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How Volatile Is Offshore Wind?

March 17, 2022

By Paul Homewood


Offshore Wind Turbines

It is commonly claimed that the wind is much more constant and reliable in the North Sea and around Britain’s coasts than it is inland. “The wind always blows!”

But how true is this?

The Low Carbon Contracts Company, who manage the CfD system, provide daily data for generation by all generators with contracts. In particular there are sixteen offshore wind projects on their database, which offer a good geographical spread. They account for about a half of total UK offshore generation:


I have analysed January 2022 data for these, and below is the daily output:


Far from being “constant”, we can see that wind power is extremely volatile. Daily production ranges from 8322 to 84984 MWh, with a monthly average of 49245 MWh.

There were thirteen days when output was below 45000 MWh, in other words more than 10% below average.

There were seven days in the month when it failed to reach 25000 MWh. The average for those days was 17000 MWh, equivalent to them working at 15% of capacity. The worst day, when output was 8322 MWh, offshore wind was only operating at only 7% of capacity.

Bear in mind as well that this is winter, not summer when you might expect low wind speeds.

We have been promised 40 GW of offshore wind by 2030, but in reality the most we can actually rely on is 3 GW.

  1. Chris Reynolds permalink
    March 17, 2022 12:21 pm

    Wind mills look like tempting targets for a missile attack or special forces demolition squads…

    • JBW permalink
      March 17, 2022 12:32 pm

      Perhaps flying over and covering them with carborundum powder might be enough to gum up the works. 🙂

    • JBW permalink
      March 17, 2022 12:32 pm

      Perhaps flying over and covering them with carborundum powder might be enough to gum up the works. 🙂

    • March 17, 2022 9:32 pm

      Perhaps more vulnerable are the cables bringing the leccy on shore. One “accidentally” dragged anchor might cause trouble.

    • Phoenix44 permalink
      March 18, 2022 9:15 am

      Why bother? Just hack the system. No electricity from anything.

      • Ray Sanders permalink
        March 18, 2022 2:17 pm

        “Just hack the system” Yep quite possibly easier than most think. Hack into roof mounted solar grid tie inverters, or smart meters or even Economy 7 signalling…the list is quite lengthy. “Control your home from your phone” was the Hive advert – more like have your system controlled by any half decent geek with a laptop. Here’s just one of them

  2. Gordon Hughes permalink
    March 17, 2022 12:27 pm

    In fact your figures are too optimistic. I am preparing a paper that examines wind conditions for every wind farm across the whole of GB using 20+ years of satellite data. If you apply National Grid’s mandated reliability standard the amount of firm power from the entire wind fleet is about 3% of total capacity. That means, in effect, that the entire fleet has to be backed up by an almost equal amount of non-wind dispatchable generation if the reliability standard is to be maintained. The inevitable conclusion is that system reliability is going to be reduced by a lot, almost certainly without publicity and/or by sleight of hand, as more wind capacity is connected to the system.

    • Gerry, England permalink
      March 17, 2022 1:15 pm

      That is the fundamental problem with unreliable wind generation – you need a generating system of double the capacity. Which, surprise surprise, costs much more than a single reliable generation system. And on top of the plant costs you have the juggling costs of trying to keep the whole farcical thing from collapsing when the wind stops suddenly.

    • March 17, 2022 2:03 pm

      See also my discussion of Drew et al 2015 at Cliscep:

      I shared this quote in that piece, because I found it extraordinary:

      …the decarbonisation of the energy system is one of the most important climate challenges that we face at the moment, but what happens is as you increase the amount of renewables that you have in your energy system, erm, you’re also increasing the vulnerability of that system to adverse weather conditions.

      And what’s interesting about this is that these weren’t adverse weather conditions ten years ago, this was just nice, pleasant weather. It’s because we’ve got more and more wind power in the system that what we need to do now is think about ways in which we can strengthen that system and make it more resilient.

      –Met Office’s Tom Butcher on Inside Science, R4, 23.ix.2021

      • Ben Vorlich permalink
        March 17, 2022 3:07 pm

        So now a high pressure with low wind and warm sunny days in summer and freezing nights in winter is adverse weather.

        That takes the biscuit.

    • Rod permalink
      March 17, 2022 11:57 pm

      I think a key investigation is available power during peak demand, say 5 to 9 pm. As a long time sailor, especially near costs, teh wind drops as the sun goes down, unless a weather system is moving through. Peak power is always the most expensive to produce.

      • Phoenix44 permalink
        March 18, 2022 9:24 am

        If you are a nuclear power station there’s no difference whatsoever by demand.

    • dennisambler permalink
      March 18, 2022 10:35 am

      Eon-Netz Wind Report from 2005, said this,
      “Their dependence on the prevailing wind conditions means that wind power has a limited
      load factor even when technically available. It is not possible to guarantee its use for the continual cover of electricity consumption. Consequently, traditional power stations with capacities equal to 90% of the installed wind power capacity must be permanently online in order to guarantee power supply at all times.

      An objective measure of the extent to which wind farms are able to replace traditional power stations, is the contribution towards guaranteed capacity which they make within an existing power station portfolio.

      Approximately this capacity may be dispensed within a traditional power station portfolio, without thereby prejudicing the level of supply reliability. In 2004 two major German studies investigated the size of contribution that wind farms make towards guaranteed capacity. Both studies separately came to virtually identical conclusions, that wind energy currently contributes to the secure production capacity of the system, by providing 8% of its installed capacity. As wind power capacity rises, the lower availability of the wind farms determines the reliability of the system as a whole to an ever increasing extent.

      Consequently the greater reliability of traditional power stations becomes increasingly eclipsed. As a result, the relative contribution of wind power to the guaranteed capacity of our supply system up to the year 2020 will fall continuously to around 4%. In concrete terms, this means that in 2020, with a forecast wind power capacity of over 48,000MW (Source: dena grid study), 2,000MW of traditional power production can be replaced by these wind farms.”

  3. March 17, 2022 12:54 pm

    I presume the figures quoted are gross output at the windmill. I wonder how much power is lost when line losses are included before it gets to the Grid and how much is lost by way of parasitic power to keep the windmills functional on cold or windless days.

  4. AC Osborn permalink
    March 17, 2022 1:53 pm

    Although I am very anti Wind & Solar I am quite impressed that thye managed to get up to just over 70% of capacity at times and averaged 41%.
    That appears to be better than onshore.

    • March 17, 2022 3:34 pm

      Bigger turbines in windier locations but more expensive to install and maintain, plus longer transmission lines (undersea of course, which has its own hazards).
      – – –
      The total figure for payments to demand reduction volunteers is going to keep getting bigger in step with the growth of market share for unreliables. Also meaning more demand reduction will be called for, obviously.

  5. Ben Vorlich permalink
    March 17, 2022 2:55 pm

    The photo in this article is probably the most depressing I’ve seen for a long time.

    • Tom Welsh permalink
      March 19, 2022 10:02 am

      I quite agree. I lived for a while on the island of Bute in the River Clyde, and there were beautiful prospects everywhere. That photograph captures the absolute vandalism of wind turbines. It’s like something that C. S. Lewis might have described in “The Hideous Strength”.

      Mind you, I now live in Basingstoke, whose town centre appears to have been designed to exhibit the maximum of soul-destroying ugliness.

  6. Stonyground permalink
    March 17, 2022 3:15 pm

    There are a couple of onshore arrays close to where I live in East Yorkshire. Recently several of the turbines have been out of action. I presume that they have to be turned off occasionally for essential maintenance and, to be fair, they aren’t usually stopped for very long. More recently some of them have been stopped for several days.

  7. Nick permalink
    March 17, 2022 4:33 pm

    What is the total nameplate capacity of the windfarms listed, and what is the load factor for the month?

  8. J Flood permalink
    March 17, 2022 5:06 pm

    We need generating capacity factors of 90% plus, not 40%. If some entrepreneur invented a generator that had a capacity factor of 50% and demanded to be let onto the Grid we’d say no. *

    Legislate for minimum capacity factor. Then the power provider would have to provide his own backup instead of the poor old customer.


    • J Flood permalink
      March 17, 2022 5:09 pm

      *On second thoughts, the brain dead and technologically illiterate dorks who end up in the Ministry of Blackouts are quite capable of saying yes even to that.


      • Chaswarnertoo permalink
        March 18, 2022 8:23 am

        Snivel serpents are generally useless and easily bribed.

  9. March 17, 2022 5:27 pm

    The performance of our fleet of offshore farms over the past 30 days is available here (scroll down to graph):

  10. March 17, 2022 5:29 pm

    Very interesting information, but it would be more complete if we knew the nameplate capacity of the listed windfarms please?

  11. Graeme No.3 permalink
    March 17, 2022 5:29 pm

    The load factor figures I have are from 2018 (12 months average)
    Dudgeon phase 1 45.2
    Walney phase 1 37.8
    Walney phase 2 44.8
    Burbo Bank 32.9

    Overall average (UK) 39.2%
    Overall average (Germany) 40.2%
    Overall average (Belgium) 36.2%
    Overall average (Danish) 40.0% (most recent 6 installed, older ones less)

  12. Gamecock permalink
    March 17, 2022 6:04 pm

    So some days England won’t have any electricity. We already knew that.

  13. March 18, 2022 2:36 am

    So what is problem. We need something like 180GW of electricity peak generation. At 7% capacity factor we need 180/0.07 = 2,600GW of capacity.
    260,000 10MW turbines would do it, and for all but one day out of the month we would be exporting electricity.

    • March 18, 2022 5:03 am

      Not necessarily. Wind turbines don’t work at low wind speed (not enough energy to turn blades) nor at high wind speeds (shut down to avoid damage). Here are some figures from the 3 years to 2018 (German I think) for capacity factor vs amount of time it was available.
      7% 90.7 percent of the time (so the equivalent of 2 days per month lost)
      11% 86.1
      20% 75.7
      25% 69.7
      30% 64
      40% 52.8
      50% 40.1
      62% 29.7
      71% 21.1
      76% 16.4
      82% 11.5
      85% 8.3
      94% 3.2
      98% 0.8

    • Phoenix44 permalink
      March 18, 2022 9:22 am

      That assumes that the 7% isn’t “fixed'”. But it probably isn’t. When there’s no wind, there’s no wind, no matter how much capacity you build. And when there is wind we would have 700% of demand. And so would all the ohyer countries we might export to.

      • March 18, 2022 9:27 pm

        It seems pretty rare that there is no output whatsoever. I was being ironic, but technically it is “simply” a question of building sufficient sufficient wind turbines and spreading them over a wide geographical area. Given unlimited resources you could probably guarantee supply for 99% of the time.

  14. March 18, 2022 7:30 am

    A fundamental of wind generators is that output is a cube law to wind speed, thus small wind speed variations bring a much larger variation in output. i.e. a 50% change in wind speed makes an eightfold variation of output, it’s not surprising that levels sometimes drop to very low figures.
    This must cause stability problems in blustery conditions and is not good at the best of times.

    • dave permalink
      March 18, 2022 1:20 pm

      Usually, the windmill reaches max output at winds of 31 mph and stays at max output until 55 mph, when the blades must be feathered and the output drop to zero.

      There is another wrinkle. The output goes with the square of the rotor length. Therefore, a unit in an exposed windy location, which for survival REQUIRES a smaller windmill, will be rated for less power than one might naively think is possible from that source of ‘free’ energy.

  15. Phoenix44 permalink
    March 18, 2022 9:25 am

    And that’s volatility by day. Businesses can’t cope with intra-day volatility.

  16. March 18, 2022 1:58 pm

    People are focussing on Windfarm Crapacity Factor
    oops I mean Capacity Factor.

    But this can be fiddled UP, by derating the turbine
    AFAIK there were grants available for small projects, so what some people did was put in a 2.5MW turbine, and derate it to below 2MW.
    Then compared to an actual 2MW turbine it would seem to have a 20% better capacity factor.
    But left alone in a perfect wind it would output at 120% capacity, so one might engineer safety circuits to make sure that 120% never shows up.

  17. tomo permalink
    March 19, 2022 6:49 am

    When are Greenies going to be treated like the cult they actually are and tolerated like Jovvies, Moonies, Hare Krishnas rather than allowed near unchallenged access to public policy out of all proportion to their actual numbers.

    • Ray Sanders permalink
      March 19, 2022 1:26 pm

      A near neighbour of mine, Historian David Starkey, makes your very point and beautifully describes Greta Thunberg as a “religious nutter”. Obviously not shown on the BBC! Well worth a watch

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