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Bad News for Wind Energy

March 5, 2013

It’s generally been  recognized that using wind to generate electricity is inefficient, costly and unreliable.

Now the news is getting out that it’s even worse than previously thought.

The report, The Performance of Wind Farms in the United Kingdom and Denmark, issued by the Renewable Energy Foundation, London, UK, established that capacity factors for on-shore wind farms decline from 24% in the first year of operation, to 15% in year ten, and 11% in year 15.

These results are amazing, in that the literature usually indicates a consistent capacity factor of 30%, which is what financial projections are typically based on.

The report holds even worse news for off-shore wind farms.

In Denmark, output declined from 40% in the first year of operation to less than 15% in year 10.

Wind Turbines off-shore Copenhagen, Denmark. Picture by D. Dears

Wind Turbines off-shore Copenhagen, Denmark. Picture by D. Dears

Another source indicates that capacity factors decline by 1 to 2% annually.

A report by Lawrence Berkeley National Laboratory said that, because developers received grants, rather than tax credits for the amount of electricity produced, they built wind farms where wind conditions were less favorable.

Now a new report by Amanda S. Adams, University of North Carolina at Charlotte, and David W. Keith, Harvard University, published in the journal Environmental Research Letters, indicates that the capacity of wind farms is overstated.

The report concludes that the shadowing effect of wind turbines on each other in a wind farm reduces the effective wind speed for turbines shadowed by other turbines.

The report suggests that wind power production is 25% to 50% of what has been previously assumed for wind farms of over 100 square kilometers. This is a huge reduction in what has been estimated for the potential electricity production from wind energy.

Smaller wind farms were also affected by the shadow effect.

One conclusion resulting from the decline in electricity production by wind farms came from a study done by Edinburgh University. Its study concluded it would be uneconomic to run wind turbines for more than 12 to 15 years, which is far less than the predicted life span of 20 to 25 years.

All of these studies bode ill for wind energy and the tax payer dollars used to support their construction.

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7 Comments leave one →
  1. Garry Buttner permalink
    March 6, 2013 4:43 pm


    Interesting article and data.

    What is the reason that installed wind turbines have a decline in capacity factor of 1% to 2% per year?


    Humm, Maybe the loss of capacity is due to the reduces aerodynamic efficiency of the blades as they kill Condors and other large endangered birds! 😉

    On Tue, Mar 5, 2013 at 9:54 AM, Power For USA

    • March 7, 2013 9:58 am

      You always ask good questions, but I may not be able to provide an entirely satisfactory answer this time.
      The studies by Lawrence Berkeley and the other about shadowing, both help establish why actual capacity factors are lower than expected, but don’t address deterioration over time.
      Here’s what the UK study says about the cause of deterioration over time:

      “There are two plausible explanations for the observed decline in average load factors as wind farms age. The first is that the turbines become less efficient over time as a result of mechanical wear and tear, erosion of the turbine blades and related factors. The second is that the turbines experience more frequent breakdowns and their operators take more time to bring them back into service because they are less concerned about the performance of older plants. Both reasons may be relevant in different circumstances and it is not possible to identify a primary explanation from the data. The frequency of extended shutdowns does seem to increase with age, but this could be a reflection of the timing of planned maintenance operations rather than breakdowns. Whatever the cause, the reduction in performance with age is much greater than would be expected for thermal generating plants.”
      “The age-performance curves in Figure 1 are derived from equations estimated by giving equal weight to each wind farm irrespective of its generating capacity. Figure 2 illustrates similar curves but in this case the estimates are constructed by weighting each wind farm by its generating capacity, referred to as capacity-weighted. This gives a better representation of performance degradation per MW of generating capacity. The striking result is that the rate of decline in the performance of UK onshore wind installations is significantly faster when capacity weights are used, which implies that large wind farms in the UK experience a more rapid decline than smaller ones. The differences are smaller in Denmark but the capacity-weighted decline in performance is more rapid than the equal weights decline for Danish onshore installations.”

      In reading the study it’s reasonably clear that their methods are sound in so far as establishing the amounts of deterioration, but don’t adequately address the cause.
      The UK study is available at for anyone interested in pursuing the question.
      Hope this is at least the beginnings of an answer.

  2. May 3, 2013 7:42 pm

    Wind energy has made enormous progress. However,due to the need for backup energy, the theoretical limit for grid coverage can not exceed 50 %.

    • May 4, 2013 9:19 am

      Thanks for your comment.
      There are, however, many people who believe that the maximum amount of wind generated electricity, without storage, on the grid is 20%.

  3. May 15, 2015 8:10 am

    REF failed to take into account that modern turbines are taller, and thus have a much higher capacity factor due to wind shear. So older turbines on shorter towers naturally have a lower capacity factor. They didn’t compare like with like.


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