
Wind power generated 7% of the electricity in the U.S. and is now the leading renewable energy source for electricity in the U.S. While wind power is one of the oldest forms of energy it has rapidly increased its contribution in the last decade. The wind blows because of uneven heating of the earth's surface, producing high and low pressure, and thus results in airflow (wind). It is a renewable energy because solar energy (heating the earth's surface) is renewable. Early windmills were used to grind grain or to pump water. When we generate electricity we use wind turbines (not wind mills).

Wind power is one of the fastest-growing sources of electricity. It is now the leading renewable energy source for electricity in the U.S. (surpassing hydroelectric power in 2018). The reason we were historically not utilizing wind is simple: fossil fuels were cheaper alternatives (and more reliable) for electricity generation. As the cost of wind-generated electricity has drastically declined over the last decade, wind-generated power has increased dramatically here and in many other nations with the potential for more improvements. That said, solar energy generation is becoming more desirable and is expected to be much of the renewable electricity increase in capacity.

So how does it work?

Wind turbines come in different shapes and sizes. The vertical ones tend to be tall to take advantage of the higher wind velocities (more energy), the slower wind velocity at ground level is caused by friction or drag with the earth's surface. One of the tallest wind turbines constructed so far is in Hawaii; the blade is longer than a football field and is 20 stories tall. The blades are shaped so from the side, they are similar to an aircraft wing, with the other side of the blade (from the point of rotation) turned the other way. The blades "push" to produce the spinning rotation. This rotating motion turns gears that produce a much faster rotation within a small generator in the nacelle — producing electricity. The blades can pitch to capture more of the wind energy or to stop the blades when the wind velocities are too high.
We are transforming kinetic energy into electricity.
Recall that KE =1/2mv2
The mass of the wind can be increased by using a bigger blade to "catch" the wind (area of a circle is Pi times the radius squared, so doubling the radius quadruples the area), or having a higher velocity wind (because more air flows within the turbine diameter, but more importantly because the energy in wind is proportional to velocity cubed). Density changes in the air can also increase the kinetic energy of the wind and thus the mass will be greater (density = mass/volume). The density of air is lower than the density of water, so water with a density of one will have much more kinetic energy than the wind at the same conditions of flow! Also, our extraction efficiency is limited, because to transform all of the kinetic energy from the wind into electricity would require the wind to have zero velocity, which if it did the turbine would not turn! Thus, there is a maximum efficiency of 59% (Betz Law).
Watch the following 2:46 minute video about how a wind turbine generates electricity.
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PRESENTER: How does a wind turbine work? You've probably seen a wind farm. But do you know how wind force is converted into electrical energy? We are going to show you how a wind turbine works.
Each wind turbine has a wind vane at the top that indicates the wind direction. This allows the turbine to rotate on the tower and face the wind. The blades also rotate on their axis for maximum resistance. Wind force, that is the kinetic energy contained in moving air currents, spins the blades.
These are designed to fully capture its energy. They can be as long as 60 meters each and are made of very light and resistant materials for ease of movement. This is why they can produce energy even with very light winds, starting from about 11 kilometers per hour. With very strong winds, above 90 kilometers per hour, the blades are placed in the feathered position, and the turbines stop spinning for safety reasons.
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The blades are attached to the wind turbine through the HUB, which is coupled to the low-speed shaft. The low-speed shaft is given this name because it spins at the same speed of the blades, between 7 and 12 revolutions per minute. To produce electricity, it is necessary to increase the turning speed of the low-speed shaft. That is the mission of the gearbox, which raises the speed over 100 times and transfers it to the high-speed shaft.
The high-speed shaft, that rotates it up to 1,500 revolutions per minute, is connected to a generator. The generator converts the kinetic energy into electricity, a source of energy that is easier to transport and use. The electricity produced in the generator is conducted through the interior of the tower to the base. There, the transformer raises the voltage for transport inside the wind farm.
From each turbine, alternating current is sent to the substation to underground cables. Here, the voltage is increased again to feed it into the power grid and transport it to end consumers. This is how we use the wind to light cities, feed industries, schools, or hospitals, or operate our household appliances in a clean and sustainable way.
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Advantages
- It is renewable
- It produces no air pollution or greenhouse gases
Disadvantages
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Land Use
It requires a large plot of land to house enough wind turbines to make the wind farm and produce enough electricity. The land below the turbines can still be used for grazing or for crops. Unfortunately, land near population centers is expensive and it is impracticable to have less populated areas like North Dakota produce lots of wind power and ship it to the more populated areas of the U.S. -
Intermittency and Low Capacity Factors
The wind does not blow all the time. Thus, you might be getting electricity at a time when it is not needed (we always try to use the cheapest electricity source). The capacity factor is a measure of how much electricity is generated in relation to the maximum quantity. For many wind turbines, this is ~34%. -
Storage
Electricity storage is a challenge. Batteries are traditionally expensive, heavy, and not a good storage option but advances in this area are producing near-term viable options but they're not quite there yet (more on this later). Pumped storage is a viable but limited option, large-scale battery operations are also starting to emerge. -
Noise Pollution
Wind farms are not the serene creaking and groaning of the old windmills. There is noise, which can be an issue if it is close to residences. Some might add that they are ugly too, but beauty is in the eye of the beholder. -
Bat and Avian Issues
Birds seem to have the tendency of flying into the blades, which kills them! For bats, it is getting close to the low-pressure region (they dodge the blades) but then get the "bends" in the decompression zone of low pressure (similar to a deep-sea diver coming to the surface too fast). In some bat sensitive locations, they do not use the turbines in select evenings when the conditions are conducive to bat activity. Many of the avian and noise issues have been solved by going to longer blades, and improved locations (avoiding migration routes). While visiting several windmill farms I could not find a single dead bird. Bats tend to like to swarm the tallest object around and the largest number of kills occur on a single summer night. Some wind turbines may have to stop running on certain evenings in the summer season if there is a lot of bat activity. -
Supply and Demand
In some cases, there is a mismatch between where the wind resource is located and where the electricity is needed (population centers). In locations such as Germany, the higher quality wind resource (higher wind speeds and higher capacity factors) is in the north while the population centers are in the south. Thus, new high voltage lines are needed to deliver the electricity, increasing the initial cost. Despite this, they are using more wind power 40% than many nations (however, they also have much higher electricity costs).
Look Further
Spend a few minutes learning more about Wind Power via the US Dept. of Energy's website on wind energy.
Also, note that part of the reason for the growth in electricity generation from wind is the lower cost allowed by using larger turbine sizes (source EWEA).

Many of the problems can be alleviated and higher energy generation can be generated using off shore wind farms. These have started to emerge as viable options and will start moving to deeper water.