You have nothing to do except disfigure your roof for 20 years in exchange for a miserable compensation of 5.5 € /m².year in the best case !!! Frankly dismal ...
100m² of PV will bring you 550 € per year in the best of cases: you can always buy your underpants!
(Extract from Natural Habitat February 2009)
There are some who are really but really shit under the guise of false ecology ...
ps: the rates of 8,5 to 12% include the tax credit obviously in reality it is closer to 5%, and without any help in France it would be 1.7%! See the photovoltaic solar scam !