Maybe the all in one system is not good in that case. I was hoping that since they already have the AC-DC inverter built in they could also do voltage stabilization.
Maybe charge the batteries from either the grid or the PV panels, and always run the house off the batteries via a separate inverter. That way, you got the inefficiency of AC->DC->AC but always have stable voltage.
In the long run I want this to be mostly off grid anyway, with the grid as just an emergency option...
Yes, that is a good idea. Get a separate charger and always run the house from the isolated side. This will be more expensive as a good inverter/charger runs in the 1k-2k Euros area and you would need two (unless you find a suitable battery charger which is not very easy). I lived offgrid for nearly a decade and built myself three different solar systems. I started with a small all in one and found out that they are limiting when you want to expand since you usually cannot add more charge controllers and/or panels (which are the easiest way to expand a system). I ended up giving it away and building the others from separate systems. My biggest mistake was starting with 24 volts instead of 48 volts. It is cheaper but it gets a bit dangerous as you step up the power usage and there aren't many options for breakers and such.
Maybe charge the batteries from either the grid or the PV panels, and always run the house off the batteries via a separate inverter. That way, you got the inefficiency of AC->DC->AC but always have stable voltage.
In the long run I want this to be mostly off grid anyway, with the grid as just an emergency option...