# Wind turbine, conceptual question

• mikelepore
In summary: This allows the turbine to produce more power.In summary, the design of wind turbine blades with a long and skinny shape is an optimization to balance the need for maximum surface area to capture wind with the need to allow a maximum mass of air to flow through the turbine. This shape is more efficient in reducing the velocity of the out flowing air while maintaining a high mass flow rate, resulting in a higher power output for the turbine. The use of long, thin blades also increases the average speed of the blades, allowing for more power generation.
mikelepore
For years I have been wondering why wind turbines are designed with very skinny blades (photo http://en.wikipedia.org/wiki/File:Turbine_aalborg.jpg ). Most of the available wind passes right through the circular "reach" of the device without touching the blades. Wouldn't it be more efficient if the blades were shaped something like those of a typical electric fan (photo http://en.wikipedia.org/wiki/File:Electric_Fan_720x1070.jpg ), or a pinwheel toy (photo http://en.wikipedia.org/wiki/File:Green_pinwheel.jpg ) ? I would have assumed that the objective would be to maximize the surface area to capture as much wind as possible. I note that the sail of a sailboat is given a shape to produce a lot of surface area. I note that expressions for flux (light, electric, magnetic) are proportional to intensity multiplied by surface area. Can anyone please explain this design shape to me?

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There is a trade-off: you also want to maximise the mass of air going through the turbine. Too much obstruction and the through-flow slows down (more air bypasses around instead) and less energy can be extracted. Also consider how fast the skinny blades can move across the wind.

Like Cesiumfrog stated, there is a trade off. Its really an optimization problem to reduce the velocity of the out flowing air as much as possible while maintaining a maximum mass flow rate. This can not be done with wide blades. This phenomenon can be described with Betz limit.

http://en.wikipedia.org/wiki/Betz'_law

Part of the overhead with an airfoil is the change in kinetic energy of a wind. By diverting more air at a slower speed, you get the same force (momentum related) but with less work done on the air (less kinetic energy change). It turns out that using long, "skinny" (high aspect ratio) wings is more efficient, than fat short ones. If the goal is to only divert a large amount of air a small amount, then a "fat" wing doesn't help since it's just wasted surface area because of the small amount of diversion.

One exception is for small wings at slow speeds, the wind speed times chord length called Reynolds Number becomes an issue and lower aspect ratio ("fatter") wings are used on small, slow speed model gliders for maximum efficiency. For contest models, the wing spans are limited by rules (1.5 meter, 2 meter, unlimite (usually 3 to 4 meters)), and the 1.5 meter models have low aspect ratios compared to the 3 meter and larger models.

Unlike a wing, the goal of a wind turbine is to generate power, not force, efficiently. However power = force x speed, and long thin blades increase the average "speed" of the blades because of the larger radius.

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## 1. How do wind turbines work?

Wind turbines work by capturing the kinetic energy of the wind and converting it into mechanical energy. This is done through the use of blades that are connected to a rotor. As the wind blows, it causes the blades to rotate, which in turn spins the rotor. The rotor is connected to a shaft that is connected to a generator, which then converts the mechanical energy into electrical energy.

## 2. What are the benefits of using wind turbines?

Using wind turbines for energy production has several benefits. They are a renewable energy source, meaning they do not produce greenhouse gas emissions or contribute to climate change. They also do not require any fuel, making them cost-effective and reducing our dependence on fossil fuels. Additionally, wind turbines can be installed in remote areas, providing electricity to areas that may not have access to traditional power sources.

## 3. How tall are wind turbines?

The height of wind turbines can vary, but on average, they are about 80 meters tall. However, some newer models can reach heights of up to 200 meters. The taller the turbine, the more wind it can capture, making it more efficient.

## 4. Do wind turbines pose any risks to wildlife?

While wind turbines can pose a risk to birds and bats, studies have shown that the overall impact on wildlife is relatively low. To mitigate these risks, proper placement of wind turbines and use of technologies such as radar systems can help reduce the risk of collisions with birds and bats.

## 5. Can wind turbines be used in all locations?

While wind turbines can be used in many locations, they are most efficient in areas with consistent and strong winds. This means that they may not be suitable for areas with low wind speeds or inconsistent wind patterns. Additionally, wind turbines must be placed in areas with enough space to avoid any potential hazards or interference with other structures.

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