Offshore wind farm

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  1. Rod, small request – in the first paragraph, “proiked” is a typo for “provoked”. I like to think my points are good, but I’m a lousy typist.

  2. It is worth noting that, in the UK, wind power has the longest preparation/licensing period of any technology. DECC’s 2010 analysis shows that offshore wind needs 5-7 years preparation before contruction starts, plus 1.5-3 years of construction. (p84-86)

    Basically anything that is not in the pipeline by now is unlikely to be generating much before the end of the decade.

  3. Andy writes:

    “We’ll also assume we’ll beat the current capacity performance for offshore wind in the UK (same source as above) of 27%, by hitting the dizzy heights of 30%.”

    Some time ago L. M. Miller, F. Gans and A. Kleidon published and article ( there they estimated maximum global land surface wind power extractability. They showed that there are not that many places in the world there the onshore extractability at the par with the north of the UK. Based on information in the article (although limited) I did some back of the envelop calculations of the capacity factor we should expect and came to approximately 26%, which is what we have here in the UK on average at the moment. It may be physically impossible to reach capacity factors higher than the currently observed figures.

    Here is my quick estimation.

    Area of the the largest wind farm ( is 545 Hа or 5450000 м^2. From fig6b in the article wind dissipation for the north part of the UK is something around 2.5….3 W/m2. In another word this is how much power can be extracted from the boundary layer. So 5450000 м^2 x 3 W/м^2 = 16.4 МWт.

    From the farm specification:
    Turbines 26
    Installed capacity 65 MW
    Capacity factor 27%
    Annual generation 154 GW·h , which roughly corresponds to 17.6MWt.

    Figures are very close. Similar estimations for other farms produce approximately similar result.
    For example to provide 10% of the UK annual electricity capacity from wind farms an area of 1440 km^2 will be required ( [(378.5 TW·h/365/24)*0.1]/3 Вт/м^2 = 1440 км^2). On average a single turbine requires 400×400 m^2. Therefore about 9000 turbines will be needed. At the moment there are about 3000 in the UK. Granted, off-shore extractability may be higher, but still the staggering number makes me wonder.

  4. @Andy,
    Thank you for writing this article and for looking at what it takes to actually do what one says that they will do.

    Have you ever looked at or know of anyone that has attempted to fully compare the reliability of wind and that of nuclear in a levelized cost analysis? I have not been able to come up with a way or find any way of incorporating the entropy into a levelized cost model. I think that until we do that we will not compare apples to apples.

    I ran some numbers from the Bonneville Power Association 2007-2011 for their wind generation. They had an expected capacity factor of 29.8% and an entropy of 9.5.

    Compare that with the NERC GAR 2009 with numbers from 2006-2009. I took those numbers from the total available hours and the forced outage hours in that period. Nuclear had an expected availability of 97.8% and an entropy of 0.11.

    There is an assumption in my wind numbers that it is required to be put on the grid when it is available allowing the expected capacity factor to be compared directly with the expected availability of nuclear.

    So the entropy (expected uncertainty) of wind is 9.5 compared to nuclear’s 0.11 almost a two order of magnitude difference! That means it takes roughly 100 more binary questions to describe wind power than nuclear. There has to be a way we can capture that in $, £, or €.

      1. @Jim,
        The best I can do is to refer you to Gibbs, Shannon, and Jaynes.

        It’s taken a study of the subject to come to my understanding. Entropy is the expected uncertainty of our state of knowledge about something. You will not find that in any thermodynamics book… you’ll get a discussion on measure of disorder and other such nonsense, which obfuscates the actual meaning.

        A good link but incomplete is:

        Gibbs used the log of a probability distribution to describe the “index of probability”. In information theory, this is the “uncertainty” of the of the probability distribution. What Gibbs. and later Shannon do is to take the expectation of that over the probability density function. This becomes Shannon’s information entropy. It also relates information entropy to thermodynamics through Boltzmann’s k.

  5. Though I’m no expert in wind generators, I do know they require regular maintenance. Anything that is placed in water, rather than land, is going to be more time consuming and expensive to maintain. These generators will need cleaning, greasing, and anti-corrosion efforts on a continual basis. The addition of new under sea power cabling is going to be very costly as well.

    Wind generators also have a “Goldilocks” sweet spot of wind speed needed to operate. Too slow and they can’t produce power. Too fast and they must be shut down otherwise they will destroy themselves.

    If anyone knows a good source of wind on sea vs. wind on land maintenance costs, please post.

    1. Jason,

      I wouldn’t be surprised if that’s a question wind pushers don’t want an answer to. Besides, in Europe and the US, reliability and maintainability are no longer desired attributes of a power system. Safety and CO2 emissions are now the metric for new electricity generation.

    2. This is what I was thinking too. Given the corrosive nature of saltwater and salt spray, I can’t help but wonder if offshore wind farms will last anywhere near as long as claimed — even with the expensive maintenance.

      1. ….. and at what point are the maintenance costs going to be so high that they equal or exceed the value of the electricity produced? These questions make the whole venture sound highly questionable from an investment perspective.

      2. Thinking of offshore experience, those ought to be designable against, and maintenance regimes available to mitigate the effects – blades tend to be made of materials like fibreglass, for example.

        What I’d expect to be the bigger problem in somewhere like the North Sea is maintenance access. It’s one thing working on an enclosed platform , entirely another trying to do maintenance work in or on the nacelle of a wind turbine several hundred feet up, in the weather that prevails between September/Occober, and May/June.

    3. The bigger ones also have an “inverse Goldilocks” zone wherein they become net consumers of power because the blades have to be kept turning at low speed even if there is no wind. They draw power from the grid to do this. That avoids damage from distortion of the windmill blade which results if it is kept motionless for any length of time. The small ones don’t have this problem because their arms aren’t long enough to sag and bend like the big ones.

  6. Rod,

    Very interesting post. Do you have any source (maybe one of your own previous blog posts) which does a similar analysis of the US and Canada?

    I might be wrong, but I think that in the US, we have, at least theoretically, a lot more potential for building wind farms on-shore. . . the main problem being, I believe, that most of the good on-shore sites are at places distant to the point of consumption. Places like the southwestern Deserts, western Plains, and midwestern Farmlands?

  7. Another problem with onshore in U.S. is that the best sites, i.e. the Appalachian ridges are also the main migratory routes for birds, raptors, and bats. Likewise, developers have applied for an “incidental take” for endangered species in a corridor from Canada to the Gulf of Mexico which also happens to be a major migratory route for endangered Sand Hill Cranes as well as waterfowl.

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