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Shutdown speed comes in two forms - steady speed, the speed at which the prop will be feathered, which typically comes with prevailing winds around the 65-75mph mark, and gust speed which is dealt with via brakes. Enough gusts will trigger a stop and feathering too.

When the odd one catches fire, it's failed to feather or brake correctly.

However, if you can count on increased wind speeds you can build equivalent power windmills with smaller sails. Thus increasing the number of them you can put per square mile while keeping them out of each other's vortices...

(And with smaller surface area, you can survive higher wind speeds and also operate at higher wind speeds!)

That depends greatly on the distribution of the speeds. If the baseline goes up then yes, you can do with smaller rotors. But if it is gusty or disturbs the laminar flow because vortices will carry further then it may very much upset existing wind power installations.

Spacing of machines is a pretty tricky balance and if the wind patterns start changing in unpredictable ways that will be a very hard thing to design for. You may end up playing it safe and under-powering the windfarm or go for maximum power generation and end up with a number of machines switched off (or worse case: damaged) for longer periods of time. Steady windspeed (narrow distribution) is the biggest single factor in wind installation efficiency.

That's why some of the earliest wind parks were set up where there was a constant source of wind with a relatively constant speed.

This is a beautiful example of one of those:

https://canwea.ca/news-release/2016/03/14/end-era-cowley-rid...

The simplicity and efficiency of that design was only possible because of the wind conditions. The black blades are an anti-icing measure.

> Spacing of machines is a pretty tricky balance and if the wind patterns start changing in unpredictable ways that will be a very hard thing to design for.

It sounds like you do have confident experience of modern wind farm specification and design.

I read that wind turbines are commonly built now with relatively over sized blades because after decades of development designers have greater confidence in their gust survivability and control mechanisms, and larger blades raise cut in speeds making better use of the most expensive part - the generator.

With your experience in these matters, can you say what percentage of modern wind turbine installations have been seriously damaged by being under specified to unpredictable wind conditions ? And very roughly what level of increased damage we might be talking about here from potential change in wind patterns.

> and larger blades raise cut in speeds

That is not necessarily true, it depends on the allowed degree of pitch and the shape of the first 1/3rd of the blade which tends to generate the torque required to get the machine going because it is generally coarser pitched than the rest of the blade.

Once it is running you can just about ignore that first 1/3rd or even the first 2/3rds of the blade, the bulk of the power is generated by the outer 1/3rd.

> what percentage of modern wind turbine installations have been seriously damaged by being under specified to unpredictable wind conditions ?

Very few turbines have seen damage from overspeed or direct wind damage to the nacelle or the tower, for now this is a non-issue but if there is a structural change in wind dynamics then for sure there will be a price to pay, either in terms of machines ending up shut down more frequently, longevity issues or breakdowns.

> And very roughly what level of increased damage we might be talking about here from potential change in wind patterns.

That all depends on the magnitude of the change.

Suffice to say that wind power is generally installed for 20-30 year life-span of the Turbines, after that they become un-economical to operate both due to increased maintenance costs, wear on the main structural components and the blades themselves (the bending stresses eventually weaken the blades) as well as technical developments making the more modern machines much more economical to operate than aging ones. So as long as the changes do not happen on a timescalle smaller than that the effects will likely be limited, if they happen (much) faster then there could be a real problem.

Gusty and turbulent airflow has a further detrimental effect on lifespan.

> > and larger blades raise cut in speeds > That is not necessarily true, it depends on the allowed degree of pitch ...

I think you are correcting a different matter here. Blade diameter in practice dominates the amount of power a which turbine can be designed to generate at lower windspeeds, aerodynamic design choices have to work with whatever diameter is provided. Increasing diameter involves significant expense and the entire reason it is payed is to raise cut in / raise generation at lower speeds / increase capacity factor.

> Suffice to say that wind power is generally installed for 20-30 year life-span

Not in recent years. 15 year contracts for windfarms are the current norm. I've read this often while following industry news and it can be observed from querying the different times [1]

> after that they become un-economical to operate both due to increased maintenance costs

Its not known to be the case that they'll become uneconomical. It may just be more economical to upgrade them, there is uncertainty involved which is the manufacturers bet.

Its a great commercial advantage of wind farms (and solar) that they can be relatively quickly online and make a profit on investment in 15 years rather than seeking 30 or 40 or 50 year supply contracts as some competing technologies do because of higher construction costs.

[1] https://duckduckgo.com/?q=industry+contract+for+wind+15+year

I worked in the wind industry for a number of years and I have never heard of anyone used the term "survivable speed" before.

That might actually be more concerning, it suggests that much of the industry doesn't give the topic much thought.

The wind energy industry gives this sort of thing a lot of thought. I think it says more about the GPs exposure to particular literature and theory than it does about the industry as a whole, also, whatever companie(s) they worked for may have simply used different terminology, it would be interesting to know what term they did use rather than to extrapolate large and unsupported conclusions from a comment like this.

Did they call it something else? It's the concept that matters, not the exact phrasing. Every structure, windmill or otherwise, has a wind speed at which it will break apart, possibly even if not rotating. It seems important to know what that speed is.

It is a very important figure and it works its way into many of the design details of the turbine as well as the tower and the foundation, if it was called something else I'd like to know what it was called as well as what kind of role GP had in the industry.

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.

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

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.

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.

Failures can cascade.

The problem with wind is it's uneven distribution across hours and days.

Because wind usually often weak and below rated speed, you need to build extra capacity to get enough electricity in normal days. When there is enough capacity, the price goes to zero or negative during days when windmills work close to rated speed, then increases dramatically when there is no wind. If wind power generates profits only when there is wind but not enough to saturate the demand, profitability suffers. Energy storage increases the price and is unsolved in large scale. Bigger smarter grids over large areas and solar compensate to some degree.

Am I the only one who thinks this is all good, in fact?

The push for extra capacity and small scale distributed energy storage increases redundancy / eliminates large single points of failure. Whereas the status quo is a huge power plant serving a city and when a blackout/brownout occurs, it's darkness and blinking lights and chaos all over.

Yeah it costs some money to get there. Cheapest isn't always the best.

Also, I feel like a large distributed network of smaller generators & storage solutions is going to foster innovation in a way that one huge power plant that stands for decades cannot.

The problem is, existing market mechanisms for power don't work well for this.

A wind operator will face a low energy price when wind is overproducing; but society needs wind to be significantly overprovisioned to avoid burning carbon.

> The push for extra capacity and small scale distributed energy storage

Storage is really hard. We don't know how to meaningfully do it yet. Maybe concentrated/thermal solar power will deliver it. Maybe power->gas->power will. Batteries are at best a small stopgap.

Further, the net result is that we have less grid stability, because we have variable loads and lots of non-dispatchable generation. The loading on transmission is fairly unpredictable, too.

I don’t really see how the law could not allow for wind farms to never have to pay for energy they generate to subsidise their existence.

> but society needs wind to be significantly overprovisioned to avoid burning carbon.

Should be "...overprovisioned in order to completely avoid burning any carbon relying on wind power alone"

> Storage is really hard. We don't know how to meaningfully do it yet.

This is plainly misunderstood. Storage can already be bought, currently costs between 165 and 305 $/MWh [1]. And the price reliably drops as there is more demand and development in it. There is no huge demand for storage yet. Long term storage can actually take the form of carbon neutral fuels and use existing thermelectric plants to generate when required. No "maybe" about that, its existing commercial tech.

[1] https://www.lazard.com/perspective/lcoe2019/

Storage is done reliably with water pumping and storage all the time. The question is efficiency.

Batteries have been scaled up to 100MW/129MWh [1]

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

> The push for extra capacity and small scale distributed energy storage increases redundancy / eliminates large single points of failure. Whereas the status quo is a huge power plant serving a city and when a blackout/brownout occurs, it's darkness and blinking lights and chaos all over.

Unfortunately most systems are "anti-islanding"; if they lose a link or go outside parameters, they shut down. A brownout is rarely because the nearest plant has gone down and more likely due to a transmission system fault.

The recent UK large outage postmortem is interesting reading: https://www.ofgem.gov.uk/publications-and-updates/investigat...

If your main goal is to get a more distributed power grid, it's great.

If your main goal is to decarbonize our grid before climate change wrecks civilization, then anything that makes that more expensive is bad. We're way behind in that race already.

>Because wind usually often weak and below rated speed, you need to build extra capacity to get enough electricity in normal days.

Luckily it's dirt cheap to build.

We're planning on building a number of new windmills today. So long as potential future increases in wind speed are taken into account in their construction, this would be a straight benefit.

Assuming those future wind increases materialize yes. But if they don't then you're going to end up with a less efficient set-up. Windmill efficiency is a notoriously hard problem and any kind of up front assumptions have immediate efficiency risks associated with them.

thanks for these insights do you have a source we could refer to that explains what you are saying?

Hanging out a couple of years on otherpower.com and the AWEA forums.

https://www.fieldlines.com/

https://www.awea.org/

Designing and building a 2.5 KW windmill from scratch also helped.