Page 252 - Hybrid-Renewable Energy Systems in Microgrids

Solar–wind hybrid renewable energy system 229

system performance assessments for wind energy systems has shown that not much
work has been reported in this specific field. The researchers mainly explored the
areas like regional wind energy assessment [46], wind speed distribution functions
[47], economic aspects of wind energy [48] and regional wind energy policies [49].
As different wind generators have different power output performance character-
istics, the performance of wind generators varies for different wind turbine models.
Selection of a suitable wind turbine model is very important for wind turbine power
simulation applications. For the successful planning and implementation of wind
power generation projects, this is a significant step.
For determining the long-term performance of wind energy systems, the hourly
simulation programs have been used as the main tools. The long-term performance of
the wind system can be obtained using the hourly wind speed data. Usually, wind tur-
bine starts power generation at the cut-in wind speed, then the power output increases
linearly with the increase of the wind speed from the cut-in wind speed to the rated
wind speed. When the wind speed reaches the cut-out wind speed, the wind turbine
will be shut down for safety considerations. A simplified model of a wind turbine is
presented in the literature to simulate the power output of a wind turbine based on
the simple assumptions stated above [50]. Some other studies have been reported in
the literature where [51,52] the similar form model has been applied in relation to the
Weibull shape parameter k. Some studies presented a model to describe the power
output of wind turbines applying the quadratic expressions for the simulation [53,54].
The mathematical model of a three-blade, horizontal-axis, and maintenance free
wind electric generator is presented by Borowy and Salameh [55]. The output of
mechanical power captured from the wind by a wind turbine [22] can be formulated
as in (Eq. (12.2)).

C P ( AV )
3
P =− λρ (12.2)
3
t 2 Pt=−CP λ ρ A V 2
and torque developed by wind turbine can be expressed as in (Eq. (12.3))

P
T = t (12.3)
t wm Tt=Ptwm

where P t is the output power, T t the torque developed by wind turbine, C p the power
3
co-efficient, λ the tip speed ratio, ρ the air density in kg/m , A the frontal area of wind
turbine, V the wind speed.

wR
λ =
v (12.4) λ=wRv

where w is the turbine rotor speed in rad/s, R the radius of the turbine blade in m, and
v the wind speed in m/s, respectively.