Wind Turbines

Somewhere in Colorado or Kansas

Charlottesville, Virginia

March 27, 2020

Wind turbines look like airplane propellers running in place—spinning round but going nowhere. They're serving a very useful purpose, however. There's energy locked in wind and their giant rotors can capture some of it and turn it instantly into electricity. Have you ever stopped to wonder how wind turbines work?

How does a turbine generate electricity?

Photo: Head for heights! You can see just how big a wind turbine is compared to this engineer, who's standing right inside the nacelle (main unit) carrying out maintenance. Notice how the white blades at the front connect via an axle (gray—under the engineer's feet) to the gearbox and generator behind (blue). Photo by Lance Cheung courtesy of US Air Force.

A turbine, like the ones in a wind farm, is a machine that spins around in a moving fluid (liquid or gas) and catches some of the energy passing by. All sorts of machines use turbines, from jet engines to hydroelectric plants and from diesel railroad locomotives to windmills. Even a child's toy windmill is a simple form of turbine.

The long rotor blades on the front of a wind turbine are the "turbine" part. The blades have a special curved shape, similar to the airfoil wings on a plane. When wind blows past a plane's wings, it moves them upward with a force we call lift; when it blows past a turbine's blades, it spins them around. The wind loses some of its kinetic energy and the turbine gains just as much. The longer the rotor blades, the more energy a turbine will generate.

Faster winds help too: if the wind blows twice as quickly, there's potentially eight times more energy available for a turbine to harvest. That's because the energy in wind is proportional to the cube of its speed.

Wind varies all the time so the electricity produced by a single wind turbine varies as well. Linking many wind turbines together into a wind farm produces a much more steady supply overall.

What are the key parts of a wind turbine?

Although we talk about "wind turbines," the turbine is only one of the parts of these machines. For most turbines, another key part is a gearbox whose gears convert the relatively slow rotation of the spinning blades into higher-speed motion—turning the drive shaft quickly enough to power the electricity generator. The generator is where electricity is actually created.

How does a wind turbine work?

1. Wind (moving air that contains kinetic energy) blows toward the turbine's rotor blades.

2. The rotors spin around, capturing some of the kinetic energy from the wind, and turning the central drive shaft that supports them. Although the outer edges of the rotor blades move very fast, the central axle (drive shaft) they're connected to turns quite slowly.

3. In most large modern turbines, the rotor blades can swivel on the hub at the front so they meet the wind at the best angle (or "pitch") for harvesting energy. This is called the pitch control mechanism. On big turbines, small electric motors or hydraulic rams swivel the blades back and forth under precise electronic control.

4. Inside the nacelle (the main body of the turbine sitting on top of the tower and behind the blades), the gearbox converts the low-speed rotation of the drive shaft (perhaps, 16 revolutions per minute, rpm) into high-speed (perhaps, 1600 rpm) rotation fast enough to drive the generator efficiently.

5. The generator, immediately behind the gearbox, takes kinetic energy from the spinning drive shaft and turns it into electrical energy. Running at maximum capacity, a typical 2MW turbine generator will produce 2 million watts of power at about 700 volts.

6. Anemometers (automatic speed measuring devices) and wind vanes on the back of the nacelle provide measurements of the wind speed and direction.

7. Using these measurements, the entire top part of the turbine (the rotors and nacelle) can be rotated by a yaw motor, mounted between the nacelle and the tower, so it faces directly into the oncoming wind and captures the maximum amount of energy. If it's too windy or turbulent, brakes are applied to stop the rotors from turning (for safety reasons). The brakes are also applied during routine maintenance.

8. The electric current produced by the generator flows through a cable running down through the inside of the turbine tower.

9. A “step-up transformer” converts the electricity to about 50 times higher voltage so it can be transmitted efficiently to the power grid (or to nearby buildings or communities). If the electricity is flowing to the grid, it's converted to an even higher voltage (130,000 volts or more) by a substation nearby, which services many turbines.

10. Homes enjoy clean, green energy.

11. Wind carries on blowing past the turbine, but with less speed and energy (for reasons explained below) and more turbulence (since the turbine has disrupted its flow).

How turbines harvest maximum energy?

If you've ever stood beneath a large wind turbine, you'll know that they are absolutely gigantic and mounted on incredibly high towers. The longer the rotor blades, the more energy they can capture from the wind. The giant blades multiply the wind's force like a wheel and axle, so a gentle breeze is often enough to make the blades spin around. Wind turbines are designed to work efficiently at a range of different speeds.

A typical wind turbine nacelle is 280 feet off the ground. There's a good reason for this. If you've ever stood on a hill that's the tallest point for miles around, you'll know that wind travels much faster when it's clear of the buildings, trees, hills, and other obstructions at ground level. So if you put a turbine's rotor blades high in the air, they capture considerably more wind energy than they would lower down. (If you mount a wind turbine's rotor twice as high, it will usually make about a third more power.) And capturing energy is what wind turbines are all about.

Since the blades of a wind turbine are rotating, they must have kinetic energy, which they "steal" from the wind. Now it's a basic law of physics (known as the conservation of energy) that you can't make energy out of nothing, so the wind must actually slow down slightly when it passes around a wind turbine. That's not really a problem, because there's usually plenty more wind following on behind! It is a problem if you want to build a wind farm: unless you're in a really windy place, you have to make sure each turbine is a good distance from the ones around it so it's not affected by them. Typically have to be spaced some distance apart (typically 3–5 rotor diameters in the "crosswind" direction, between each turbine and the ones either side, and 8–10 diameters in the "downwind" direction, between each turbine and the ones in front and behind).