Power Ministry approves proposal to declare Ocean Energy as Renewable Energy

The Ministry of Power and New & Renewable Energy (IC) has approved a proposal to declare ocean energy as Renewable Energy. The decision would give a boost to ocean energy in India. The Ministry has clarified that energy produced using various forms of ocean energy such as tidal, wave, ocean thermal energy conversion etc. shall be considered as Renewable Energy and shall be eligible for meeting the non-solar Renewable Purchase Obligations (RPO).

Renewable Purchase Obligation

Renewable Purchase Obligation is a mechanism by which the State Electricity Regulatory Commissions are obliged to purchase a certain percentage of power from renewable energy sources. RPO is being implemented throughout the country to create demand for renewable energy.

There are two categories in RPO:

• Non-Solar
• Solar

Further to address the mismatch of renewable energy resources in the States and their RPO requirements, Renewable Energy Certificates are issued. Obliged entities can fulfil their RPOs by purchasing RECs. The Renewable Energy Certificates are traded on the Indian Energy Exchange and the Power Exchange of India Ltd.

Ocean Energy

Oceans covers 70 per cent of the earth’s surface and represent an enormous amount of energy in the form of the wave, tidal, marine current and thermal gradient.

The total identified potential of Tidal Energy in India is about 12455 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 in India along the country’s coast is estimated to be about 40,000 MW. The OTEC has a theoretical potential of 180,000 MW in India subject to suitable technological evolution.

Ocean energy is currently under-utilized. Ocean energy is mostly exploited by just a few technologies: Wave, Tidal, Current Energy and Ocean Thermal Energy.

Tidal Energy 

The tidal cycle occurs every 12 hours due to the gravitational force of the moon. The difference in water height from low tide and high tide is potential energy. Similar to traditional 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 the high civil construction and high power purchase tariff.  To capture sufficient power from the tidal energy potential, the height of high tide must be at least five meters (16 feet) greater than low tide. The Gulf of Cambay and the Gulf of Kutch in Gujarat on the west coast have the locations in the country where the potential exists.

 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.

Wave conversion devices 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 wave energy conversion 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.

 Current Energy

Marine current is ocean water moving in one direction. This ocean current is known as the Gulf Stream. Tides also create currents that flow in two directions. 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

Ocean thermal energy conversion (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 focuses 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 vapour 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.