Where to add 3rd battery to 2 inverter system with BU interface?

[Steeler.Fan]

My PV system currently consists of 2 SE7.6 kW energy hub inverters, 60 330w panels with optimizers, a SE Backup interface, 2 LG Chem RESU 16h batteries and a SE EV charger. My home is in a very sunny and hot part of Hawaii, where electricity is very expensive to begin with but now more expensive since a significant portion of our fuel used to come from Russia. My primary inverter has a 17 panel string facing west and a 17 panel string facing south. My secondary inverter has a string with 13 east facing panels and a string with 8 east and 5 west facing panels. (My primary inverter has more panels because it was originally a SE 10kW HD-Wave inverter but I replaced it with a 7.6 energy hub because I wanted to add batteries. 10kW energy hubs were not being produced at that time.) Each inverter has a battery attached directly.

I plan to 6 more south facing 360w panels and another LG Chem RESU 16h battery. I need the 3rd battery so that I can power my home with batteries from 5 pm til 9 am. After that, I will plan to switch to TOU with On Peak (5-10p) @ $0.0638/kWh, Off Peak (10p-9a) @ $0.0572/kWh, Mid-Day (9a-5p) @ $0.0236/kWh rates. I can charge my 2 EVs mainly during the day. I will top off my batteries (at Mid-Day rates by 5 PM @ 7 kW) if necessary on cloudy/rainy days.
My questions are whether to add the 3rd battery to my primary or secondary inverter and whether to add the 6 new panels to the primary or secondary inverter?

If I attach the 3rd battery to the primary inverter, I will want to be sure that it has sufficient power to charge both batteries. Should I add the 6 new panels to the primary inverter, as well? That would give me 13.38 kW/7.6 kW = 176% oversize. Theoretically, these energy hub inverters can be oversized to 200%.
HOWEVER, I have had THREE SE10 kW inverters die that were attached to the two 17 panel strings. My latest 7.6 kW energy hub inverter replacing the 10 kW inverter shut off last week once because of overheating and once because of an arc fault??? Should I instead add the 6 new panels to the secondary inverter to balance the loads between the inverters? Then where should I attach the 3rd battery?

A 3rd alternative is to add a 3rd energy hub inverter to my system and balance the strings so that the oversize % is more equal between them. The 3rd inverter could have the 3rd battery attached to it.

I am working with my very friendly SE field rep who is planning on reviewing the data from the three 10 kW inverters that died to see if he can figure why.

Any friendly and constructive comments and suggestions are most welcome.
Thanks

[Srrndhound]

If I attach the 3rd battery to the primary inverter, I will want to be sure that it has sufficient power to charge both batteries.

Should I add the 6 new panels to the primary inverter, as well? That would give me 13.38 kW/7.6 kW = 176% oversize. Theoretically, these energy hub inverters can be oversized to 200%.

If you have access to mySolarEdge monitoring, it will give you the actual wattage maxima you experienced with the current panels, which might inform which inverter is the better target for the 6 new ones. My feeling is that the panels should be connected to the inverter with the least production so as to best balance stress between the two inverters.

Looking at the monitor data will also tell you what time of day the existing batteries reach 100% charge. I suspect well before noon. That means you have plenty of time (and juice) to charge a second battery from either inverter before sundown. That being the case, it would not seem to matter which inverter services the new battery. IMHO.

Having said that, it would also be useful to look at the historical data for production under "worst case" sun conditions (cloudy and winter) to see which inverter harvests the most daily energy. If you find many days where the batteries are not fully charged, the one that does best may be the better candidate for the new battery. OTOH, if your system rarely or never fails to fully charge the batteries before noon, it won't matter.

My latest 7.6 kW energy hub inverter replacing the 10 kW inverter shut off last week once because of overheating

If your inverter is like my SE11400H, the passive cooling heatsink is against the wall. I put some 4"cooling fans on top and it makes a definite drop in heatsink temperature. My unit is inside the garage so the fans do not get rained on. This might not be an option if yours are outside. Are they in the shade all day?

[Steeler.Fan]

SRRNDHOUND
My inverters are both in my warm (80-9suggestions.
I drain my 2 batteries down to my reserve each night and they are usually charge by 3 pm on sunny days. My storage profile is minimize imports.
Thanks for your suggestions.

[Srrndhound]

SRRNDHOUND
My inverters are both in my warm (80-9suggestions.

I'm not sure I received your entire message, but I'll just say that anything you can do to keep the electronics cool ought to extend its life.

I have had THREE SE10 kW inverters die that were attached to the two 17 panel strings. My latest 7.6 kW energy hub inverter replacing the 10 kW inverter shut off last week once because of overheating and once because of an arc fault???

I hope your installer digs deep into the arc fault matter. That might expose something that hastened the demise of the previous inverters. Maybe you have already asked Mr. Google about it. If not, this article is illuminating.

I drain my 2 batteries down to my reserve each night and they are usually charge by 3 pm on sunny days. My storage profile is minimize imports.

Hmmm, I wonder why it takes until 3pm to fully charge. Maybe your home is demanding significant power in the morning hours and the inverter cannot steer energy to the batteries -- AC is running? That would suggest the new panels and new battery should be on the same inverter if there's to be any chance of fully utilizing their capacity.