How Do Windmills Work? Discover What Windmills Do!

Windmills have enjoyed enduring popularity in America. They’ve become synonymous with traditional Americana as well as green energy.

If you want to know what windmills do, how do windmills work, and how efficient are windmills, read on. In this article, we’ll tell you what you want to know about windmills!

What is a Windmill?

A windmill is a machine on a tower that uses rotating blades to convert kinetic wind energy into mechanical energy or electricity.

How Do Windmills Work?

3 windmills on a lake in the sunset are traditionally used for milling grain and pumping irrigation water.
Windmills have been used for centuries. Traditional windmills like these are used to mill grains, saw lumber, and pump irrigation water.

The three-bladed turbines seen today work quietly and efficiently to harvest as much energy from prevailing winds as possible. They turn kinetic energy into electricity.

The wind turns two or three blades around a rotor that is connected to the main shaft of the windmill. The main shaft contains a generator to generate electricity. We’ll discuss the generators in the next section.

The rotor, which is the blades and hub combined, is mounted 100 feet or more above the ground to take advantage of the faster, less turbulent wind.

The rotor is attached to a pitch system that turns the blades out of the wind to control the rotor’s speed.

How a Wind Turbine Pitch System Works

The pitch system is connected to a low-speed shaft that turns at about 30-60 rotations per minute.

The low-speed shaft is connected to the gearbox which converts the low rotational speeds into the high rotational speeds of 100-1800 RPMs required by the generator.

When winds are too high or too low to produce electricity the pitch system prevents the rotor from turning.

High winds will break the rotor and generator by causing overheating, so high winds can’t be harvested for energy. The pitch system turns the blades to avoid the highest winds while allowing them to turn.

How a Wind Turbine Brake System Works

Today’s turbines also consist of a brake system that can mechanically, electrically, or hydraulically stop the rotor in emergencies.

It is paired with a controller that starts the windmill up at wind speeds that are between 6 to 16 mph and shuts the windmill off when wind speeds are above 55 mph to prevent damage.

An anemometer measures the wind speed and transmits the data to the controller so the turbine will be automatically protected in high winds.

4 Types of Wind Turbine Generators

The generator can be one of 4 types.

Type of Wind Turbine GeneratorHow The Generator Works
DC (direct current) DynamosThe generator contains poles and copper wiring that will produce an electromagnetic field when scraped by graphite or carbon brushes. The brushes are powered by the windmill. This generates electricity with a unidirectional current that usually is converted to alternating current as it leaves the windmill.
AC (alternative current) Synchronous GeneratorsProduces 3-phase power using brushes like the DC generator, but the power output is synchronized to the rotation of the shaft. The magnets are stationary so the generator is efficient and has relatively low maintenance, though the brushes wear out.
AC Asynchronous GeneratorsAlso known as induction generators, they work the same as synchronous generators but the power output can be faster than the rotor speed. These are brushless generators and are the most popular types of generators for wind turbines because the maintenance is very low.
Switched Reluctance Wind Turbine GeneratorThis generator operates by the natural resistance of magnetic poles. The phase currents excited by the rotor create DC current. These are robust, simple, and inexpensive to manufacture and maintain. There are no magnets or brushes in the rotor assembly.

No matter which type of generator is used in a wind turbine, the electricity is collected and converted to AC or DC as needed, transferred down the tower, and converted to the same voltage as the energy grid.

Here’s a TED-Ed video that explains, in simple terms, how wind turbines work and how we can use wind power as part of our global energy portfolio.

Read More: FUN Facts About Wind Energy. Here are some wind energy facts you may not know!

Early Development of Wind Energy

The power of the wind was first harnessed by sailors, who understood lift and could harness the wind’s power through sails to propel a ship forward without oars.

This knowledge led to the development of the first vertical axis sail-type windmill used by the ancient Persians and Chinese for grinding grain and pumping water.

They consisted of vanes called sails or blades that when prompted to turn by the wind, converted the wind’s kinetic energy into mechanical energy that could be utilized for work.

Early European windmills with horizontal axis systems were the foundation for current wind turbine technology used for energy production.

When Were Windmills Invented?

An ancient windmill on a hill with tourists observing the ancient technology.
Ancient windmills used fabric sails to capture the wind and turn the rotor. Later models had wooden blades which were finally replaced with steel in the late 1800s.

There is no concrete evidence on who exactly was the first to invent the windmill, whether it was the Chinese or the Persians is up for debate.

Regardless, both cultures began using this technology around the same time for the same purposes. Early windmills were used for pumping water and moving grindstones to mill grain.

Some believe that windmill technology was brought to Northern Europe as a result of the crusades. However, design differences make this unlikely.

Early Eastern windmills used a vertical axis whereas European windmills had a horizontal axis. This evidence suggests that the Europeans discovered wind energy and designed windmills independently.

The first existing illustrations from 1270 A.D. show blueprints of the post mill type of windmill.

The post mill was composed of a four-bladed mill mounted onto a central post.

It used wooden cog-and-ring gears to convert the motion of the horizontal shaft to vertical motion that turned a grindstone.

The wooden cog-and-ring gear was used by Vitruvius, a first-century Roman engineer/architect, to develop the first horizontal axis water wheel.

The tower mill design is believed to have come into existence around the late 1300s, with the earliest known illustration being of a Normandy Mill between 1430 and 1440.

The tower mill was made with sloping walls, a cap that could be rotated, a horizontal wind shaft, and vertical sails.

The smock mill, developed by the Dutch in 1526 based on the tower mill, is a vertical tapered tower with four to six sides topped with a cap that rotates to bring the sails into the wind.

The smock mill was named from its resemblance to the smocks worn by farmers at the time.

Over the next 500 years, windmills gained many diverse applications beyond just water-pumping and grinding grain.

New uses included irrigation, drainage pumping, sawmills, and processing of various goods including:

  • Tobacco
  • Spices
  • Cocoa
  • Paints
  • Dyes
  • Hundreds of other products that needed to be sorted, milled, or ground

The windmill was a watershed invention for humans. It replaced human labor and animal labor for a lot of heavy work.

Development of Modern Wind Turbines

Rear view of the gearbox on a wind turbine that contains the generator. The anemometer and aircraft visibility lights are seen on the rotor box.
The anemometer, aircraft visibility lights, and gearbox are visible when you look behind a wind turbine. The footprint of a wind turbine is very small in relation to the power output.

Mechanical water pumping mills were first developed in the United States in 1854. These mills originally consisted of four wooden blades, with steel blades replacing them in 1870.

  • More than six million mechanical windmills were installed in the United States between 1850 and 1970. Their main applications were for stock watering and water for farmhouses.
  • Very large windmills were used to pump water for steam trains.
  • The first windmill to generate electricity was invented in 1887 by a Scottish professor, James Blyth. Though he powered his cottage and a local infirmary with this invention, the locals were distrustful of the new technology.
  • The second electrical windmill developed was Charles Brush’s 144-blade windmill finished in 1888. It powered his Cleveland, Ohio laboratory until 1900 when public electricity became available.

In today’s society windmills used to generate electricity are referred to as wind turbines.

The years 1972-1986 were times of heavy windpower development. The windmill went from a tiny 1-25 kW home windmill to 50-600 kW turbines that could power the needs of small offices.

Over this time period, more than 20 different designs were engineered and tested, most proving to be unfeasible and inefficient.

Wind turbines evolved from the four-bladed systems first created in the United States, to two-bladed systems, and finally to the three-bladed systems commonly seen in wind farms today.

Today’s wind turbines that are installed in wind farms generally produce about 2.5-3 megawatts – 6 million kW per year. That’s enough to power a neighborhood.

How Efficient are Wind Turbines?

In general, wind turbines operate at 30-50% efficiency. They can only capture a certain amount of energy in the wind, and not all of it is converted into electricity.

In very windy areas windmills can run about 70-80% of the time. This can make them one of the more reliable alternatives to fossil fuels.

What do Windmills do?

A wind farm located on the shores of the ocean catches the prevailing off-shore wind and converts it to electricity.
A wind farm located on the seashore is an eyesore to many, but it has a higher operational efficiency than most, thanks to constant offshore winds.

A windmill harnesses the power of the wind for purposes like grinding grain, pumping water, and generating electricity.

Wind causes its blades to spin, turning kinetic energy into mechanical energy. The spun blades turn a shaft that uses gears to tune the wind speed to a usable output for the generator to produce electricity.

One of the main pros of wind energy is that it can use one of our best renewable natural resources – the wind – to produce electricity and help offset our need for fossil fuels.


Are Windmills and Bird Deaths Connected?

Yes. Wind turbines are deadly to birds. Studies conclude between 600,000 and 1 million birds are killed by wind turbines every year. That number will grow as wind farms proliferate.

Many think that birds will simply veer around the spinning rotors, and most do, but many are struck by these foreign devices that have been introduced into their native habitats and migration routes.

Eagles and other raptors are especially vulnerable as they hunt for fish along waterways and shorelines that are now occupied by spinning wind turbines.

A large percentage of bird deaths are suffered by migratory flocks whose natural migratory paths take them through wind farms.

Are Windmills Bad for the Environment?

They are generally considered good for the environment with a few notable exceptions.

  • Windmills require a lot of fossil fuels during manufacturing and construction.
  • Windmills are not recyclable. Metal components can be recycled, but the massive fiberglass turbines will go into landfills.
  • Wind turbines are known to have a negative impact on birds and bats. The federal government does not require reporting on this information, so the general public is unaware of the devastation that wind turbines have on native species.

However, from the perspective of natural resource preservation and limiting our dependence on fossil fuels, wind turbines are good for the environment.

Are There Windmills in the Ocean?

Yes, there are offshore wind farms.

These wind turbines are massive – much larger than ones located on land. The power output is much greater and they operate much more consistently due to prevailing winds.

They have drawbacks because they also result in the deaths of shorebirds.

Environmental scientists suspect that the vibrations from the towers and generators also cause confusion and stress for dolphins, fish, whales, and other marine mammals.

What Does “Tilting at Windmills” Mean?

Brass sculptures of Don Quixote and Sancho in Madrid, Spain.
This bronze statue of Don Quixote and Sancho stands in Madrid, Spain, honoring the beloved elderly knight-errant and his author, Miguel de Cervantes.

This is an English idiom that comes from the story, Don Quixote (key-HOE-tay). It means to fight or attack imaginary foes or to build arguments against fanciful enemies.

It can refer to any type of offensive or defensive position that someone might take in response to an imaginary or unimportant threat.

Here’s the origin of the idiom. In Cervantes’ story, Don Quixote desires to be an idealistic and chivalrous knight. He has no such opportunity because the mere idea is already far out-of-date.

Undeterred, Don Quixote sets out in search of adventure and social wrongs that he can right. He misinterprets everything he sees.

Don Quixote’s altered view of reality is elevated to the ridiculous when he sees windmills on the horizon and imagines that they are giants. He attacks the windmills with his jousting lance.

Jousting matches are fought as 2 opponents face off on horseback with lances. The goal is to knock the opponent off his horse.

The act of jousting is called “tilting.” Thus, Don Quixote was said to be tilting at windmills.

Final Thoughts

Windmills have come a long way since their inception. Modern advances in turbine technology are helping wind power become an environmentally friendly substitute for fossil fuels.

In the 21st century, we’re starting to see many advances in the wind power industry including bladeless technologies and generators that don’t require a gearbox.

These exciting developments mean that wind power technology is only going to get cheaper, quieter, and more efficient.

What do you know about windmill technology? Have you used a windmill for mechanical power or electrical energy? Tell us all about it in the comments below!