Tidal Power

Strictly, tidal power comes from the movement of the tides, and wave power comes from the movement of the waves. There are two kinds of tidal power stations:

• Tidal stream systems, which use turbines turned by the moving water to generate electricity. Very like wind power.
• Barrage systems. These are like dams built across rivers. After the tide comes in, the gates are closed. When the tide is low enough on the downstream side, the water flows through turbines rather like a hydro-electric dam.

Wave power consists of harnessing the movement of the waves. There are various pilot schemes of this at the moment.

• It reduces the dependence upon fossil fuels
• Tidal and wave energy is free, renewable, and clean source of energy
• It produces clean electricity, with no production of greenhouse gas or pollution.
• Tidal and wave energy generation and consumption creates no liquid or solid pollution
• Highly efficient resource (compared with coal and oil at 30%, tidal power efficiency is about 80%)
• Energy capturing and conversion mechanism may help protect the shoreline
• Energy capturing and conversion mechanism has little visual impact
• About 60 billion watts of energy from tides can be used for electricity generation
• Tides are active 24 hours a day, 365 days a year
• Tidal power is a renewable source of energy.
• It produces energy for free, once the initial costs are recovered.

There are some devices that are very environmentally friendly like for example, the Salter Duck. This is a floating device that moves in a nodding motion with the passage of waves, generating electricity efficiently in the process. It cause no destruction to the marine animals and to the environment. This device can also serve as shelters for fish, seabirds and even seals.

• It is not cost effective because fossil-fuel power stations do not pay for the cost of their carbon emissions to the planet. This will change as fossil fuel is valued at its real price.
• It leads to the displacement of wild life habitats.
• It can only be used where there is suitable tidal flow or wave motion. So it can not be used inland.
• It only produces electricity during tidal surges.
• Barrage systems require salt resistant parts and lots of maintenance.
• The frames of the turbines can disrupt the movement of large marine animals and ships through the channels on which the barrage is built.
• today, power produced from tidal fences is still a bit expensive than that using conventional plants using coal and natural gas (but it can be cheaper if improved technologies and large-scale generation is applied).
• the barrage systems have the disadvantages of disrupting fish migration and killing fish passing through the turbines, therefore, there is also the risk of destruction of ecosystem that rely on the coming and going of tides.
• the ecosystem is disrupted during the construction of building the tidal fence. this affects the fishes and also the fishermen who depends their life on it.
• Fossil fuels can be moved to just about anyplace to create energy on the spot. This is what allows a car to work while moving.
• Tidal energy can only be created on a coast with a good tidal differential. Worthless for a landlocked country, has to be converted to something else to be transported
• The main detriment is the cost of those plants, for constructing and running this facility with an annual output of 3423 GWh, is a cost about 1.2 billions, but this doesn't include operational and maintenance cost (coal and oil are cheaper).
• Construction of strong, cheap and efficient conversion devices may be problematic
• Technology isn't fully developed
• Problems exist with the transportation of hydroelectricity
• Ecological impacts relating to the alteration of tides and waves is not fully understood
• Appropriate waves and tides are highly location dependent
• Waves are a diffuse energy source, irregular in direction, durability and size
• Extreme weather can produce waves of great intensity

The tide moves a huge amount of water twice each day, and harnessing it could provide a great deal of energy - around 20% of Britain's needs.

Although the energy supply is reliable and plentiful, converting it into useful electrical power is not easy.

There are eight main sites around Britain where tidal power stations could usefully be built, including the Severn, Dee, Solway and Humber estuaries.

Only around 20 sites in the world have been identified as possible tidal power stations.

Despite the fact that it's expensive, the technique isn't fully developed. There are still some uncertainties surrounding the conversion devices.

Advantages of Tidal energy:

• It's free, after the initial setup
• It's green with no harmful emissions
• It's reliable and regular (unlike solar and wind)
• Birdies fly high and flowers smell nice
• it is constant
• reliable
• needs no fuel
• produces no green house gases

Tidal stream systems are cheaper than the dam types and do less damage to the environment.

Disadvantages of Tidal energy:

• Barrage (or dam) types are big, expensive and damage the environment somewhat like dams in a river.
• kills fishies=(

  Advantages:

The electricity generated is renewable.

The set-up is non-polluting, no carbon-dioxide or other emissions.

There are two tides every day and they can be relied on. So the electricity supply is constant.

Disadvantages:

Some tidal power stations block a bay or estuary with dams or barrages making it difficult for shipping or fish.

It will decrease the wear on the shoreline, and transfer less material to the shoreline.

Disadvantages

• Causes a continual loss of mechanical energy in the Earth-Moon system (Due to pumping of water through the natural restrictions around coastlines and viscous dissipation at the seabed and in turbulence.
• Loss of energy has caused the rotation of the Earth to slow in the 4.5 billion years since formation losing 17% of its rotational energy.
• May take additional energy from the system, increasing the rate of slowing over the next millions of years.
• Pose same threats as large dams, altering 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
• Turbidity decreases as a result of smaller volume of water being exchanged between the basin and the sea.
• The average salinity inside the basin decreases, also affecting the ecosystem
• A barrage across an estuary is very expensive to build, and affects a very wide area - the environment is changed for many miles upstream and downstream. Many birds rely on the tide uncovering the mud flats so that they can feed.
• There are few suitable sites for tidal barrages.
• Only provides power for around 10 hours each day, when the tide is actually moving in or out.
• It only provides about 7% of the power needed for England and Whales that means that some people get their energy close to free and some pay a lot of money
• It changes the coastline completely and the estuaries are flooded so any mud flats or habitats that birds or animals live on are destroyed
• Water is not replenished, it cannot flow away so any dirt or pollution lingers around the coast much longer
• Silt builds up behind the barrage
• Disrupts creatures' migration in the oceans
• Needs a very big piece of sea to be cost effective
• Cannot be used inland
• Only produces energy during tidal surges
• The frames of the turbines can disrupt the movement of large marine animals and ships through the channels on which the barrage is built.
• Barrage systems require salt resistant parts and lots of maintenance
• Affects the lives of the people who rely on fishing for a means of living
• Limited because the tide never speeds up or slows down, and occurs on 6 hour cycles. It is also dependent on the fetch distance. The fetch is the distance the tide rises and falls, so some beaches have a very small fetch, and others have a big fetch but hardly any have a large enough fetch to support tidal energy
• Tidal energy is currently more expensive to generate than conventional energy or that from many other renewable sources.
• Many sea animals require unobstructed access to migratory paths for feeding, reproduction and seasonal migration.
• Effects on marine life during construction phases.
• Operation and control must be provided remotely and maintenance is complicated due to sea-basing of the generation facilities.
• Sea-based moorings and towers to hold the generators must be placed on the sea bottom.
• The generating facilities and mooring infrastructure are potential navigational hazards.
• reduced flushing, winter icing and erosion considerably change the ecosystem
• Is only available in a small number of regions - it requires a basin or gulf that has a mean tidal amplitude of 7 metres or above. Also need semi-diurnal tides where there are two high and low tides everyday.
• Even with the best barrage designs, fish mortality rate per pass through the barrage is about 15%. Solutions to this problem have either failed or are too impractical and too expensive.
• Tides are predictable, but power stations only generate power when the tide is flowing in or out of the basin, which only happens during certain times of the day.
• Dams used in the production of tidal power can raise tide levels.
• The altering of the ecosystem at the bay
• Damages like reduced flushing, winter icing and erosion can change the vegetation of the area and disrupt the balance.
• only available in a small number of regions
• Expensive to construct
• Power is often generated when there is little demand for electricity
• Limited construction locations
• Barrages may block outlets to open water. Although locks can be installed, this is often a slow and expensive process.
• Barrages affect fish migration and other wildlife- many fish like salmon swim up to the barrages and are killed by the spinning turbines. Fish ladders may be used to allow passage for the fish, but these are never 100% effective. Barrages may also destroy the habitat of the wildlife living near it
• Barrages may affect the tidal level - the change in tidal level may affect navigation, recreation, cause flooding of the shoreline and affect local marine life

Advantages:

• Once you've built it, tidal power is free.
• It produces no greenhouse gases or other waste.
• It needs no fuel.
• It produces electricity reliably.
• Not expensive to maintain.
• Tides are totally predictable.
• Offshore turbines and vertical-axis turbines are not ruinously expensive to build and do not have a large environmental impact.

· Tidal energy is renewable. The tides will continue to ebb and flow, and the energy is there for the taking.

• Doesn't require any fuel
• A plant is expected to be in production for 75 to 100 years
• Clean and renewable
• Does not generate emissions or wastes
• Uses an abundant, inexpensive fuel source (water) to generate power
• Electricity is reliably generated (tides are predictable)
• May protect coastline against damage from high storm tides and provide a ready-made road bridge

In most cases, nothing can stop tidal flows as they are huge masses of water with lots of energy behind them. As long as the moon exists, and as long as the earth spins, the tides will come in and go out and rotate a turbine - all for an initial upfront one-off cost with a whole pile of maintenance considerations.

A disavantage about tidal energy is that it harms fish

No pollution to the environment to generate.

Disadvantages

• Causes a continual loss of mechanical energy in the Earth-Moon system (Due to pumping of water through the natural restrictions around coastlines and viscous dissipation at the seabed and in turbulence.
• Loss of energy has caused the rotation of the Earth to slow in the 4.5 billion years since formation losing 17% of its rotational energy.
• May take additional energy from the system, increasing the rate of slowing over the next millions of years.
• Pose same threats as large dams, altering 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
• Turbidity decreases as a result of smaller volume of water being exchanged between the basin and the sea.
• The average salinity inside the basin decreases, also affecting the ecosystem
• A barrage across an estuary is very expensive to build, and affects a very wide area - the environment is changed for many miles upstream and downstream. Many birds rely on the tide uncovering the mud flats so that they can feed.
• There are few suitable sites for tidal barrages.
• Only provides power for around 10 hours each day, when the tide is actually moving in or out.
• It only provides about 7% of the power needed for England and Whales that means that some people get their energy close to free and some pay a lot of money
• It changes the coastline completely and the estuaries are flooded so any mud flats or habitats that birds or animals live on are destroyed
• Water is not replenished, it cannot flow away so any dirt or pollution lingers around the coast much longer
• Silt builds up behind the barrage
• Disrupts creatures' migration in the oceans
• Needs a very big piece of sea to be cost effective
• Cannot be used inland
• Only produces energy during tidal surges
• The frames of the turbines can disrupt the movement of large marine animals and ships through the channels on which the barrage is built.
• Barrage systems require salt resistant parts and lots of maintenance
• Affects the lives of the people who rely on fishing for a means of living
• Limited because the tide never speeds up or slows down, and occurs on 6 hour cycles. It is also dependent on the fetch distance. The fetch is the distance the tide rises and falls, so some beaches have a very small fetch, and others have a big fetch but hardly any have a large enough fetch to support tidal energy
• Tidal energy is currently more expensive to generate than conventional energy or that from many other renewable sources.
• Many sea animals require unobstructed access to migratory paths for feeding, reproduction and seasonal migration.
• Effects on marine life during construction phases.
• Operation and control must be provided remotely and maintenance is complicated due to sea-basing of the generation facilities.
• Sea-based moorings and towers to hold the generators must be placed on the sea bottom.
• The generating facilities and mooring infrastructure are potential navigational hazards.
• reduced flushing, winter icing and erosion considerably change the ecosystem
• Is only available in a small number of regions - it requires a basin or gulf that has a mean tidal amplitude of 7 metres or above. Also need semi-diurnal tides where there are two high and low tides everyday.
• Even with the best barrage designs, fish mortality rate per pass through the barrage is about 15%. Solutions to this problem have either failed or are too impractical and too expensive.
• Tides are predictable, but power stations only generate power when the tide is flowing in or out of the basin, which only happens during certain times of the day.
• Dams used in the production of tidal power can raise tide levels.
• The altering of the ecosystem at the bay
• Damages like reduced flushing, winter icing and erosion can change the vegetation of the area and disrupt the balance.
• only available in a small number of regions
• Expensive to construct
• Power is often generated when there is little demand for electricity
• Limited construction locations
• Barrages may block outlets to open water. Although locks can be installed, this is often a slow and expensive process.
• Barrages affect fish migration and other wildlife- many fish like salmon swim up to the barrages and are killed by the spinning turbines. Fish ladders may be used to allow passage for the fish, but these are never 100% effective. Barrages may also destroy the habitat of the wildlife living near it
• Barrages may affect the tidal level - the change in tidal level may affect navigation, recreation, cause flooding of the shoreline and affect local marine life

Advantages:

• Once you've built it, tidal power is free.
• It produces no greenhouse gases or other waste.
• It needs no fuel.
• It produces electricity reliably.
• Not expensive to maintain.
• Tides are totally predictable.
• Offshore turbines and vertical-axis turbines are not ruinously expensive to build and do not have a large environmental impact.

· Tidal energy is renewable. The tides will continue to ebb and flow, and the energy is there for the taking.

• Doesn't require any fuel
• A plant is expected to be in production for 75 to 100 years
• Clean and renewable
• Does not generate emissions or wastes
• Uses an abundant, inexpensive fuel source (water) to generate power
• Electricity is reliably generated (tides are predictable)
• May protect coastline against damage from high storm tides and provide a ready-made road bridge

In most cases, nothing can stop tidal flows as they are huge masses of water with lots of energy behind them. As long as the moon exists, and as long as the earth spins, the tides will come in and go out and rotate a turbine - all for an initial upfront one-off cost with a whole pile of maintenance considerations.

The use of tidal energy is very beneficial for the environment and has no disadvantages. The only investment is expensive.

The tide moves in and the tide moves out. You want to be ale to generate power in either situation so the turbines must be able to reverse.

Wherever possible, you could capture energy as the water flows in at high tide, then again when it flows out at low tide. This is not always feasible, as some designs concentrate the flow of water, and this is straightforward for one-direction flow, typically as part of the tidal outflow.

A simple turbine.

Air is drawn into the engine continuously and compressed by a series of rotating blades. Fuel is sprayed into the combustion chamber and burnt increasing the gas temperature to around 1200C.

The hot high pressure gas expands through a second set of blades mounted on the same shaft as the compressor blades. The energy of the gas is partially expended powering the compressor, but has a residual energy which is either expended as a hot jet (resulting in thrust) or which drives a further independent set of blades to power a propeller or other device.

see http://www.rolls-royce.com/education/schools/how_things_work/journey02/index.html

answ2. The tides are caused by the attraction of gravity.

On the side of the Earth nearest the Moon, the attraction of the Moon lessens the strength of the local perceived gravity field.

On the side of the earth farthest from the Moon, the ocean there sees the gravitational pull of the whole Earth-Moon system, but the effective centre of this system is further away than the real centre of the earth. Thus the gravity field is seen as slightly less and there will be high tides there as well.

When the Sun and the Moon are in alignment with the Earth, (New Moon), we have the strongest gravitational force and the tides are at their maximum height.

When the Sun is on the opposite side of the Earth from the Moon, (Full Moon) then we have a weaker gravitational force, and the high tides are not quite as high as for the New Moon case.

There are no tidal wave power stations.

Tidal waves are unpredictable. There is no way at present to capture their energy. We can capture the energy of tides and also of waves, but not of tidal waves.