To determine how long anything will last "accelerated aging testing" is used. For that to be effective though you need to know what will cause the damage / degradation. From the little I know the actual PV cells should last a very long time with a gradual degradation in efficiency as the article says. Then there's the problem of their housing and interconnections. I've seen reports of some having issues within a few years but that's because of improper curing of some polymer inside the housing causing acetic acid to be released. The housing and interconnections are probably the biggest concern and that depends on the environment. I'm on the sidelines of a largish remote install close to the ocean. The suppliers want us to use marine grade panels because of the salt. The housing for these is fibreglass but I'm not very confident about how well that will hold up under the UV load. I'd prefer they used marine grade stainless but that's expensive.