Over 70% of the Earth’s surface is covered by the Oceans and they are the storehouse of an enormous amount of renewable energy such as tidal, wave, thermal gradient and marine current. To harness these energies, numerous types of technologies are being developed throughout the world. Although there is a limited development presently, yet, the sector has a high growth potential, ability of fuelling the economic growth, reducing carbon footprints and generating huge employment opportunities along the coast as well as in the inland supply chains.
As the Indian government intends to accomplish the target of contemplating its Renewable energy & climate change objectives post 2022, it would be felicitous for exploring all the feasible avenues for stimulating innovation, fostering economic growth, generating employment opportunities and reducing carbon footprints. India has got the massive geographical advantage with more than 2000km long coast line along the South Indian Coast with estuaries & gulfs, where the difference in temperature remains above 20 degree Celsius throughout the year. This certifies that approximately 1.5 x106sq km of tropical water is within the Exclusive Economic Zone of India with 0.2 MW/km2 of power density. Tidal energy has the potentiality of generating 12455MW, with major potential locations being identified in the regions of Khambat & Kutch, and large backwaters where there are provisions of using barrage technology. It is estimated that wave energy has the potentiality of generating around 40000MW of energy along the coastline. However, it is less intensive from what is available in the northern & southern latitudes. OTEC or Ocean Thermal Energy Conversion has a theoretical potential of generating around 180000 MW of energy in the country subject to effective R&D and technological evolution.
Although, Ocean energy is under-utilized today but it is largely exploited by a handful of technologies – Tidal, Wave, Current Energy and Ocean Thermal Energy.
Tidal Energy – After every 12 hours due to the moon’s gravitational force, tidal cycle takes place. The potential energy which is generated is due to the difference in the height of the water between the high tide and the low tide. Just as hydropower is generated from the dams, tidal energy can be generated by capturing the tidal water during high tides in a barrage across an estuary and forced by a hydro-turbine at the time of low tides. Establishment of tidal power plants are very costly due to huge power purchase tariff and massive civil constructions. Moreover, for acquiring the sufficient power, the difference between the high & low tides’ height must be at 5 meters. The Gulf of Kutch and Gulf of Cambay in Gujarat on the western coast are perfect locations in India where the potential of tidal energy exists.
Wave Energy– Wave energy is the transport & trapping of energy of ocean surface waves for generating electricity. It is also known as ocean wave energy. It is generated by the movements of equipment either floating on the ocean surface or moored to the floor of the ocean. Unlike above mentioned tidal energy that uses the ebb & flow of the tides, the wave energy uses the surface water’s vertical movement which produces tidal waves. Wave conversion equipment which floats on the water surface maintain joints which are hinged with each other and form an arch with the waves. Fluid gets pumped by this kinetic energy through turbines and generates electricity. In other words, wave energy is the concentrated form of solar power which is created by the action of wind that passes over the ocean’s surface and can be used as renewable source of energy.
Current Energy– Marine current is referred as the ocean water flowing in one particular direction. Current energy technologies are known as hydrokinetic technologies that converts the kinetic energy of flowing water into electrical energy. The kinetic energy is captured from the ocean currents & tidal currents with underwater turbines which looks similar to miniature wind turbines. Just like the wind turbines, here the rotor blades are moved by the flowing marine currents for generating electricity.
Ocean Thermal Energy Conversion (OTEC)– OTEC or Ocean Thermal Energy Conversion uses the temperature difference between the surface of the ocean & its depth below 1000m for extracting energy. The disposable energy can only be extracted when the difference in temperature is 20°C. There are two kinds of OTEC plants, rather technologies used for extracting the thermal energy & converting it into electrical energy: Open cycle & closed cycle. In Closed cycle OTEC, a closed loop of pipeline having filled with fluid such as ammonia gets pumped with the help of a heat exchanger & vaporised. Other than ammonia, propane or any other low boiling refrigerant can also be used. The turbine is run by this vaporized steam. The freezing water found at the ocean beds helps in condensing the vapour to fluid where it arrives back to heat exchanger. On the other hand, inside a vacuum chamber the warm top water is pressurized for converting it to steam for running the turbine in Open cycle OTEC.
Advantages: OTEC is clean & green renewable energy which does not involve any burning of fossil fuels that neither produces greenhouse gases nor releases any toxic air pollutants. According to researches, OTEC helps in reducing over-reliance on fuels like petroleum, thereby decreasing the ‘collateral’ damages suffered by the word from an economy highly dependent on oil – including pollution in water from tanker spills & wars over oil. Secondly, OTEC is very useful power resource for tropical islands for making them self-sufficient in energy resources. OTEC can be highly beneficial for Andaman & Nicobar and Lakshadweep Islands. Thirdly, Open cycle OTEC can be useful in providing pure and useable ocean water. Fourthly, OTEC can be exercised for producing fuels like hydrogen – the electricity produced can be utilized for powering electrolysis plants capable of splitting seawater into oxygen and hydrogen that could be piped ashore and used for powering fuel cells used in electric cars. Fifthly, waste cooling water which is used by OTEC plant can be utilized in aquaculture, air conditioners and for refrigeration.
Disadvantages: The biggest issue faced by OTEC is that it is regarded to be relatively inefficient. According to the law of physics, heat engines should operate below 100% efficiency and as OTEC plant uses a relatively less temperature variation between its hot & cold fluids, results in in inadequate efficiency level. Secondly, OTEC requires high establishment cost due to enormous civil construction. Thirdly, suitable area for an OTEC plant is tropical seas where temperature gradients are relatively large. Fourthly, due to high human intervention in sea temperature balance, there remains a possibility rather tendency of having environmental impacts in the surrounding areas. Fifthly, pumping cold ocean bed water to the surfaces results in releasing carbon dioxide – the greenhouse gas highly responsible for global warming. However, the amount released is very less comparable to fossil-fuelled power plants. Lastly, huge on-shore OTEC plants might have environmental impacts on shorelines that are very often home to fragile & already menace ecosystems like coral reefs and mangroves.
Offshore Solar – Since more than 70% of the Earth’s surface is covered by Oceans, an immense amount of solar energy is received by them. Waves, deep ocean currents and winds are outcome of radiant energy of sun & differential heating of the oceans & Earth’s surface. Currently there are hardly any evidences of commercially operating offshore solar energy farms. Solar energy is green and renewable source of energy and hence if this could be harnessed effectively by using technologies like concentrating solar power and photonic technology, an enormous amount of clean electricity can be generated.
In India, nuclear energy are becoming unsustainable and its time that Ocean energy becomes its perfect substitute. Ocean energy has been declared as renewable source of energy by the Ministry of New and Renewable Energy. The ministry said that it would be ‘eligible for meeting the non-solar Renewable Purchase Obligations’. This was indeed much needed as 6780MW nuclear power plants of India had not even contributed to 3% of the country’s electricity generation. The cost of generating electricity from nuclear energy is becoming relatively costlier every day. The cost of electricity generated by the 22 existing reactors was approximately Rs. 2.80 a kWhr. However, establishing new plants that would cost Rs. 15-20cr per MW, will generate energy which could not be commercially sold below Rs. 7 a unit. Hence, nuclear power is becoming too expensive for the country.
Moreover, it takes almost a decade for a new nuclear power plant to be established therefore it is very difficult to predict the cost when the plant ultimately begins the production. At this stage, though ocean energy is also expensive, yet it is a better option over nuclear source of energy. It is a renewable source of energy, does not need fuels to create, incurs less maintenance cost, do not have big impacts on environment and most importantly once established it does not incurs much cost. Recently, it has engaged a massive global attention also. With the improvement in technology and scale-effect in days to come, ocean energy will surely gain a friendlier look. Moreover, solar and wind energy are now capable of standing on their own legs, hence government can now give those subsidies to ocean energy and set up plants in much less time than expected.