Windmills: From Ancient Persia to Modern Renewable Power

Background

A windmill is a device that harnesses wind energy by rotating adjustable blades. Historically, windmills powered grain mills and water pumps, and today they are the foundation of modern wind turbines that provide clean electricity.

History

Humans have used wind for centuries, initially to propel sailboats. The first recorded windmill design dates back to Persia (A.D. 500‑900) and was originally a vertical‑axis water‑pumping machine before being adapted for grain grinding. While early Chinese windmills date to A.D. 1219, Persia is credited with the earliest documented use.

Following the Crusades, the concept spread to Europe, where the earliest surviving designs (A.D. 1270) featured horizontal axes, likely inspired by the existing water‑wheel technology and for greater efficiency. European millwrights, especially the Dutch and English, refined the design, introducing the tower mill, multi‑story smock mills, and automated controls.

Windmills served as the “electric motors” of pre‑industrial Europe, powering sawmills, textile dyeing, and tobacco processing. The rise of steam power in the 19th century, coupled with the intermittent nature of wind, led to a decline in large windmills, though smaller fan‑type mills continued to thrive—particularly in America where over six million were built between 1850 and 1970.

Design

Windmills are categorized into horizontal‑axis and vertical‑axis types. The former, including post, smock, tower, and fan mills, has become dominant due to higher efficiency.

Post mills feature a single upright post that supports the entire body, allowing the mill to pivot to face the wind. Smock mills improve on this by having a fixed body and a rotating cap, enabling larger sails and more robust construction. Tower mills extend this concept further with a permanent, often round, stone or brick tower that offers superior weather resistance.

Fan‑type mills—compact, individual units—consist of a mast, a wheel, a tail assembly, and a pump. Masts range from 10 to 15 feet (3–4.5 m) tall, with blades between 6 and 16 feet (1.8–4.9 m) in diameter.

Raw Materials

Post mills are primarily wooden, using lightweight balsa for blades and sturdier hardwood for the frame, finished with paint or resin. Smock and tower mills use timber, bricks, and stone. Fan‑type mills feature galvanized steel for the tower, lightweight steel or aluminum blades, and bronze or brass pumps to resist freezing. Leather or synthetic polymers are used for washers and O‑rings.

The Manufacturing Process

Windmills are built on site from pre‑made components. The following outline describes the construction of a fan‑type mill:

Making the Tower Parts

• Galvanized steel coils are straightened, cut, and, where necessary, welded. Finished pieces are drilled with precision holes and coated before packaging.

Making the Gearbox

• Die‑cast gears, axles, and rotors are hand‑assembled into a weather‑resistant housing that supports the wheel and tail assembly.

Making the Fan

• A steel rim is rolled into a hoop, drilled, and fitted with a central axle and spokes. Blades, cut from sheet metal, are bent and secured to the rim with bolts and clamps.

Preparing the Site

• Locate a site with a prevailing wind of at least 15 mph (24 km/h). Clear obstructions, and elevate the foundation with a concrete slab or mound to improve airflow.

Final Assembly

• Assemble the tower on the ground, then lift it vertically. Bolt the tower to the base, tension stay wires, and test stability. Attach the gearbox, main shaft, fan, tail, and pump in sequence to make the mill operational.

Quality Control

Visual inspections at each manufacturing stage catch defects. On‑site construction demands meticulous workmanship; regular maintenance ensures long‑term efficiency.

The Future

While traditional windmill designs remain largely unchanged, advances in materials and turbine technology are reshaping the industry. Government investment in wind farms—particularly in California—demonstrates a shift toward large‑scale, grid‑connected turbines that offer a sustainable alternative to fossil fuels.

Where to Learn More

Books

Baker, T. Lindsay. North American Windmill Manufacturers’ Trade Literature. University of Oklahoma Press, 1998.

Clegg, Alan John. Windmills. Horseshoe Publications, 1995.

Hills, Richard L. Power from Wind: A History of Windmill Technology. Cambridge University Press, 1994.

Hooker, Jeremy. In Praise Of Windmills. Circle Press Pubns, 1990.

Watts, Martin. Water and Wind Power. Shire Publications, 2000.