My son recently did a home photovoltaic solar cell analysis on his blogspot:

http://invioletlight.blogspot.com/

He concluded that it would take 16 years to recover the investment in rooftop solar cells from a lower electric bill.

Here is a similar analysis done by someone else:

http://www.redorbit.com/news/business/1541562/solar_panels_take_100_years_to_pay_back_installation_costssolar/index.html

The guy who did this analysis concluded it would take 100 years to recover the investment cost. On the other hand, the article reports on an advocate of solar cells who concludes that payback will take 13 years. However, he ignores maintenance, which, as Brad points out, could be large in North Texas where hailstorms destroy roofs more often than every 13 years. Another factor that is difficult to accurately assess in the economic analysis of solar cells is the future cost of electricity from the grid. Solar cells could be attractive if the price of electricity went up by a factor of four or five, but that seems unlikely to happen.