If wind turbine blades are so long and heavy, how is the wind able to rotate them?
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They are heavy, sure, but they are very well balanced which means it takes very little force to rotate them. And those long blades give a lot of surface area for the wind to act on. So, it doesn’t take much air movement to get some rotation started.
Wind is able to rotate long, heavy wind turbine blades the same way wind is able to propel sailboats (and tallships!) to great speeds: enough windforce pushing against a large surface area.
Also they don’t have to do a dead start. Wind turbines have a motor that can start the blades turning, and the wind itself will keep them turning.
Also the weight of the blades are counterbalanced for ideal movement.
The blades aren’t as heavy as you think. They’re made of various composite materials and they’re mostly hollow!
Because they catch a lot of wind, and a strong enough wind will eventually move it. It’s not like they’re heavy enough to stop the wind from blowing altogether.
That’s the thing, they’re *not* very heavy compared to how big they are and how much surface they have for the wind to push on. Also they’re balanced around the center hub so it takes less force to rotate the wheel of them. It’s not like the wind has to actually lift the weight of a whole blade, the weight of the opposing blade does that!
The reason for e shape: It’s called aspect ratio:
Basically, the wind pushes the blade, ok nice.
The problem is that wind is lazy and doesn’t want to push the blade.
So the wind will try to escape from doing any work. It cannot escape the blade by preceding it, or going behind it, (leading edge/trailing edge) as it would still draw air on the profile and do some work. It cannot escape toward the center of the rotor of course.
But it can escape at the tip, the wind will run toward the outer part of the rotor disc, to do this escape.
The longer the blade the more the win has to “run” to make its escape, the narrower (cord-wise) the blade is the less the wind perceive it has to “run” away from working.
A very high aspect ratio blade, is a blade that is very thin and long. This blade is the best to capture wind and prevent most of it to escape.
Aspect ratio is very very important at low speeds. The slower the speed the more time the wind has to escape. That’s why sailplanes have very high aspect ratio, aka thin long wings.
About how the blade is made: fiberglass is 3 time stronger than steel (for same volume) and it’s more than enough to hold the blade together. Actually, it’s so strong that the blade is still mostly hollow.
About loads, you just need the blade to stay one piece when standing still on the side position. That’s the bigger stress. Once you have wind the rotor spin and the centrifugal force will keep the blade straight, at that point the blade could even be made of rope and still do the job.
kinda like how a the wings of a jet can lift a couple hundred passengers, all their luggage and cargo, thousands of gallons of fuel and the weight of the jet itself.
all because the shape of the wing, thicker on one side than the other
Think of a pulley with equal weight on both sides, kinda like an elevator with its counter balance.
When the elevator (wind turbine) moves, the motor (wind) doesn’t have to lift the full weight of the elevator (blades). The majority of that weight is already balanced by the counter balance (other turbine blades).
The motor (wind) just has to apply enough force to move the balanced weight not actually lift it.
Some (usually larger) wind turbines use electric motors to first get the blades moving so the wind only has to keep it moving and not start it from standstill.
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