Chapter 7 Multiple Choice Questions

1) In the northern hemisphere, the prevailing wind direction in the latitudes between 0 and 30 degrees is expected to be…

Northerly.

North-Easterly.

Southerly.

Westerly.

2) In the 1970s, there was interest in developing wind power because of…

an oil crisis.

concern over global warming.

improvements in wind turbines.

3) The mean wind speed at site A for a wind farm is 10% higher than at site B. What would be the expected increase in electricity production at site A compared to site B?

10%

20%

30%

33%

4) Which of the following statements about vertical axis wind turbines (VAWTs) are true?
Please select all that apply.

They can be easier to maintain.

They have a higher efficiency.

They can well suited for urban sites.

For large turbines, they tend to be cheaper.

5) The fraction of power in the wind that a modern wind turbine can extract is approximately…

90%.

59%.

50%.

6) Typical cut-in, rated, and cut-out wind speeds for a wind turbine operating in mean wind speed of 8 m s^-1 are…

5, 15, 35 m s^-1.

3, 12, 25 m s^-1.

1, 10, 20 m s^-1.

7) Which of the following statements about the width and twist of a wind turbine blade is true?

The width halfway along is twice that at the tip and the blade is more twisted.

The width halfway along is four times that at the tip and the blade is more twisted.

The width halfway along is twice that at the tip and the blade is less twisted.

8) Turbine blades designed for three bladed turbines with the same tip-speed ratio have the same shape.

Yes

No

9) A wind turbine designed for a tip-speed ratio λ = 9 is operating in a mean wind speed of 12 m s^-¹. The turbine blades are 50 m long. Estimate the number of revolutions made by the turbine in 30 years taking the capacity factor as 30%.

10⁸

3 x 10⁷

3 x 10⁸

10) A typical spacing between turbines in a wind farm in terms of their rotor diameters D, when space is not a premium, is approximately…

5D × 8D

2D × 3D

15D × 20D

11) Which of the following statements about the capacity factors (CF) of wind farms are true?
Please select all that apply.

Onshore CF ~20–30%

Onshore CF ~30–40%

Offshore CF ~40–50%

Offshore CF ~60–70%

12) The power output per square kilometre of a wind farm consisting of turbines with rotor diameters D in a mean wind speed u_m depends approximately on…

D²u_m²

D³u_m³

u_m³

13) In a region where the mean wind speed is 8 m s^-¹, the area of land required for a wind farm to produce 2 TWh per yea is…

80 km².

120 km².

200 km².

14) Which of the following statements about off-shore wind are true?
Please select all that apply.

Wind speeds are generally higher at the same height and more constant than onshore.

There is more turbulence and, as a consequence, more fatigue.

There is more potential for expansion than for onshore.

Transmission distances from offshore wind farms can be shorter than for onshore ones.

15) The ______ of wind can be accommodated by having a mix of electricity generators, good ______with different regions, energy _____ available, and the ability to vary _____ to suit supply.

16) The increase in______ _______ saw costs fall over the period 1984–2014 from around 57 to 7 cents per kWh from wind farms.

17) The global technical onshore wind potential is about…

1000 GWe.

20,000 GWe.

100,000 GWe.

18) There has been an annual growth in global installed wind capacity since 2010 of…

7%.

14%.

28%.

19) Match the installed wind power capacities (in GW) in 2019 to the countries.

19a.

China

19b.

USA

19c.

Germany

19d.

India

19c.

UK

20) Which of the following statements about wind power are true?
Please select all that apply.

It helps combat global warming and provide energy security.

When there is no demand, the wind farm output has to be curtailed.

It causes more bird deaths per GWh than fossil fuel power plants.

It could provide ~20000 TWh per year of electricity demand by 2050.

It will be 2030 before offshore wind is competitive with fossil fuel generation.

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