Everyone talks about pay back with renewable energy (RE). I think that is the wrong way to look at it. Really wrong. Let me explain.
When you buy a refrigerator, or a hot water heater, or a furnace, or new truck, do you look at pay back? Nope. But when you buy a PV system, everyone talks about pay back. Seems odd to me. I know I am going against the grain here, but worth the thought.
My hot water heater makes hot water and lasts 10 years. What is the pay back on that system?
I look at a PV system in terms of return on investment (ROI), not pay back. I think you should look at any RE based upon ROI.
When you consider ROI, take a look at what the system will be worth. Assume you install a big 5 KW PV system. Cost 45K (rough guess). Do you want a 5% return? 10% return? Can you get 2,250 dollars of value every year? That is a 5% return. Or do you demand a 10% return of 4,500 dollars a year?
Keep in mind, after 10 years of use that 45K system is till worth 45K, if not more. And, at 5% return, you have made 22,500 dollars. This assumes the cost of power stays the same (anyone believe that???

).
And, the best thing about this 5% ROI, is that it is not taxed!!!!!!!!!!!! So maybe we are looking at 7% return??? Unlike other investments, this is tax free. And the 45K is not part of your property tax burden (the tax law exempts it).
Then we have Federal tax credits and in many states, rebates.
So, when someone tells you about pay back, think about it differently.
One caveat, this assumes you plan on living in your location for a decade.
If the buyer of your home sees value in your PV system, life is great!
If the buyer does not want it, then sell your wind genny or PV system. There will be plenty of buyers!
I know I have made a lot of assumptions. Just think about it.
Bob
PS Let the replies start!