How Do Wind Turbines Work? From Breeze to Grid
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The largest wind turbines now have blades longer than a football pitch, hubs higher than a fifty-storey building, and each one produces enough electricity for around 20,000 homes when the wind blows, and the wind blows on them, being out at sea, most of the time. They are the fastest-growing source of electricity in the world and one of the cheapest, and they work on a principle that a Dutch miller of 1600 would recognise, with a refinement he would not: the blades are not paddles pushed by the wind but wings pulled through it.
Lift, not push
An old windmill's sails were flat boards that the wind shoved round, and they wasted most of it. A modern blade is an aerofoil, the same shape as an aircraft wing in cross-section, and it works the same way: air flowing over the curved surface creates a pressure difference across the blade, and the resulting lift force acts at right angles to the wind, which for a blade fixed on a hub means around the circle. The blade is twisted along its length because the tip, sweeping a far larger circle, meets the air at a different angle from the root, and it is pitched by motors at the hub to keep the angle right as the wind changes and to feather it flat, spilling the wind, in a gale. A modern rotor extracts almost half of the energy in the wind passing through it, close to the theoretical maximum of 59 percent that a German physicist calculated in 1919, since a turbine that took all the energy would leave the air stationary and block itself.
The nacelle
The blades turn a hub at a stately 10 to 20 revolutions a minute, and the rotation passes into the nacelle, the housing behind the hub, where it is either geared up to the 1,500 revolutions a generator likes or, in newer direct-drive machines, fed to a large slow generator with hundreds of magnetic poles that needs no gearbox. The generator makes alternating current of varying frequency, electronics convert it to the grid's exact frequency, and a transformer raises the voltage for transmission. Sensors on the nacelle measure wind speed and direction, and a yaw motor turns the whole assembly to face the wind. The main parts:
- •Rotor: three blades of fibreglass or carbon fibre, up to 120 metres each, on a hub
- •Pitch system: motors that rotate each blade about its axis to control power and stop the machine
- •Gearbox or direct drive: matching the slow rotor to the generator
- •Generator and converter: producing electricity and conditioning it for the grid
- •Tower: steel or concrete, 100 to 150 metres, since wind is stronger and steadier with height
- •Foundation: concrete on land, and at sea a monopile driven into the seabed or, in deep water, a floating platform anchored by chains
Why so big
The power available from the wind rises with the square of the rotor's diameter, since that sets the area swept, and with the cube of the wind speed, which is why the industry has raced upward and outward. Doubling a blade's length quadruples the energy captured, and building higher reaches the faster, smoother wind above the turbulence of the ground. A turbine from 1990 stood 40 metres tall and made 300 kilowatts; the largest offshore machines of 2024 stand 260 metres to the blade tip and make 15 megawatts, fifty times as much, from a single tower. The limits are the length of blade that can be built as one piece and moved by road, which is why offshore machines, shipped by sea, are bigger, and the fatigue of a structure that flexes with every rotation for twenty-five years.
When the wind does not blow
A turbine produces its full rated power only in strong wind, and over a year a typical onshore machine delivers about a third of what it could if the wind were always ideal, an offshore one nearer half. That variability is the technology's main problem and the reason a grid cannot run on wind alone. The answers are geography, since the wind is usually blowing somewhere across a continent-sized grid; forecasting, which now predicts wind output a day ahead to within a few percent; storage in batteries and pumped water, which is growing fast; and gas plants that fill the gaps and run less each year. Denmark gets over half its electricity from wind, Britain about a third, and the days on which wind is the largest single source of power in Europe are no longer news.
Costs and objections
Onshore wind is now among the cheapest electricity there is, below new coal or gas in most of the world, and offshore has fallen in price by about two thirds in a decade. The objections are local and real: turbines change a landscape, they kill birds and bats, though far fewer than cats, windows and cars, and the low-frequency noise at close range is a genuine nuisance that siting rules address. The blades, made of composite that is hard to recycle, have been going to landfill, and the first plants to grind and reuse them opened in 2022. A turbine repays the energy used to build it within about six months and runs for twenty-five years, and the carbon dioxide per unit of electricity over its life is about a fiftieth of a gas plant's.
The takeaway
A wind turbine's blades are aerofoils that generate lift as the wind flows over them, turning a hub whose slow rotation is geared up or fed directly to a generator in the nacelle, converted to grid frequency and stepped up for transmission, with the blades pitched and the nacelle yawed to suit the wind. Power rises with the square of the blade length and the cube of wind speed, which is why the machines have grown to 260 metres, and their variability is managed by geography, forecasting, storage and backup.