PV power generation is not only environmentally friendly, but also a prudent economic investment for both residential and commercial rooftop electric power. In the continental U.S., the rooftop solar investment typically has simple payback periods of 3-7 years and continues to produce power for another 25 years or more thereafter. However, mounting PV to a roof with a service life shorter than the PV array may not make financial sense.  

Because roof and solar functions are interdependent, they together should be considered as a single asset within the financial analysis.

The financial analysis offered at the point of sale presumes the roof will last for the entire life expectancy of the solar, yet this is often a mistaken assumption. With such an analysis, systems become cash-positive within the first seven years of operation and show internal rates of return in the range of 15-40% over a 30-year period. Similarly, solar lease-back programs are cash positive from day one. But such an analysis is only valid if the roof outlasts the solar. Most roofs do not.
Solar is a financially prudent investment – provided roof replacement is not necessary.