Yes. And "backup" is probably an oversimplification. On a cloudy day my 10kW system can go from producing 9kW to 3kW a few minutes later, and back up to 8 or 9kW a few minutes after that. If my A/C is running I might be consuming 5kW (including incidentals like clocks and dehumidifier, etc.) fairly constantly while the A/C is running. So my battery "backup" is being called on for only a few minutes while a cloud is over my house, then charged back up when the cloud is gone a few minutes later. Then of course after the sun goes down my battery is my "backup" until it drains. I have it set to stop draining from the batteries when the battery charge gets to 30% (20% is the ultimate line for my warranty, but I set it at 30% to hopefully give me past my 2,000 guaranteed discharges, which is over 19 years). Given that I use only 70% of my batteries' capacity, count it as me having 21kWh of usable backup.
During the summer I usually don't have enough battery backup power to last through the night (because my A/C consumes so much). But over half the days during the spring are days I hardly pull from the grid.
You in lower, mid or north Alabama? I’m curious about how local power feeds into the payback …
PM if that is better for you. I’m in N. Alabama.