Page 31 - Fluid Power Engineering

CHAPTER2

Basics of Wind

Energy and Power

It should be possible to explain the laws of physics to a barmaid.
—Albert Einstein

Introduction
In this chapter, basic concepts of physics as they relate to energy and
power of wind are discussed. The treatment of the concepts is at the
high school or first-year college level. However, since most do not
remember it anymore, this chapter will provide a quick overview.
Basiclawsofphysicslikeconservationofmass,conservationofenergy,
and Newton’s second law are used to explain concepts related to the
amountofenergythatisavailableinwindandthelimitsontheamount
of energy that can be captured by wind turbines.
The chapter starts with kinetic energy of wind and its relationship
to rotor radius and wind speed. Next, conservation of mass, energy,
and momentum are described in the context of wind energy. These
concepts are used to derive the Betz limit. It defines a limit on the
amount of energy that can be extracted by a rotor disk turbine as a
percentageofthetotalenergycontainedinwind.Finally,acomparison
between water and wind turbines is presented.

Kinetic Energy of Wind
The kinetic energy contained in wind is:
1 2
E = mv (2-1)
2
2
2
where m is mass and v is speed; units of energy are kg m /s = Joule.
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