Chapter 7

Question 1

Equation for kinetic energy

Answer 1

Ke=half x m x v2

Question 2

Why can’t 100% of the winds energy be extracted by a wind turbine

Answer 2

Because wind has velocity downstream

Question 3

What is the betz limit

Answer 3

The amount of energy (59.3%) that can be extracted from the wind due to this required downstream velocity

Question 4

Why can’t turbines ever reach the betz limit

Answer 4

Mechanical:(friction) which causes thermal losses
Electrical:(resistance) which causes thermal losses

Question 5

State the relationship between pout and kA

Answer 5

Pout=kA

Question 6

State the relationship between power output and swept area

Answer 6

Power output is directly proportional to swept area

Question 7

Equation for swept area

Answer 7

A=pie x r2

Question 8

State the relationship between power output and wind speed

Answer 8

Power output is directly proportional to the cube of wind speed

Question 9

State the relationship between a wind turbines blade diameter and power output

Answer 9

Pout is directly proportional to the square of blade diameter

Question 10

State the relationship between pout and air density

Answer 10

Pout is directly proportional to air density

Question 11

How does temperature affect pout

Answer 11

Higher temperature=lower pout as higher temperature means lower air density and air density and pout are directly proportional
Lower temperature= higher pout as lower temperature means higher air density and pout and air density are directly proportional

Question 12

What is altitude

Answer 12

Altitude is how a specific point is above the earth it is measure from the sea level
Higher altitude means lower air density
Lower altitude means higher air density

Question 13

What 8 parameters affect maximum energy production in wind turbines

Answer 13

Wind speeds
Air density
Cop
Swept area
Obstructions
Hub height
Temperature
Altitude

Question 14

Equation for repayment period of a wind turbine

Answer 14

Repayment period in years = project costs/ revenue produced per year

Question 15

Four factors used to determine hub height

Answer 15

Wind resource assessment- seeing what the levels of wind are like in the area
Terrain- are there any obstructions
Wind turbine size
Visual impact - will it cause shadow flicker

Question 16

Equation for the weight of a new wind turbine

Answer 16

Mn=Mo(BLn3/BLo3)

Question 17

State the relationship between turbines performance and blade length, strength of materials and siting requirements

Answer 17

Bigger Blades = more power but larger blades mean higher cut in speed
Heavier materials mean in can withstand more but will have higher cut in speeds and vice versa
Siting requirements ideally you want a location with no obstructions

Question 18

Definition of wind survival speed

Answer 18

The maximum wind speed that is designed to withstand before sustaining damage

Question 19

Testing methods used to determine wind survival speed

Answer 19

Destructive testing product is tested under extreme conditions until it breaks

Question 20

What name is given to the method of rotating the blades of a turbine to control the rate of power production

Answer 20

Pitching

Question 21

What is yawing

Answer 21

The turning of a turbine to ensure it aligns with the wind this helps maximise power output

Question 22

Issues affecting energy output of a wind turbine

Answer 22

The turbine selected
Topography
Orientation of the site
Available wind speeds
Altitude and air density

Question 23

Issues affecting cost of wind turbines

Answer 23

Installation costs
Grid connection costs
Servicing
End of life costs
Surveys

Question 24

Environmental and social issues of wind turbines

Answer 24

Visual issues
Noise pollution
Communication links
Environmental impact assessment
Local objections