Excerpted from: http://www.windpower.org/en/tour/wres/enrspeed.htm
The Power of the Wind: Cube of Wind Speed
The wind speed is extremely important for the amount of energy a wind
turbine can convert to electricity: The energy content of the wind varies
with the cube (the third power) of the average wind speed, e.g. if the wind
speed is twice as high it contains 2 3 = 2 x 2 x 2 = eight times as much
energy.
Now, why does the energy in the wind vary with the third power of wind
speed? Well, from everyday knowledge you may be aware that if you double
the speed of a car, it takes four times as much energy to brake it down to
a standstill. (Essentially this is Newton's second law of motion).
In the case of the wind turbine we use the energy from braking the wind,
and if we double the wind speed, we get twice as many slices of wind moving
through the rotor every second, and each of those slices contains four
times as much energy, as we learned from the example of braking a car.
Philip
At 12:12 PM 1/27/2008, you wrote:
I keep hearing different claims about the force in an increasing wind.
Some say it goes up to the cube, some say to the square.
Since E=M times Vsquared, and I find that people generally tend to
exaggerate to make their points seem stronger, I would put my money on the
force going up to the square of the velocity.
Norm
S/V Bandersnatch
Lying Julington Creek FL
30 07.72N 081 38.4W
> [Original Message]
> From: Arild Jensen <[EMAIL PROTECTED]>
> To: TWL2: <[EMAIL PROTECTED]>
> Date: 1/25/2008 2:19:16 PM
> Subject: (T&T: & TWL2:) Look. It's a Freighter. It's a Sailboat. It's.
Both
>
>
>
>
> > -----Original Message-----
> > (SNIP) However the theory is that being a kite it can get up to a higher
> > altitude where wind speeds can be consistently over 50 knots, and even
> higher they
> > can often be found at 100 knots or more. So this small sail would have
to
> > be very tough and have a long line,
>
>
> Wind force increases according to the cube rule.
> Double the wind speed and the force increases by cube. 2 x 2 X 2 = 8
> Therefore doubling the wind speed increases the force 8 times.
>
> A sailboat spinnaker is fairly close to the sea surface. A kite 100 - 200
> feet up can well experience wind speeds twice as fast. That means the same
> sail will deliver 8 times the pulling force compared to having it close to
> sea surface.
>
> Yes the sail has to be very strong. But we routinely use parachutes to
brake
> returning space shuttles, arrest landing jet air craft and air drop
> complete tanks and other cargo. It not exactly experimental technology.
> Cheers
> Arild
>
>
>
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Philip & Marilyn Lange
AE4OV & KD4JRC,
ORYOKI
Witness 35 Catamaran
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