How does a wind turbine work?
Modern wind turbines usually have three blades that meet in the rotor. That rotor is attached to a housing (the gondola) that sits on top of a long mast. The higher the mast, the more wind the turbine blades catch and the more energy can be generated. Wind turbines of 150 meters high are no longer an exception, while the really large turbines are almost the same size as the Eiffel Tower.
The gondola can be rotated to ensure that the turbine's rotor blades are optimally positioned on the wind. So far there is not that much difference with the traditional Dutch windmill that could also be rotated in the wind, albeit manually - by the miller himself – instead of with a special motor. In the gondola of the wind turbine, a large dynamo is placed that transforms the rotation of the rotor into electricity. This generator is connected to a transformer that converts the low voltage generated by the dynamo into high voltage. The wind turbine is connected to external networks with modern means of communication, so that the mill can be operated remotely.
Of course, the amount of energy that can be generated with a wind turbine depends primarily on the wind. But more about that later. The yield also depends on the ‘hardware’: the type of wind turbine, the power that the generator can generate and how effectively the wind energy can be converted into electricity. But no wind energy without wind. Important here is the amount of available wind (indicated over the years in the Dutch ‘Windex’) and the wind speed. In order to run a wind turbine, a minimum wind force 2–3 is required. At wind force 10 to 12, windmills are stopped because otherwise they can become overloaded. The wind speed is determined by:
- The location: coastal and open sea wind is usually stronger than inland wind;
- The height of the wind turbine: wind us usually stronger at higher altitudes, although the wind speed inland during the day is stronger below 90 meters than above;
- The time of day: on average the wind above land at a height of up to 90 meters is stronger during the day than at night;
- The season: The wind is stronger in winter than in summer;
- The air temperature: Warm air is thinner and has less energy;
- The variation of the wind direction and the speed with which the wind turbine can be adjusted accordingly.
Thanks to improved technology a modern wind turbine provides much more wind energy than a wind turbine from thirty years ago. Not only because increasingly larger wind turbines can be built, but also because they have become more efficient and can generate more and more power. For example, the wind turbines that were placed in the Netherlands in the early eighties had a power yield of 85 kilowatts (kW). Many modern onshore wind turbines now have a capacity of 3-5 megawatts (1 MW = 1,000 kW) and there are even offshore wind turbines with a capacity of 12 MW.
How much energy a wind turbine generates depends on the power of the windmill and the amount of wind. If a windmill has been running at full power for an hour, we call it a full-load hour. For example, if a turbine with a capacity of 2 MW generated 4,000 MWh of energy in one year, the wind turbine would have run 2,000 full-load hours. The amount of full-load hours depends on the location, the height of the windmill and the length of the blades.