“70-85% of the time”

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During the recent storm over UK Energy Minister John Hayes’ rather silly comments about onshore wind farms, the Green Party leader Natalie Bennett made a quite curious intervention to the debate. Most curious was the following challenge, a taunt if you will, to those who say the intermittency of wind is a problem:

No energy source functions 100% of the time – but still as Green Party leader I still get the truly clueless question from media sources that really should know better, variations of: “But the wind doesn’t blow all of the time so wind power can’t work, can it?” In fact, wind turbines produce electricity 70-85% of the time and last year generated enough electricity for more than 3.5 million homes.

Now, saying wind turbines produce electricity 70-85% of the time is a rather meaningless thing to say, rather like saying a professional golfer turns up to 70-85% of the tournaments. It doesn’t quite get to the core of the issue.

So, what does happen 70-85% of the time? Fortunately you can get historic UK production data for every five minutes for the last few years. Let’s begin with 2011, and first look at maximum electricity production from wind each month, and compare it with the average. (I haven’t labelled the curves, but it should be clear what is what.)

We can see clearly that the monthly average output is normally less than half the monthly maximum output, with monthly maximum averaging just under 2.5 times higher than the average throughout the year.

Now, let’s compare the average amount of electricity generated each month with the minimum amount that’s generated 70 and 85% of the time.

Again, it’s very clear that we don’t always have decent output 70-85% of the time. In fact, 85% of the time we are only guaranteed about 17% of maximum monthly output, and just under half of the average output.

Has it fared any better in 2012? Here’s a comparison of the monly averages with the output produced 70-85% of the time.

The overall numbers are up due to new capacity coming online, but again we see that 70-85% of the time there is no guarantee of good output.

Now, does this mean that wind farms are useless? Absolutely not. Onshore wind is perhaps the cheapest source of low carbon power, and certainly the cheapest source of renewable energy, with costs about half those of offshore wind in the UK.

(source Committee on Climate Change “Renewable Energy Review“)

If we are serious about dealing with climate change cost effectively, then onshore wind will probably be part of the mix. However we must recognise that wind power presents problems, which cannot be covered up simply by using the language of the PR guru.


13 thoughts on ““70-85% of the time”

    Decarbonise SA said:
    November 12, 2012 at 8:50 pm

    “However we must recognise that wind power presents problems, which cannot be covered up simply by using the language of the PR guru.”

    Well said, that really gets to the heart of it for me. In the rush to defend wind, some parties believe the strategy is to ignore or downplay the actual shortcomings. That helps no one. It would be like me saying “the high capital cost of nuclear is an exaggerated problem”. It isn’t, it’s a real problem, and so it the intermittency and low capacity factor of on-shore wind. Great post.

    South Australia has very high penetration of wind per capita, and I wrote about it here for those interested. http://decarbonisesa.com/2011/09/14/the-good-the-hard-and-the-windy/


      Robert Wilson said:
      November 16, 2012 at 3:39 pm

      Thanks Ben

      Agree entirely. One of the biggest problems here is the level of special pleading. In the UK it’s now almost a taboo in some circles to say anything bad about wind power. An absurd example is this Guardian piece (http://www.guardian.co.uk/environment/damian-carrington-blog/2012/jun/21/wind-power-subsidies)

      You can see how naive people are about wind if you look at the current UK debate over new gas capacity. Massive amounts of outrage over the possibility of 20 GW of new gas being built. Yet, no one seems to realize the scenario they dream up (80% renewables) would in fact require a hell of a lot more than 20 GW of gas capacity, simply to keep the lights on when it’s not windy. In fact the only way to stop this “dash for gas” is to build nuclear. This is actually quite clear if you write consultant documents for the UK government’s Committee on Climate Change, but I’m going to try to blog on this in the next month to get some ball park analysis out there.


    Fabian said:
    November 12, 2012 at 9:55 pm

    Hello, shouldn’t the ordinate axes on your diagrams be labeled “MW” rather than “GW”? The UK has only about ~5 GW installed onshore wind capacity (http://www.businessgreen.com/bg/news/2207382/uk-onshore-wind-capacity-breezes-past-5gw-mark) so they don’t generate >500 GW, that would be more than the UKs primary energy consumption! 😉
    But I like your article, it’s an important point to make: Renewables often get over-hyped by Greens, especially in Germany where I live.


    robertwilson190 said:
    November 12, 2012 at 9:57 pm

    Thanks Fabian

    You are absolutely right. It was stupid typo in my code. I will fix it now.


    Ed said:
    November 13, 2012 at 12:21 am

    Do your wind costs factor in that wind is required to have a backup power source (usually natural gas) to level out the unreliable nature of wind?


      robertwilson190 said:
      November 13, 2012 at 12:30 am

      At current penetration levels there is no real need for additional back up power sources for wind power compared to what’s on the grid already. In effect the variation in wind power acts rather similarly to variation in electricity demand, so the grid can handle it at no extra cost.

      This is probably true up to about 20% penetration. DECC estimates however that around 30% penetration there will be added costs of £10/MWh for grid integration. So long as the UK has a mix of renewables and nuclear (i.e. around 40/40) this is not likely to be a major issue.


    johnrussell40 said:
    November 13, 2012 at 2:49 pm

    Solar, of course, is right up there at over 30p/kWh because the government came up with such a daft level of early feed in tariff (FIT), to attract uptake. I would hope it should come down now that they have dropped solar FITs to a more sensible level. The problem for the moment though is the huge number of early domestic adopters claiming at the starting rate of 43p+, compared with a much smaller number of those who missed the boat and are therefore on more sensible rates below 20p/kWh.

    The take-home from this is to remember that any future solar will never cost anything like that level again.

    Loved the ‘professional golfer’ analogy, Robert.


      Robert Wilson said:
      November 13, 2012 at 10:54 pm

      Thanks John

      Well, the government was only following the German government in terms of daftness. My own view is that we should build out the cheapest first. That means onshore wind and nuclear. Neither of which are particularly popular. Strangely there is an inverse relationship between the cost of a low carbon energy source and its cost. A reason I am suspicious of government’s “picking winners.” The German situation shows where it can grow wrong. In the last year they increased the electricity from solar far more than wind. Astonishing consider the latter is still much cheaper. I sometimes wonder if the only thing Greens care about the cost of is nuclear power.


        Jean-Marc Desperrier (@jm_desp) said:
        November 16, 2012 at 12:27 pm

        As useful as studying the past is, it can still lead to incorrect interpretation.
        Especially when you miss like here a very important trends (quite obviously, the constant manipulation of the cost values by the Green has obscured it and mislead you).

        The important trend I’m referring too is the fact that wind turbines have since the mid-2000 became a mature technology that doesn’t have massive cost gains anymore. This US report http://eetd.lbl.gov/ea/emp/reports/lbnl-3716e-ppt.pdf show on page 32 that between 2005 and 2009 there was no gain in price in the cost of wind.
        Since then there’s has been some gain, but they fully came from moving production from the west to China.
        Meanwhile the cost of solar went down so much that the FIT in France and Germany went down to around 10/12 €c/KWh.

        This means that the raw cost curves are not very far from crossing each other, and the actual gap with market costs (it you take into account wind turbine frequently produce in the night when the wind is worth almost nothing and the subsidy has to make up for a much higher gap with the FIT), might already have in many markets.

        So with FIT at a level of 30 €c/KWh, solar was deeply non-competitive with wind, and unfortunately for them the Germans have deployed a lot of solar at that price. But at todays price, I think solar is probably better than wind. Especially if you consider that in the very long term, the maintenance cost of wind rises until you have to replace it whilst the one of solar stays the them.


        jmdesp said:
        November 26, 2012 at 7:50 pm

        Actually I have another source for rising costs of onshore wind, and believe it or not, it’s the very same “Renewable Energy Review” that you extracted the figure above from.

        Yes I know that figure says onshore wind is the cheapest, and the estimates claims it will continue go down by about 10% a year. But that just an estimate, and well what if we were looking at facts instead ? And the facts are there in the study, just very well hidden.

        Look page 67. There’s a graph of “gov estimate of generation costs”. And there it shows that the cost estimates in 2006 was around 6p/KWh (source: energy review), and in 2010 became 10.5 p/KWh (Mott Mac Donald). So whilst the study claims it will go down, the actual, factual, numbers it contains are that it went up.

        If we go see that Mott Mac Donald study it doesn’t actually contain any cost for wind.
        That’s very surprising, since it gives costs for everything else but not wind. But it has this to say in paragraph 5.6.2 :
        “EPC costs for almost all the renewable technologies have risen in the last five years […] Wind has seen probably the greatest increase, as there have been serious bottlenecks in the supply of wind turbine generators (WTG) and in some of the construction support services (vessels and cranes)”

        That’s nice to see it may be just a short-time bottleneck but the more recent US study of costs of electricity generation I’ve put my hands on (an interesting one to read fully) still doesn’t see it going down. The 2010 cost estimate for the 2011 report are up 21% from the 2009 estimates for the 2010 report :
        “Overnight costs for onshore wind increased by about 21 percent relative to AEO 2010 assumptions”
        Whilst solar did go down in the same time-frame.

        All in one, whilst it’s not actually my intend to badmouth wind power, it’s shocking to see how much effort has been made to hide the true fact, and affirm that cost are going down when they are not. And that’s very misleading since it takes a very careful examination of documents to find out that some the cost-reduction claims are not based on anything that actually occurred.


    […] Instead I’ll consider a rather obvious problem: the wind does not always blow, and whether this means 100% wind power is impossible. Of course some people imagine that if it’s not windy in one place, it will be windy some place else. Well, the data indicates that such talking points need to be reconsidered. […]


    […] Instead I’ll consider a rather obvious problem: the wind does not always blow, and whether this means 100% wind power is impossible. Of course some people imagine that if it’s not windy in one place, it will be windy some place else. Well, the data indicates that such talking points need to be reconsidered. […]


    […] Instead I’ll consider a rather obvious problem: the wind does not always blow, and whether this means 100% wind power is impossible. Of course some people imagine that if it’s not windy in one place, it will be windy some place else. Well, the data indicates that such talking points need to be reconsidered. […]


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