What is a Wind Turbine
Author: EnviroCitizen
A wind turbine is a machine that uses rotating blades to convert the kinetic energy of wind into mechanical energy. If the mechanical energy is used directly by machinery, the machine is called a windmill. If the mechanical energy is converted into electricity, the machine is called a wind generator, wind power unit, or wind energy converter.
Often, Wind Power Density is used to calculate the effective wind in a familiar location. This allows data to be expressed in terms of the elevation above ground level or over a period of time. Wind velocity and mass is also taken into account. Color coded maps are used to describe "the mean annual power density at 50 meters." These results are applied to an index developed by the National Renewable Energy Lab and are referred to as "NREL CLASS." The larger the WPD calculation, the higher it is rated by class.
Wind turbines are separated into two types, based on the axis. Horizontal-axis turbines are much more common than vertical-axis turbines. Horizontal-axis wind turbines have the main rotor shaft and the electrical generator at the top of the tower. This must be pointed into the wind. Smaller turbines are pointed by a simple wind vane, while large turbines use solar sensors. Most of these solar sensors, also known as servo motors, have a gearbox, which increases the rotation of the blades as needed.
Wind turbines produce turbulence behind them, with the turbine usually pointed upwind of the tower. Because of this the turbine blades are made of stiff and strong material to prevent the blades from being pushed into the tower by high winds. The blades are also placed a safe distance from the tower, and are tilted slightly upward to avoid danger.
Downwind turbine machines have been developed, despite turbulence problems, because they don't need an additional mechanism to keep them in line with the wind. In this situation the blades are allowed to bend, which reduces wind resistance. This often leads to fatigue failures.
There are many advantages to horizontal-axis wind turbines. The variable blade pitch allows for the angle of attack to be remotely adjusted for greater control. This allows for greater energy collection. The tall tower of the horizontal wind turbine allows for strong wind sites with rear shear. Horizontal wind turbines are also high in efficiency, since the blades move perpendicularly to the wind, allowing it to receive power through the entire rotation.
There are, however, disadvantages to horizontal-axis wind turbines. The tall towers and blades are so difficult to transport, that transportation can be up to 20% of the overall equipment cost. They are also difficult to install, requiring tall and expensive cranes. The construction of the tower is required to support all the blades, the gearbox, and the generator.
Article Source: http://www.articlesbase.com/science-articles/what-is-a-wind-turbine-3303382.html
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Typically in 29 Palms, you get 8 hours of good wind per day (four hours in the morning, and four hours as the sun begins to set.) The wind speed needs to be around 25 mph to produce sufficient wind to generate at maximum capacity. You’d produce 60 kilowatts of electricity for about 8 hours a day with a 60k wind turbine. That is 8 hours*60 kw, or 480 kw/h. You’d sell that power at about $0.08 per kw/h, so you’d get (480 * $.08=) $38.40 per day from a 60k wind farm. You’ll see soon, as you do the math that it doesn’t justify the cost, unless the wind turbines are HUGE. (Remember the formula for calculating the area of a circle is pi times the radius squared.) The blades need to be large enough to overcome the ratio of the cost of the blades, and that works out to be about 80 to 100 feet long. If the blades aren’t that long, you won’t get the project to pay for itself (without tax subsidies or some other income.)
Now, building even one really big turbine starts paying off spectacularly: but it will be measured in Megawatts, not kilowatts. A GE 1.5MW machine pays for itself (cost is about $2,250,000.00.) There are other manufacturers building at that size and scope too, but GE is a good example.
A GE 1.5MW machine using the same math earns the owner 1500 kw * 8 hours * $0.08 per kw/h = $960.00 per day. In a 365 day year it would generate $350,000.00 per year, and pay off in about 6.5 years. (In actual practice, give it 8 years, because there are Operation and Maintenance cost issues that you must pay for: Someone has to oil the machine!)
What is the monthly yield on a 60K wind turbine if it’s planted in a wind farm?
I want to purchase a 60K wind turbine and plant it in 29 Palms, CA wind farm. If all the electricity produced is returned to the power company, what would the monthly yield be?
What factors affect the efficiency of a wind mill/wind turbine? What is the physics related to it?
What physics is related to it (secondary school – to early university level physics)? Also, how would a basic wind turbine be constructed and how would you go about testing the factors that affect the efficiency?
What is the best design for a small scale wind turbine blade?
I have to design a wind turbine blade for school and it needs to be small scale, no more than two feet long. What is the best design to do this?
The below web site gives the basic design concepts of wind turbine blades
http://www.windmission.dk/workshop/BasicBladeDesign/bladedesignleft.html#anchor674887
Efficiency (the ratio of actual power out to theoretical power out) is not the primary design goal for a windmill or turbine. The real goal is minimizing total cost per unit energy.
Efficiency is a factor, but initial cost, ease of maintenance, suitability to the context, etc. are all more important. (Just as with gasoline and diesel engines).
Thus, it is clear that theoretical efficiency goes up with the number of blades, but going from 1 blade to 2 increases efficiency by only 6%. Going from 2 to 3 blades increases efficiency by 3%.
http://en.wikipedia.org/wiki/Wind_turbine_design#Blade_count
Going from 2 blades to 3 blades might pay, but while 4 blades would be a little bit more efficient, the gain just isn’t worth the costs. Similarly, a 3_D helical turbine can be more efficient that a planar turbine, but would be much too hard and expensive to build.
For another example, Darrieus wind turbines are never as efficient as propellor type turbines, but are still considered practical for power generation:
http://en.wikipedia.org/wiki/Darrieus_wind_turbine
For one thing, they never have to rotate to face the wind; and their electronics can all be at ground level for ease of access:
http://en.wikipedia.org/wiki/Vertical-axis_wind_turbine
That’s even more true of Savonius turbines:
http://en.wikipedia.org/wiki/Savonius_wind_turbine#Use
A subtle point is determining which “theoretical power” to count. In general, the higher you go the faster the wind and power goes up as the cube of the velocity.
http://en.wikipedia.org/wiki/Betz%27_law
So when you consider a vertical propellor, do you use the wind velocity at the axis? at the top tip? (In theory, you have to do an integral, but that assumes you know the distribution of wind speeds.)
And what do you do about storms? When the winds are too fast, the turbine cuts back on generating power, but what speed is “too much”? Do you design the turbine to handle 90% of the wind or 99% of the wind? You may get twice as much total energy out of the 99% turbine (because the 9% of the time that it is working while the other isn’t, the wind is fast and has lots of energy) but the costs are much greater.
(BTW, recent analysis suggests that the best possible planar (simple propellor-type) turbine can only come away with 30% of the energy in the wind that goes through it.)
http://www.math.le.ac.uk/people/ag153/homepage/Gorlov2001.pdf
How much would it cost me to install a complete wind turbine system?
With my electricity bill as high as it is, I’m considering going off of city power and installing a wind turbine system that can power my whole house. I live in the state of Oregon. Can someone give me a ball park cost for such an endeavour and what kind of performance I could expect? Thanks.
A few years ago a coworker looked into this because they found out after they moved a mobile home onto their property that it was going to cost about $10,000 to have electric brought in. The wind turbine setup was also about the same price. Remember that your generator needs to be larger than your average load to charge batteries for when the wind does not blow. I am in Oklahoma where we have some of the best conditions for wind generation and still would need considerable storage.
I helped a friend build his own to power a storage/shop building. He did it cheap by getting an old windmill from a farmer for $100 including the tower. Bought a used truck alternator at Pick a part junkyard. for $25. The batteries and inverter cost another $500.
Most of them never payback without a government subsidy and are really installed to make a pro-green statement. The few installed in Boston (with great fanfare) have to be shut down and then reset every time that the winds go above 20 mph. Ones that are in some western locations generate well but there are not enough high voltage transmission lines to get most of the energy sold into the grid and they end up shutting them off for much of the day.
What is the payback time for a giant wind turbine?
Given the investment required in building a wind turbine, how long does it take for one to recoup the investment given the value of the energy it produces?