Ever watched a wind turbine up close? Are there any near your home?
You may have driven past wind turbines. Have you ever stopped the car to stare at these mammoth pinwheels? Ever wondered how they generate electricity? Or what happens when the air is still?
Once you begin to focus your attention on wind turbines, more questions will pop up. Why do some wind turbines not spin even on a windy day? Can too much wind harm them? When there is no wind, will the wind turbine work? Is wind an absolute necessity for wind turbines to work?
This article attempts to find answers to these questions and more. Before we move on to the trickier questions, let’s understand wind turbines and how they generate electricity.
What is a wind turbine?
Often confused with windmills for their similarity in appearance and basic principle, a wind turbine is a device to harness the power of the wind and use it to generate electricity.
Windmill, on the other hand, is a structure with sails or blades to capture the wind power, convert it into rotational energy, and use it to mill grains. At times, the term windmill is used to refer to windpumps or even wind turbines. The common factor for all these devices is the ability to capture and convert wind power for useful purposes.
Wind turbines come in a variety of sizes to suit the purpose. Smaller and portable wind turbines can be used to power small electrical devices, slightly bigger can be used to provide power to RVs, boats, remote cabins, and traffic lights. Then, there are bigger ones to power homes and mammoth ones to generate electricity for utility services.
How do wind turbines generate electricity?
The blowing wind contains kinetic energy. When the blades of a wind turbine are perpendicular to the wind’s flow, the blades “catch” the wind, causing it to turn. This is similar to how sailboats use wind power to move forward. The wind tries to push the blade out of its way and the design of the blade is such that it turns when pushed against.
Typical wind turbines come with 2 or 3 blades. When wind exerts the same force in the same direction on all the blades, the combined force will make the blades turn faster. As the blade turns, the rotor attached to it also turns. This movement is transmitted through a series of cogs in a gearbox to turn the rotor of the generator.
The gearbox is designed to amplify the rotations of the wind turbine blades before it is conveyed to the generator. The electricity generated may be used on the site or transmitted to power stations for distribution.
How much does wind direction affect wind turbines?
The way the wind will blow is not always predictable, though prevailing winds can be predicted for a given location. However, due to unforeseen atmospheric formations of low and high-pressure conditions, the wind direction may change.
For the turbine blades to “catch” the wind, it needs to be perpendicular to the direction of the wind. If this is not the case, the wind will blow past the turbine blades without turning them. Or the blades may not be able to capture the full force of the wind. The blades will turn less, generating less electricity. So, how is this resolved?
Utility-scale wind turbines have wind detection systems in-built in them to detect the direction of the wind and turn their faces so that the blades are in the right position to harness the full strength of the wind.
The direction and strength of wind are detected using a wind vane and anemometer located on the top of the nacelle. The built-in controller processes this information to decide the optimum placement of blades. It sets in motion the motors that will eventually turn the nacelle in the desired direction, along with the blades attached to it. This is called yaw. The yaw system is responsible for the orientation of the blades and thereby the rotor of the wind turbine towards the wind.
How much wind is needed to turn the blades?
The design of the wind turbine is such that it offers no resistance to wind. Even when a mild breeze hits the blade, it will turn. However, the amount of electricity generated is directly proportional to the strength of the wind. The stronger the wind is, the faster the blades will turn, and more electricity is generated.
This means with weaker wind speeds, the wind turbine may not produce enough electricity to be efficient and profitable. Wind energy experts tell us that wind turbines need a minimum wind speed to work efficiently. The average annual wind speed for a location needs to be at least 9 mph.
On the other hand, to make a wind turbine profitable, the wind speeds need to be higher. Industry experts calculate that only when the annual average wind speed of the location is above 25 mph, the installation of a wind turbine is profitable.
Does a wind turbine work when it is not windy?
The simple rule regarding a wind turbine is no wind, no power production. Without any wind, wind turbines will not work.
However, this is not the case on most occasions. The wind speed will be so low that it is almost imperceptible. Sometimes the wind blows harder, at other times, it is just a mild breeze or it may even seem like the air is still. What happens with the wind turbine on these occasions?
The wind is indeed a variable factor in all parts of the world. It is never a constant. So, the trick is how to account for the “variable” aspect of wind to figure out the feasibility and profitability of installing a wind turbine?
Standalone wind turbine
If the wind turbine is a standalone one, this may cause problems with the power supply if there are no arrangements for backup or energy storage.
Connecting to the grid using a net-metering arrangement can resolve this issue. When the wind turbine is producing more electricity than needed because of strong winds, the excess energy will get exported to the grid. On the other hand, when the wind is weak and the wind turbine is falling short in energy generation, you can always draw the shortfall from the grid.
Another choice is to have a battery to store the excess energy when the wind is stronger for use when the wind is weaker.
Utility-scale wind turbine
In wind farms, there will be thousands of wind turbines generating power. The electricity generated is added to the grid for distribution.
In a utility-scale power distribution network, wind energy is not the only energy source. Usually, the mainstay of a power distribution network would be coal-fired thermal power. There may be inputs from nuclear, solar, and hydroelectric energy as well. Besides the wind farms, solar farms, and power stations, inputs from individual consumers also get added to the grid through the net-metering arrangement.
Each one of the above energy sources is variable, whether nonrenewable or renewable energy. Energy production from one or more may go up while others go down. Utility companies are well-prepared to deal with these variable factors without affecting the energy output. Besides the energy production, they also need to account for the fluctuations in energy demand at different times of the day or week or even seasonal variations.
Adding a renewable energy source like wind power to this equation doesn’t make matters worse or better. In fact, studies have shown that having a mix of energy sources adds to the stability of power output rather than makes it more fragile.
Moreover, if the wind turbines in one location aren’t working, it may be compensated by the higher energy output from another location. For example, if onshore wind turbines are not generating electricity, offshore wind turbines may be working more to compensate.
Installing wind turbines spread across different places is highly recommended to overcome this situation. This way, it is possible to guarantee a steady combined wind capacity from all locations.
Though this may come as a surprise to a layperson, wind in a given location is relatively predictable several days in advance. This gives power planners enough time to make adjustments from other power sources to meet the power demand, whether it will be windier or less windy.
FAQs on wind turbines
Why do wind turbines turn when there is no wind?
Wind turbines are highly sensitive, well-lubricated machines that can “catch” even the slightest breeze. This means that even when we cannot feel the wind, there may be sufficient movement in the air to turn the blade.
Another reason is that wind turbines take time to come to a stop. When the wind is blowing, with each turn of the blades, it gains momentum. Even after the wind slows down or stops, the blades will continue to spin for a long time until it stops.
In cold regions of the world, wind turbines draw small amounts of energy from the grid to keep spinning when the wind is too slow. Or else, the turbines may freeze over or turn rusty.
What happens when there is too much wind?
Modern wind energy technologies ensure that the turbines have a maximum wind speed limit after which they will get automatically cut off. As the anemometer registers wind speeds above the cutoff limit, the wind turbine will stop working. Some are programmed to stop only when the wind persists for a specified duration, while others are designed to stop immediately once the wind speeds cross the limit. This is calculated based on the wind patterns in a given location.
Bottom line
Does wind energy have a role to play in the future?
The simple answer is yes. As the world countries are trying so hard to wean away from fossil fuels to combat climate change, wind energy is a good renewable energy alternative at least in windy regions of the world. Another factor in favor of wind energy is that it is available locally. It will help countries like the United States gain self-reliance in energy.
Low carbon emissions, low levels of pollution, minimal environmental impact, free fuel, and long lifespan – wind energy has so much going in its favor. Clean, green, renewable, and sustainable, wind power is gaining popularity across the world, especially in the United States in recent years.
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