Tidal%20Energy

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Tidal Energy

• Most of the energy sources we have been
  discussing derived their energy from the sun.
• Tides are driven by gravity
• Gravity is a force that exists between any two
  objects based upon their mass and the distance
  between them
• Fg GmM/R2 where M and m are the masses of the
  two objects, R is the distance between them and G
  is the gravitational constant 6.67300 10-11
  m3 kg-1 s-2

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Tides

• So the moon and Earth exert a force of gravity on
  each other. The motion of the moon around the
  Earth counteracts the Earths pull, so the moon
  does not fall into the Earth.
• The moons pull on the Earth causes any material
  that can flow on the Earths surface, like large
  bodies of water, to pile up underneath the moon.
• See we do understand the tides!!!

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Tides

• The sun also causes tides the Earth, though the
  effect is small, unless the sun and moon line up
  and work together (spring tide) or are at right
  angles to each other and work against each other
  (neap tides).
• In areas where there are natural basins on the
  coastline, water flows in and out of these
  basins.
• So there are regular, predictable motions in the
  oceans which could be used as an energy source.

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Capturing Tidal Power

• Dams or barrage with gates are usually built
  across the mouth of basins
• This allows the current to be directed into the
  turbines and enhances the effect.

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Rance River Tidal Power station in France
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Current and Future tidal power stations

• Rance River, France 240Mw
• White sea, Russia 1 MW
• Annapolis River, Nova Scotia, Canada, 18mW
• Two most favorable sites in the US Cook Inlet
  and Bristol Bay in Alaska and Bay of Funday which
  covers the Northeastern US and southeastern
  Canada.
• Development of the Bay of Funday would provide
  15,000mW to the northeastern US and 15,000mW to
  Canada

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Bay of Fundy
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Power

• Power P Cp x 0.5 x ? x A x V³
• Cp is the turbine coefficient of performance
• P the power generated (in watts)
• ? the density of the water (seawater is
  1025 kg/m³)
• A the sweep area of the turbine (in m²)
• V³ the velocity of the flow cubed (i.e. V x
  V x V)

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Environmental Issues

• alters 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
• Some species lost their habitat due to La Rances
  construction, but other species colonized the
  abandoned space, which caused a shift in
  diversity.
• 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.
• If the turbines are moving slowly enough, such as
  low velocities of 25-50 rpm, fish kill is
  minimalized and silt and other nutrients are able
  to flow through the structures . Tidal fences
  block off channels, which makes it difficult for
  fish and wildlife to migrate through those
  channels. Larger marine mammals such as seals or
  dolphins can be protected from the turbines by
  fences or a sonar sensor auto-breaking system
  that automatically shuts the turbines down when
  marine mammals are detected
• As a result of less water exchange with the sea,
  the average salinity inside the basin decreases,
  also affecting the ecosystem
• 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.

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Innovative strategies

• East River in New York-tidal river
• Plans for 30 underwater turbines to tap the
  rivers 4
  knot tidal flow and produce 1mW
• Already tested with a prototype, took
• 3 attempts. First two the blades were torn
• off by the currents.
• If permits are approved, on schedule
  for a
  fall installation
• Tidal Lagoons
• Artificial lagoons with high walls.
• Lagoon fills and empties through apertures,
  turbines are spun and generate electricity
• doesnt disturb current environmental conditions
  as much and expands locations by only requiring
  large tidal variations

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Wave Energy

• It is estimated that there is 2-3 million mW of
  energy in the waves breaking on the world
  coastlines, with energies derived ultimately from
  the wind
• In Great Britain alone, almost twice the current
  electricity demand breaks on the countries
  coastlines every day.
• A vast untapped resource, but how to harness it?

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How are waves formed

• As wind blows along the surface of a body of
  water, a surface wave develops.
• As the wind blows, pressure and friction forces
  perturb the equilibrium of the water surface
• These forces transfer energy from the air to the
  water, forming waves.
• The water molecules actually move in circular
  motion
• When a wave can no longer support its top, it
  collapses or breaks.
• Usually happens when a wave reaches shallow
  water, such as near a coastline.

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Harnessing the energy

• LIMPET (Land Installed Marine Powered Energy
  Transformer)
• Breakwater Design
• PowerBuoys
• Pelamis

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LIMPET

• Takes the wave into a funnel and drives air
  pressure past two turbines, each of which turns a
  250 kW generator.
• Installed on the island of Islay, off Scotlands
  west coast.

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Breakwater

• Installed where there would normally be a
  breakwater
• a series of layered reservoirs up a carefully
  calculated slope.
• This is then converted to kinetic energy (by
  falling down), and this turns the
  turbine/generator.
• A 500m breakwater can produce respectable 150 kW
  generator capacity
• Only in design phase, non of these up and running
  yet

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PowerBuoys

• In a permanent magnet linear generator buoy, an
  electric coil surrounds a magnetic shaft inside
  the buoy
• the magnetic shaft is anchored to the sea floor.
  When waves cause the coil to move up and down
  relative to the fixed magnetic shaft, voltage is
  induced and electricity is generated.
• Each buoy could potentially produce 250 kilowatts
  of power.
• A fleet of about 200 such buoys could power the
  business district of downtown Portland.

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PELAMIS

• made of large semi-submerged sections, like a
  submarine cut into pieces
• the wave action makes the Pelamis bend between
  the sections.
• This bending action forces hydraulic pistons to
  move in the device and push fluid around
  generating a linear flow, which produces energy.
• A 1 sq kilometer farm could produce 30 Megawatts.

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Geothermal Energy

• Based on the heat that naturally occurs in the
  Earths interior
• Sine the Earths interior is hotter than the
  surface, this heat flows from the interior
  towards the surface.
• Heat is the result of decay of radioactive nuclei
  inside the Earth, heat left over from the
  formation of the Earth and heat from the friction
  of heavier material sinking towards the center.
• Earths core temperature is 7200 F, which is
  close to the temperature on the Suns surface.

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Radioactive Decay

• the process in which an unstable atomic nucleus
  loses energy by emitting ionizing particles and
  radiation.
• Most important source of heat inside the earth
• loss of energy results in an atom of one type
  (parent nuclide) transforming to an atom of a
  different type, (daughter nuclide).
• Eg a carbon-14 atom (the "parent") emits
  radiation and transforms to a nitrogen-14 atom
  (the "daughter").
• Inside the Earth, the main elements that decay
  are 235U, 238U 232Th, 40K .
• This is a random process on the atomic level, in
  that it is impossible to predict when a given
  atom will decay, but given a large number of
  similar atoms the decay rate, on average, is
  predictable.

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Radioactive decay
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Thorium Decay
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Uranium 238 decay
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Geothermal

• Not a new idea
• Used the heat from inside the Earth for thousands
  of years for bathing (hot springs) and space
  heating.
• First electric power use was by Prince Piero
  Ginori Conti tested the first geothermal power
  generator on 4 July 1904 in Larderello, Italy.
• In 1958 New Zealand built a plant of its own.
• First geothermal power plant in the United States
  was made in 1922 by John D. Grant at The Geysers
  Resort Hotel.
• In 1960, Pacific Gas and Electric began operation
  of the first successful geothermal power plant in
  the United States at The Geysers. The original
  turbine installed lasted for more than 30 years
  and produced 11 MW net power.

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The Geysers

• The Geysers is a geothermal power field located
  72 miles (116 km) north of San Francisco,
  California.
• It is the largest geothermal development in the
  world.
• It is currently outputting over 750 MW. It
  consists of 22 separate power plants that utilize
  steam from more than 350 producing wells.