About Ocean Energy
About Ocean Energy:
- Oceans cover 70 percent of the earth’s surface and represent an enormous amount of energy in the form of wave, tidal, marine current and thermal gradient.
- Deployment of ocean energy is currently limited but the sector has the potential to grow, fuelling economic growth, reduction of carbon footprint and creating jobs not only along the coasts but also inland along its supply chains.
Technologies exploring Ocean Energy:
- Tidal Energy
- Tidal energy is any form of renewable energy in which tidal action in the oceans is converted to electric power.
- 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.
- Tidal water can be captured in a barrage across an estuary during high tide and forced through a hydro-turbine during low tide.
- Examples: The Gulf of Cambay and the Gulf of Kutch in Gujarat on the west coast have the locations in the country where potential exists.
- Identified Potential of Tidal Energy : 12455 MW, with potential locations identified at Khambat & Kutch regions, and large backwaters, where barrage technology could be used.
- Tidal energy is considered as an intermittent source of energy, as it can only provide electricity when the tide surges, which happen about approximately 12 hours per day on average.
- Tidal energy facilities need to be constructed close to land, which is also the place where technological solutions that come with them are being worked on.
- The capital cost for tidal energy power plants is very high due to 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.
- Wave Energy
- Wave power converts the periodic up-and-down movement of the oceans waves into electricity by placing equipment on the surface of the oceans that captures the energy produced by the wave movement and converts this mechanical energy into electrical power.
- Wave energy is generated by the movement of a device either floating on the surface of the ocean or moored to the ocean floor.
- Different techniques for converting wave energy to electric includes:
- 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.
- Identified Potential of Wave Energy in India along the country’s coast: about 40,000 MW .This energy is however less intensive than what is available in more northern and southern latitudes.
- Wave energy conversion devices are location dependent requiring suitable sites were the waves are consistently strong.
- Intermittent power generation as the waves come in intervals and does not generate power during calm periods.
- Offshore wave energy devices can be a threat to navigation that cannot see or detect them by radar.
- High power distribution costs to send the generated power from offshore devices to the land using long underwater cables.
- They must be able to withstand forces of nature resulting in high capital, construction and maintenance costs.
- Visual impact of wave energy conversion devices on the shoreline and offshore floating buoys or platforms is also not good, which may impact tourism.
- Ocean Current Energy
- Ocean current energy can be harnessed using underwater turbines, also known as tidal turbines, to generate power.
- It is location specific as it need Ocean current velocity to be fast, large and stable ocean current.
- Equipment and suspensions corrosion caused by seawater.
- The extremely high cost of installing and maintaining underwater turbines.
- Opposition from trawler fishermen, who claim that the turbines compete with their fishing areas.
- Ocean Thermal Energy Conversion (OTEC)
- Ocean Thermal Energy Conversion (OTEC) is a process that can produce electricity by using the temperature difference between deep cold ocean water and warm tropical surface waters. A temperature difference of only 20°C can yield usable energy.
- OTEC plants pump large quantities of deep cold seawater and surface seawater to run a power cycle and produce electricity.
Types of OTEC technologies:
- a) Open Cycle: 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.
- b) Closed 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.
- Potential in India : OTEC has a theoretical potential of 180,000 MW in India , “subject to suitable technological evolution
- Capital investment is very high.
- Due to small temperature difference in between the surface water and deep water, conversion efficiency is very low about 3-4%.
- Low efficiency of these plants coupled with high capital cost and maintenance cost makes them uneconomical for small plants.
Present Status of Ocean Energy technologies in India:
- As on date, India does not have any installed ocean energy capacit.
- Most types of technologies are currently at pre-research and development (R&D) or demonstration stage or the initial stage of commercialisation.
- Basic R&D is being looked after by the ministry of earth sciences (National Institute of Ocean Technology, Chennai).
- The MNRE intends to support demonstration projects of proven technologies and as approved by expert committee constituted by the MNRE.
- The Ministry of New and Renewable Energy has clarified that energy produced using various forms of ocean energy such as tidal, wave, ocean thermal energy conversion among others shall be considered as renewable energy .
Significance of the move:
- Various forms of Ocean energy shall be eligible for meeting the non-solar Renewable Purchase Obligations (RPO)
What is a Renewable Purchase Obligation (RPO)?
- RPO 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.
- RPO is of two categories
- Non Solar
- The proportion is fixed by state power regulators.
Renewable Energy Certification (REC)
- RECs are aimed at addressing the mismatch of renewable energy resources in the States and their RPO requirements
- The discoms can also buy renewable energy certificates in lieu of mandated clean energy supplies, from the developers or renewable power generators.
- In line with RPOs there are two categories of Renewable Energy Certificates (RECs) – Solar & Non-Solar.
- Solar RECs include both PV and CSP technologies.
- Non-solar RECs include renewable energy technologies such as biomass, wind, biofuel, cogeneration & small hydro and now also includes Ocean energy technologies.