When the thought of wind energy came to my mind recently, I wondered how wind turbines capture the wind when they turn their blades. So, I did some research to find out how wind energy is harnessed.
How is wind energy harnessed? Wind turbines spin their blades according to the speed and force that the wind exerts on them. From this movement, the turbine is able to capture the wind’s kinetic energy and convert it into electricity within itself.
When considering the functions of a wind turbine, many people assume that creating electricity from the wind is as simple as a few blades spinning around. However, there are multiple components that work together inside wind turbines to harness its energy.
Related: How Is Wind Energy Formed?
How Wind Energy Works
The concept of taking energy from the wind and converting it into electricity has been around for thousands of years.
The original process included windmills that usually served a single purpose such as pumping water or grinding grains through its components, and used the wind’s energy to power itself and carry out these specific functions. Over the years, this process has improved and newer machines have been created that are more efficient and take up less space.
The modern method of extracting energy from the wind is by using a machine called a wind turbine. Wind turbines consist of thousands of components within them, with several parts that work together to pump out electricity to the masses.
The four main parts of a wind turbine are the foundation, tower, nacelle, and rotor blades. The foundation is built into the ground to keep the entire wind turbine in place without allowing it to move or collapse onto its side due to higher wind speeds. Foundations for wind turbines on land are typically made of concrete, all though they can sometimes be constructed from steel.
Offshore turbines that are located in the ocean will usually have steel foundations that hold them up in the water. Almost all modern wind turbines stand up on a cylindrical tower that serves the purpose of holding the blades up toward the wind to collect as much energy as possible at all times.
The nacelle is one of the biggest pieces on the wind turbine, with enough space to hold a small airplane on its back. It sits at the top of the tower directly behind the rotor blades, connecting them to their base.
There are multiple smaller components located within the nacelle that work together to convert the received energy into electricity, including the generator, controller, gearbox, and speed shafts. This area is where the majority of the wind turbine’s functions take place internally.
The rotor blades are placed at the tip of the nacelle, this part consists of any number of blades from 2 all the way to 6, as well as a rotor hub in the center of all of them. The blades are rotated about the axis of the tower according to the current wind speeds.
Although most wind turbines consist of the same basic building blocks and functions, there are many different categories that they can fall under. Some of the differentiating factors between wind turbines include their size, energy capacity, and location.
Wind turbines can range from smaller, residential sizes that can be used to power a single home or farm, all the way to massive utility-scale machines that are designed to distribute electricity to multiple homes and businesses all at one time.
The energy capacity can be calculated by kilowatts, which is equal to one thousand watts, or megawatts for the larger machines that are equal to one million watts instead. For reference, the average small scale wind turbine will have a capacity of anywhere from 5 to 20 kilowatts, and a single utility turbine can hold about 2 megawatts on its own.
To effectively power a single family home, it is necessary for the wind turbine to have a capacity of around 5 kilowatts.
As mentioned before, wind turbines can be located onshore or offshore. Onshore turbines are usually built on farmlands in fields of grass to collect the wind that passes through the area. Alternatively, offshore turbines emerge from the ocean near the shore.
In general, offshore turbines are reported to have higher efficiency than their counterparts, because the levels of wind and turbulence that pass over the ocean are higher and more consistent than the wind that is received by turbines that are on land.
However, these offshore turbines are more prone to damage by extreme weather and additional wear and tear that onshore turbines do not experience as regularly.
In the event of a natural disaster, offshore wind turbines in the water are less likely to be able to withstand the conditions, having a high probability of damage being done to the machine’s hardware and even bending the blades backward in some cases.
Wind energy is collected when the turbine’s blades collect the wind’s kinetic energy. From there, the energy is taken through the inside of the machine and transformed into a different kind of energy.
This newly created energy then goes through a separate process where its voltage is multiplied in order to create electricity that is ready for distribution.
How Wind Turbines Work
The step by step process that wind turbines go through to harness energy from the wind begins with the anemometer. The anemometer is one of the smallest pieces on the exterior of the machine. It sits on top of the nacelle and spins with the wind in order to gauge its exact speed.
There are a minimum and maximum speed threshold that is programmed into every wind turbine, and the anemometer will follow this range when gauging the wind’s speed.
Once it picks up on a wind speed that is ideal for the turbine to effectively produce energy, it will send a signal through the interior of the nacelle to reach the controller. The controller is the part that controls the speed the blades will spin and initiates the movement by pushing it forward through the other components within the nacelle.
The controller sends its message to the high or low-speed shafts, depending on the current speed of the wind, and they will initiate movement outward toward the blades, allowing them to rotate and collect the wind’s energy.
The energy from the wind enters the turbine through its rotor hub in the center of the blades and is first consumed by the generator piece. Inside the generator, the wind’s energy is spun around loops of copper wire and is transformed into a different type of energy.
This type of energy is called mechanical energy, which is the result of the wind’s kinetic energy added to the turbine’s potential level of energy. During this process, electrons are given off from the copper wires that will turn the energy into electricity.
After the wind’s energy is completely transformed into an electrical form, it is then transported through to the step-up transformer where its capacity is multiplied by 5.
When the wind’s energy has been successfully passed through the entire machine and converted into electricity, it is ready to be exported from the turbine and prepared for distribution to consumers.
How Wind Energy Is Distributed
The energy that is harnessed from the wind has the ability to provide energy to anything from a single home or farm to entire neighborhoods including homes, schools, and businesses. Basically, wind energy can be used for anything that is powered by other more traditional methods of electricity.
After the wind’s kinetic energy has been received by the turbine and changed into usable electricity, it will begin to travel down the machine’s tower and enter the underground cables below it. These cables will take the electricity to something called a substation.
The substation is essentially the middle man in the entire process of distributing the wind’s energy. When it received the newly created electricity, it will further multiply its voltage to make it usable for the masses and ensure that it will survive long-distance travel through the transmission grid without becoming depleted along the way.
The transmission grid is composed of multiple power lines that connect the substations to the locations where the wind’s electricity is in demand and will be used. In the United States, the three most major transmission grids are located in the east and west regions of the country, plus one additional grid that is located in Texas which connects both grids together.
When the electricity travels through the cables after departing from the substation and finally reaches the demand center, the amount of voltage that was previously multiplied by the substation will be deducted. The deduction will cause the electricity to shrink down to approximately 10,000 volts or lower. It will then get transported once again to a smaller more local grid to prepare for distribution.
This smaller grid is directly connected to the consumers that will be using the electricity. The electricity will go through one final process before becoming usable to consumers. This is initiated when the electricity is moved through an additional transformer where it is converted to the correct voltage, usually lower than the current amount, that will be practical and usable for the consumers it will be distributed to.
Wind energy that is created by turbines all over the country are transmitted through the same grids, so customers who purchase wind energy will likely receive the electricity that is collectively created by hundreds of wind farms in the area.
The wind energy that is produced by turbines can also be saved for later use in times where the demand is increasing but wind supply is low. Since wind speeds and weather conditions are unpredictable, it is impossible to always know when the wind will blow and how much energy can be extracted from it at any given time.
When there is more wind in the atmosphere that is needed on a certain day, the turbines will collect the excess energy from the wind and transform it to be stored in above-ground tanks or underground caverns.
This process is formally known as Compressed Air Energy Storage. To create compressed air storage on a utility scale, the wind’s energy will travel down the turbine into an underground cavern below it. These caverns have extremely large capacities, with some being able to hold almost 20 million cubic feet of stored air.
With a height of about 100 feet or more, you can picture the total depth of one of these caverns to be as long as a mid-sized commercial building with approximately 10 stories. Most of these caverns are able to hold over one thousand pounds of wind energy per square inch of capacity.
When it comes time for this energy to be distributed for use, the stored air will be pumped into the cavern during off-peak hours. The first process the air will undergo is called compression mode. The compression stage is exactly what it sounds like.
The air will be packed tightly into the walls of the cavern before it goes into generation mode. The generation stage is initiated when the compacted air is released and routed upwards to the recuperator component.
Inside the recuperator, the air is heated to over 500 degrees Fahrenheit before the hot air is transferred into a piece called a high-pressure combustion chamber. Within the combustion chamber the air is heated once again, but this time the temperature is multiplied to approximately one thousand degrees Fahrenheit from its previous temperature that was in the hundreds.
The hot air will once again travel through the system and will end up inside of something called a high-pressure expander, where it is reheated to almost two thousand degrees Fahrenheit. This extremely hot air will then enter the low-pressure expander before it flows into the same recuperator component once again.
Now, the air is discharged into the atmosphere at a significantly lower temperature of under three hundred degrees Fahrenheit. The high and low-pressure expanders initiate movement of the generator until it begins spinning.
Once this action the stored electricity will be able to be pumped into homes and businesses in the area that need to use it.
How Often Do Wind Turbines Spin Their Blades to Collect Energy?
Wind turbines spin their blades according to the speed of the wind that pushes them along and gives them lift. The process of lift occurs when wind speeds are high enough to create friction against the blades that will cause them to begin movement.
Since the wind is not always blowing, the frequency of the blades spinning will never be consistent or predictable. However, statistics have shown that the average wind turbine will spin approximately 70 to 85 percent of the time they are in use throughout their lifetimes.
There is a theory known as Betz’s Law, which basically states that it is only possible for wind turbines to capture up to 59.3 percent of the wind’s energy at any given time. In other words, even when wind turbines are spinning their blades at full capacity, they can only ever receive just under 60 percent of the energy being given off by the wind.
Why Do Wind Turbines Stand Still At Certain Times?
Wind turbines have two different internal settings that determine when they will spin their blades. These settings are the minimum and maximum speeds, which can also be referred to as the cut-in or cut-out speeds.
Depending on where the current wind speeds fall on this spectrum, the turbine will send a signal outward to its blades letting them know whether to stay still or begin turning. When wind speeds are too high or weather conditions are too severe for the turbine to handle, it will initiate one of three braking functions: aerodynamic/pitch, mechanical, or electrical.
How Do Wind Turbines Carry Out Different Braking Functions?
Aerodynamic braking, or pitch braking, is the slowest and most natural process and will be initiated first when a wind turbine needs to stop its blades from turning.
In the most simple of terms, pitch braking will spin the blades slowly so they can avoid the wind and eventually come to a complete stop on their own. This is similar to electrical braking, which is a function that is enabled in certain wind turbines.
Think of this process as the most similar thing to the braking function of a car. The blades will gently rotate in the opposite direction until movement comes to a complete stop. Mechanical braking, on the other hand, usually happens in case of an emergency when the alternative braking methods are not working.
Mechanical braking is essentially a forced stop that will keep the blades locked in place until they are released, no matter what level of force is being pushed onto them. This is not the ideal process, because it causes the components to grind together and can cause internal damage.
If you’re serious about learning more about wind energy, I recommend the Wind Energy Handbook on Amazon. This book is great for both students and professionals, and it holds invaluable information on the subject of wind power.