Vestas is a Danish company that is a leader in wind turbine technology,
and has a lot of turbines installed worldwide. They currently have
about 40,000 turbines installed, and today they install a new turbine
someplace in the world every 4 hours.
I am a little familiar with the company because we have considered and
are still somewhat considering purchasing a Vestas wind turbine on the
Bluffton University campus. This would be huge (either 2 MW or 3 MW)
and costing about 3 M$ for turbine and installation. We've already done
the initial short-term wind study that indicates our site is suitable.
There are four 1.8 MW turbines in the city of Bowling Green, OH just 40
miles north of Bluffton, and they have been working nicely for several
years.
Anyway, we have had representatives here talking about wind power and
talking about the specific Vestas turbines available. You can go to
their website and download advertising brochures. These do not have a
lot of technical data, but some data, including power curves.
I think the power curves started as real data, then got "pretty-fied" by
graphic-design folks. I assume they are still reasonably close to the
truth, but I don't know for sure. Here is the link to the page where
you can download the brochures in PDF format...
The brochures for the different sizes and models are not identical in
terms of the way the data are displayed. For example, the
top-of-the-line V90-3.0MW brochure shows a single line on the power
curve. But the V80-2.0MW and V80-1.8MW models show some additional
lines for situations in which you are trying to reduce noise.
The way I understand it, these turbines synchronize to the power grid by
electronic conversion rather than running the generator at synchronous
speed. They have variable-pitch blades and also a variable-ratio
gearbox. The blades can rotate over a range of roughly 8 rpm up to
about 20 rpm. The generator can run over a range of roughly 1500 rpm to
1900 rpm. These can be adjusted independently to provide some
combination of lower noise or higher power, and can also provide more
steady power in varying wind conditions. The V80-1.8 and V80-2.0
brochures show that the blades can be pitched to run more slowly, and
then the gearbox is adjusted for higher speed for the generator to keep
it close enough for the electronic synchronization with the grid to be
within operating specs. This reduces the very high speed of the blade
tips, and that is where the noise reduction occurs. If noise reduction
is not necessary (e.g. offshore locations) they can rotate the blades
faster.
There are some additional graphs in the brochures that are probably more
fabricated, and there is an aspect of them that is either incorrect, or
I don't completely understand. For example, in the V90-3.0MW brochure
some graphs show how the wind speed varies, the blade pitch adjusts the
blade speed, the gear-box adjusts the generator speed, and the power
output remains steady. That makes sense to me if the wind speed is
above the minimum speed needed to provide the rated power. But the
graphs show steady output of 3 MW even when the wind speed drops a
little bit below the speed the power-curve shows is necessary for 3 MW.
Either the graphic designers of the brochure goofed, or there is
something going on that I don't understand.
Michael D. Edmiston, Ph.D.
Professor of Chemistry and Physics
Bluffton University
Bluffton, OH 45817
(419)-358-3270
edmiston@bluffton.edu