September 2019 pricing at retail, two poly panels for 200 watts $150.00 – Amazon $0.75 per watt. Grape Solar 4 panel 1060 watt poly $1234.81 $1.20 watt, Lowes. Grape Solar 16 panel @ 265 watt per panel $10,942.47 or $2.58 per watt, includes inverter and solar controller.
Solar mounting kits usually handle 20 panels, the full kit about is 16 panels, you can build your own racking system for $500.00
Solar panel watts, expect in southern climates up to 2,200 watt hours or 2.2 kw hours per solar panel watt.
So at $.075 payback could be less than 5 years, at $3.00 per watt payback could take 20 years, not including maintenance and replacement of panels, inverters, controllers, etc.
Panels also need cleaning, fresh water, windex several times a year.