Option C: By solar energy Explanation & Concepts: OTEC (Ocean Thermal Energy Conversion) is a renewable energy process that produces electricity by utilizing the temperature difference (thermal gradient) between the warm surface water and the cold deep ocean water. This temperature gradient is primarily maintained by the absorption of solar radiation at the ocean surface. Working Principle: The surface of the ocean absorbs solar energy, keeping the upper layer warm, while the deep ocean water remains cold due to lack of sunlight. A working fluid with a low boiling point (such as ammonia) is vaporized by the warm surface water to drive a turbine connected to a generator. The vapor is subsequently condensed back into a liquid using the cold deep-water intake, creating a continuous heat engine cycle. Key Formulas: $\eta_{max} = 1 - \frac{T_{cold}}{T_{warm}}$ — represents the theoretical maximum thermal efficiency (Carnot efficiency) based on absolute temperatures. Key Points: OTEC requires a temperature difference of at least 20°C between the surface and deep water.; It acts as a continuous base-load power source unlike solar PV or wind.; The process involves a thermodynamic cycle: Rankine cycle is typically employed. Advantages: Provides constant base-load power 24/7.; Produces desalinated water as a valuable byproduct. Disadvantages: High initial capital cost for offshore infrastructure.; Environmental concerns regarding the discharge of deep-sea cold water. Applications: Island nation power generation.; Desalination plants.; Mariculture (using cold, nutrient-rich water). Additional Info: The temperature difference is a result of the Earth's absorption of solar heat at the ocean surface.. Option A is incorrect because wind energy is mechanical kinetic energy, not thermal.. Option B is incorrect because geothermal energy refers to heat from the Earth's interior crust, not the solar-heated ocean. Answer: C is correct — OTEC exploits the temperature gradient created by solar energy heating the surface of the ocean. Exam Tip: Remember that OTEC is a form of indirect solar energy harvesting, similar to wind and hydroelectric power.

Option D: By gravitational force

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How is OTEC caused?

By wind energy

By geothermal energy

By solar energy

By gravitational force

Correct Answer

Concept & PrincipleElectricalPower Generation

Option C

By solar energy

Quick Summary: OTEC (Ocean Thermal Energy Conversion) is a renewable energy process that produces electricity by utilizing the temperature difference (thermal gradient) between the warm surface water and the cold deep ocean water. This temperature gradient is primarily maintained by the absorption of solar radiation at the ocean surface.

💡 Explanation

OTEC (Ocean Thermal Energy Conversion) is a renewable energy process that produces electricity by utilizing the temperature difference (thermal gradient) between the warm surface water and the cold deep ocean water. This temperature gradient is primarily maintained by the absorption of solar radiation at the ocean surface.

🔢 Key Formulas

$\eta_{max} = 1 - \frac{T_{cold}}{T_{warm}}$ — represents the theoretical maximum thermal efficiency (Carnot efficiency) based on absolute temperatures.

⚙️ Working Principle

The surface of the ocean absorbs solar energy, keeping the upper layer warm, while the deep ocean water remains cold due to lack of sunlight. A working fluid with a low boiling point (such as ammonia) is vaporized by the warm surface water to drive a turbine connected to a generator. The vapor is subsequently condensed back into a liquid using the cold deep-water intake, creating a continuous heat engine cycle.

📌 Key Points

▸
OTEC requires a temperature difference of at least 20°C between the surface and deep water.
▸
It acts as a continuous base-load power source unlike solar PV or wind.
▸
The process involves a thermodynamic cycle: Rankine cycle is typically employed.

✅ Advantages

▸
Provides constant base-load power 24/7.
▸
Produces desalinated water as a valuable byproduct.

❌ Disadvantages / Limitations

▸
High initial capital cost for offshore infrastructure.
▸
Environmental concerns regarding the discharge of deep-sea cold water.

🛠️ Applications / Uses

▸
Island nation power generation.
▸
Desalination plants.
▸
Mariculture (using cold, nutrient-rich water).

📄 Additional Information

▸
The temperature difference is a result of the Earth's absorption of solar heat at the ocean surface.
▸
Option A is incorrect because wind energy is mechanical kinetic energy, not thermal.
▸
Option B is incorrect because geothermal energy refers to heat from the Earth's interior crust, not the solar-heated ocean.

📊 Diagram / Illustration

✅

C is correct — OTEC exploits the temperature gradient created by solar energy heating the surface of the ocean.

Core Concepts Used

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Ocean Thermal Energy Conversion Thermodynamic cycles Solar radiation absorption

💡 EXAM TIP

Remember that OTEC is a form of indirect solar energy harvesting, similar to wind and hydroelectric power.

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