Wind turbines

by Chris Woodford. Last updated: October 2, 2023.

Wind turbines look like airplane propellers 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: 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 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.

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). This is a 900kW turbine with a 55m (182ft) diameter rotor mounted on a tower 33m (110ft) off the ground. Photo by Lance Cheung courtesy of US Air Force.

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 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.

Photo: In theory, wind is still at ground level and blows faster the higher from the ground you go, in a region that's known as the boundary layer. Generally, the taller a wind turbine, the better, although there are practical limits and diminishing returns from going ever higher.

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.

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 to 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. This one is 17m (56ft) high and produces ~150 kilowatts of power. Photo by courtesy of US National Archives.

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. [1] The world's biggest offshore wind turbines can now make 13 megawatts, since they can be built much taller and winds are stronger and more persistent out at sea. If a 2MW turbine can power 1000 homes, simply scaling up the numbers, you'd expect a 13MW turbine to be able to power about 6500 homes. In practice, however, because new turbines are more efficient and operate more of the time, a 13MW offshore turbine can actually make enough power for about 12,000 homes. [2]

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, or three times as many for a wind farm working at 30 percent capacity. [3]) 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.

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 is the Ponnequin Wind Farm in Colorado, United States. Photo by Warren Gretz courtesy of NREL.

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). [4] 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). [5] 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 20–25 years. [6] 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).

Artwork: Wind turbines are much bigger and more powerful than they were just a few decades ago. Each one of these turbines shows how the state of the art has improved dramatically every five years since the mid 1980s. The numbers on top are the rotor diameter and maximum power. Artwork by Joshua Bauer courtesy of NREL.

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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.

Photo: One way to overcome some of the drawbacks of wind turbines is to site them out at sea where they take up less room and generate more energy. This is Block Island Wind Farm, the first offshore farm in the United States, near Rhode Island. Photo by Dennis Schroeder courtesy of NREL.

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?" [PDF] 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.

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, while in May 2021, wind energy provided almost two thirds of Britain's entire electricity. 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 two thirds 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.

Which countries have most wind power?

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, Ireland, and Germany lead the pack, the United States is 13th, the UK isn't much better, China manages only 16th place, and India (not even on the chart) comes in at number 33.

Chart: Wind energy per capita (top-20 countries). Drawn by Explainthatstuff.com using 2021 wind capacity data courtesy of [PDF] Renewable Capacity Statistics 2021, International Renewable Energy Agency (IRENA), Abu Dhabi, 2021, and 2020 population data compiled by the World Bank. These are the most recent publicly available datasets available at the time this article was last updated in January 2022. If you're interested in how things have moved on, compare this chart with the one I drew a few years ago using 2017 figures, courtesy of the Global Wind Energy Council and World Bank.

I think another interesting thing about this chart is not how much wind energy we're making, but perhaps how little. Most countries here are making about 300–400 watts of power for each person, which is fine as long we don't all want our 300–400 watts at exactly the same time. But think for a moment how much power you use—a kettle, toaster, or vacuum cleaner can easily gobble over 2000 watts, for example—and you'll see just how much more renewable energy needs to grow to provide anything like the power we all need.

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. This article uses a number of wonderful photos and artworks sourced from NREL and elsewhere—and I'm very grateful to the photographers and artists.

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On this website

• Climate change and global warming
• Electricity
• Energy
• Environmentalism
• Recycling
• Renewable energy
• Solar cells (photovoltaic)

On other sites

• Wind with Miller: A great introduction to wind energy from the Danish Wind Industry Association. This one's for younger readers.

News articles

• A Monster Wind Turbine Is Upending an Industry by Adam Vaughan. The New York Times, 1 January 2021. A closer look at the world's biggest (13MW) wind turbine,
• With Much of the World's Economy Slowed Down, Green Energy Powers On by Stanley Reed. The New York Times, June 30, 2020. Why the outlook for the future remains positively windy.
• Biggest offshore windfarm to start UK supply this week by Adam Vaughan. The Guardian, 11 February 2019. Large windfarms are now capable of supplying gigawatt-sized amounts of power—as much as typical, conventional power plants.
• Wind power overtakes nuclear for first time in UK across a quarter by Adam Vaughan. The Guardian, 16 May 2018. How wind has made spectacular gains in Britain.
• How Windmills as Wide as Jumbo Jets Are Making Clean Energy Mainstream by Stanley Reed et al. The New York Times, 23 April 2018. A fascinating interactive article from the NYT explores cutting-edge turbine technology.
• For the First Time, Wind Power Will Be Profitable Without Subsidies by Peter Fairley. IEEE Spectrum, 26 June 2017. Offshore wind is now competitive with coal, solar, and nuclear, even without subsidies.
• Solar and Wind Energy Start to Win on Price vs. Conventional Fuels by Diane Cardwell. The New York Times, November 23, 2014. Renewable power is now competitive with (and sometimes cheaper than) coal and gas.
• A Tricky Transition From Fossil Fuel: Denmark Aims for 100 Percent Renewable Energy by Justin Gillis. The New York Times, November 11, 2014. What problems is Denmark likely to face as it moves toward its goal of 100 percent renewable energy?
• Sun and Wind Alter Global Landscape, Leaving Utilities Behind by Justin Gillis. The New York Times, September 13, 2014. Wind and solar are changing the economics of power production, prompting traditional electricity producers to rethink how they do business.
• Little Limit to the Amount of Wind Energy by Dave Levitan. IEEE Spectrum, September 2012. How much wind energy is there on Earth? Is there an upper limit? How much of humankind's energy could we really make from the wind?
• Three steps to build a wind farm by David Shukman. BBC News, 15 August 2011. How do you build an offshore wind farm? This great interactive feature from the BBC explains all you need to know.

Books

• Renewable Energy Resources by John Twidell and Tony Weir. Routledge, 2015. Covers all kinds of renewable energy. Chapters 7 and 8 focus on wind.
• Wind Energy: Renewable Energy and the Environment by Vaughn Nelson. CRC Press, 2013. Covers all aspects of wind energy, from wind turbines to grid connection.
• Wind Turbines: Fundamentals, Technologies, Application, Economics by Eric Hau. Springer, 2013. A hugely detailed reference.
• Onshore and Offshore Wind Energy: An Introduction by Paul A. Lynn. John Wiley, 2011. Very readable and easy to understand.

Statistics and market reports

• Wind Market Reports: 2021 Edition: Wind Energy Technologies Office. Definitive facts and statistics for the United States.
• Wind energy in the UK: June 2021: Office for National Statistics. A comprehensive collection of facts and statistics about UK wind power.
• IEA: Wind: Global overview of the current state of wind power, 2020.
• Wind energy: global data and analysis: Which countries are most aggressively pursuing wind energy? Facts and figures from the Global Wind Energy Council.
• Wind Energy in Europe: Outlook to 2022 by WindEurope, 2019. The latest market outlook for onshore and offshore wind energy.
• Global Wind Report 2021 by the Global Wind Energy Council. The current state of energy worldwide.
• [PDF] Wind Energy Scenarios for 2030 by European Wind Energy Association, 2015.

Technical reports and journal articles

Recent

• [PDF] Future of Wind: International Renewable Energy Agency (IRENA), 2019. What part will wind play in the global energy future?
• [PDF] How is Denmark Integrating and Balancing Renewable Energy Today? by Eric Martinot, January 2015.
• Wind Power Myths Debunked by Michael Milligan et al, IEEE Power & Energy Magazine, November/December 2009. A clear, easy-to-understand explanation of how wind power can be integrated into a grid network.
• Wind: Physicist David MacKay looks at how much of a contribution wind power can realistically make to the UK's total energy needs in his book Sustainable Energy Without the Hot Air, 2009.
• [PDF] Characteristics of the UK wind resource: Long-term patterns and relationship to electricity demand by Graham Sinden. Energy Policy, Volume 35, Issue 1, January 2007, Pages 112–127. This detailed paper studies wind power production over a period of 34 years at 66 different UK sites and debunks the myth that wind turbines are unproductive for much of the time. [Archived via the Wayback Machine]

Older, but still useful

• [PDF] Society's Cost of Electricity by Siemens Wind Power, 2014. A detailed comparison of wind and other forms of power generation, which attempts to take into account the full range of their costs and benefits (not just simple economic costs). [Archived via the Wayback Machine]
• [DOC] Assessing Backup Requirements for Wind Power by John Twidell, Institute of Physics (IOP) Energy Group Newsletter, November 2010. [Archived via the Wayback Machine]
• [PDF] The Economics of Wind Energy by Søren Krohn et al, European Wind Energy Association, 2009. A comprehensive economic evaluation of the costs and benefits of wind power.
• Warwick Wind Trials: A detailed UK study of micro-wind carried out between 2006 and 2008. [Archived via the Wayback Machine.]

Photographs

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

• US Department of Energy/National Renewable Energy Laboratory Photo Library: Enter the search term "wind turbine" and you'll find a couple of thousand photos of turbines. As works of a US Federal Government agency, some of these photos are in the public domain, but others (supplied by turbine manufacturers) are copyright restricted.
• Flickr: Wind turbines: Some Flickr photos are published under Creative Commons licences (allowing limited reuse under certain conditions); others are copyright images.

Videos

• Inside a wind turbine: A fascinating seven-minute tour of a turbine at Crystal Rig Wind Farm in Scotland by Fred Olsen Renewables.
• A reality check on renewables by Professor Sir David MacKay, YouTube, June 26, 2013. An eloquent introduction to renewable energy: if you want to use solar or wind, you need an awful lot of it to make any difference, and you can expect it to take up a vast land area. Wind is discussed at 8m 6s, where David concludes that if the UK wanted to produce all its energy from wind, it would need to cover half the country with wind farms.

References

1. ↑   Estimates like this are obviously very rough, because homes use different amounts of electricity and the electrical energy a single wind turbine makes can vary. But if we average over many homes and study the output of turbines over a long period, we can come up with a reasonable figure. I take this particular estimate from the British green energy company Ecotricity in a 2013 web page titled Where Our Numbers Come From [Archived via the Wayback Machine, retrieved in January 2022]. This calculates that a 2.3MW turbine can supply about 1,345 homes based on a capacity factor (effectively, how much of the time the turbine is working at maximum capacity) of 27.7 percent. Offshore wind farms now achieve much higher capacity factors than this, though it's still a decent figure for onshore wind (see note 3 below).
2. ↑   The figure of 12,000 homes is based on the GE Haliade-X and comes from A Monster Wind Turbine Is Upending an Industry by Stanley Reed, The New York Times, 1 January 2021.
3. ↑   The "capacity factor" of wind farms varies quite a bit, but 30–50 percent is a decent, working range. A blog called Energy Numbers suggests that typical UK offshore farms vary between about 33 percent and 50 percent for 2021. For the United States, Walt Musial of NREL quotes [PDF] capacity factors of 40–50 percent for offshore wind in a document dated March 2018. The capacity factor for onshore wind farms is significantly lower. For 2021, RenewableUK quotes UK government figures of 26.46 percent for onshore wind farms and 39.94 percent for offshore.
4. ↑   For details of turbine spacing and placing, see Wind Energy Explained: Theory, Design and Application by James F. Manwell, Jon G. McGowan, Anthony L. Rogers, Wiley, 2010, p.423.
5. ↑   The figure of 5 percent originally came from the Altamont Pass wind farm; see The New Global Oil Market: Understanding Energy Issues in the World Economy by Siamack Shojai (ed), Praeger, 1995, p.163.
6. ↑   What happens to all the old wind turbines? by Padraig Belton, BBC News, 7 February 2020.