Oceans occupy more than 70 per cent of earth’s surface and are an inexhaustible source of renewable energy. Ocean energy is the energy harnessed from ocean waves, tidal range (rise and fall) & tidal streams, temperature gradients and salinity gradients. Only few commercial ocean energy power plants have been commissioned till date. Around 536 MW of installed ocean energy capacity is in operation at the end of 2016, with major share of two large scale tidal barrage plants i.e. the 254 MW Sihwa plant in the South Korea (completed in 2011) and the 240 MW La Rance tidal power station in France (completed in 1966). Apart from tidal barrage plants which use established tidal turbine technology, other ocean energy technologies are still largely in pre-commercial development stages.

Ocean Energy: World Scenario

Leading countries in Ocean Energy technology are UK, USA, Sweden, Canada, France, South Korea. Examples of few large scale Tidal (Barrage) Plants are 254 MW at South Korea (2011), 240 MW at France (1966), 20 MW at Canada, etc. Ocean Technology, such as Tidal (Current), Wave, Ocean Thermal Energy Conversion (OTEC) are still at pre R&D stage/Kilo Watt level.

Ocean Energy: India Scenario

Renewable Energy technologies such as geo-thermal and ocean energy still remain at a nascent stage in India. As per study conducted by IIT Madras, Theoretical Potential for tidal Energy in India is 12500 MW, Promising locations are Gulf of Khambhat & Gulf of Kutch (GJ), Sunderbans (WB), Western Ghats(MH), etc. Theoretical Potential for Wave Energy in India is 41,000 MW, Promising locations are Western Coast of Maharashtra, Goa, Karnataka, Kerala, Kanyakumari,Southern tip of India, etc. However, resource survey at target locations i.e. Western Ghats, Eastern Ghats, etc. may be undertaken to assess/ validate actual potential. These technologies are more suitable for off grid electricity generation in remote coastal areas/mangroves/ islands where Tariff is very high @ Rs 25/Kwh for diesel based captive power generation. Major bottlenecks for deployment are high upfront cost i.e. Rs 60 Crore for 1.125 MW wave energy plant at A&N islands and Rs 2000 Crore for 8 MW plant by Indian Navy, high tariff @ Rs 15.69/ KWh with 50 per cent grant for A&N wave energy plant

Technologies for Ocean Energy

Tidal Energy

The tidal cycle occurs every 12 hours due to the gravitational pull of the moon. The difference in water level from low tide and high tide is potential energy that can be harnessed. Similar to hydropower generated from dams, tidal water is captured in a barrage across an estuary during high tide and forced through a turbine during low tide. The capital cost for tidal energy power plants is very high due to high civil construction that results in high power tariff. In order to harness power from the tidal energy, the height of high tide must be at least five meters (16 feet) greater than low tide.

Wave Energy

Wave energy is generated by the movement of a device either floating on the surface of the ocean or moored to the ocean floor by the force generated by the ocean waves. Many different techniques for converting wave energy to electric power have been developed. Wave conversion devices floats on the surface have joints hinged together that moves with the waves. The kinetic energy pumps fluid through turbines and generates electric power. Moored wave energy conversion devices use pressure fluctuations produced in long tubes from the waves moving up and down. This wave motion drives a turbine.

Current Energy

Ocean current is ocean water moving in one direction. This ocean current is also known as the Gulf Stream. Kinetic energy can be captured from the Gulf Stream and other tidal currents with submerged turbines that are very similar in appearance to miniature wind turbines. Similar to wind turbines, the movement of the marine current moves the rotor blades to generate electric power.

Ocean Thermal Energy Conversion (OTEC)

Ocean thermal energy conversion, or OTEC, uses ocean temperature differences from the surface to depths lower than 1,000 meters, to harness energy. A temperature difference of even 20°C can yield energy efficiently. Research focuses are on two types of OTEC technologies to extract thermal energy and convert it to electric power: closed cycle and open cycle.

In the closed cycle method, a working fluid, such as ammonia, is pumped through a heat exchanger and vaporized. This vaporized steam runs a turbine. The cold water found at the depths of the ocean condenses the vapor back to a fluid where it returns to the heat exchanger. In the open cycle system, the warm surface water is pressurized in a vacuum chamber and converted to steam to run the turbine. The steam is then condensed using cold ocean water from lower depths.

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