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« Communicating the pause | Main | Met Office tweaks the evidence »

Wind power eases off

Readers will remember the ding-dong between Gordon Hughes and DECC's Chief Scientist David Mackay over the rate of decline of wind turbine performance over the years. Hughes had written a paper that suggested that this was significant, with Mackay arguing that Hughes' approach was flawed.

At the time Mackay pointed to a forthcoming paper by Staffell and Green that he said would support his case. This has now appeared in the journal Renewable Energy and it indeed supports Mackay's case.

The Renewable Energy Foundation, who published the original report, have issued a statement that suggests the story is far from over:

This study uses different methods, and though it confirms the finding that performance declines significantly over time, it reports a lower rate, of about 1.6% per year, with “average load factors declining from 28.5% when new to 21% at age 19.” Staffell & Green note that this has the effect of increasing the levelised cost of electricity from wind by 9%.

REF believes that the debate has moved on from whether wind farm performance declines with age, as that is clearly confirmed, to the technical issues involved in measuring the rate and profile of the decline. The Staffell and Green paper proposes an approach that compares actual output with ideal output based on interpolated wind data. The potential difficulties of this specification are outlined in the Appendix to Professor Hughes’s paper and are not resolved in the new paper. Hence, we are not convinced that the Staffell and Green’s approach is superior to the statistical methods employed by Professor Hughes.

In one respect, we believe that the Staffell and Green analysis is clearly inferior to the Hughes specification. Namely, their model does not allow for the effect of technical progress in the wind industry through improvements in operating and maintenance practices, which can be treated separately from changes in turbine design. This was built into the Hughes specification and few would dispute that such technical progress has occurred in the past.

Work carried out by Professor Hughes – and made available to Dr Staffell and Professor Green – shows that the rate of such technical progress has fallen markedly since 2008. The reason this matters is that Staffell & Green and Hughes have both confirmed that specifications that allow for such technical progress yield higher estimates of the rate of decline in performance with age than those, including the new paper, which do not. In statistics this is known as omitted variable bias.

In summary, REF’s view is that while the new paper makes a useful contribution to public discussion of the performance of wind farms, Staffell and Green’s methods are not statistically superior to those used in the Hughes study. Indeed, Staffell and Green’s specification contains an assumption that results in a significant downward bias in the estimate of the rate at which performance declines with age. We will provide fuller details of these points in due course.


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Reader Comments (27)

So in layman's terms, this study gives a different answer to one that superior methods, so laypeople should not take the latest one too seriously.

Feb 26, 2014 at 8:25 AM | Unregistered CommentersandyS

The first paragraph of the abstract, repeated in the intro and conclusion, gives me cause for concern. It is stated that the output/performance of all forms of power generation decline with age. This is not true. Wind turbines have a life of about 20 years and there is no doubt that their performance degrades with time, regardless of maintenance. However, modern conventional generators have lifetimes of about 60 years and ongoing maintenance/refurbishment mean that it is economic to maintain their output at the original design value - indeed, with technological advancements, the output is often increased over time.

Feb 26, 2014 at 8:38 AM | Registered CommenterPhillip Bratby


In your postings on wind power I've seen nothing on oil useage.

So check the comment by IHRunner towards the start of

FYI - Mobil 1 is a synthetic oil and our local dealer'c comment was "The expensive one".

Feb 26, 2014 at 8:44 AM | Unregistered CommenterAnother Ian

Here's a super efficient way to make the most money from your wind farm:

Feb 26, 2014 at 8:53 AM | Unregistered CommenterPaul

Figure 9 (b) is very revealing. Manufacturers of wind turbines usually quote a design life of 20 years. Figure 9 (b) shows that at about 18 years turbine performance falls off a cliff (it wouln't look quite so bad if the origin was shown).

Feb 26, 2014 at 8:56 AM | Registered CommenterPhillip Bratby

"Wind turbines have a life of about 20 years and there is no doubt that their performance degrades with time, regardless of maintenance."

That does seem hard to argue with. DECC presumably were under the impression that they kept working at full output until the last moment, when they would just stop!

Feb 26, 2014 at 8:57 AM | Registered Commenterjamesp

Paul: We've known about the scam for nearly 2 years now. The government has done nothing about it, despite all the promises (sounds familiar).

Feb 26, 2014 at 8:58 AM | Registered CommenterPhillip Bratby

Though the point may seem arcane to anyone outside the power industry, is the decline from decreased availability or just deterioration of the plant? Basically, does it break down more or can the old plant just not produce the same power under the same conditions as it could when new. This would be a different answer for each machine type. Chinese experience seems to be about a third never run. Whether this is from poor QA and they erect duds to meet targets, or just no use for the power I don't know.
The reason is that the first can possibly be addressed by new technology retrofitting key components like the hub bearings, while the other is beyond hope. The latter generally happens because it has been built too cheaply and would need near total replacement to bring it back. With the emphasis on lowering costs, this would new plant has an even shorter life expectancy than those of 10 years ago.
From what I have read and seen, wind turbines mostly seem to just break down from the failure of critical components. This means they sit there until a large crane can be mobilised to repair them. That sometimes means having to wait until a number are dead to minimise crane mobilisation costs.
Whatever the reason, it is lunacy relying on them for power.

Feb 26, 2014 at 9:09 AM | Unregistered CommenterChrisM

ChrisM: You will find the reports are somewhat speculative about the reasons. Part is due to gradual degradation of the surface of the blades (cracking, pitting, erosion, dirt build-up) which reduces aerodynamic efficiency. Part is due to mechanical wear of eg gearboxes, bearings, due to the huge and varying stresses. Part is due to poor maintenance and long breakdown times. Your last sentence says it all, but your Government disgrees.

This report only considers onshore wind trubines. The problems are much worse for offshore turbines> This may explain why several proposals for new offshore wind farms and extensions to existing ones have recently been pulled. Developers may at last be realising that the turbine manufacturers and the wind industry (RenewableUK etc) have for years been lying about wind turbine performance.

Feb 26, 2014 at 9:18 AM | Registered CommenterPhillip Bratby

Thanks for that Phillip but to correct you, I'm from NZ. We have them here at a lot higher load factor (up to 45% I believe) but there are just as many dead.
Rather than speculation, it would nice to have real data. What is really needed is the GADS info as that will give the true outage times. Anything that isn't outage would be deterioration.

Feb 26, 2014 at 9:24 AM | Unregistered CommenterChrisM

In essence what these guys are arguing over is the windmills will go from delivering f&c£k all powerhouse even less that f&@k all over the course of a few short years.


Feb 26, 2014 at 10:23 AM | Unregistered CommenterMailman

Turbines in power stations rarely stop turning. Even if they are not currently generating electricity they are turned slowly and maintained at the same temperature so as to protect the shaft and bearings from any damage. They are physically monitored 24 hours a day and minor maintenance, even if it is just topping up the oil, can be carried out instantly. This extends the life of the turbine and keeps it as efficient as possible.

Wind turbines, on the other hand, turn intermittently, have a great big weight on the end of the shaft, can have daily temperature swings of 25-30C and are seldom physically inspected. This will result in a degradation of the shaft and bearings. Bearing this in mind, the figure of 1.6% per annum seems low to me.

Feb 26, 2014 at 10:38 AM | Unregistered CommenterTerryS

"just as many dead" (ChrisM)

Am I right in thinking that the dead/defunct/taken out of service ones are excluded from the DECC stats? It would explain why their figures are so low!

It reminds me of the oft-quoted figures for life expectancy in undeveloped areas or those with high infant mortality. The averaged results suggest that adults die early, although what really happens is that a few make it happily into old age (Robert Mugabe for scary example), but high levels of younger deaths skew the figures. Victorians didn't all drop off the twig at 45 - they just lost a lot of children...

Feb 26, 2014 at 11:20 AM | Registered Commenterjamesp

They don't like strong winds either. A few were seen in flames after the past storms. Ther should automatically ''feather'' when the wind speed exceeds the maximum but sometimes this safety system fails with brilliant results.

Another point for King Coal.

Feb 26, 2014 at 11:24 AM | Unregistered CommenterJohn Marshall

The reality is, if the critique above is to be believed, that we are to be *happy* that a megawatt of wind turbine rating only delivers, optimistically, 28% of that megawatt. Is that 280kw at the turbine, or delivered to the grid? The way wind promoters consistently behave, I bet it is before the extensive power cleaning that must be done to get the power from turbine to grid in a form that has the quality needed for a grid.

Feb 26, 2014 at 11:39 AM | Unregistered Commenterhunter

A presentation made to the German wind industry associations about the financial return of wind farms, in particular those which are community owned, has demonstrated that the reality has been very different from the theory used to justify the initial investment:

(a) The actual electricity produced has been significantly lower, on average only 86% of what has been claimed for in the investment decision.

(b) The operating costs have been much higher due to more maintenance, etc, amounting to some 27.5% of the yields from electricity sales.

The study related to the evaluation of 1,150 wind park annual accounts in which the investors in the years 2002 to 20011 have received dividends in average of 2.5% per year. Over the sum of the years this was 25% of their investments, while according to the sales literature 60 to 80% had been promised. A differential analysis results in a more catastrophic picture.

• 25 of 127 of the wind farms have indeed no dividends > 2% = 20%

• 22 of 127 of the wind farms have only provided dividends in 1 year = 17%

• 27 from 127 wind farms have only provided dividends in 2 years = 21%

As the study concluded:

1. Around half of all commercial onshore wind parks run so poorly, that as a result their investors could be pleased, if after the 20 years their investment capital could be got back.

2. Community wind parks have the same problems as commercial wind parks. However, as they as a rule had more favourable manufacturing costs and lower bank debts, the chances of their investors for a small return on investment are somewhat better.

Feb 26, 2014 at 12:29 PM | Unregistered CommenterPat Swords

Turbines? - I'm not a big fan (though I have a mini wind-farm riveted to the roof of my car for reliable, predictable power).

Feb 26, 2014 at 12:36 PM | Unregistered CommenterAlan Reed

Noe of this takes into account the effect of 'wind shadow' - which creates a situation where, over time, the actual 'amount' of wind in the vicinity of a large wind farm decreases. This phenomenon resulted in a paper by the Emiritus Professor of Physics at Harvard (no less) - who's name escapes me. This was reported on a few months ago in my 'trade' journal (Professional Engineering). I've never seen any counter-argument - even by Renewables UK...

Slightly off-topic - but relevant to the whole scam of course - there's a fascinating row going on in Peterborough City Council over a plan to cover a huge area of prime agricutural land which the Council owns and which is farmed by tenant farmers - with solar panels. The Chief Executive is vehemently in favour (can't think why) especially as the Councils own Scrutiny Committee say the figures don't add up..! And the purpose of a Scrutiny Committee is...??
The solar farm will (allegedly) produce enough electricity to power 7000 homes (on a sunny afternoon in July, when the power isn't needed) as opposed of course to a Big Fat Zero at four in the afternoon in December (when it is needed)...
Draw your own conclusions...

Feb 26, 2014 at 2:09 PM | Unregistered Commentersherlock1

sherlock1: "None of this takes into account the effect of 'wind shadow' - which creates a situation where, over time, the actual 'amount' of wind in the vicinity of a large wind farm decreases."

Presumably you're referring to the paper summarized here, which cites a conclusion, "Keith believes the peak generating capacity of windfarms larger than 100km2 may therefore be between 0.5 and 1W/m2, considerably lower than previous estimates of between 2 and 7W/m2."

The paper itself isn't linked there (tsk, tsk), but is presumably this one.

Feb 26, 2014 at 2:41 PM | Registered CommenterHaroldW

I tried to look at the data in BP's Statistical Review of World Energy - an invaluable repository of energy data, mostly culled and compiled from official sources. It gives figures for installed capacity and power production for wind by country annually.

What immediately becomes clear is that the statistics are fudges, or at least from incompatible sources. There are implausible swings in utilisation, even after accounting for years in which capacity grew rapidly. Some reported implied utilisations are obviously false (as high as 98% over a year!). I suspect that in some cases, output has been deemed rather than measured (just as it is with some simple solar installations for example).

It seems there is an effort to hide reality from public view working in many countries across the globe. Reported average utilisation over the period 1997-2012 ranges from 13.8% in China to 36.5% in New Zealand (the "true" numbers will be higher than this because capacity is as at year end).

China is an object lesson:

China's renewables industry is headed for collapse

Feb 26, 2014 at 5:04 PM | Unregistered CommenterIt doesn't add up...

The study from Germany seems very powerful. Surely there are equivalent analyses for Denmark which is even more heavily dependent on wind generated power - in terms of economic returns, full lifetime cost data and equipment degradation.

Feb 26, 2014 at 8:01 PM | Unregistered Commenterbernie1815

"However, modern conventional generators have lifetimes of about 60 years and ongoing maintenance/refurbishment mean that it is economic to maintain their output at the original design value - indeed, with technological advancements, the output is often increased over time." Phillip Bratby

I always thought the foresight of putting conventonal turbines in a building with a bloody great crane, locating the building near places where contractors and employees might hang out had to be an advantage over wind turbines.

Feb 26, 2014 at 8:32 PM | Unregistered CommenterTinyCO2

HaroldW - yes, that's the one - thank you - sadly I'm not very good at links...

Feb 27, 2014 at 1:28 PM | Unregistered Commentersherlock1

Philip Bratby/TinyCO2 - fully endorse your views on the true viability of conventional generators (indoors) versus wind turbines (far away and outdoors) - myself being ex-Hinkley Point 'A' as a boy engineer in maintenance planning...
There is, frankly, no contest...

Feb 27, 2014 at 1:35 PM | Unregistered Commentersherlock1

Noticed a couple of interesting articles in German press Die Welt, apparently even with marginally reduced subsidy offshore wind is not worth pursuing. Investors are coming up with negative Net present values. What a surprise? I suppose they have also noted the drastically reduced anticipated lifespan and the horrendous OPEX figures. Adequate translation in Chrome for non German speakers

Feb 27, 2014 at 5:02 PM | Unregistered CommenterJRM Wheel

A lot of the fall off will be due to deterioriating surface of the blades, but that is a much bigger problem for 20 year old small (2-500kW) turbines than for newer bigger blades that are 2-4 times the dimensions (depends on relative scale of the roughness to the blade)

Feb 28, 2014 at 6:37 AM | Unregistered CommenterRobL

In the meantime, now that the UK weather has gone all - er - normal, I see that wind is back down to producing around 1% of (what is relatively low) electricity demand...

Off-topic - and I hate the things with a passion that borders on irrational - but have no developers ever thought to paint wind turbines a sort of bluey-grey..?

Mar 1, 2014 at 2:20 PM | Unregistered CommenterSherlock1

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