Image:  Close up of wind turbine nacelle and blade

Development of wind technology

 

The earliest recorded (traditional) windmill dates from the year 1191 at the Abbey of Bury St Edmunds in Suffolk. Replacing animal power for grinding grain, the popularity of windmills grew steadily until by 1400 there were some 10,000 in England, mostly in the East of England, Kent and Sussex. With the introduction of iron components in the 19th century, the traditional windmill reached its high point and was a common sight in towns and villages across the country.

 

The first use of a windmill to generate electricity was by a Charles F Brush in Cleveland, Ohio in 1888 and by 1908 there were over seventy in operation, with capacities ranging from 5-25 kW. By the 1930s windmills with capacities as high as 100 kW were in widespread use as a source of electricity, particularly in areas where centralised distribution systems had not been installed.

 

In the modern era the rate of technological development has increased dramatically, driven mainly by rising fossil fuel prices and concerns over climate change, and turbine capacity has roughly doubled every five years:

Date

Typical

capacity

Typical

blade length

Typical technology

Mid 1990s

400-500 kW

15-25m

Fixed rotational speed and fixed blade pitch angle

2000

1,000 kW

25-35m

Dual rotational speed and fixed blade pitch angle

Today

2,000-3,000 kW

35-45m

Variable rotational speed and variable blade pitch angle

Within 5 years*

3,000-7,000 kW

45-60m

 

* already in limited commercial use

Image:  Pitstone Mill. nr Aylesbury, Bucks, built in 1627 (the oldest surviving post mill in the UK)

 

 

Image:  Sibsey trader windmill, nr Boston, Lincolnsire, built in 1877

 

Today wind turbines are generally considered to be the most mature form of renewable energy technology, with industrial giants such as Siemens and GE amongst the leading manufacturers. In 2006, some 11,000 turbines were produced with a combined capacity of 16,000 MW and the global market was worth an estimated £13,000 million. Installed capacity is expected to pass 100 GW in 2008, the equivalent of 50-100 nuclear power stations.

 

 

How a wind turbine works

 

As the wind starts to blow, yaw motors turn a turbine’s nacelle so that the rotor and blades face directly into wind. The blades are shaped with an aerofoil cross section (similar to an aircraft wing) and this causes air to move more quickly over one side than the other. This difference in speed causes a difference in pressure which in turn causes the blade to move, the rotor to turn and a rotational force (or torque) to be generated.

 

The rotor is connected to a gearbox (on most turbines) and in turn to a generator housed in the nacelle that converts the torque into electricity. The electricity is then fed into a transformer located either inside or just outside the turbine which steps up the voltage to reduce losses in transportation. From there the electricity travels through underground cables to a small sub-station, usually on the wind farm site, where the voltage is stepped up through further transformers and exported to the local grid.

 

Typically turbines start to generate electricity in wind speeds of 3-4 m/s (7-9 mph) which in the UK are generally experienced 75%-85% of the time. The amount of torque (and so electricity) generated increases with wind speed up to around 15 m/s (34 mph) where the maximum (or rated) capacity of the turbine is reached. Output is then maintained at this level until a turbine is shut down when the wind reaches high speeds of around 25m/s (57 mph) to protect it from excessive loads - though the turbines are in fact designed and certified to withstand wind speeds up to 70 m/s (157 mph).

 

The basic components of a turbine are described in the interactive diagram below.

Image:  Wind turbine components 1: Rotor 2: Pitch motors 3: Gearbox 5: Turbine tower 6: Generator 7: Anemometers/vane 4: Yaw motors 8: Nacelle

Image:  Wind turbine nacelle

 

 

Image:  Wind turbine rotor hub

 
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