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Overview of Ocean Energy

Ocean energy is replenished by the sun and through tidal influences of the moon and sun gravitational forcesNear-surface winds induce wave action and cause wind-blown currents at about 3% of the wind speedTides cause strong currents into and out of coastal basins and riversOcean surface heating by some 70% of the incoming sunlight adds to the surface water thermal energy, causing expansion and flowWind energy is stronger over the ocean due to less drag, although technically, only seabreezes are from ocean energy

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Tidal Energy

Tidal mills were used in the Tenth and Eleventh Centuries in England, France, and elsewhereMillpond water was trapped at high tide by a gate (Difficult working hours for the miller)

Rhode Island, USA, 18th Century, 20-ton wheel 11 ft in diameter and 26 ft wideHamburg, Germany, 1880 “mill” pumped sewageSlade’s Mill in Chelsea, MA founded 1734, 100HP, operated until ~1980Deben estuary, Woodbridge, Suffolk, England has been operating since 1170 (reminiscent of “the old family axe”; only had three new handles and two new heads!)Tidal mills were common in USA north of Cape Cod, where a 3 m range exists [Redfield, 1980]Brooklyn NY had tidal mill in 1636 [?]

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Tidal Energy (continued)

Tides are produced by gravitational forces of the moon and sun and the Earth’s rotationExisting and possible sites:

France: 1966 La Rance river estuary 240 MW stationTidal ranges of 8.5 m to 13.5 m; 10 reversible turbines

England: Severn RiverCanada: Passamaquoddy Bay in the Bay of Fundy (1935 attempt failed); Truro Bay site operational.California: high potential along the northern coast

Environmental, economic, and esthetic aspects have delayed implementationPower is asynchronous with load cycle

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Tidal Energy (continued)

Tidal Energy (continued)

Potential energy = S integral from 0 to 2H (ρgz dz),where S is basin area, H is tidal amplitude, ρ is water density, and g is gravitational constantyielding 2 S ρ gH2

Mean power is 2 S ρ gH2/tidal period; semidiurnal betterTidal Pool Arrangements

Single-pool empties on ebb tideSingle-pool fills on flood tideSingle-pool fills and empties through turbineTwo-pool ebb- and flood-tide system; two ebbs per day; alternating pool useTwo-pool one-way system (high and low pools) (turbine located between pools)

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Tidal Energy (continued)

Tidal Water Turbines

Current flow converted to rotary motion by tidal currentTurbines placed across Rance River, FranceLarge Savonius rotors (J. S. Savonius, 1932?) placed across channel to rotate at slow speed but creating high torque (large current meter)Horizontal rotors proposed for Gulf Stream placement off Miami, Florida

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Tidal Energy (continued)

Tidal Energy (continued)

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Tidal Flow: Rance River, France

240 MW plant with 24, 10 MW turbines operated since 1966Average head is 28 ftArea is approximately 8.5 square milesFlow approx, 6.64 billion cubic feetMaximum theoretical energy is 7734 million kWh/year; 6% extractedStorage pumping contributes 1.7% to energy levelAt neap tides, generates 80,000 kWh/day; at equinoctial spring tide, 1,450,000 kWh/day (18:1 ratio!); average ~500 million kWh/yearProduces electricity cheaper than oil, coal, or nuclear plants in France

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Tidal Flow: Passamaquoddy, Lower Bay of Fundy, New Brunswick, Canada

Proposed to be located between Maine (USA) and New BrunswickAverage head is 18.1 ftFlow is approximately 70 billion cubic feet per tidal cycleArea is approximately 142 square milesAbout 3.5 % of theoretical maximum would be extractedTwo-pool approach greatly lower maximum theoretical energyInternational Commission studied it 1956 through 1961 and found project uneconomic thenDeferred until economic conditions change

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Tidal Energy (continued)

Other Tidal Flow Plants under Study

Annapolis River, Nova Scotia: straight-flow turbines; demonstration plant was to be completed in 1983; 20 MW; tides 29 to 15 feet; Tidal Power Corp.; ~$74MExperimental site at Kislaya Guba on Barents Sea

French 400 kW unit operated since 1968Plant floated into place and sunk: dikes added to close gaps

Sea of Okhotsk (former Sov. Union) under study in 1980White Sea, Russia: 1 MW, 1969Murmansk, Russia: 0.4 MWKiansghsia in China

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Other Tidal Flow Plants under Study (continued)

Severn River, Great Britain: range of 47 feet (14.5 m) calculated output of 2.4 MWh annually. Proposed at $15B, but not economic.Chansey Islands:20 miles off Saint Malo, France; 34 billion kWh per year; not economic; environmental problems; project shelved in 1980San Jose, Argentina: potential of 75 billion kWh/year; tidal range of 20 feet (6m)China built several plants in the 1950sKorean potential sites (Garolim Bay)

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Wave Energy

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Wave Energy (continued)

Change of water level by tide or wave can move or raise a float, producing linear motion from sinusoidal motionWater current can turn a turbine to yield rotational mechanical energy to drive a pump or generator

Slow rotation speed of approximately one revolution per second to one revolution per minute less likely to harm marine lifeTurbine reduces energy downstream and could protect shoreline

Archimedes Wave Swing is a Dutch device [Smith, p. 91]

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Wave Energy (continued)

Wave energy potential varies greatly worldwide

Source: Wave Energy paper. IMechE, 1991 and European Directory of Renewable Energy (Suppliers and Services) 1991

Figures in kW/m

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Wave characteristics

Wave Energy: Salter “Ducks”

Scottish physicist Prof. Stephen Salter invented “Nodding Duck” energy converter in 1970Salter “ducks” rock up and down as the wave passes beneath it. This oscillating mechanical energy is converted to electrical energyDestroyed by stormA floating two-tank version drives hydraulic rams that send pressurized oil to a hydraulic motor that drives a generator, and a cable conducts electricity to shore

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Ref.: www.fujita.com/archive-frr/ TidalPower.html©1996 Ramage

http://acre.murdoch.edu.au/ago/ocean/wave.html

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Wave Energy: OWEB

Ocean Wave Energy Web (OWEB) perspective view shows the operation of an interconnected OWEC module array.

Fluid-Driven Wave Turbines

Waves can be funneled and channeled into a rising chute to charge a reservoir over a weir or through a swing-gate

Water passes through waterwheel or turbine back to the oceanAlgerian V-channel [Kotch, p.228]

Wave forces require an extremely strong structure and mechanism to preclude damageThe Ocean Power Delivery wave energy converter Pelamis has articulated sections that stream from an anchor towards the shore

Waves passing overhead produce hydraulic pressure in rams between sectionsThis pressure drives hydraulic motors that spin generators, and power is conducted to shore by cable750 kW produced by a group 150m long and 3.5m diameter

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Wave Energy: Pelamis

Fluid-Driven Wave Turbines

Davis Hydraulic Turbines since 1981Most tests done in Canada4 kW turbine tested in Gulf Stream

Blue Energy of Canada developing two 250 kW turbines for British ColumbiaAlso proposed Brothers Island tidal fence in San Francisco Bay, California 1000 ft long by 80 ft deep to produce 15 – 25 MWAustralian Port Kembla (south of Sydney) to produce 500 kW

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Air-Driven Wave Turbines

British invention uses an air-driven Wells turbine with symmetrical bladesIncoming waves pressurize air within a heavy concrete box, and trapped air rushes upward through pipe connecting the turbineA Wavegen™, wave-driven, air compressor or oscillating water column (OWC) spins a two-way Wells turbine to produce electricityWells turbine is spun to starting speed by external electrical power and spins the same direction regardless of air flow directionEnergy estimated at 65 megawatts per mile

2.2.2.2 020402http://www.bfi.org/Trimtab/summer01/oceanWave.htm

Photo by Wavegen

Air-Driven Wave Turbines (Con’t)

A floating buoy can compress trapped air similar to a whistle buoyThe oscillating water column (OWC) in a long pipe under the buoy will lag behind the buoy motion due to inertia of the water columnThe compressed air spins a turbine/alternator to generate electricity at $0.09/kWh

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The Japanese “Mighty Whale” has an air channel to capture wave energy. Width is 30m and length is 50 m. There are two 30 kW and one50 kW turbine/generators

http://www.earthsci.org/esa/energy/wavpwr/wavepwr.html

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Hydraulic Pressure Absorbers

Large synthetic rubber bags filled with water could be placed offshore where large waves pass overhead

Also respond to tidesA connecting pipe conducts hydraulic pressure to a positive displacement motor that spins a generatorThe motor can turn a generator to make electricity that varies sinusoidally with the pressure

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http://www.bfi.org/Trimtab/summer01/oceanWave.htm

Ocean Thermal Energy Conversion (OTEC)

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OTEC (continued)

Il fisico francese Jacque D’Arsonval ha proposto per primo questo sistemanel 1881Georges Claude costrì Matanzos Bay, Cuba una centrale da 22 kW nel 1930Keahole Point, Hawaii ospita un sistema sperimentale Statunitense da 50 kWOTEC necessita di una differenza di temperatura fra l’acqua superficiale e quella fonda almeno di 7-16°CCentrali a ciclo aperto vaporizzano l’acqua calda e condensano usandol’acqua fredda del mare. I prodotti sono acqua dolce ed elettricità.Le centrali a circuito chiuso utilizzano cicli ad ammoniaca con unatemperatura massima di circa 25°C

Ref.: http://www.nrel.gov/otec/achievements.html

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OTEC (continued)

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OTEC (continued)

OTEC: infrastrutture

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OTEC (continued)

OTEC

E’ possibile che unastazione mobile OTEC dotata di sistemicombinati per l’energiasolare ed eolica sia un mezzo convenienteper la produzionedell’idrogeno?

OTEC Nemesis: Biofouling

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Correnti Oceaniche

Correnti Oceaniche (continued)

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Correnti Oceaniche (continued)

Turbine Oceaniche

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Ocean Energy: Summary

Le maree e l’energia termica rappresentano un’enormefonte di energiaL’azione delle onde si aggiunge all’energia sumenzionata ma è inferiore a quella associata alle mareeLe principali correnti (per es. corrente del golfo) possonoessere sfruttate mediante l’uso di appositi rotoriI venti sul mare sono di intensità maggiore e non cisono ostacoli.

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Link utili

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geothermal.marin.org/ on geothermal energywww.dieoff.org. www.ferc.gov/ Federal Energy Regulatory Commissionwww.hawaii.gov/dbedt/ert/otec_hi.html#anchor349152 dataweb.usbr.gov/html/powerplant_selection.html

http://www.nrel.gov/otec/