16 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 ...
  • 11.3k
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 ...
  • 3,701
9 votes
Accepted

How to correctly size the blades for a small educational wind turbine?

As it happens, I just recently went through that calculation myself for a different site. Given the following facts from a quick web search, it isn't difficult to work out the numbers. The maximum ...
  • 6,759
9 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 ...
  • 22.9k
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 ...
  • 15.1k
5 votes

To what degree are wind and water turbines exchangeable?

Given that water is roughly 1000× as dense as air, and incompressible besides, it should be fairly obvious: A wind turbine would be destroyed by the forces that water would put on it, and a ...
  • 6,759
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 ...
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

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
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 ...
  • 3,701
3 votes

Identifying category of wind turbine

The design looks like a Savonius turbine, but horizontally mounted, instead of the typical vertical mounting that you see with this design. I'm really not sure why this would be mounted this way ...
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

Is it possible to generate energy from indoor draft by opening windows on opposite sides of the building?

The two main considerations concerning wind power generation is the speed of the air and the duration of wind (air flow). The more of both, the better. Trying to harness wind flow within a building ...
  • 9,527
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 ...
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 ...
  • 14.2k
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 ...
  • 9,527
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

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 ...
  • 3,701
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 ...
  • 7,499
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 ...
  • 3,745
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:
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 ...
  • 22.9k
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 ...
  • 21.2k
3 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 ...
  • 3,745
3 votes

Expected power increase when replacing old (>20 years) wind turbines

Wind turbune efficiency is limited to 59% by Betz law Modern turbines are close to this limit, about 75% of optimum. Older turbines, that are also of the same type, will have almost the same ...
3 votes

Why not build a wind turbine like a vertical Kaplan turbine?

Another reason, is that with hydroplants the water's natural motion is downwards, and its flow can naturally continue. In the case of air the natural flow is horizontal. Diverting the air would be ...
  • 22.9k
2 votes

How to correctly size the blades for a small educational wind turbine?

Try to cut a few from balsa wood to see what you get. Experimentation is probably the best method on such a small scale, and the math won't get you very far without an extensive knowledge of the ...
  • 394
2 votes

what is 1P frequency in rotor (wind turbine)?

The constant rotational speed is the first excitation frequency, mostly referred to as 1P. The second excitation frequency is the rotor blade passing frequency: NbP in which Nb is the number of rotor ...
  • 21
2 votes

Do 3 blade wind turbines generate more power than a 9 blade, all else being equal?

Very basically in modern wind turbines which act as a wing and get lift, if you add too many blades because of the wake interference you will get kind of a stall in lift because you will develope a ...
  • 21.2k

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