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|Is this wind turbine in downtown Toronto too close to civilization?|
Some people describe it as music, others describe it as noise. No, we’re not talking about the latest wailings of the Pussy Cat Dolls. We’re talking about the sound that comes from wind turbines.
Unless we’re in the middle of a hurricane, most of us are usually unaware of the sound the wind makes. Sure, we may hear it rustle the leaves on the trees, assuming we’re not in the middle of the city where trees are a rare commodity. But the sound of the wind in the trees is usually perceived of as a good thing. However, too much of a good thing is … too much. And some people perceive the sound of the wind through a wind turbine as too much.
It’s usually not the sound of the wind flowing over the blades of the turbine that causes the problem. Instead, when wind passes between the turbines and the tower supporting the turbines, it may resonate, and with each pass of the blade create a low-frequency pulse.
Another source of noise is the gearbox and generator. We’re turning kinetic energy into electrical energy. That’s bound to create friction. The friction, in turn, creates noise.
How bad is the noise? Several factors affect the answer.
How many turbines are there? A single turbine obviously won’t create as much noise as a wind farm consisting of dozens of turbines.
What kind of turbines are they? Turbines come in many flavors: horizontal axis with the blades leading the tower (these seem particularly prone to generating low-frequency pulses), horizontal axis with the blades trailing the tower, vertical axis (like egg beaters). And there are others, with new designs coming out all the time. Some reduce the amount of gearing, thereby reducing the likelihood of mechanical noise. Some are better suited to operating with high-velocity winds or variable-velocity winds.
How fast is the wind blowing? Even the quietest turbines will likely produce more noise in high winds. And if the wind is rapidly changing speed and direction — gusting — you can bet that will affect the noise coming from the turbines.
In what direction is the wind blowing? If we’re downwind of the turbines we’ll likely hear more noise than if we’re upwind.
How far are we from the turbines? The closer we are, the louder they’ll be. As wind turbines grow in popularity, some governments are establishing guidelines and laws stipulating how close the devices can be to residential neighborhoods.
What’s the ambient noise level? We’re less likely to notice the noise of the turbines if we’re in an industrial area where there’s already a lot of noise from other sources, than if we’re in a quiet rural setting.
How sensitive are we? We’re speaking physically, not emotionally. Some people seem to be more sensitive to noise, even to sub-sonic vibrations, than others.
What is our attitude toward the turbines? This is a touchy subject. If we see them as a nuisance, we’re likely to be more troubled by the noise than if we perceive them in a positive light. If our utility bills go down when the turbines go up, or if the air smells better when the turbines replace the coal-fire plant, the noise might not bother us so much.
One thing is certain: until someone comes up with a better way of generating electricity, or with an alternative to electricity, it’s likely we’re going to see more turbines popping up across the countryside. That leaves us with two options: quit complaining and learn to live with them, or invent something better.
Read Wind Energy Systems: Control Engineering Design from Amazon.