Green Engineering

Green Engineering 1
GREEN ENGINEERING
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Green Engineering 2
Section A wind Turbine Technology and Application
Question (1)
Solution (i)
λ =5
λ = ΩR/U
Ω = λU/R=(5.0)(12)/35= 1.714rad/s
Nrotor= (Ω rad/s)(60s/min)/2π rad/rev
= 16.38rpm
(ii)
Utip=Ω λ = (35m)(1.714ra/s)
= 59.99m/s
(iii)
Ngen =1800 rpm; Nrotor = 16.38rpm
Gearbox ratio = Ngen /Nrator = 1800/16.38
= 109.89
(iv)
P=1/2 pπR2CpηU3; assume betz limit: Cp= 16/27
Then η= p/0.5pπR2CpU3

Green Engineering 3
= 1.37
Question (2)
The graph below shows the power output verses wind speed for a typical industrial wind turbine
(i) According to Wu & Port (2011), cut-in speed refers to insufficient torque enacted by
the wind over the turbines due to slow speed of wind to make the turbines rotate.
Although with the increasing speed of wind, the turbines tend to start rotating thus
producing current electricity. Cut-in speed is the speed at which the first rotation of
the turbines occur.
(ii) With reference to rated wind speed, it is the speed of wind that is reached as the wind
goes beyond the cu-in speed. It always somewhere around 13 and 8 meters per second
where the power output limit is reached which the electrical generator is able to
produce (Wu & Porté-Agel,2011, p. 341).

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(iii) Cut-out wind speed. With the speed going above the output rate of the wind speed, it
leads to increase of forces exerted at the turbines which creates the risk of destroying
the rotor. The cut out speed thus refers to the breaking system that stops the rotor and
is usually when the speed reaches 25m/s
Question 3
0 200 400 600 800 1000 1200 1400 1600 1800
0
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Y-Values
The graph above holds onto the following assumptions
The graph presumes that the assumption of constant variance does not work here. The graph
further holds onto the assumption that power output is directly proportion to velocity of wind.
The graph also assumes that the velocity of wind increases with height
(3b)
when comparing the energy
(i) At 360hours of 8 m/s, the energy contained in 1m2
360 (3600)kwhr(8)/2