Tag Archives: Power Consumption

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.

Wolfe Island Shoals Economic Impact

The Wolfe Island Shoals project was the largest contract awarded in the last round of wind projects, with a capacity of 300MW.  It is located at the eastern end of Lake Ontario and is slated to be the first “off-shore” wind project in at least Canada, and may end up beating out Cape Wind for that dubious honour in North America.

The project developer (Windstream) thought it would be a good idea to remind everybody how many jobs are at stake and what the economic impact of the project’s construction and operation would be.  So their project manager (Ortech) hired a consultant (Aecom) to write a paper entitled “Potential Employment and Income Impacts in Ontario from the WI Shoals Project“.  The executive summary sounds impressive.  It’s a $1.36B (yes, that’s a “B”) construction project, 1900 jobs and $89M in labour income  for 5 years.  Then 175 jobs and $9M in labour income for 20 years.  No mention of labour income to dismantle the project – they must have just forgotten to mention it.  I am (of course) more interested how they got those numbers and what other details they forgot to mention. Continue reading Wolfe Island Shoals Economic Impact

Power Consumption

It might seem intuitive that turbines must produce a lot more power than they consume, but without actual numbers, who really knows? It is fairly easy to find out how much power is being generated by most wind farms. What is so far been impossible is to find out how much power they consume during their operation. So far I’ve looked for information on both wind farm and individual turbine consumption and have found nothing. Without this information it is impossible to know how much of a contribution a wind farm actually makes to the grid, and this in turn affects the calculations of CO2 savings and so on. Continue reading Power Consumption