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Pumped Storage Hydropower: Energy, Efficiency and the Grid — MCQs with Answers

Test what you know about Pumped Storage Hydropower: Energy, Efficiency and the Grid with 10 UPSC Prelims-style questions. Try each one first, then tap “Show answer” for the correct option and its explanation.

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  1. Q1. Consider the following statements about a pure pumped-storage cycle: 1. It can provide a useful grid service even when electrical output is less than charging input. 2. Pumping must be confined to night hours irrespective of the generation mix. 3. Its stored energy is primarily gravitational potential energy. Which statements are correct?

    1. 1 and 2 only
    2. 2 and 3 only
    3. 1 and 3 only
    4. 1, 2 and 3
    Show answer

    Correct answer: (C) 1 and 3 only

    Explanation

    Correct Answer: (C). Statements 1 and 3 are correct. Storage can move electricity from a surplus period to a higher-value period despite conversion losses. Pumping raises the potential energy of water. Statement 2 is incorrect because strong daytime solar availability can favour midday charging; the appropriate schedule follows system conditions rather than darkness.

  2. Q2. A fully charged facility has 3,600 MWh of usable electrical output and a maximum discharge rate of 600 MW. With no recharge, inflow or further derating, which service can it provide?

    1. 600 MW for six hours
    2. 900 MW for four hours
    3. 600 MW for eight hours
    4. 1,200 MW for three hours
    Show answer

    Correct answer: (A) 600 MW for six hours

    Explanation

    Correct Answer: (A). Duration at the rated output is 3,600 divided by 600, or six hours. The four-hour and three-hour alternatives preserve the energy total but exceed the stated power limit. The eight-hour alternative respects the power limit but requires 4,800 MWh, more than the usable energy available. Both constraints must be satisfied.

  3. Q3. Charging electricity costs ₹2 per kWh. A storage cycle has 80% round-trip efficiency and sells output at ₹2.40 per kWh. Ignoring all other costs and revenues, which conclusion is correct?

    1. The margin is positive because ₹2.40 exceeds ₹2
    2. The margin is zero because losses affect energy rather than cost
    3. The charging cost per delivered kWh is ₹1.60
    4. The charging cost per delivered kWh is ₹2.50, so the margin is negative
    Show answer

    Correct answer: (D) The charging cost per delivered kWh is ₹2.50, so the margin is negative

    Explanation

    Correct Answer: (D). One delivered kWh requires 1 divided by 0.8, or 1.25 kWh of charging electricity. At ₹2 per input kWh, this costs ₹2.50, exceeding the ₹2.40 sale revenue. Comparing purchase and sale unit prices without adjusting for efficiency overlooks the extra input required for each unit actually delivered.

  4. Q4. Regarding closed-loop pumped storage, consider: 1. Classification depends on ongoing hydrological connectivity, not the source of charging electricity. 2. Initial filling and replacement of water losses may still be required. 3. Absence of a continuous river connection removes the need to assess land and habitat impacts. Which statements are correct?

    1. 2 and 3 only
    2. 1 and 2 only
    3. 1 and 3 only
    4. 1, 2 and 3
    Show answer

    Correct answer: (B) 1 and 2 only

    Explanation

    Correct Answer: (B). Statements 1 and 2 are correct. Closed-loop identifies the water-system relationship and does not prescribe a clean charging source. Filling and make-up water can remain necessary. Statement 3 is incorrect because reservoirs, roads, tunnels and lines may affect land and habitats even without a continuous connection to a natural river.

  5. Q5. A storage reservoir has spare capacity, while a nearby solar region is curtailing output. A congested transmission corridor prevents additional electricity from reaching the pumps. What follows most directly?

    1. Spare storage volume alone cannot absorb the inaccessible surplus
    2. The water-storage capacity must be increased before any network action
    3. Curtailment proves that solar generation is technically unavailable
    4. Higher turbine efficiency alone removes the transmission constraint
    Show answer

    Correct answer: (A) Spare storage volume alone cannot absorb the inaccessible surplus

    Explanation

    Correct Answer: (A). Storage needs an electrical path to charging energy. Empty reservoir capacity does not solve the stated transmission bottleneck, and greater turbine efficiency addresses a different part of the system. Curtailment can occur precisely because available generation cannot be accepted by the network, not because the resource is technically absent.

  6. Q6. Charging electricity has emissions of 0.4 kg per kWh. Round-trip efficiency is 80%. Ignoring construction and all other emissions, the charging-related emissions per delivered kWh are:

    1. 0.32 kg
    2. 0.40 kg
    3. 0.50 kg
    4. 0.80 kg
    Show answer

    Correct answer: (C) 0.50 kg

    Explanation

    Correct Answer: (C). Each delivered kWh requires 1.25 kWh of input, so charging-related emissions are 1.25 multiplied by 0.4, or 0.5 kg. Multiplying the input intensity by efficiency incorrectly reduces the attributed emissions. This limited calculation is not a full lifecycle assessment and does not determine whether the displaced generation has higher emissions.

  7. Q7. Statement-I: Two storage plants with identical MW ratings can provide different full-power durations. Statement-II: Duration depends on usable energy relative to discharge power, rather than power alone. Which relationship is correct?

    1. Both are correct, but II does not explain I
    2. I is correct, but II is incorrect
    3. I is incorrect, but II is correct
    4. Both are correct, and II explains I
    Show answer

    Correct answer: (D) Both are correct, and II explains I

    Explanation

    Correct Answer: (D). Both statements are correct, and the second supplies the reason for the first. Equal discharge power does not imply equal usable energy. A larger energy reserve can sustain the same output for longer, subject to the stated operating assumptions. Confusing MW with MWh conceals this difference in service capability.

  8. Q8. Consider the following comparisons: 1. The appropriate technology should be assessed against a common duration and response requirement. 2. Batteries are restricted by definition to very short storage durations. 3. Comparing projects only by cost per MW can conceal differences in usable energy. Which statements are correct?

    1. 1 and 2 only
    2. 1 and 3 only
    3. 2 and 3 only
    4. 1, 2 and 3
    Show answer

    Correct answer: (B) 1 and 3 only

    Explanation

    Correct Answer: (B). Statements 1 and 3 are correct because service requirements and stored energy must be comparable. Statement 2 converts a common deployment tendency into a false definitional restriction. Batteries can be designed for different durations, while pumped storage can also offer rapid response; no single power-cost number settles the complete comparison.

  9. Q9. In an idealised comparison, two reservoirs hold equal usable masses of water. Project X has twice the effective vertical height difference of Project Y. With equal conversion efficiency, which inference is justified?

    1. X has twice the potential energy available from that water, but feasibility still needs separate assessment
    2. X necessarily has twice the maximum power rating and identical construction cost
    3. X needs no additional charging energy despite the greater height
    4. Y cannot operate because height differences must exceed a universal fixed threshold
    Show answer

    Correct answer: (A) X has twice the potential energy available from that water, but feasibility still needs separate assessment

    Explanation

    Correct Answer: (A). Potential energy is proportional to mass, gravitational acceleration and height difference. Holding mass and efficiency constant, doubling the effective height doubles the idealised energy available. This does not fix turbine power, civil-work costs or overall feasibility. A higher lift also requires more charging work, rather than providing additional energy without input.

  10. Q10. A planning document lists a large pumped-storage potential. Which additional evidence most directly establishes dependable supply during a particular evening peak?

    1. The number of geographically identified sites alone
    2. Commissioned equipment, adequate state of charge and usable grid access for the required output
    3. The proposed projects’ aggregate power rating regardless of completion
    4. A national potential estimate larger than the evening demand
    Show answer

    Correct answer: (B) Commissioned equipment, adequate state of charge and usable grid access for the required output

    Explanation

    Correct Answer: (B). Identified potential and proposals are not operational supply. Dependable output requires commissioned capability, enough stored energy and an adequate connection for the required delivery. Surveys, approvals, finance and construction can separate a promising site from a working project. Even a completed installation needs sufficient charge to support the specified peak period.

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