New Wind Generator Being Developed

[Buckanear Bill]

The power in the wind is proportional to wind speed cubed. Simply stated, when the wind speed doubles, the power available in the wind is 8 times greater. That is just a guide, because you still need to capture it.

[StuM]

Originally Posted by Buckanear Bill

The power in the wind is proportional to wind speed cubed. Simply stated, when the wind speed doubles, the power available in the wind is 8 times greater. That is just a guide, because you still need to capture it.

I don't see how that can be in so, even in theory. It is proportional to speed squared!

I've already said it a few posts back, but since it appears to be a common misconception, I'll amplify that comment.

In practice it is definitely not so. Just look at the power curve on a wind generator. Here's the D400 as an example.

10knots approx 45W
20 knots approx 190W
10 x 2 = 20: 45 x 4 = 190

15 knots approx 115W
30 knots approx 375W
15 x 2 = 30: 115 x 3.25 = 375W

So a bit less than ^2 on average, not ^3.

(Same as load on a sail - which is also a speed squared function.)

[Stumble]

Originally Posted by StuM

I don't see how that can be in so, even in theory. It is proportional to speed squared!

I've already said it a few posts back, but since it appears to be a common misconception, I'll amplify that comment.

In practice it is definitely not so. Just look at the power curve on a wind generator. Here's the D400 as an example.

10knots approx 45W
20 knots approx 190W
10 x 2 = 20: 45 x 4 = 190

15 knots approx 115W
30 knots approx 375W
15 x 2 = 30: 115 x 3.25 = 375W

So a bit less than ^2 on average, not ^3.

(Same as load on a sail - which is also a speed squared function.)

The formula for theoretical power available to a turbine is...

Density x swept area ^2 x velocity^3 x Constant

So no the available power doesn't go up by a cube of wind speed, but as a factor of the cube of wind speed.

The real issue since you can't do anything about the wind speed is that the larger the swept area the more power there is available, which is why turbines should be as large as possible.


And actual power generated is meaningless. turbines are designed for a specific speed, or more likely for a low cut in speed. Which makes then less efficient at higher wind speeds. For any given wind speed there is an optimal shape, exced that range and efficiency drops.

[TrentePieds]

StuM:

Here is a simple statement of the calculation of the power of wind:

Where:
P = Power output, kilowatts
Cp = Maximum power coefficient, ranging from 0.25 to 0.45, dimension less (theoretical maximum = 0.59)
ρ = Air density, lb/ft3
A = Rotor swept area, ft2 or π D2/4 (D is the rotor diameter in ft, π = 3.1416)
V = Wind speed, mph
k = 0.000133 A constant to yield power in kilowatts. (Multiplying the above kilowatt answer by 1.340 converts it to horse- power [i.e., 1 kW = 1.340 horsepower]).

Here is a much better explanation:

http://www.raeng.org.uk/publications...3-wind-turbine



Here is a nice calculator to play with:

Wind Turbine Power Generator Equation Formulas Design Calculator



TrentePieds

[StuM]

Stumble, TrentePieds.

Thank you . I stand corrected.

And apologies to Buckanear and Chuck!


I've always gone on the basis of empirical evidence and never looked at the formula.

(Interesting that the theoretical ^3 is less than ^2 in practice)

[TrentePieds]

Never pick an argument with anyone named Betz - he'll only confuse you ;-)!

TrentePieds

[Stumble]

Originally Posted by TrentePieds

Never pick an argument with anyone named Betz - he'll only confuse you ;-)!

TrentePieds

And take all your money.

[Buckanear Bill]

No problem, StuM! Engineers (my team!) know the real world is different from the theoretical one. Complex aerodynamics and stuff like that tend to trump the theory. That's why you can't capture even the theoretical (Betz) limit. So the D400 conforms to your analysis because of all those complicating real world factors. So you need to take into account the cubing effect of the wind speed, because that's what is impacting a wind turbine, even though it can't capture all that power. One my company's designs is designed for maximum efficiency at 17 - 18 mph wind. Above and below that the blades are not so efficient. Here is another source of wind turbine info: iowaenergycenter.org/wind-energy-manual/wind-and-wind-power/wind-speed-and-power/

[Rustic Charm]

So is the concenus with all you wind guru's is that the new design is bunkem?

[Stumble]

It's right up there with the oscillating wind generator. It may have a narrow specialized application where it works well, but generally I doubt it will work. I don't think it's bunk, because I am willing to give this guy the benefit of the doubt that he believes it will work.

[Gadagirl]

Originally Posted by Stumble

It's right up there with the oscillating wind generator. It may have a narrow specialized application where it works well, but generally I doubt it will work. I don't think it's bunk, because I am willing to give this guy the benefit of the doubt that he believes it will work.

I am admittedly pretty ignorant of wind generation technology. So to enable my understating of why oscillating technology does not work, could you explain to me why? I want to understand, but please remember to explain in lay person language and for average IQ.

[Stumble]

The design is to place an unfixed turbulence generator into the breeze. As it rocks and rolls back and forth the ball joint it is attached to converts the motion to electricity. The problem is that the forces from a tall turbulence generator. As I understand it they worked at the small scale, but as they get bigger the wind shear and forces become uncontrollable.

[Rustic Charm]

These oscillating generators are on our states marine building. They are said to be very efficient.

[socaldmax]

Originally Posted by Buckanear Bill

No problem, StuM! Engineers (my team!) know the real world is different from the theoretical one. Complex aerodynamics and stuff like that tend to trump the theory. That's why you can't capture even the theoretical (Betz) limit. So the D400 conforms to your analysis because of all those complicating real world factors. So you need to take into account the cubing effect of the wind speed, because that's what is impacting a wind turbine, even though it can't capture all that power. One my company's designs is designed for maximum efficiency at 17 - 18 mph wind. Above and below that the blades are not so efficient. Here is another source of wind turbine info: iowaenergycenter.org/wind-energy-manual/wind-and-wind-power/wind-speed-and-power/

Sounds like a good case for variable geometry blades.

[socaldmax]

Originally Posted by Rustic Charm

These oscillating generators are on our states marine building. They are said to be very efficient.

Those look like vertical axis wind generators to me. I've heard they are not as efficient as HAWT.