So I got size for the medium system 8.16 by the Tesla advisor. I sent him my SCE bill and he took the highest usage month which was 29kwh/day. I also told him I will be getting a Tesla very soon and he did some calculations on his end to ensure my system would be sufficient enough to cover the charging and power the house. At this point I’m just trying to figure out if paying the extra $10k would be worth the investment for powerwall?
You could go to PVwatts, plug in your address, and it will tell you what an 8.16 system on your roof would produce.
But let's just say its 12,000 kwh a year.
Let's further say you use, on average, 1,000 kwh a month.
OK, so then, you figure out what your utility is doing, because a system sized exactly for what the house will use depends on a 1 to 1 net metering to make the math simple. That means if when the system is producing more than you use (in the day) you get credit at the same rate as when you are buying power at night.
If the rate is not the same, lets say your utility will do a time of use rate schedule. That might be, who knows, half of your usage? So for 6000kwh per year it might still "cost" the differential, or say $300 bucks a year if the differential is 5 cents. Six hundred a year if its 10 cents.
Not a disaster, the panels still save money, and $300 bucks will not, per year, cover the cost of a powerwall, so there is a possible answer.
By the way, a Model 3 has a 75 kwh battery, so if you charge it 50 times a year that's 3,750kwh you have to account for.