Creating energy from wind - The conversion process
A wind turbine works the opposite way to a fan. Instead of using electricity to make wind by turning the blades of the fan, a turbine uses wind to make electricity. The wind turns the blades; these spin the shaft, which connects to a generator in-order to produce electricity. The electricity is sent through transmission and distribution lines to a substation and then on to homes, business and schools. Tall towers, or posts, are used to position the turbine at a sufficient height to have unobstructed access to the wind, so that the rotor faces the strongest and steadiest possible winds. As the wind direction changes, the wind turbine needs to face into the wind. With large turbines this is achieved using electric motors whilst for very small turbines this is done passively by using a vane as part of the tail at the back of the turbine.
Design features of wind turbines
The diagram below shows some of the pieces and parts inside a wind turbine: |
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The fundamental design parameters are:
- the number of blades; three being the optimum for balancing the rotor
- the length of the blades; the turbine power increasing as the swept area (i.e. square power of the length)
- position of the blades with respect the tower; almost all blades are positioned upwind to avoid generating noise when the blade passes through the tower shadow.
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The mechanics of a wind turbine – note this turbine has its blades in an upwind position – (source Alliant Kids Energy) |
Types of micro-wind turbines
Vertical and horizontal axis turbines
There are two main classes of wind turbine which spin in different directions, or around different ‘axes’. Those that spin around a horizontal axis (like the London Eye or a traditional Dutch windmill) and those that spin on a vertical axis (like a merry-go-round).
Sizing wind systems
The best size turbine for an average sized house would be between 1 & 2.5 kilowatts, 1.5 metres or less. These turbines are often attached to the buildings they are powering (known as buildings integrated turbines). Community scale systems, of 5 to 15 kilowatts, can be used to provide power to a school, office, hall or a small group of houses. These larger turbines are usually put on top of masts (or posts), between 10m & 15m high, some distance (at least 100m) from any buildings excluding the building(s) they are powering.
Independent/stand-alone or grid-connected systems
Small scale wind power is very good for supplying electricity where it is expensive to supply energy through normal means (i.e. the National Grid in the UK) such as remote locations and small islands. These ‘off-grid’ systems require batteries to store the electricity they make and are often combined with diesel generators to supply energy at times of low wind speed.
Wind systems can also be used where there is a connection to a country’s national grid system, here no batteries are required. Any unused electricity can then be fed in to the national grid and sold to electricity companies, who can sell it to electricity consumers. This can be used to generate income which can help pay off some of the costs of building the turbine.
