How much wind power is left over after going thru a wind turbine?

Question

So would 59% of the energy taken from the wind be anoff to turn the wind turbine w/o wind? Be able to turn the rotor at the same speed the wind was when it produced the 59%? or would it take more like 80%

Ok, so lets say the wind coming in is at 100% wind speed to turn the rotor and get the 59% of energy out of the wind. What is the wind speed % that is leaving the other side of the turbine? 41%? or would it be less from friction and other "energy loss"? anyone know what the exact % left should be?

Answer 1

Modern large wind turbines are able to extract a maximum of about 30% of the incident wind energy at rated speed.

This information is taken from the Cp (coefficient of performance) tables provided by the wind turbine manufacturers for use in detailed system models of their turbines.

While the theoretical maximum may be much higher, there are many factors taken into account by the wind turbine engineers when choosing how to design a turbine.

For instance, if a turbine is rated for 1 MW of continuous power output at 15 m/s wind, with a 30% wind energy conversion efficiency, it will 'spill' extra wind above this level or shutdown altogether. This is simply because operating the equipment (turbine blades, hub, gearbox, generator, electrical interconnection, and the tower) beyond its design limits can shorten its operating life, sometimes catastrophically.

After passing through the turbine swept area, the wind will retain approximately 89% of its original speed. This is calculated by using (1-efficiency)^(1/3).

Answer 2

There is a theoretical maximum power that can be extracted by a wind axis turbine, I think it's 59%. It's in Mark's Mechanical Engineering Handbook, unfortunately my copy is at work so I can't look it up for you. Here's a passage from Wind Power for Home and Business by Paul Gipe. "We must strike a balance between a rotor that completely stops the wind and one that allows the wind to pass through unimpeded, between the amount of wind striking the rotor and the amount flowing through. Albert Betz demonstrated mathematically that this optimum is reached when the rotor reduces wind speed by one-third." Since wind energy goes up by the third power of wind speed, this looks more like 70% of the power is extracted (under ideal conditions). It's kind of an interesting problem. If you try to extract too much power (more blades) then the wind slows down (sort of gets stuck in the windmill) and the wind coming along behind it just goes around avoiding the windmill completely.