Introduction

Ocean can produce two types of energy: thermal energy from the sun's heat, and mechanical energy from the tides and waves.

Tidal Energy[i]

Tides are generated through a combination of forces exerted by the gravitational pull of the sun and the moon and the rotation of the earth. The relative motion of the three bodies produces different tidal cycles which affect the range of the tides. In addition, the tidal range is increased substantially by local effects such as shelving, funneling, reflection and resonance.

Energy can be extracted from tides by creating a reservoir or basin behind a barrage and then passing tidal waters through turbines in the barrage to generate electricity. Tidal energy is extremely site specific requires mean tidal differences greater than 4 meters and also favorable topographical conditions, such as estuaries or certain types of bays in order to bring down costs of dams etc.

Since India is surrounded by sea on three sides, its potential to harness tidal energy has been recognized by the Government of India.

Technology

Tidal Barrage[ii]

A way of converting the energy of tides into electric power. A tidal barrage works in a similar way to that of a hydroelectric scheme, except that the dam is much bigger and spans a river estuary. When the tide goes in and out, the water flows through tunnels in the barrage. The ebb and flow of the tides can be used to turn a turbine, or it can be used to push air through a pipe, which then turns a turbine.

Comprehensive Information on Tidal Technology

Commercial Status of Tidal Stream Devices (as on 2009)

Comprehensive List of Tidal Stream Devices

Potential of tidal energy in India[iii]

The most attractive locations are the Gulf of Cambay and the Gulf of Kachchh on the west coast where the maximum tidal range is 11 m and 8 m with average tidal range of 6.77 m and 5.23 m respectively. The Ganges Delta in the Sunderbans in West Bengal also has good locations for small scale tidal power development. The maximum tidal range in Sunderbans is approximately 5 m with an average tidal range of 2.97 m.

The identified economic tidal power potential in India is of the order of 8000-9000 MW with about 7000 MW in the Gulf of Cambay about 1200 MW in the Gulf of Kachchh and less than 100 MW in Sundarbans.

Proposed tidal power projects in India

Kachchh Tidal Power Project [iv]

• In, 1970, the CEA had identified this tidal project in the Gulf of Kachchh in Gujarat. The investigations were formally launched in 1982. Sea bed analysis and studies for preparation of feasibility report were of highly specialized and complex nature without precedence in the country. More than twelve specialized organizations of Govt. of India and Govt. of Gujarat were involved in the field of investigations. The techno-economic feasibility study has been completed in a very scientific and systematic manner and the feasibility report completed in 1988.

• The proposed tidal power scheme envisages an installation of 900 MW project biggest in the world, located in the Hansthal Creek, 25 Kms. from Kandla Port in Distt.. Kachchh of Gujarat State. It comprises of the following:

• The main tidal rockfill barrage of 3.25 Km length was proposed to be constructed across Hansthal Creek which will accommodate the power house, sluice gates and navigational lock.

• It envisages installation of 900 MW capacity comprising of 36 geared bulb type turbo-generators units of 25 MW each and 48 sluice gates each of 10 M. x 12 M. size would generate 1690 Gwh of energy annually. Unfortunately, this project execution has not been taken up so far because of unknown reasons.

Durgaduani Creek

• The country's first tidal power generation project is coming up at Durgaduani Creek of the Sundarbans. The 3.75 mw capacity Durgaduani Creek tidal energy project is a technology demonstration project and will span over an area of 4.5 km. (Oct 2008 data).

Tidal Barriers Problems Faced in Exploiting Tidal Energy

• Intermittent supply - Cost and environmental problems, particularly barrage systems are less attractive than some other forms of renewable energy.

• Cost - The disadvantages of using tidal and wave energy must be considered before jumping to conclusion that this renewable, clean resource is the answer to all our problems. The main detriment is the cost of those plants.

• The altering of the ecosystem at the bay - Damages like reduced flushing, winter icing and erosion can change the vegetation of the area and disrupt the balance. Similar to other ocean energies, tidal energy has several prerequisites that make it only available in a small number of regions. For a tidal power plant to produce electricity effectively (about 85% efficiency), it requires a basin or a gulf that has a mean tidal amplitude (the differences between spring and neap tide) of 7 meters or above. It is also desirable to have semi-diurnal tides where there are two high and low tides everyday. A barrage across an estuary is very expensive to build, and affects a very wide area - the environment is changed for many miles upstream and downstream. Many birds rely on the tide uncovering the mud flats so that they can feed. There are few suitable sites for tidal barrages.

• Only provides power for around 10 hours each day, when the tide is actually moving in or out.

• Present designs do not produce a lot of electricity, and barrages across river estuaries can change the flow of water and, consequently, the habitat for birds and other wildlife

• Expensive to construct

• Power is often generated when there is little demand for electricity 
  

• Limited construction locations

• Barrages may block outlets to open water. Although locks can be installed, this is often a slow and expensive process.

• Barrages affect fish migration and other wildlife- many fish like salmon swim up to the barrages and are killed by the spinning turbines.

• Fish ladders may be used to allow passage for the fish, but these are never 100% effective.

• Barrages may also destroy the habitat of the wildlife living near it

• Barrages may affect the tidal level - the change in tidal level may affect navigation, recreation, cause flooding of the shoreline and affect local marine life [v]

• Tidal plants are expensive to build
• They can only be built on ocean coastlines, which mean that for communities which are far away from the sea, it's useless.[vi]

Wave power

Ocean wave energy is captured directly from surface waves or from pressure fluctuations below the surface. Wave power systems convert the motion of the waves into usable mechanical energy which in lump can be used to generate electricity.

Waves are caused by wind blowing on the surface of the water. Whereas tidal power relies on the mass movement of the water body, waves act as a carrier for kinetic energy generated by the wind.

Technology[vii]

1. Float Or Buoy Systems that use the rise and fall of ocean swells to drive hydraulic pumps. The object can be mounted to a floating raft or to a device fixed on the ocean bed. A series of anchored buoys rise and fall with the wave. The movement is used to run an electrical generator to produce electricity which is then transmitted ashore by underwater power cables.

2. Oscillating Water Column Devices in which the in-and-out motion of waves at the shore enters a column and force air to turn a turbine. The column fills with water as the wave rises and empties as it descends. In the process, air inside the column is compressed and heats up, creating energy. This energy is harnessed and sent to shore by electrical cable.

3. Tapered Channel rely on a shore mounted structure to channel and concentrate the waves driving them into an elevated reservoir. Water flow out of this reservoir is used to generate electricity using standard hydropower technologies.

Potential of Wave energy in India

The potential along the 6000 Km of coast is about 40,000 MW. This energy is however less intensive than what is available in more northern and southern latitudes.

In India the research and development activity for exploring wave energy started at the Ocean Engineering Centre, Indian Institute of Technology, Madras in 1982. Primary estimates indicate that the annual wave energy potential along the Indian coast is between 5 MW to 15 MW per meter, thus a theoretical potential for a coast line of nearly 6000 KW works out to 40000-60000 MW approximately. However, the realistic and economical potential is likely to be considerably less.

Wave energy projects in India[viii][ix]

Commercial Status of Wave Technologies (as of 2009)

Comprehensive List of Wave Devices

 Barriers

• Depends on the waves – variable energy supply
• Needs a suitable site, where waves are consistently strong
• Some designs are noisy
• Must be able to withstand very rough weather
• Visual impact if above water or on shore
• Poses a possible threat to navigation from collisions due to the low profile of the wave energy devices above the water, making them undetectable either by direct sighting or by radar
• May interfere with mooring and anchorage lines with commercial and sport-fishing
• May degrade scenic ocean front views from wave energy devices located near or on the shore, and from onshore overhead electric transmission lines. 
  

Ocean Thermal Energy

The main objective of ocean thermal energy or Ocean Thermal Energy Conversion (OTEC) is to turn the solar energy trapped by the ocean into useable energy. OTEC systems use the ocean's natural thermal gradient”the fact that the ocean's layers of water have different temperatures to drive a power-producing cycle. As long as the temperature between the warm surface water and the cold deep water differs by about 20°C (36°F), an OTEC system can produce a significant amount of power.

Potential[x]

OTEC has a potential installed capacity of 180,000 MW in India.

Current OTEC Projects in India[xi] 

 Barriers

• OTEC-produced electricity at present would cost more than electricity generated from fossil fuels at their current costs.
• OTEC plants must be located where a difference of about 40 degrees Fahrenheit occurs year round.
• Ocean depths must be available fairly close to shore-based facilities for economic operation.
• Construction of OTEC plants and laying pipes in coastal waters may cause localized damage to reefs and near-shore marine ecosystems

Ocean energy research centres

Susi Global Research Centre Susi Global Research Centre located at Udupi is a tidal energy research centre.
Eco-friendly research projects of Susi Global Research Centre includes:

• Electricity generation from tidal (wave) energy.
• Electricity generation from gravitational force.
• Enhancement of power output of existing hydel projects.

Department of Ocean Engineering, Indian Institute Of Technology Chennai, India The Department has been functioning as an academic department since 1982.
The Department was created with the following objectives:

• To create infrastructure and expertise in order to carry out R & D work in areas of Ocean Engineering and related fields, which have direct relevance in the national context.
• To create educational and research opportunities at graduate and doctoral levels.
• To extend educational facilities and train the manpower from industry, R & D organizations and other educational institutions in order to enable them to carry out tasks in areas of Ocean Engineering.
• To collaborate with user organizations on need based problems.

Apex Bodies

Indian Ocean Research Group 
Centre for the Study of Geopolitics
Department of Political Science
Arts Block VI 
Panjab University - 160 014
India 
Telephone: +91 172 253 4757 
Telefax: +91 172 278 4695 

West Bengal Renewable Energy Development Agency
( Department of Power & NES, Govt. of West Bengal )
Bikalpa shakti Bhavan
J-1/10, EP & GP Block
Sector-V, Salt Lake
Kolkata - 700 091
West Bengal, India

[i] http://www.geda.org.in/other_sources/other_re_sources.htm

[ii] http://www.daviddarling.info/encyclopedia/T/AE_tidal_barrage.html

[iii] http://www.geda.org.in/other_sources/other_re_sources.htm

[iv] http://www.powertoday.co.in/fut4.html

[v] http://www.virtualsciencefair.org/2006/wong6j2/tidal.html

 [vi] http://www.accessv.com/~shawgrp/energy.htm

[vii] nptel.iitm.ac.in/courses/Webcourse.../pdf/.../student_slides08.pdf

[viii] http://www.niot.res.in/projects/desal/desalination_waveenergyin.php

[ix] www.ese.iitb.ac.in/.../Sceneario%20of%20renewable%20energy%20in%20india(R.B.).pdf –

 [x] http://www.ioes.saga-u.ac.jp/english/about-india-otec_e.html