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« Josh 56 | Main | Why four degrees? »
Thursday
Dec022010

Wind capacity again

Another interesting assertion by Prof Anderson on the earlier thread was what he had to say about capacity factors for wind turbines:

...the capacity factor for turbines - which ranges from low 20 to 50 depending on size and location (well sited on land probably 25-35%, with well sited offshore and bigger (3-5MW) 35 to 50%) - I recall a few years back some 3MW turbines near the Shetlands reached 52% over the year - though the Shetland is a particularly good site.

When we discussed this the other day, we were looking at figures that were much lower than this - more like 10%. Can anyone explain the discrepancy?

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Reader Comments (76)

dave B; The bulk of the power probably goes to spinning the blades as the wind approaches cut-in speed to keep the machine synchronised.

Is this right? I'd always believed the generators were dc machines, using electronic dc/ac conversion and so not needed to be synchronised like a turbo generator in a power station before being connected in.

The "éoliennes" around Normandy seem to me to spin at various speeds - close to each other, but not identical.

Dec 2, 2010 at 6:58 PM | Unregistered CommenterMartin A

NIMBY =df Someone who defends a neighborhood which I wish to profit by damaging.

Dec 2, 2010 at 7:01 PM | Unregistered Commentermichel

@ Martin A

Technically, both are possible by using either mechanical or electronic synchronisation. From Wikipedia;

Some models operate at constant speed, but more energy can be collected by variable-speed turbines which use a solid-state power converter to interface to the transmission system. All turbines are equipped with protective features to avoid damage at high wind speeds, by feathering the blades into the wind which ceases their rotation, supplemented by brakes.

Dec 2, 2010 at 7:15 PM | Unregistered Commentersimpleseekeraftertruth

To address Bishop Hill's original question:

When we discussed this the other day, we were looking at figures that were much lower than this - more like 10%. Can anyone explain the discrepancy?

if you check the comments to Rob Schneider's post from which the 10% figure came, you will find that he is unintentionally comparing total installed UK capacity with a record of actual output for a subset of the UK sites, so the 10% figure is not correct.

Dec 2, 2010 at 8:23 PM | Unregistered Commenterohnevermind

Pertinent to this discussion are these comments by Howard C. Hayden, physics professor emeritus of the University of Connecticut, in Environment & Climate News, Nov 2008: "Wind turbines have improved considerably since the 1970s, not so much in efficiency but in both power output (typically 100 kw in the 70s to 2,000 mw presently) and mechanical reliability. The capacity factor has “improved” from about 22 percent to about 35 percent, but because of something no more profound than a changed philosophy of design. There is a simple way to make a wind machine with any desired capacity factor. To get zero percent, attach a child’s pinwheel to a 1 mw generator. The average power would be zero watts. Divide that by 1 megawatt and you get zero. To make a wind machine with a capacity factor approaching 100 percent is just as easy: Attach a 100-meter-diameter rotor to a 1 watt generator. A device that big should almost always be able to produce one watt, so the CF would be near 100 percent. Both of these devices would be worthless, of course. In other words, one can design a system to have any given capacity factor by establishing the ratio of generator capacity to blade diameter. These days, wind systems are designed to have capacity factors of about 35 percent." Read it all at http://www.heartland.org/full/24041/Pickens_Plan_Fails_to_Account_for_Limitations_on_Wind_Power.html

Dec 2, 2010 at 8:39 PM | Unregistered CommenterOldSalt

Gareth mention the Burradale Wind Farm with the record for average capacity. This record was set on a wind farm with only three turbines; there are now five. This is a backyard "wind garden", not a practical "wind farm". http://www.burradale.co.uk/Projects.html

In 2009, the National Grid issued a reported on electricity generation in 2020 under the "Gone Green" scenario - 30% of power from wind. The report was then sent out for review by their power suppliers and apparently was viewed as being realistic. http://www.nationalgrid.com/NR/rdonlyres/32879A26-D6F2-4D82-9441-40FB2B0E2E0C/39517/Operatingin2020Consulation1.pdf

a) National Grid anticipates an average of 15% of nameplate capacity from wind in 2020. (Statement 6.43). They refuse to say how much reserve capacity they need for times when the wind is low. However, if one looks at Figure 12, the operating reserve will roughly double by 2020 accommodate periods of low wind. Furthermore, their standard wind forecasting error at 4 hours ahead is currently around 10% (rms) of wind generation CAPACITY (Statement 6.3) or about 2/3 of the expected average capacity. As best I can tell, this means that the 30% of power Britain expects to get from wind needs to be backed up by a reserve of 20% from fossil fuel plants that are operating in reserve mode!

b) Figures 10 and 11 (p34 and 35) show average wind power was available during times of peak demand in Great Britain. At highest and second highest peak demand in 2009, wind was producing 12% and 6% of nameplate capacity. The average wind speed across all of Britain over the past 25 years on the highest five days of demand was barely the minimum speed needed start a turbine, but this number is hard to interpret. Turbines are not sited at locations and heights of average wind and the average wind speed doesn't tell us how much lower the low is.

c) National Grid expects to fall short of demand in 2020 (Figure 13).

Dec 2, 2010 at 8:43 PM | Unregistered CommenterFrank

DaveB

OTOH, I recall seeing a video clip of a turbine sited close to an industrial chimney stack. The turbine is spinning away fit to bust while smoke from the chimney is rising as vertical as a guardsman's back and up . . . up . . . and away. As it does when there is absolutely no wind.

Interesting. I wonder if they weren't running the turbine in capacitance. That is, as a motor to counteract impedance created by loads on the grid. Running generators that way can help keep phase shifts from being too pronounced. It's been 25 years since I messed with power grids, and my memory is a bit hazy, and I was just the marketing geek. Perhaps there is a real electric power engineer out there who could explain it all correctly.

Dec 2, 2010 at 8:44 PM | Unregistered CommenterDon Pablo de la Sierra

ohnevermind,
Since ERCOT, the org assigned to keep the power grid of Texas up and running, assigns a grid reliability factor of 8.7% of nameplate capacity, I think using 10% is not a wild or unreliable number.

Dec 2, 2010 at 9:31 PM | Unregistered Commenterhunter

@ ohnevermind.

You are correct. The 10% figure is too low as the numerator/denominator are not in sync (I suspected that at the time). Gets back to so far I don't know what generation devices included and/or excluded in the National Grid data. Looks like with a lot of work I can get that info from the Renewables Obligation data, although at first glance not clear. Will pursue that. 21% for Denmark is a darn sight different than the larger numbers I hear bandied about for achievable Load Factors. It was these large assumed load factors which original captured my curiosity. If only I had a staff...

Dec 2, 2010 at 10:47 PM | Unregistered CommenterRob Schneider

With reference to energy requirements for windmills, I believe the turbine housing's are temperature and humidity controlled, this must be very costly. As well, some of the blades need to be in motion constantly to prevent warping. These modern giants have very little on board that Mr. Tesla and the Wright brothers wouldn't recognize.

Dec 2, 2010 at 10:52 PM | Unregistered CommenterC.M. Carmichael

As many of you have mentioned above typical capacity factors in the UK vary from 20 - 35% with occasional outlier such as Burradale (which set a world record a few years ago). However CFs do not tell the whole story as there is no point in generating electricity when we have little demand such as in the middle of the night. I have heard it said by professionals in the generation industry that the "dispatchability factor", or the average energy generated at an appropriate time as a percentage of the nameplate rating of the turbine, is approximately half of the capacity factor. This means that their useful energy output in the UK varies from 10 to 17.5%.

I consider one of the biggest looming energy disaster to be the UKs headlong rush to develop CCS for deployment in our new coal plants. This will result in the need for 30 - 40% more coal to generate the same amount of electricity as a non CCS plant due to the huge energy costs required to operate the capture process, pressurise the CO2, transport it and pump it underground. This is quite breathtaking stupidity. We may be unsure about how long it will be until coal reserves run low but this will certainly make it happen a lot faster. It would make you wonder who is advising Chris Huhne if we didn't know the answer to that question already thanks to the Bishop.

Dec 2, 2010 at 11:32 PM | Unregistered CommenterEdbhoy

@Rob Schneider,
I would ask you to review my link to the ERCOT of Texas and tell me what is wrong with what they are saying. Living in Texas, this oculd make a difference in my bill, if they arein fact under-rating the impact of windmill power.

Dec 2, 2010 at 11:33 PM | Unregistered Commenterhunter

Some points of clarification here. I make my living in high-performance motor and generator control (mostly industrial), and have done some work on the design of wind turbine generators over the years.

1. Wind turbines do not need to be "motored" up to the speeds where they can perform effective generation to the grid. If there is enough wind so that they can generate power into the grid, the wind can easily rev the turbine up to the speed to start generation because this is done without any load on the turbine. The challenges in this process are to keep the turbine from "overspeeding" while unloaded, and to properly manage the transition as the relays are engaged to connect it to the grid, suddenly loading the turbine. (Gas turbines face this challenge as well.)

2. Features like the feathering and braking of the blades are "failsafe" in any serious design, so do not require any continuous power when not operating. They are designed so they can be (and will be automatically) forced in the case of grid failure to the full feathered state (with battery power if necessary) and held there by a brake that requires no power to hold in position.

3. The "parasitic loads", as they are called, are quite low, a few percent. Seven percent sounds a little high to me, but may be reasonable. Certainly they do not approach 20-30%.

4. All designs, old and new, that I have ever seen, use AC generators. The older designs tended to use asynchronous AC induction generator that electrically modulated the motor "slip" and mechanically modulated rotor speed to keep the generator, which was directly tied to the grid, properly synchronized to it. Most newer designs use synchronous AC generators with permanent-magnet rotors. The AC output of these generators is electronically converted to DC, then converted back to an AC form that is synchronized to the grid. The advantage of this method is that the turbine can spin at the speed that produces the most power, even if that does not produce synchronous power directly out of the generator. Also, it can accelerate in gusts and decelerate in lulls, which greatly reduces wear and tear. The losses in the conversion are only a couple of percent, about the same as the losses in the rotor of the induction generator.

5. It is important to distinguish between the average power percentage produced by a collection of wind turbines, which is usually in the 20s, and the minimum that can be counted on, which is usually below 10%, and can be as low as 0%. The ~8% numbers people have quoted above are the second type. This number is important because it tells you how much other generating capacity can be replaced (usually not much).

Dec 3, 2010 at 12:20 AM | Unregistered CommenterCurt

It should be of interest that the various coal mine and coal industry shares are increasing in the market at a fairly good clip. This year's "global warming" appears to be due to all the coal the power utilities are going to have to burn to keep the US and Europe from freezing in the dark. This in addition to what China has been buying like a drunken sailor. And now that the Obama administration has again effectively put a ban of offshore drilling for oil, coal is going up in demand. Also, watch for Natural Gas futures to rise sharply.

So much for the "Green Revolution".

Western-Coal-shares-are-a-buy

Dec 3, 2010 at 12:36 AM | Unregistered CommenterDon Pablo de la Sierra

diggerjock: "the consumer .. would be well advised to come along at night and cut the cables ( or e.g. to encourage some terrorists to come along and blow them up)"

Green hedge fund investors excepted, blowing up wind turbines does not involve any terror or any risk to human life (other than to that of an incompetent saboteur). So terrorists will not be required, though politicians will no doubt seek to apply the label to the saboteurs. Some departmental science honcho said recently that wind farms, unlike nuclear power stations, do not need troops to guard them. That may be true now but it won't remain true when sabotage starts. Given their typical locations, they will be hard to guard. And the costs of guarding them will be substantial.

Dec 3, 2010 at 12:56 AM | Unregistered CommenterJane Coles

Dutch bureau of Statistics bulk figures i.e. (Installed Power*24*356)/(real produced kWh):
offshore Netherlands 25% of installed power
onshore netherlands 20% of installed power
this is including downtime for maintenance.

Dec 3, 2010 at 1:28 AM | Unregistered CommenterHans Erren

Capacity factor reflects the total electricity generated. Capacity value reflects the actual electricity taken into the grid. The grid operators calculate this. Typically less than 50% of the electricity generated is actually taken into the grid. This is why wind farm operators desperately wish to discover a way to store power. The national grid numbers are the one to pay attention to. 15% is a little high but is probably close to accurate. Denmark achieves their high 20 % capacity value because they can offload power to Norway when it is not needed in Denmark. Norway simply restrains the flow of water into their hydroelectric generators at there dams. This scheme in effect creates energy storage at the dam.

Dec 3, 2010 at 3:10 AM | Unregistered CommenterRich Carroll

After analyzing wind production data for over a year now, all I can say is that weather patterns do have a large effect on the output.

The main factor in comparing wind power for Industrial Wind Turbines seems to be location. That simple.

Here is a link to an article I did -- there is lots more on the site:
http://ontariowindperformance.wordpress.com/2010/09/24/chapter-3-1-powering-ontario/

There is a link to a previous paper at the end and a link to the data sources.

If you click on the TOC button at the top there are many more articles. Many directly addressing the capacity factor issue.

It really is hard to know how to answer your question, but in Ontario Canada, the Wind Turbine sites are highly correlated over a wide area, but the siting of the turbines and the quantity in an area (they seem to affect each other) are the big issues. Wolfe Island appears to have particularly poor output many days and hence has a low overall capacity factor. Sites near the western end of Lake Erie and on the shores of Lake Huron seem to do better.

Cheers!

Dec 3, 2010 at 5:42 AM | Unregistered CommenterDavid Robinson

Rich Carroll

Thank you for pointing out one of the most serious issues with wind power, which is electricity can not be stored unless you convert it to some other form of potential energy.

This is typically done by pumped hydro power. One aborted attempt was the Storm King Mountain project in the 1970s that Con Ed wanted to build as the worlds largest wet battery near New York City. Fortunately, it was stopped. It would have destroyed one of the most beautiful parts of the Hudson River valley.

We do have a number of such projects out here in California, typically used to store irrigation water as well. One such is the San Luis Reservoir near I5 in Merced County not far from San Jose. They use "surplus" power to pump water up into the reservoir during low peak periods and let the water run out to generate power.

Not very practical for electric power storage, but is vital to supplying water for the farmers during the summer. However, since the pump motors can also act as generators, they do use it as a secondary source of income.


Curt

Nice explanation of how the wind generators work. What most people miss is the bloody expensive kit that you need to convert DC back to AC.

Dec 3, 2010 at 6:16 AM | Unregistered CommenterDon Pablo de la Sierra

Interestingly, the Mafia seem to be taking an intense interest in wind farms in Italy. Now, you might think that this organisation has suddenly decided to 'go green' - you know, trading in Black Merc limos for Fiat 500s - that sort of thing - but of course the real explanation is encapsulated in a single word.
Money.
Like in the UK and other heads-where-the-sun-don't-shine governments, the Italian government provides subsidies for 'renewable energy' projects - so of course these lads see this as a great opportunity to make a quick buck (like, for instance, our Prime Minister's father-in-law).
Simply put, without subsidies, wind farms are just not viable.

Dec 3, 2010 at 10:20 AM | Unregistered CommenterDavid

@Hunter,

I took at look at http://noconsensus.wordpress.com/2010/09/15/10326/ which I think is the link you were referring to. I can't take much exception to anything written there. I continue to observe focus is on so-called "name-plate" capacity and how many homes would be powered by the new wind farm operating at this "name-plate" capacity--which is of course not realistic. Hence the design/planned "load factor" is important. There appears to be big differences between what is said to be planned vs. what history suggests is achievable. Those big differences are evident in this article where the power achieved for homes suggests a load factor of 100%, another link refers to achieving 33-47% "as long as minimum criteria are met for wind speed and turbine height", and ERCOT said to claim 8.7%. From the Wikipedia data (see above), over the last 20 years Denmark, claimed by many to be a leader in this industry, it's about 21%. The numbers are all over the place. I would expect that as there are so many factors which affect power output. This is why I'm trying to think of this as a probabilistic thing. Basing decisions/forecasts on one number doesn't seem prudent. And assuming we can get nameplate power (or even > 30% or so) out of a wind machine (as effectively claimed by much of what we read in the mainstream press also seem not prudent.

Dec 3, 2010 at 10:28 AM | Unregistered CommenterRob Schneider

Surely the true measure of efficiency is how much electriciity you get per quid spent. If you pay enough to get one nuke or an array of windmills and their support equipment, how much electricity do you get from each. Include decommissioning costs and show your working....

JF

Dec 3, 2010 at 12:20 PM | Unregistered CommenterJulian Flood

@ Julian Flood,

You'd think so, but from what's report in the press about these investments and the few government planning documents I've been able to find (Scotland), this doesn't seem to be the case. I'm sure I'm missing something and I suspect it's all confidential (even though there is large amount of government funding involved, e.g. the Viking Wind Farm in Shetland).

Dec 3, 2010 at 7:51 PM | Unregistered CommenterRob Schneider

Here's an open letter to DECC; The Wind Energy Association or any related intested party:
Please advise the total amount of electricity generated by UK wind farms for the period 28th November 2010 to 4th December 2010.

Dec 4, 2010 at 6:41 PM | Unregistered CommenterDavid

#David
You can find out for yourself from http://www.bmreports.com/bsp/bsp_home.htm - near the bottom is the "Generation by fuel type graph" - then hit the "current/historic" button and scoop the data into Excel.

I get 173,935 MWh.

But this is only about half the story. Only 2430 MW out of over 5000 MW is visible to the this system. You can pro-rate it if you like, but there is no way to get at accurate realtime information for the missing / embedded turbines. NB the metered turbines are nearly all in Scotland rather than being geographically representative.

Dec 5, 2010 at 12:13 AM | Unregistered CommenterFujirobin

Late to this thread but I second David Robinson's comment. The power is in the wind - turbines are a conversion mechanism. IMO there is a great need for published, transparent, measured, location and height specific wind regime data. There is also a need for transparent, post build performance evaluation reports. I also support the comments re: load matching and energy storage - at the moment there is an EU "technical strategy" pursuing wind generation which, AFAIK, does not have evidenced solutions for these other two essential features of renewable generation.

Dec 5, 2010 at 1:59 PM | Unregistered Commenternot banned yet

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