Tidal Energy

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TIDAL ENERGYAANCHAL GUPTA 1RV07EC001

The Current Situation Tidal Energy is sustainable, clean, reliable, widely distributed renewable source of energy, and can offer significant benefits to many marine nations. Tidal Energy can be captured in an efficient and cost-effective way. Overall potential of 3000 giga-watts from movement of tides. Tidal energy projects are extremely site specific. The quality of the topography of the basin also needs to facilitate civil construction of the power plant. Only 40 sites around the world. Tidal Energy is not yet recognized as an energy resource that should receive support and funding for its development.

Introduction The daily rise and fall in the level of ocean water relative to the coastline is referred to as tide. Tides generated by the combination of the moon and sun s gravitational forces and the rotation of the earth The relative motion of the three bodies produces different tidal cycles which affect the range of the tides. The tidal range is increased substantially by local effects such as shelving, funneling, reflection and resonance. Greatest affect in spring when moon and sun combine forces Bays and inlets amplify the height of the tide For the tidal energy method to work effectively, the tidal difference should be at least 4m.

Introduction (Cont..) Environmental concerns exist mainly to do with higher silt formation at the shore and disruption to marine life near the tidal basin. Wave energy projects have lesser ecological impact than tidal wave energy projects but tidal energy projects are more predictable than those harnessing solar or wind energy, since occurrences of tides are fully predictable.

Origin The moon exerts a larger gravitational force on the earth, though it is much smaller in mass, because it is a lot closer than the sun. This force of attraction causes the oceans to bulge along an axis pointing towards the moon. Tides are produced by the rotation of the earth beneath this bulge in its watery coating, resulting in the rhythmic rise and fall of coastal ocean levels. The gravitational attraction of the sun also affects the tides similarly, but to a lesser degree. The oceans also bulge slightly towards the sun. Coastal areas experience two high and two low tides over a period of slightly above 24 hours .

Spring TideWhen the earth, moon and sun are positioned in a straight line i.e on the occasion of a full or new moon, the gravitational attractions are combined, resulting in very large spring tides.

Neap TideAt half moon, the sun and moon are positioned at right angles, resulting in lower neap tides.

Ocean Shore

Generating MethodsTidal power can be classified into three generating methods: Tidal stream generator TSGs make use of the kinetic energy of moving water to power turbines, in a similar way to wind turbines that use moving air. This method is gaining in popularity because of the lower cost and lower ecological impact compared to tidal barrages. Tidal barrage Tidal barrages make use of the potential energy in the difference in height (or head) between high and low tides. Barrages are essentially dams across the full width of a tidal estuary, and suffer from very high civil infrastructure costs, a worldwide shortage of viable sites and environmental issues.

Generating Methods Dynamic tidal power DTP is a theoretical generation technology that would exploit an interaction between potential and kinetic energies in tidal flows. It proposes that very long dams (for example: 30 50 km length) be built from coasts straight out into the sea or ocean, without enclosing an area. Tidal phase differences are introduced by the dam, leading to a significant water level differential (at least 2 3 meters) in shallow coastal seas featuring strong coast-parallel oscillating tidal currents such as found in the UK, China and Korea. Each dam would generate power at a scale of 6 - 15 GW.

How it Works?

First Generation, Barrage-Style Tidal Power Plants It involves building a dam, across a bay or estuary that has large differences in elevation between high and low tides. Water retained behind a dam at high tide generates a power head sufficient to generate electricity as the tide ebbs and water released from within the dam turns conventional turbines. Though they have proven very durable, barrage-style power plants are very expensive to build and are fraught with environmental problems from the accumulation of silt within the dam catchment area (requiring regular, expensive dredging). Accordingly, they are no longer considered.

First Generation, Barrage-Style Tidal Power Plants The basic elements of a barrage are caissons, embankments, sluices, turbines and ship locks. Sluices, turbines and ship locks are housed in caisson (very large concrete blocks). Embankments seal a basin where it is not sealed by caissons. The sluice gates applicable to tidal power are the flap gate, vertical rising gate, radial gate and rising sector. Sites in France (La Rance), Canada (Annapolis), and Russia Future sites possibly on Severn River in England, San Francisco bay.

First Generation, Barrage-Style Tidal Power Plants

Barrage Style Tidal Power Plant

Second-Generation Tidal Power Plants It use turbines to generate electricity via large current areas such as Cook Strait in New Zealand. Engineers have recently created two new kinds of devices to harness the energy of tidal currents (AKA tidal streams ) and generate renewable, pollution-free electricity. These new devices may be distinguished as Verticalaxis and Horizontal-axis models, determined by the orientation of a subsea, rotating shaft that turns a gearbox linked to a turbine with the help of large, slowmoving rotor blades. Both models can be considered a kind of underwater windmill.

Second-Generation Tidal Power Plants While horizontal-axis turbine prototypes are now being tested in northern Europe (the UK and Norway) a vertical-axis turbine has already been successfully tested in Canada More efficient because they allow for energy production on both the ebbing and surging tides One site has potential to equal the generating power of 3 nuclear power plants

Second-Generation Tidal Power Plants

Tidal Energy can be captured efficiently and inexpensively using the helical turbine

Schematic view of the helical turbine mounted in a frame.

Features of the Helical Turbine:Basic Concept designed for hydroelectric applications in free-flowing water operates in ocean, tidal, and river currents does not require expensive dams that can harm the environment

Features of the Helical TurbineOperation self-starting with flow as low as 0.6 m/s smooth-running rotates in same direction regardless of the direction of flow, making it ideal for tidal applications

Features of the Helical Turbine35% Efficiency

Features of the Helical TurbinePower increases 8 times when velocity doubles2500 2000 Power (watts) 1500 1000 500 0 0 1 2 3 4 5 6 7 8 9 10

I Knot = 1.69 ft/sec I M/sec = 3.28 ft/sec

Free Flow (Ft/sec)

Source: GCK Technology

Features of the Helical Turbine Installation Cost: dollars/kw14000 13000 12000 11000 10000 9000 8000 7000 6000 5000 4000 3000 2000 1000 0

Red: high estimate Blue: low estimate

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Source: GCK Technology, Inc.

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The Worldwide Distribution of Tidal Energy

Developing Nations that could receive significant benefits from Tidal Energy________________________________________

Indian Ocean: Comoros, Madagascar, Maldives, Seychelles. Asia: China, India, Indonesia, Korea, Philippines, Vietnam. Pacific Ocean: Fiji, Kiribati, Micronesia, Palau, Papua New Guinea, Samoa, Solomon Islands, Timor, Tuvalu, Vanuatu. Central and South America: Argentina, Brazil, Ecuador, Guyana, Panama, Surinam. Atlantic Ocean: Cape Verde. All coastal nations with tidal passes between coral reefs or offshore islands.

La Rance Tidal Power Station The world's first tidal power station located on the estuary of the Rance River, in Brittany, France. With a peak rating of 240 Megawatts, generated by its 24 turbines, it supplies 0.012% of the power demand of France. The annual output is approximately 600 GWh. The barrage is 750 m long, from Brebis point in the west to Briantais point in the east. The power plant portion of the dam is 332.5 m (1,091 ft) long. The tidal basin measures 22.5 km2(9 sq mi).

Aerial View of La Rance Tidal Power Station

Indian Context India being surrounded by sea on three sides has a high potential to harness tidal energy. The three most potential locations in this regard are Gulf of Cambay, Gulf of Kutch (west coast) and Ganges Delta, Sunderbans, West Bengal (east coast).

The total potential of tidal energy in India is estimated at 8,000 MW with Gulf of Cambay accounting for over 90 per cent.

Proposed Tidal Power Projects in India

Kachchh Tidal Power Project It was identified in 1970 by the CEA. More than twelve specialized organizations of Govt. of India and Govt. of Gujarat were involved in the field of investigations for sea bed analysis. The proposed tidal power scheme envisages an installation of 900 MW project biggest in the world, located in the Hansthal Creek. 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