I am beginning to believe that you have made a recent commitment to Solar Panels. And, therefore, are required to convince yourself of their efficacy despite all evidence to the contrary.

a) An 8-year payback is achievable, sure. With a subsidy. Who pays that subsidy is the issue.
b) An 8 - 11 year payback is achievable without a subsidy, sure. Assuming the time-value of the invested money is 0, and inflation is 0.
c) And, assuming a) & b), there is no maintenance of any nature required. Which, of course, is not the case.

One more point not yet mentioned: The typical life-span of a grid-tie inverter is about 10 years, with the outside being 20 years. A 6KW inverter, installed, will be about $2,000. We are also ignoring battery storage, and an uplink transformer as we are assuming a single residential installation, not a Utility Scale installation (much cheaper per watt).

Peter Wieck
Melrose Park, PA