How Does a Wind Turbine Work?
By Harry Sherwood
It’s the evening of October 1987, and you look out of your window as you tuck into a meal to see the trees swaying in the breeze. You laugh, and reassure yourself; remembering back to the BBC weather forecast you watched.
“Earlier on today, apparently, a woman rang the BBC and said she heard there was a hurricane on the way… well, if you’re watching, don’t worry, there isn’t!”
The Great Storm of 1987 turned out to be the worst storm to ever hit the United Kingdom. Wind speeds were recorded to exceed 120 mph, over £2 bln worth of damage was done and twenty-two people were killed. Clearly, wind is a force to be reckoned with.
The UK alone has over 5,000 wind turbines currently installed, and countries such as Denmark glean a third of their energy through wind power, but how does this technology work?
It is obvious that you can transfer energy by giving an object with mass some velocity. For example, if you throw a ball at a tin can, you can impart sufficient force to knock it over. Wind is just the flow of air, and air is just a collection of particles of gas. Each of these particles, whether they are nitrogen, oxygen or even small amounts of helium and neon, have a mass. This means that you can transfer energy from one place to another by moving a gas – a wind.
Wind is caused by differences in air pressure in the atmosphere. The sun heats the ground and the air in certain places, and colder air (often from the poles) is drawn because of this difference. This is the air flow which forms the basis of wind energy. In the same way that an aeroplane wing generates lift when it passes through air, a wind turbine ‘blade’ experiences a rotational force when wind passes over it. These blades are attached to an axle or spindle. This axle rotates a series of gears which change the speed of the rotation. Another axle comes out of the gearbox which rotates at the right speed – this is fed into a dynamo.
A dynamo is like the opposite of a motor. With an electric motor, electricity is fed in and the rotation of the spindle can be used to do all sorts of useful things. A dynamo works in reverse: rotational energy from the outside world (in this case from the turbine blades) allows the motor to produce electricity. The steps leading to this seem quite understandable, but the conversion of motion into electricity is the piece in the puzzle that requires the most careful explanation.
Michael Faraday’s place of retirement and death is a ten second walk from Lipmann Walton & Co. office. His discovery that moving a wire through a magnetic field generates a current in the wire is crucial if we are to understand how an electric generator/dynamo works. The reason that that moving a wire perpendicularly through a magnetic field can generate a current is that the field causes the electrons (negatively charged particles) to move toward one end of the wire. Here, they build up. Lots of small negative (-) charges build up to a more significant charge. Therefore, at one end of the wire there won’t be very many negative charges and at the other end there will be lots. This difference of charge is what we call a voltage, and the movement of these charges around a circuit is what we call current. The electrical power produced is therefore simply the voltage across the generator terminals multiplied by current that the generator in the turbine produces. It is worth noting that often these generators produce an ‘alternating’ current. In these generators, the rotation causes electrons to rush in one direction and then in the other direction within the wire at a specific rate.
An electric generator works on these same principles, with added scientific seasoning. For example, instead of a single wire, generators use multiple coils of wires spaced around a circle. Large, specially shaped neodymium magnets are used to encase the rotating coils. Sometimes, the setup is completely different, with the magnet rotating and the coils surrounding. Either way, a current is produced by the rotation of the axle.
In this way, energy can be fed back onto the power grid to power houses, factories and cities.