[engineerDave]

Depending on where you live, e.g. proximity to the equator, you will probably never recoup the initial investment or if you do the panels will probably be at their end of life when you do. So you'll never really "make money". But you will insulate yourself from demand spikes and give you an emergency backup.

[greedo]

Most panels have 25-30 year warranty. And even then, they'd still operate at around 80% of rated performance.