Ocean Wave Energy full report
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Ocean Wave Energy
The search of future power raises us to know about the powers like Ocean wave power.The developing countries like India has to think on it today or in future to become developed.
The content of this topic are mainly related to the basic study of ocean and its wave ,the ways to harness energy,the new technologies to convert this energy into electrical energy,its cost effectiveness,its effect on environment and the future market conditions for this energy.The hopes of tommorows world are mainly concentreted on ocean wave energy(O.W.E.)
Ocean wave energyâ„¢s different forms are discussed in the following topic with the techniques depends on it.it has huse capacity to save the world if we harness it properly at proper time.The different countries and national institutes also searching for its effectivness with economy.
First, we need to explain how waves are created. Wind is caused by differences in temperature due to the solar heating of the earth's atmosphere. When this wind skims over the sea, an interaction is caused in which energy is exchanged between the wind and the sea surface. At first, little ripples arise on the surface. Then, the wind that skims along these ripples causes higher air pressure at the front of the wave than at the back. As a result the ripples change into small waves. As this process continues, the waves become higher and the distance between the tops (wave length) becomes longer. The amount of converted energy depends on the wind speed, the time the wind blows over the waves, and the distance it covers. During a wave's voyage, it shapes into a more regular wave, commonly referred to as a swell. At ocean shores, swells are very regular and discernable, even when the sea is calm.
Wave energy, then, can be seen as a concentrated form of solar energy. During this process of conversion, the energy is concentrated more and more, up to a power level of over 100 kW per meter of wave front.
There is effectively no impact to the shoreline or to any sea life in the vicinity. Some of the oldest ocean energy technologies use tidal power. All coastal areas consistently experience two high and two low tides over a period of slightly greater than 24 hours. For those tidal differences to be harnessed into electricity, the difference between high and low tides must be at least five meters, or more than 16 feet. There are only about 40 sites on the Earth with tidal ranges of this magnitude. However conditions are good for tidal power generation in both the Pacific Northwest and the Atlantic Northeast regions.
Ocean energy mainly consists of the following 3 types;
1] Tidal power:-due to high and low tides over a day.
2] Ocean current:-they are due to temperature gradient in the different part of sea.
3] Surface waves;-These are the waves due to wind over the surface of a sea.
Generating technologies for deriving electrical power from the ocean include tidal power, wave power, ocean thermal energy conversion, Ocean currents, ocean winds and salinity gradients. Of these, the three well-developed technologies are tidal power, wave power and ocean thermal energy conversion.
Tidal power It requires large tidal differences. Ocean thermal energy conversion is limited to tropical regions,. Wave energy conversion takes advantage of the ocean waves caused primarily by interaction of winds with the ocean surface. Wave energy is an irregular and oscillating low-frequency energy source that must be converted to a 60-Hertz frequency before it can be added to the electric utility grid. Although many wave energy devices have been invented, only a small proportion have been tested and evaluated. Furthermore, only a few have been tested at sea, in ocean waves, rather than in artificial wave tanks. As of the mid-1990s, there were more than 12 generic types of wave energy systems. Some systems extract energy from surface waves.
Others extract energy from pressure fluctuations below the water surface or from the full wave. Some systems are fixed in position and let waves pass by them, while others follow the waves and move with them. Some systems concentrate and focus waves, which increases their height and their potential for conversion to electrical energy.
A wave energy converter may be placed in the ocean in various possible situations and locations. It may be floating or submerged completely in the sea offshore or it may be located on the shore or on the sea bed in relatively shallow water. A converter on the sea bed may be completely submerged, it may extend above the sea surface, or it may be a converter system placed on an offshore platform. Apart from wave-powered navigation buoys, however, most of the prototypes have been placed at or near the shore.
Ocean wave energy as renewable or non renewable energy:
The oceans have a tremendous amount of energy and are close to many if not most concentrated populations. Some believe that ocean power will provide a substantial amount of new renewable energy around the world. Difficulties arising from marine life attaching to energy systems in the seas require these to be easily cleanable.
Renewable ocean energy
The ocean presents a vast source of renewable energy in the form of winds, waves and tides. In addition, there is vast quantity of energy in the form of thermal difference which can be extracted. Several means of extracting energy from the ocean have been tried, some with limited success.
1. Ocean current energy
2. Ocean thermal energy conversion (OTEC)
3. Salinity gradient energy
4. Tidal power
5. Wave power
6. Wind power (offshore)
Non-renewable ocean energy
Oil and gas beneath the ocean floor are increasingly important sources of energy. An ocean engineer is concerned with all phases of discovering, producing, and delivering offshore petroleum resources, a complex and demanding task. Also of central importance is the development of new methods to protect marine wildlife and coastal regions against the undesirable side effects of offshore oil production.
Oceanography of the waves:-
Theory and principles of waves, how they work and what causes them
When the wind blows across the water, it changes the water's surface, first into ripples and then into waves. Once the surface becomes uneven, the wind has an ever increasing grip on it. Storms can make enormous waves, particularly if the wind, blows in the same direction for any length of time. Learn to understand the principles behind all surface waves.
¢ 1] Waves in the environment
. Waves cannot exist by them for they are caused by winds. Winds in turn are caused by differences in temperature on the planet, mainly between the hot tropics and the cold poles but also due to temperature fluctuations of continents relative to the sea.
Without waves, the winds would have only a very small grip on the water and would not be able to move it as much. The waves allow the wind to transfer its energy to the water's surface and to make it move. At the surface, waves promote the exchange of gases: carbon dioxide into the oceans and oxygen out. Currents and eddies mix the layers of water which would otherwise become stagnant and less conducive to life. Nutrients are thus circulated and re-used.
The large ocean currents transport warm water from the tropics to the poles and cold water the other way. They help to stabilise the planet's temperature and to minimise its extremes.
¢ 2] Wave motion
Anyone having watched water waves rippling outward from the point where a stone was thrown in should have noticed how effortlessly waves can propagate along the water's surface. Wherever we see water, we see its surface stirred by waves. Indeed, witnessing a lake or sea flat like a mirror, is rather unusual. Yet, as familiar we are with waves, we are unfamiliar with how water particles can join forces to make such waves. Waves are oscillations in the water's surface. For oscillations to exist and to propagate there must be a returning force that brings equilibrium... The oscillations that are passed to the air are different in that they travel in widening spheres outward. These traveling waves have a direction and speed in addition to their tone or timbre. In air their returning force is the compression of the air molecules. In surface waves, the returning force is gravity, the pull of the Earth. Hence the name 'gravity waves' for water waves.
. Water is a liquid and its molecules are allowed to move freely although they are placed closely together. In all these media, waves are propagated by compression of the medium. However, the surface waves between two media (water and air), behave very different and solely under the influence of gravity, which is much weaker than that of elastic compression, the method by which sound propagates. The specific volume of seawater changes by only about 4 thousands of 1 percent (4E-5) under a Pressure change of one atmosphere (1 kg/cm2). This may seem insignificant, but the Pacific Ocean would stand about 50m higher, except for compression of the water by virtue of its own weight, or about 22cm higher in the absence of the atmosphere. Since an atmosphere is about equal to a column of water 10m high, the force of gravity is about 43 times weaker than that of elastic compression.
In the diagram some familiar terms are shown. A floating object is observed to move in perfect circles when waves oscillate harmoniously sinus-like in deep water. If that object hovered in the water, like a water particle, it would be moving along diminishing circles, when placed deeper in the water. At a certain depth, the object would stand still. This is the wave's base, precisely half the wave's length. Thus long waves (ocean swell) extend much deeper down than short waves (chop). Waves with 100 meters between crests are common and could just stir the bottom down to a depth of 50m. Note that the depth of a wave has little to do with its height! But a wave's height contains the wave's energy, which is unrelated to the wave's length. Long surface waves travel faster and further than short ones. Note also that the forward movement of the water under a crest in shallow water is faster than the backward movement under its trough. By this difference, sand is swept forward towards the beach.
¢ 3] Waves and wind
On a perfectly calm sea, the wind has practically no grip. As it slides over the water surface film, it makes it move. As the water moves, it forms eddies and small ripples. Ironically, these ripples do not travel exactly in the direction of the wind but as two sets of parallel ripples, at angles 70-80º to the wind direction. The ripples make the water's surface rough, giving the wind a better grip. The ripples, starting at a minimum wave speed of 0.23 m/s, grow to wavelets and start to travel in the direction of the wind. At wind speeds of 4-6 knots (7-11 km/hr), these double wave fronts travel at about 30º from the wind. The surface still looks glassy overall but as the wind speed increases, the wavelets become high enough to interact with the air flow and the surface starts to look rough. The wind becomes turbulent just above the surface and starts transferring energy to the waves. The rougher the water becomes, the easier it is for the wind to transfer its energy. The waves become steep and choppy. Further away from the shore, the water's surface is not only stirred by the wind but also by waves arriving with the wind. These waves influence the motion of the water particles such that opposing movements gradually cancel out, whereas synchronizing movements are enhanced. The waves start to become more rounded and harmonious. Depending on duration and distance (fetch), the waves develop into a fully developed sea.
Waves entering shallow water
As waves enter shallow water; they slow down, grow taller and change shape. At a depth of half its wave length, the rounded waves start to rise and their crests become shorter while their troughs lengthen. Although their period (frequency) stays the same, the waves slow down and their overall wave length shortens. The 'bumps' gradually steeper and finally break in the surf when depth becomes less than 1.3 times their height. Note that waves change shape in depths depending on their wave length, but break in shallows relating to their height!
How high a wave will rise, depends on its wave length (period) and the beach slope. It has been observed that a swell of 6-7m height in open sea. Going back to the 'wave motion and depth' diagram showing how water particles move, we can see that all particles make a circular movement in the same direction. They move up on the wave's leading edge, forward on its crest, down on its trailing slope and backward on its trough. In shallow water, the particles close to the bottom will be restricted in their up and downward movements and move along the bottom instead.. The forward/backward movement over the sand creates ripples and disturbs it.
¢ 5]Wave reflection
Like sound waves, surface waves can be bent (refracted) or bounced back (reflected) by solid objects. Waves do not propagate in a strict line but tend to spread outward while becoming smaller. Where a wave front is large, such spreading cancels out and the parallel wave fronts are seen traveling in the same direction. Where a lee shore exists, such as inside a harbor or behind an island, waves can be seen to bend towards where no waves are. In the lee of islands, waves can create an area where they interfere, causing steep and hazardous seas. When approaching a gently sloping shore, waves are slowed down and bent towards the shore. When approaching a steep rocky shore, waves are bounced back, creating a 'confused sea' of interfering waves with twice the height and steepness
There are several methods of getting energy from waves, but one of the most effective works like a swimming pool wave machine in reverse. At a swimming pool, air is blown in and out of a chamber beside the pool, which makes the water outside bob up and down, causing waves. At a wave power station, the waves arriving cause the water in the chamber to rise and fall, which means that air is forced in and out of the hole in the top of the chamber. We place a turbine in this hole, which is turned by the air rushing in and out. The turbine turns a generator. A problem with this design is that the rushing air can be very noisy, unless a silencer is fitted to the turbine. The noise is not a huge problem anyway, as the waves make quite a bit of noise themselves. once you've built it, the energy is free, needs no fuel and produces no waste or pollution. One big problem is that of building and anchoring something that can withstand the roughest conditions at sea, yet can generate a reasonable amount of power from small waves. It's not much use if it only works during storms!
There are three basic ways to tap the ocean for its energy. We can use the ocean's waves, we can use the ocean's high and low tides, or we can use temperature differences in the water
Kinetic energy (movement) exists in the moving waves of the ocean. That energy can be used to power a turbine. In this simple example, to the right, the wave rises into a chamber. The rising water forces the air out of the chamber. The moving air spins a turbine which can turn a generator.
When the wave goes down, air flows through the turbine and back into the chamber through doors that are normally closed.
This is only one type of wave-energy system. Others actually use the up and down motion of the wave to power a piston that moves up and down inside a cylinder. That piston can also turn a generator.
Most wave-energy systems are very small. But, they can be used to power a warning buoy or a small light house.
Wave power devices extract energy directly from surface waves or from pressure fluctuations below the surface. Renewable energy analysts believe there is enough energy in the ocean waves to provide up to 2 terawatts of electricity. (A terawatt is equal to a trillion watts.)Wave power can't be harnessed everywhere.
Wave energy can be converted into electricity through both offshore and onshore systems.
¢ Offshore Systems
Offshore systems are situated in deep water, typically of more than 40 meters (131 feet). Sophisticated mechanisms”like the Salter Duck”use the bobbing motion of the waves to power a pump that creates electricity.
Specially built seagoing vessels can also capture the energy of offshore waves. These floating platforms create electricity by funneling waves through internal turbines and then back into the sea.
Onshore Systems
Oscillating water column
The oscillating water column consists of a partially submerged concrete or steel structure that has an opening to the sea below the waterline. It encloses a column of air above a column of water. As waves enter the air column, they cause the water column to rise and fall. This alternately compresses and depressurizes the air column. As the wave retreats, the air is drawn back through the turbine as a result of the reduced air pressure on the ocean side of the turbine.
2 Tapchan
The tapchan, or tapered channel system, consists of a tapered channel, which feeds into a reservoir constructed on cliffs above sea level. The narrowing of the channel causes the waves to increase in height as they move toward the cliff face. The waves spill over the walls of the channel into the reservoir and the stored water is then fed through a turbine.
3 Pendulor device
The pendulor wave-power device consists of a rectangular box, which is open to the sea at one end. A flap is hinged over the opening and the action of the waves causes the flap to swing back and forth. The motion powers a hydraulic pump and a generator.
Tides are 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. Only about 20 locations have good inlets and a large enough tidal range- about 10 feet- to produce energy economically. The simplest generation 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, also known as the ebb tide. There are two-way systems that generate electricity on both the incoming and outgoing tides.
Tidal barrages can change the tidal level in the basin and increase turbidity in the water. They can also affect navigation and recreation. Potentially the largest disadvantage of tidal power is the effect a tidal station can have on plants and animals in the estuaries.
There are currently two commercial sized barrages in operations. One is located in La Rance, France; the other is in Annapolis Royal , Nova Scotia , Canada .
The other ways to use tidal power is to use tidal turbines which are recent and more effective way.They has to place at sea-bed as shown in the figure.
Waves are caused by the wind blowing over the surface of the ocean. There is tremendous energy in the ocean waves. The total power of waves breaking around the worldâ„¢s coastlines is estimated at 2-3 million megawatts.
One way to harness wave energy is to bend or focus the waves into a narrow channel, increasing their power and size. The waves can then be channeled into a catch basin or used directly to spin turbines. There are no big commercial wave energy plants, but there are a few small ones. Small, on-shore sites have the best potential for the immediate future; they could produce enough energy to power local communities. Japan , which imports almost all of its fuel, has an active wave-energy program.
The energy from the sun heats the surface water of the ocean. In tropical regions, the surface water can be 40 or more degrees warmer than the deep water. This temperature difference can be used to produce electricity. The OTEC system must have a temperature difference of at least 25 degrees Celsius to operate, limiting use to tropical regions. Hawaii has experimented with OTEC since the 1970â„¢s. There is no large-scale operation of OTEC today. There are many challenges. First, the OTEC systems are not very energy efficient. Pumping water is a giant engineering challenge. Electricity must also be transported to land. It will probably be 10 to 20 years before the technology is available to produce and transmit electricity economically from OTEC systems.
Tidal Energy is a largely untapped, renewable ENERGY source based on lunar gravitation rather than solar radiation. The potential of tidal HYDROELECTRICITY has long been recognized. However, compared to river dams, tidal-power project and implimentations are very expensive, since massive structures must be built in a difficult saltwater environment. The relatively low head of water above the turbines restricts the capacity of individual generators to about 25-50 megawatts (MW = 106 watts); therefore, many machines are needed to produce a significant block of power. The machinery also has to withstand the rigours of salt-water operation.
For all this investment, the average electric power output is severely limited by the twice-daily ebb and flow of tides: average output of tidal electricity is less than 40% of the installed generating capacity; production of power from river dams typically averages 70-100% of installed capacity. Finally, the lunar cycle of 24 hours 50 minutes means the raw production of tidal energy moves in and out of phase with the normal, solar-oriented daily pattern of electrical consumption. Unlike the energy from river dams, the daily, monthly and annual availability of tidal energy is fully predictable, but it must be either stored or integrated with other sources of generation that can be adjusted to accommodate the fluctuations of tidal generation.
There are relatively few coastal locations in the world where the tidal range (i.e., the difference between high and low tides) is large enough to justify exploitation of the available tidal energy. Not only must there exist a sufficiently high tidal range (at least 5 m) for construction of an economically feasible plant, but the site should also include a natural bay which can store a large volume of seawater at high tide and be so situated within the estuary that the operation of the plant will not significantly change the tidal resonant system.
The world's most powerful tides occur in the upper reaches of the Bay of Fundy, where tidal ranges up to 17 m are not uncommon. UNGAVA BAY and estuaries along the coast of BC also exhibit fairly high tides. The coasts of Argentina , NW Australia, Brazil , France , India , Korea , the UK , the USSR and the American states of California , Maine and Alaska possess coastal configurations and sufficiently large tidal ranges to provide sites at which potentially large sources of tidal energy may be exploited. The aggregate total capacity of all potential tidal-power sites in the world is currently estimated at about one billion kilowatts, with an expected electrical-energy output of 2-3 trillion kilowatt-hours annually, i.e., 10 times Canada's present combined electrical output.
Recent development.
1) Terminator devices extend perpendicular to the direction of wave travel and capture or reflect the power of the wave. These devices are typically onshore or near shore; however, floating versions have been designed for offshore applications.
2) A point absorber is a floating structure with components that move relative to each other due to wave action (e.g., a floating buoy inside a fixed cylinder). The relative motion is used to drive electromechanical or hydraulic energy converters.
3) Attenuators are long multisegment floating structures oriented parallel to the direction of the waves. The differing heights of waves along the length of the device causes flexing where the segments connect, and this flexing is connected to hydraulic pumps or other converters.
4) Overtopping devices have reservoirs that are filled by incoming waves to levels above the average surrounding ocean. The water is then released, and gravity causes it to fall back toward the ocean surface. The energy of the falling water is used to turn hydro turbines. Specially built seagoing vessels can also capture the energy of offshore waves. These floating platforms create electricity by funneling waves through internal turbines and then back into the sea.
Device for converting wave energy into electrical energy
It is a floating device tethered with chains to piles driven to ocean bottom. The wave action raises the heavy partially buoyant piston that drives the overhead crankshaft by half turn. The receding wave drops the piston completing the balance half turn. One revolution is obtained for every wave. Using gear box and generator the current is produced continuously.
[2] Tidal stream generators
A relatively new technology, tidal stream generators draw energy from currents in much the same way as wind turbines. The higher density of water, 832 times the density of air, means that a single generator can provide significant power. Similar to wind power, selection of location is important for the tidal turbine. Tidal stream systems need to be located in areas with fast currents where natural flows are concentrated between obstructions, for example at the entrances to bays and rivers, around rocky points, headlands, or between islands or other land masses.
Shrouded tidal energy turbines
An emerging tidal stream technology is the shrouded tidal turbine enclosed in a Venturi shaped shroud or duct producing a sub atmosphere of low
Pressure behind the turbine, allowing the turbine to operate at higher efficiency in one case nearly 4 times higher power output than the same minus the shroud.
The Race Rocks Tidal Current Generator before installation.
This working example of a shrouded turbine in the photo was deployed by Clean Current Power at Race Rocks in southern British Columbia in 2006. It operates bi-directionally and has proven to be efficient in contributing to the integrated power system of Race Rocks.
Considerable commercial interest has been shown in shrouded tidal stream turbines due to the increased power output. They can operate in shallower slower moving water with a smaller turbine at sites where large turbines are restricted. Arrayed across a seaway or in fast flowing rivers shrouded turbines are easily cabled to a terrestrial base and connected to a grid or power produced supplied to a remote or island community. Alternatively the property of the shroud that produces an accelerated flow velocity across the turbine allows tidal flows formerly too slow for commercial use to be utilized for energy production.
. All tidal stream turbines constantly need to face at the correct angle to the water stream in order to operate
Types of shroud
Not all shrouded turbines are the same - the performance of a shrouded turbine varies with the design of the shroud. Not all shrouded turbines have undergone independent scrutiny of claimed performances, as companies closely guard their respective technologies, so quoted performance figures need to be closely scrutinized. Claims vary from a 15%-25% to a 384% improvement over the same turbine without the shroud. Shrouded turbines do not operate at maximum efficiency when the shroud does not intercept the current flow at the correct angle, which can occur as currents eddy and swirl, resulting in reduced operational efficiency. At lower turbine efficiencies the extra cost of the shroud must be justified, while at higher efficiencies the extra cost of the shroud has less impact on commercial returns. Similarly the added cost of the supporting structure for the shroud has to be balanced against the performance gained.
Connection to consumer (User frindly)
Cabled to the mainland, they can be grid-connected or can provide energy to remote communities where large civil infrastructures are not viable. Described as 'eco-benign', the slow R.P.M.of tidal stream turbine does not interfere with marine life or the environment and has little or no visual amenity impact. They are ideal for remote communities that are far from grid-connected infrastructure such as islands and rivers.
¢ A shroud of suitable geometry can increase the flow velocity across the turbine by 3 to 4 times the open or free stream velocity allowing the turbine to produce 3 to 4 times the power than the same turbine without the shroud.
¢ More power generated means greater returns on investment.
¢ The number of suitable sites is increased as sites formerly too slow for commercial development become viable.
¢ Where large cumbersome turbines are not suitable, smaller shrouded turbines can be sea-bed-mounted in shallow rivers and estuaries allowing safe navigation of the water ways.
¢ Hidden in a shroud, a turbine is less likely to be damaged by floating debris.
¢ Bio-fouling is also reduced as the turbine is shaded from natural light in shallow water.
¢ The increased velocities through the turbine effectively water-blast the shroud throat and turbine clean as organisms are unable to attach at increased velocities.
¢ Most shrouded turbines are directional, although one exception is the version off Southern Vancouver Island in British Columbia . One-direction fixed shrouds may not capture flow efficiently - in order for the shroud to produce maximum efficiency to use both flood and ebb tide they need to be yawed like a windmill on a pivot or turntable, or suspended under a pontoon on a marine swing mooring allowing the turbine to always face upstream like a wind sock.
¢ Shrouded turbines need to be below the mean low water level. This can be accomplished by marine monopiles to the sea/riverbed or suspended under a pontoon where inclement surface events don't buffet the turbine.
¢ Shrouded turbine loads are 3 to 4 times those of the open or free stream turbine, so a robust mounting system is necessary. However, this mounting system needs to be designed in such a way as to prevent turbulence being spilled onto the turbine or high-pressure waves occurring near the turbine and detuning performance. Streamlining the mounts and or including structural mounts in the shroud geometry perform two functions, that of supporting the turbine and providing a net benefit of 3 to 4 times the power output.
¢ Shrouded turbines may be hazardous to marine life, as fish or marine mammals can get sucked into the turbine blades, through the Venturi.
1] 2] 3]
Fig 1] Rance tidal power plant
2] A tidal barrage, including embankments, a ship lock and caissons housing a sluice and two turbines.
3] Severn Barrage and road link proposed in 1989.
With only three operating plants globally Rance River, Bay of Fundy and Kislaya Guba the barrage method of extracting tidal energy involves building a barrage as in the case of the Rance River in France. The barrage turbines generate as water flows in and out the estuary bay or river. These systems are similar to a hydro dam that produces Static Head or pressure head when the water level outside of the basin or lagoon changes relative to the water level inside, the turbines is 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 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.
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.
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 ebbs.
2] 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.
3] 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 favorable geographies, however, which are well suited to this type of scheme.
Bourneâ„¢s River Star (Patent Pending) Kinetic Energy System is a self-contained energy module composed of a stabilizer, energy absorber, energy transmission and mooring system and energy conversion and control system. It is designed to be sited in-river in interconnected arrays. River Star does not require a dam and reservoir;
instead it harvests hydropower along a section of a river.
Each River Star is connected at a depth of ten feet to the next River Star module by a high strength steel cable. Both ends of the cable are anchored into the shoreline at the same depth. The mooring cable includes the power transmission and control lines. River Starâ„¢s turbine is stabilized by the combination of the cable, the strut connected to a streamlined float and a rudder that maintains a precise attitude to the river current. The turbine drives a proprietary generator module.
Each River Starâ„¢s generating capacity of up to 50 kilowatts in a4 knot current (varies with current speed).
.In industrialized, populated river sites River Star can blend in as small islands, sand bars and rocky embankments. In rural sites vast numbers of arrays of River Star modules can be seeded across rivers. Farmers across the country who are already growing corn for ethanol and soybeans for biodiesel and leasing their land to wind farms may soon harvest the power of rivers that border their property.
Each TidalStar (Patent Pending) tidal power system uses a proprietary turbine design to produce approximately 50 kW at peak capacity. TidalStar has many advantages over current tidal power systems. It does not require tidal barrages, embankments, caissons or sluices. Environmentally neutral, TidalStar does not increase sediment, accumulate pollution nor affect the salinity of the water.
Tidal Star utilizes an interconnected array of energy absorbing modules placed across a tidal flow.
The Ocean Star (Patent Pending) wave power system represents a new approach to the complex problem of extracting energy from the world's oceans.
Current ocean power systems are dominated by the use of floating devices that
capture wave motion and convert it into electric energy through complex
mechanical and hydraulic means. Ocean Star captures the underlying pressure wave, amplified ocean wave to accelerate and collapse through a series of small turbine generators. This is an elegant and rugged solution to harnessing the power of waves, which is energy and cost efficient.
Several miles of Ocean Star arrays can be moored offshore to provide a
significant source of clean power while reducing the force of storm surges
upon fragile shoreline areas that are becoming increasingly stressed and unstable.
The Pelamis Wave Energy Converter
is a new technology that uses the motion of ocean surface waves to create electricity. The first prototype was installed at the European Marine Energy Centre in Orkney, Scotland,
2 of 3 P-750 engines in the harbour of Portugal
The Pelamis is an attenuating wave device designed for survivability at sea rather than highly efficient energy conversion. This means that rather than absorbing all of the energy available in a wave, it converts only a portion of that energy to electricity. This is principally so that the device can survive in dangerous storm conditions which could do considerable damage to a wave device attempting to absorb all the available energy.
The Pelamis device consists of a series of semi-submerged cylindrical sections linked by hinged joints. The wave-induced relative motion of these sections is resisted by hydraulic rams which pump high pressure oil through hydraulic motors via smoothing hydraulic accumulators. The hydraulic motors drive electrical generators to produce electricity. Power from all the joints is fed down a single umbilical cable to a junction on the sea bed. Several devices can be connected together and linked to shore through a single seabed cable.
Pelamis offers technological, economic and environmental advantages including:
¢ Survivability ˜built in™
¢ 100% available technology
¢ No maintenance carried out at offshore site
¢ No offshore intervention required
¢ 'Hands Free' operation
¢ Lowest kWh costs in the market
¢ High return potential
¢ Commercial track record
¢ Verified and insured
Current production machines are 140m long and 3.5m in diameters with 3 power conversion modules per machine. Each machine is rated at 750kW. The energy produced by Pelamis is dependent upon the conditions of the installation site. Depending on the wave resource, machines will on average produce 25-40% of the full rated output over the course of a year. Each machine can provide sufficient power to meet the annual electricity demand of approximately 500 homes.
¢ Blue Energy Technology
The Blue Energy ocean turbine acts as a highly efficient underwater vertical-axis windmill and has several remarkable advantages conferred upon it arising from the following basic science: Sea water is 832 times denser than air, and it is a non-compressible medium, therefore an 8-knot tidal current provides the equivalent force of a 390 km/hr wind (approximately). Developed by veteran aerospace engineer Barry Davis, the Blue Energy vertical-axis turbine represents two decades of Canadian research and development. Four fixed hydrofoil blades of the turbine are connected to a rotor that drives an integrated gearbox and electrical generator assembly. The turbine is mounted in a durable concrete marine caisson, which anchors the unit to the ocean floor, directs flow through the turbine further concentrating the resource supporting the coupler, gearbox, and generator above it. These sit above the surface of the water and are readily accessible for maintenance and repair. The hydrofoil blades employ a hydrodynamic lift principal that causes the turbine foils to move proportionately faster than the speed of the surrounding water. Computer optimized cross-flow design ensures that the rotation of the turbine is unidirectional on both the ebb and the flow of the tide.
The design of the Blue Energy Ocean Turbine requires no new construction methodology; it is structurally and mechanically straightforward. The transmission and electrical systems are similar to thousands of existing hydroelectric installations. Power transmission is by submersible kV DC cabling and safely buried in the ocean sediments with power drop points for coastal cities and connections to the continental power grid. A standardized high production design makes the system economic to build, install and maintain.
Renewable energy commercialization
¢ Cost
Renewable energy systems encompass a broad, diverse array of technologies, and the current status of these can vary considerably.
Some technologies are already mature and economically competitive (e.g. geothermal and hydropower), others need additional development to become competitive without subsidies. This can be helped by improvements to sub-components, such as electric mass production levels, and of the establishment of an emissions trading scheme and/or carbon tax which would attribute a cost to each unit of carbon emitted; thus reflecting the true cost of energy production
by fossil fuels which then could be used to lower the cost/kWh of these renewable energies
Market development of renewable heat energy
Renewable heat is the generation of heat from renewable sources. Much current discussion on renewable energy focuses on the generation of electrical energy, despite the fact that many colder countries consume more energy for heating than as electricity. The United Kingdom consumes 350 of electric power, and 840 TWh of gas and other fuels for heating annually. The residential sector alone consumes a massive 550 TWh of energy for heating, mainly in the form of gas.
Renewable electric power is becoming cheap and convenient enough to place it, in many cases, i.e.OCEAN WAVE ENERGY which is available in large amount but the cost to harness it is much more but day by day the newly developed schemes of o.w.e. Are becoming more efficient and can solve future problem.so most of developed contries has paid full attention on the different technologies related to o.w.e.They try to achieve the international market of energy by lowering the prizes and make them within reach of the average consumer. By contrast, the market for renewable heat is mostly inaccessible to domestic consumers due to inconvenience of supply, and high capital costs. Heating accounts for a large proportion of energy consumption, however a universally accessible market for renewable heat is yet to emerge. Solutions such as geothermal heat pumps may be more widely applicable, but may not be economical in all cases.
¢ OES could become a major contributor to electricity generation, particularly in remote regions with poor grid cover.
¢ OES could make a major contribution to the reduction of greenhouse gas emissions, but sustainable energy production will only be viable if the energy production costs can be reduced to or below the costs of energy from conventional sources. R&D will play a key role in achieving this.
The costs of present concepts are too high compared with conventional electricity generation. Prototypes have highlighted that installation difficulties are due more to logistic and civil engineering reasons than to the concept itself. Thus most of the existing technologies are still at the prototype testing stage and their availability, reliability and pre-commercial demonstration costs have not been validated.
¢ Component and infrastructure costs are the two major factors influencing OES installation economics. Sites that offer the best energy potential because of strong waves and currents are also difficult and dangerous to access, so there is a need for reliable and easily maintained components, which could limit on-site work.
¢ The long lead-up time between concept model testing in a wave tank and prototype testing in a marine environmental involves high technical and financial risks. There is a need for improved marine condition simulations to shorten the time needed to produce an operational system.
Cost reduction: This can be achieved through component improvements, extended lifetimes, and improved tool and complete system design and efficiency.
¢ Technical barriers
¢ High Cost: Research should be aimed at reducing both component and system costs.
¢ Deployment: Installation represents the highest cost and risk. So it is necessary to develop cheap and safe deployment procedures for both personnel and equipment.
¢ Design tools: Simulation tools should be developed to facilitate system design and development and reduce the time and cost needed to bring a concept to a marketable stage. This will require development of a complex marine model which could also be used in power generation capacity prediction, resource assessment and as a control strategy for autonomous operation.
¢ Power offtake systems: A new power offtake system is designed and tested for each new ocean energy conversion concept. Therefore there is a need to improve the common tools available to speed up their development.
¢ Major non-technical barriers
Energy market liberalization means that with increased competition, energy companies will be reluctant to invest in new, risky, sustainable technologies. The technology then needs to become socially and economically acceptable.
Research priorities
The main long-term objective for Ocean Energy Systems is to achieve an electricity generation cost equal to or below that for electricity from conventional sources. Target costs are 0.08‚¬/kWh by 2010 and 0.04‚¬/kWh by 2020. Total installation costs should be below 1000‚¬/kWe for economic viability. In order to achieve this research should be focused on:
- Autonomous operation with high degree of reliability and availability.
- Low operating and maintenance (O&M) costs and environmentally friendly life cycle systems.
- Reducing costs for existing shoreline concepts.
- Development of safe, reliable and easily deployed offshore systems.
- Advanced and reliable power offtake systems.
- Improved resource assessment and design tools.
- Development of new non-electric applications..
¢ Conclusions:
Wave power (and tidal power) is beginning to come into their own. They have many benefits, including:
¢ Renewable and sustainable resource
¢ Reduces dependence upon fossil fuels
¢ Produces no liquid or solid pollution
¢ Little visual impact
¢ Construction of large scale offshore devices results in new areas of sheltered water, attractive for fish, sea birds, seals and seaweed
¢ Present no difficulty to migrating fish (except tidal fences)
¢ Shelter the coast, useful in harbour areas or erosion zones
¢ Resource exists on a worldwide scale from deep ocean waters
¢ Short time scale between investing in the modular construction and benefiting from the revenue
Clearly there are still technical difficulties to overcome, but in the next few years, countries will begin to see wave power connected to national supplies. It will be a big market.
These are some of the challenges to deploying wave power devices:
¢ Efficiently converting wave motion into electricity; generally speaking, wave power is available in low-speed, high forces, and the motion of forces is not in a single direction. Most readily-available electric generators operate at higher speeds, and most readily-available turbines require a constant, steady flow.
¢ Constructing devices that can survive storm damage and saltwater corrosion; likely sources of failure include seized bearings, broken welds, and snapped mooring lines. Knowing this, designers may create prototypes that are so overbuilt that materials costs prohibit affordable production.
¢ High total cost of electricity; wave power will only be competitive when the total cost of generation is reduced. The total cost includes the primary converter, the power takeoff system, the mooring system, installation & maintenance cost, and electricity delivery costs.
Environmental impact and view
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.
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 to penetrate the water further, improving conditions for the phytoplankton. The changes propagate up the food chain, causing a general change in the ecosystem.
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.
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.
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, cavitations, etc.). Alternative passage technologies (fish ladders, fish lifts, 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
As with most renewable energy sources, wave devices have no emission during generation but the energy associated with the construction of the device does have small associated emissions
With careful siting, most of these impacts would be small and easily reversible.
¢ The energy is free - no fuel needed, no waste produced.
¢ Not expensive to operate and maintain.
¢ Can produce a great deal of energy.
¢ depends on the waves - sometimes you'll get loads of energy, sometimes nothing.
¢ Needs a suitable site, where waves are consistently strong.
¢ Some designs are noisy.
Note: Must be able to withstand very rough weather.
1] http://www.wikipedia.com
2] Renewable energy â„¢THE FUTUREâ„¢ by grseg clofer (volume 3)
3] ˜ New Ways of power™by alka datta
4] Site: http://www.patentstorm.com
5] Powerpedia.com
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