Wind Turbine Efficiency

December 30, 2008

According to David Rosser- director of CBI Wales the wind only blows strongly enough 10% of the time for a wind energy project to work. According to James May from Top Gear on his latest TV show, wind turbines only work 30% of the time . Why do people who are anti-wind energy keep using this against wind when they are so easily proven wrong? People with responsibility for disseminating information should check their facts.

To try and help stop the confusion, here are the facts:

1) A modern wind turbine has a maximum capacity of around 2000 kilowatts (kW) or 2 Megawatts (MW)
2) There are 8760 hours in a year (365 days x 24 hours)
3) A 2 MW wind turbine will generate around 30% of its maximum theoretical capacity resulting in 5256 Megawatt hours (MWh) generated per turbine per year
4) Taking all of the above into consideration a wind turbine will generate enough green electricity for the average annual needs of around 1100 homes, using an average demand of 4700 kWh per house based on electricity consumption figures from Digest of UK Energy Statistics

Wind turbines usually operate 75-90% of the time – but not at full capacity.

For further information this British Wind Energy Association web-page is helpful.

Picture above taken from www.science.nationalgeographic.com

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25 Responses

  1. David Johnson

    November 13th, 2009

    Why do wind turbines only produce, on average throught a year, 30% of their rated output if they “usually operate 75-90% of the time? Clearing, for a significant part of that 75-90% they are producing negligible power.

    While I agree that generating power from wind is “greener” than burning coal (assuming material and maintenace costs are constrained), I am curious to understand how “green” energy may be generated to supply demand when wind generation is not effective?

  2. This is because it is more efficient to build turbines that generate 30% of their rated output than it is to build ones that would generate say 90% . The % of a turbine’s rated output that is generated depends on the amount of energy from the wind that is applied to the generator . This energy is collected from the wind by the blades. If turbine engineers wanted a higher % of rated output to be generated then they would simply place larger blades on the turbine relative to the capacity of the generator. However,its not efficent to do this because of the cost of larger blades relative to the cost of the generator. Therefore the optimal design is for turbines that generate at about 30% of the maximum capacity of the generator. The whole focus on this number as a measure of efficency is very misleading. The generator is only one part of the whole turbine and to focus on maximising the amount of utilsation of that one particular componenet would be sub optimal.

    Another way to look at this is that we could take an existing 2 MW turbine , generating at 30% of capacity and replace it’s its generator with a 1 MW machine. The blades would still capture the same amount of energy so the generator might be expected to generate the same anount of electricity.. now 60% of its maximum output. Using the misleading measure of wind turbine efficency this turbine would now be twice as efficent. However, that isnt what happens, and it isnt because wind turbine engineers are stupid. There would be additional losses of energy and the overall design would be sub optimal.Its important to match the size of the generator with the size of the blades and the best design is one where the generator ( a relatively small cost of the whole turbine) works at a capacity of about 30%.

  3. Just a quick comment ; this article is out of date anyway. I’ve proven that it’s possible to use the output of a generator prior to its dissipation in a load to compensate for the Lenz effect which is the reason for the requirement for high torque i.e. large blade swept area. No-one believes me but I have a prototype which demonstrates this beyond doubt. You have my email address.

  4. When the wind stops blowing the lights go out. you therefore need a gas fired power station on back up to maintain a continuous supply of electricity. This adds to the cost of wind turbines. A study carried out by the Royal Acedmy of engineering in 2004 showed that a kw hour of electricity produced by an onshore wind turbine, including the cost of standby generation, was 5.4p; more than double that of power from gas (2.2p), nuclear (2.3p) or coal fired plants (2.5p). Off shore wind platforms are even worse; at 7.2p per kw hour the cost is three times as much.

  5. I am intrigued by PUMPED HYDRO ELECTRIC schemes, which seem to be an essential adjunct to the massive offshore wind installations currently considered.
    YANBURU Okinawa is a pioneering project using sea water and a man (made,modified?) header lake on the cliff top. Dinorwic is one of five UK sites using two lakes.

    Ireland has TURLOUGH Hill whose egg shaped upper lake is plain to see on aerial view of Wicklow Mountains.
    This provides 240MW for 6 hours within 60 seconds at 78pc efficiency.
    N.Ireland has Camlough similar sized system, mothballed but likly to be revived.
    The seawater PSE schemes might be seen to avoid the massive rockboring of the mountain lake options. However a massive upscaling of storage volumes nay be required. Any comments welcome.

  6. Dodgy Geezer

    April 20th, 2011

    “…. wind turbines only work 30% of the time . Why do people who are anti-wind energy keep using this against wind when they are so easily proven wrong?”

    Perhaps because reality is even worse? The figures are now down to 25%. http://www.jmt.org/assets/pdf/wind-report.pdf refers…

  7. If you had read the post and the thread you would understand that most turbines do not only work only 30% of the time. Many turbines operate at 30 % of their maximum theoretical output and this is not the same as only working 30% of the time.

  8. Joshua Francis

    May 18th, 2011

    I know the cost to build these wind turbines is high;however,after they are built it would seem the cost would be little to maintain.

  9. If these turbines operate at 30% efficiency for 100% of the time they are running.Then what is the overall efficiency when you factor in the time they are not running ?

  10. It sounds to me that people are getting lost in the efficiency of the individual components of the turbine. We’re losing site of the main objective of a wind turbine which is to take wind energy and create electricity. Therefor the efficiency we need to discuss is the conversion from potential wind energy to electrical energy output. Then see how wind energy stacks up to coal, nuclear and hydro. Lets start comparing apples to apples…

  11. you all know nothing it is used in the frmer feilds witch is pointless because when you use solar panels you can put it on roofs of homes and not in the farmers feilds, did you know that a bird dies every 2 min because thry fly into the blades of the wind tubines.

  12. The 5256 MWH is measured at the turbine. It does not measure line loss, which for a wind turbine is considerable due to the wide range of power output which has to be transformed to usable levels.

  13. slim shady

    April 24th, 2012

    birds are stupid

  14. Daniel Raeman – No I didn’t. And in fact nor do you.

    Did you know that every time a man throws an apple out of his car window a cat dies? .. and every time a cat dies a little peruvian child eats an ice cream? There’s your evidence. I AM THE EVIDENCE!

  15. Alex Simpson

    May 14th, 2012

    I think Wind Turbines can be efficiently used if they are put in less populated areas. They would be an easy way to power a small town.

    Who cares about stupid birds. Did you know every 2 minutes every other bird in the world DOESN’T die!

    Also, in Denmark, pigs outnumbe humans 4:1. How many pigs don’t die from wind turbines? all of them?! I thought so.

  16. Wind Turbines are pretty efficient as they stand now, apart from birds hitting them and stuff.

    And you are true, of course, pigs dont die from Wind Turbines, and they also dont fly, and I for one, Alex Simpson do care about birds.

    When they hit the Turbine they slow it down, reducing energy efficiency, and if a bird dies every 2 minutes, among other things like hunting and predators, we might soon run out of birds? What will you do then?

    Remember Alex Simpson, I’m Bird. You are too. Do you want to die in 2mins? I didn’t think so.

  17. Here is what I don’t understand. Why are we not using Wind power in correlation with let’s say hydroelectric. There is a hydroelectric facility named Raccoon Mountain in Tennessee. It consists of two parts, a holding facility at the top of the mountain “Lake” and a holding facility at the bottom of the dam another “lake.” During the day the water drops down through the dam and then at night when peak power consumption is down. They pump the water back to the top. Instead of having to use the dam to pump the water back to the top use the wind turbines.

  18. careful joseph, you’ll end up ‘committing suicide’ with forward thinking ideas like that..

  19. This has not answered the question. The usual gobldygook. Efficeiency is measured in Engineering terms as energy out over energy in and ususally expressed as a percentage. What is being discussed here is the Utlisation of the plant which is a totally different thing. And an even bigger question is value of energy produced over capital and maintainance outlay with no subsidies to skew the answer.

  20. I don’t see why anyone would think that 30% effeciency is a valid reason wind power should not be harnessed. The average efficiency of a fossil-fuel plant is……………. 28% to 32%. And coal must be burned to produce it.

  21. Firstly

    1) If the wind doesn’t blow there is no electricity.
    2) It doesn’t blow at the right sort of speed for more than 30% of the year.
    3) Ergo for 30% of the year there’s no electricity!
    4) In winter when the power is most domestically needed the wind hardly blows at all.

    Answer; build a more traditional power station to plug the gap knowing that such power station can’t practically be turned on or off that easily.

    Secondly, how green is green?

    1) Making a wind turbine involves processing a good deal of rather nasty materials that consume vast amounts of land to find the ores, vast amounts of energy to process and refine the hydrocarbons and the concrete and after a short 15 to 20 years we’re left with a load of stuff and junk that’s exceedingly difficult to recycle
    2) For the fifteen or twenty year we destroy the beauty of the countryside, wreak havoc with the local ecology and erect thousands of pylons to get the product to the consumer.

    When are we going to wake up to the fact that wind turbines are not the answer and accept that the low carbon argument is based on bad science and hogwash put about by people whose only interest is make lots of money!

    Sunlight, tidal power, wave power, geothermal power, adopting a step changes in building insulation, district heating systems from burning waste instead of chucking it into a hole in the ground and poisoning the water table, anything but stop making me pay an energy levy for something that doesn’t work forced on me by a government that’s bereft of any meaningful idea’s

  22. Wally Waba

    March 3rd, 2013

    With so many wind turbines already operating when are we ready to decommission just one dirty coal fired power station anywhere on earth.

  23. This article was titled “Wind Turbine Efficiency” but the discussion is almost entirely about how much of the rated capacity WT’s deliver, problems of intermittency etc. this discussion is primarily about utilisation factor which is completely different from efficiency. Efficiency is about how much of the energy in the wind is converted to electrical energy. One could argue that on a windless day turbines are 100% efficient; zero wind energy and zero output, output = input = 100% efficiency. The reality is that the maximum efficiency of a wind turbine is about 60%, large turbines achieve a somewhat less than this at optimum speed but still much better than rooftop solar.

    The real issues are:
    1. Wind turbines are ENERGY collectors; they can supply/generate a large amount of clean but intermittent ENERGY, but only when the wind is blowing.

    2. The energy available in the wind is proportional to the cube of the wind speed, e.g. wind at 10mph has 1000 times more energy than at 1mph, hence the large variability in WT output.

    3. The grid requires a large amount of reliable POWER (non-intermittent energy)

    4. To turn large amounts of intermittent energy into large amounts of power requires large amounts of energy storage.

    5. If wind, or other intermittent RE sources, are supplemented with backing (fossil) generation this only makes sense where peak intermittent generation is less than minimum demand minus base load (nuclear) otherwise during periods high RE availability and low demand there will be excess RE generation that can’t be used, this reduces the economic viability of RE generation and creates the problem of energy dumping to maintain grid stability.

    6. The solution to large amounts of energy storage is ‘Green Coal!’ and I don’t mean biomass/biofuels, but that’s another topic.

  24. Central Scrutiniser

    September 17th, 2013

    Wind turbines could be 1% efficient, but it wouldn’t matter – as long as they could produce electricity cheaper than the alternative methods they would be fine.

    But they can’t. They rely on subsidies paid for by all consumers and businesses.

    Currently the UK energy policy on climate change is adding around 17% to all domestic electricity bills, and that is set to rise to 41% by 2030 as more low-carbon energy production comes on line. Highly energy reliant businesses are set to see electricity bills that are up to 71% more expensive than they would be without these policies in place. All because of renewable energy and carbon fetishism.

    So wind farms are not only grossly inefficient, they are costing every single person and business in the country a significant amount of money.

    For what?

    The objective is to reduce our dependence on fossil fuels, not because we don’t want to use them all up too quickly, but because of carbon dioxide. So how effective can wind turbines and all the other mechanisms of carbon emissions reduction be in the UK?

    In the ten years to 2011 we succeeded in reducing our annual emissions by 63 million metric tons, which sounds a lot until you realise that over the same period China increased its annual emissions by 86 times as much.

    In fact, ALL the emissions savings made by ALL the nations who are indulging in this futile conscience-salving nonsense, including the USA which for a long time was regarded as the baddie in this respect, have been cancelled out ELEVEN TIMES OVER by the 167 nations who are not participating.

    This means that our paltry savings (despite the fact that the cost of achieving them is not paltry to the UK) cannot possibly have any discernible impact on global carbon dioxide levels. Or putting it another way, if we did nothing about renewable energy and thereby avoided the 71% surcharge on energy costs that we are putting in place for our industries, it would not make any discernible difference either.

    The answer is therefore simple – by stopping all subsidy of and investment in renewable energy NOW and by continuing to use conventional power generation instead, we will save all electricity consumers a significant amount of money by 2030. This would make no discernible difference to global carbon dioxide levels, which are going to rise at the same rate no matter what we do.

  25. I agree that generating power from wind is greener and perhaps better than burning coal, how can green energy be generated to supplied to such high demands if wind generation is not effective?

    Is using wind farming worth the expense if only 30 percent is effective?

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