Wind speed law

Posted: February 21, 2015 by tchannon in weather, wind

I decided to show something useful instead of waiting until perfect data is available.


Frequency plot of wind speed over the whole of the UK. The characteristic is logarithmic.

There are data problems, ignore this please[1].

The Met Office in common with all national meteorological services continue to use cup anemometers rather than eg. ultrasonic This is the advice[2] from WMO (World Meteorological Organisation) specifically to maintain continuity of data for climatic purposes since there are significant differences between cup and other types.

You will notice the law fails at low and high speeds.

The low is about instruments having a low limit on proportionality and about low speed aerodynamics, the way air behaves.

At high speeds the cause is less clear but I am sure it is primarily about the over-speed problem of cup anemometers combined with the growing depth of boundary layer turbulence.

The over-speed is caused by a difference in the acceleration and deceleration rate under non-steady wind conditions, where there is a tendency to over-read. A further problem is when the wind alignment is not horizontal, as happens in turbulence. There are many papers on these kinds of effect.

Very high wind speeds are under-represented. Under severe storm weather stations tend to fail, either instrument damage or often communication failure. I suspect this has no material effect on the result.

Wind power generation

Power generators generally start producing at about 10 mph, reach rated output at about 30 mph and shut down at some point higher than that.

The sites chosen have high wind speeds but the law will be the law.


Image from and annotation with mph conversion
Using meteorological wind data to estimate turbine generation output: a sensitivity analysis
M. L. Kubik 1,* , P. J. Coker 2 , C. Hunt 3

This agrees with what I remembered as typical figures.

Given the logarithmic wind speed frequency it is obvious why wind turbines operate at a small fraction of their maximum rating for most of the time.

Gust speed also follows a log law.

1. To the best of my knowledge.

A problem was identified with the supplied data. After extensive investigation here a support ticket was raised during January. Support have now escalated the matter.

Hopefully when the problem is fixed I will be able to get replacement correct data and post again showing the real thing.

Give them time.

Met Office do not provide access to archived data (at BADC) except for formal academic work, why I am creating an archive here.

The plot is minimising visible effect, there are missing points.

2. WMO

This paper is useful. A great deal of literature exists.

Intercomparison of cup anemometer and sonic anemometers on site at Uccle/Belgium
Luis Gonz´ alez Sotelino, Nicolas De Coster, Peter Beirinckx, Pieter Peeters
Royal Meteorological Institute of Belgium

Post by Tim

  1. Petrossa says:

    Reblogged this on Petrossa's Blog and commented:
    Unfortunately this will not stump ‘the energy for nothing’ exponents whose deep seated beliefs overcome all logic and facts. As long as governments pump billions into the wind industry in the mistaken belief that it generates longterm employment no amount of pointing out the obvious will help. But thanks for the clear and simple piece, it at least shows yet another main problem with wind energy.

  2. Joe Public says:

    That’s an interesting visualisation, Tim. Thanks.

  3. Wayne Job says:

    Being an old aircraft engineer, old prop aircraft are wonderful, but the only real success of wind generators was in the 1930’ties a Mr Jacob i believe made very efficient and long life examples.

    They were DC and did not need exotic elements, they were also totally reliable over long periods, the yanks put one on their first Antarctic base, going back about twenty years later it was still working.

    Propellors became inefficient when jet engines arrived on the scene, the pioneering of Jacobs was the basis of modern prop design for aircraft. This design criteria for wind generators is 85 year old technology with computer control, the old stuff was OK until about 60kts then feathered off.This new stuff is a bit pussy.

    The only way wind generated power will ever be reliable is huge ducted fans tethered in the jet stream, as that is between 28 and 50,000 Ft up that would require some serious sky hooks.

  4. John de Melle says:

    Petrossa:- You note “As long as governments pump billions into the wind industry in the mistaken belief that it generates longterm employment …..”

    I have a Wind Farm a few kms from where I live. It is not often that I pass it and not seeing a white van at the base of one of the towers, with someone doing some maintenance. These two technicians do have long-term employment.

  5. Kelvin Vaughan says:

    We don’t get heatwaves like this anymore.

  6. Kelvin Vaughan says:

    or this

  7. tchannon says:

    A quick look at what the wind turbines would do.

    Reverse engineer the V80 plot, easy.
    Taken time series of hourly wind from on disk here, plug together.

    Where is sensibly windy?
    Try Lerwick, average output 36% of maximum rating and of course there is an output time series. (37% if it doesn’t cut out)

    Where is not windy?
    Try Kew Gardens, average output 0.004%

    Where is hell on earth?
    Try Cairngorm summit, average 53% (68% if it doesn’t cut out) Have to be the version for cold and ice too.

    (all are common average)

    I could program this up to do all stations and then lots more could be figured out to see how it fits with what actually seems to be happening.

    What I am doing is not strictly fair nor entirely representative, can think of various objections but then I also know of additional loss factors such as geographic, grid losses are considerable.
    Amortisation, maintenance, oops.

    The pregnant question is how come I can do this but government with vastly more resources had not done it, published and acted upon? Or have they, if so show me.

  8. tallbloke says:

    Thanks for this Tim. The Ed Hoskins post on European renewables I’ve just reblogged says it all too. Offshore wind around 35 times more expensive than gas fired generation. And that’s before you build the cables and lay them.

    Our government needs locking up.