U Minn and Vestas Reality Check

A commenter recently pointed me to a University of Minnesota at Morris study  from 2008 that contained a wealth of interesting information about their one Vestas V82 1.65 mw turbine and how it has performed in 2006 through 2008.  The V82 is a rather common wind turbine, deployed in large numbers throughout the world.  Falmouth’s turbines are V82’s.  Thank you John.

Recently I’ve been working on the apparent decline of Capacity Factor over time and since this report appeared to have fairly granular hub wind speeds and production levels perhaps I could see if it suffered the same loss (somewhere between 1.5% and 2% per year) as has been noted in Ontario, Denmark and now Ireland.  The trend was in fact slightly downward, but the numbers weren’t consistent enough for just one turbine over just three years for me to put much confidence in that conclusion.  But during my examination of the report I came across a number of other interesting tidbits.

Electricity Production

In Vestas’ Life Cycle Assessment [backup link] of the V82 they “calculated”, per page 20, that at a Danish “typical” average wind speed of 7.38 m/s it would generate at a Capacity Factor of 40.8%, or an average of 673.2 kw out of its 1650 kw capacity.  I took UMinn’s daily average production and wind speed figures and produced the following clickable chart:

UMinn Reality vs Vestas Claims
UMinn actual production

The Vestas’ claim is represented by the yellow dot, which is clearly above the actual average of about 500kw – a decrease of 25%.  This is not trivial.  Adding to the exaggeration, below are the actual Capacity Factors for a selection of European countries – DK stands for Denmark.  So their “typical” and their “calculation” are each off by about 25%.  So instead of 40.8% we have 22.8%.

This exaggeration cannot be unintentional or uninformed.  The value of the turbine is slightly over half of what they claim.

Power Consumption

I have long been trying to nail down how much electricity a wind turbine consumes.  The wind industry seems quite reluctant to publish this.  As an example, in the V82 Life Cycle Assessment they lump all the manufacturing, operation, transportation etc. together into a 20-year lifetime total of 3392 mw-h, not willing to break it out.  Luckily, the UMinn’s reports include negative production numbers when the wind isn’t blowing enough to produce – about 3.5 m/s.  Each day they listed the minimum production, along with the minimum wind speed.  UMinn didn’t reveal the time increments, but fully 85% of the days during the 3 years had a negative-production period.  I graphed the results:

Daily minimum production vs wind speed
U Minn Minimum Wind Chart

The above chart shows the minimum productions plotted against the minimum wind speeds.  As you might expect, whenever the wind speed is above the 3.5 m/s cut-in speed the turbine starts producing, but not getting consistently into positive territory until about 4.5 m/s.  Notice the results when the wind doesn’t get above 3.5 m/s – typically there’s a MINUS 50kw of production.  This is power that must be supplied from the grid just to keep the turbine in business.  And 50kw seems to be what the turbine uses to stay alive in good weather.  In the winter it gets slightly higher – the highest negative numbers were in the 80 kw range.

So, finally, we have a measurement of just how much electricity they consume!  50 kw is quite a bit higher than my previous findings, which originated in industry statements and cash flow calculations.  Recall that the average Danish turbine produces about 376 kw (1650 * .228).  So a V82 operating in Denmark consumes roughly 13% of what it produces.  No wonder they want to keep this quiet.

I think the reason it is so high for the V82 is that the generator must use an electromagnet, compared with newer turbines that use rare-earth-based “super” permanent magnets.  In their Life Cycle Assessment for the V82 they mention the iron and copper in the generator but do not mention any rare earths.

Wind Shear

The wind gets stronger the higher above the ground you get, generally in a logarithmic manner.  The rate at which it gets stronger is embodied in the Wind Shear Exponent, which varies from 0.1 over water to 0.4 in urban areas.  UMinn’s exponent was 0.244, which is typical of a rural landscape with trees and small buildings.  UMinn produced the picture below which graphically represents how the wind shear affects the wind turbine.

U Minn wind shear
U Minn Wind Shear

Note that at the bottom of the rotors the average wind speed is 6 m/s, while at the top it is over 8 m/s.  This is a big difference in terms of the forces, which flex the blades every rotation and no doubt contribute to their wear.  This also contributes to noise generation, and may be responsible for the very annoying “thumping” that wind turbines sometimes produce.

17 thoughts on “U Minn and Vestas Reality Check”

  1. The hourly production values that the IESO (picked up by Sygration) reports are net of station service. Hourly output would be reported as 0 if the unit was a net consumer for that hour. This means that using the IESO hourly data to estimate capacity factors will always overstate the actual capacity factor by the amount of station service consumed while stationary. Except when a turbine is using heating system while stationary, I’d be surprised if the amount of usage while stationary is significant.

  2. From this article:


    The University of Maine, UM, decided to install a 600 kW wind turbine made by RRB Energy Ltd, an Indian company, at its Presque Isle Campus. Results from a 20-month wind resource assessment indicated the campus receives enough wind for a community wind project, not a commercial wind project. 

    Community wind power is defined as locally-owned, consisting of one or more utility-scale or a cluster of small turbines, totaling less than 10 MW, that are interconnected on the customer or utility side of the meter. The power is consumed in the community and any surplus is sent to the utility which supplies power as needed.

    The purpose was to generate power and to use the wind turbine as a teaching tool for the students. Because it is almost impossible to obtain operating data from the vendors, owners and financiers of wind facilities, UM, to its credit, decided to make available all of its wind turbine operating data. 


    Capital Cost and Power Production

    Estimated capital cost $1.5 million
    Actual capital cost $2 million; an overrun of 33%
    The project was financed by UM cash reserves and a $50,000 cash subsidy from the Maine Public Utilities Commission.
    Estimated useful service life about 20 years.

    Predicted power production 1,000,000 kWh/yr
    Predicted capacity factor = 1,000,000 kWh/yr)/(600 kW x 8,760 hr/yr) = 0.190

    Actual power production after 1 year 609,250 kWh
    Actual capacity factor for 1 year = 609,250 kWh/yr/(600 kW x 8,760 hr/yr) = 0.116; a shortfall of 39%
    Value of power produced = 609,250 kWh/yr x $0.125/ kWh = $76,156/yr; if O&M and financing costs amortized over 20 years are subtracted, this value will likely be negative. 

    Actual power production after 1.5 years 920,105 kWh
    Actual capacity factor for 1.5 years = (920,105 kWh/1.5 yrs)/(600 kW x 8,760 hr/yr) = 0.117

    Operation and Maintenance

    According to the European Wind Energy Association: “Operation and maintenance costs constitute a sizable share of the total annual costs of a wind turbine. For a new turbine, O&M costs may easily make up 20-25 percent of the total levelized cost over the lifetime of the turbine.” 

    Power Used by the Turbine (Parasitic Power)

    Parasitic power is the power used by the wind turbine itself. During spring, summer and fall it is a small percentage of the wind turbine output. During the winter it may be as much as 10-20 % of the wind turbine output. Much of this power is needed whether the wind turbine is operating or not. At low wind speeds, the turbine power output may be less than the power used by the turbine; the shortfall is drawn from the grid. 

    Two little-wind days were selected; a summer day and a cooler winter day to show that in summer the parasitic power is less than in winter. In winter, the wind speed has to be well above 4.5 m/s, or 10.7 miles/hour, to offset the parasitic power and feed into the grid. Speeds less than that means drawing from the grid, speeds greater than that means feeding into the grid. 

    This will significantly reduce the net power produced during a winter. On cold winter days, even at relatively high wind speeds of 10.7 miles/hour, or greater, power is drawn from the grid, meaning the nacelle (on big turbines the size of a greyhound bus) and other components require significant quantities of electric power; it is cold several hundred feet above windy mountain ridges.

    14 May, 2010, wind speed 2.9 m/s (6.9 miles/hour), net power output  -0.3 kW.
    20 Nov, 2010, wind speed 4.5 m/s (10.7 miles/hour), net power output -5.6 kW.

    Below is a representative list of equipment and systems that require electric power; the list varies for each turbine manufacturer.

    – rotor yaw mechanism to turn the rotor into the wind
    – blade pitch mechanism to adjust the blade angle to the wind
    – lights, controllers, communication, sensors, metering, data collection, etc.
    – heating the blades during winter; this may require 10%-20% of the turbine’s power
    – heating and dehumidifying the nacelle; this load will be less if the nacelle is well-insulated.
    – oil heater, pump, cooler and filtering system of the gearbox
    – hydraulic brake to lock the blades when the wind is too strong
    – thyristors which graduate the connection and disconnection between turbine generator and grid
    – magnetizing the stator; the induction generators used to actively power the magnetic coils. This helps keep the rotor speed constant, and as the wind starts blowing it helps start the rotor turning (see next item)
    – using the generator as a motor to help the blades start to turn when the wind speed is low or, as many suspect, to create the illusion the facility is producing electricity when it is not, particularly during important site tours. It also spins the rotor shaft and blades to prevent warping when there is no wind.


    The huge difference between predicted and actual capital cost and capacity factor would be disastrous for a commercial installation. Because this is for “teaching purposes” such a detail is apparently not that important. The capital cost and any operating costs in excess of power sales revenues will likely be recovered by additions to tuition charges.

    UM should find less expensive ways to educate students in all areas, not just wind power. Cost per university student in the US is already well over 2 times that of Europe, a competitive disadvantage.

  3. It is my understanding that the parasitic loads on wind turbines are primarily related to the pumps for the lubrication systems. I would think that the magnet in the motors draw more reactive power (KVAR) instead of active power (KW).

    As for the size of the parasitic load, I looked at the second by second wind “generation” at the 3 windmills operated by Kodiak, Alaska. They nominally can produce a total of about 4,500 KW. During October 2010, the maximum production (for 1 reported second) was 4,748 KW. The modal value (for 11,866 seconds) was 4,565 KW. The data included many negative numbers where the grid was providing the parasitic load while the generators were idle. The maximum parasitic load (for 1 reported second) was 77 KW. The modal value (for 57,935 seconds) for the parasitic load was 38 KW.

  4. So are you saying that once the turbine is generating electricity it then supplies its electromagnet with its own power? And that this is accounted for in the production numbers? At least the positive ones? What happens when there is no generation – is the magnet kept energized? If not, how does the generation get started?

    You have access to second-by-second production records? The best I’ve ever come across are minute-by-minute, and I’ve only come across one of those (Katzenstein and Apt). Are these records public?

  5. As I interpreted the system from the numbers I obtained, the meter was between the wind farm and the utility, producing net power flow each second. Any parasitic load, whether due to oil pumps or charging the magnet, reduces the flow from the wind farm to the utility and when the wind generation is low or zero, the meter then “turns backward” showing the size of the parasitic load.

    It is my understanding that the charging current for magnets is mostly reactive power (KVAR) instead of active power (KW), but I don’t know the proportions or the size relative to the oil pumps.

    I reported once before to this group on my look at these Kodiak wind data, with the emphasis then on the second by second swings in the wind generation levels. I used these Kodiak wind data in a presentation FERC at its Staff Technical Conference on Increasing Real-Time and Day-Ahead Market Efficiency through Improved Software, Docket No. AD10-12-003, this past Wednesday, June 25, 2012. My presentation was “Competitive Market For Imbalances,Not Penalties”
    FERC webcast most of the proceeding, and then archived all of the proceeding. The above link accesses the slides and the archive of the proceeding. Look for me late on the Wednesday broadcast.

    As to second by second or even minute by minute data, there is little need to report the data since it is of little consequence unless you are going to create a payment stream, such as I discuss in my FERC presentation.

  6. A fascinating article. I believe this exposes the reason actual production numbers are not given, but capacity is substituted. This is the type of information citizens and leaders need in order to make smart decisions about wind energy in this country. Parasitic power perfectly describes wind energy. Thanks so much for taking the time to put this together and publishing it. It’s important information!

  7. The University of Maine at Presque Isle has a 600 KW turbine on its campus and aspires to make all data public, for educational purposes. The turbine was built in May of 2009 and was on line in July of 2009.
    For the past two years the turbine and its data reporting equipment have been plagued by breakdowns and glitches. One total breakdown was for 290 days. Lately it has been reporting current net power and total net power (since the latest repair).
    Over a recent low-wind 120-hour period (five days) current “power” was reported negative almost all of the time and the net total dropped by 40 KWH. That’s an average parasitic warm-weather draw from the grid of 3 KW. Another tidbit of information.

  8. it appears you have no idea how to calculate capacity factor or energy output of a wind turbine. Please learn how to do this before spewing misinformation and calling it “reality”. Maybe come back here and post what it really is? Hint… it’s not 22.8%

  9. This sort of comment is typical of wind proponents. They offer up personal attacks but no substantive facts. If “b” thinks its not 22.8% (and that number came from a peer-reviewed journal), then I’d like “b” to tell us what it is, and how he got to that number. I’m not holding my breath.

  10. Hi Mike, I see you’ve got your own blog going. Thanks for pointing us to your take on this issue. I noticed you didn’t mention my actual publicly-available measurements.

  11. Wayne,

    In areas with low CFs, such as the Northeast at about 0.25, about 30% of the hours of the year the windspeed is insufficient, less than 3.5 meter/sec, to turn the rotors, parasitic energy is being consumed, the meter is running backwards and will run forwards again when the wind picks up and the output overcomes the parasitic draw.

    Placing a meter that measures only the backwards flow of the energy over a period, say a year, would show the effect on annual CF.

    We need a special ops team of the CIA to install the meter with wireless telemetry.

  12. > If “b” thinks its not 22.8% …

    A year later and no one has done the math? Shameful! :-)

    The DK data:

    Nameplate capacity: 3.1 GW
    Annual production: 6.1 TWh
    Capacity factor: 22.8%
    I don’t know what “load share” is, probably electricity exports. Don’t need it.

    From the annual production, the average production is the former divided by the hours:

    6100/(24 * 365) = 0.70 MW

    That divided by nameplate capacity is the load factor:

    0.70 / 3.1 = 22.5%


    Note – there were only two places of accuracy. If the nameplate capacity was 3.07 GW, then I would have gotten the “better” 22.8%.

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