Environmental Technology - AS > Wind > Flashcards

Wind Flashcards

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1
Q

What are the two main types of wind turbines

A

Horizontal axis wind turbine (VAWT)

Vertical axis wind turbine (HAWT)

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2
Q

What are the differences between a HAWT & VAWT?

A

HAWT: Constant wind direction, high wind speeds, high rpm, high vibrations, has high noise levels and its rotor axis is horizontal

VAWT: Any wind direction, low wind speeds, low rpm, low vibrations, has low noise levels and its rotor axis is vertical

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3
Q

What is the nacelle

A

Nacelle: This is the housing that contains all the main components

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4
Q

Hat is the blades?

A

Blades: The molecules of the gases in air strike the blades and make them turn. Some systems have two blades while some have three.

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5
Q

What is the Hub?

A

Hub: The part of the turbine the blades are attached to.

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6
Q

What is the rotor?

A

Rotor: The blades and hub collectively.

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7
Q

What is the low speed shaft?

A

Main shaft connected to the hub which turns at a low RPM

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8
Q

What is the high speed shaft?

A

After the gearbox that rotates at a high RPM for the generator

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9
Q

What is the gearbox?

A

Links the shafts attached to the rotor and the generator. Increases the low RPM to high RPM

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10
Q

What is the generator?

A

Produces electricity using electromagnetic induction

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11
Q

What is the wind vane?

A

Establishes wind direction

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12
Q

What is the anemometer?

A

Determines the wind speeds to asses the turbines performance

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13
Q

What is the tower?

A

The large pole to support the nacelle

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14
Q

Equation for kinetic energy?

A

Ke = 1/2 m v^2

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15
Q

How do you find the volume of air passing through swept area in one second

A

The velocity of the air X Swept Area

Vu X Au = Vd X Au

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16
Q

Why can a turbine not have only one blade?

A

The majority of air would pass through making the upstream and downstream area very similar so little energy would be extracted

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17
Q

Why can a turbine not have infinite blades?

A

The blades would act like a solid disk the the downstream velocity would be 0. Acting like a blockade and extracting no energy.

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18
Q

What is the betz limit?

A

Typically 2 or 3 blades are the most optimal for deriving the max amount of energy from the wind as possible which is 59.3 %

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19
Q

Why is it impossible to fully extract betz from the wind?

A

Some energy is lost in sound and thermal leaving us in the 25-45 % range for what can normally be extracted

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20
Q

What is TSR?

A

Tip speed ratio
How fast the turbine is spinning

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21
Q

How is TSR used.

A

To ensure the rotor is not spinning to slow and missing energy or too fast and hitting turbulent air:

If at 2 TSR the COP is 0.1 the blades are too slow
If at 10 TSR the COP is 0.25 the blades are too fast
If at 6 TSR the COP is at 0.45 the blades are perfect

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22
Q

What is COP?

A

Coefficient of Performance
The amount of energy the turbine can extract from the wind
0.55 means 55% and 0.2 means 20%

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23
Q

What is the rotor collected energy.

A

The exact amount of energy extracted from the wind

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24
Q

Why can a turbine not covert the full rotor collected energy to electrical energy?

A

Due to, mechanical losses as friction from the moving parts rubbing against each other and converting ke into thermal. Can be minimised with bearings and lubricant

Also due to, electrical resistance as any current moving through a cable will encounter reis causing the wire to heat up and convert electrical energy to thermal

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25
What is rated output energy?
The amount of energy that can be extracted from the wind by a turbine
26
Why is rated output energy lower than the rotor collected energy?
Due to thermal losses in the shafts and wires
27
Equation for Pout of a turbine?
Pout = ½ ρ A v^3 COP Where: Pout = Useful output energy in W P = Air density in Kg A = Swept area in m^2 V = Wind speed in m/s COP = Coefficient of Performance
28
What is the relative between Pout and Swept Area
Pout is directly proportional to swept area^2
29
How do you find the swept area of a turbine?
A = pi r^2 The radius is the blade length and always convert to m
30
What is the relationship between Pout and Wind speed? What happens to Pout out if the wind speed doubles or halves?
Pout is directly proportional to v^3 So if wind speed is doubled: V^3 = 2V^3 = 2^3 V^3 = 8v^3 Pout is x8 If the wind speed is halved: V^3 = 0.5V^3 = 0.5^3 V^3 = 0.125v^3 Pout is x0.125
31
What is the cut in speed?
The minimum wind speed required to produce power is called the cut in speed
32
What is the rated power?
The max power a wind turbine can produce as determined by the power rating of the generator
33
What is the relationship between the Pout and swept area?
Directly proportional
34
What is the relationship between the Pout and radius and diameter of the rotor
Pout is directly proportional to r^2 Pout is directly proportional to d^2
35
What is the relationship between Pout and air density
They are directly proportional
36
What is the relationship between Pout and temperature and why?
High temp = lower Pout Molecules of the gases in air have more ke and move with a greater speed between collisions. Making the gas expand and the particles move further apart. Giving a lower air density. Low temp = High Pout Molecule of gases in air have less ke and move with smaller speeds between collisions. Making the gas contract and molecules get close. Giving a higher air density
37
What is the relationship between Pout and altitude?
Higher altitude = Lower air density = Lower Pout Lower altitude = Higher air density = Higher Pout
38
What is the definition of altitude?
Altitude is how high a specific point is above the surface of the Earth,  most often sea level
39
What factors that affect maximum energy production in wind turbines within the context of cost-benefit analysis?
Wind speeds, air density, COP, Swept area, Obstructions, Hub height, Temp and an altitude.
39
What is a CBA, its aims and how to carry it out.
The aim of a cost-benefit analysis is to establish if the project will produce a satisfactory return for the investor. Repayment period in years = Project costs / Revenue per year
40
What is the hub height?
Hub height is the distance from the ground (seawater level for an offshore turbine) to the centre of the hub.
41
What is the rotor diameter?
Rotor diameter is the diameter of the swept area of the turbine. Note that the rotor diameter is also the radius multiplied by 2.
42
What four factors help determine the hub height?
- Wind Resource Assessment - Terrain - Wind turbine Size - Visual Impact
43
Explain a wind resource assessment?
Low cost desktop studies can provide some info but for more an anemometer is paced on a steel pole vertically above the ground. The pole is placed in various locations and the anemometer at various heights on the pole to find the optimum wind speed. A wind vane can also be placed to find the wind direction and find if different heights are very different speeds. 6 months of this data required by banks for loans.
44
How does the Blade Length influence turbine performance?
Pout is directly proportional r^2 so Pout increases But increased BL also increases the inertia so the longer blades require a larger cut in speed, they are also under more stress
45
What is formula is sued to find the mass of new wind turbines?
Mn = Mo(Bln/Blo)^3 Mn = Mass of the new turbine in kg or tonnes. Mo = Mass of the old existing turbine in kg or tonnes. BLn = Blade length of a new wind turbine in m. BLo = Blade length of an old wind turbine in m.
46
How does the strength of materials influence turbine performance?
Lightweight materials reduce transport costs and cut in speeds but break easily under these forces. Very strong materials do not break but often increase cut in speeds. The optimum design will be composite materials which offer high strength to weight ratios. They can resit the stresses and have a low cut in speed.
47
How does the siting requirements influence turbine performance?
In an exposed location free from obstacles to keep out of turbulent air. Turbulent air 20m behind any obstructions and 2m up
48
What is inertia?
The tendency of an object to resist a change in motion.
49
What is the maximum wind speed?
The maximum wind speed that a turbine is designed to withstand before sustaining damage
50
What is the cut-out speed?
The Cut-Out speed is the wind speed the turbine stops rotating to protect itself from damage.
51
What do you call the testing for these light materials?
Destructive testing and they are tested under extreme conditions until it fails.
52
What is pitching?
Pitching is the process of turning the blades orientation relative to wind direction, to control the rate of power production.
53
How do you stop power production and what is it called?
Feathering is the process of turning the blades to be parallel to wind direction to stop power production
53
Why is pitching needed?
If there is no method of controlling the rte of power production a turbine can only operate at the cut-out speed and then shut down as any faster may be dangerous.
54
At what 3 stages to the blades orientation change and how?
The first stage is from the cut in speed up to the rated power output.  Here the blades are positioned to facilitate maximum power production.  The second stage is from the rated power to the cut-out speed.  As the wind speeds increase the blades need to pitch to control the RPM of the rotor.  The third stage is from the cut-out speed upwards.  At the cut-out speed the blades need to be pitched such that they are parallel to the wind direction, to stop rotation.
55
What is passive pitching?
Small turbines keep costs down by being designed to naturally twist in higher wind speeds but this mean achieving rated power is only possible at a unique wind speed
56
What is Active pitching?
Uses an anemometer to send signals on wind speed to hydraulic ram systems to precisely change the angle.
56
What is yawing?
Yawing is turning the swept area of a turbine to be perpendicular to wind direction for maximum energy extraction.
57
What are the two option for carrying out yawing?
1. A cheap wind vane on the back but only works on small turbines. 2. An anemometer and wind vane in a control unit sends signals to the yaw mechanism.
58
Problems with yawing?
1. If blades are not properly aligned with wind direction some power is lost and induces torsional forces which fatigues the materials. 2. Yawing can be used to shut down the rotor by turning the blades parallel to wind the direction but this induce very large torsional forces.
59
What issues affect the energy output of a wind turbine:
Type of turbine, COP, Bl, Swept, Materials, Topography, Orientation, Wind Speeds and Altitude
60
What issues affect costs:
Installment costs, connection to grid costs, servicing, decommissioning and surveys.
61
What issues affect the environment:
Visual, Noise ,Disrupting communication ,destroying habitats, and locals may object.
62
What does RPM stand for?
revolutions per minute
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