this system is dumb, makes no sense at all and is how people get suckered
So let's see..... I'll assume (and I'm being liberal) that this thing in cyclic use will return 10 years of power with an average drawdown of 50%. Drawdown percentage is critical; a pack that can handle 3,000 cycles with a 50% drawdown can probably only handle 1,000 if the drawdown is in the 70-80% range.
This in turn means that the actual capacity of the pack, in real use, isn't 7kWh -- it's half that, or 3.5kWh.
So you're paying $350/year for 3.5kWh of storage. Now double that investment for the grid-tie inverter and wiring, and by the way, inverters don't last forever either. We'll assume that's good for 10 years as well although you might do better on the inverter.
Now we have a $700 annual cost, before the cost of the money (which isn't zero!) and we haven't actually done anything but provision a storage bank for power; we have no source yet.
So how much power does that $700 buy? About 7,000 kWh at the average cost of about 10 cents/kWh around the country. Some areas pay more, some less.
The average house can run for anywhere from several months to nearly a full year on 7,000 kWh and, you haven't bought the solar panels yet.
I see utterly no reason to buy such a system. The so-called "backup" system is even more idiotic; a 5kW backup generator can be had for under $1,000, is portable as it requires no permanent installation and will run for as long as you can feed it gasoline.
We haven't looked at the environmental and other sunk costs of producing the batteries; lithium is mined, and is a pretty nasty business -- never mind that most of it is produced from third-world nations.