Wind Energy Questions and Answers – Effects of Wind Speed and Grid Condition (System Integration) – 1

This set of Wind Energy Multiple Choice Questions & Answers (MCQs) focuses on “Effects of Wind Speed and Grid Condition (System Integration) – 1”.

1. What happens to wind speed when many turbines operate collectively?
a) Wind speed reduces
b) Wind speed increases
c) Wind speed does not change
d) Wind speed increases exponentially and then decreases linearly

Explanation: Wind turbines are used to extract kinetic energy from the incoming wind. When multiple turbines operate collectively, the wind speed of the atmospheric flow reduces after crossing each turbine. This affects the efficiency of the turbines.

2. Which of the following is true?
a) More than 50% of the land area on earth can generate 1W per square meter
b) Less than 5% of the land area on earth can generate 1W per square meter
c) 60 – 80% of the land area on earth can generate 1W per square meter
d) More than 80% of the land area on earth can generate 1W per square meter

Explanation: After multiple simulations, research has shown that less than 5% of land area can actually generate 1W per square meter. A global climate model was used to simulate scenarios of different wind energy across all continents.

3. Lower wind speeds result in ________
a) higher wind energy obtained
b) no wind energy obtained
c) lower wind energy obtained
d) 100% energy conversion for half the operation time and less than 10% energy conversion for the remaining half of the operation time

Explanation: Wind speeds disproportionally affect the electricity generation from wind turbines. Lower wind speeds result in much lower wind energy. This further decreases the conversion efficiency resulting in extremely low powers.

4. What happens to the output power when the wind turbine blades rotate faster for the entire operation time?
a) The output power first increases then decreases
b) The output power first decreases then monotonically increases
c) The output power decreases
d) The output power increases

Explanation: When the wind turbine blades rotate faster for the entire operation time, the output power increases. The output power increases until the speed of rotation is decreased.

5. Higher wind speeds _________ the speed of rotation of the wind blades.
a) increase
b) decrease
c) monotonically decrease
d) first increase and then decrease

Explanation: Higher wind speeds increase the speed of rotation of the wind blades. This in turn generates more output power as the net mechanical energy increased due to increase in rotational speed of the wind blade.
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6. What is cut-in wind speed?
a) Wind turbine stops generating output power
b) Wind turbine starts generating output power
c) Wind turbine stops functioning
d) Wind turbine starts functioning

Explanation: Wind turbines are designed to operate within a specific range of wind speeds. The cut-in wind speed is that wind speed at which the wind turbine starts generating output power. It is not the speed at which the turbine starts functioning.

7. What is rated speed?
a) Wind turbines generate least output power
b) Wind turbines do not generate any output power
c) Wind turbines generate maximum output power
d) Wind turbines have no rated speed as the output power always increases

Explanation: The rated wind speed is that wind speed at which the wind turbines generate maximum output power. Maximum power point tracking (MPPT) is used to ensure that the wind turbines always operate in the neighbourhood of the rated wind speed.

8. Which of the following are the limits of the range of wind speeds for which the turbines are designed?
a) Elasticity
b) Threshold voltage
c) Networking
d) Cut-in speed and cut-out speed

Explanation: Since wind turbines are designed to operate within a specific range of wind speeds, they have limits. The lower limit is called the cut-in speed and the upper limit is called the cut-out speed. Elasticity is the ability of a material to come back to its original shape after stretching. Threshold voltage is related to electrical devices like diodes, BJTs, etc.

9. How does the output power vary between cut-in speed and the rated speed?
a) cubically
b) linearly
c) square
d) exponential

Explanation: Between the cut-in speed and the rated speed, the output power of the wind turbines varies cubically. The output power cubically increases until the rated speed is reached – if the wind speed doubles, the output power increases by 8 times.

10. What is the cut-out speed?
a) Wind turbine starts generating output power
b) Wind turbine must be shut down
c) Wind turbine stops functioning
d) Wind turbine starts functioning but does not generate output power

Explanation: Cut-out speed is the wind speed at which the wind turbine must be shut down. This prevents damage to the equipment used in the wind turbines. The cut-out speed is decided prior to wind turbine construction.

11. Power output is not related to the local air density.
a) False
b) True

Explanation: Power output is related to the local air density. Air density is defined as the mass per unit volume of the earth’s atmosphere. It depends on various physical factors.

12. Which of the following does the local air density depend upon?
a) Soil
b) Lightning
c) Altitude and pressure
d) Nitrogen and oxygen

Explanation: Air density depends on altitude, pressure and temperature. It does not depend on soil and its topography as well as on lightning. Nitrogen and oxygen are types of gases and are components of air.

13. Higher air density leads to higher power output.
a) True
b) False

Explanation: Higher air density results in higher output power. This is because denser air exerts more pressure on the wind blades which increases the speed of rotation. Thus, an increase in the speed of rotation increases output power.

14. What is feather of wind turbine blades?
b) Reducing the weight of wind turbine blades
c) Reducing the angle of pitch
d) Increasing the angle of pitch

Explanation: Increasing the angle of pitch is called feathering of wind turbine blades. It is achieved by turning the blades to orient them in a direction parallel to the air flow. This minimized the net drag on the wind turbine blades.

15. Why is feathering of wind turbine blades required?
a) To increase drag
b) To reduce drag
c) To prevent the blades from being destroyed by strong winds
d) To extract power from strong winds originating from storms

Explanation: Feathering of wind turbine blades is used to prevent the blades from destruction by storm winds. By orienting the wind blades in a direction parallel to the incoming air flow, the net drag from a stopped propeller is minimized and the system is shut down.

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