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Renewable Energy Sources
for Coastal Regions
Part 2: Tidal and Current
© M. L. Anderson, 2007
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The Problem
The dependence on petroleum products to generate electricity. High cost.
Transportation of these products.
Occasional shortages due to long distance transportation.
Pollution from use of carbon-based energy sources.
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AlternativesCoastal governments seek
alternative fuel sources forthe generation of electricity.
Solar power cells
Wind
Other marine sources ofenergy such as Tidal power
Current power
Wave energy
Ocean thermal energyconversion
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The Broader Impact
Widespread concern over globalclimate change
Environmental impact of reliance
on fossil fuels Climate change is one of the
greatest challenges humanity willface this century.
It will take a radical change in the
way we produce and consumeenergy – another industrialrevolution, this time for cleanenergy, conservation andefficiency.
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The Broader Impact
All forms of energy haveassociated costs.
Fossil fuels are limited inquantity and create vastamounts of pollution.
Large- scalehydroelectric power floodsvalleys and destroysanimal and human habitat.
Nuclear power is veryexpensive and createsradioactive waste that iseven more expensive anddifficult to dispose of.
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The Broader Impact
As global commitment to renewable energyincreases in the future, more attention islikely to become focused on the immensestores of energy associated with the ocean.
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Alternative Marine
Power Resources
Development of modernoffshore engineeringcapabilities coinciding with the
need to find large newrenewable energy resourcesmakes this a technicallyfeasible and economically
viable possibility.
Ocean energy comprises onlya miniscule proportion of
worldwide energy supply .
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What can ocean energy contribute to
regional security?
Renewable technology, not dependent on foreign oil. Modular technology, ease of instillation. Distributed generation, can function off grid. Economic growth.
Capital used for oil imports can be used for local social andinfrastructure improvements.
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Why use the Ocean?
Concentrated resource, more so than solar Intermittent and FREE like the wind Currents, tides and winds are predictable Minimal visual impacts and small footprint
Modular development, so projects can be “phasedin”
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Alternative Marine Power Resources
Renewable energy fromthe ocean would most likelyimprove the environmentby replacing fossil fuelplants and reducing carbonemissions.
The ocean probably storesenough energy in the formof heat, currents, waves,and tides to meet totalworldwide demand for
power many times over. It will be critically importantto ensure that thedevelopment of new oceanenergy be environmentallyfriendly.
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Overview of Marine Technologies
The use of kinetic energy via tidal currents (Tidalcurrent generators)
The use of kinetic energy via waves (Wave
energy converters)
The use of potential energy via tidal dams.
Ocean Thermal Energy Conversion (OTEC)
Off shore trade winds (Wind turbines)
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Cost Issues (U.S. Prices)
Source Best Price (/kWh)
New Coal 3.5 cents
New Gas Comb. Cycle 2.6 cents (price volatility)
Wind 4.7 cents (average, w/out 1.8 cent PTC) 2.9
Solar Thermal 11 cents
Photo voltaic 18-27 cents
Wave Energy 7-13 cents (average, 1 MW demo all
technologies);
Tidal / Current Energy 6 cents for (per EPRI report)
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Historic Perspective on Cost
Power Source Cost
Wind, early 1980s 25 cents /kWh
Wind, present 4-6 cents /kWh (w/out Power Tax Credit
U.S. (PTC)) 2.9-4
Wind, present 3.3 -5.3 cents /kWh
Ocean/ Wave, present 7-16 cents /kWh for demoproject; no PTC
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Tidal Energy
Tides are caused by the gravitational attraction of the
moon and the sun acting upon the oceans of the
rotating earth.
The relative motions of these bodies cause the surfaceof the oceans to be raised and lowered periodically,
according to a number of interacting cycles.
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Tidal Energy
Tidal energy is exploiteddirectly from marinecurrents induced by thecombined lunar and solargravitational forces
responsible for tides. Extraction of energy from
the tides is practical onlyat those sites where theenergy is concentrated in
the form of large tidesand the geographyprovides suitable sites fortidal plant construction.
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Tidal Energy
The tidal range can beamplified by reflection of thetidal wave by the coastline orresonance.
This occurs in long, funnel-
shaped estuaries, when thelength of the estuary is closeto one quarter of the tidalwave length
Where coastal morphologycreates natural constrictions:around headlands or betweenislands.
This phenomenon produces
strong currents, or tidalstreams.
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Tidal Energy
The tidal range can varysubstantially between differentpoints on a coastline.
The amount of energyobtainable varies with location
and time. Output changes as the tide
ebbs and floods each day.
Tidal energy is highly
predictable in both amount andtiming.
The available energy isapproximately proportional tothe square of the tidal range.
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How does it work?
Tidal Barrage
-serves to let water
flow through it into abasin as the tidecomes in
-power can be
generated in bothdirections
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How does it work?Turbines
-used to pump extra waterinto the basin at periods of
low demand
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How does it work?
Tidal Fence
-looks like turnstiles that
turn via tidal currentstypical of coastal waters
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How does it work?
Tidal Stream
-fast flowing bodies
of water cause bythe motion of thetides
-occur in shallow
seas where naturalconstriction existsand causes water tospeed up
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How does it work?Offshore Turbines
-can either be partially orcompletely submerged
-partially submerged areless costly formaintenance
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How does it work?
Swanturbine
-blades are
connected directly tothe electricalgenerator
-more efficient than
other devices
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Tidal Energy:
Impoundment/Turbines
4 lane road tops this
242 MW tidal power
plant
La Rance Estuary, France
242 MW Operating Since 1967
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The La Rance tidal power plant
It is located in La Rance,France
The oldest and the largestTidal Plant is the La Rance
240 megawatt barragelocated near St. Malo, inBrittany, Northern France.
This tidal power plant wasbuilt for commercialproduction and beganoperating in 1966.
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The La Rance Tidal Power Plant It is highly automated,
requiring only two people tooperate it on weekends and inthe evening,
It supplies 90% of Brittany's
electrical needs. After 30 years of productivity,
the power plant is undergoinga $78 million renovation.
To provide uninterruptedpower production, the plant's24 turbines are beingupgraded one at a time over a
10 year period.
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Annapolis River Tidal Power Plant
The Annapolis TidalPower Plant was thefirst to transform tidalenergy to electricityin the U.S. (courtesy
Tidal Power Corp).
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H d t i P M d l d d
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Hydroventuri Power Module used underSan Francisco Bay Bridge
Rochester Power Module
Where maximumpressure drop
occurs air or wateris sucked from thesurface through asystem of pipes
The suction created inthis circuit is
sufficient to driveturbines
The flow is passedthrough a venturi
This causes the waterto accelerate andthe pressure to
drop
Water enters the module
© 2002, Hydroventuri, Inc. All rights reserved
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South Korea
South Korea plans on building the largest tidal energypower plant to be known as the Sihwa Tidal Power Plant.
It will be designed to generate 260 MW from constantflow of water in and out of the seaside bay.
Cost – $250 million US dollars.
Project expected to be completed by 2009.
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Tidal and Current Technologies
Main Characteristics Similar principle to wind
turbines, but current
drives turbines Both vertical and
horizontal turbines Potential uses for
ocean and rivers
Estimated costs as lowas 6 cents/kWhbecause of economiesof scale with windindustry (EPRI)
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Kinetic Energy
Systems viaTidal Streams
The level of power available from kinetic-energy extractionschemes is generally much lower than from the potentialenergy of impounded basins.
They do not require construction, high maintenance andoperation of dams and gates.
They have much less environmental impact.
much lower installation costs per kilowatt of capacity.
Marine Current Turbines
Blue Energy Canada Tidal Fence
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Tidal Stream EnergyTidal stream energy generation has a number of attractive
features:
predictability of tidal streams
high power density of water flow
lack of extreme flow speeds
minimal visual impact.
Obstacles include:
the expense involved in marine construction in thepresence of strong currents
the cost of cable-laying
cost of possible grid reinforcement.
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Marine Current Technologies
Verdant Power
– Current projectproposed for East
River in NYC – Each unit 25-250
kW
– Authorized to install6 unit configurationand generate powerexperimentally byend of August 2006
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Tidal DemonstrationEast River, New York City
Verdant Powerreceived fundingfrom NYSERDA andother participating
state, federal, andprivateorganizations for aprototypedemonstration.
FERC has issued apreliminary permitfor the prototypetidal project.
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Tidal DemonstrationEast River, New York City
The proposed East Riverturbine field, shown in
green, will progress over4 years, beginning in2004. The 1 mile long by270 feet wide and 30-40feet deep tidal plant willultimately provide 5-10MW.
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Tidal Demonstration
East River, New York CityVerdant Power expects to
complete this $20million East Riverproject, including powerconditioning and gridconnection, within fouryears. Subsequent sites
are expected to bedeveloped in less thanone year.
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Kinetic Energy Systems via
Marine Currents
Marine current turbines work likesubmerged windmills, but driven byflowing water rather than air.
They can be installed in the sea atplaces with high tidal currentvelocities, or in places with fastenough continuous ocean currents,to take out energy from these huge
volumes of flowing water. These flows have the major
advantage of being an energyresource which is as predictable asthe tides that cause them.
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Marine Currents
The submerged turbines are rated atfrom 750 to 1500kW per unit(depending on the local flow patternand peak velocity),
will be grouped in "farms" under thesea, at places with high currents,much the same way that windturbines in a wind farm deployed.
Independent environmental impact
analyses confirm that the technologydoes not offer any serious threat tofish or marine mammals.
The rotors turn slowly (10 to 20rpm).
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Marine Current Technology
Marine CurrentTechnologies
– 300 kW pilot testedin Lynmouth UK with
positive results – Dual turbine
technology underinvestigation, 500kw – 1 MW each
– Examining othersites, with delaysdue to permittingproblems
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Images Cross-section of a tidal barrage
Tidal Turbine
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Advantages of Using Tidal
Energy The primary advantages of tidal power plants
are: regularity of power production from year to
year with less than 5% annual variation permits the simultaneous use of the dam for a
road or rail road long-term operational lifetime of plant
protects vulnerable coastlines from stormwaves and flooding
provides a non-polluting and inexhaustiblesupply of energy.
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Disadvantages
Some disadvantages of tidal power plants are: high capital costs for initial construction limited number of potential sites. A minimum
tidal range (the difference between high and lowtide levels) is needed if tidal power is to bepractical. A range of 5 m is often cited as theminimum. Over the past three decades, thefeasibility of using ocean tides to generate
electric power has been investigated at manysites throughout the world.
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Limited Sources The potential for economic
development is small with onlysix suitable areas representingwell over half of the potentialfor development of tidalenergy.
1. The headwaters of the Bayof Fundy (Canada)2. The Severn estuary (UnitedKingdom)3. The Gulf of St. Malo(France)
4. The south-east coast ofChina5. The Russian coastbordering the White Sea6. The Russian coastbordering the Sea of Okhotsk
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Limited Sources
Other potentially feasible sitesinclude:
The Mersey estuary and smaller
sites bordering the Irish Sea and The Bristol Channel (United
Kingdom),
The Gulf of Kachch (India),
The west coast of Korea,
The north-west coast of Australia,
Cook Inlet (Alaska), and
The Gulf of San Jose (Argentina)
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Environmental Challenges
Leads to smaller water volumes = more light =
change in ecosystem
Pollution increased
Technologies disturb sea life migration
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Disadvantages Potential for negative environmental impacts such
as water quality, estuarine feeding areas for birdsand other animals, and the passage of migratoryfish.
Few studies have been conducted to assess theenvironmental impacts of constructing a tidalpower plant.
It has been generally determined that eachspecific site is different and the impacts dependgreatly upon local geography.
Local tides changed only slightly due to the La
Rance barrage, and the environmental impact hasbeen negligible. This may not be the case for all other sites. Very
little is understood about how altering the tides canaffect incredibly complex aquatic and shoreline
ecosystems.
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