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Here is a compilation of essays on ‘Tidal Energy’ for class 8, 9, 10, 11 and 12. Find paragraphs, long and short essays on ‘Tidal Energy’ especially written for school and college students.
Essay on Tidal Energy
Essay Contents:
- Essay on the Introduction to Tidal Energy
- Essay on the Meaning of Tidal Energy
- Essay on the Generation of Tidal Energy
- Essay on the Tidal Power Generation Methods
- Essay on the Barrage Method of Extracting Tidal Energy
- Essay on the Scenario of Tidal Energy in India
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Essay # 1. Introduction to Tidal Energy:
The tides rise and fall in eternal cycles. Tides are changes in the level of the oceans caused by the gravitational pull of the moon and sun and the rotation of the earth. Near shore water levels can vary up to 40 feet, depending on the season and local factors. Only about 20 locations have good inlets and a large enough tidal range—about 10 feet—to produce energy economically.
The generation of electricity from tides is similar to hydroelectric generation, except that tidal water flows in two directions. The simplest generating system for tidal plants involves a dam, known as a barrage, across an inlet. Sluice gates on the barrage allow the tidal basin to fill on the incoming high tides and to empty through the turbine system on the outgoing tide, known as the ebb tide.
Flood-generating systems that generate power from the incoming tide are possible, but are less favoured than ebb generating systems. Two-way generation systems, which generate electricity on both the incoming and ebb tides, are also possible.
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The construction of a tidal barrage in a inlet can change the tidal level in the basin. It can also have an effect on the sedimentation and turbidity of the water within the basin. In addition, navigation and recreation can be affected. A higher tidal level can cause flooding of the shoreline, which can affect the local marine food chain.
Potentially the largest disadvantage of tidal power is the effect a tidal station has on the plants and animals that live within an estuary. Since few tidal barrages have been built, very little is known about the full impact of tidal power systems on the local environment. In every case, it will depend on the local geography and marine ecosystem.
There are currently two commercial sized barrages in operation—a 240 MW turbine at La Ranee, France and a 16 MW plant at Annapolis Royal, Nova Scotia, Canada. Several other tidal power stations are being considered, including the Severn project in England.
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The United States has no tidal plants and only a few sites where tidal energy could be produced economically. France, England, Canada and Russia have much more potential. The keys are to lower construction costs, increase output and protect the environment.
Tidal fences can also harness the energy in the tides. A tidal fence has a vertical axis turbines mounted within a fence structure called a caisson that completely blocks a channel, forcing all of the water through it. Unlike barrage stations, tidal fences can be used in unconfined basins, such as in a channel between the mainland and a nearby offshore island or between two islands.
As a result, tidal fences have much less impact on the environment, because they do not require flooding the basin. They are also significantly cheaper to install. Tidal fences have the advantage of being able to generate electricity once each individual module is installed.
Tidal fences are not free of environmental and economic impacts, however, since the caisson can disrupt the movement of large marine animals and shipping. A 55 MW tidal fence is planned for the San Bernadino Strait in the Philippines.
Tidal turbines are a new technology that can be used in many tidal areas. Tidal turbines are basically wind turbines that can be located wherever there is strong tidal flow, as well as in river estuaries. Since water is about 800 times as dense as air, tidal turbines will have to be much sturdier than wind turbines. They will be heavier and more expensive to build, but will be able to capture more energy.
Essay # 2. Meaning of Tidal Energy:
Tidal power, also called tidal energy, is a form of hydropower that converts the energy of tides into electricity or other useful forms of power. The first large-scale tidal power plant (the Ranee Tidal Power Station) started operation in 1966.
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Although not yet widely used, tidal power has potential for future electricity generation. Tides are more predictable than wind energy and solar power. Among sources of renewable energy, tidal power has traditionally suffered from relatively high cost and limited availability of sites with sufficiently high tidal ranges or flow velocities, thus constricting its total availability.
However, many recent technological developments and improvements, both in design (e.g., dynamic tidal power, tidal lagoons) and turbine technology (e.g., new axial turbines, cross-flow turbines), are suggesting that the total availability of tidal power may be much higher than previously assumed, and that economic and environmental costs may be brought down to competitive levels.
Historically, tide mills have been used, both in Europe and on the Atlantic coast of North America. The earliest occurrences date from the Middle Ages, or even from Roman times.
France is currently the only country that has significantly harnessed tidal energy and has the largest tidal power station in the world. Built in 1966, the La Ranee tidal power station of Electricite de France (EdF) in Mont Saint Michel (Northern France) has a generating capacity of 240 MW. It has 24 bulb-type turbines, each of 10 MW rating.
The Severn Barrage is a proposed tidal power station to be built across the Bristol Channel (Severn Estuary) in UK. The River Severn has a tidal range of 14 m, making it perfect for tidal power generation. The Severn Barrage would involve the construction of a 16-km long barrage between Lavernock Point (Wales) and Brean Down (England). A total of 214 turbines each of 40 MW would be built into the barrage, making it a colossal of power plant of 8,560 MW of installed capacity with an average annual generation of 17 GWh.
Essay # 3. Generation of Tidal Energy:
Tidal power is the only form of energy which derives directly from the relative motions of the Earth-Moon system, and to a lesser extent from the Earth-Sun system. The tidal forces produced by the Moon and Sun, in combination with Earth’s rotation, are responsible for the generation of the tides.
Other sources of energy originate directly or indirectly from the Sun, including fossil fuels, conventional hydroelectric, wind, biofuels, wave power and solar. Nuclear energy is derived using radioactive material from the Earth, geothermal power uses the Earth’s internal heat which comes from a combination of residual heat from planetary accretion (about 20%) and heat produced through radioactive decay (80%).
Tidal energy is generated by the relative motion of the water which interact via., gravity. Periodic changes of water levels, and associated tidal currents, are due to the gravitational attraction by the Sun and Moon. The magnitude of the tide at a location is the result of the changing positions of the Moon and Sun relative to the Earth, the effects of Earth rotation, and the local shape of the sea floor and coastlines.
Because the Earth’s tides are caused by the tidal forces due to gravitational interaction with the Moon and Sun, and the Earth’s rotation, tidal power is practically inexhaustible and classified as a renewable energy source.
A tidal generator uses this phenomenon to generate electricity. The stronger the tide, either in water level height or tidal current velocities, the greater the potential for tidal electricity generation.
Tidal movement causes a continual loss of mechanical energy in the Earth-Moon system due to pumping of water through the natural restrictions around coastlines, and due to viscous dissipation at the seabed and in turbulence. This loss of energy has caused the rotation of the Earth to slow in the 4.5 billion years since formation.
During the last 620 million years the period of rotation has increased from 21.9 hours to the 24 hours we see now; in this period the Earth has lost 17% of its rotational energy. While tidal power may take additional energy from the system, increasing the rate of slowdown, the effect would be noticeable over millions of years only, thus being negligible.
Essay # 4. Tidal Power Generation Methods:
Tidal power can be classified into three generating methods:
i. Tidal stream systems make use of the kinetic energy of moving water to power turbines, in a similar way to windmills that use moving air. This method is gaining in popularity because of the lower cost and lower ecological impact compared to barrages.
ii. 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.
iii. Dynamic tidal power exploits a combination of potential and kinetic energy by constructing long dams of 30-50 km in length from the coast straight out into the sea or ocean, without enclosing an area. Both the obstruction of the tidal flow by the dam – as well as the tidal phase differences introduced by the presence of the dam (which is not negligible in length as compared to the tidal wavelength) – leads to hydraulic head differences along the dam.
Turbines in the dam are used to convert power (6-15 GW per day). In shallow coastal seas featuring strong coast-parallel oscillating tidal currents (common in the UK, China and Korea), a significant water level differential (2-3 meter) will appear between both sides of the dam.
Modern advances in turbine technology may eventually see large amounts of power generated from the ocean, especially tidal currents using the tidal stream designs but also from the major thermal current systems such as the Gulf Stream, which is covered by the more general term marine current power.
Tidal stream turbines may be arrayed in high-velocity areas where natural tidal current flows are concentrated such as the west and east coasts of Canada, the Strait of Gibraltar, the Bosporus, and numerous sites in Southeast Asia and Australia. Such flows occur almost anywhere where there are entrances to bays and rivers, or between land masses where water currents are concentrated.
The various types of turbine used in tidal power generation are:
i. Axial turbine.
ii. Vertical and horizontal axis cross-flow turbines.
iii. Oscillating devices using aerofoils.
iv. Venturi effect.
Turbine Power:
Various turbine designs have varying efficiencies and therefore varying power output. If the efficiency of the turbine “ξ” is known the equation below can be used to determine the power output of a turbine.
The energy available from these kinetic systems can be expressed as:
where, ξ = the turbine efficiency
P = the power generated (in watts)
ρ = the density of the water (seawater is 1025 kg/m3)
A = the sweep area of the turbine (in m2)
V = the velocity of the flow
Relative to an open turbine in free stream, depending on the geometry of the shroud shrouded turbines are capable of as much as 3 to 4 times the power of the same turbine rotor in open flow.
Resource Assessment:
While initial assessments of the available energy in a channel have focus on calculations using the kinetic energy flux model, the limitations of tidal power generation are significantly more complicated.
For example, the maximum physical possible energy extraction from a strait is given by:
P= 0.221 ρg ΔHmax Qmax
where, ρ = the density of the water (seawater is 1025 kg/m3)
g = gravitational acceleration (9.81 m/s2)
ΔHmax = maximum differential water surface elevation across the channel
Qmax = maximum volumetric flow rate though the channel.
Essay # 5. Barrage Method of Extracting Tidal Energy:
The barrage method of extracting tidal energy involves building a barrage across a bay or river. Turbines installed in the barrage wall generate power as water flows in and out of the estuary basin, bay, or river. These systems are similar to a hydro dam that produces Static Head or pressure head (a height of water pressure). When the water level outside of the basin or lagoon changes relative to the water level inside, the turbines are able to produce power.
The basic elements of a barrage are caissons, embankments, sluices, turbines, and ship locks. Sluices, turbines, and ship locks are housed in caissons (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.
Only a few such plants exist. The largest is the Ranee Tidal Power Station, on the Ranee river, in France, which has been operating since 1966, and generates 240MW. Smaller plants include one on the Bay of Fundy, and another across a tiny inlet in Kislaya Guba, Russia). A number of proposals have been considered for a Severn barrage across the River Severn, from Brean Down in England to Lavernock Point near Cardiff in Wales.
Barrage systems are affected by problems of high civil infrastructure costs associated with what is in effect a dam being placed across estuarine systems, and the environmental problems associated with changing a large ecosystem.
The tidal power scheme may be design to operate in following modes:
1. Ebb Generation:
The basin is filled through the sluices until high tide. Then the sluice gates are closed. (At this stage there may be ‘Pumping’ to raise the level further). The turbine gates are kept closed until the sea level falls to create sufficient head across the barrage, and then are opened so that the turbines generate until the head is again low.
Then the sluices are opened, turbines disconnected and the basin is filled again. The cycle repeats itself. Ebb generation (also known as outflow generation) takes its name because generation occurs as the tide changes tidal direction.
2. Flood Generation:
The basin is filled through the turbines, which generate at tide flood. This is generally much less efficient than ebb generation, because the volume contained in the upper half of the basin (which is where ebb generation operates) is greater than the volume of the lower half (filled first during flood generation).
Therefore the available level difference important for the turbine power produced between the basin side and the sea side of the barrage, reduces more quickly than it would in ebb generation. Rivers flowing into the basin may further reduce the energy potential, instead of enhancing it as in ebb generation. Of course this is not a problem with the ‘lagoon’ model, without river inflow.
3. Pumping:
Turbines are able to be powered in reverse by excess energy in the grid to increase the water level in the basin at high tide (for ebb generation). This energy is more than returned during generation, because power output is strongly related to the head.
If water is raised 2 ft (61 cm) by pumping on a high tide of 10 ft (3 m), this will have been raised by 12 ft (3.7 m) at low tide. The cost of a 2 ft rise is returned by the benefits of a 12 ft rise. This is since the correlation between the potential energy is not a linear relationship, rather, is related by the square of the tidal height variation.
4. Two-Basin Schemes:
Another form of energy barrage configuration is that of the dual basin type. With two basins, one is filled at high tide and the other is emptied at low tide. Turbines are placed between the basins. Two-basin schemes offer advantages over normal schemes in that generation time can be adjusted with high flexibility and it is also possible to generate almost continuously.
In normal estuarine situations, however, two-basin schemes are very expensive to construct due to the cost of the extra length of barrage. There are some favourable geographies, however, which are well suited to this type of scheme.
5. Environmental Impact:
The placement of a barrage into an estuary has a considerable effect on the water inside the basin and on the ecosystem. Many governments have been reluctant in recent times to grant approval for tidal barrages. Through research conducted on tidal plants, it has been found that tidal barrages constructed at the mouths of estuaries pose similar environmental threats as large dams.
The construction of large tidal plants alters the flow of saltwater in and out of estuaries, which changes the hydrology and salinity and possibly negatively affects the marine mammals that use the estuaries as their habitat The La Ranee plant, off the Brittany coast of northern France, was the first and largest tidal barrage plant in the world. It is also the only site where a full-scale evaluation of the ecological impact of a tidal power system, operating for 20 years, has been made.
French researchers found that the isolation of the estuary during the construction phases of the tidal barrage was detrimental to flora and fauna, however; after ten years, there has been a “variable degree of biological adjustment to the new environmental conditions”.
Some species lost their habitat due to La Ranee’s construction, but other species colonized the abandoned space, which caused a shift in diversity. Also as a result of the construction, sandbanks disappeared, the beach of St. Servan was badly damaged and high-speed currents have developed near sluices, which are water channels controlled by gates.
6. Turbidity:
Turbidity (the amount of matter in suspension in the water) decreases as a result of smaller volume of water being exchanged between the basin and the sea. This lets light from the Sun penetrate the water further, improving conditions for the phytoplankton. The changes propagate up the food chain, causing a general change in the ecosystem.
7. Tidal Fences and Turbines:
Tidal fences and turbines can have varying environmental impacts depending on whether or not fences and turbines are constructed with regard to the environment. The main environmental impact of turbines is their impact on fish. If the turbines are moving slowly enough, such as low velocities of 25-50 rpm, fish kill is minimalized and silt and other nutrients are able to flow through the structures.
For example, a 20 kW tidal turbine prototype built in the St. Lawrence Seaway in 1983 reported no fish kills Tidal fences block off channels, which makes it difficult for fish and wildlife to migrate through those channels.
In order to reduce fish kill, fences could be engineered so that the spaces between the caisson wall and the rotor foil are large enough to allow fish to pass through. Larger marine mammals such as seals or dolphins can be protected from the turbines by fences or a sonar sensor auto-breaking system that automatically shuts the turbines down when marine mammals are detected.
Overall, many researchers have argued that while tidal barrages pose environmental threats, tidal fences and tidal turbines, if constructed properly, are likely to be more environmentally benign. Unlike barrages, tidal fences and turbines do not block channels or estuarine mouths, interrupt fish migration or alter hydrology, thus, these options offer energy generating capacity without dire environmental impacts.
8. Salinity:
As a result of less water exchange with the sea, the average salinity inside the basin decreases, also affecting the ecosystem. ‘Tidal Lagoons’ do not suffer from this problem.
9. Sediment Movements:
Estuaries often have high volume of sediments moving through them, from the rivers to the sea. The introduction of a barrage into an estuary may result in sediment accumulation within the barrage, affecting the ecosystem and also the operation of the barrage.
10. Fish:
Fish may move through sluices safely, but when these are closed, fish will seek out turbines and attempt to swim through them. Also, some fish will be unable to escape the water speed near a turbine and will be sucked through. Even with the most fish-friendly turbine design, fish mortality per pass is approximately 15% (from pressure drop, contact with blades, cavitation, etc.).
Alternative passage technologies (fish ladders, fish lifts, fish escalators etc.) have so far failed to solve this problem for tidal barrages, either offering extremely expensive solutions, or ones which are used by a small fraction of fish only. Research in sonic guidance of fish is ongoing. The Open-Centre turbine reduces this problem allowing fish to pass through the open centre of the turbine.
Recently a rim of the river type turbine has been developed in France. This is a very large slow rotating Kaplan type turbine mounted on an angle. Testing for fish mortality has indicated fish mortality figures to be less than 5%. This concept also seems very suitable for adaption to marine current/tidal turbines.
Essay # 6. Scenario of Tidal Energy in India:
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. Tidal energy is a clean mechanism and does not involve the use of fossil fuels. However, environmental concerns exist mainly to do with higher silt formation at the shore (due to preventing tides from reaching the shore and washing away silt) and disruption to marine life near the tidal basin.
Wave energy projects have lesser ecological impact than tidal wave energy projects. In terms of reliability, tidal energy projects are believed to be more predictable than those harnessing solar or wind energy, since occurrences of tides are fully predictable.
Since India is surrounded by sea on three sides, its potential to harness tidal energy has been recognized by the Government of India. Potential sites for tidal power development have already been located. The most attractive locations are the Gulf of Cambay and the Culf 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.
The country’s first tidal power generation project is coming up at Durgaduani Creek of the Sundarbans. National Hydro-electric Power Corporation (NHPC) and West Bengal Renewable Energy.
Development Agency (WBREDA) will jointly set up India’s first tidal power plant on Durgaduani Creek in the Sunderbans at an estimated cost of Rs 50 crore. The project is expected to be commissioned by 2010.
The project comprises two barrages to be built across the upstream and downstream ends of the Durgaduani creek which runs between the Gosaba and Bali-Bijoynagar islands and connects Bidyadhari and Gomti rivers.
France is currently the only country that has significantly harnessed tidal energy and has the largest tidal power station in the world. Built in 1966, the La Ranee tidal power station of Electricite de France (EdF) in Mont Saint Michel (northern France) has a generating capacity of 240 MW. It has 24 bulb-type turbines, each of 10 MW rating. The Severn Barrage is a proposed tidal power station to be built across the Bristol Channel (Severn Estuary) in UK.
The River Severn has a tidal range of 14m, making it perfect for tidal power generation. The Severn Barrage would involve the construction of a 16-km long barrage between Lavernock Point (Wales) and Brean Down (England). A total of 214 turbines each of 40 MW would be built into the barrage, making it a colossal of power plant of 8,560 MW of installed capacity with an average annual generation of 17 GWh.