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Wind Turbines: The Ghost in the Gearbox

I first came across this shocking industrial wind turbine (IWT) gearbox problem some time back and posted about it (Here) and originally (Here). The basis of these posts was this article (Here)

This long running problem is so serious that since 2007, the US Government has been coordinating research into it through the NREL. (More on that further down.)

By the looks of it nothing has got better, although there is a lot of industry spin claiming the fix is just over the hill. Some of it quite recent  (See Here)

So what is the problem and why is it kept so quiet?

Industrial Wind turbines (IWT's) have a generic, long standing and apparently intractible problem with gearbox reliability.

Many gearboxes need a rebuild within 5 -7 years instead of lasting 25 years as designed. Many suffer catastrophic failure within the 5-7 period or even earlier. Depending on the age of the turbine, a gear box failure may effectively write it off. Even when repaired, these gearbox failures are highly expensive and often take out the turbine for months.

Replacing the gearbox adds massively to the overall cost of the IWT. Manufacturers increase the cost to cover warranty repairs in the first 5 years. When out of warranty, the cost of a maintenance contract sky-rockets, eventually to a point where the operation of the IWT becomes untenable.

Why does this matter? After all it is the operators/manufacturers problem isn't it?

It matters because IWT's are capital intensive. That means that most of their operating cost is mostly soaked up in purchasing the thing - and maintaining it. If the IWT has a much shorter life (or a much higher maintenance cost) and so produces less money than anticipated, their ability to ever live without massive government subsidy becomes an even bigger illusion than it already is.

So, you may say, "It is only a technical glitch 'll all come right in the end."

Well, maybe. But first of all this is a glitch that has lasted since the 1980's

Unfortunately the evidence suggests that nobody actually knows what to fix yet let alone how too fix it. So possibly the answer is - maybe not.

We need to get an idea of how bad this problem is but for obvious reasons the wind industry isn't telling and they are certainly not releasing any meaningful figures

But there are a number of alarming markers out there.

The  US Government (in association with the wind industry) formed a little known group called the "Gearbox Reliability Collaborative" (GRC) (See Here) ** The GRC is no less than a section of the USA government NREL. (That National Renewable Energy Laboratory).

** [2017 - This website is no longer publicly available and returns a 404. The advertising brochure for the GRC is still publicly available at This Link. It appears the research papers linked to below are also still available]

In other words the problem is so bad the US Government is having to tackle the problem.

The leading sentence on the GRC website blandly states...
Premature gearbox failures have a significant impact on the cost of wind farm operations.

To quote from the latest finding report from GRC testing...(Here)
Despite reasonable adherence to these accepted design practices, many wind turbine gearboxes do not achieve their design life goals of 20 years—most systems still require significant repair or overhaul well before the intended life is reached. 

These guys in the NRC are (to put it mildly) clever people. But they have been at this since 2007 and so far they are still, by all appearances, quantifying the problem. In otherwords on a scale of ten, the intractibility of the gearbox issue probably rates a nine.

The NREL does not allocate such significant resources lightly. This is a bad problem.

The GRC are trying to build a failure database as well as running a series of tests on prototype gearboxes. Unfortunately this failure database is not for public consumption and is subject to a strict NDA so we will probably never know the full facts.

Manufacturing members of the GRC can (and mostly do) remain anonymous. One exception is Vestas. While I have little time for any wind industry company at least Vestas appear to be willing to stand up and be identified rather than just pretend their is no problem like the rest.

Of course, while we do not have full access to the database we do have some access to data held within it from the research papers published by GRC

For example, from an early sample set from 2010 and This Paper  covering 37 failures we have this:

Notice that while this early table covers 37 failures there were many more problems found in the strip downs. It looks like the problem is poorly localised and is probably caused by a number of different issues.

So what is the point of this post?

Simply to show that the current fleet of IWTs (yes - whole fleet ) are really not fit for a production environment. They are still suffering intractible and major operational problems and are highly unlikely to ever be able to operate without a huge government subsidy. To suggest they have a lifespan of 25 years is laughable.

This is bad enough for land based turbines.

But anyone who suggests that we can successfully and economically place these things out in the North Sea and English Channel for long term energy generation, is in need of medication.


  1. Excellent post, thanks for this. I've been aware of the gearbox issues, and your research adds meat to the bare bones.

    The first proper computer program I wrote was for gearbox design (On a BBC Micro!), at technical college. It had subroutines which worked out required mass (strength), longevity etc.

    Given the operating conditions of wind turbines; sudden high torques, bearing end loads etc, it's not a surprise to me the experts haven't been able to solve the issues. Laymen (and policy makers) tend to believe the hype that technology can solve any problem. Production engineers know otherwise.

  2. Interesting. The table suggests that the bearings are at least as troublesome as the gearboxes. Any idea why that is? I know the size of the things is problematic, and is the reason that they have to be kept turning (as with propellor shafts on large ships), but AFAIK, ships don't have to have new bearings every five minutes, although they probably have more regular preventive maintenance.

    Perhaps that's the answer - IWT's are just too big to be 'fit and forget', but their maintenance (especially offshore!) is horrendously expensive and difficult.


  3. As a retired mechanicla engineer, I've been banging on along these lines for years - particularly in relation to offshore turbines.
    There is not a cat-in-hell's chance of these things lasting the projected 25 years..

  4. I work on large turbines daily and can confirm it's at least as bad as this article suggests. After working (maintenance) on onshore only for six years, and seeing the multitude of different failures, I got to see my first serious gearbox failure on an offshore turbine in June. I was shocked at the level of corrosion within the gearbox mechanism on a 22 month old machine, but that wasn't the cause of the failure which resulted in the need for a complete new gearbox. The terminal problem was simply caused by resonance. It was only after investigating further I discovered nearly 20% of one manufacturers offshore turbines have suffered from serious failure requiring major gearbox reconstruction within their first 30 months of operation.

  5. Your table suggests that bearings are just as much of a problem, with (I surmise) a similar cause - the machines are just too big.

    Already, they have to be kept turning when there is no wind, in the same way that large ships have to keep their propshafts turning (because of their weight and tendency to 'sag'). Keep a really large ball or roller bearing static and it won't stay properly round, or last, for long.

    All part of the same problem, IMO.

  6. Someone should check whether mineral or synthetic oils are being used in the gearboxes. If they are using mineral oils to save costs then it will come back to bite them.

  7. Reply to Tallbloke... I guess the majority of the issues with IWT gearboxes & bearings is simply related to having large complex machinery operating in a chaotic and constantly changing environment. I don't think the general public appreciates that operating any form of such machinery in similar conditions requires enormous amounts of maintenance along with fail-safe component exchange (before a failure can happen). While this is OK for (say) aircraft it renders an IWT totally impracticable except in niche applications. But try getting that message beyond the green spin...

    Reply to J Bonington Jagworth... I think you hit the nail on the head with why (say) ship gearboxes are more reliable... Lots more preventative maintenance. But of course, maintenance is very expensive. For an IWT to even pretend to be cost effective, maintenance must be minimimal. Sadly as we all know, a minimal maintenance schedule and a chaotically changing operating environment do not mix.

    Reply to Sherlock... I feel your pain. Any engineer with experience of real world applications would scoff at the fairy-land claims made for IWTs. (I suppose the more experience the more the pain ;-)) The trouble is getting the technologically illiterate politicos to understand the issues. Mostly they fall hook line and sinker for the green-wash.

    Reply to Anonymous...Thank you for your brave comment. Your comment is both shocking and enlightening. None of us can turn our backs on this. The only way forward for both energy generation and the development of wind power is to admit the deficiencies and address them before spending billions implementing a (currently) failing technology. Unfortunately the head long pursuit of wind generation is driven by a mixture of greed, wishful thinking and technological ignorance. The only way forward is for honest and capable engineers to follow your example and stand up and tell it as it is. Good luck to you.

  8. Direct Drive only! What?? Too simple???

  9. How is maintenance going to occur safely in stormy weather?What is the maximum wind for working with regard to Beaufort Scale?What percentage of the year do the winds blow above the safe working limit?
    Is there a maximum wave height above which it is too dangerous to move from vessel to wind turbine : if so what is it and what percentage of the year does this occur?

    As turbine blade is moving, is it possible to land by helicopter on platform?

  10. "Industry spin". Gears, Chuckle.

  11. Here's an interesting article:

    A wind turbine might deliver 1.5MW peak. What is the conversion efficiency? 90%? This means there is at least 150KW of waste energy to deal with. This is a mix of electrical and mechanical wattage. It's a huge engineering challenge and it's idiocy to take it lightly.

  12. But the accountants and pols have checked the figures they cannot be wrong look at the revennue they siphon off whether the windmill produces power or not.

    And that sums up every problem the nation has penpushing morons who dont have one iota of common sense, morals or practical ability.
    If accountants were cavemen without a society to parasite from they would sit in the dark with no fire and no food.

    The obvious thing to do when faced with a parasite problem is to rid yourself of such vermin.

  13. I'm not an engineer, far from it however this article and the following comments make it clear these IWT's are too large. Downsize the turbine or consider a vertical blade rather than the centuries old horizontal shaft propeller design.

  14. Someone asked "how is maintenance going to be carried out safely in stormy weather".

    The answer is that it isn't, it took three days and two attempts to get me on to my first offshore turbine in June. I'll admit I'm not fond of boats at the best of times, but it's completely impractical to use a helicopter to transfer personnel to a moving turbine in rough weather, and ship to turbine transfer also has unacceptable risks(not least to the turbine)in rough seas.

  15. "But anyone who suggests that we can successfully and economically place these things out in the North Sea and English Channel for long term energy generation, is in need of medication. "

    Medication?? I don't think so. Regular public whippings would be MUCH more effective.

  16. Hi I see off shore wind turbines are fitted with diesel engines to keep the internals free from condensation, warm and cosy and generating for maintenance.
    Just where are the co2 savings ???
    Oh just off to diesel up the turbines.
    General public are being ripped off big time.


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