There are still old ARCO solar PV panels manufactured in the 1970's that are in use today. The 20 to 25 year figure is an industry standard for the warranty period of the panels. The panels should put out 80% or greater power of a new panel after the 20 to 25 year period. With the price of panels at a low, it is now possible to over design a system and put in 25 to 35% capacity over what is "just" needed to get by. Manufacturing has improved as well as panel sealing and connection technology. If a manufacturer is willing to warranty their product for 25 years, then how long will they really last and put out good usable power? From some of the old ARCO panels still being used today, perhaps an expected 50 year lifespan for the solar panels could be common. How much air pollution would an equivalent gas powered peaker plant create over a 50 year period? Cost to maintain and operate? Cost to meet new clean air standards?