V80 vs V82 – Early Days

It has been interesting comparing the difference in production between the three turbines for the last few weeks.

I don’t have perfect data.  The communications to the north turbine were not completed until Nov 14, so while the turbine was producing, the only way I could gather data from it would be to drive out to it.  I prefer doing such things from my desktop, so I have limited data for comparison for much of the time.

The new turbines have had a little bit of work done to them.  Vestas has installed internal cranes which were not available at commissioning.  And there have been a few other bugs.  No big deal, but the turbines are off line for a day or two to do that.  To top it off, the V80 had a warranty repair on its bearings, which kept it off line for awhile.  So I don’t have a large data set.

But here is what I do have.  The V82’s produced more than the V80 in 7 out of 9 time samples taken at the same time.  The V82’s produced between 4% and 72% more power than the V80 during the times they outperformed.  And the V80 beat them by 8% and 12% for the two times they were beaten.

So early indications are that the V82 is more productive at this site.  But why is this?

First, the V82 has 1 metre longer blades, and so it has a swept area that is 5% larger.  More air equals more production, in general.

The V80 has higher cut in/cut out speeds.  The cut in speed is 4 m/sec, and the cut out speed is 25 m/sec.  For the V82, the cut in wind speed is 3.5 m/sec, and the cut out wind speed is 20 m/sec.  This means the V82 will produce in low winds, when the V80 is not producing.  And the V80 will produce 1800 kW maximum in high winds, compared to the 1650 kW for the V82.  The V82 will cut out earlier, and so produce nothing at times when the V80 is producing at maximum.

The cut in/cut out wind speeds are not directly comparable though.  They use different logic.  I am not certain what the logic is, but if one model uses a rolling 10 minute average wind speed, and another uses a 1 minute average, or a 10 minute average, but not rolling, then the results would be different.  The V82 will cut out less than one would expect based purely on its rated cut out wind speed.  The winds in November have not been high enough to cut out either turbine.  If November had very high winds (>20 m/sec) for a very long period (I wish…), the results could be dramatically different.
Micrositing has something to do with the wind turbines’ productivity.  The middle turbine is about 10 feet higher in elevation than the south turbine (the V80), and about 5 feet higher than the north turbine.  This matters.  How much?  Time will tell.  The two new turbines are closer together, and somewhat separate from the V80.  That means they will incur array losses when winds are from the NNE or SSW.  The new turbines will affect the V80 somewhat, and vice versa, but the 900 m distance to the nearest one will minimize that affect.  I have definitely witnessed array losses at one time, when the north turbine outproduced the middle turbine by 64% for a few hours in light winds.

The turbines have different exposure to obstacles in different directions.  While the area the turbines are located is fairly open, there are some trees, and a few houses and barns, and small hills, and these will affect  production when the wind is from a particular direction.

Over the course of a year, the wind models predict that the V82 will out produce the V80 in this location by about 4-5%, assuming similar availability.  Time will tell, but early indications are that this may be a  conservative estimate.

And there is one other very significant implication.  Different turbine models will produce at different levels in different wind speeds and directions.  And more turbines will increase this variability in output.  The result of multiple turbines producing different amounts depending on the winds will be that wind turbines will supply firmer power, because when one turbine is producing more, another may be producing less, and so there is less total variability.  Throw in some geographic dispersion, which will vary the winds more, and the power produced will become even less variable.

One can hope that system planners understand this.

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