your F.I.T all depends on the tarriff you have chosen and how much you have said you will feed back to the grid. Most don't have meters on (yet) to measure how much is going back to the grid so they pay a flat fee. A solar application should pay back in it's life time of 25 years but that is income and savings from the system, it does not include how much value/saleability it adds to your property.