At 5 solar hours/day you get about 1.8 kWhr / watt.
At 7% interest the dollar would have given you 7 cents toward buying the power from the grid.
Rule of 72 for 7% gives 1.5 times sum of payments at 14 1/4 years. So assuming that you'll have to replace the panels after that time you're talking another 4.7 cents per year to save for panel replacement. That's 6.5 or so cents/kWhr.
Do a system big enough that the inverter, two sets of batteries (assuming batteries last about 6 years or so and you have to replace 'em once), and miscellaneous infrastructure are in the same ballpark price as the panels and you double your cost per kWhr, to 13 cents, which puts it right in the ballpark of grid power.
That would be, what, about $10k for inverter batteries, etc.? 10Kw would be about 50 kWhr/day - about twice what the power company estimates for a "typical household".
On the other hand, if your power rate is in the 26 cents/kWhr range you'd be way past breakeven with such a system. You could put it in, burn twice the power as you'd be buying from the grid for the same money, and laugh. Electric drier, electric oven/stove/grill, etc. You can burn a lot of power and still average only 2 kWhr 24/7. B-)
