In the context of energy from the oceans, OTEC stands for:

OTEC is a technology that generates electricity by using the difference in temperature between the warm surface water of the ocean and the cold water found at depths of about 1,000 metres.

How OTEC works:

• In tropical oceans, the surface water is about 25 to 29 degrees Celsius, while the water at about 1,000 metres depth is only about 4 to 6 degrees Celsius.
• A temperature difference of at least about 20 degrees Celsius is needed for OTEC to work.

Closed-cycle OTEC: Warm surface water heats a working fluid with a low boiling point, such as ammonia, turning it into vapour. The vapour drives a turbine connected to a generator. Cold deep water is then used to condense the vapour back into liquid, and the cycle repeats.

Open-cycle OTEC: Warm sea water itself is boiled at low pressure to produce steam, which drives the turbine. The steam is condensed by cold water, producing fresh water as a by-product.

Advantages:

• It is a renewable source of energy, since the oceans are constantly heated by the Sun.
• Unlike solar and wind power, it can produce electricity continuously, day and night.
• Open-cycle plants also produce desalinated drinking water.
• The cold, nutrient-rich deep water can be used for aquaculture and air-conditioning.

Disadvantages:

• It requires very large and expensive pipes to bring up cold water from great depths.
• Its efficiency is low (about 3 percent), because the temperature difference is small.
• It is suitable only for tropical regions with deep water close to the coast.

OTEC in India:

• India has good potential for OTEC because of its tropical location and deep waters near its coasts and islands.
• The National Institute of Ocean Technology (NIOT), Chennai, is developing an OTEC-powered desalination plant at Kavaratti in Lakshadweep.
• Good to know
• These expansions are incorrect; OTEC refers to using the ocean's thermal (temperature) difference.