just on standby as the GTI's are running your MINI GRID.
I trust this helps?