[abirkill]

As an example, the Vestas V164-8MW seems to be one of the largest off-shore wind turbines, and has a rotor diameter of 164m and a rotational speed of between 4.8 and 12.1rpm. [1]

Unless I'm miscalculating, that means that the tip of one of the rotors will travel 515 metres per revolution, which at 4.8-12.1rpm is a tip speed of between 2,472 metres per minute and 6,231 metres per minute.

To put that in more common units, that's between 148km/h and 373km/h.

[1] https://stateofgreen.com/en/profiles/vestas/solutions/v164-8...

[jerven]

Yes all correct. Those top 'tip' speeds where reached with smaller turbines as well. Max tip speed is a design limitation on blades (induced vibrations due to turbulence). What it means is that small turbines had much higher RPM, and the average speed along the blade was much higher in smaller turbines.

Second benefit of larger turbines is much more of the swept area is outside of the normal flight heights of birds. Either too low for migration patterns or too high for most hunting and scooting flight heights (relative to nearest surface).

So one 8MW turbine is likely to kill a lot less than 8 * 1 MW and much, much less than 80 * 100kw, even if it has a much larger swept area.

Now as these are offshore turbines, and Hywind, being for quite deep water. Likely to be far offshore, there are not that many birds around too get hit in the first place.

The nice thing about the slower RPMs compared to smaller tubines (especially pre 2000's) is that slower RPM's make it easier to spot the turbine for birds. High RPM's give optical effects that make it hard to predict where something is going (e.g. wheel looks like rotating backwards etc...) so bigger is easier too avoid for birds.