Tidal and Wave Energy Questions and Answers

Q: The ocean thermal energy conversion system that is meant to generate power in most suitable in :

Ocean thermal energy conversion is most suitable in the tropical region.OTEC runs a heat engine between warm surface water and cold deep water. It needs a temperature difference of at least about 20 °C between the surface and a depth of about 1000 m, and that difference is found year-round only in tropical seas, where the surface stays at 25-28 °C. India's coasts and island territories, such as Lakshadweep, are suitable for this reason.In sub-tropical, moderate and cold regions the surface water is cooler and the difference too small or too seasonal for an OTEC plant to run economically.

The ocean thermal energy conversion system that is meant to generate power in most suitable in :

A.Sub-tropical region
B.Tropical region
C.Cold region
D.Moderate climate region

Exam Year(s)

MH SET - 2019, SET Exam - 2019,

Answer: B

Ocean thermal energy conversion is most suitable in the tropical region.

OTEC runs a heat engine between warm surface water and cold deep water. It needs a temperature difference of at least about 20 °C between the surface and a depth of about 1000 m, and that difference is found year-round only in tropical seas, where the surface stays at 25-28 °C. India's coasts and island territories, such as Lakshadweep, are suitable for this reason.

In sub-tropical, moderate and cold regions the surface water is cooler and the difference too small or too seasonal for an OTEC plant to run economically.

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The maximum tidal energy potential in India is

A.in Gulf of Khambhat
B.in Gangetic delta in Sundarbans
C.along the coast of Odisha
D.along the coast of Chennai

Exam Year(s)

UGC NET - 2012,

Answer: A

The maximum tidal energy potential in India is in the Gulf of Khambhat, option A. The Gulf has a large tidal range, of several metres, because of its funnel shape, and it has the highest tidal power potential of the Indian sites, with the Gulf of Kutch next.

The Gangetic delta in the Sundarbans (option B) has a much smaller potential. The coast of Odisha (option C) and the coast of Chennai (option D) have small tidal ranges and are not sites for tidal power. The range of the tide is what decides the potential.

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Assertion (A) : Tropical and subtropical seas are most suitable for OTEC.

Reason (R) : There is a certain minimum vertical gradient (\(\gt\) 25 °C/km) required for OTEC to become feasible.
Codes :

A.Both (A) and (R) are true and (R) is the correct explanation .
B.Both (A) and (R) are true, but (R) is not the correct explanation.
C.(A) is true, but (R) is false.
D.(A) is false, but (R) is true.

Exam Year(s)

UGC NET - 2013,

Answer: A

The keyed answer is that both statements are true and (R) explains (A).

Ocean thermal energy conversion runs a heat engine between warm surface water and cold deep water, so it needs a large temperature difference between the two. Tropical and subtropical seas have the warmest surface water, so they are the most suitable, which is the assertion. The reason states the need for a minimum temperature gradient with depth before OTEC becomes feasible, and that is why only such seas qualify. The codes calling (A) or (R) false are not supported.

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The minimum temperature gradient (°C/km) required for OTEC is about

A.20
B.10
C.40
D.60

Exam Year(s)

UGC NET - 2013,

Answer: A

The minimum temperature difference between warm surface water and cold deep water needed for ocean thermal energy conversion is about 20 °C. This is the figure for the gradient given in the key, and the question asks for the least value required.

The values 10, 40 and 60 are not the accepted minimum: 10 is too small for a practical cycle, while 40 and 60 are far above what tropical oceans offer.

Testing each of the remaining options against the same fact shows that every one of them fails on the point the question is asking about, which confirms the keyed answer.

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Consider an Ocean Thermal Energy Conversion (OTEC) process operating between 30 °C and 5 °C. What would be the maximum possible efficiency for an electricity generator station operating with these temperatures ?

A.8%
B.15%
C.25%
D.40%

Exam Year(s)

UGC NET - 2014,

Answer: A

The maximum possible efficiency of any heat engine working between two temperatures is that of the Carnot engine, with the temperatures taken in kelvin. Here the hot reservoir is the warm surface water at 30 \(^{\circ}\)C, which is 303 K, and the cold reservoir is the deep water at 5 \(^{\circ}\)C, which is 278 K:

\[ \eta = 1 - \frac{T_{c}}{T_{h}} = 1 - \frac{278}{303} \]

\[ \eta = 0.0825 \approx 8\% \]

So the answer is (A). The values 15, 25 and 40 per cent are far above what such a small temperature difference allows, and a real OTEC plant does even worse than this limit.

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Assertion (A) : Large scale OTEC development may not be good for environment.

Reason (R) : Release of CO2 from ocean depths into the atmosphere could exacerbate GHG effect.
Codes :

A.Both (A) and (R) are true and (R) is the correct explanation of (A).
B.Both (A) and (R) are true, but (R) is not the correct explanation of (A).
C.(A) is true, but (R) is false.
D.Both (A) and (R) are false.

Exam Year(s)

UGC NET - 2014,

Answer: A

Both the assertion and the reason are true, and the reason explains why large scale OTEC may be harmful. The water brought up from the ocean depths contains dissolved carbon dioxide, which is released on warming and could add to the greenhouse effect.

The options calling the reason false, or calling the reason an unrelated true statement, are wrong, since the release of CO2 is the basis of the concern.

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