I just ordered my Model 3. Will need/want to factor that in as well.
The issue is we just moved to the Sacramento area and I know we will want to run the AC from 2-7 and those are smack at peak times. Have to imagine there is a fast/clear ROI here..
$300/month is $3600/yr, electric car will probably be $1000/yr. So a $15,000 investment should be reasonable if it completely eliminates those costs.
Need to learn more..
Something to think about...
The solar payback can be tricky and things seem to be changing rather quickly. A friend has a system and he warns that you really cannot get paid for your solar production, there is an annual true-up at wholesale rate, and that has a cap!
He said you should plan to offset your usage, but that becomes difficult when the utilities introduce TOU plans and rates are higher when you cannot produce. You can make it work out and reduce your cost quite a bit; however, here is the thing to think about.
IF your solar system break-even is 5 years, which I think is optimistic, consider an alternative. Right now you can find secure share accounts paying over 3% amortized quarterly. A $15k deposit will have a value over $17k in 5 years. Continue compounding that to 10 years and you've kicked that panel system's payback square in the nads.
Now, if you could go completely off-grid, then things might change slightly.
Batteries wear out and right now the tech is not there. You get only so many cycles out of them (kWhr). The cost of the battery alone is about equal per kWhr as what the utilities charge, so you pay more for that system. TOU could change that and you might be able to get ahead, but your payback will be linear vs compounded. Over time, that make a big difference.