Overview of Ocean Energy - Arturo de Risi
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Overview of Ocean Energy
z Ocean energy is replenished by the sun and through
tidal influences of the moon and sun gravitational forces
z Near-surface winds induce wave action and cause wind-
blown currents at about 3% of the wind speed
z Tides cause strong currents into and out of coastal
basins and rivers
z Ocean surface heating by some 70% of the incoming
sunlight adds to the surface water thermal energy,
causing expansion and flow
z Wind energy is stronger over the ocean due to less drag,
although technically, only seabreezes are from ocean
energy
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1
Tidal Energy
z Tidal mills were used in the Tenth and Eleventh Centuries in
England, France, and elsewhere
z Millpond 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 wide
Hamburg, Germany, 1880 “mill” pumped sewage
Slade’s Mill in Chelsea, MA founded 1734, 100HP, operated until ~1980
Deben 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)
z Tides are produced by gravitational forces of the moon
and sun and the Earth’s rotation
z Existing and possible sites:
France: 1966 La Rance river estuary 240 MW station
Tidal ranges of 8.5 m to 13.5 m; 10 reversible turbines
England: Severn River
Canada: Passamaquoddy Bay in the Bay of Fundy
(1935 attempt failed); Truro Bay site operational.
California: high potential along the northern coast
z Environmental, economic, and esthetic aspects have
delayed implementation
z Power is asynchronous with load cycle
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2
Tidal Energy (continued)
Tidal Energy (continued)
z 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 constant
yielding 2 S ρ gH2
z Mean power is 2 S ρ gH2/tidal period; semidiurnal better
z Tidal Pool Arrangements
Single-pool empties on ebb tide
Single-pool fills on flood tide
Single-pool fills and empties through turbine
Two-pool ebb- and flood-tide system; two ebbs per day;
alternating pool use
Two-pool one-way system (high and low pools) (turbine located
between pools)
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3
Tidal Energy (continued)
Tidal Water Turbines
z Current flow converted to rotary motion by tidal current
z Turbines placed across Rance River, France
z Large Savonius rotors (J. S. Savonius, 1932?) placed
across channel to rotate at slow speed but creating high
torque (large current meter)
z Horizontal rotors proposed for Gulf Stream placement
off Miami, Florida
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4
Tidal Energy (continued)
Tidal Energy (continued)
5
Tidal Flow: Rance River, France
z 240 MW plant with 24, 10 MW turbines operated since 1966
z Average head is 28 ft
z Area is approximately 8.5 square miles
z Flow approx, 6.64 billion cubic feet
z Maximum theoretical energy is 7734 million kWh/year; 6%
extracted
z Storage pumping contributes 1.7% to energy level
z At neap tides, generates 80,000 kWh/day; at equinoctial spring
tide, 1,450,000 kWh/day (18:1 ratio!); average ~500 million
kWh/year
z Produces electricity cheaper than oil, coal, or nuclear plants in
France
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Tidal Flow: Passamaquoddy, Lower
Bay of Fundy, New Brunswick, Canada
z Proposed to be located between Maine (USA) and New Brunswick
z Average head is 18.1 ft
z Flow is approximately 70 billion cubic feet per tidal cycle
z Area is approximately 142 square miles
z About 3.5 % of theoretical maximum would be extracted
z Two-pool approach greatly lower maximum theoretical energy
z International Commission studied it 1956 through 1961 and found
project uneconomic then
z Deferred until economic conditions change
[Ref.: Harder]
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6
Tidal Energy (continued)
Other Tidal Flow Plants under
Study
z 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.; ~$74M
z Experimental site at Kislaya Guba on Barents Sea
French 400 kW unit operated since 1968
Plant floated into place and sunk: dikes added to close gaps
z Sea of Okhotsk (former Sov. Union) under study in 1980
z White Sea, Russia: 1 MW, 1969
z Murmansk, Russia: 0.4 MW
z Kiansghsia in China
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7
Other Tidal Flow Plants under
Study (continued)
z Severn River, Great Britain: range of 47 feet (14.5 m)
calculated output of 2.4 MWh annually. Proposed at
$15B, but not economic.
z Chansey Islands:20 miles off Saint Malo, France; 34
billion kWh per year; not economic; environmental
problems; project shelved in 1980
z San Jose, Argentina: potential of 75 billion kWh/year;
tidal range of 20 feet (6m)
z China built several plants in the 1950s
z Korean potential sites (Garolim Bay)
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Wave Energy
8
Wave Energy (continued)
z Change of water level by tide or wave can move or raise
a float, producing linear motion from sinusoidal motion
z Water 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 life
Turbine reduces energy downstream and could protect shoreline
z Archimedes Wave Swing is a Dutch device [Smith, p.
91]
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Wave Energy (continued)
z Wave energy potential varies greatly worldwide
Figures in kW/m
Source: Wave Energy paper. IMechE, 1991 and
European Directory of Renewable Energy (Suppliers and Services) 1991
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9
Wave characteristics
Wave Energy: Salter “Ducks”
z Scottish physicist Prof. Stephen Salter
invented “Nodding Duck” energy
converter in 1970
z Salter “ducks” rock up and down as
the wave passes beneath it. This
oscillating mechanical energy is
converted to electrical energy
z Destroyed by storm
z A 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
Ref.: www.fujita.com/archive-frr/ TidalPower.html
©1996 Ramage
http://acre.murdoch.edu.au/ago/ocean/wave.html
2.2.1 020402
10Wave Energy: OWEB
Ocean Wave
Energy Web
(OWEB)
perspective
view shows the
operation of an
interconnected
OWEC module
array.
Fluid-Driven Wave Turbines
z 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 ocean
Algerian V-channel [Kotch, p.228]
z Wave forces require an extremely strong structure and mechanism
to preclude damage
z The 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 sections
This pressure drives hydraulic motors that spin generators, and
power is conducted to shore by cable
750 kW produced by a group 150m long and 3.5m diameter
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11Wave Energy: Pelamis
Fluid-Driven Wave Turbines
z Davis Hydraulic Turbines since 1981
Most tests done in Canada
4 kW turbine tested in Gulf Stream
z Blue Energy of Canada developing two 250 kW turbines
for British Columbia
z Also proposed Brothers Island tidal fence in San
Francisco Bay, California 1000 ft long by 80 ft deep to
produce 15 – 25 MW
z Australian Port Kembla (south of
z Sydney) to produce 500 kW
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12Air-Driven Wave Turbines
z British invention uses an air-driven Wells turbine with symmetrical
blades
z Incoming waves pressurize air within a heavy concrete box, and
trapped air rushes upward through pipe connecting the turbine
z A Wavegen™, wave-driven, air compressor or oscillating water
column (OWC) spins a two-way Wells turbine to produce electricity
z Wells turbine is spun to starting speed by external electrical power
and spins the same direction regardless of air flow direction
z Energy estimated at 65 megawatts per mile
Photo by Wavegen
http://www.bfi.org/Trimtab/summer01/oceanWave.htm 2.2.2.2 020402
Air-Driven Wave Turbines (Con’t)
z A floating buoy can compress trapped air similar to a
whistle buoy
z The oscillating water column (OWC) in a long pipe under
the buoy will lag behind the buoy motion due to inertia
of the water column
z The compressed air spins a turbine/alternator to
generate electricity at $0.09/kWh
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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13Hydraulic Pressure Absorbers
z Large synthetic rubber bags filled with water could be
placed offshore where large waves pass overhead
Also respond to tides
A connecting pipe conducts hydraulic pressure to a
positive displacement motor that spins a generator
The motor can turn a generator to make electricity
that varies sinusoidally with the pressure
http://www.bfi.org/Trimtab/summer01/oceanWave.htm
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Ocean Thermal Energy
Conversion (OTEC)
14OTEC (continued)
z Il fisico francese Jacque D’Arsonval ha proposto per primo questo sistema
nel 1881
z Georges Claude costrì Matanzos Bay, Cuba una centrale da 22 kW nel 1930
z Keahole Point, Hawaii ospita un sistema sperimentale Statunitense da 50
kW
z OTEC necessita di una differenza di temperatura fra l’acqua superficiale e
quella fonda almeno di 7-16°C
z Centrali a ciclo aperto vaporizzano l’acqua calda e condensano usando
l’acqua fredda del mare. I prodotti sono acqua dolce ed elettricità.
z Le centrali a circuito chiuso utilizzano cicli ad ammoniaca con una
temperatura massima di circa 25°C
Ref.: http://www.nrel.gov/otec/achievements.html
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OTEC (continued)
15OTEC (continued)
OTEC: infrastrutture
16OTEC (continued)
OTEC
E’ possibile che una
stazione mobile OTEC
dotata di sistemi
combinati per l’energia
solare ed eolica sia un
mezzo conveniente
per la produzione
dell’idrogeno?
OTEC Nemesis: Biofouling
021230
17Correnti Oceaniche
Correnti Oceaniche (continued)
18Correnti Oceaniche (continued)
Turbine Oceaniche
021230
19Ocean Energy: Summary
z Le maree e l’energia termica rappresentano un’enorme
fonte di energia
z L’azione delle onde si aggiunge all’energia su
menzionata ma è inferiore a quella associata alle maree
z Le principali correnti (per es. corrente del golfo) possono
essere sfruttate mediante l’uso di appositi rotori
z I venti sul mare sono di intensità maggiore e non ci
sono ostacoli.
Revised 021010
Link utili
http://www.nrel.gov/otec/
geothermal.marin.org/ on geothermal energy
www.dieoff.org.
www.ferc.gov/ Federal Energy Regulatory Commission
www.hawaii.gov/dbedt/ert/otec_hi.html#anchor349152
dataweb.usbr.gov/html/powerplant_selection.html
Revised 020115
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