Wind Energy Flashcards
What does and wind rose show
The probability, speed and direction of wind in one diagram
For HAWT how many blades produces the peak coefficient of performance
3 bladed rotors
What is the value of Betz limit
0.593
What is the meaning of the Betz limit
This is the factor of the max possible power that could be extracted from the wind by a perfect wind turbine
What factors make a typical wind turbine operate bellow the Betz limit
Wake loss and Aerofoil drag
What is an upwind turbine and what is a downwind turbine
Upwind the blades are before the mast with relation to the wind direction and a downwind the blades are downwind of the mast
What are the advantages and disadvantages of an downwind turbine verses an upwind one
Downwind means are blade design isn’t effected by the mast but more wake will be produced
What is an active yaw for a wind turbine
Provides the turbine with motors to turn the turbine to face the wind direction
What is stored in the nacelle of a wind turbine
Gearbox, Generator and drive shaft
How should the nacelle of a wind turbine be designed to improve efficiency
It should be streamline to reduce vibration and prevent turbulence
How should the angle of attack be effected at high wind speeds It should be increased
It should be increased
How far apart should wind turbines should be placed to reduce wake loss
6-10 diameters
What equation relates Betz limit and power
Pmax = 0.593 x Pwind
When operating at betz limit what will be the wake wind velocity and axial velocity of the rotor plane
Vw = V/3 Vd = 2V/3
For a standard air density what is the expression for power of wind in the swept area
0.61AV^3
What is an expression for the annual output for a wind turbine
KWh per year = K x V^3 x A X Number of turbines
K=3.2
What is a typical load factor for a wind turbine
20-32%
Why does a wind turbine benefit from a tall mast
Less turbulent wind due to boundary layer when meeting the ground
How far away down/up wind should a wind turbine be placed of an obstacle with given height
20 x height down wind
2x height upwind
How large a turbulent zone will a forest create
50% obstacle height
Is the downwind slope of a hill a good place to place a turbine
Yes due to the increased wind speed (streamlines squeezed together)
Is behind a hill a good place to place a wind turbine
No due to flow separation zone
For a down wind cliff where would you find flow separation zones
Base of cliff and top of cliff
How far does the wake of a wind turbine dissipate over
10x rotor diameter
