Ever Wonder About Wind Turbines?
During my summer vacation driving around the continent with my family, I was surprised by the number of places where I saw wind turbines. I wondered how much a thing they were and how they worked.
As with most ways to generate electricity — waterfalls, coal, or nuclear power plants — wind turbines rely on the wonder of magnets rotating past conductive wires to generate electricity. The attraction of wind power is that it can turn these turbines without taking up much land, contributing to greenhouses gases, or producing toxic emissions. In addition, they can be set up on land that is being used for cattle or agriculture, providing extra income for ranchers and farmers. Wind energy is the fastest growing source of electricity in the world. In Canada, wind power grew by an average 15% per year between 2012 and 2017 and now supplies about 6% of Canadian electricity demand with 295 wind farms from coast to coast.
From a distance, a wind turbine consists of three main parts: the blades, the nacelle, and the tower.
All the wind turbines I saw had three blades. This turns out to be true for 90% of them. If they had only two, they would have have to spin faster to generate the same amount of power, which causes more stress on the components and makes more noise, which people don’t like. If they had four blades, they would cost more to make. So three seems to be the Goldilocks solution.
When you’re whizzing by in your car its hard to appreciate the scale of these things, particularly against the wide open spaces where they are often installed. Each blade is about 46 m (150 ft.) long, which is in between the length of a blue whale and the height of Niagara Falls. The blades have a cross-section similar to airplane wings, with a larger rounded leading edge that tapers. Wind passing over the blade results in a difference in air pressure that forces them to move.
The wind has to be about 12 km/h for the blades to begin turning. On the Beaufort Wind Scale, this is a 3, which means a moderate breeze that can move small branches, dust, and loose paper. If the wind reaches about 88 km/h, which is 9 going on 10 on the Beaufort scale, meaning a strong gale that can loosen or blow off roofing shingles, an internal brake shuts down the system. As the blades absorb energy from the wind, the downstream velocity is decreased, but it never gets to zero. The theoretical peak efficiency is known as Betz’ limit, which is about 60%.
This unassuming box with an obscure name connects the blades to the tower is the brains of the operation. Nacelle means "little boat" and originally referred to the gondola of an airship. It later referred to the cockpit of an airplane and now to the part of the wind turbine that is sort of like a cockpit.
To keep the blade oriented optimally to the wind, a wind vane measures wind direction. This information is sent to the yaw drive, which swivels the nacelle to orient the blades into the wind.
An anemometer senses wind speed and sends this information to a controller. This adjusts the angle of the blade with respect to the wind, so that it rotates quickly enough to produce a steady current without generating too much noise or stress on the system.
The blades turn an axle which is connected to gears that increase the speed of rotation, from about 50 rotations per minute up to about 1800 rpm enabling the turbine to generate the electricity. The eletricity generated travels down the tower to a step-up transformer in the base that modifies the output so that it can be incorporated into an electrical grid that distributes power as needed.
Further away from the ground, the wind tends to be faster and less turbulent, which are both preferable properties for more productive wind turbines. Industrial wind turbine towers are usually over 60 m or about 200 ft., which is slightly taller than the leaning tower of Pisa or the Cinderella castle at Walt Disney World. Usually turbines are set up in suitably windy areas in groups called wind farms. Offshore turbines can be larger and generate more power
The electricity generated is sent to a substation which then distributes through a power grid. So even though wind varies at a given location, by using various sources, operators can even out the supply.
Locations for wind farms tend to be far from where the electricity is used, so energy losses in transmitting the power can undermine their efficiency. Despite the complaints of some people, the noise of wind turbines does not seem to affect health and newer models are quieter. The impact of wind turbines on birds is probably overblown, particular when compared to other issues associated with bird declines. A more significant concern is the the effect of wind turbines on bats because they have trouble detecting the blades with echolocation and the low pressure at the blade tips can damage their internal systems. Early studies on bats in Alberta led to wind farms turning off the turbines when winds were low during bat migration season. And some people think wind turbines ruin the landscape. I don't know what to say about that, though perhaps as the song goes, "The answer, my friend, is blowing in the wind."