tidal current energy

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Renewable Energy Sources

for Coastal Regions

Part 2: Tidal and Current

© M. L. Anderson, 2007



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.



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



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.



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.



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.



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 .



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.



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”



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.



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)



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)



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



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.



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.



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.



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.



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



How does it work?Turbines

-used to pump extra waterinto the basin at periods of

low demand



How does it work?

Tidal Fence

-looks like turnstiles that

turn via tidal currentstypical of coastal waters



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



How does it work?Offshore Turbines

-can either be partially orcompletely submerged

-partially submerged areless costly formaintenance



How does it work?

Swanturbine

-blades are

connected directly tothe electricalgenerator

-more efficient than

other devices



Tidal Energy:

Impoundment/Turbines

4 lane road tops this

242 MW tidal power

plant

La Rance Estuary, France

242 MW Operating Since 1967



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.



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.



Annapolis River Tidal Power Plant

The Annapolis TidalPower Plant was thefirst to transform tidalenergy to electricityin the U.S. (courtesy

Tidal Power Corp).



H d t i P M d l d d



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



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.



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)



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



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.



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



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.



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.



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.



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.



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).



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



Images Cross-section of a tidal barrage

Tidal Turbine



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.



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.



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



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)



Environmental Challenges

Leads to smaller water volumes = more light =

change in ecosystem

Pollution increased

Technologies disturb sea life migration



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.

tidal current energy

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