Energy from the wind Flashcards
Name the two types of wind turbines
Vertical Axis Wind Turbine (VAWT) and
Horizontal Axis Wind Turbine (HAWT)
What is a VAWT and what does it do
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.
What’s the advantages and disadvantages of a VAWT
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
What is a HAWT
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
What’s the advantages and disadvantages of a HAWT
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
List the main components of a HAWT
Anemometer Blades Brake Controller Gearbox Generator Nacelle Pitch system Rotor Tower Yaw Drive Yaw Motor Wind vane
What equation is used to calculate the energy available to a wind turbine at different speeds
Ke(J) = 0.5 x mass(Kg) x {Velocity(m/s)} ²
What are the three parameters that effect wind energy available to a turbine
Density of the air
Swept area of the blades
Velocity of the air
What is the equation to calculate the air density
Density = Mass (kg) / Unit Volume (m³)
In some cases you can use g/ cm³
How does air density affect the wind turbines performance
Low temperature = High density = High wind energy = More electric = more ££
Higher temperature = Lower density = low wind energy = less electric
How does the area of the blades affect wind turbines performance
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’
What is the equation to calculate the velocity
Velocity = distance / time taken v=l/t
What is the equation to calculate the wind energy
Ke = 0.5 x m x v²
What is the equation to calculate the power from the wind
power = 1/2 P x A x v³
Define cut in speed
The speed at which the turbine first starts to rotate and generate electrical power.
What is the rated output speed
It is the limit that the electrical generator is capable of. Typically between 12 and 17 metres per second.
What is the cut out speed
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.
What are the factors that affect maximum energy production in wind turbines.
Air density
Hub height
Explain the two factors that affect the energy production of a wind turbine.
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.
What’s the difference between efficiencies for a well designed turbine and a poor designed turbine.
Well designed is 40% efficient
Poor designed is 20% efficient
What is the pitch control
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.
What is the passive stall control
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.
What is active stall control
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.
What is a controlling yaw
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.
What it the betz limit
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.
