Environmental Engineering Reference
In-Depth Information
3.2.2. Wind Energy and Power
Calculation the energy available in the wind [8] relies on knowledge of
basic geometry and physics behind kinetic energy. Kinetic energy of collection
of objects KK with total mass M and velocity V is given by expression
KE = ½
.
M
.
V
2
(1)
In order to define kinetic energy of the molecules of air we can define volume
of the air particles in the shape of a huge hockey pack with thickness D that
has geometry of collection of air molecules passing through the A plane of a
wind turbine blade over a given time.
The volume of the pack is determined by
Vol = A
.
D
If ρ = M / Vol
Then we can write that
KE = ½ ρ
.
V
3.
A
.
T
(2)
If the kinetic energy is divided by time, T, the power available from air parcel
can be expressed as
Pwr = ½ ρ
.
V
3.
A
If the Pwr is divided by the cross section of parcel, A, then we can obtain
expression
Pwr / A= ½ ρ
.
V
3
(3)
This term is called the ― Wind Power Density‖. It can be noticed that the WPD
depends the density of air and the wind speed and size, the efficiency wind
power plant.
The wind speed is defined with average wind velocity obtained by the
geometry of blade and its local position.
The average wind velocity is characterized by two parameters: wind
frequency and wind speed. Since both of these parameters are time dependent
