Windmills: What are they used for? What do they do?

Historically, sailors were among the first to harness the power of the wind, as they were the first to understand lift and harness the wind’s power through sails. It was based on this knowledge that the first vertical axis sail-type windmill was developed, which was used by the ancient Persians and Chinese for milling grain as well as pumping water.

They were made up of vanes known as sails or blades, which, when prompted to turn by the wind, converted the wind’s energy into rotational energy that could be used for various purposes.

Early European windmills with horizontal axis systems laid the groundwork for today’s wind turbine technology, which is used in the production of electricity.

It is the purpose of this article to discuss the history of windmills, how they evolved into modern designs, and how they function.

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Early History of Windmills

According to current evidence, it is unclear who was the first to invent the windmill, with some speculating that it was the Chinese or the Persians. What’s important is that both cultures began utilizing this technology at approximately the same time for similar purposes.

The Crusades are credited with bringing windmill technology to Northern Europe; however, the horizontal axis design of the European windmill, rather than the vertical axis system, makes it just as likely that the Europeans discovered their windmill on their own. The earliest known illustrations date back to 1270 A.D. and depict blue-prints for the post mill type of windmill.

The post mill was composed of a four-bladed mill mounted on a central post, which used wooden cog-and-ring gears to convert the motion of the horizontal shaft to vertical motion, which turned a grind stone, as well as a horizontal shaft and grind stone. Vitruvius, an engineer of the Augustan Age, used a wooden cog-and-ring gear to create the world’s first horizontal axis water wheel, which is still in use today.

The tower mill design is thought to have originated in the late 1300s, with the earliest known illustration depicting a Normandy Mill from between 1430 and 1440, according to historical evidence. It had sloping walls, a rotating cap, a horizontal wind shaft, and vertical sails, all of which contributed to the tower mill’s efficiency.

This vertical tapered tower with four to six sides and a cap that rotates to direct the wind is based on the tower mill and was invented by the Dutch in 1526. The sails are brought into the wind by the cap, which is rotated to direct the wind by the sails. The smock mill got its name because it looked a lot like the smocks that farmers wore back in the day.

The next 500 years saw the development of a wide range of applications for windmills that went beyond water pumping and grain milling. These included irrigation, drainage, saw milling of timber, and the processing of tobacco, spices and cocoa as well as the production of paints and dyes.

Modern Advances

Pumping mills for mechanically moving water were first developed in the United States in 1854. These mills were originally made up of four wooden blades, with steel blades becoming available in 1870, when the mills were modernized.

Over six million mechanical wind mills were installed in the United States between 1850 and 1970, according to the American Wind Energy Association. Their primary uses were for stock watering and for providing water to farm houses and outbuildings. Windmills of enormous size were used to pump water for steam locomotives.

An engineer from Ohio named Charles Brush invented the world’s first working windmill in 1888, and it was used to generate electricity. The windmill, which had a rotor that was 56 feet in diameter and could generate up to 12 kilowatts of electricity, stood sixty feet tall and had a rotor that was 56 feet in diameter.

Wind turbines are the term used to refer to windmills that are used to generate electricity in today’s society.

Within a five-year period between 1973 and 1986, the wind turbine market evolved from small-scale machines in the 1 to 25 kilowatt range for domestic and agricultural applications to intermediate-scale machines in the 50 to 600 kilowatt range for interconnected utility wind farm applications.

There were over 20 different designs engineered and tested during this time period, with the majority proving to be unfeasible and inefficient after extensive testing.

Wind turbines have evolved from the four-bladed systems that were first developed in the United States to two-bladed systems, and finally to the three-bladed systems that are now commonly found in wind farms.

What do Windmills do?

A windmill is a structure that is used to harness the power of the wind for a variety of purposes such as grinding grain, pumping water, and generating electricity, among other things. Wind causes the blades of the wind turbine to spin, resulting in the generation of kinetic energy. The spinning blade turns a shaft, which in turn spins other blades, which are attached to generators that generate electricity as a result of the spinning.

Historically, the earliest documented windmills were vertical axis systems, with vertical sails made of reeds or wood that were attached to a vertical shaft with a stone for grinding purposes by horizontal struts, as opposed to horizontal axis systems. The post mill, which had a horizontal axis system and a four-bladed mill attached to a central post, was the first windmill to appear in Europe. It was the first of its kind.

Post mill, according to Mostert’s Mill, is a structure that is balanced and pivots on a vertical central post that is held upright by crosstrees and angled quarter bars, with the ends of the post mill supporting four upright stone or brick pillars.

There were two main parts to the mill: a wallower, which was a large brake wheel located on the same shaft as the sails and transferred power to a smaller gear, and a sail. The wallower shared a vertical shaft with the great spur wheel, which was driven by a stone nut that was attached to the wallower’s vertical shaft.

Unlike the post mill, the tower mill had multiple floors, which were used for a variety of purposes including storing grain, removing chaff, grinding grain, as well as housing for the windsmith and his family.

Probably the most significant feature of the tower mill was a cap (roof) that could pivot in response to shifting wind patterns. In contrast to the post mill, where the entire structure had to be moved in order to orient the mill, only the cap had to be moved in order to orient the tower mill.

Original designs called for manual wind orientation for both the tower and the post mills, which was accomplished by pushing a lever located on the back of each mill. Edmond Lee invented the fan tail for the windmill in 1745. The fan tail was mounted at right angles to the sails on the back of the mill and rotated automatically, causing the sails to be drawn into the wind by the fan tail.

Smock mills are similar in appearance to tower mills, with the main difference being that smock mills were octagonal or hexagonal in shape, rather than circular, with six to eight sides. Smock mills were used for a variety of purposes, including grinding grain. A similar rotating cap design to that of the tower mills was used in smock mills, which were typically much larger.

The first mechanical mills to appear in the United States had four wooden blades that resembled paddles, and most of them were equipped with “tails” that oriented them into the wind when in operation. Some of these mechanical mills, referred to as weather-vaning mills, were, on the other hand, designed to operate downwind.

Mechanical mills with speed control provided by hinged blades that folded back in high winds, reducing the thrust by decreasing the rotor capture area, were used in some applications. Because of the high speed of steel blades, a reduction gear was required to ensure that the standard reciprocal pumps were running at the proper speed to ensure that the mill functioned as it should.

The three-bladed turbine systems that are commonly seen today operate in a manner that is very similar to that of the original post mill. In order to generate electricity, wind turns two or three blades around a rotor that is connected to a main shaft that spins a generator to turn the blades.

The rotor, which is comprised of the blades and hub combined, is elevated 100 feet or more above the ground in order to take advantage of faster, less turbulent winds. The rotor is connected to a pitch system that directs the blades away from the wind in order to control the rotor’s rotational speed.

During periods of insufficient wind generation (either too high or too low), the pitch system prevents the rotor from turning.

Approximately 30-60 rotations per minute are made by a low-speed shaft that connects the pitch system to the rest of the machine. In order to generate electricity, the low rotational speed shaft is connected to a gear box, which converts the low rotational speeds into the high rotational speeds of 100-1800 rpms, which are required by the generator, which is attached to the gearbox.

A brake system that can mechanically, electrically, or hydraulically stop the rotor in an emergency, as well as a controller that starts the machine up at wind speeds between 6 and 16 mph and shuts it down at wind speeds greater than 55 mph to prevent damage, are also included in today’s turbines. The wind speed is measured by an anemometer, which then transmits the information to the controller.

After that, the electricity is transferred down the tower and converted to the same voltage as the local energy distribution system.


Considering how far windmills have progressed since their inception, and the latest advances in turbine technology are demonstrating that wind energy is a viable and environmentally friendly alternative to fossil fuels.

In the twenty-first century, we are beginning to see a number of advancements in the wind energy industry, including bladeless technologies and generators that do not require a transmission system. However, they are still in the early stages of development.

Wind energy is one of the most promising solutions to the world’s growing energy demands because, unlike fossil fuels, it is environmentally friendly and does not emit harmful emissions when it generates electricity.

We’d love to hear about your experiences with windmills and/or modern wind turbines in the comments section below.


Featured Image Credit: Alter Wolf @ Flickr