If a turbine is more efficient than a propeller for planes producing wind force, why isn’t it used for wind energy the other way around?


If a turbine is more efficient than a propeller for planes producing wind force, why isn’t it used for wind energy the other way around?

In: Engineering

I’m not sure I understand the question… do you mean to ask if a propeller would be more efficient for generating wind power for electricity?

It’s not. There’s a bunch of things going on here, but a propeller is significantly more efficient than other ways of creating thrust. That’s why wind turbines look like giant propellers.

A turbine does not create thrust (“wind force” in your question). But definition, a turbine takes energy *out* of a moving fluid. Things that make thrust are putting energy *in* to the fluid. We call those propellers or fans; there’s no rigorous definition difference, although in aviation “propeller” means “thing without a shroud” and “fan” means “thing with a shroud.”

*If* you don’t have a speed constraint, a propeller is the most efficient way to add energy to a fluid. That’s why small aircraft, commercial turboprops, and boats all use propellers. They don’t go fast enough to run into the speed problem. Commercial & military jets, however, go so fast that the efficiency of propellers drops way off because they start getting near supersonic speeds. That’s why they use fans instead.

You have to be going a couple of hundred miles an hour, at least, before this becomes an issue. Since that “never” happens with wind turbines, they also don’t have to deal with the speed issue and they use a design that looks a lot like propeller. It’s a turbine, not a propeller, because it’s taking energy *out* of the fluid.

There are systems called ducted fan wind turbines include a stationary sleeve which wraps around the circumference of the area where the blades rotate. This increases the amount of power you can generate with a given size of rotors, but the increased weight and complexity of the system means that it’s easier to just build more of the “normal” kind of turbine as long as you have the space to put them.

A turbine will extract more energy from the air you ram though it

It will also bring a lot more stress into the system and require *everything* to be stronger/heavier/expensive

Engineering is all about optimizing competing goals.

A wind turbine needs to capture energy from the wind, but it needs to do this cost effectively, that means no exotic materials or insane structural requirements.

If you force the wind through a turbine you’ll extract more power from it but also put a much large load on the tower as it effectively brings a big swath of air to a dead stop. Long propeller like blades do a decent job of extracting energy from the wind without putting much side load on the tower.

Turbines are also effective mainly when spinning very quickly, and for lower speed operations a propeller with a few blades often ends up being more efficient.

We’re not trying to build a wind turbine that can extract *all* the energy from the wind, we’re building a wind turbine that can extract energy from the wind *while balancing competing goals* so you get one thats kinda good but also kinda cheap and kinda fast to design rather than one that’s extremely good but also expensive and slow to design/build.

A propellor without power is a turbine if you blow on it. However, propellor blades are designed for high rotational speeds from the engine being on and also high air speeds from flying on a plane. On the other hand wind turbine blades are specially designed to have optimum aerodynamics at the rotation and air speeds involved with wind power. In fact turbine blades adjust their shape to do this better at a range of speeds. Propellers can do this too but designed for a much “higher speed” range of speeds.