Ocean Thermal Energy is harnessed through a process called Ocean Thermal Energy Conversion (OTEC). OTEC is a process or technology for producing energy by harnessing the temperature differences (thermal gradients) between ocean surface waters and deep ocean waters. The OTEC system uses a temperature difference of at least 20 degrees Celsius to power a turbine to produce electricity. India has a theoretical potential of 180,000 MW of ocean thermal energy. India is geographically well-placed to generate ocean thermal energy, with around 2000 kms of coastal length along the South Indian coast, where a temperature difference of above 20 degree Celsius is available throughout the year.
To tap ocean thermal energy, the National Institute of Ocean Technology, under the Union Ministry of Earth Sciences (MoES) is establishing an Ocean Thermal Energy Conversion Plant with a capacity of 65 kilowatts (kW) in Kavaratti, Lakshadweep. The plant will power the one lakh litres per day low temperature thermal desalination plant, which converts seawater into potable water. The plant is the first of its kind in the world as it will generate drinking water from sea water using indigenous technology, green energy and environmentally friendly processes.
However, progress in this regard has been slow due to various challenges:

• High cost: Setting up of OTEC plants for harnessing thermal energy potential requires significant costs of pumping and piping infrastructure. It is economical at very large scales only. The small land based OTEC plants need kilometres of piping to move a high volume of cold water from deep ocean. Its cost could be up to 75% of the total power plant costs.
• Restricted location: The suitable locations to harness OTEC are reduced to equatorial and tropical zones.
• Lack of technology: Most technologies are currently at pre-R&D demonstration stage of the initial stage of commercialization.
• Environmental concerns: It can have potential impact on marine organisms and ecosystems due to discharge of cooler, denser and nutrient rich water from the plants, entanglement in cables, entrapment, noise generation and pollutants. It can also lead to biofouling i.e. unwanted accumulation of algae, microorganisms, plants etc.

Remedial measures required in this context:

• Policy support is required for harnessing the potential of ocean thermal energy. It should not only include a robust national policy, but a proper plan of financial deployment to accelerate the existing program.
• There is a requirement of investment in R&D. Private sectors should be encouraged and be given incentives to contribute to technological development in this regard.
• India should take efforts to promote international collaborations in the field of utilising ocean energy and also bring littoral countries on a single platform for contributing in this field.
• There is a need to develop more demonstration projects at feasible sites so that a careful study of EIA can be done.

Ocean thermal energy has the potential to generate a constant, clean source of electricity unlike intermittent electricity from renewable resources like wind and solar. So, there is a need to create awareness about the potential of ocean thermal energy and its long-term benefits including reduction in carbon dioxide emissions.