If you have a south facing roof at a reasonable angle and a utility which pays the same both ways as many do, the payback can be around 6 or 7 years regardless of the application.  After that your electricity generated is essentially free.  Panels and inverters are generally guaranteed for 25 years.

A ground mount takes up more space but can be a better angle.  Not difficult to do much of the work yourself which really improves the ROI.  A much better investment than many others these days.  Check with your utility website on "Grid-Tie" systems where your power can come from the grid or your panels or both or excess fed back into the grid.

Traveling through Iowa NE to SW and back again to a bull sale last week, I was surprised that I did not see an ag building with solar panels on the roof. A nearby implement dealer has the south facing section of his dealership's roof covered with solar panels. He told me it dramatically reduced his electric bills. The economics is all in the time to payback the investment. ROI is often in the 8-12% range or higher depending on the system, mounting, etc.