There’s only really one straight forward upgrade option and that is to add a second AIO. You’ll need a G99 or a G100 for any additional battery storage so the DNO issue will have to be overcome either way.
If you add battery storage to the hybrid inverter then the AIO and the hybrid will cross charge, potentially up to full max rate charge and discharge. In of itself cross charging isn’t a “problem” but its clearly wasteful as you will loose about 15-20% of the stored kWh when you shift it from one battery to another.
If you go down the Home Assistant control route then you can write scripts to balance the two inverters, but this will write a lot of commands to your inverter, maybe one a minute, and this can potentially lead to an inverter failure.
The only way round this is to manually control the times that you let your batteries discharge. Programming say the hybrid inverter to discharge slowly all day, and the AIO to pause until the evening and then switch to Eco mode. This will lose out on capturing excess solar during the day.
If you look on YouTube then Oliver’s “speak to the geek” you tube channel describes how he firstly setup his AIO and I think 8.2 hybrid and battery with load balancing, and then another video where he describes why this is not a good idea in terms of the number of inverter writes this causes.
Another issue with having two inverters with batteries is that any export limit will become much more complicated for your installer to configure. I guess you’d have to limit each inverter individually.
You will probably get a much better payback from adding more solar panels than adding more battery storage.
In my area, night rate is 8.5p on Go and day rate is 27.1p so you save 27.1-8.5=18.6p minus 20% conversion losses=14.9p/kWh
AIO is 13.5kW capacity so 13.5x14.9=£2 saving each day
Circa £6k fitted and installed so 3000 days breakeven. 10-20 years depending on how many days a year you need the extra capacity.
Not good.
