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A line of seven wind turbines in a wind farm with a truck in the foreground for scale.

Wind turbines

by Chris Woodford. Last updated: August 23, 2016.

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: Left: A small wind farm in Colorado, United States. These are relatively small turbines: each one produces about 700kW of energy (enough to supply 225 homes). The turbines are 79m (260ft) high (from the ground to the very top of the rotors) and the rotors themselves are 48.5m (159ft) in diameter. The top part of each turbine (called the nacelle) rotates on the tower beneath so the spinning blades are always facing directly into the wind. Photo by Warren Gretz courtesy of US Department of Energy/NREL (DoE/NREL).

How does a turbine generate electricity?

A man standing inside an open wind turbine nacelle.

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 whose gears convert 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, and the "lamp" is a light in someone's home dozens of miles away. Read more in our main article about generators.

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.

How does a wind turbine work?

A simple numbered cutaway diagram showing how a turbine converts wind into electricity.

  1. Wind (moving air that contains kinetic energy) blows toward the turbine's rotor blades.
  2. The rotors spin around slowly, capturing some of the kinetic energy from the wind, and turning the central drive shaft that supports them.
  3. The rotor blades can swivel on the hub at the front so they meet the wind at the best angle for harvesting energy.
  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 (about 16 revolutions per minute, rpm) into high-speed (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. A typical turbine generator will produce 1–2 megawatts (MW) of power at about 700 volts.
  6. Anemometers (wind-speed monitors) and wind vanes on the back of the nacelle provide measurements about 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 the wind speed rises too much, brakes are applied to stop the rotors from turning (for safety reasons). The brakes can also be applied for 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 lower speed and lower energy (for reasons explained below) and more turbulence (since the turbine has disrupted its flow).

How turbines harvest maximum energy

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 70m or 230 feet in diameter, which is about 30 times the wingspan of an eagle) multiply the wind's force like a wheel and axle, so 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 anemometers—automatic speed measuring devices—built into them and brakes that lock the blades if the wind speed is too high.)

A typical wind turbine 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. (If you make a wind turbine twice as high, it will make roughly a third more power.) And capturing energy is what wind turbines are all about.

Darrieus wind turbine

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.

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.

Advantages and disadvantages of wind turbines

Drawbacks

At first sight, it's hard to imagine why anyone would object to clean and green wind turbines—especially when you compare them to dirty coal-fired plants and risky nuclear ones, but they do have some disadvantages.

One of the drawbacks of wind turbines is that they don't generate anything like as much power as a conventional coal, gas, or nuclear plant. A typical turbine has a maximum power output of 1–2 megawatts (MW), which is enough to run 500–1000 electric toasters simultaneously—and enough to supply about 500–1500 homes. The world's biggest offshore wind turbines can now make 6–8 megawatts and power up to 5500 homes. In theory, you'd need about 1000–2000 turbines to make as much power as a really sizable (2000 MW) coal-fired power plant or a nuclear power station (either of which can generate enough power to run a million toasters at the same time); in practice, because coal and nuclear power stations produce energy fairly consistently and wind energy is variable, you'd need rather more.

As we've just seen, you can't jam a couple of thousand wind turbines tightly together and expect them to work effectively; they 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). Put these two things together and you arrive at the biggest and most obvious disadvantage of wind power: it takes up an awful lot of space. If you wanted to power an entire country with wind alone, you'd need to cover an absolutely vast land area with turbines (the late, brilliant physicist David MacKay explored these sorts of arguments at length). You could still use the land between the turbines for farming; a typical wind farm removes only 3–10 percent of land from production, and some of that is for access roads. You could mount turbines out at sea instead, but that would make it harder and more expensive to get the power ashore. Even onshore, connecting 1000 wind turbines to the power grid is obviously a bigger hurdle than wiring up a single, equivalent power plant; farmers and local communities often have objections to new power lines crossing their land.

Advantages

On the plus side, wind turbines are clean and green: unlike coal stations, once they're constructed, they don't make the carbon dioxide emissions that are causing global warming or the sulfur dioxide emissions that cause acid rain (a type of air pollution). Once you've built them, the energy they make is limitless and (except for spare parts and maintenance) free. That's even more of an advantage than it sounds, because the cost of running conventional power plants is heavily geared to risky things like wholesale oil and gas prices and the volatility of world energy markets.

Wind turbines contain quite a bit of metal, and some reinforced concrete to stop them falling over (a typical turbine has 8000 parts in total), so constructing them does have some environmental impact. (Remember that we're talking about a minimum of 1000–2000 turbines to replace a single power plant, so the amount of material isn't trivial.) Even so, looking at their entire operating lifespan, it turns out that wind turbines have among the lowest carbon dioxide emissions of any form of power generation, significantly lower than fossil-fueled plants, most solar installations, or biomass. Now nuclear power plants also have relatively low carbon dioxide emissions (roughly the same as wind turbines, measured over their lifespan). But wind turbines don't have the security and pollution problems many people associate with nuclear plants, and they're much quicker and easier to construct. They're also much cheaper, per kilowatt hour of power they produce: half the price of nuclear and two thirds the price of coal (according to 2009 figures quoted by Milligan et al). According to the Global Wind Energy Council, a turbine can produce enough power in 3–6 months to recover the energy used throughout its lifetime (constructing, operating, and recycling it).

In summary

Pros

Cons

Arguable

Is wind the energy of the future?

Bar chart showing the ten countries with the most installed wind capacity in MW, 2015.

It certainly has a part to play, but how big a part depends on where in the world you are and whether there are better alternatives suited to your local geography. In sunny Australia, for example, solar would probably make more sense. In countries that have windy winters (when electricity demand is at its highest), wind turbines could be a strong contender; on August 11, 2016, for example, wind turbines in (windy) Scotland produced enough energy to power the whole country. Countries with lots of fossil-fueled plants and no plans to retire them soon might find investments in carbon capture and storage (scrubbing the carbon dioxide from the emissions of coal and other fossil plants) a wise option, though that remains a largely unproven technology. Ultimately, it's a political choice as well as a scientific one. In Germany, where people have strong opposition to nuclear power, there have been huge investments in wind energy. Denmark, another European country, plans to move to 100 percent renewable energy with a massive commitment to wind. Although China is investing heavily in wind power, it still makes about three quarters of its electricity from coal. In short, while the growth of wind power is impressive, it still plays a relatively small part, overall, in providing the world's electricity.

Chart: Which countries are making the most of their wind? This chart shows the ten countries with the most installed wind capacity as of 2015. It's no surprise to find big countries like China, the United States, and India topping the list, but it is interesting to see much smaller nations like Germany and Spain investing so heavily in wind. Drawn by Explainthatstuff.com with statistical data courtesy of the Global Wind Energy Council.

But what if the wind doesn't blow?

Some people worry that because wind is very variable, we might suddenly lose all our electricity and find ourselves plunged into a "blackout" (a major power outage) if we rely on it too much.

The reality of wind is quite different. "Variable" does not mean unreliable or unpredictable. Wherever you live, your power comes from a complex grid (network) of intricately interconnected power-generating units (ranging from giant power plants to individual wind turbines). Utility companies are highly adept at balancing power generated in many different places, in many different ways, to match the load (the total power demand) as it varies from hour to hour and day to day. The power from any one wind turbine will fluctuate as the wind rises and falls, but the total power produced by thousands of turbines, widely dispersed across an entire country, is much more regular and predictable. For a country like the UK, it's pretty much always windy somewhere. As Graham Sinden of Oxford University's Environmental Change Institute has shown, low wind speeds affect more than half the country for only 10 percent of the time; for 60 percent of the time, only 20 percent of the UK suffers from low wind speeds; and only for one hour per year is 90 percent of the UK suffering low speeds (Sinden 2007, figure 7). In other words, having many wind turbines spread across many different places guarantees a reasonably steady supply of wind energy virtually all year round.

Wind farm in Altamont Pass, California

Photo: You can put lots of turbines together to make a wind farm, but you need to space them out to harvest the energy effectively. Combining the output from many wind farms in many different areas produces a smoother and more predictable power supply. This wind farm is at one of the world's windiest places: Altamont Pass, California, United States. Photo by courtesy of US Department of Energy.

While it's true that you might need 1000 wind turbines to produce as much power as a giant coal or nuclear plant, it's also true that if a single wind turbine fails or stops turning, it causes only 1/1000th (0.1 percent) of the disruption you get when a coal or nuclear plant fails (which happens more often than you might think). It's also worth bearing in mind that wind is extremely predictable several days in advance so it's easy for power planners to take account of its variability as they figure out how to make enough power to meet expected demands.

Opponents of wind power have even suggested that it might be counter-productive, because we'd still need to have backup coal or nuclear plants (or some way of storing wind-generated electricity) for those times when there's not enough wind blowing. That would certainly be true if we made all our energy from one, single mega-sized wind turbine—but we don't! In reality, even countries that have large supplies of wind energy have plenty of other sources of power too; as long as wind power is making less than half of a country's total energy, the variability of the wind is not a problem. (Denmark, for example, makes 20 percent of its electricity—and meets 43 percent of its peak load—with wind; Eric Martinot's article "How is Denmark Integrating and Balancing Renewable Energy Today?" gives an excellent overview of how that country has managed to integrate huge amounts of wind power into its grid.)

Micro-wind turbines

Rutland Windcharger 914 micro wind turbine against blue sky.

If small is beautiful, micro-wind turbines—tiny power generators perched on a roof or mast—should be the most attractive form of renewable energy by far. Some manufacturers have pushed the technology aggressively, hinting to consumers about big savings on electricity bills and major benefits for the environment. The reality is a little different: micro-turbines do indeed bring economic and environmental benefits if they're sited in reliably windy areas, but they're less helpful in towns and cities where buildings make "energy harvesting" more of a challenge. So are micro-wind turbines really worth the investment? How do they compare with their big brothers?

Photo: Micro power to the people! This small, mast-mounted Rutland Windcharger is designed to trickle-charge 12V and 24V batteries, such as those used in small boats, far from the grid. At a wind speed of 40–55 km/h (20–30 knots), it will produce a handsome 140–240 watts of power. At 20 km/h (10 knots), it produces a rather more modest 27 watts.

How micro-wind turbines compare

These figures are simply designed to give a rough comparison of the differences between large-scale and micro-wind turbines. Bear in mind that there's a huge variety of micro-turbines.

Large Micro
Mounting Tower roughly 80–100m (260–344ft) high. Roof, or mast typically ~10m (30ft) high.
Rotor diameter Up to 90m (300ft). 1–4m (3–12ft).
Energy production 1–8 megawatts (1000–8000 kilowatts). 400–40,000 watts (0.4–40 kilowatts).
Operates in wind speeds 10–55mph (16–90 km/h). 10–40mph (16–64 km/h).
Cost $1–2 million per MW. $500–100,000.
Provides power to 500–5500 homes. 1 home.

How to set up your own micro-wind turbine

If you want to build your own micro-wind turbine, what do you need? Apart from the turbine itself, you also typically need a piece of electrical equipment called an inverter (which converts the direct-current electricity produced by the turbine's generator into alternating current you can use in your home) and appropriate electrical cabling. Your turbine will also need either a connection into the grid supply or batteries to store the energy it produces.

Micro-wind turbine and solar panel powering a road construction sign.

Aside from the equipment, here are a few pointers worth bearing in mind:

Photo: Although micro-wind turbines on homes have proved controversial, they definitely have their place. Here's the Rutland Windcharger from our top photo helping to charge the batteries in a go-anywhere, portable highway construction sign. It's getting help from the large flat solar panel mounted on top. This is a great example of how micro-wind turbines can be useful if you put them in the right place, at the right time.

Acknowledgments

My thanks to Prof. John Twidell for suggesting that I add this new material on the variability of wind power (a very broad, very simplified summary of the kind of arguments made in the papers by Michael Milligan et al and John Twidell, which you'll find listed in the references below).

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