It depends on a lot of factors, like how much electricity costs where you are putting up the panels.
I have 7.6 kW of panels on my roof. It was cloudier this winter, so they didn't do as well as I would have liked.
My electricity from the local power folks is way too heavy on coal generation, so I have supplemented my car (and house) usage by having solar panels.
I think it will take ten to twelve years to break even in my situation.
It is worth it in many ways, I think we need to get going (NOW) on renewable energy.
As for getting my money out of it in my location, it will be a slow process.