Solar panels are extremely long lived. Unless you're hit by a hurricane, they should last for over 20 years. The output depends on the lighting, the temperature range (which affects efficiency), the number of couldy days... most resellers have data tables to inform you on that.

What is difficult to advise you on is your local regulations. In Europe, the government subsidizes this to a large extent and in 5 years at most it is paid back. The arrangement seems different in the US.