26
votes
Why are wind turbines installed slightly "nose up" as opposed to the blade disk being perpendicular to the ground?
Short answer- because the pylon causes too much interference otherwise. Tipping the rotor up increases the clearance to the pylon and reduces flow perturbations and their associated vibration problems....
- 4,607
15
votes
Accepted
Why don't we just build a giant wind turbine?
Not everything scales linearly. In particular, the cross-sectional area of supports required scales faster than height of a structure, all else held constant. This explains why ants have tiny thin ...
- 11.4k
11
votes
Is the main goal for wind turbines to take maximum energy for a given diameter?
The function of the wind turbine is to extract as much as possible energy from the moving mass of air. The energy of a mass $m$ of air is
$$KE = \frac{1}{2}m v^2$$
and the power is (because the mass ...
- 24.3k
11
votes
Wind farms that wind up in the wind, and then unwind producing energy when the wind is still
The storage part of the RES systems is probably the biggest challenge today.
There are several ways to store energy. By far the most used way today is Pumped storage hydroelecticity systems.
...
- 24.3k
9
votes
Relationship between wind velocity, turbine rotor diameter, and power output
It's not a simple relationship.
First let's deal with the kinetic energy of the wind passing through the rotor.
The mass of air passing through it in one second, $m$, is equal to the the density of ...
- 3,751
6
votes
Why isn't it possible to build a car moved by wind power?
The fundamental problem in this case is that the turbine in not powered by 'wind' as such but by the relative motion of the car through the air.
This is not 'free' energy, because the turbine must ...
- 15.2k
6
votes
Wind farms that wind up in the wind, and then unwind producing energy when the wind is still
You've described energy storage, or physical batteries. You wouldn't need half of each wind farm dedicated to this; you would simply store the excess, beyond what is used at a given time. It's not ...
- 821
6
votes
Wind farms that wind up in the wind, and then unwind producing energy when the wind is still
I suppose what you had in mind with your question was something like, every single turbine winches up a heavy weight to its tower while surplus energy is available, then lowers it again to recuperate ...
- 191
5
votes
Wind turbines with down tower power units. Why aren't they more common?
The math doesn't make any engineering sense.
A 5MW turbine typically rotates at about 10 RPM, near enough 1 radian per second.
Assuming you had reasonably big sprockets on the chain drive, say 2 ...
- 12.5k
5
votes
Accepted
Advantages/Disadvantages of two-bladed windmill?
A 2-bladed wind turbine is less stable mechanically than 3 (or more) blades.
Because the two blades are in line, it is much easier to twist the hub of the turbine in the direction along the line of ...
- 12.5k
5
votes
Why don't we just build a giant wind turbine?
The cost of a wind turbine is not proportional to its size - like everything that needs to be manufactured, the cost exponentially increases as manufacturing becomes more complex, beyond what has been ...
- 587
5
votes
Wind farms that wind up in the wind, and then unwind producing energy when the wind is still
You're describing a Gravity Battery. While the other answers have pointed out that water is the most common lifted weight, EnergyVault is a Swiss company that's basically lifting concrete blocks. The ...
- 151
4
votes
What is the power and max flow rate required to rotate a 300 W wind turbine?
You need to push air through the turbine at 11 m/s, or just above. That's what the rated windspeed means: it's the lowest windspeed at which the turbine hits rated power, at standard atmospheric ...
- 3,751
4
votes
How do 3 blade turbines come so close to the Betz Limit?
The Betz limit is based on an extremely crude model for an actuator disk. If you want to compare the performance of the product of a billion dollar industrial development program, let's at least use a ...
- 4,607
4
votes
Accepted
Why wind turbine dont use high lift coefficient airfoils?
I've finally got a few minutes to try to answer this.
Torque is bad. It's necessary, but it is bad. Ideally, you want the turbine to spin infinitely fast at almost zero torque, not slowly at high ...
- 4,607
4
votes
Why are wind turbines installed slightly "nose up" as opposed to the blade disk being perpendicular to the ground?
Most airfoil blade shapes; forward orientation is slightly bent upward 10-15 degrees because this creates the most lift with the least amount of drag.
The now slightly turbulent air flow isn't just ...
- 544
3
votes
Accepted
Do 3 blade wind turbines generate more power than a 9 blade, all else being equal?
Because in the real world, all else is never equal, but let's start there analytically.
What does "all else being equal" actually mean?
With respect to a flat swept disk perpendicular to an ideal ...
- 4,607
3
votes
Why not design a Wind Turbine like an Anemometer?
One other reason is that the propeller-type turbine allows it to be rotated to avoid damage in high winds. When the air is flowing transverse to the axis of the propeller it encounters relatively ...
- 47
3
votes
Why not design a Wind Turbine like an Anemometer?
Because the back of the cups create a lot of drag thereby reducing the power produced.
The blade profile used in classic 3-bladed HAWTs is also used in VAWTs and they look like "egg beaters" needing ...
- 15.5k
3
votes
What determines the cost of the wind turbines?
Where does the power for a wind turbine come from? Answer - the wind.
So how do you get 15kW from the wind rather than 11kW? Answer - you either need a location with a higher wind speed, or you need ...
- 3,135
3
votes
Accepted
What theoretical efficiencies can wind / hydro turbines achieve?
The theoretical maximum efficiency of a wind turbine is the Betz Limit, which is $\frac{16}{27}$ ( ~ 59.3%).
The result dates back to 1919.
The Betz limit is, as you note, speed invariant. To get an ...
- 3,751
3
votes
Accepted
Relationship between wind velocity, turbine rotor diameter, and power output
The Betz limit will give you a good theoretical maximum from your wind velocity and swept area. Your real world turbine will fall somewhere below this number based on its efficiency.
For measuring ...
- 7,904
3
votes
Advantages/Disadvantages of two-bladed windmill?
One of the advantages of two blades over three blades is less materials are required to make the blades.
The disadvantage of a two bladed rotor compared to a three bladed rotor is due to the ...
- 9,642
3
votes
Accepted
Why does my model of a wind turbine show high RPM with low power output?
I don't think you really designed a 1300 W wind turbine. You assumed your generator would be able to produce the necessary current but to be able to produce 1300 W you have to build a wind turbine big ...
- 181
3
votes
Accepted
Wind turbine that is efficiant from all angles
You are looking for a “vertical axis wind turbine”.
See below for some design examples:
- 7,726
3
votes
Accepted
Is transmitting windmills' mechanical power to ground level that complex?
TL;DR:IMHO, the driver for keeping the electrical generation closer to the hub is for primarily for eliminating -as much as possible- moving parts for safety concerns. The secondary benefit is the ...
- 24.3k
3
votes
Accepted
Could the St. Louis Gateway Arch be used as a support structure for a giant vertical axis wind turbine?
The arch has been designed to resist wind loads but just the wind load its 630 feet arch can cause.
The motto of not over designing the structure to reduce the weight of the structure to a manageable ...
- 22.1k
3
votes
Is the main goal for wind turbines to take maximum energy for a given diameter?
Aside from the efficiency, the blades of wind turbines are basically a wing, aerofoil, the actual upwash and downwash zone are much greater than the wing's cross-section.
If the blades are too close ...
- 22.1k
3
votes
Why wind turbine dont use high lift coefficient airfoils?
One reason I can think of is Because increasing the $c_L $ increases also significantly the coefficient of drag.
The increase of drag is a result of increasing flow detachment from the airfoil.
...
- 24.3k
3
votes
Why wind turbine dont use high lift coefficient airfoils?
The wind turbines are designed to work under a wide range of wind velocities.
They adjust their angle of attack and $ C_l$ to the optimal for the existing condition.
They use high $C_l$ for when the ...
- 22.1k
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