Wind Energy

Question 1

What does and wind rose show

Answer 1

The probability, speed and direction of wind in one diagram

Question 2

For HAWT how many blades produces the peak coefficient of performance

Answer 2

3 bladed rotors

Question 3

What is the value of Betz limit

Answer 3

0.593

Question 4

What is the meaning of the Betz limit

Answer 4

This is the factor of the max possible power that could be extracted from the wind by a perfect wind turbine

Question 5

What factors make a typical wind turbine operate bellow the Betz limit

Answer 5

Wake loss and Aerofoil drag

Question 6

What is an upwind turbine and what is a downwind turbine

Answer 6

Upwind the blades are before the mast with relation to the wind direction and a downwind the blades are downwind of the mast

Question 7

What are the advantages and disadvantages of an downwind turbine verses an upwind one

Answer 7

Downwind means are blade design isn’t effected by the mast but more wake will be produced

Question 8

What is an active yaw for a wind turbine

Answer 8

Provides the turbine with motors to turn the turbine to face the wind direction

Question 9

What is stored in the nacelle of a wind turbine

Answer 9

Gearbox, Generator and drive shaft

Question 10

How should the nacelle of a wind turbine be designed to improve efficiency

Answer 10

It should be streamline to reduce vibration and prevent turbulence

Question 11

How should the angle of attack be effected at high wind speeds It should be increased

Answer 11

It should be increased

Question 12

How far apart should wind turbines should be placed to reduce wake loss

Answer 12

6-10 diameters

Question 13

What equation relates Betz limit and power

Answer 13

Pmax = 0.593 x Pwind

Question 14

When operating at betz limit what will be the wake wind velocity and axial velocity of the rotor plane

Answer 14

Vw = V/3 
Vd = 2V/3

Question 15

For a standard air density what is the expression for power of wind in the swept area

Answer 15

0.61AV^3

Question 16

What is an expression for the annual output for a wind turbine

Answer 16

KWh per year = K x V^3 x A X Number of turbines

K=3.2

Question 17

What is a typical load factor for a wind turbine

Answer 17

20-32%

Question 18

Why does a wind turbine benefit from a tall mast

Answer 18

Less turbulent wind due to boundary layer when meeting the ground

Question 19

How far away down/up wind should a wind turbine be placed of an obstacle with given height

Answer 19

20 x height down wind

2x height upwind

Question 20

How large a turbulent zone will a forest create

Answer 20

50% obstacle height

Question 21

Is the downwind slope of a hill a good place to place a turbine

Answer 21

Yes due to the increased wind speed (streamlines squeezed together)

Question 22

Is behind a hill a good place to place a wind turbine

Answer 22

No due to flow separation zone

Question 23

For a down wind cliff where would you find flow separation zones

Answer 23

Base of cliff and top of cliff

Question 24

How far does the wake of a wind turbine dissipate over

Answer 24

10x rotor diameter

Question 25

How close together should wind turbines be places (perpendicular to wind direction)

Answer 25

2x rotor diameter

Question 26

What needs to be constructed for onshore wind turbines

Answer 26

Borrow pits
Access roads
Foundations
Drainage reservoirs

Question 27

What types of foundations are used for off shore wind turbines

Answer 27

Gravity
Buckets
Tripod
Monopiles

Question 28

How far away from a wind turbine will there be considered no noise problems

Answer 28

400m

Question 29

What effects can wind turbines have on nature

Answer 29

Birds and bats can fly into blades
Peatland ecosystems damaged due to drainage
Marine habitat disturbed by construction