POWER GENERATION FROM SEA WAVES
S.K. ANSARI AND SEEMA ANSARI
Jan 17 - 23, 2011
Wave energy is, in effect, a stored and concentrated form of solar energy, since the winds that produce waves are caused by pressure differences in the atmosphere arising from solar radiation. Waves transmit this energy thousands of miles with minimal loss. Wave size is a function of the wind's speed.
The above examples have three things in common. First, in each case the disturbance travels, or propagates, with a definite speed through medium. This speed is called the speed of propagation, or simply wave speed. Second, the medium itself does not travel through space; its individual particles undergo back-and-forth or up-and-down motions around their equilibrium positions. Third, to set any of these systems into motion, we have to put in energy by doing mechanical work on the system. The wave motion transports this energy from one region of the medium to another. Waves transport energy, but not matter, from one region to another.
The total power released by waves breaking along the world's coastlines is estimated at 2-3 million megawatts, equivalent to several thousand large power plants. Although this vast amount of energy is spread over thousands of miles of coasts, in favorable locations, the energy density can average 65 megawatts per mile of coastline. Favorable wave energy sites are generally western coastlines facing the open ocean such as those in North America and Northern Europe.
NEW METHOD FOR CONVERTING SEA WAVE ENERGY
High force of sea waves is a huge renewable energy resource and sea waves will play an important role in tomorrow's electricity production. There are many methods present for converting sea wave energy to continuously crank shaft motive force by a new apparatus named engine for producing energy from sea waves. Thereby, this apparatus can be used for producing AC electricity from sea waves, which are also economically important in sea wave energy converting. Besides, this apparatus generates positive moment (crankshaft moment) from sea wave and there are other devices to produce electricity from the tidal current mechanism.
Every wave motion has energy associated with it; the energy that we receive from sunlight and the destructive effect of ocean surf and earthquakes bear this out. To produce any of the wave motions either in the sea or ocean or in the ponds, a force to a portion is applied to the wave medium.
HOW TIDAL POWER PLANTS WORK
The power of the rise and fall of the sea level or tidal power can be harnessed to generate electricity. Tidal power traditionally involves erecting a dam across the opening to a tidal basin. The dam includes a sluice that is opened to allow the tide to flow into the basin; the sluice is then closed, and as the sea level drops, traditional hydropower technologies can be used to generate electricity from the elevated water in the basin. Some researchers are also trying to extract energy directly from tidal flow streams.
The energy potential of tidal basins is large - the largest facility, the La Rance station in France, generates 240 megawatts of power, making enough energy from tides to power 240,000 homes.
Currently, France is the only country that successfully uses this power source. French engineers have noted that if the use of tidal power on a global level is brought to high enough levels, the Earth would slow its rotation by 24 hours every 2,000 years.
THREE WAYS OF USING THE TIDAL POWER OF THE OCEAN
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.
1. WAVE ENERGY
Kinetic energy (movement) exists in the moving waves of the ocean. That energy can be used to power a turbine. In this simple example, 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. The streamlines of air are closer together over a crest and the air moves faster. It follows from Bernoulli's theorem that the air pressure is reduced, so the amplitude increases and waves are generated. As a wave crest collapses, the neighboring elements of fluid are displaced and forced to rise above the equilibrium level.
The motion of the fluid beneath the surface decays exponentially with depth. About 80 per cent of the energy in a surface wave is contained within a quarter of a wavelength below the surface. Thus, for a typical ocean wavelength of 100 m, this layer is about 25 m deep. We now derive an expression for the speed of a surface wave using intuitive physical reasoning.
2. TIDAL ENERGY
Another form of ocean energy is called tidal energy. When tides come into the shore, they can be trapped in reservoirs behind dams. Then when the tide drops, the water behind the dam can be let out just like in a regular hydroelectric power plant.
In order for this to work well, you need large increases in tides. An increase of at least 16 feet between low tide to high tide is needed. There are only a few places where this tide change occurs around the earth. Some power plants are already operating using this idea.
3. OCEAN THERMAL ENERGY
The final ocean energy idea uses temperature differences in the ocean. If you ever went swimming in the ocean and dove deep below the surface, you would have noticed that the water gets colder the deeper you go. It's warmer on the surface because sunlight warms the water. But, below the surface, the ocean gets very cold. That's why scuba divers wear wet suits when they dive down deep. Their wet suits trap their body heat to keep them warm.
Power plants can be built to use this difference in temperature to make energy. A difference of at least 38 degrees Fahrenheit is needed between the warmer surface water and the colder deep ocean water.
Using this type of energy source is called Ocean Thermal Energy Conversion or OTEC. It is being used in both Japan and in Hawaii in some demonstration projects. The generation of tidal wave energy is an entirely clean process. It does not involve the use of any greenhouse gases that lead to global warming. Some generators of tidal wave power work in a similar way to wind energy generators, and they are called tidal turbines. The generators of tidal wave power are placed offshore into a tidal stream, using a tidal turbine for tidal power generation. The water flow makes the turbine move, which generates energy. Tidal power generation has huge potential and it really is the future of alternative energy, which is just waiting to be tapped into.
Other ways of generating tidal wave energy exist as well. One of them is called tidal barrages. First, the tide has to reach the shore, where it flows through a one-way gate into a reservoir. Then the water is stored until the tide becomes low again, after which it is released back into the sea though turbines. The turbine rotation is what generates electricity, and is very similar to the way power is generated at hydroelectric power plants.
HOW TIDAL ENERGY WORKS?
When water levels are high in oceans and tides are producing and rushing to and fro, it has potential to produce electricity out of it. For producing electricity out of such wild potential oceans barrage is installed around the corner of river, then water turbines are installed inside the barrage. When water rushes through these turbines, it produces electricity.
For producing significant amount of energy out of tidal water turbines, range of tides should be high and substantial amount of water should be there for pushing water through the turbine. Approximately 4 to 5 meters ranges of tides are required to produce significant amount electricity.
It is significantly important to spot the appropriate place which provides suitable and sustainable conditions to produce tidal energy. There are plenty of places around the globe, which provide good conditions for installing water turbines and then produce electricity use tidal power of oceans in the location. For instance in Canada, there is place with name of Bay of Fundy which produces highest and largest tide ranges in the world. Its average range is 10.8 meters.
In Pakistan, the same types of wave's formation were founded on the Balochistan costal areas where this type of tidal power plant is very effective.
There are many ongoing tidal power projects worldwide, out of which the largest tidal energy station is in Europe. It is in Rance estuary in north France, and it was developed in 1966. This tidal station is only one in entire Europe.
The cost associated for developing tidal power station can vary from project to project. If capacity of generating electricity of the project is in megawatts the cost is obviously high, in contrast to if capacity is limited in kilowatts. We generally do not see tidal power plants capacity worth in kilowatts. It is more suitable and economical when developed for large scale electricity generation.
For instance, project Severn Estuary in UK cost US $15 billion, which produces 8000 MW. The other project of 2200 MW worth of tidal power station project in San Berandino cost US$ billion.
ADVANTAGES OF TIDAL ENERGY STATION
There are lot of advantages associated with renewable energies such tidal energy when we compare it with fossil fuels. Below are the bullets, which are convincing enough to raise the vote for tidal energy and against the consumption of current fossil fuel sources.
* Once tidal power plant is built, electricity is free.
* It does not emit greenhouse gasses, carbon emission gasses, which pollute environment.
* It does not have any dependency of any fossil fuel including furnace oil, gasses, etc; it needs no oil whatsoever to produce electricity.
* Tidal power technology is renewable energy, which uses tidal and waves of same water for producing electricity over and over again.
* Tidal power technology like all renewable energy is clean energy and does not leave much impact on environment.
* Tidal power plants do not require much maintenance. Therefore, its maintenance cost free.
* Tidal energy stations have about 80 per cent efficiency ratio, whereas fossil fuels have approximately 30 per cent for efficiency levels.
* The better tides and wave strengths of the oceans improve the efficiency of the station.
* Electricity does not fluctuate on large scale using tidal energy as it happens in solar power technology.
DISADVANTAGES OF TIDAL ENERGY STATION
There are some disadvantages associated with tidal power technology. Following are some of the most obvious points.
* There are not many places in the world where tidal power plant can be built; it needs oceans, which provide certain flow of waves and tides of water.
* Tidal power plants can only be built in water; it cannot be built on inland area, like solar power plant, wind power plants etc.
* Electricity can only be produced when tides are high in the sea, once ocean is calm and does not flow certain level of waves, it cannot produce electricity. Therefore, electricity can be produced for only 10 hrs a day in presence of tides.
* Wings of turbine inside water can affect life under water, and in some cases can produce distraction on the way of ships passing through the area around tidal power station.
* Turbines can be faulty some times repairing of which is very tough job to do. Tidal technology is used but its technology is not yet fully developed.
Good locations can be found at the entrances to bays and rivers and between islands or other land masses where the currents become concentrated forces. There are a number of designs for tidal stream systems.
Ocean waves are a tertiary form of solar energy. Due to the contours of the earth's surface, there is unequal heating of the earth from the sun. This generates wind and wind blowing over water makes waves. Waves power refers to the energy of ocean waves and the capture of that energy to do useful work, including generating electricity, desalination processes and pumping water. When the wind blows over the surface of offshore water, such as oceans and seas, waves are created by the progressive transference of energy from the wind. Wave energy is stored, concentrated wind energy.
The larger the wave, the more powerful it is. Wave power is determined by wave height, wave speed and water density. Almost 75 per cent of the world's surface is water. However, waves are a largely unexplored source of energy compared with the progress of solar and wind energy systems.
The motors drive electrical generators to produce electricity. Power from all the joints is fed through an 'umbilical cable' to a junction on the seabed. Several devices can be connected and linked to shore through a single seabed cable.
TIDAL WAVE GENERATORS
* Tidal wave generators are underwater turbines, which can generate electricity from tidal currents.
* The tides can be very powerful, and contain large amounts of energy that can be harnessed.
* Tidal wave generators are a safe and clean alternative to fossil fuel use.
* Tidal wave generators are a safe and clean alternative to fossil fuel use.
Tidal wave generators are also known as tidal turbines, and the technology used is very similar to that used with wind power. There are some differences, because the turbines must be much heavier to withstand the weight of the water and must be built very strongly, because severe weather can cause extremely rough seas. Tidal wave generators are placed underwater directly into the flow of the tide, and the flowing water causes the turbine blades to turn.
Tidal wave generators are considered very environmentally friendly because there are no emissions or fossil fuels used, but these machines can have an impact on the marine life in the area. Some sites being evaluated and tested around the world have shown various effects, so these turbines should be placed where they will have the least effect on marine life and the underwater habitat. Fish and other marine animals may get caught up in the equipment, especially when the tidal current is moving fast or the turbines are placed closely.
Newer technology has been able to minimize this impact, but these machines should be placed in areas where there are not large numbers of marine life when possible. Tidal wave generators and the power facilities they supply around the world use monitoring equipment to ensure that the fish and other marine life in the area are not harmed in large numbers. American has over twelve thousand miles of coastal lands.
Tidal wave generators can provide one answer to the future of energy, but this will not be the only solution. These energy devices will be used alongside other alternative renewable energy sources. In the future, the energy grid will be very flexible, and accept power from a number of green sources, including the tides. This will allow for an end to foreign oil and fossil fuel dependence, and provide the energy needed without causing environmental damage or polluting the planet.
Ocean waters are a source of usable energy by virtue of their physical and chemical characteristics. The energy of waves, tides, currents, and temperature and salinity gradients can be harnessed by existing technologies, and could some day be a more widespread source of power.
Hydropower dam sites tend to have a large impact on the local population. Over 1.1 million people were displaced by the Three Gorges dam in China and it has been estimated that 30ñ60 million people worldwide have had to be relocated due to hydropower.
Proposed hydropower plants often provoke controversy and in some countries, public opposition to hydropower has stopped all construction except on small-scale projects. Also, dams sometimes collapse for various reasons, e.g. over spilling of water, inadequate spillways, foundation defects, settlement, slope instability, cracks, erosion, and freak waves from landslides in steep-sided valleys around the reservoir.
As with nuclear plants, the risk of major accidents is small but the consequences can be catastrophic. Given the long lifetime of dams, even a typical failure rate as low as one per 6000 dam years means that any given dam has a probability of about one per cent that it will collapse at sometime in its life. In order to reduce the environmental impact and the consequences of dam failure, the question arises as to whether it is better to build a small number of large reservoirs or a large number of small ones. Though small reservoirs tend to be more acceptable to the public than large ones, they need a much larger total reservoir area than a single large reservoir providing the same volume of stored water.
An argument in favor of hydropower dam is that it does not produce greenhouse gases or acid rain gases. However, water quality may be affected both upstream and downstream of a dam due to increases in the concentrations of dissolved gases and heavy metals. These effects can be mitigated by inducing mixing at different levels and oxygenating the water by auto-venting turbines. The installation of a hydropower dam installation can also have a major impact on fish due to changes in the habitat, water temperature, flow regime, and the loss of marine life around the turbines.
The capital cost of construction of hydropower plants is typically much larger than that for fossil fuel plants. Another cost arises at the end of the effective life of a dam, when it needs to be decommissioned. The issue as to who should pay for the cost involved in decommissioning is similar to that for nuclear plants: the plant owners, the electricity consumers, or the public? On the positive side, production costs for hydropower dam are low because the resource (rainfall) is free. Also, operation and maintenance costs are minimal and lifetimes are long: typically 40-100 years. The efficiency of a hydroelectric plant tends to decrease with age due to the build-up of sedimentation trapped in the reservoir. This can be a life-limiting factor because the cost of flushing and dredging is usually prohibitive.
There are two high tides and two low tides around the earth at any instant. One high tide is on the longitude closest to the moon and the other on the longitude furthest from the moon. The low tides are on the longitudes at 90 degree to the longitudes where the high tides are situated. On any given longitude, the interval between high tides is approximately 12 hours 25 minutes. The difference in height between a high tide and a low tide is called the tidal range. The mid-ocean tidal range is typically about 0.5 ñ 1.0 meters but is somewhat larger on the continental shelves. In the restricted passages between islands and straits the tidal range can be significantly enhanced, up to as much as 12 m in the Bristol Channel (UK) and 13 m in the Bay of Fundy (Nova Scotia). Tidal power has the advantage over other forms of alternative energy of being predictable. For conventional tidal power generation, it is necessary to construct huge tidal basins in order to produce useful amounts of electricity. However, in recent years, an alternative technology for exploiting strong tidal currents has been under development using underwater rotors, analogous to wind turbines.
COUNTRY SITE MEAN TIDAL RANGE (M) BASIN AREA (KM2) CAPACITY (GW) Argentina Golfo Nuevo 3.7 2376 6.6 Canada Cobequid 12.4 240 5.3 India Gulf of Khambat 7.0 1970 7.0 Russia Mezan 6.7 2640 15.0 Russia Penzhinsk 11.4 20,530 87.4 UK Severn 7.0 520 8.6
COUNTRY CAPACITY IN MEGAWATTS EXPECTED YEARS FOR COMPLETION Canada, CORE Project 15 MW 2011 South Korea, Wando Hoenggan Waterway 300 MW 2015 New Zealand, Kaipara Harbour 200 MW 2018 Scotland, Pentland Firth Tidal Energy Project 10 MW Not Mentioned Scotland, Islay Project 2 MW Not Mentioned
TIDAL POWER IN PAKISTAN
Pakistan is a country with a huge coastline; there are many bays and lagoons, particularly on the Balochistan coastal areas which can be used to generate this kind of electrical power. We have many big cities that are located on the coast and would get benefits greatly from this kind of power generation.