Good morning,
During power assist, the net is on (pass through) and the inverter delivers also power, or, the inverter delivers power alone, during net outage, then the ripple is most visible.
Ripple has nothing to do with net outage, as it is DC side related.
As explained above before by Bjorn, check my topic, there is a link to a pdf sheet (ripple eliminators) where you can find the solution for your issue.
No, not one inverter supplier can be held responsable for making capacitor banks, simple, all installs are different, therefore we made in my topic 3 standard ripple eliminators for the most common installs, and that involved already quite some calculations based on our experiences with installs we did and do.
Now, recently we assisted Matt (18x15KW 3phase install), he obtained great results adding capacitors based on our advice, once more, read this topic and switch over to there (with a question) if you want help from us for your install with ripple.
With the very best regards, Jeroen.