How much energy is in the wind?
How efficiently can wind turbines convert the kinetic energy in the wind to mechanical energy of the rotating blades and then via the hub, shaft and gearbox and generator to electric energy?

In this video I will answer these questions, covering the following topics along the way:
formula for kinetic energy in wind
how the air flowing over a wind turbine blade creates a lift force which has a torque component that acts to turn the blade (wind turbine blade velocity triangle)
formula for power available in the wind
why a wind turbine can't extract all the energy from the wind
law of conservation of mass
the Betz limit maximum possible efficiency of a wind turbine
ducted and shrouded turbines and how they can "beat" the Betz limit
the wind turbine stream tube

This video is the first in a series on "How do wind turbines work?". Keep an eye out for future videos where I will explain 2D classical aerodynamic theory that you can use to analyse and design a wind turbine blade.

Image attributions
Betz portrait – public domain

Ducted/ shrouded turbines at 4:00 with permission Paul Gipe WindWorks.org
He also has some great information on alternative wind energy and has followed the progress of some of the more dubious designs out there. A very good read if you want to get better at sorting hype from reality in renewable energy technologies.

http://www.windworks.org/cms/index.p...

Wind Lens image at 4:05
Tomon7 / CC BYSA (https://creativecommons.org/licenses/...)

WindLens power output at 4:07
Yuji Ohya et al Creative Commons Attribution 4.0 International

The software I used to explain the lift/drag to torque/thrust vectors at 0:40 is Ashes:
https://bit.ly/3cpasvJ

The Betz limit derivation can be found in Burton's "Wind Energy Handbook." This is the book that I quickly zoom through in the video, and it is by far my favourite resource for wind energy engineering theory.

Available to buy from Amazon, or your university library probably has it!
https://amzn.to/32Pb1fh

There is also a decent explanation of the Betz limit on Wikipedia :)
https://en.wikipedia.org/wiki/Betz%27...

Other videos on wind turbine engineering that you might like:
Wind turbine aerodynamics: stall vs pitch regulation
   • Wind Turbine Aerodynamics: Stall vs P...  

Why do wind turbines (usually) have 3 blades?
   • Should Wind Turbines Have TWO Blades?  

Engineering design lifetime why don't engineers design products to last longer?
   • Why Don't Engineers Design Products t...