Chapter 13 · Chapter 13 Tidal Energy ©2015 Cengage Learning Engineering. ... Cengage Learning...
Transcript of Chapter 13 · Chapter 13 Tidal Energy ©2015 Cengage Learning Engineering. ... Cengage Learning...
Chapter 13
Tidal Energy
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Sustainable Energy
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Learning Objectives
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● The reasons for tidal motion and resonance effects in enclosed basins.
● The energy associated with tidal movement.● The design of barrage systems.● The availability and utilization of tidal energy based
on barrage systems.● Environmental and other factors that affect the
viability of barrage systems.● The design of tidal current energy systems.● Experimental and commercial tidal current
systems.
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Tidal energy
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Tidal energy is a manifestation of the gravitational interaction between the oceans and the moon and the sun.
The principal component of the tidal period is the diurnal period and is determined by the lunar day (12h 25m).
Gravitational interaction of the sun complicates tidal movements.
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Diurnal tidal period and effects of solar position
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Diurnal, semidiurnal and mixed tides
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Resonance effects in enclosed basins
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The period of tidal motion can be near the resonant period of a basin.
This can cause a substantial increase in tidal range.
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Resonance effects in a tank of water
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Generating waves with a period equal to the natural period of the tank will increase wave amplitude
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Extreme tides in the Bay of Fundy
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Analysis of tidal power
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The volume of water that cycles through a tidal basin during one period is
the factor of two is from the rising and falling of the tide
The mass of this water is
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Gravitational energy and tidal power
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The gravitational potential energy is therefore
and the average power over one tidal period is
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Tidal barrage systems
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Sluice gates
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Sluice gates allow water to be trapped inside or outside the basin
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Gated turbines
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Turbine gates allow water to flow through the turbines when the water on the two sides is at different levels
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Ebb generation scheme
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Water is trapped in the basin and is allowed to flow out into the ocean when the ocean level is lower
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Flood generation scheme
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Water is not allowed to enter the basin as the ocean level rises and then is allowed to flow into the basin when the ocean level is higher
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Capacity factor
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Because the water is raising or lowering on the other side of the barrage as it is flowing through the turbines, only about half of the available energy can be extracted.
In a one directional flow scheme power is generated only during half of the tidal cycle.
These two factors yield a typical net capacity factor of about 25%.
A bidirectional flow scheme is slightly better.
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Operational barrage systems -Rance River, France
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The first major barrage system to become operational (1966) was on the Rance River, France (rated at 240 MWe)
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Rance River turbine design
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Rance River uses horizontal Kaplan-type turbines as are commonly used for low head applications
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Annapolis Royal, Nova Scotia
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20 MWe rated capacity became operational in 1984
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Sihwa, South Korea
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Recently, a 254 MWe tidal barrage system became operational in South Korea (Sihwa Tidal Power Plant).
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Environmental consequences of tidal barrages
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Possible adverse effects include:
• Changes in tidal range outside basin because of changes in resonant period
• Effects on navigation• Effects on fish and marine mammal movement• Effects on sediment transport
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Non-barrage tidal power systemsTidal lagoons
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Artificial enclosures which take the place of natural basins
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Proposed tidal lagoon facility - Swansea, UKBidirectional generation scheme
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Underwater turbines
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Power per unit rotor area follows along the lines of derivation for wind turbines(C = capacity factor)
P/A= (1/2) Cρv3
Major difference is density of water (sea water 1025 kg/m3) compared with air (1.204 kg/m3).
Larger capacity factor than for wind turbines because of more predictable tidal currents (compared with wind).
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Operational tidal turbine at Strangford Lough, Northern Ireland
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rated at 1.2 MWe
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Location of Strangford Lough Tidal Turbine
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Tidal turbine projects
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Some tidal Power Plant locations under consideration
• Bay of Fundy, Nova Scotia, Canada
• Puget Sound, Washington, USA
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Shrouded Turbines
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Shrouded Turbines direct water into turbine and may be suitable for underwater devices
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Tidal fences
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Barrage with open turbines to allow water to flow freely in locations of extreme tidal currents
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Location of possible tidal fence project
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Mouth of Severn, UK
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Summary
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• Tidal energy results from the gravitational interaction between the oceans and the moon and sun
• Greatest tidal range exists in resonant basins• Barrage systems trap water from tidal movements
inside or outside a basin• Power is generated when water is allowed to flow
through gated turbines• Barrage systems have potential environmental
consequences• Tidal turbines are in the early stages of commercial
development in several areas