Wind Energy Question Paper on “Wind Energy Storage – 2″.
1. What is depth of discharge?
a) Percentage of the battery that is discharged during a cycle
b) Percentage of the battery that is discharged
c) Amount of charge discharged from a battery during a cycle
d) Amount of charge discharged from a battery
Answer: a
Clarification: Depth of discharge (DoD) is the percentage of the battery that is discharged during a cycle. It has a wider use because it indicates a percentage instead of an absolute value. Indicating the absolute value of the charge discharged is not practical as it is unique for every battery and cannot be generalized.
2. What is charge-to-discharge ratio?
a) Time taken to charge the device
b) Ratio of time taken to charge the device relative to the time taken to discharge the device
c) Ratio of the amount of charge during charging cycle to the amount of charge during discharge cycle
d) Time taken to discharge the device
Answer: b
Clarification: Charge-to-discharge ratio is the ratio of time taken to charge the device relative to the time taken to discharge the device. For instance, if a device takes 2 times longer to charge than to discharge, it has a charge-to-discharge ratio of 2:1.
3. What is memory effect?
a) Electro-hydrogen generation
b) Pumped storage
c) Remembering a charging level
d) Electric grid
Answer: c
Clarification: Memory effect is mainly used to describe rechargeable batteries. If they are not fully charged for long periods of time then they ‘remember’ that charging level. Thus, they lose some of their capacity. The other options are storage techniques of wind energy.
4. Which of the following have large power (>50MW) and storage capacities (>100MWh)?
a) Memory effect
b) Battery energy storage (BES) and flow battery energy storage
c) Super capacitor energy storage and flywheel energy storage
d) Pumped hydro-electric storage and underground pumped hydro-electric storage
Answer: d
Clarification: Pumped hydro-electric storage (PHES) and underground pumped hydro-electric storage (UPHES) are grouped under the category of large power (>50MW) and storage capacity (>100MWh). Compressed air energy storage (CAES) is another example of this category. Memory effect is a parameter used to describe a rechargeable battery.
5. Efficiency of pumped hydro-electric storage is in the range of _________
a) 50% — 80%
b) 80% — 120%
c) 10% — 20%
d) 45% — 50%
Answer: a
Clarification: Efficiency of pumped hydro-electric storage is in the range of 50% — 80%. It has large power (>50MW) and storage capacity (>100MWh). The efficiency is further being improved using variable speed machines.
6. How does pumped hydro-electric storage work?
a) Pumps water from higher level to a lower level
b) Pumps water from lower level to higher level
c) Uses electrical energy present in the water
d) Uses nuclear energy present in the water molecules
Answer: b
Clarification: PHES uses the gravitational potential energy of water to generate electricity. During off-peak hours, water is pumped from a reservoir at a lower level to a reservoir at a higher level and stored. When required, the water falls from the higher level and rotates turbines connected to an electrical generator.
7. Which of the following is an application of pumped hydro-electric storage?
a) Energy source
b) Frequency regulation only in pumping mode
c) Frequency regulation in both pumping and generation modes
d) Absorbs power to increase the net expenses
Answer: c
Clarification: Pumped hydro-electric storage is used for frequency regulation in both pumping and generation modes. In fact, it absorbs power in a more cost-effective manner and boosts efficiency upto 3%.
8. What is a major disadvantage with pumped hydro-electric system?
a) No dependence on geographical locations
b) Small scale construction for effective functioning
c) Low initial costs of construction
d) Depends on specific geographical locations for the construction of the two reservoirs