Windmill vs. Wind Turbine: What's the Difference?

A windmill and a wind turbine are different in structure and purpose, even though many people use the terms interchangeably. A windmill is a very old technology that uses the wind to either mill grains into flour, drive machines, or move water. A wind turbine converts wind energy into electricity by turning a turbine.

How Do Windmills Work?

Windmills do not produce electrical energy but rather use mechanical energy—originally to grind grain in grist mills. Vertical windmills, the kind familiar to rural America or Holland, use sails of sailcloth or wood that rotate along a horizontal axis.

From there, rotational force (torque) moves through gears to rotate a millstone. This allows for a range of uses, like grinding grain, driving a shaft to pump water, running a reciprocating saw, and producing paper pulp

History of the Windmill

Windmills may date back to the ancient world, but their first verified appearance is from 9th-century Persia, modern-day Iran. Windmills made their way across Eurasia along with the spread of Islam in subsequent centuries.

By the early 17th century, windmills could be found pumping water and grinding grain in the Netherlands, United Kingdom, and much of northern Europe—where, unlike the rivers that drive waterwheels, wind doesn't freeze. From there, windmills made their way to North America. As early as 1662, a windmill was grinding grain at the foot of Manhattan.

Beginning in the 19th century, windmills made farming in the American Great Plains and the Australian Outback possible. They were a mainstay of rural America until their height in the 1930s when New Deal rural electrification mostly replaced them. Even the historic windmills of Holland are derelict, preserved mostly for tourism purposes.

How Do Wind Turbines Work?

A turbine is a machine that generates electricity through a rotating camshaft. The camshaft passes a wire back and forth through a magnetic field, generating an electric current.

Turbines are not specific to wind energy: they are used to generate electricity in thermo-electric power plants (nuclear, coal, and natural gas, for example), which boil water, which rotates a turbine as it turns to steam. Hydroelectric dams use the force of gravity (falling water) to turn turbines and generate electricity.

Likewise, wind turbines use the rotational force of blades (sometimes called sails or vanes) attached to a camshaft, which rotates the turbine.

History of Wind Turbines

The first wind turbine used to generate electricity dates from 1887—merely five years after Thomas Edison developed the first electric power station running on coal. Scottish professor James Blyth built a wind turbine to store electricity in a battery that lit his home. In 1895, Poul la Cour of Denmark created the first wind turbine-driven power plant, providing electricity to a local village. By 1900, Denmark was home to 2,500 wind turbines. Today, Denmark is once again a powerhouse in wind technology.

An overlooked pioneer of renewable wind energy, James Blyth spent the next decade promoting wind energy, decrying the inefficiency of using gas to light homes and calling coal-powered steam engines “wasteful middlemen.” In Great Britain, where coal was cheap in price though high in human cost, the middlemen won the day. The story would be repeated as wind power made its way the following year to North America, failing to compete against inexpensive coal and oil.

Length

Since 2000, the length of wind turbine blades has increased year after year. Longer blades generate more electricity, just as the larger front chainring on a 10-speed bike generates more power. Three turns of a 100+ meter blade can fully charge a Tesla Model 3.

Longer blades also capture wind from a larger area: doubling the length of the blade quadruples the area it covers as it spins. This means more wind energy is captured with each turn of the blade—an important factor given the intermittency of wind and climate change-induced shifts in wind patterns. Longer blades also reduce the number of blades needed per wind farm, lowering costs.

In June 2022, Siemens Gamesa contracted with a Scottish offshore wind farm to produce the longest blades to date: 60 wind turbines with blades 108 meters (354 ft.) long—two yards short of the length of an American football field. Each blade of the three-blade turbine is capable of producing enough electricity to power, on average, 800 U.S. homes. This world record won't last long, however.

Height

To accommodate longer blades, wind turbine towers have increased in height. This has also increased their efficiency, since generally speaking, the taller the tower, the more wind energy available to be captured. Winds are stronger at higher altitudes, due to less ground friction and lower air density.

By mid-2022, the tallest wind turbines reached 280 meters (918.6 ft). (By comparison, the Empire State Building in New York City stands 443.2 meters (1,454 ft.) tall, including its antenna.) Around the world, the tallest towers are often placed miles offshore, out of sight from land, and where winds tend to be stronger.

Wind Turbines and Wildlife

Animal lovers may be wondering where migrating birds and bats fit into the conversation on windmills and wind turbines. Traditional windmills are much less of a concern today than modern, high-speed wind turbines.

Does a larger area swept by longer turbine blades increase the chances of bird and bat collisions? Or do the more slowly rotating blades decrease collisions?

In order to measure the impact on migrating wildlife, the mortality rate, location of the wind farm, and migration patterns need to be considered. According to one California study, larger blades had no impact on bat and bird mortality: the greater energy produced on a smaller footprint offset the higher rate of mortality per turbine.

A recent Japanese study, however, found that longer turbine blades reduced the number of bird collisions per megawatts of energy produced.

Broader comparative studies of wind farms across different locations (within and outside avian migration routes) may provide more definitive answers. But it's worth keeping in mind that the number one threat to birds today is climate change, and the proper siting of wind farms is more important than turbine size in protecting wildlife.

Key Differences

Windmills have historically been used in small-scale, low-tech operations on a single site, meant to grind mill, power saws, pulp wood for paper, and other functions that require mechanical energy but not necessarily electricity.

By comparison, wind turbines tend to be large-scale providers of electricity to the grid for use offsite. Like most power plants, they are situated in remote locations, whether onshore or offshore, delivering electricity to predominantly urban customers many miles away.

But just as solar energy can be scaled to accommodate the needs of both individual homeowners and utility-scale power plants, so too can wind energy. “Distributed wind resources” are small-scale wind turbines suitable for single electricity customers, such as a dairy farm seeking to offset its own electricity use or a net-zero homeowner seeking to use clean energy to live off the grid. There are, indeed, numerous ways to harvest the power of the wind.