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Green Tech Corner

OTEC - Ocean Thermal Electricity Conversion
By Saranya Acharya

Ocean Thermal Energy Conversion (OTEC) is a technology that converts solar radiation into electricity by using the oceans natural thermal gradient. The sea act as huge collectors of solar radiation (better than the artificial collectors)and efficient energy storage system. The OTEC process uses the temperature difference between warm seawater at the surface of the ocean and cold seawater at between 800M-1000M depth to produce electricity. The warm seawater is used to produce a vapour that acts as a working fluid to drive the turbines and the cold water is used to condense the vapour and ensure the vapour pressure difference drives the turbine. The technology is viable primarily in equatorial areas of the earth where year round temperature difference between the deep cold and warm surface water is greater than 20oC.

Types of OTEC -Based on working fluid system

  • Open Cycle OTEC : which uses seawater as the working fluid In this the surface warm seawater is pumped into a flash evaporator where low pressure causes the water to boil and the steam generated is used to drive the turbine and generate electricity. The steam then passes through condenser using cold seawater from depth of the ocean and condenses the steam into desalinized or the fresh water as the byproduct which can be further used for drinking or agricultural purposes.
  • Closed Cycle OTEC : which uses ammonia In this the surface warm seawater flowing through the evaporator vaporizes the working fluid and as the vapour expands it drives the turbine. The vapour on condensation is again pumped to the evaporator and the cycle is repeated with same amount of working fluid, hence the name Closed Cycle.
  • Kalina OTEC : is a sub-type of Closed cycle OTEC which uses a mixture of ammonia and water as working fluid
  • Hybrid Cycle OTEC : which combines the Closed-and-Open-cycle systems. OTEC plants can be land-based, moored to the sea floor or floating, the former involves high installation costs for both piping and land-use whereas the floating system has comparatively lower land use and impact.


  • Since OTEC exploits renewable solar energy, recurring costs to generate electrical power are minimal.
  • It acts as a continuous source of electricity with high capacity factor of about 90-95%.
  • The production of fresh water with electricity generation in open cycle and hybrid cycle OTEC, is an added advantage for countries with water scarcity and where water is produced by desalination.
  • The OTEC power can act as a source of electricity for offshore settlements, islands and communities


  • High up-front capital costs which is the major barrier dampening its utilization as an alternative energy resource
  • Lack of experience building OTEC plants at scale.
  • Construction of OTEC plants and laying of large pipes to transport volumes of water required to produce electricity can                   damage the reefs and near-shore marine ecosystem.


In India, OTEC has a potential installed capacity of 180,000MW. And alsoIndia tested a 1MW floating OTEC prototype in 2002 in Tamilnadu. The plant was not successful due to the failure of the deep sea cold water pipe but it laid a good foundation and the government continues to sponsor research for a sustainable tomorrow.

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