Electricity is a 12 cent/kw delivered price in my area.
My electric bill dropped significantly, to where including payments for the system, I am at net -$1300/year. If I had taken the tax credit and put it toward the loan instead of other investments, it would be net $0. Sure, I am still paying on the system, but it will be paid off in 20 years (from the start of the loan, more like 16, now), but then, electricity may well rise before then, too, and even if it doesn't, the next decade of warrantied performance (and into the beyond?) will more than pay for the system.
My panels are rated at 19% efficiency. They were "good panels" when I bought them, but not "Peak performance!". I think back then peak performance was a bit over 20%. Now we have 24-25% performance. The days of rapidly evolving panel performance are over unless we go to mono-wafers, but those are stoopid expensive and will likely remain NASA only.