> […] nuclear plants if maintained can effectively last forever.

That's a very ambitious statement, every piece of hardware has lifecycle limitations. Engineering things for "infinite" lifetime significantly drives up the cost of the resulting product in most cases.

I would certainly hope the radiation-exposed parts of nuclear power plants are engineered for a very long life, but… there's water and metal involved, these things do need maintenance. And the non-irradiated parts probably need to be maintained much more frequently, e.g. the turbines certainly won't live forever.

As a matter of fact, solid state devices tend to last much longer, and PV is one of very few completely solid state power generation technologies. (It does, unfortunately, suffer from general sun exposure damage.) Personally speaking, without some digging I wouldn't make any claims which of them lives longer, it feels like it could go either way by quite a bit of margin.