TIDAL+ENERGY+-+Megan

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== =BY MEGAN LIU=

Tidal Energy: the kind of energy that can only be achieved through the changing sea levels, the shift of tide from high to low. It's a type of renewable energy. This means that it's not permanently depleted when used. Instead of burning or consuming energy source, it only uses the energy from the changing of the tides. This is known to be "inexhaustible because the tides always rise and fall due to gravity."

HOW IT WORKS


Water could be trapped or contained in a reservoir called a tidal lagoon. When the tide goes to the reservoir, the lagoon slowly gets filled with water.

As the tide shifts from high to low, there's a pressure difference between the water in the lagoon and the open water course. This forms a head pressure, or hydrostatic pressure on the lagoon. Then, when the contained water is released, there will be potential energy which can be utilized.

When the open body of water reaches a low level because of a low tide, the water within the reservoir is released though outlets that are equipped with turbines. The force of the water will spin the turbines which would turn the power generators and would generate electricity.

In this energy, we are focusing on gravitational potential energy is increased. This potential energy could then be released and then converted into electricity through the modern technology. Tidal energy, compared to the other renewable resources, would be most effective and economical to produce if tidal levels are strong enough.

"Worldwide, approximately 3000 gigawatts (1 gigawatt = 1 GW = 1 billion watts) of energy is continuously available from the action of tides although there are insufficient suitable sites to harness this fully." -

ADVANTAGES
Once the lagoon is constructed, the energy produced in absolutely free. It doesn't generate greenhouse gases, or toxic waste to contribute to climate change. It functions without fuel requirement, only the simple natural use of water and waves. It has little maintenance cost and is a consistent source of energy - one that would be very beneficial right now in our time of need. The construction in very economical and doesn't have a huge ecological effect.

DISADVANTAGES
Tidal energy can only be produced in places with drastic water level changes. Around 20% of the energy produced is actually lost and only 80% of the gravitational energy is generated for electricity. Also, the tidal cycle is sometimes unexpected and it doesn't necessarily generate power when needed. It all depends on the cycle of the moon and the seasons. Caption: This is a picture of the neap and spring tides when the moon is in different phases.

ENERGY CHANGE
=Gravitational Potential Energy --> Kinetic Energy --> Electricity=

CURRENT TIDAL POWER STATIONS

 * LA RANCE**: The first tidal power station was constructed in France, on the mouth of the La Rance river estuary on the northern side of France. It produces 240 megawatts, generated by its 24 turbines, therefore, it supplies 0.012% of the power demand of France. The La Rance generating station has started operating since 1966 and has became a reliable source of electricity for France. This barrage has caused silting of the Rance ecosystem - sand eels and plaice have disappeared. However, sea bass and cuttlefish have returned to the river. The tides still flow and the operators work to minimize the biological impact. This site attracts approximately 200,000 visitors per year. Departmental highway 168 crosses the dam and allows vehicles to travel between Dinard and Saint-Malo. There is a drawbridge where the road crosses the lock which may be raised to allow larger vessels to pass.


 * ORKNEY**: A huge tidal turbine arrived in Orkney for testing on August 2010. The device is 22.5m tall, weighs 1,300 tonnes and has two sets of blades on a single unit. It has been designed to generate one megawatt of power - enough electricity for 1,000 homes. The AK1000's two sets of blades have been programmed to move slowly underwater and Atlantis Resources stated that they wouldn't pose a threat to sea life.


 * SEVEREN**: In 2008, the UK government had started on a big project - the "Tidal Reef" across the Severen Estuary. This is similar to a tidal barrage, but it doesn't block water movement a lot and therefore, the environmental consequences would be much less. it would be built in sections so that the power generated could start sooner. The migratory fish could escape and the mud flats could be exposed at low tide. It would be able to generate power for more hours in the tidal cycle. It would be built so that it could be used to control tidal levels further upstream, to prevent flooding on low-lying land nearby. However, the Severn Barrage would have a massive impact on migrating birds - especially because of its size, and the cost would be potentially spiraling from 15 billion - 30 billion pounds.[[image:image001.gif align="right"]]

"But one other key downside to the barrage was that it was so big. Ministers decided that there would have been little technology learning from public investment in a project of this size."

On the 18th of October 2010, UK's "most iconic green energy, reaching 10 miles across the Severn Estuary from Cardiff to Weston-super-Mare" plans have been scrapped. It would've produced up to 5% of UK's energy. Chris Huhne said the scheme's costs were "excessive" and said that a feasibility study found that there was "no strategic case" for the scheme. Other ministers say that it is too expensive and too risky of a project to conduct, especially during this financially unstable time. It was also stated that it wouldn't be the end for UK's tidal power plans. They are keen to hear proposals for barrages in other estuaries and have decided to go forward with a smaller scheme in the Severn in the future - perhaps in the 2020s or the 2030s.

Below are some articles related to the Severen controversy: [|Severn barrage tidal energy scheme scrapped by Huhne] [|Scientist's 'regret' over the axed Severn barrage scheme] (Dr. Rob Kirby spent 40 years dedicated to the Severn estuary)

EXAMPLE OF A TURBINE: (DELTASTREAM)
DeltaStream’s tidal stream turbines are just like wind turbines underwater, only being designed to suit the density of seawater which is 800 times greater than air and flow rates typically one fifth of wind.

DeltaStream uses the same concept of horizontal axis rotors in wind turbines and ship’s propellers. By using these proven technologies we can be confident that the devices will be reliable as the technology, components and know-how are well proven.

According to the Carbon Trust, tidal stream energy is ready to become a significant provider of clean energy for the UK and the Globe. Some 15-20% of the UK’s electricity demand could come from marine renewables.

Under proposed new EU rules, the UK is obliged to achieve a ten-fold increase in the energy it derives from renewable resources by 2050.

As onshore wind and other currently exploited renewable sources of energy are rapidly reaching saturation point, there is a substantial opportunity available to exploit tidal stream resources.