ENERGY from OCEAN and TIDESS. Sridhar

IntroductionRenewable energy technologies provide alternatives to fossil-fueled power plants for the generation of electricity, an essential step towards reducing our nations dependence on fossil fuels.

One category of emerging renewable energy technologies relates to OCEAN ENERGY.

IntroductionAmong other types of renewable energy, oceans contain energy in the form of

Waves

Tidal currents

-History of Wave Energy-1799: First patent of a device designed to use ocean waves to generate power1910: First oscillating water column was built by Bochaux-Praceique to power his house1940s: Yoshio Masuda experimented with many concepts of wave power2004: Wave power was delivered to an electrical grid for the first time

Wave Facts:Waves are caused by a number of forces, i.e. wind, gravitational pull from the sun and moon, changes in atmospheric pressure, earthquakes etc. Waves created by wind are the most common waves. Unequal heating of the Earths surface generates wind, and wind blowing over water generates waves.This energy transfer results in a concentration of the energy involved: the initial solar power level of about 1 kW/m2 is concentrated to an average wave power level of 70kW/m of crest length. This figure rises to an average of 170 kW/m of crest length during the winter, and to more than 1 MW/m during storms.Wave energy performance measures are characterized by diffuse energy, enormous forces during storms, and variation over wide range in wave size, length, period, and direction. Wave energy is an irregular and oscillating low-frequency energy source that must be converted to a 60-Hertz frequency before it can be added to the electric utility grid.

Wave Energy - What causes waves?

Where does wave energy originate?Differential warming of the earth causes pressure differences in the atmosphere, which generate winds

As winds move across the surface of open bodies of water, they transfer some of their energy to the water and create waves

Wave energy densitiesThe power in a wave is proportional to the square of the amplitude and to the period of the motionLarge amplitude (~2 m), long period (~7-10 s) waves have energy fluxes commonly exceeding 40-50 kW/m width of oncoming waveWave energy is unevenly distributed over the globe

Wave EnergyThe strongest winds blow between 30 and 60 in latitude. Western coastlines at these latitudes experience the most powerful waves.

Global Wave Energy Resource Distribution (measuring the amount of power in kW contained in each linear meter of wave front)

Wave climate in EuropeThe wave climate along the western coast of Europe is characterized by particularly high energy. The UK has over half the wave energy potential in Europe, up to 75 kW/m off Ireland and Scotland Wave climate in the US The West Coast is the most promising area with wave energy densities in the 25 40 kW/m range

Wave EnergyThe amount of energy transferred and the size of the resulting wave depend on the wind speedthe length of time for which the wind blowsthe distance over which the wind blows, or fetch

Therefore, coasts that have exposure to the prevailing wind direction and that face long expanses of open ocean have the greatest wave energy levels.

How do we harness wave energy?In order to extract this energy, wave energy conversion devices must create a system of reacting forces, in which two or more bodies move relative to each other, while at least one body interacts with the waves.

There are many ways that such a system could be configured.

Wave Energy TechnologiesWaves retain energy differently depending on water depth

Wave energy conversion devices are designed for optimal operation at a particular depth range

Wave Energy TechnologiesTherefore, devices can be characterized in terms of their placement or location.At the shorelineNear the shorelineOff-shore

One wave energy conversion system that has proven successful at each of these locations is the OSCILLATING WATER COLUMN.

Wave energy convertersFour different types of WECs:

Oscillating water columns (OWC) Point absorbersSurging devices Floating devices

Wave Power DesignsAlthough many wave energy devices have been invented, only a small proportion have been tested and evaluated. Only a few of these have been tested at sea, in ocean waves, rather than in artificial wave tanks. Large scale offshore devices and small scale shoreline devices have been ocean tested. The total power of waves breaking on the world's coastlines is estimated at 2 to 3 million megawatts. In favorable locations, wave energy density can average 65 megawatts per mile of coastline.

Oscillating Water Columns (OWC) These devices generate electricity from the wave-driven rise and fall of water in a cylindrical shaft. The rising and falling water column drives air into and out of the top of the shaft, powering an air-driven turbine. Floats or Pitching Devices These devices generate electricity from the bobbing or pitching action of a floating object. The object can be mounted to a floating raft or to a device fixed on the ocean floor. Wave Surge or Focusing Devices These shoreline devices, also called "tapered channel" systems, rely on a shore-mounted structure to channel and concentrate the waves, driving them into an elevated reservoir. These focusing surge devices are sizable barriers that channel large waves to increase wave height for redirection into elevated reservoirs.

Oscillating Water ColumnThe type of turbine used is a key element to the conversion efficiency of an OWC.

Traditional turbines function by gas or liquid flowing in one direction and at a constant velocity. When the flow is not always from the same direction or at a constant velocity such as in the OWC traditional turbines become ineffective.

Oscillating Water ColumnAn Oscillating Water Column (OWC) consists of a partially submerged structure that opens to the ocean below the water surface. This structure is called a wave collector.

This design creates a water column in the central chamber of the collector, with a volume of air trapped above it.

Wave energy convertersThe oscillating water columnPartly submerged structure with an opening to the sea below the water lineWaves cause the water column to rise and fall, which alternately compresses and depressurizes the air column This air flows through a turbine which drives an electric generator

Oscillating Water ColumnAs a wave enters the collector, the surface of the water column rises and compresses the volume of air above it.The compressed air is forced into an aperture at the top of the chamber, moving past a turbine.As the wave retreats, the air is drawn back through the turbine due to the reduced pressure in the chamber.

Oscillating Water Columns

The Nearshore OWC rests directly on the seabed and is designed to operate in the near-shore environment in a nominal mean water depth of 15m.Nearshore OWC units also act like artificial reefs, improving environments for fishing while calming the water for a harbor.OWC designs typically require high maintenance, costly, taut moorings or foundations for operation while only using the extreme upper strata of an ocean site for energy conversion. While focusing devices are less susceptible to storm damage, massive structuring renders them most costly among wave power plant types.Since 1965, Japan has installed hundreds of OWC-powered navigational buoys and is currently operating two small demonstration OWC power plants. China constructed a 3 kW OWC and India has a 150 kW OWC caisson breakwater device.A 75 kW shore-based demonstration plant by Queens University, Belfast, using the OWC process described above has operated on the Scottish island of Islay for 10 years

These shoreline systems consist of a tapered channel which feeds into a reservoir constructed on a cliff. The narrowing of the channel causes the waves to increase their amplitude (wave height) as they move towards the cliff face which eventually spills over the walls of the channel and into the reservoir which is positioned several meters above mean sea level. The kinetic energy of the moving wave is converted into potential energy as the water is stored in the reservoir. The water then passes through hydroelectric turbines on the way back to sea level thus generating electricity.

Oscillating Water ColumnDifferent types of turbines have been developed for the OWC to address this problem.

The technologies have been demonstrated to work in a number of locations, with varying degrees of efficiency.Wavegens LIMPETEnergetechs Australia Wave Energy System

Turning Waves into Usable EnergyOscillating water columnIncoming waves force air up column to turn the turbineOutgoing waves suck air down column to turn the turbinehttp://www.acre.murdoch.edu.au/ago/ocean/wave.html

LIMPETPictured here is the LIMPET (Land Installed Marine Powered Energy Transformer), an Oscillating Water Column located on the Isle of Islay, Scotland, and designed by Wavegen

LIMPET

Constructed in a man-made gully on a rocky shoreline facing the open Atlantic ocean

LIMPETTo overcome the problems of traditional turbines, LIMPET employs a Wells turbine that turns in the same direction irrespective of the airflow direction.

LIMPETThe collector is tilted such that the resonance of the internal water column coincides with the peak energy period of the waves, easing passage of water into the water columnThe collector was divided into 3 chambers, with large holes at the top of each dividing wall to allow the air above the 3 water columns to combine to feed the turbine-generation systemThis design optimized performance for annual average wave intensities of 15 25 kW/m

LIMPETThe system contains a pair of Wells turbines, each of which is connected to a 250 kW induction generatorLIMPET has a generation capacity of 500 kWDesigned to supply power into the Islay grid

On-shore versus Off-shoreIn spite of the success of this technology in an on-shore application, most wave energy experts agree that off-shore or near-shore devices offer greater potential than shoreline devices.

On-shore technologiesAdvantagesEasier to access for construction and maintenanceLess installment costs and grid connection chargesCould be incorporated into harbor walls or water breaks, performing a dual service for the community

DisadvantagesLimited number of suitable sites / high competition for use of the shorelineEnvironmental concerns for on-shore devices may be greaterMuch less energy available to on-shore devices because water depth usually decreases closer to the shore

Energetechs Australia Wave Energy System

Pictured here the Australia Wave Energy System, an Oscillating Water Column located off the coast of Port Kembla, New South Wales, Australia and designed by Energetech

Energetechs Australia Wave Energy SystemLocated 200 meters from the Port Kembla Harbour BreakwaterTypically waves at Port Kembla exceed 1m in height 63% of the time (producing greater than 110kW on those occasions) and exceed 2m in height 5.5% of the time (producing greater than 400 kW on those occasions).

Energetechs Australia Wave Energy SystemDesigned to generate 500 kW, enough to power 500 homesThe system uses a variable pitch turbine called a Denniss-Auld turbine, potentially with a higher conversion efficiency than the Wells turbineThe turbine drives an induction generator

Energetechs Australia Wave Energy SystemSystem components are computer controlled The computer uses a sensor system with a pressure transducer to measure the pressure exerted on the ocean floor by each wave as it approaches the collectorThe transducer sends a signal proportional to that pressure to a Programmable Logic Controller which adjusts various parameters Optimizes conversion for the particular conditions and energy content of the waveProtects system components and ensures safety

Oscillating Water ColumnThe turning of the turbine drives a generator, producing electricity!

ConclusionThere is a large supply of wave energy availableThe technology already exists for extraction of this energyThe technical challenges are solvableThe problems lie in facilitating the testing and development of the technology to make it more affordableNeed federal fundingNeed a regulatory process conducive for rapid deployment of prototypes and research equipment

This vs. ThatAdvantages The energy is free - no fuel needed, no waste produced. Most designs are inexpensive to operate and maintain. Waves can produce a great deal of energy. There are minimal environmental impacts.

DisadvantagesDepends on the waves - sometimes you'll get loads of energy, sometimes nothing. Needs a suitable site, where waves are consistently strong. Must be able to withstand very rough weather. Disturbance or destruction of marine lifePossible threat to navigation from collisions because the wave energy devices rise only a few feet above the water.Degradation of scenic ocean front views from wave energy devices located near or on the shore, and from onshore overhead electric transmission lines.

Conclusion: Waves harness a lot of the suns power, but they are better for surfing than generating electricity.

Point absorbers

Wave energy convertersPoint absorbersThey provide a heave motion that is converted by mechanical/ hydraulic systems in linear or rotational motion for driving electrical generators

FLOATING DEVICES

Floating Devices The Salter Duck, Clam, Archimedes wave swing, and other floating wave energy devices generate electricity through the harmonic motion of the floating part of the device. In these systems, the devices rise and fall according to the motion of the wave and electricity is generated through their motion. The Salter Duck is able to produce energy very efficiently, however its development was stalled during the 1980s due to a miscalculation in the cost of energy production by a factor of 10 and it has only been in recent years when the technology was reassessed and the error identified.

Floating Devices(Salter Duck, Clam, Archimedes)Salter Duck-Electricity is generated through the movement of the device on the wave (bobbing up and down)

http://energy.saving.nu/hydroenergy/wave.shtmlhttp://www.fujitaresearch.com/reports/tidalpower.html

-Wave Power-Salters Duck design Could stop 90% of wave motion and could convert 90% of that to electricityShut down because of an error in calculating the cost, which wasnt discovered until 2008, and the program had been shut down in 1982

-How it Works-The duck device bobs back and forth as waves pass, this motion moves a pendulum that is connected to a generator that produces electricity http://www.permaculture.org.au/images/ocean_power_salters_duck.gif

SURGING DEVICES

Wave energy convertersSurging devicesSurging devices exploit the horizontal particle velocity in a wave to drive a deflector or to generate pumping effect of a flexible bag facing the wave front

Offshore devices The PelamisIs a semi-submerged structure composed of cylindrical sections linked by hinged joints

Offshore devices The Pelamis The wave induced motion of these joints is resisted by hydraulic rams which pump high pressure oil through hydraulic motors via smoothing accumulatorsThe hydraulic motors drive electrical generators to produce electricity

Offshore devices The PelamisSeveral devices can be connected together and linked to shore through a single seabed cable

Offshore devices The PelamisA typical 30MW installation would occupy a square kilometre of ocean and provide sufficient electricity for 20,000 homesOcean Power Delivery haswon a bid for a 750kW project off Islay, Scotland and has recently signed a memorandum of understanding with BC Hydro to develop a 2 MW project off the coast of Vancouver Island, Canada

LOCATION OF WAVE ENERGY DEVICES

Placement of wave energy convertersThree locations ShoreNear shoreOffshore

Placement of WECsOther factorsEngineering challengesConstruction costsMaintenance and/or installation costsTransmission costs and losses Environmental impactsThe scale of electricity production

AdvantagesAdvantages of offshore wave energy

Sea waves have high energy densities, the highest among renewable energy sources Wave energy is generally considered to provide a clean source of renewable energy with limited negative environmental impactsIt could become a significant source of energy not involving CO2 emissions

Advantages The natural seasonal variability of wave energy follows the electricity demand in temperate climatesNegligible demand on land use Could secure energy supplies in remote regionsLarge-scale implementation of wave power technologies will stimulate declining industries, e.g. shipbuilding

Disadvantages Disadvantages of offshore wave energy

The main wave energy barriers result from the energy carrier itself: The seaThe peak-to-average load ratio in the sea is very high and difficult to predictThe structural loading in the event of extreme weather conditions, such as hurricanes, may be as high as 100 times the average loading

Disadvantages High construction costs induce high power generation costs, thus making the technology uncompetitiveThe incidence of wave power at deep ocean sites is three to eight times the wave power at adjacent coastal sites, but the cost of electricity transmission from deep ocean sites is often prohibitively high

Environmental impacts considerationsDisturbance or destruction of marine life.Threat to navigation or transportation from collisions due to the low profile of some wave energy devices above the water.Degradation of scenic ocean front views from wave energy devices near or on the shore.Disturbance of recreation in near-shore environments.Alteration of sediment patterns Offshore wave energy devices may be a potential navigation hazard to ships.Near shore devices will have a visual impact .Wave energy devices could have an effect on some forms of recreation . Impacts on the marine environment.

S. Sridhar

Why do we want to use Tidal Energy?

Pollutionreduction CO2 emmissionAlternative forms EnergyRenewable Forms

-History of Tidal Energy-787: simple technique of a waterwheel by the Spanish, French, and British1966: La Rance tidal power plant went in operation.2001: British Parliament states the world can no longer neglect the massive potential of wave and tidal energy2002-present: Large investments in research and prototypes spark proposals in Turkey, China, and United States; among others

Energy from the moonTides generated by the combination of the moon and suns gravitational forcesGreatest affect in spring when moon and sun combine forcesBays and inlets amplify the height of the tideIn order to be practical for energy production, the height difference needs to be at least 5 metersOnly 40 sites around the world of this magnitudeOverall potential of 3000 gigawatts from movement of tides

How tides Work:The moons and suns gravity cause rise and fall of waterTides AnimationMost places have 2 high tides and low tides each dayTides change every 6 hours

The Tides Tidal energy comes from the gravitational forces of the Sun and the Moon on the Earths bodies of water, creating periodic shifts in these bodies of water.

These shifts are called tides.

Tidal EnergyMillions of gallons of water flow onto shore during tidal flows and away from shore during ebb tide periods.The larger the tidal influence, the greater the displacement of water and therefore the more potential energy that can be harvested during power generation.The tides are perfectly predictable, regular, and the US contains miles of coastline for energy exploitation.

The Tides

Turning Tides into Usable EnergyEbb generating systemA dam (barrage) is built across the mouth of an estuary.Sluice gates allow incoming tides to fill the basin.As the tide ebbs, the water is forced through a turbine system to generate electricity.http://www.acre.murdoch.edu.au/ago/ocean/tidal.html

Types of Turbineshttp://www.unesco.org/courier/1998_08/photoshr/33.htmhttp://www.acre.murdoch.edu.au/ago/ocean/tidal.html

Bulb turbine used at La Rance tidal plant on the Brittany coast in France

Turbines, cont.Rim turbine used at Annapolis Royal in Nova ScotiaTubular turbine proposed for use in the Severn tidal project in Great Britainhttp://www.acre.murdoch.edu.au/ago/ocean/tidal.html

Other PossibilitiesTidal FencesCompletely blocks a channel so as the tide rises, water is forced through the styles to turn them. Can be used between islands or between a mainland and an island as opposed to only across the mouth of a confined bay.http://abcnews.go.com/sections/scitech/DailyNews/tidalpower010404.htmlhttp://www.acre.murdoch.edu.au/ago/ocean/tidal.html

Tidal TurbinesOnly been feasible for about 5 yearsSimilar to wind turbines, they use tidal currents to turn propellers mounted on the seabed to generate power. http://www.fujitaresearch.com/reports/tidalpower.html

The Long History of Tidal Energy Tidal power buildings were built as early as the 9th Century throughout Europe.

This building was built in Ohalo, Portugal circa 1280.

Tidal EnergyTidal energy is one of many forms of hydropower generation.Tidal power has many advantages as compared to other forms of renewable energy.It is predictableGlobal Climate Change should only increase its generating capacity due to higher ocean levels.It is completely carbon neutral like wind or hydro energy.Its main drawbacks include: higher cost of installation, limited availability for ideal siting, environmental impacts on local area, including flooding and ecological changes, and the inflexible generation schedule (not timed to peak consumption).

Different Types of Tidal PlantsTidal BarragesThese involve the creation of mammoth concrete dams with sluices to create grander scale operations than the 12th century tide mills.Tidal Stream GeneratorsVery similar to the principles in wind power generation water flows across blades which turn a turbine much like how wind turns blades for wind power turbines.Dynamic Tidal PowerThis is a technology that is not currently commercial viable, but in which the UK, Korea, and China invested heavily to research. It involves a partial dam which raises the tidal height and several hydropower generators. The differences in height between the head of the dam and the low tide coast force water through the generator, much like a traditional hydropower dam.

Ways to extract energy from tides:Tidal Stream Farms

Barrages

Tidal Lagoons

Tidal Stream FarmsTurbines similar to wind turbines placed in tidal currents

Good locations would be Gulf Stream and Straits of Gibraltar.

Constant and reliable source of energy

TIDAL BARRAGES

Tidal Barrage The first commercial tidal power plant in the world since the middle ages is the La Rance Tidal Barrage in France.

The barrage was constructed in 1960 and consists of a 330m long dam with a 22km2 basin. The effective tidal range is 8m.

The work was completed in 1967 when 24 5.4m diameter bulb turbines, rated at 10MW each, were connected to the French power network with a 225kV transmission line.

The French authorities decided on a bulb turbine with axial power generation because it suited the style of a tidal barrage as it flows from the head of the dam to the basin through the turbine.

Barrages sluice gatesopen allowing the tide to flow in. Then closed at high tide At low tide water released Generator activated Energy converted into electricity

How Tidal Barrages Work

-Barrage Tidal Power: Rance Power Station-Located on Rance River, France750 meters long24 TurbinesCapacity of 240MWAnnual output of 600GWh Supplies 0.012% of Frances power supply.Opened 1966http://www.energysavers. gov/renewable_energy/ocean/index.cfm/mytopic=50009

How it worksFirst generation, barrage-style tidal power plantsWorks by building Barrage to contain water after high tide, then water has to pass through a turbine to return to low tideSites in France (La Rance), Canada (Annapolis), and Russia Future sites possibly on Severn River in England, San Francisco bay, Passamaquoddy

TIDAL ENERGY

Tidal Energy

-Calculations: Tidal Stream Generators-P = the power generated (in watts) = the turbine efficiency = the density of the water (seawater is 1025 kg/m) A = the sweep area of the turbine (in m) V = the velocity of the flow *Power equation is based on the kinetic energy of the moving water*

-Calculation: Barrage Tidal Power-E = energy = the density of the water (seawater is 1025 kg/m) A = horizontal area of the barrage basin G = Gravity (9.81m/s2)H = Vertical Tide Range

* The potential energy available from a barrage is dependent on * the volume of water.

Tidal LagoonsAn area of water cut off from the rest of the seaTide drops water is released through turbinesTide rises water is pushed through turbine

-Environmental Impact-Mortality rates of fish swimming threw the turbine is around 15%Sonic guidance to get fish to avoid the turbinePlacement of barrage turbines into estuaries can change entire ecosystemsAlters flow of saltwater possibly changing hydrology & salinitySediment movement also can effect the ecosystem

-Environmental Impact-Noise pollutionDisplace productive fishing sitesChange the pattern of beach sand nourishmentAlter food chains and disrupt migration patternsOffshore devices will displace bottom-dwelling organisms where they connect into the

Amount of Energy GeneratedHuge amounts

E.g. Severn Barrage: Generates as much electricity as 3 nuclear power stations

-Advantages and Disadvantages-AdvantagesDisadvantages

AdvantagesAfter construction, tidal energy is freeIt produces no greenhouse gases or wasteIt doesnt need fuelIt is reliable and predictableOff-shore turbines dont have a large environmental impactThe energy is free no fuel needed, no waste producedNot expensive to operate and maintainCan produce a great deal of energy

DisadvantagesLarge structures such as barrages are very expensive to buildBarrages change the environment It only provides power 10 hours each day when the tide is movingThere are few suitable locations for barrages Depends on the waves sometimes youll get loads of energy, sometimes almost nothingNeeds a suitable site, where waves are consistently strongSome designs are noisy. But then again, so are waves, so any noise is unlikely to be a problemMust be able to withstand

Is it really renewable? Tidal energy is renewable.

The tides will continue to ebb and flow, and the energy is there for the taking.

AdvantagesRenewable Abundant (estimated that it could produce 16% of worlds energy.)Pollution free (except during construction)Relatively consistent (unlike wind that is inconsistent and is highly concentrated in certain areas depending on the topography.)Water is a free resourcePresents no difficulty to migrating aquatic animals (avoidable)

http://www.hawaii.gov/dbedt/ert/wavereport/wave.pdfhttp://www.geology.wisc.edu/~pbrown/g410/tidal/tidal.html

DisadvantagesDisturbance/Destruction to marine life (effect wave climate that effects shallow/shore plant life)Expensive to construct (estimated 1.2 billion dollars.)Reliability ( have not been around long so we do not know long-term reliability is.)Recreational costs (visual impact, sport fishing, swimming, etc.)Cost of Maintenance HigherPower transmission from offshore facilities harderPower quality (waves fluctuation)

http://www.hawaii.gov/dbedt/ert/wavereport/wave.pdfhttp://www.geology.wisc.edu/~pbrown/g410/tidal/tidal.html

Present use of Tidal Energy

Tidal power has on a small scale been used through out the history of mankind. It was not until the twentieth century that large scale tidal projects were considered. Today, sites suitable for the utilization of tidal power exist in many places around the world. France United Kingdom (Apsley Strait) Former Soviet Union Canada United States

The extraction of large quantities of tidal energy is possible however, large scale tidal power operations are not technologically or economically feasible at the present time. Tidal sites are therefore limited to more modest developments.

http://www.geology.wisc.edu/~pbrown/g410/tidal/tidal.html

disadvantagesPresently costlyExpensive to build and maintainA 1085MW facility could cost as much as 1.2 billion dollars to construct and runConnection to the gridTechnology is not fully developedBarrage style only produces energy for about 10 hours out of the dayBarrage style has environmental affectsSuch as fish and plant migrationSilt depositsLocal tides change- affects still under study

AdvantagesNo pollutionRenewable resourceMore efficient than wind because of the density of waterPredictable source of energy vs. wind and solar Second generation has very few disadvantagesDoes not affect wildlife Does not affect silt depositsLess costly both in building and maintenance

Tidal Barrage ContdCalculating the total energy production of the La Rance plant is easy if you know some key facts:The La Rance plant has 24 generators with a 10MW capacity:The equation is as follows:

Maximum Electricity generated per annum (kWh) =Generator capacity * time + Cf (capacity factor)

The particular generator used in this plant had a Cf of 40%, resulting in 3504MWh per year per generator.

Tidal Barrage DrawbacksThere are notable complications with tidal barrage energy generationWhile they generate comparable power to hydropower plants, they also have economic and environmental issuesThe necessary infrastructure to build a tidal barrage is cost prohibitive.Tidal barrages negatively affect the turbidity, water levels, and ecology of the separated areas.

Tidal Barrage Drawbacks ContdBenthic habitats may change due to the bottom stress from modified waves and currents.Migratory fish may be impeded although fish passes can be constructed to facilitate migrations. Fish and marine mammals may suffer injuries and death when colliding with the barrage/turbines. Estuaries that are currently providing breeding spaces for fish, may not be suitable for this purpose after construction.

Other Ecological EffectsThe increasing sea exchange (due to pumping to increase water head, and therefore generating capacity) has increased the invertebrate breeding capacity.The outer estuary is now being fed by the inner estuary, which is a role reversal due solely to the barrages effect on the ecology and hydrology of the region.

Ecological Effects ContdShorebird prevalence has increased, but this is a nationwide trend across France.The primary attributing force for the increased shorebird populations are the increasing invertebrate life which is the primary source of food for shorebirds.Like shorebirds, fish diversity and biomass have increased due to the greater availability of invertebrate life that sustains these fish stocks.However, some fish species cannot traverse through the barrage and these species are no longer present.The new types of fish have displaced these original fish stocks and have thrived.Due to the dual flow nature of tidal barrages, fish mortality from turbine blades is nearly twice that of other hydropower.

Economic IssuesThe capital costs of a barrage like La Rance are tremendous because of the sheer scope of a project and the few sites around the world that are suitable for tidal power generation.The company that administers the La Rance power plant now claims that the capital investments in the barrage have been paid off and currently the power plant generates cheaper electricity than a nuclear power plant. (1.6 cents per kWh vs. 2.5 cents per kWh for a nuclear plant).

The Future of Tidal Barrages

Tidal Stream Generators

Tidal Stream Generator

(Contd)

Tidal Stream Generators

Tidal Stream Generator Specifics

Tidal Stream Generators The worlds only operational commercial-scale tidal turbine, SeaGen, was installed in Strangford Narrows in Northern Ireland in 2008.

The prototype SeaGen turbine produces 1.2MW with currents of 2.4m/s or more. The capacity factor exceeds 60%.

The facility is an accredited UK power station, and can contribute up to 6,000MWh annually to the UK grid, the equivalent of approximately 1500 homes.

Drawbacks of Tidal Stream GeneratorsHigh start-up and construction costs: due to limited experience of installing, operating and maintaining plants, contractors perceptions of risk are likely to be reflected in higher costs.Like the wind, waves and tidal streams are variable renewable energy sources. Their intermittent generation has implications for large scale grid integration. Because the amount of energy tidal streams naturally varies over time, the power output of wave energy converters and tidal stream energy generators will also vary. This has implications for grid integration, particularly balancing supply and demand.

Environmental Impacts of Tidal Stream Generation

Conclusion

*U.S. Department of Energys Office of Energy Efficiency and Renewable Energy, Exploring Ways to Use Ocean Energy, available at http://www.eere.energy.gov/consumer/renewable_energy/ocean/index.cfm/mytopic=50007*World Energy Council, Wave Energy, available at http://www.worldenergy.org/wec-geis/publications/reports/ser04/fuels.asp?fuel=Wave%20EnergyTom Heath, Realities of Wave Energy, available at http://www.wavegen.co.uk/pdf/art.1727.pdf**Robert W. Thresher, Wave and Tidal Energy: Whats Happening? available at http://www.mms.gov/offshore/PDFs/WaveTidal%20Energy_1-RobertThresher.pdfWorld Energy Council, Wave Energy, available at http://www.worldenergy.org/wec-geis/publications/reports/ser04/fuels.asp?fuel=Wave%20EnergyTom Heath, Realities of Wave Energy, available at http://www.wavegen.co.uk/pdf/art.1727.pdf, last visited .

**World Energy Council, Wave Energy, available at http://www.worldenergy.org/wec-geis/publications/reports/ser04/fuels.asp?fuel=Wave%20Energy

*U.S. Department of Energys Office of Energy Efficiency and Renewable Energy, Hydrokinetic and Wave Energy Technologies Technical and Environmental Issues Workshop, available at http://hydropower.id.doe.gov/hydrokinetic_wave/pdfs/hydro_workshop_proceedings.pdf*U.S. Department of Energys Office of Energy Efficiency and Renewable Energy, Hydrokinetic and Wave Energy Technologies Technical and Environmental Issues Workshop, available at http://hydropower.id.doe.gov/hydrokinetic_wave/pdfs/hydro_workshop_proceedings.pdfTom Heath, The Construction, Commissioning and Operation of the LIMPET Wave Energy Collector, available at http://www.wavegen.co.uk/pdf/Consruction,commission%20&%20operation%20of%20LIMPET.pdf*U.S. Department of Energys Office of Energy Efficiency and Renewable Energy, Hydrokinetic and Wave Energy Technologies Technical and Environmental Issues Workshop, available at http://hydropower.id.doe.gov/hydrokinetic_wave/pdfs/hydro_workshop_proceedings.pdf**Energetech, Technology, available at http://www.energetech.com.au/index.htm?http://www.energetech.com.au/content/port.html*Hydrokinetic and Wave Energy Technologies Technical and Environmental Issues Workshop, available at http://hydropower.id.doe.gov/hydrokinetic_wave/pdfs/hydro_workshop_proceedings.pdf*Model from http://www.daedalus.gr/DAEI/PRODUCTS/RET/General/OWC/OWCindustry.htm

*Alternative Fuels, Ocean Power: Waves, available at http://irishfuelprices.com/alternativefuels/wave.htmlResearch Institute for Sustainable Energy, Wave Energy, available at http://www.rise.org.au/info/Tech/wave/index.htmlBBC News, How it Works: Wave Power, available at http://news.bbc.co.uk/1/hi/sci/tech/1032148*Energetech, Technology, available at http://www.energetech.com.au/index.htm?http://www.energetech.com.au/content/port.html

*Research Institute for Sustainable Energy, Wave Energy, available at http://www.rise.org.au/info/Tech/wave/index.htmlHydrokinetic and Wave Energy Technologies Technical and Environmental Issues Workshop, available at http://hydropower.id.doe.gov/hydrokinetic_wave/pdfs/hydro_workshop_proceedings.pdf

*Tom Heath, The Construction, Commissioning, and Operation of the LIMPET Wave Energy Collector, available at http://www.wavegen.co.uk/pdf/Consruction,commission%20&%20operation%20of%20LIMPET.pdf*World Energy Council, Wave Energy, available at http://www.worldenergy.org/wec-geis/publications/reports/ser04/fuels.asp?fuel=Wave%20Energy

*Tom Heath, The Construction, Commissioning, and Operation of the LIMPET Wave Energy Collector, available at http://www.wavegen.co.uk/pdf/Consruction,commission%20&%20operation%20of%20LIMPET.pdf*Wavegen, Islay available at http://www.wavegen.co.uk/what_we_offer_limpet_islay.htm*Hydrokinetic and Wave Energy Technologies Technical and Environmental Issues Workshop, available at http://hydropower.id.doe.gov/hydrokinetic_wave/pdfs/hydro_workshop_proceedings.pdf

*Hydrokinetic and Wave Energy Technologies Technical and Environmental Issues Workshop, available at http://hydropower.id.doe.gov/hydrokinetic_wave/pdfs/hydro_workshop_proceedings.pdf

*Energetech, Sustainable and Innovative Energy, available at http://www.energetech.com.au/index.htm*Energetech, Port Kembla Project, available at http://www.energetech.com.au/index.htm?http://www.energetech.com.au/content/port.html*Energetech, Technology, available at http://www.energetech.com.au/index.htm?http://www.energetech.com.au/content/port.html*Energetech, Technology, available at http://www.energetech.com.au/index.htm?http://www.energetech.com.au/content/port.html

*Research Institute for Sustainable Energy, Wave Energy, available at http://www.rise.org.au/info/Tech/wave/index.html*Tom Heath, Realities of Wave Energy, available at http://www.wavegen.co.uk/pdf/art.1727.pdf*Pictures from http://www.waveenergy.dk/wave_teknik/2dk_anlaeg/pointabsorber/teknik_pointabsor.htmland http://www.owec.com/NewFiles/drawing.html

*Model from http://www.worldenergy.org/wec-geis/publications/reports/ser/wave/wave.asp

*Pictures from http://www.oceanpd.com/ *Picture from http://www.oceanpd.com/

*Picture from http://www.gridclub.com/fact_gadget/1001/earth/sea/133.html**Hydrokinetic and Wave Energy Technologies Technical and Environmental Issues Workshop, available at http://hydropower.id.doe.gov/hydrokinetic_wave/pdfs/hydro_workshop_proceedings.pdf

****Photo: Boyle, Renewable Energy, Oxford University Press (2004).*http://upload.wikimedia.org/wikipedia/en/0/00/Tide_type.gif*Historic Tidal mill in Portugal: http://cdn.wn.com/pd/8f/b9/0060eea52cd83c78005a38fcba61_grande.jpg*Boyle, Renewable Energy, Oxford University Press (2004).*Boyle, Renewable Energy, Oxford University Press (2004).*****http://www.esru.strath.ac.uk/EandE/web_sites/01-02/RE_info/tidal1.htm.

Photo: http://interestingenergyfacts.blogspot.com/2008/04/tidal-power-tidal-energy-facts.html***http://www.esru.strath.ac.uk/EandE/Web_sites/01-02/RE_info/Tidal%20power%20files/image004.jpg************Roger H. Charlier and John Justus. Ocean Energies: Environmental, Economic, and Technological Aspects of Alternative Power Sources. Elselvier, 1993. (p. 325).

J Wolf, IA Walkington, J Holt, R Burrows. Environmental Impacts of Tidal Power Schemes. Proudman Oceanographic Laboratory, The University of Liverpool, Department of Engineering, p.2.*J Wolf, IA Walkington, J Holt, R Burrows. Environmental Impacts of Tidal Power Schemes. Proudman Oceanographic Laboratory, The University of Liverpool, Department of Engineering, p.3.

*http://webarchive.nationalarchives.gov.uk/+/http://www.berr.gov.uk/files/file31334.pdf*http://webarchive.nationalarchives.gov.uk/+/http://www.berr.gov.uk/files/file31334.pdf

http://www.wyretidalenergy.com/tidal-barrage/la-rance-barrage*http://www.wyretidalenergy.com/tidal-barrage/la-rance-barrage*http://www.inhabitat.com/wp-content/uploads/turbine1.jpg*http://www.seattlepi.com/dayart/20070509/tidal-turbine.gifhttp://media.photobucket.com/image/Tidal%20Stream%20Generators/greenthoughts/verdant.jpg

*http://blog.syracuse.com/progress_impact/2008/02/0211_progress_wave_turbines.gif*http://www.reuk.co.uk/OtherImages/lunar-energy-tidal-turbine2.jpg*http://www.lunarenergy.co.uk/media/NewTurbinenodolphin.jpg*http://www.esru.strath.ac.uk/EandE/web_sites/01-02/RE_info/tidal1.htm.

The commercial system under development by MCT is known as SeaGen . The prototype is operational in Strangford Narrows, Northern Ireland, and uses twin 16m diameter rotors to develop a rated power of 1.2MW at a current velocity of 2.4m/s. The system is accredited to OFGEM as an official UK generating station and regularly runs at full rated power. It has the capability to deliver about 10MWh per tide, which adds up to 6,000MWh per year. This is approximately the rate of energy capture that a wind turbine of about 2.4MW rated capacity can typically produce. So SeaGen shows that the tides are not only more prodictable than wind but twice as productive.

Photo: http://interestingenergyfacts.blogspot.com/2008/04/tidal-power-tidal-energy-facts.html*http://www.marineturbines.com*Image: http://www.treehugger.com/verdant-power-turbine-j003.jpg

http://webarchive.nationalarchives.gov.uk/+/http://www.berr.gov.uk/files/file31334.pdfhttp://www.marineturbines.com/21/technology/29/environmental_impact/**Picture from http://www.energy.ca.gov/development/oceanenergy/