[jacquesm]

That's funny, because I've designed a windmill from scratch and plenty of the literature used that term.

I just checked Google to see if I'm mistaken but even the Wikipedia page on wind turbine design uses it:

https://en.wikipedia.org/wiki/Wind_turbine_design

"For a given survivable wind speed, the mass of a turbine is approximately proportional to the cube of its blade-length."

So I'm not sure why you've never heard that term but it definitely is in use.

[strainer]

I don't believe its a term in general use in the industry (of large wind turbines). Since "survivable" means "might survive" - that's not a very useful engineering target. Wind turbines have to be rated to reliably withstand specific gust speeds, so talk of certain speeds being "survivable" should be non-technical.

Afaik modern turbines are specified to reliably withstand an "extreme 50 year gust" estimated by their locales "Wind Class" [1] Some headroom is likely as with all large constuctions, building, bridges.. The matter of what stronger gust speeds might be survivable by the majority of installations is not specified.

[1] https://en.wikipedia.org/wiki/IEC_61400

[londons_explore]

It is surprising to me that windmills seem to have such a large structural headroom with this "50 year gust". Farms of windmills around me of 1000's of units have had zero collapses. When your business is offshore wind farms, why not remove all the headroom, make the structure far cheaper and lighter, and aim for say 25% of windmills to collapse around 30 years? The cheaper capital costs will surely pay for increased decommissioning costs of collapsed windmills and loss of production 30 years later after compounded cost of capital.

[strainer]

Heh, well maybe - adopt an Elon Musk development strategy : "Failure is an option here. If things are not failing, you are not innovating enough." it more than works for his projects, but if you're competing for policy support and you happen to get your 20 year gusts this year it looks really bad, even if a low percentage of turbines actually caught them from a bad direction and happen to need new blades.

Also with offshore windfarms, the big extra expense is in installing the towers and cabling. They are getting significant subsidy to be built for 15 year power purchase contracts, but once those towers and cables are built the farm can remain very valuable at the end of the contract, if refurbishment is required it could be remarkably cheap especially with a fleet of specialized ships to it carry out, some of which are already at work putting them up.

[jacquesm]

Failures can cascade.