alt Hacker NewsPayback time in Scotland is 6-ish years. Same seems to be true in Massachusetts. Solar Panels have a lifespan of around 25 years. Inverters may need to be replaced sooner than that, but still last at least a decade.
So it pays for itself 3-4 times over.
There is no way that is true unless those solar panels are very subsidized. The energy needed to make a PV is 2x what that panel would harvest over its entire lifetime in Scotland for example. Scotland is a terrible place for PV. The numbers you give are probably accurate for central Mexico though. Also, the mean lifetime of a PV panel is 20 years.