We sell it and we have the battery back ups which are huge but after the rolling black outs in texas last winter we said fuck that every 20 mins power went out annoying us to get solar i guess. We didn't get the bigger battery option that will power your ac/heat too, we just got what we thought we needed enough to back up our refrigerator, deep freeze, lights, and a few other things (grow lights) for 3 days worth. The house kicks on back up once a day to cycle the batteries keeping them healthy and such.
As for ROI my poor father that lives with us put the stuff in is name as the door knockers are the one who conned him into this, i sleep during the day so door knockers piss me off, so i couldn't give you the ROI but i know our power bill went down $200 a month. i'll get more details when i speak to him about it, i care so much i don't even have that Enphase app that shows the in and out on power, my father loves it tho always trying to show me our peak hours of usage and such. hope
@Suki813 can help more than me