I have a solar plus battery off grid setup at one of my homes. My comment that is the top on this item (https://news.ycombinator.com/item?id=40877337) describes what I did for my solar setup. Two years in, everything has paid for itself. I expect the system to produce for 7-13 years without meaningful maintenance costs.

At the 7 year mark my cost per kwh will be below $0.02 . Power in my area (southwest US) is $0.12 per kwh. Some factors are complex to measure. Such as how much more I run the AC because it is essentially 'free' than I would if it were still $0.12 per kwh. Another complex factor is that I can generate much more power than I consume currently. If I found a sensible use for the surplus power then costs drop even lower even faster. My consumption is about 50% of max, on an annual basis.