it would be interesting if this is a material science issue where UV exposure just breaks things down to the point that after a certain point they are just unsafe from to be spinning at the rates and mass involved. that's a lot of kinetic energy if an unscheduled rapid disassembly were to occur.
Yes, it's a material science issue. With stronger materials they would just make the blades longer because the power produced is proportional to the square of blade length (or cube?). Anyway, the blades will be at the limits of material strength (over a reasonable lifetime).
