You are here: Home page > Energy > Wind turbines
Advertisement

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: September 15, 2016.

Wind turbines look 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 their giant rotors 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 about 400 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.

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 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 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 instead. The wind loses some of its kinetic energy (energy of movement) and the turbine gains just as much. As you might expect, the amount of energy that a turbine makes is proportional to the area that its rotor blades sweep out; in other words, the longer the rotor blades, the more energy a turbine will generate. Obviously, 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 large farm, and linking many wind farms in different areas into a national power grid, produces a much more steady supply overall.

Key parts of a wind turbine?

Although we talk about "wind turbines," the turbine is only one of the parts inside these machines. For most (but not all) 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 an essential part of all turbines and you can think of it as being a bit 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 miles away. In practice, wind turbines use different types of generators that aren't very much like dynamos at all. (You can read about how they work, more generally, in our main article about generators.)

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, 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. On smaller turbines, the pitch control is often completely mechanical. However, many turbines have fixed rotors and no pitch control at all.
  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: the turbine has produced no greenhouse gas emissions or pollution as it operates.
  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 (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 a gentle breeze is often enough to make the blades turn around. Even so, typical wind turbines stand idle about 14 percent of the time, and most of the time they don't generate maximum power. This is not a drawback, however, but a deliberate feature of their design that allows them to work very efficiently in ever-changing winds. Think of it like this. Cars don't drive around at top speed all the time: a car's engine and gearbox power the wheels as quickly or slowly as we need to go according to the speed of the traffic. Wind turbines are analogous: like cars, they're designed to work efficiently at a range of different speeds.

A typical wind turbine nacelle 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 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.

Darrieus wind turbine

Photo: This unusual Darrieus "egg-beater" wind turbine rotates about a vertical axis, unlike a normal turbine with a horizontal rotor. Its main advantage is that it can be mounted nearer to the ground, without a tower, which makes it cheaper construct. It can also capture wind coming from any direction without using things like pitch and yaw motors, which makes it simpler and cheaper. Even so, turbines like this suffer from a variety of other problems and are quite inefficient at capturing energy, so they're very rare. Photo by courtesy of US Department of Energy.

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 characteristics of a wind turbine is that it doesn't generate anything like as much power as a conventional coal, gas, or nuclear plant. A typical modern turbine has a maximum power output of about 2 megawatts (MW), which is enough to run 1000 2kW electric toasters simultaneously—and enough to supply about 1000 homes, if it produces energy about 30 percent of the time. The world's biggest offshore wind turbines can now make 6–8 megawatts, since winds are stronger and more persistent out at sea, and power about 6000 homes. In theory, you'd need 1000 2MW turbines to make as much power as a really sizable (2000 MW or 2GW) coal-fired power plant or a nuclear power station (either of which can generate enough power to run a million 2kW 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. (If a good nuclear power plant operates at maximum capacity 90 percent of the time and a good, brand new, offshore wind farm manages to do the same 45 percent of the time, you'd need twice as many wind turbines to make up for that.) Ultimately, wind power is variable and an efficient power grid needs a predictable supply of power to meet varying demand. In practice, that means it needs a mixture of different types of energy so supply can be almost 100 percent guaranteed. Some of these will operate almost continually (like nuclear), some will produce power at peak times (like hydroelectric plants), some will raise or lower the power they make at short notice (like natural gas), and some will make power whenever they can (like wind). Wind power can't be the only form of supply—and no-one has ever pretended that.

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 a lot of space. If you wanted to power an entire country with wind alone (which no-one has ever seriously suggested), you'd need to cover an absolutely vast land area with turbines. You could still use almost all the land between the turbines for farming; a typical wind farm removes less than 5 percent of land from production (for the turbine bases, access roads, and grid connections). You could mount turbines out at sea instead, but that raises other problems and costs more. Even onshore, connecting arrays of wind turbines to the power grid is obviously a bigger hurdle than wiring up a single, equivalent power plant. Some farmers and landowners have objections to new power lines, though many earn handsome profits from renting out their land (potentially with a guaranteed income for a quarter of a century), most of which they can continue to use as before.

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 over a typical lifetime of 25 years. 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 turbine towers and nacelles contain quite a bit of metal, and concrete foundations to stop them falling over (a typical turbine has 8000 parts in total), so constructing them does have some environmental impact. Even so, looking at their entire operating lifespan, it turns out that they have among the lowest carbon dioxide emissions of any form of power generation, significantly lower than fossil-fueled plants, most solar installations, or biomass plants. Now nuclear power plants also have relatively low carbon dioxide emissions, but wind turbines don't have the security, pollution, and waste-disposal problems many people associate with nuclear energy, 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

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 or goes offline for maintenance (which happens more often than you might think). It's also worth bearing in mind that wind is relatively 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 need to build extra backup coal, nuclear, biomass, or hydro 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.) In practice, every country's electricity has always come from a mixture of different energy sources, and the ideal mix varies from one country to another for geographical, practical, and political reasons.

How can we store the power of the wind?

Animation showing how a pumped storage hydroelectric plant works.

Wind could play a bigger part in the future if we could find cost-effective ways of storing electricity produced on windy days for times when there's little or no wind to harvest. One tried and tested possibility is pumped storage: low-price electricity is used to pump huge amounts of water up a mountain to a high-level lake, ready to be drained back down the mountain, through a hydroelectric turbine, at times of high demand when the electricity is more valuable. (In effect, we store electricity as gravitational potential energy, which we can do indefinitely, and turn it back to electricity when it suits us.) Batteries could also be a contender—if we had enough of them. There have been suggestions about using a fleet of electric cars as a giant collective battery, for exactly this purpose, but even large-scale batteries hooked up to individual wind farms could be very helpful. Statoil, for example, plans to install a huge wind-powered battery called BatWind in Scotland. Flywheels (heavy, low-friction wheels that store energy as they spin) are another possibility.

Photo: How pumped storage works: When there's lots of cheap electricity about (at night or when the wind is blowing), water is pumped up the mountain to the high-level lake at low cost. When electricity is more expensive and valuable (in the day, at peak times), the water drains from the high lake to the low one, powering a hydroelectric turbine.

Is wind the energy of the future?

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 be cheaper. 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? It's no surprise to find the biggest countries (China, the United States, and India among them) topping the list of countries with the most installed wind capacity, measured in gigawatts. But if we measure installed capacity per capita, we get this very different chart. Now European countries such as Denmark, Sweden, and Germany lead the pack, the United States is 10th, China manages only 20th place, and India comes in at number 32. Drawn by Explainthatstuff.com using 2015 wind capacity data courtesy of the Global Wind Energy Council and 2015 population data compiled by the World Bank.

Bar chart showing the 20 countries with the most installed wind capacity per capita, 2015.

Micro-wind turbines

Rutland Windcharger 914 micro wind turbine against blue sky.

If small is beautiful, micro-wind turbines—tiny power generators of about 50–150 W capacity, perched on a roof or mast—should be the most attractive form of renewable energy by far. They're certainly very widely used for all kinds of portable power, typically for recharging batteries in things like yachts and canal boats, and for powering temporary traffic lights and road signs.

Some manufacturers have pushed micro-wind technology aggressively, hinting that people could make big savings on electricity bills, and benefit the environment, by putting a little turbine on their roof to feed energy into the national power grid. The reality is a bit different: micro-turbines linked to the grid 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 and there's much more turbulence from obstructions. 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). 50–40,000 watts (0.05–40 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 (or single site).

How to set up your own micro-wind turbine

If you want to build your own micro-wind turbine, what do you need? The first thing to bear in mind is that small wind turbines spin at dangerously high speeds, so technical skill and safety are paramount: ideally, get your turbine installed by a professional. 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

For useful comments and suggestions on this article, I'm extremely grateful to Dr John Twidell (author, with Tony Weir, of the excellent Renewable Energy Resources); Robert Norris of RenewableUK; and Robert Preus of NREL. Needless to say, any errors and inaccuracies are entirely my responsibility.

Find out more

On this website

On other sites

Technical and journal articles

News articles

Books

Photographs

Need photos for a school project on wind power? Have a look at:

Videos

Statistics

Sponsored links

If you liked this article...

Atoms Under the Floorboards book cover

You might like my new book, Atoms Under the Floorboards: The Surprising Science Hidden in Your Home, published worldwide by Bloomsbury.

Please do NOT copy our articles onto blogs and other websites

Text copyright © Chris Woodford 2007, 2016. All rights reserved. Full copyright notice and terms of use.

Follow us

Rate this page

Please rate or give feedback on this page and I will make a donation to WaterAid.

Share this page

Press CTRL + D to bookmark this page for later or tell your friends about it with:

Cite this page

Woodford, Chris. (2007/2016) Wind Turbines. Retrieved from http://www.explainthatstuff.com/windturbines.html. [Accessed (Insert date here)]

More to explore on our website...

Back to top