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Ocean & Wind Energy > Wind Energy > Flashcards

Wind Energy Flashcards

1
Q

How much of the world wide energy consumption comes from fossile fuel?

A

68%

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2
Q

How much of the world wide energy consumption comes from nuclear energy?

A

11%

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3
Q

How much of the world wide energy consumption comes from wind energy?

A

2,7%

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4
Q

Define “Renewable energy”.

A

Renewable energy is energy that comes from natural energy resources, such as sunlight, wind, waves, tides and geothermal energy, that are naturally replenished. But nothing, not even the sun is finite, so an extension to the definition would be: - which comes from energy stores that are so large that its exploitation will not exhaust its reserves within any time conceivable to mankind.

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5
Q

The sun radiates energy upon the earth. Where does this energy go? Basic mechanisms overview.

A

Incoming solar radiation, reflected energy by clouds and atmosphere, energy absorbed by atmosphere, energy absorbed by surface of the earth.

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6
Q

The earth radiates energy as well. Where does this energy go? Basic mechanisms overview.

A

Surface radiation –> Energy absorbed by the atmosphere, atmosphere emmits energy as well, reflected energy by greenhouse gases.

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7
Q

According to Kaltschmitt; how much of the solar radiation is ending up as convection of the atmosphere?

A

9%. This includes thermal energy, so the theoretical potential of the wind energy is much lower.

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8
Q

Accoriding to Kleidon; how much of the solar radiation ends up as mechanical energy, i.e. as winds?

A

0,6%. Later in the lectures 0,2% is presented as the number. The latter corresponds to an amount of 400TW, where about 1% = 4TW is technically accessible.

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9
Q

What is the theoretical potential of the energy of the earth?

A

power or energy per year that is globally available within the area considered.

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10
Q

What is the technically exploitable potential?

A

power or energy per year that can be exploited taking into account insurmountable technical (and possibly ecological potential and structual) barriers such as available conversion technology etc.

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11
Q

What is the economically feasable potential?

A

power or energy per year that can be exploited by building all the conversion plants that are economically feasable at the time being, i.e. the current energy prices, capital cost and manufacturing etc.

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12
Q

How are winds formed?

A

Its all about the sun creating high and low pressure regions, and the conservation of angular momentum due to the earths rotation. Corriolis effect/force. See slides 13 - 17.

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13
Q

What is the practically feasable wind energy potential within the EU?

A

0,2TW

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14
Q

What is the practically feasable wind energy potential within Germany?

A

35 - 70 TW

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15
Q

Installed turbine capacity in world and Germany, as of 2014?

A

World: 370GW, Germany: 38GW

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16
Q

What does wind maps tell us?

A

Either the avg wind velocity or the Wind Power Density (WPD)

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17
Q

Formulae for energy contained in wind?

A

See slide 19.

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18
Q

Formulae for power contained in wind flowing through a cross sectional area?

A

See slide 19.

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19
Q

How is wind power density defines?

A

See slide 19.

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20
Q

Give a brief history of the wind turbine.

A

See slide 21 - 25.

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21
Q

Give two different ways of classifying wind turbines.

A
  1. Orientation of the rotational axis; horizontal and vertical.
  2. Working aerodynamic principle
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22
Q

List advantages and disadvantages of a Darrious turbine. Classification?

A

Class: Vertical axis, or lift force turbine.
+ no yawin mechanism needed.
+ generator and gearbox near the ground.
- normally not self starting.
- low specific speed and power coefficient

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23
Q

Define the power coefficient and its formula.

A

see slide 30.

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24
Q

Define the tip speed ratio and its formula.

A

See slide 30.

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25
Q

What are the advantages and disadvantages with a hight tip speed ratio?

A

+ smaller gearbox transmission ratio
+ direct drive: smaller generator
+ smaller torque, lighter structure, smaller loads
- difficult to keep noise emission within limits.

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26
Q

For a HAWT, what are the advantages and disadvantages with a low blade number?

A

+ lower cost (why)
+/- higher speed, smaller gearbox rato (+), more noise(-)
- visual impact
- mechanically unbalanced, add cost.

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27
Q

List some examples of rotors using drag force.

A

Savonius rotor, anemometer, chinese, persian.

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28
Q

What is the Magnus Effect, and how can it be used to propel a ship?

A

see slide 35

29
Q

What are the claimed advantages with the “High Wind System” (kite system)?

A

Wind availability for operation approx. 90%, 3 x more efficient, Scalable and suitable for almost any territory, Operational cost below fossile fues(!!!)

30
Q

What are the claimed disadvantages with the “High Wind System” (kite system)?

A

Premission procedures, public acceptance, operation security, maintanence, availability?

31
Q

What is the principle of the high wind system?

A

Combination of a kite and a rollercoaster, The rollercoaster is for energy conversion, kite is to induce high wind velocities from low ones.

32
Q

What is the technology behind the BAT (Buoyant Airbourne Turbine? Problems?

A

Helium filled shell that lifts the turbine up to high velocity winds and stableizes it there. Portable ground stations. Prototype 300m, 30kW.
Basically a ducted wind turbine that does not take advantage of the ducting.

33
Q

What are the elementary components of a HAWT? (5)

A

Foundation, Tower, Yaw, Nacelle, rotor Hub

34
Q

Mention 4 different types of towers.

A

Steel lattice tower, concrete tower, steel tube tower, plywood tower.

35
Q

List some advantages of the wooden tower.

A

+ fully recycable
+ completely CO2 neutral
+ strong and durable
+ assembly on site, can be transported on normal roads

36
Q

Give a disadvantage of the ATS HYbrid tower.

A

Transport problems due to large diameter bottom sectons.

37
Q

What components are found in the nacelle?

A

Gearbox, disc break, generator, gear, yaw drive, hydraulic supply, turbine shaft etc.

38
Q

What are some advantages with a variable speed operation?

A

beneficial for high efficiency over the whole range of useful wind speeds.
Offers more degrees of freedom.

39
Q

List a few generators.

A

Permanent magnet, DC excited syncronous, DFIG, BDFTSIG

40
Q

What are the adv. and disadvantages og a Permanent magnet generator?

A

See slide 48.

41
Q

What are the adv. and disadvantages og a DC excited generator?

A

see slide 48.

42
Q

What are the adv. and disadvantages og a DFIG?

A

see slide 48 and 50.

43
Q

What are the adv. and disadvantages og a BDFTSIG?

A

see slide 48 and 50.

44
Q

Adv. and disAdv. with a synchronous generator w/frequency converter.

A

+ high efficiency
+/- reactive power compensation within limits
- expensive and delicate power electronics
- power ranges above 2-3MW requires converter
- converter losses, 2-3%

45
Q

What does a rectifier do?

A

AC –> DC

46
Q

What does a inverter do?

A

DC –> AC

47
Q

What is a converter?

A

AC->DC—->DC->AC

48
Q

What additional protective systems must a wind turbine have? How and why?

A

Lightning protection, and de-icing systems (northers offfshore turbines)

49
Q

What are some adv. and disadv. of offshore wind power plants?

A

see slide 54, 55.

50
Q

Foundations of offshore wind turbines?

A

Suction caisson, gravity foundation, monopile, tripod, jacket, floater.

51
Q

How are offshore wind turbines installed?

A

see slide 58

52
Q

What types of floating offshore turbines do we have?

A

Single floater and multiple floater.

53
Q

Give adv and disadv. of HVAC transmission from offshore wind turbines.

A

+ easy voltage transformation
+ low transmission losses
- underground subsea cables: cable capacity leads to high ractive currents
- reactive current is prop to cable lenght.
- only feasable for short distances, approx 30km.

54
Q

Does high voltage transmission increase or decrease transmission losses? Equation connection?

A

Yes, and see slide 61.

55
Q

Give adv. and disadv. for HVDC transmission.

A

+ no reactive current, unlimited distance
+ phase and frequency decoupling
- requires rectifiers and inverters for very high voltages
- expensive

56
Q

Explain how energy is converted in a wind turbine.

A

see slides 65 - 72.

57
Q

What are the forces that act on an airfoil, and how does the angle of attack influence these forces?

A

see slide 74 - 76.

58
Q

Explain Betz momentum theory, and what is its results?

A

see slide 77 - 80.

59
Q

Derive the power coefficient for turbines using drag forces.

A

see slide 81 and 82.

60
Q

Explain the Darrious turbine kinematics (4 step pos)

A

see slide 83.

61
Q

What is meant by exit swirl loss, how does it happen and what is it in proportion to?

A

see slide 84 and 85

62
Q

Give three devices used to measure the wind speed.

A

cup anemometer, turbine anemometer, ultrasonic anemometer.

63
Q

How does a wind farm offshore generally start to get planned?

A

Setting up a research plattform that measures metrological data, hydrological data and environmental impact.

64
Q

How is the wind speed in a certain area genrally distributes?

A

Weibull distribution.

65
Q

How is the load factor defined, and what kind of an efficiency measure is it?

A

energy output/installed power. Economic efficiency measure.

66
Q

What is EROI?

A

Energy Returned on Enegy Invested.

EROI = Energy yield/Energy expended. Large = good.

67
Q

How does the presence of wind turbines affect the local environment?

A

noise emmision, shadow flickr, visual impact, impact on animal life, hazards due to potential mechanical failure.

68
Q

Give 5 principles for controlling the power output of wind turbines, and how do they work?

A

Yaw controll, tip break, stall controll, pitch controll, active stall controll

Ocean & Wind Energy (3 decks)

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