How does wind spin those giant turbines? It seems like even high-speed winds wouldn’t move it very quickly with how heavy the turbine blades must be.
In: Planetary Science
Is anyone else puzzled by how thin wind turbine blades are? It seems like wider blades would catch more wind and therefore make more power.
Watch big trees sway in the wind. Unoiled, very heavy and ridged enough for us to build multi-story homes out of, wind over surface area builds similar to a ship’s sail. Sailing ships move through dense water with wind power alone, why not mega-structures designed to harvest wind for energy?
You mistake the forces at work.
You see, the forces at work are not the wind perse, rather wind is the catalyst for attracting the true force at work, the atmosphere.
On one side, the air passes a flat smooth side, and on the other it passes over a large curve. When air passes over a curved shape, such as a turbine blade, you create a pressure differential. Faster air, lower pressure.
The atmosphere then sees this lower pressure area around the blade and says “absolutely fucking not” and slams the surrounding air towards it.
If the blades were any wider, the drag from the surrounding air would negate the atmospheric force significantly. So thin it is.
Put three blades at 120° on an axis and you have a wind turbine.
The large commercial turbines are typically designed to start moving at 10-15 mph winds, but do their best work between 25 and 55 mph. Many of them have a way to slow themselves down or stop if the wind gets too strong.
The size of the blades are very large, which means they have a lot of surface area and since it’s common to have 3 blades total this means there is 3 times the surface to catch the wind; or another way to look at it is each blade only has to do 1/3 of the work to help spin.
Air is quite powerful. It carries planes across the sky, it carries ships across the sea.
Try this. Your palm is probably 4 inches wide. Stick it out the window of your car at speed and feel how much force it is.
A large windmill has a blade length of over 2,000 inches, and it has 3 of them.
Thats a whole lot of force!
It’s a similar principle as to how a plane gets up into the sky despite being really heavy. The blades generate lift when the wind passes over them.
Whilst there are many good answers here, they don’t fully give the reason why the blades move.
The blades aren’t “pushed round by the wind” like you would logically thing, instead, the blades are shaped like the wing of an aeroplane (or airplane). As the wind passes over the blade, an area of low pressure is formed on one side of the blade, and high pressure on the other side. This causes the blade to be “pulled” (by the low pressure) and “pushed” (by the high pressure).
As the blades are all connected on a very low friction hub and are very long, this relatively weak force is converted in to rotational force for drive the generator, which is connected to the hub through a gear box.
In addition, the blades are built to be incredibly light for their size, with modern construction techniques, and our made from glass fibre and are hollow.
Source: I have worked in the renewable energy market for more than the last ten years.
And:
https://www.energy.gov/eere/wind/how-wind-turbine-works-text-version
“When wind flows across the blade, the air pressure on one side of the blade decreases. The difference in air pressure across the two sides of the blade creates both lift and drag. The force of the lift is stronger than the drag and this causes the rotor to spin.”
Everybody is talking about surface area. This isn’t entirely the correct why to look at it.
The blades are highly cambered (high lift producing) aerofoils. They are not “catching” the wind using surface area, they are producing lift in the direction of rotation.
It can be thought of as the inverse of a helicopter which uses rotational power to create lift tangential to the blade.
They are Thanos level perfectly balanced to the center, so a human could turn them if you could reach.
Turbines are powered by the grid and create wind. That’s why on windy days they’re spinning so fast.
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