In a decision that could give boost ocean energy in India, the Ministry of New and Renewable Energy (MNRE) has approved a proposal to declare ocean energy as renewable energy (RE). Accordingly, MNRE has clarified to all the stakeholders that energy produced using various forms of ocean energy, such as tidal, wave, current energy, ocean thermal energy conversion (OTEC) etc. shall be considered as renewable energy and be eligible for meeting the non-solar Renewable Purchase Obligations (RPO).
The total identified potential of tidal energy is about 12,455-MW, with potential locations identified at Khambat & Kutch regions, and large backwaters where barrage technology could be used. The total theoretical potential of wave energy, according to preliminary estimates, is estimated to be about 40,000-MW. OTEC has a theoretical potential of 180,000-MW in India subject to technology evolution.
The tidal cycle occurs every 12 hours due to the gravitational force of the moon. The difference in water height from low and high tide is potential energy. Similar to hydropower, generated from dams, tidal water can be captured in a barrage across an estuary during high tide and forced through a hydro-turbine during low tide. The capital cost for tidal energy power plants is very high, due to high civil construction. To capture sufficient power, the height of hightide must be at least five meters greater than low tide. The Gulf of Cambay and Kutch are locations where potential exists.
Wave energy is generated by movement of a device floating on the ocean surface or moored to the ocean floor. Those that float on the surface have joints hinged together that bend with the waves. This kinetic energy pumps fluid through turbines and creates electric power. Stationary devices use pressure fluctuations produced in long tubes from the waves swelling up and down. This bobbing motion drives a turbine when critical pressure is reached. Other stationary platforms capture water from waves on their platforms. This water is allowed to runoff through narrow pipes that flow through a typical hydraulic turbine.
Marine current, known as the Gulf Stream, is ocean water moving in one direction. Kinetic energy can be captured from it and other tidal currents with submerged turbines similar to miniature wind turbines, in which movement of marine current moves rotor blades to generate electric power.
Ocean thermal energy conversion (OTEC)
OTEC uses ocean temperature differences from the surface to depths lower than 1,000 meters, to extract energy. A temperature difference of only 20°C can yield usable energy. Research is focused on OTEC technologies: closed cycle and open cycle. In the former, a working fluid, such as ammonia, is pumped through a heat exchanger and vaporized. This vaporized steam runs a turbine. Cold water from the depths of the ocean condenses the vapour back to a fluid, which is returned to the heat exchanger. In the open cycle system, warm surface water is pressurized in a vacuum chamber and converted to steam to run a turbine. The steam is then condensed using cold ocean water from the depths.
The objective of the technology programme is to accelerate and enhance support for the resource assessment and deployment of ocean energy in the country and to harness it for power generation. The technology programme is open to public and private sectors to carry out projects in India. Industry-led R&D proposals are invited from stakeholders, for solving problems in Indian conditions. Basic R&D is being looked after by the Ministry of Earth Sciences, and carried out at institutes such as the National Institute of Ocean Technology, Chennai.
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