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A story of decline

Gerard Wynn at Reuters reports on the performance of windfarms, both on and offshore, in the UK. It is not a pretty sight:

Garrad Hassan's report, "Offshore wind: Economies of scale, engineering resource and load factors", sought to "provide a supported opinion on the likely load factors for offshore wind power in the UK Round 1 and 2 offshore wind farms".

Government studies have since cited it as a reference.

The report calculated a range of load factors from 33 to 38 percent, for wind speeds ranging from 8.5 to 9.5 metres per second (See Chart 4).

Actual annual average load factors in fact only passed 35 percent for the first time last year, according to the Department of Energy and Climate Change's (DECC) "Digest of United Kingdom Energy Statistics 2012".

For previous years they were in the range 26-30 percent, or 28-35 percent depending on whether they are measured including or excluding turbines under construction.

More recent data show that load factors this year dipped back below the bottom end of the Garrad Hassan range.


The full article is here, and is well worth a look. It appears that "wake losses" i.e. losses from some turbines being in the wind shadow of others, are the problem.

Bigger windfarms required I guess.


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Reader Comments (31)

Wouldn't bigger windfarms create bigger wake losses? Sounds like smaller is better.. :-)

Dec 13, 2012 at 3:34 PM | Registered Commenterjamesp

Some minor inaccuracies in the Reuter's article. 18GW by their own figures will deliver 6GW which is not 20% of our supply. Currently electricity usage is 52GW. The proposed 33GW will likely deliver 11GW which is about 20% usage. Presumably, on-shore windmills will be added to that potentially giving 30% of our supply. That is when 'balancing the grid' poses serious problems with under or over supply depending on the vagaries of the wind.
I look forward to Philip B. instructive comments.

Dec 13, 2012 at 3:55 PM | Unregistered CommenterG.Watkins

I seem to recall that turbines in the "downstream" part of the arrays also incur a significantly greater amount of downtime. Stresses are increased by the turbulent air stream. Wrong type of wind?

Not sure they have chosen their terminology well with "wake". I have always been of the opinion that wind farms were deserving of a good "wake":-)

Dec 13, 2012 at 4:05 PM | Unregistered CommenterGreen Sand

"Bigger windfarms required I guess."

No, fewer turbines.

Dec 13, 2012 at 4:41 PM | Unregistered CommenterJoe Public

Just for fun I've been monitoring how much electricity has been generated over the last couple of cold days (since 14:30 on 11th).

14% of the time it has been below 5% metered capacity (<265MW)
55% of the time it has been below 10% metered capacity (<530MW)
86% of the time it has been below 15%
98% of the time it has been below 20%

In fact it is only in the last hour that it reached the 20% mark.

It is just as well we don't need as much electricity on cold days.

Dec 13, 2012 at 4:43 PM | Unregistered CommenterTerryS

Within the Reuters Report:
The first link to CHART ONE is actually a full report by renewable energy consultancy Garrad Hassan in 2003. During this report they point out that they have absolutely no previous experiences to inform them since no country tried anything like this before. Despite having nothing to go on they then come up with a huge thumbs up for reducing the predicted costs of both building and maintaining the wind farms, clever guys these.

Dec 13, 2012 at 4:48 PM | Registered CommenterDung

"Bigger windfarms required I guess."

Each tower taller than the one in front...

Dec 13, 2012 at 4:49 PM | Unregistered CommenterJohn in France

This reminds me an amazing photo of 'wake effect' on an off-shore wind farm that I saw way back. A quick google image search and, voila, here it is again.

Dec 13, 2012 at 4:51 PM | Unregistered CommentersHx

My analysis is based on 26% average Capacity Factor convolved with a 30% loss because by 2020, according to the NGC, wind farms will be disconnected 11% of the time to save the grid transformers.

That means ~18% CF. The industry and the consultants claim much more when it is unreal.

Dec 13, 2012 at 4:52 PM | Unregistered CommenterAlecm

I have a Garrad Hassan report for an onshore wind farm where they quote wake losses of about 5%. One would expect bigger wake losses for huge offshore wind farms because of the nature of the wind flow. Average wind speeds have on average been dropping for the last several years (blame it on climate change). There are a lot of other losses that have to be taken into account (up to 10%) but one thing is pretty certain, breakdowns will be more frequent offshore and maintenance and repair will take longer and be more expensive.

There is no real surprise that the performance is less than expected. RenewableUK (BWEA) and the wind industry in general have been exaggerating the performance of wind turbines for years and the Government has bought into the industry lies. I've seen more than one application for onshore turbines that have claimed expected capacity factors of over 50%!

Dec 13, 2012 at 4:53 PM | Registered CommenterPhillip Bratby

Mrs J has come up with the suggestion that the way round the wake problem is for the specs to call for "each turbine to be higher than the others".
I'm sure some of our wind fans could devise a way of making that possible! RenewablesUK might like to look at a research grant!

Dec 13, 2012 at 5:16 PM | Registered CommenterMike Jackson

The problem with Mrs J's suggestion is that the wake spreads out (as you can see in the photo of sHx) and so the downstream turbines would have to be very high. Furthermore, when the wind changes direction then it gets really complicated deciding the relative heights. All turbines would need to be built on telescopic towers so that they could be adjusted to suit the wind speed and direction. Big research grant needed.

Dec 13, 2012 at 5:31 PM | Registered CommenterPhillip Bratby

Thanks for that, but I'm not quite 100% certain that you've read what I wrote!!
In case it still eludes you, Mrs J has a wicked sense of humour.

Dec 13, 2012 at 5:50 PM | Registered CommenterMike Jackson

This is hardly unexpected.

Research back in the 1990's found that a distance of 15 blade diameters between towers was necessary to avoid turbulence effects. (sorry, no link). The distance of 7 blade diameters was a compromise (reducing the cost of cables, connection, 'land' costs).

As the photo shows the rows of turbines in Horns Rev 1 are affected by those in front. It was claimed that removing row 6 (of the 7) would actually increase the output of electricity. This wasn't done, possibly due to the heavy load of maintenance trying to keep the turbines operational.

A single row of turbines at 90 degrees to the prevailing wind direction would seem the ideal solution, but experience at Albany, W.A. proves otherwise.
For the benefit of those unfamiliar with that farm, it consists of 12 x 1.8MW units in a row, on a peninsula. The land is gently sloping fore and aft, giving elevation above sea level turbulence, and situated between 2 rounded hills supposed to divert extra wind through the gap. The line runs NW to SE across the prevailing SW wind from the ocean. Don't know the directionality of the wind but 70%+ is likely.
The original figure for Capacity Factor was 40-41% and perhaps unwisely available from the site plaque.
Actual CF figures are not published, but are 31-33%. See

Dec 13, 2012 at 5:55 PM | Unregistered CommenterGraeme No.3

John in France

"Each tower taller than the one in front.."

And how does one designate which ".....will be the one in front.." ????

Dec 13, 2012 at 6:13 PM | Unregistered CommenterJoe Public

"All turbines would need to be built on telescopic towers so that they could be adjusted to suit the wind speed and direction. Big research grant needed."

Requires some unconventional thinking I believe. I'm sitting on my computer chair which has gas damping, allowing you to raise and lower the chair without any effort. Given the massive resources of shale gas off- and onshore, it could be used to raise and lower the business end of the windmills.

Here concludes my application for funding and, if I may be so presumptious, my Nobel prize submission.

Dec 13, 2012 at 6:45 PM | Unregistered Commenterstun

Unfortunately the obvious solution to the problem of wake losses would be to spread the turbines out over a larger area. In the case of onshore wind turbines that would mean despoiling an even larger area of our countryside.

No doubt the Greens would consider that a price worth paying.

Dec 13, 2012 at 7:10 PM | Unregistered CommenterRoy

'When Esbjorn Wilmar, of Infinergy, which builds and operates turbines, introduced himself to the Duke (of Edinburgh) at a reception in London, he found himself on the end of an outspoken attack on his industry. “He said they were absolutely useless, completely reliant on subsidies and an absolute disgrace,” said Mr Wilmar. “I was surprised by his very frank views.” Mr Wilmar said his attempts to argue that onshore wind farms were one of the most cost-effective forms of renewable energy received a fierce response from the Duke. “He said, 'You don’t believe in fairy tales do you?’” said Mr Wilmar. “He said that they would never work as they need back-up capacity.” One of the main arguments of the anti-wind farm lobby is that because turbines do not produce electricity without wind, there is still a need for other ways to generate power.'

Probably everyone has heard that. But how about arch global warming alarmist Charles?

'The Prince of Wales believes that wind farms are a "horrendous blot on the landscape" and that their spread must be halted before they irreparably ruin some of Britain's most beautiful countryside.
The Telegraph can reveal that Prince Charles, who has an abiding interest in environmental issues, has told senior aides that he does not want to have any links with events or groups that promote onshore wind farms.'

Dec 13, 2012 at 7:20 PM | Registered CommenterPharos

Given that turbines use what is basically a damn great propeller, you would think the proponents would know a little more than they appear to about wake turbulence. In virtually any aviation situation wake turbulence (or vortices) are to be avoided - those who've got too close to the plane in front often find out the hard way. Commercial aircraft are categorised according to weight and wing design - the greater the vortices, the greater the separation distances are recommended. Bigger turbines will need to be further apart. The only way to avoid this disturbed air would be to have them in a single row, but that isn't going to be much use unless the wind direction remains constant and predictable. The report of the Horns Rev site investigation went into some detail of the cumulative affects on the turbines behind the front row. IIRC there was more than 50% loss of output at the furthest down wind units.

Dec 13, 2012 at 7:21 PM | Unregistered Commenterdave ward

If I comment on your comment, can I claim a Nobel prize too?

Dec 13, 2012 at 7:40 PM | Unregistered CommenterMessenger

This is easily solved by placing the wind farm on a lattice with each corner attached to a hydraulic pump so it can be raised or lowered as needed when the wind changes.

Obviously this will require power, so you need another wind farm nearby to power the raising lattice.

Dec 13, 2012 at 9:15 PM | Unregistered CommenterMrPotarto

A relevant side comment over at GWPF -

Phillip Bratby - you have sir commented in the past on the (probably unmeasured) amount of electricity used by a turbine for a number of functions before we get any useful output at all; probably at best purchased at base cost, possibly not paid for at all. Do you have a feel for whether this amount of "loss" will be more or less for offshore as opposed to onshore?

Looking at how little output has been available in the link above, it is surely possible that 0.6% is a wide exaggeration when the electricity used to operate the turbine is taken into consideration.

Dec 13, 2012 at 10:30 PM | Registered Commenterretireddave


The gas damping on my computer chairs usually lasts 2 - 3 years, would your research grant allow you to improve on that?
By the way; sod the wind farms I just need better chairs ^.^

Dec 14, 2012 at 12:28 AM | Registered CommenterDung

With these regimented wind farms do the turbines all turn in the same direction? I was wondering if a contra-rotating turbine on the back side of each nacelle would help but then you'd never get a helicopter near it to drop off the maintenance people.


If you used water in hydraulic accumulators to lift the turbines you could use it as a pumped storage system.

Dec 14, 2012 at 12:39 AM | Unregistered CommenterGareth

Reading the report from Harrad Hassan I am dumbfounded by the lack of specificity in cost estimates. How in the world can any self-respecting government engage in such a dubious enterprise, at taxpayers' expense?!

Dec 14, 2012 at 6:11 AM | Unregistered CommenterJBirks

The non-application of economies of scale have been known for some time regarding wind turbines. The amount of energy that can be harvest is dependent on the circumference of the blades - hence the development of larger turbines. The problem is that the larger the turbine, the greater the eddy caused which is why the recommendation is that spacing between turbines should have a squared relationship to its size to maximise efficiency.

Its not just the wind speed that's important but the quality of the wind sheer.

Dec 14, 2012 at 10:57 AM | Unregistered CommenterLiT

I've got the answer.
Get someone at the Department of Energy and Climate Change to change the climate, so that wind blows from everywhere at once.

Dec 14, 2012 at 1:24 PM | Unregistered CommenterDavid

Seriously, folks...
As a retired mechanical engineer who spent much of what is laughingly-called a 'career' trying to keep production machinery going indoors and miles from the sea, I have grave doubts about the long-term viability of off-shore wind turbines.
Ships and (e.g.) oil rigs, have maintenace crews aboard, who can quickly carry out repairs - or switch to 'back-up' systems etc. Wind turbines are stuck out there in what can be ferocious weather conditions; any repairs requiring at least benign sea conditions, and more serious repairs also requiring a floating crane.
I predict that offshore turbines in UK waters will start failing after five years; and whole farms will be abandoned (when it gets too expensive to repair them) after twelve years.
Also - how long before there's a collision with a ship which has lost power..?

Dec 15, 2012 at 12:50 PM | Unregistered CommenterDavid

David - look at the abandoned early turbines in the US. IMO operators should be obliged to pay into a ring fenced decommissioning fund.

Dec 15, 2012 at 1:28 PM | Unregistered Commenternot banned yet

Actually, just as a guess,mounting the turbines in a circle might be the best way to use the space efficiently while minimising turbulence. Of course it would all depend on selecting the proper diameter of circle to match turbine blade size.

Dec 17, 2012 at 11:47 PM | Unregistered CommenterJoe Crawford

Please tell me where these cradle to grave figures are incorrect.
Because at the electricity production cost you could still sell power at a profit.

Project: Single wind turbine (800kw)
Location: Balloo Wood, Bangor, Co. Down, Northern Ireland
Turbine: 800kw Enercon E48
Dimensions: 56m hub height, 24m blade length, 80m overall height
NGR: 350760E 379503N (lat 54.6411N, long 5.6656W)
Status: Operational

build £ 889,650.00 install
planning etc £ 434,583.00 install

maintenance 0.0055 perkwh
maintenance/year for delivered 280kwh £ 562.49 per year
routine expenses £ 30,000.00 per year
rating 1000 kwh
load factor 28%
deliverd power 280 kwh

Balancing Cost £ 0.014 per kWh
Short term Reserve £ 0.007 per kWh

total install cost= £ 1,324,233.00
install cost/delivered kwh £ 4,729.40
conventional backup costs/year £ 51,544.08 per 280 kWh/year
running cost/year £ 82,106.57 per 280 kWh/year

over n years 25
total install over 25 yrs £ 1,324,233.00
running cost over 25 yrs £ 2,052,664.13
total cost over 25 yrs £ 3,376,897.13
decomissioning cost (guess=.5*build) £ 444,825.00
total cradle to grave cost £ 3,821,722.13
power generated over 25 yrs 61362000 kWh

cost per kwh over 25 yrs £ 0.062 per kWh

most data from

This seems a reasonable figure but the decommissioning costs are pure guess work. The life time of most wind turbines is believed to be 25 years. The warranty period is 12years for this turbine.


Then please tell me how windpower affects the price of oil/gas/coal - these have increased in price faster than electricity.

Dec 18, 2012 at 12:52 PM | Unregistered Commenterthefordprefect

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