Energy from the wind

Question 1

Name the two types of wind turbines

Answer 1

Vertical Axis Wind Turbine (VAWT) and

Horizontal Axis Wind Turbine (HAWT)

Question 2

What is a VAWT and what does it do

Answer 2

It is a vertical axis wind turbine in which the rotor blades rotate about a vertical axis. These can harness the wind when it blows from any direction without having to adjust the position of the rotor to face the wind.

Question 3

What’s the advantages and disadvantages of a VAWT

Answer 3

ADV
Harness the wind at any direction
Low wind speed required
It has low amount of vibration
Low amount of noise generated
DisADV
Lower efficiency than a HAWT
Low RPM

Question 4

What is a HAWT

Answer 4

It is a horizontal axis wind turbine which means the rotating axis of the turbine is horizontal or parallel with the ground. The most common type of turbine

Question 5

What’s the advantages and disadvantages of a HAWT

Answer 5

ADV
More efficient than a VAWT
Its able to produce more electricity from any given amount of wind
DisADV
Very heavy
Doesn't produce well in turbulent air-winds
High wind speed required
High vibration
High noise level

Question 6

List the main components of a HAWT

Answer 6

Anemometer
Blades
Brake
Controller
Gearbox
Generator
Nacelle
Pitch system
Rotor
Tower
Yaw Drive
Yaw Motor
Wind vane

Question 7

What equation is used to calculate the energy available to a wind turbine at different speeds

Answer 7

Ke(J) = 0.5 x mass(Kg) x {Velocity(m/s)} ²

Question 8

What are the three parameters that effect wind energy available to a turbine

Answer 8

Density of the air
Swept area of the blades
Velocity of the air

Question 9

What is the equation to calculate the air density

Answer 9

Density = Mass (kg) / Unit Volume (m³)

In some cases you can use g/ cm³

Question 10

How does air density affect the wind turbines performance

Answer 10

Low temperature = High density = High wind energy = More electric = more ££
Higher temperature = Lower density = low wind energy = less electric

Question 11

How does the area of the blades affect wind turbines performance

Answer 11

Force is directly proportional to the area
If the area doubles, force doubles
The area that the blades of a turbine ‘cut’ through are known as the ‘swept area’

Question 12

What is the equation to calculate the velocity

Answer 12

Velocity = distance / time taken v=l/t

Question 13

What is the equation to calculate the wind energy

Answer 13

Ke = 0.5 x m x v²

Question 14

What is the equation to calculate the power from the wind

Answer 14

power = 1/2 P x A x v³

Question 15

Define cut in speed

Answer 15

The speed at which the turbine first starts to rotate and generate electrical power.

Question 16

What is the rated output speed

Answer 16

It is the limit that the electrical generator is capable of. Typically between 12 and 17 metres per second.

Question 17

What is the cut out speed

Answer 17

As the speed increases above the rate output wind speed, the forces on the turbine structure continue to rise and at some point there is a risk of damage to the rotor, the brakes are to bring the rotor to a standstill.
This is usually around 25 metres per second.

Question 18

What are the factors that affect maximum energy production in wind turbines.

Answer 18

Air density

Hub height

Question 19

Explain the two factors that affect the energy production of a wind turbine.

Answer 19

Air density- It must be stressed that sir density is not always constant as it will decrease as both temperature and altitude increase.
Hub height- Wind speeds tend to be higher as height increases from ground level, but there is environmental factors to be considered

• Every location will be different with issues to be considered such as average wind speeds, distribution of winds, any potential obstructions to the flow of wind, and local environmental considerations.
• The topography or terrain of the site which would be analysed during a preliminary site assessment.
• The size of the turbine itself, the bigger the turbine the higher the hub requirement, larger swept area etc.
• Visual impact.

Question 20

What’s the difference between efficiencies for a well designed turbine and a poor designed turbine.

Answer 20

Well designed is 40% efficient

Poor designed is 20% efficient

Question 21

What is the pitch control

Answer 21

This system alters the pitch, or angle between the blade of the rotor and the wind to slow down the blade rotation. The turbines controller monitors the turbines power output.

Question 22

What is the passive stall control

Answer 22

In this system the blades are attached to the rotor at a fixed angle but are designed so that the twists in the shape of the blades themselves will apply the braking effect if the wind becomes too fast making the rotor slow down.

Question 23

What is active stall control

Answer 23

The blades in this type of power control system are of variable pitch, similar to the blades in a pitch controlled system. An active stall system reads to power output in the way that a pitch controlled system does, but instead of pitching the blades out of alignment with the wind, it pitches them to produce stall.

Question 24

What is a controlling yaw

Answer 24

A more sophisticated system for controlling yaw on larger scale wind turbines uses an anemometer on the rear of the hub to measure wind direction and a system known as the yaw drive turns gears within the hub of the rotor to align the blades with the wind.

Question 25

What it the betz limit

Answer 25

The Betz limit is the theoretical maximum efficiency for a wind turbine, conjectured by German physicist Albert Betz in 1919. Betz concluded that this value is 59.3%, meaning that at most only 59.3% of the kinetic energy from wind can be used to spin the turbine and generate electricity. In reality, turbines cannot reach the Betz limit, and common efficiencies are in the 35-45% range.
Wind turbines work by slowing down passing wind in order to extract energy. If a wind turbine was 100% efficient, then all of the wind would have to stop completely upon contact with the turbine. In order to stop the wind completely, the air wouldn’t move out of the way to the back of the turbine, which would prevent further air from coming in—causing the turbine to stop spinning.