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Comment by Invictus0 | Hacker News Reader

Why is it that the turbines can be turned into a bridge and a playground but can't continue to be used? What is the failure mode for these things?

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Spinning turbine blades are under significant mechanical stress. Individual blades are getting as tall as a 30 story buildings, but they rotate so you need to support all that weight from one end. Further, the tips are spinning at 100+MPH constantly so dust in the air is eroding the surface.

On top of this weight savings are a major goal so their designed to just barely work for a given lifespan. So, blades that where pulled from a working turbine are still really strong, they are simply more likely to fail at some unknown point in the future.

PS: Turbines from 20+ years ago are much smaller, but faced similar issues. For scale compare the turbine blade with cars in this shot and think this thing is rotating: https://www.technology.org/2018/03/23/here-is-the-worlds-lar...

Are there any recorded instances of this happening? A turbine falling apart when taken past its design lifetime?

About 3,800 wind turbine blades fail per year, according to an insurer.[1] About 0.5% per year. A detailed analysis of blade failure modes: [2] There's an industry devoted to blade repair.[3] What they do looks a lot like body work for carbon-fiber aircraft, except that it's done in midair.

Transmissions and bearings are more of a problem. "Turbine gearboxes are typically given a design life of 20 years, but few make it past the 10-year mark."[4]

[1] https://www.enr.com/articles/42352-are-four-wind-turbine-fai... [2] https://backend.orbit.dtu.dk/ws/portalfiles/portal/118222161... [3] http://fairwindres.com/wind-industry-maintenance/blade-repai... [4] https://www.windpowerengineering.com/wind-turbine-gearboxes-...

> Turbine gearboxes are typically given a design life of 20 years, but few make it past the 10-year mark.

That's why the biggest and best are direct drive.

It is all about trying to avoid having a broken/breaking wind turbine. A spinning wind turbine falling apart is no fun for bystanders involved [0].

[0]: https://www.youtube.com/watch?v=7nSB1SdVHqQ

That's a towerstrike and overspeeding, nothing to do with the blades being worn out.

I.e. cumulative fatigue damage from the constant flexing of the blades.

The failure mode is not as other posters have said mechanical, but is in fact usually a business decision. Plenty are lasting much longer than 25 years.

Many wind turbines were built with subsidies to run them for 25 years. As soon as that time is up, they may no longer be worth running, especially since in many places wholesale power costs have dropped due to other subsidised wind and solar.

Also, finding sites to build wind turbines is getting tricky - you need good wind, no complaining neighbours, good road and crane access, and a good grid connection. That usually makes existing wind turbine sites excellent candidates for building bigger better turbines which are 10x the size.

I was not suggesting me mechanical stress was the only issue, rather blades that needed to be able to withstand much larger stresses as part of a wind turbine than as playground equipment or as bridge components. However, it does directly cause problems. “The main reason to create fatigue in the wind turbine blades is cyclic loads. Variation of wind speed, annual gust, rotation of rotor, and variation of weight vector direction toward the local position of the blade [17] are the production sources of the cyclic loads.“ https://www.intechopen.com/books/wind-turbines-design-contro...

Study of fatigue damage in wind turbine blades “The inspection of damages detected in some blades of 300 kW wind turbines revealed that the nature of these damages was probably due to a fatigue mechanism. The causes that had originated the failure (superficial cracks, geometric concentrator, abrupt change of thickness) have been studied, verifying, by means of the simplified evaluation procedure of fatigue life of the “Germanischer Lloyd” (GL) standard, that these causes can explain the failure detected in the period of time in which it happened.“

https://www.sciencedirect.com/science/article/abs/pii/S13506...

That seems like a relatively old study now. I think blade design and manufacture has developed rapidly. Here is a short piece on the testing of much larger modern blades designed to last at least 25 years offshore [1]

[1] https://www.youtube.com/watch?v=5m-jwwM3qRs

This article is about blades that are actually 25 years old and being replaced. The video is testing is to ensure new blades can handle both peak stresses in the static test and less stressful cyclical loading for 25 years. So, 25 years from now those blades will also reach the end of their service life and need to be replaced.

That said monitoring and inspection can maximize the lifespan of individual turbines even if nobody is aiming for 50+ year service life.

I'm not suggesting they could be expected to last beyond their design. Just when this is the state of blades being built in unprecedented number today, a twelve year old review of much smaller ones made 35 years ago could easily be largely outdated.

It's a 30 storey fiberglass building spinning at speed. The stress is high and the material fatigues over time. Eventually it will crack, a stress concentration will occur and the crack will propagate somewhere important and it will fail completely.

Now take that same material and give it a much shorter span/length, and a much lower loading, and fatigue becomes less of an issue.

I'm not sure what bridge they're talking about in specific but I don't see why they couldn't be beams for a pedestrian bridge providing. I bet the manufacturer has a lot of testing data too.

Cumulative fatigue damage goes up as the cube of the stress, if I recall correctly.

Wouldn't that imply that a modest over-design could significantly improve blade life?

They are designed to be constructable, affordable, reliable, and somewhat maintainable (as maintainable as a giant windmill full of electricity generating equipment can be I guess).

If it was easy and cheap to make them last longer someone would do so and win the market.

yes

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