1) the government won't pull the plug on the system
2) the goverment won't change the rate (VERY LIKELY), thus eating into your profits
3) The panels don't have any issues (damage, repairs, etc etc)
4) The panels will produce the amount of elec. all the models forcast they will (PS- are u gonna go and shovel snow off them in the winter time if there is snow on them)
5) It's going to be as sunny as the models predict (if you're looking at the data, look if they based it on 1 year, 10 year average, 5 year average, or if they just took the sunniest year on record)
If you can live with all this then go for it, personally I don't trust points 2,4 and 5.
I already called out 1 company in their presentation about their data and their sources... never heard back from where they got their data.