Alternative energy

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Alternative energy

• Tidal power-stations

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What is a Tide ?

• Tides are the rising and falling of Earth's ocean
  surface caused by the tidal forces of the Moon
  and the Sun acting on the oceans.

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What is the Tidal force ?

• The tidal force is the vectorial difference
  between the gravitational force of the Earth and
  the gravitational force of the Moon.

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About tidal power

• Tidal power, sometimes called tidal energy, is a
  form of hydropower that exploits the movement of
  water caused by tidal currents or the rise and
  fall in sea levels due to the tides.
• Although not yet widely used, tidal power has
  potential for future electricity generation and
  is more predictable than wind energy and solar
  power.

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History of Tidal power stations

• An early attempt to build a tidal power plant
  took place at Aber-Wrac'h in the Finistere in
  1925, but due to financial problems, it was
  abandoned in 1930.
• Tidal mills have long existed in areas affected
  by tides. In Europe, tide mills have been used
  for over a thousand years, mainly for grinding
  grains.

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Principle of tidal power stations

• 1. Barrages make use of the potential energy from
  the difference in height (or head) between high
  and low tides. Barrages suffer from the problems
  of very high civil infrastructure costs, few
  viable sites globally and environmental issues.

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• 2. Tidal stream systems make use of the kintetic
  energy from the moving water currents to power
  turbines, in a similar way to wind mills use
  moving air. This method is gaining in popularity
  because of the lower cost and lower ecological
  impact.

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Examples of tidal power stations

• La Rance The first and largest tidal plant in
  operation is the 240 MW plant built for
  commercial production across the La Rance estuary
  in north-western France between 1961 and 1967.
  The tidal power plant has 24 bulb-type Kaplan
  turbines with a rated capacity of 10 MW each.

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• Annapolis The second commercially operated tidal
  power plant built in 1984 in the Western
  hemisphere is a 18 MW plant at Annapolis Royal on
  the Nova Scotia coast of the Bay of Fundy in
  Canada.

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• Other sites Other plants include the 400 kW
  experimental unit at Kislaya Guna, built in 1968
  in Russia on the Barents Sea, and the 3.4 MW
  Jianxia station built in China between 1980 and
  1986. Most of the technically available tidal
  resources in Europe are in the UK. The site in
  the Severn estuary in south-western England
  represents a potential of 8 GW and has been the
  object of several feasibility studies. Large
  potential also exists in northern France, at the
  Cotentin Peninsula in Normandy.

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Advantages of using tidal power

• Predictable source of green" energy during
  lifetime of barrage
• It produces no greenhouse gases or other waste
  it needs no fuel.
• Not expensive to maintain.
• Tidal energy has an efficiency of 80 in
  converting the potential energy of the water into
  electricity
• Vertical-axis tidal generators may be joined
  together in series to create a tidal fence
  capable of generating electricity on a scale
  comparable to the largest existing fossil
  fuelbased, hydroelectric and nuclear energy
  generation facilities

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Disadvantages of using tidal power

• 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
• it provides power for around 10 hours each day,
  when the tide is actually moving in or out, which
  is not very much
• Existing ecosystems would be heavily altered,
  with new species moving in and perhaps dominating
  old species
• Tidal power schemes have a high capital cost

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Global enviromental impact

• A tidal power scheme is a long-term source of
  electricity. A proposal for the Severn Barrage,
  if built, has been projected to save 18 million
  tonnes of coal per year of operation. This
  decreases the output of greenhouse gases into the
  atmosphere.
• If fossil fuel resource is likely to decline
  during the 21st century, as predicted by Hubbert
  peak theory, tidal power is one of the
  alternative source of energy that will need to be
  developed to satisfy the human demand for energy.

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• Made by Grec Marcel
• Topliceanu Liviu