Typically, you'll see warranties for PV panels at 20-25 years, and guarantee something like 80% of the original panel rating at that time. But since a WHOLE LOT of the solar industry is fairly new, the question is "what kind of degrade can one expect over the years?" is a valid concern. Here's a link to an article in Fine Homebuilding that suggests the life span of panels may be a whole lot longer than many think.....that just like a "best used by" date on a can of food, they have to put SOMETHING in the way of a limit if they are going to offer a warranty, but they may be rating them way too conservative. The article: Testing a Thirty-Year-Old Photovoltaic Module | GreenBuildingAdvisor.com In the article, the author tests 30 year old solar panels he bought about 1980. These ancient ( by today's standards ) Arco brand panels ( bought out by, and now Solarworld ) are still right at 100% of their rated output ! I took a course over at Appalachian State U at Boone, NC, to get certified for NABCEPT ( the solar installer certification ), and the had some of those old ARCO panels there....we also tested them, and found they too were producing about their rated output, after 30 years. In light of the article, and my own observation, I conclude solar panels are probably gonna be good to go for about as long as you want to use them.....in fact, more likely ( assuming the world doesn't fall apart ), the technological improvements in panels to come down the road is what will push the older panels out the door.