# Homework Help: Efficiency of Wind Turbine

1. May 1, 2007

### bacnka

I'm doing an experiment (at A-Level) to see the efficiency of a wind turbine. I'm doing this by changing the number of blades and varying the wind speeds. I wondered if anyone had an equation that could look at efficiency?

I have the current and the voltage (and wind speed).

Sorry if I've been a bit vague, I'm not very good with this area of physics.

Any help would be greatly appreciated.

Thanks

2. May 1, 2007

### Andrew Mason

You have to determine what you mean by efficiency. Normally efficiency would be the ratio of electrical output to energy input. In the case of a wind turbine, input energy has to be measured in some way.

You could put the input energy/unit time as the energy of the mass of air that flows through the turbine/unit time. That would be $\frac{1}{2}v^2dm/dt$. But not all of that energy is really available, since the air has to have some energy after passing through the turbine. It is a bit of a catch-22: if you try to capture 100% of the wind energy, you stop the wind so you capture none of it. There must be a balance between capturing some of the wind energy while letting it flow through.

If you were interested in how efficient the turbine is in turning mechanical energy into electrical, the input energy would be the work done on the turbine by the wind, which is less than the energy of the air flowing through it. This would be a function of the pressure difference (from one side of the turbine to the other) and the air volume/unit time flowing through the turbine.

AM

3. May 1, 2007

### lalbatros

Measure the speed at the input and the output of the turbine (reasonnable distances).
In this way you can have the variation of kinetic energy of the gas stream and the corresponding power absorbed by the turbine.
You can compare this power to the electric power produced.
You can also compare this power to the initial power of the wind (initial kinetic energy flux).
Note that the rotation speed of the turbine is also a parameter of the problem.

4. Jul 8, 2008

### taylaron

Is this like a propeller deisgn or is it a VAWT (vertical axis wind turbine) or a horizontal?
It would be great if the results of that experiment could be posted here. i'm making a wind turbine at home and i would like some outside data to compare with my own. i'm sure i'm not the only one that would appreciate it either.
Thanks Lalbatros

5. Aug 8, 2008

### WindGenerator

Best Design, three-bladed designs with the rotor position maintained upwind, on the windy side of the tower. Turbines sold in markets worldwide have this design for a reason, it's all proven now.

Theoretical advantages of vertical axis turbine:

1) Generator, gearbox etc. on the ground, may not need a tower for the machine.
2) No need for yaw mechanism to turn the rotor against the wind.
3) A few others which are more propaganda than fact

1) Wind speeds are low close to ground, you may save a tower, but wind speeds will be lower on the lower part of your rotor, towers are good features.
2) Vertical axis machines (actual) performance is not impressive.
3) Some not self-starting, most sucessful, a Darrieus, need a "push" before it starts.
4) May need guy wires to hold it up, guy wires are impractical to footprint.
5) To replacing main bearing, must remove the rotor, tearing the whole machine down.
6) Vertical can't apply leverage principles like horizontal can, simply not as powerful.

6. Aug 14, 2008

### taylaron

Hey guys,
Im going to construct a VAWT made of vacuum formed polyethlene in the shape of a helix. very similar to the "helix wind" turbine .

however, not only is it difficult to make the little pockets (cavity's) that you see in each of the fins (the helix design consists of 2 "wings", and on each "wing" are 10 separate "fins" that are stacked on top of each other) each of these fins includes a sloped back in the video.

because of the level of difficulty in home constructing this turbine, im curious as to whither or not its is any more efficient to have a smooth surface (without the sagging curve).

can anyone support some data that says the design with the cavity is more or less efficient at capturing airflow than the smooth design?