I just tested this out and can verify you found a limitation of the 18 and it behaves exactly as you have described. I'm basically regurgitating below what you wrote already, but hopefully made it easy for those following to understand.
As for tech support saying ac power is in addition to grid power, it is not, since 18 derates power to ac charge as you also described in detail.
When setting (in your case) max grid power to 9kW, then AC charge power to 9Kw...
As long as regular loads are less than 9kW, AC charge will send energy towards Batts and max grid limitation setting is respected.
As loads increase, AC batt charging will get derated until batt charging goes to zero, but grid will be tasked to keep providing power all non ac charge over 9Kw.
Example:
Loads 5kW, 4kW goes to AC charge.
Loads 7kW, 2kW goes to AC charge
Loads 9kW, zero goes to AC charge
Loads 11kW, 18 will try to pull 11kW from grid (and potentially trip breaker.)
Grid power cannot be supplemented from Batt.
There is no solution for you, at least at this time, sorry.
If you want to post your data logs, perhaps we can figure out a way to work around the limitation, or minimize its effect.
Oh, in your settings, I would set your V to 55.2V - 56.8V depending on what is at the battery terminals. 59.2V is too high and more than likely drive BMS to disconnect. If batts are allowed to reach lower V in that setting first, 18 will put batts in standby, even doing a small discharge but BMS will always be ready to go.
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So a friend of mine who has installed a lot of solar tells me that this is a very basic thing. All inverters he has installed from various brands can do this. Meaning adding grid power to supplement battery power draw or adding battery draw to grid draw to power loads.
He is suggesting that I'm still missing some fine tuning on the settings.
And that all major inverters that have been designed fairly recently should have no problems with this.
So maybe people can help me identify what else I may need to try?
Under AC Charge: What would be the point to set "Charge Last" enabled? Charging batteries as last priority? I'm not sure what the purpose would be. Relevance?
What is the point of Battery Backup Mode settings?
Enabling PV charge priority? Does it matter if PV production goes to loads or battery first? Not sure how this whole section is used and relevant.
Forced Discharge seems to be something I would want. Hovering over the "?" It says "Forcably discharges batteries to supply loads demand" This seems like something helpful. Discharge batteries to cover load. I would interpret this as exactly what I'm missing. Using the batteries to cover any load not covered by grid. What am I missing? Is also says "OR export to grid when Grid sellback is enbable" (which is disabled and not relevant)
Not sure the Peak Shaving, AC couple and Smart Load settings are relevant or useful to my situation.
Suggestions?
If this is truly a lost cause, I will probably add 5 chargeverters to my system (back up to 8 units on my wall).
I will then disconnect both grid and generator from my 3 x 18k EG4s completely and just let them handle my load full time (36kw total power max) and handle solar and charging/discharging battery with solar.
The chargeverters consume only 10 W each to function. And I'd add 5. Before I had 9 Growatts each consuming 70W per hour.
Essentially I would set up 2 x 5000 chargeverters and connect them to grid on the AC side and to my battery bank. If SOC < 20%, charge, until SOC back up to 50%.
I would set up 3 x5000 more (15kw total) to connect to my generator.
IF SOC < 10%, start generator, turn off at 50%.
Here's the beauty of this setup (similar to my old setup)
My EG4 18k x 3 just handle loads and solar and will never know about the grid and generator. So they will just run. Simple.
My first set of chargeverters will turn on the grid when SOC falls and add 10k of charging power in the background that's turned on and off.
My second set of chargeverters will turn on the generator is SOC still falls. (or grid failed and we further fell). But it can also add to what the grid is already providing.
So if my bank is low and the grid isn't keeping up with 10kw, the generator is added for another 15 kw in addition, for a total of 25kw of charging power between the two. And my load can be up to 36kw at any moment, not limited to either 10kw (grid) or 15kw (gen).
This is essentially what I had with my previous setup, but I only had the generator backup for 15kw, no grid at all. Inserting the grid here makes my generator runs way less likely and common than before, but also beefs up my total charging capacity in the background.
Technically, if my load is 10 kw in the middle of the night, then what the grid puts on the battery bus bar gets passed directly to load in this system and the battery is neither charged nor discharged.
I was actually hoping to not have to go this route with my new shiny EG4 18kw and was assured they could do everything I needed. I'm still hoping someone has the secret settings handy or combination of settings so I can do what I need with these instead of adding the chargeverters back into the mix.
Thanks.
