Wind Energy

Question 1

How do wind turbines work?

Answer 1

They convert kinetic energy of wind into electrical energy

Question 2

What is the relationship between power, swept area and wind speed?

Answer 2

The power is proportional to the swept area and cube of the wind speed

Question 3

What is the theoretical maximum fraction of wind power that can be converted into mechanical work?

Answer 3

0.593 which is the Betz limit

Question 4

What are some of the perceived problems of wind energy?

Answer 4

1. Cost –> Expensive to implement and operate
2. Planning Permissions & Public Opinion (Noise, Visibility, Environmental/Ecosystem Damage)
3. Availability –> Wind energy usually harnessed in winter months so not reliable for all year round energy
4. Difficult to transport components of the wind turbine by land –> Blades are very big + End of life cycle leaves excess material from very large components

Question 5

What are the potential solutions to the perceived problems?

Answer 5

1. Cost –> UK renewable energy is subsidised by the government
2. Availability –> Combined with solar energy (Summer months there’s more sun)

Question 6

What are the benefits of wind energy?

Answer 6

• Renewable Energy
• Doesn’t produce any CO2 after implemented
• Investment in wind energy is gradually increasing
• This is attractive to smaller companies/players in the industry
• Viable to build in small scale

Question 7

How do you find the Wind Energy Penetration?

Answer 7

Total amount of wind energy produced (GWh) / Total annual electricity demand (GWh)

Question 8

How do you find the Wind Power Capacity Penetration?

Answer 8

Installed Wind Power Capacity (GW)/ Peak load (GW)

Question 9

What is the capacity credit of wind?

Answer 9

Capacity of conventional plants displaced by wind power whilst maintaining the same degree of system security/ reliability

Question 10

What is the installed capacity?

Answer 10

The installed capacity is based on the “nameplate capacity” or “rated capacity” of the wind turbines

Question 11

What is the rated capacity?

Answer 11

The rated capacity is the manufacturers claimed output at a specific wind speed and is the maximum power that can be continuously delivered.
The actual delivered capacity is usually 20-40% of the rated capacity

Question 12

How do you find the capacity factor?

Answer 12

Actual MWh pa/ (rated capacity x 24 x 365)

Question 13

How much energy is generated by wind in the UK in 2019?

Answer 13

More than 50% of the electricity generated by renewables is by wind energy

Question 14

Where should Wind farms be located?

Answer 14

Located near the coast and further up longitudinally.
Near the equator the potential for wind energy is very low due to low winds speeds from global wind circulation patterns.
Near the coasts and sea there’s a lower friction factor so wind speeds are higher

Question 15

How do you find the Kinetic Power Flux?

Answer 15

ρ0.5u^3

ρ = 1.225 kg/m^3

units = W/m^2

Question 16

What is the UK’s potential for wind energy and what’s the current average electricity production from wind energy?

Answer 16

UK technical potential ~ 610GW
Current UK average electricity production ~ 50GW

Question 17

Describe the problem with integration for wind energy in UK?

Answer 17

More than 15% of energy used for wind farms crosses one or more borders.
There can be political problems between different regions for energy supply and demand

Question 18

What factors affect wind conditions?

Answer 18

• Terrain and geographical location
• The latitude of the location
• The presence of land mass and mountains
• Obstacles like trees and buildings

Question 19

What is used to measure accurate wind speeds?

Answer 19

An anemometer

Question 20

Describe the atmospheric boundary layer

Answer 20

Wind speeds generally increase as elevation increases away from the ground
This is because there’s less friction from obstacles near the ground/ friction from the ground

Question 21

How would you accurately measure wind speed?

Answer 21

• Anemometer mast numbers and placement vary based on site size and topography.
• The Earth features a boundary layer (wind shear profile).
• Boundary layer’s thickness (gradient height) spans several hundred meters.
• Ideal measurement occurs at hub height, typically above 100 meters.
• Minimum recommended measurement height is at least 75% of hub height.
• Weather station data is commonly recorded at 10 meters.
• Typically, data should be collected hourly or half-hourly for a minimum of one year.

Question 22

Are wind speed statistics accurate?

Answer 22

• An annual mean wind speed is not accurate as the wind speeds can vary greatly throughout the year
• Mean wind speed variation usually follows a Weibull distribution

Question 23

Explain why wind variation is a problem for wind power

Answer 23

Wind speed varies with time of day, weather, time of year. There’s no phase relationship between variations in available wind power and variations in demand
- Wind power is non-dispatchable

Question 24

What is dispatchable power?

Answer 24

Power than can be turned on and off by grid operators to match the demand - neither base load (e.g: nuclear) nor intermittent sources (e.g: wind) fit the bill

Question 25

What is a solution to non-dispatchable power?

Answer 25

• Have a flexible generating capacity to balance supply and demand variations and emergency back up
• Pumped storage hydro is a balancing solution and provides large storage capacity

Question 26

What is the trend in wind speed and turbine power?

Answer 26

As the velocity increases, the turbine power increases up to a certain velocity then the turbine power remains constant

Question 27

What is the effect of too much turbulence from wind gusts?

Answer 27

Can cause buckling and rotors can be blown off.

Question 28

Define drag and lift

Answer 28

Drag: the force in the direction of the relative wind
Lift: the force normal to the direction of the relative wind

Question 29

What factors affect the power coefficient?

Answer 29

• Tip Speed Ratio TSR
• Reynolds number
• TSR and Re are a function of the wind velocity

Question 30

What are the typical arrangements of wind farms?

Answer 30

Irregular arrays (Typical for onshore wind farms)
Regular Arrays (Typical for offshore wind farms)
Staggered Arrays (Typical for offshore wind farms)

Question 31

What is the Betz analysis?

Answer 31

The simplest analysis approach for rotor power. Obtained by 1 dimensional momentum and energy balance carried out along a stream tube

Question 32

What are the types of offshore wind turbines?

Answer 32

• Offshore towers feed into seabed (onshore)
• Floating offshore wind turbines (floating platform)
• Floating offshore wind tubing with Spar-Buoy type

Question 33

What are the problems with offshore wind technology?

Answer 33

• Wind energy uncertainty
• Constructibility
• Offshore access
• Offshore logistics installation
  -Turbine foundations
• Subsea cables
• Grid connection and integration
• Marine conditions/Weather
• Regulatory regime

Question 34

What are the current problems for wind energy industry?

Answer 34

1. Scaling up: Increasing flexibility, gravitational loads, gating, larger rotor diameters
2. Wake effects in wind farms decreasing efficiency
3. Offshore deployment (maintenance, fixed or floating foundations, wave loading)
4. Public perception: Visibility, noise, availability/reliability
5. Sustainability at the end of the life-cycle of a turbine