Wind turbines

Last updated: July 5, 2007.

Wind turbines are like airplanes running on the spot—spinning round but going nowhere. They're serving a very useful purpose, however. There's energy locked in wind and these giant propellers can capture some of it and turn it instantly into electricity. Have you ever stopped to wonder how wind turbines work? Let's take a closer look.

Photo: A series of wind turbines in Montford, Wisconsin, United States. The top part of each turbine rotates on the tower beneath so the spinning blades are always facing directly into the wind. Photo by courtesy of US Department of Energy.

Turbines and generators

A turbine 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 power plants and from diesel railroad locomotives to windmills. Even a child's toy windmill is a simple form of turbine.

The huge rotor blades (propellers) on the front of a wind turbine are the "turbine" part. As wind passes by, the kinetic energy (energy of movement) it contains makes the blades spin around (usually quite slowly). The blades have a special curved shape so they capture as much energy from the wind as possible.

Although we talk about "wind turbines," the turbine is only one of the three main parts inside these giant machines. The second part is a gearbox that converts the slow speed of the spinning blades into higher-speed rotary motion—turning the drive shaft quickly enough to power the electricity generator.

The generator is the third main part of a turbine and it's exactly like an enormous, scaled-up version of the dynamo on a bicycle. When you ride a bicycle, the dynamo touching the back wheel spins around and generates enough electricity to make a lamp light up. The same thing happens in a wind turbine, only the "dynamo" generator is driven by the turbine's rotor blades instead of by a bicycle wheel.

Photo: Big blades in Tehachapi, California. You can see just how big the blades of a turbine are compared to these two engineers who are maintaining them. Photo by courtesy of US Department of Energy.

Practical details

If you've ever seen a wind turbine, you'll know that they are absolutely gigantic and mounted on incredibly high towers. The bigger the rotor blades, the more energy they can capture from the wind. The giant blades (typically 70 m or 230 feet in diameter, which is about 30 times the wingspan of an eagle) work like wheels and axles (which are examples of simple machines). Even a gentle breeze is enough to make the outer edges of the blades turn around. Although the blades rotate quite slowly, the inner axle and turbine rotate with greater force—enough to turn the generator and make electricity. (Wind turbines usually have automatic speed measuring devices built into them and a mechanism that locks the blades if the wind speed is too high.)

A typical wind turbines is 85 meters (280 feet) off the ground—that's like 50 tall adults standing on one another's shoulders! 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. 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 thin air, 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.

Photo: You can put lots of turbines together to make a wind farm, but you need to space them out to harvest the wind's energy effectively. This farm is at one of the world's windiest places: Altamont Pass, California, United States. Photo by courtesy of US Department of Energy.

Are they worth it?

One of the drawbacks of wind turbines is that they don't generate anything like as much energy as a conventional power plant. Each turbine makes about 1 megawatt of power, which is enough to power 500 electric toasters running simultaneously—enough to supply nearly 1100 homes. You'd need about 1000-2000 turbines to make as much power as a really sizeable coal- or nuclear-fired power plant (which can generate enough power to run a million toasters at the same time). But on the plus side, wind turbines are clean and green: unlike coal stations, they don't make the carbon dioxide emissions that are causing global warming or the sulfur dioxide emissions that cause acid rain. And they don't have the security and pollution problems many people associate with nuclear power. Is wind the energy of the future? It just might be!

Photo: This unusual Darrieus "egg-beater" wind turbine rotates about a vertical axis, unlike a normal propeller turbine. Its main advantage is that it can be mounted nearer to the ground, without a tower, which makes it cheaper and simpler to construct. Photo by courtesy of US Department of Energy.

Further reading

Favorite websites

• Ecotricity: The leading British wind energy company has a very informative website, with lots of photos showing how its wind turbines were constructed. There's also a helpful cutaway illustration showing what's inside a turbine.
• Wind with Miller: A great introduction to wind energy from the Danish Wind Industry Association. This one's for younger readers.
  
• Guided tour on wind energy: A deeper introduction to wind energy for older readers, also from the Danish Wind Industry Association. Includes a detailed look at all the parts of a wind turbine and what they do.