The tip speed in modern wind towers may be up to 6 times the wind speed.
They are shut off at high wind speeds so tip speed will never be near the
speed of sound (maybe 1/5th max). The wind close to ground level will be
very turbulent and unsuitable to power generation - as well there is more
wind high above the ground. Tower heights approximately twice to triple the
blade length have been found to balance material costs of the tower against
better utilisation of the more expensive active components. So the bottom or
the blade will be at least half the tower height above the ground.
A large high fan would be more visible, one would hope, and so the birds
would have more chance of seeing it and avoiding it.
See more at http://en.wikipedia.org/wiki/Wind_turbine#Tower_height
In the end, any power generation will damage the environment. I believe Wind
Power is relatively begin, compared to other sources.
Tim Murphy
-----Original Message-----
From:
Behalf Of Robert Inglis
Sent: Wednesday, 12 April 2006 12:47 PM
To: birding-aus
Subject: Windfarms and Birds
Ref: Paul Taylor's posting Wed, 12 Apr 2006 08:25:54 +1000.
Note: I am not criticising Paul Taylor; I am simply commenting on a
statement in the content of the
posting.
Paul is quoting from another source and I am suspicious of sources such as
Wikipedia.
Quote:
"The small turbines are dangerous to various raptors that hunt
California Ground Squirrels in the area. The larger units turn slower
and, being elevated higher, are less hazardous to the local wildlife."
I don't understand the reasoning.
If the squirrels can climb the towers then it wouldn't matter how high they
were.
I would have thought that tall towers would be more hazardous to birds,
including raptors.
Larger turbines would have longer blades. Longer blades would probably spin
at lower revolutions
than shorter blades.
However, the tip speed of longer blades would still be extremely high even
at low revs.
I believe that the tip speed may be in excess of the speed of sound.
(Hence the noise problem.)
At such speeds the significant part of the blade would probably be
'invisible', at least to human
eyes.
Perhaps they are also 'invisible' to the eyes of birds?
I would also think that the height of the tower has more to do with the
length of the blades than
anything else and, no matter how high the tower, the tips of the blades
would always be at about the
same minimum height from the ground.
Also:
Ref: "windfarms" posted by Terry Bishop, Tue, 11 Apr 2006 18:43:21 +1000.
Terry said:
"Located on Carcoar Dam, south of Orange NSW, Blayney Wind Farm is one of
the largest in New South
Wales. The wind farm consists of 15 turbines. Each of these is 45 meters
high with a rotor diameter
exceeding 45 meters. The capacity of each turbine is 660kW and the total
generation of the farm is
9.9MW."
Such a windfarm is, in my opinion, insignificant and is not a reasonable
example to quote when
examining the issues involved.
Before wind generation of power could be considered viable in this country
that farm would have to
be magnified several thousand times.
Imagine that!
Of course, the provision of windfarms will probably follow the same
principle as that used in 'land
development': small windfarms will be installed at a regular rate spaced a
significant distance
apart;
these farms would then be expanded gradually until they join up in several
very big farms covering
very large tracts of land. By the time the effect is really noticeable it is
too late.
Cheers
Bob Inglis
Sandstone Point
SE Qld
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