We are on our second year of an 8 kW grid tied system -- which was 110% of our yearly use. Our average monthly bill before solar was about $95, but our heat and hot water are propane. Our county had a solar program going and 5 companies competed to provide special incentives.
The cost of the system was about $35K. 1/3rd of the cost was automatically rebated to the solar installer (Astrum), and 1/3rd was returned back to us in tax credits. We financed the other 1/3 through a special arrangement NY state has with NYSEG. The financing, planned to be equivalent to the average bill of $95, is added to the electric bill. Theoretically, the "free" electricity should be equivalent to the loan. Of course, it does not really work that way, in part because part of the bill is not for electricity, but taxes and delivery charges. The highest our bill are, like now, are about $145 month. In the summer, they are about $30.
The loan should be paid off after at total of 11 years. The panels and inverters (micro in our case) have a warranty of 20 years (90% function), should still be at 80-90% at 25 years. These are roof mounted on a directly south facing 9/12 pitch roof. I figure the shingles will need be changed at 20-25 years, at which time we'll take down the panels, install them on the ground or garage or shed, and put in the latest/greatest thin film solar shingles.
Overall, no problems. I'll be happier when they are paid off. If I lived in a place down south, like TX, they would have been up long ago.