PV Payback

I spent time this morning re-calculating my projected PV payback. I am looking at sixteen years, or until midway through the year 2023.

I had originally estimated sixteen years, before I knew my actual production numbers which were much higher than I expected. But...it's still sixteen years! However, I now include the following assumptions which I didn't consider earlier:

1) PV production will fall 5% in 5 years, and 10% in ten years.
2) A new inverter will be needed in 10 years, at a future value ($1,740) of a present value of $1,068 at 5%.
3) 5% inflation for both energy from my utility and the new future inverter.

So I will have reached payback in about 16 years, and assuming a total PV system life of 25 years, my $7,389 outlay will have returned $17,973.

Because I paid for the system from savings up front, I did not finance this endeavor, so no interest payments. Even assuming that I plow the monthly energy savings right back into savings, I still incur a lost opportunity cost of not having invested my money over that time frame, But look at the markets today, sheesh! I sold high in 2007 to buy my system that today is more expensive from a mutual fund that is devalued. And 5% energy inflation...well, you know my bias towards higher future energy costs, personally I think they will be higher than 5% but I'll be conservative.

I'm coming out ahead in all accounts.