>> I've also heard that over a certain windspeed that it is unsafe for the
>> turbines to operate which seems rather ironic
>
> I was watching some wind farms, and wondered why the older, smaller ones go
> slower than the huge new ones. I could think
> of some engineering reasons that might apply.
The manufacturers have different designs. Most of the large wind
turbines have transmissions between the hub and and generator. This
allows them to change rotational speeds. Also, the blades feather in
higher winds to prevent overspeed. They've got a lot of control over
them. There is also a braking system and shaft locking. Finally, they
can always adjust angle to the wind. Lots of ways to control
rotational speeds under most conditions. However, there is one time
the operators will idle their turbines. That's when a supercell is
rolling through with a strong wind-shift. Due to the gyroscopic
effect, you can only change direction on these things so quickly and
if the wind sheer is to violent, it can't redirect fast enough.
Speaking of wind sheer, this is one reason why they idle the turbines
because the boundary layer is deep enough that you have too much of a
differential in wind speed or direction from top of disk to bottom of
disk. That's really hard on some of them.
Base line generating plants, such as nuclear or coal, need to be run
near maximum capacity 24/7. Nuclear doesn't take kindly to load
variations and coal plants are only running at maximum efficiency
after everything is stabilized at precise settings which can take many
hours to achieve. Predictions of wind capacity are done days in
advance and the power plant generating capacity is determined
accordingly. If the wind is stronger than expected, they will idle
wind turbines. If it's less than expected, they have to supplement
with natural gas boost plants or fire up another coal boiler which is
a nightmare. So, operators with large windfarms will project to
something like 75% maximum capacity for projected winds and idle some
of the turbines as necessary.
Cost per MW or BTU and determining payback is a joke. The fact is that
a well designed wind energy facility capacity is a win-win. The
natering nabobs of negativism (driven by the coal/oil industry and
east-coast media idiots) say that wind and ethanol are negative
energy. It takes more energy to build/maintain/operating them than the
energy you get out of them in return. Ethanol is frequently the brunt
of this unfounded criticism. The reality is that if you applied the
same exact rules of calculation to coal or oil you would find that it
would take about 1.5 barrels of oil to get 1 barrel of oil out of the
ground. Some of the things are laughable.
My favorite point of entertainment has to do with the theoretical
calculations for maximum wind turbine density. The aerodynamicists
recognize that you can't stack them too closely together because of
the turbulance coming off of the blades (which is being addressed with
new blade designs). The axe-grinding folks say that each turbine sucks
up 30% of the energy out of the wind and that's why you can't put them
too closely together because the downwind turbines won't get enough
wind to turn. Their calculations assume closed tube air movment.
That's not how it works in the real world. In fact, my own experience
being around high-density wind farms is that the wind is still blowing
at the same speeds as measured by the airport weather systems.
Wind energy works extremely well when the entire energy production
ecosystem is built around it. You need base-line production of
coal/nuclear/hydro which provides gross minus renewable production.
Then you have natural gas powered boost plants which share the
responsibility with the wind. When the wind turbines are at 100%, the
gas plants are idle. When the wind ain't blowing, they're at 100%.
--
Ken Norton
ken@xxxxxxxxxxx
http://www.zone-10.com
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