This is a typical "lifespan" of these types of projects, that is to say, the lifespan where it produces sufficient amounts of energy versus the degradation of the equipment to justify upkeep costs (which may be greater for offshore wind than on-shore). It's not going to break down over night after 35 years, it could go 50 or even more, but at lower energy production. The other reason for these lifespan calculations is that, in 35 years, the technology may far out pace what is currently installed in likely a prime location, and maybe local energy demands have changed. If that's the case, a "repower" may occur where existing infrastructure is adapted to new equipment which produces far more energy.