why wind turbines have such skinny blades. Wouldn’t more surface area be more effective?
In: Engineering
It’s all about mechanical efficiency; same reason there are generally 3 blades and not 10 blades…..or a vertical array of 3 fans with 10ft blades instead of 1 fan with 50 ft blades
long and slender wings are more efficient for most use cases where you don’t need high accelerations or low flight speeds.
this leads to similar solutions for airliners, sailplanes, long range drones, U-2s, and rotors of any kind.
for rotors there’s another limitation, and that’s adding too many blades leads to the blades disturbing each other. so engineers tend to go for a low number of blades for wind turbines (for helicopters there’s other considerations like maximum tip velocities and noise generation but that’s a we bit too much for ELI5 here).
two blades or even only one blade with a counterweight are sometimes projected, but in many cases 3 or more blades are easier to balance mechanically (again, some helicopters like original Hueys use 2 blade rotors but mainly for simplicity of design)
Sure, covering more area allows you to generate more torque with the same wind, but this isn’t cost-effective – heavy blades need stronger towers to keep them steady, and the primary purpose of wind turbines is to make cheap electricity.
So building many skinny 3-blade towers is cheaper and good enough per tower that this is the winning design.
In the future it might change, there is active research for single-bladed and twin blade designs which will be even cheaper.
Wind turbines need high speed, low torque, rotation to power a generator. To get this from the wind, smaller sails angled to the wind are best, allowing the wind to push them into a fast spin. Windmills use much wider sails that are not angled as much. If you’ve seen a video of them you know they rotate gracefully slow, because they need to move a heavy stone to mill grain, the slow speed is the trade off, but a welcome safety feature I am sure.
You see the same thing with old sailing ships, which use large sales to move a relatively blunt boat full of cargo verses modern racing sailboats which use thin carbon fiber wings on super aerodynamic boats that hardly touch the water.
Turbine blades are designed to create the maximum amount of rotational energy with the least amount of possible drag. Wind turbine tests and experience has shown this to be the most efficient design.
No because they would also have more drag and resist movement. What you see is the goldilocks zone of big enough to be rotated easily by the winds without having too much resistance. The only thing that determines the output of a wind turbine is the speed it’s rotating at so skinny blades are favored for this.
Wind turbines extract energy from the air by slowing it down. If you have wider blades you slow down the air more. However that slow air still needs to go *somewhere*, and ends up being pushed out to the sides – but that takes work. The more you slow down the air, the more energy from the incoming wind is used to push the slow air out to the sides. This means additional blade surface area beyond current designs doesn’t give much more energy.
Secondly for a given amount of material (cost) a longer blade sweeps a larger area – which goes up with the square of blade length. Energy extracted goes up with swept area, so you get a lot of extra energy for a little bit of extra length. Blade width doesn’t give you much more energy. This means you get more bang for your buck from longer blades. It’s usually better to build more cheaper turbines than a few more expensive ones.
Weight and air resistance. Also, with a wide blade, the air slows down before it crosses the blade and the power diminishes before it gets past the blade.
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