Tidal Power

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Tidal Power

• Lucas ONeil
• Elec 395
• May 30, 2006

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Introduction

• Alternative Energy Sources/Renewable Energy
• Overview of Tidal Generation
• -Tides
• -Basic methods of generating electricity from
  tides
• -Geography
• -Pros/Cons
• -Environmental concerns
• Different types of tidal generators
• -Tidal fence
• -Tidal lagoons
• -Tidal turbines
• Conclusions
• References

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Alternative Energy Sources

• Use of any given energy source in human society
  encounters limits to expansion. At the beginning
  of the 21st century some issues have achieved
  global dimension. Principal fossil energy
  sources, such as oil and natural gas are
  approaching exhaustion that may occur within the
  span of a generation
• Closely linked to energy development are
  concerns about the environmental effects of
  fossil fuel energy use, such as global warming,
  and health issues due to air pollution. Energy
  development issues are part of the much debated
  sustainable development problem.
• Canada and the United States have incredibly high
  energy consumption per capita

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• Need to move away from fossil fuels
• Need safe and clean energy sources that dont
  create significant amounts of waste.
• Renewable Energy Sources offer this.

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Renewable Energy

• Renewable energy sources capture their energy
  from existing flows of energy, from on-going
  natural processes, such as sunshine, wind,
  flowing water (hydropower), biological processes,
  and geothermal heat flows. Renewable energy is
  from an energy resource that is replaced rapidly
  by a natural process such as power generated from
  the sun or from the wind.
• Examples of Renewable Energy Sources

Wind
Solar
Hydroelectric
And....
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Tidal Power

• Tidal power generators derive their energy from
  movement of the tides.
• Obviously requires large bodies of water nearby.
  Not viable on the prairies for example.
• Has potential for generation of very large
  amounts of electricity, or can be used in smaller
  scale.
• Tidal power is not a new concept and has been
  used since at least the 11th Century in Britain
  and France for the milling of grains.
• There are a number of places around the world
  that have adopted pilot projects for different
  types of tidal generators

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Tides

• Tidal power utilizes the twice-daily variation in
  sea level caused primarily by the gravitational
  effect of the Moon and, to a lesser extent the
  Sun on the world's oceans. The Earth's rotation
  is also a factor in the production of tides.
• The interaction of the Moon and the Earth results
  in the oceans bulging out towards the Moon (Lunar
  Tide). The suns gravitational field pulls as
  well (Solar Tide)
• As the Sun and Moon are not in fixed positions in
  the celestial sphere, but change position with
  respect to each other, their influence on the
  tidal range (difference between low and high
  tide) is also effected.
• If the Moon and the Sun are in the same plane as
  the Earth, the tidal range is the superposition
  of the range due to the lunar and solar tides.
  This results in the maximum tidal range (spring
  tides). If they are at right angles to each
  other, lower tidal differences are experienced
  resulting in neap tides.

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How do tides changing Electricity?
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How do tides changing Electricity?

• As usual, the electricity is provided by spinning
  turbines.
• Two types of tidal energy can be extracted
  kinetic energy of currents between ebbing and
  surging tides and potential energy from the
  difference in height (or head) between high and
  low tides.
• The potential energy contained in a volume of
  water is
• E xMg
• where x is the height of the tide, M is the mass
  of water and g is the acceleration due to
  gravity.
• Therefore, a tidal energy generator must be
  placed in a location with very high-amplitude
  tides. Suitable locations are found in the former
  USSR, USA, Canada, Australia, Korea, the UK and
  other countries

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• The generation of electricity from tides is very
  similar to hydroelectric generation, except that
  water is able to flow in both directions and this
  must be taken into account in the development of
  the generators.
• The simplest generating system for tidal plants,
  known as an ebb generating system, involves a
  dam, known as a barrage across an estuary.
• Sluice gates on the barrage allow the tidal basin
  to fill on the incoming high tides and to exit
  through the turbine system on the outgoing tide
  (known as the ebb tide).
• Alternatively, flood-generating systems, which
  generate power from the incoming tide are
  possible, but are less favored than ebb
  generating systems.

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Ebb Generation

• The basin is filled through the sluices and
  freewheeling turbines until high tide. Then the
  sluice gates and turbine gates are closed.
• They are kept closed until the sea level falls to
  create sufficient head across the barrage and the
  turbines generate until the head is again low.
  Then the sluices are opened, turbines
  disconnected and the basin is filled again.
• The cycle repeats itself.
• Ebb generation (also known as outflow generation)
  takes its name because generation occurs as the
  tide ebbs.

Estuary
Ebb generating system with a bulb turbine
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Some Turbine Types
Rim Type
Bulb Type

• In systems with a bulb turbine, water flows
  around the turbine, making access for maintenance
  difficult, as the water must be prevented from
  flowing past the turbine.
• Rim turbines reduce these problems as the
  generator is mounted in the barrage, at right
  angles to the turbine blades. Unfortunately, it
  is difficult to regulate the performance of these
  turbines and it is unsuitable for use in pumping.
  
• Tubular turbines have been proposed for use some
  UK projects. In this configuration, the blades
  are connected to a long shaft and orientated at
  an angle so that the generator is sitting on top
  of the barrage.

Tubular Type
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Environmental/Ecological Concerns

• Tidal power generation can offer significant
  advantages, including improved transportation due
  to the development of traffic or rail bridges
  across estuaries and reduced greenhouse gas
  emissions by utilizing tidal power in place of
  fossil fuels.
• However there are also some significant
  environmental disadvantages which make tidal
  power, particularly barrage systems less
  attractive than other forms of renewable energy.

La Rance, France (240MW)
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• Tidal Changes
• The construction of a tidal barrage in an estuary
  will change the tidal level in the basin. This
  change is difficult to predict, and can result in
  a lowering or raising of the tidal level. This
  change will also have a marked effect on the
  sedimentation and purity of the water within the
  basin. In addition, navigation and recreation can
  be affected as a result of a sea depth change due
  to increased sedimentation within the basin. A
  raising of the tidal level could result in the
  flooding of the shoreline, which could have an
  effect on the local marine food chain.
• Ecological Changes
• Potentially the largest disadvantage of tidal
  power is the effect a tidal station has on the
  plants and animals which live within the estuary.
  As very few tidal barrages have been built, very
  little is understood about the full impact of
  tidal power systems on the local environment.
  What has been concluded is that the effect due to
  a tidal barrage is highly dependent upon the
  local geography and marine ecosystem.
• Wales have been caught in tidal generators.
• Fish may move through sluices safely, but when
  these are closed, fish will seek out turbines and
  attempt to swim through them. Also, some fish
  will be unable to escape the water speed near a
  turbine and will be sucked through.

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Different Generator Types

• Tidal Fences
• Tidal Lagoons
• Tidal Turbines

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Tidal Fences

• Tidal fences are composed of individual, vertical
  axis turbines which are mounted within the fence
  structure, known as a caisson.
• Kind of like giant turn styles which completely
  block a channel, forcing all of the water through
  them.
• Unlike barrage tidal power stations, tidal fences
  can also be used in unconfined basins, such as in
  the channel between the mainland and a nearby off
  shore island, or between two islands.

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Tidal Fences (cont.)

• Since they do not require flooding of the basin,
  tidal fences have much less impact on the
  environment, and are significantly cheaper to
  install.
• Unlike barrage generators, tidal fences have the
  advantage of being able to generate electricity
  once the initial modules are installed.
• Since a caisson structure is still required,
  which can disrupt the movement of large marine
  animals and shipping, there are still ecological
  concerns

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Tidal Fences (cont.)

• A 2.2GW tidal fence using the Davis turbine, was
  being planned for the San Bernadino Strait in the
  Philippines to be constructed by the Blue Energy
  company. The project, estimated to cost US 2.8
  Billion is unfortunately on hold due to political
  instability
• according to Michael Maser a Blue Energy
  spokesman.

Davis Hydro Turbine
http//www.bluenergy.com/
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Tidal Lagoons

• Tidal lagoons are an adaptation of the barrage
  system. Similar to standard barrage models, tidal
  lagoons retain a head pond and generate power via
  conventional hydro-turbines.
• The difference is that the conventional barrage
  designs exploit the natural coast line to
  minimize barrage length. However, this entails
  blocking the estuary regardless of how deep it
  is. This raise the costs considerably.
• However, a lagoon, for a low cost can pretty much
  be built anywhere that there is a high tidal
  range.
• The lagoon has relatively little visual impact,
  as it is below the high water tide mark and
  appears like a normal sea wall at low tide.

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Tidal Lagoons (cont.)

• The lagoon can be built using loose aggregates
  found in quarries or demolished structures. This
  rubble would be dumped until an impound wall
  was complete. As any aggregate can be used, it is
  possible to restrict construction costs by
  implementing the cheapest materials available
• This construction technique also has the added
  benefit of creating an artificial reef. As well,
  a calm water lake would be created in the middle
  where smaller fish and birds could flourish
• Migrating fish can swim around unimpeded and
  without the danger of sluices or negotiating
  turbines.
• Tidal Electric is planning to test the concept in
  Swansea Bay with a relatively small 30MW output
  plant.
• Design being implemented in China in the future.
• The Chinese government has expressed its
  enthusiastic support of Tidal Electrics
  ambitious 300 MW offshore tidal lagoon in the
  waters near the mouth of the Yalu River by
  signing an agreement pledging to cooperate with
  the development. At 300 MW, the project would be
  the largest tidal power project in the world,
  topping the capacity of the 240 MW French tidal
  power plant in LaRance.

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Tidal Turbines

• Proposed shortly after the oil crisis of the
  1970s, tidal turbines have only become reality in
  the last decade, when a 10-15kW 'proof of
  concept' turbine was operated on Loch Linnhe.
  Resembling a wind turbine, tidal turbines offer
  significant advantages over barrage and fence
  tidal systems, including reduced environmental
  effects.
• Tidal turbines utilize tidal currents that are
  moving with velocities of between 2 and 3 m/s (4
  to 6 knots) to generate between 4 and 13 kW/m2.
  Fast moving current (gt3 m/s) can cause undue
  stress on the blades in a similar way that very
  strong gale force winds can damage traditional
  wind turbine generators, whilst lower velocities
  are uneconomic.

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Tidal Turbines (cont.)

• Tidal turbines offer significant advantages over
  barrage and fence tidal systems (and other
  renewable energy sources)
• High energy intensity A 1MW tidal turbine can
  access five to ten times as much energy per
  square meter of rotor than a 1MW wind turbine,
  resulting in a smaller and potentially lower cost
  machine.
• Minimal environmental impact tidal turbines are
  visible enough to be avoided by mariners but they
  have a low visual impact on the seascape, they
  produce no pollution or noise and their slow
  moving rotors which turn at less than one
  revolution in four seconds (15 rpm) are
  considered unlikely to harm marine life.
• High energy return on energy invested tidal
  turbines should offer faster energy payback than
  most other renewables.

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Tidal Turbines (cont.)

• SeaFlow, a 300 kW prototype turbine was the
  worlds first offshore tidal turbine and was
  installed off Lynmouth, Devon in May 2003.

Cost 3.4 million and was funded by a consortium
of private companies and the UK and German
governments.
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Future Expansion of Tidal Turbines

• Tidal Farms. Sets of up to hundreds of tidal
  turbines working in conjunction.
• Potential for giga-watts of power
• Marine Current Turbine (MCT) created SeaFlow
  (300kW), is following up with SeaGen (1MW), which
  will expand to a 5 turbine tidal farm that will
  provide 5MW.
• The Norwegian company, Hammerfest Strom, believes
  that they will have their first tidal farm of
  over 20 second generation devices operational
  before the end of 2008. This would be the 3rd
  phase of their 'Blue Concept' project and would
  result in a tidal farm that would produce 10MW of
  renewable electricity.

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Conclusions

• Tidal power is a renewable, potentially zero
  emission (during operation) energy source.
• Tides have the advantage of being completely
  predictable, unlike solar and wind power.
• Different types of Tidal Generators suit
  different areas and energy needs.
• There are environmental concerns that need to be
  addressed when developing this technology further.

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References

• RISE Research Institute for Sustainable Energy
• http//rise.org.au/reslab/resfiles/tidal/text.h
  tml
• Wikipedia
• http//en.wikipedia.org/wiki/Tidal_power
• http//en.wikipedia.org/wiki/Renewable_energy
• http//www.hie.co.uk/aie/tidal_power.html
• Marrine Current Turbines Ltd.
• http//www.ifremer.fr/dtmsi/colloques/seatech04/m
  p/proceedings_pdf/presentations/4.20courants_mari
  ns/MCT.pdf

http//web.uvic.ca/loneil/elec395/elec395.htm
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QUESTIONS?