me tidal

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Energy and Environmental Combustion Laboratory

http://www.energy.washington.edu

HARNESSING THEPOWER OF THE MOON

How dowe go

from

to

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Tides rise and fall with great predictability

each day. How can we use this resource?Option 1: Tidal Barrage

Build a dam across the mouth of an

estuary (like a hydro-electric dam)

Option 2: In-Stream Tidal

Harness kinetic energy of the tides

Lets take a closer look at each option

Harness potential energy of tides

Underwater wind turbine

All pictures of in-stream turbines all available from the publicly accessible

Electric Power Research Institute website (www.epri.com/oceanergy)

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Tidal barrage systems work like

hydro-electric dams

Ocean Estuary

Barrage Dam

Low Tide

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On the incoming tide (flood tide),

water flows into the estuary

Ocean Estuary

Barrage Dam

Low Tide High Tide

Then the dam shuts

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Once the tide goes out, there is a height

(potential energy) difference between ocean

and estuary

Ocean Estuary

Barrage Dam

Low Tide High Tide

Then the dam opens

Low Tide

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As water flows through the dam, a turbine

extracts energy from the flow

Ocean

Estuary

Barrage Dam

Low Tide High Tide

Turbine

Low Tide

Then the entire process repeats on

the next tide

Since the ocean is much moremassive than the estuary, its

height does not change

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Tidal barrages have issues

Cost ($$$) The infrastructure required is enormous and so the

cost of construction is very high

A project in the Severn Estuary (UK) was projected to

cost $8 billion and take 10 years to build!

Who can afford something like that?

Variable Power

Production

Huge amount of power twice each day when dam in

operation, but no power in between (most of the day)

How can utilities integrate that with the grid?

Environmental

Impact

Operation of dam completely alters circulation in

estuary Dam turbines kill fish and cant accommodate marine

mammals

It is unlikely that a tidal barrage would ever be constructed again

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So how about in-stream tidal energy?

Its like a wind turbine but underwater.

Harnesses tidal currents rather than wind

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Tidal currents are generated by rise and fall

of the tides (water flows downhill)

Seabed

Estuary

Inlet

Estuary

BasinFlood

tide

Estuary

Inlet

Slack water

Constant water heightNo velocity

Flood Tide

Water level higher outsideestuary than in main basin

Water flows into estuary

Ebb Tide

Water level higher in mainbasin than outside estuary

Water flows out of estuary

Ebb Tide

EstuaryInlet

Tidal turbines harness both ebb and flood tides

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Tides are caused by the pull of the moon

and sun on the earths oceans

Gravitational mass of sun and

moon pulls on ocean, causingwater to rise and fall Strongest tides when sun and moon pull

in same direction (spring tide)

Weakest tides when sun and moon in

opposition (neap tide)

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Since currents are driven by tidal range, when

the range is greatest, currents are fastest

-4

-3

-2

-1

0

1

2

3

1-Feb 6-Feb 11-Feb 16-Feb 21-Feb 26-Feb

Date

CurrentVelocit

y(m/s)

Neap Tides (weakest)

Spring Tides (strongest)

Tidal currents vary with the lunar cycle (14 days)

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Tidal in-stream energy is in the

early stages. Lots of ideas.

Lets take a closer look at them

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All in-stream turbines have the

same basic components

RotorExtracts power from

flow

Foundation Secures turbine to

seabed

Horizontal axis

Vertical axis

Monopile

Gravity

Chain Anchors

Gearbox Steps up rotationalspeed from rotor

Planetary Gears Hydraulics

Generator Converts rotational

power to electricity

Induction

Permanent Magnet

I

II

III

IV

Component Function Options

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Marine Current Turbines

Power trainHorizontal axis (2 bladed)

Planetary gearbox

Induction generator

Rated from 1.22.5 MW

FoundationMonopile drilled or driven

into seabed

MaintenanceLifting mechanism pulls

turbine out of water

Development3 years of testing prototype

in UK (300 kW)Large Scale

(18 m diameter)

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Lunar Energy

Power trainHorizontal axis (ducted)

Hydraulic gearbox

Induction generator

Rated at 2 MW

FoundationGravity foundation using

concrete and aggregate

MaintenanceBarge recovers cassette

with all moving parts

DevelopmentTank testing

Nearing end of design for

first large scale unit

Large Scale(21 m diameter inlet)

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Open Hydro

Power train Horizontal axisNo gearbox

Rim-mount permanent

magnet generator

Rated at 1500 kW


into seabed

Maintenance

Divers, barge recovery?

DevelopmentSmall scale demonstration

unit off barge

Large Scale(15 m diameter)

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Verdant

Power trainHorizontal axis (3 blades)

Planetary gearbox

Induction generator

Rated at 34 kW


into seabed

MaintenanceBoat recovers entire power

train (pops off)

DevelopmentInstalling 6 turbines off

Roosevelt Island, NY CitySmall Scale(5 m diameter)

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GCK (Gorlov Helical Turbine)

Power trainVertical axis (3 blades)

Power train in development

Rated at 7 kW

Foundation Foundation in development

MaintenanceDivers, boat recovery?

DevelopmentTesting off barges and in

rivers

Small Scale(1 m diameter)

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So where should turbines be sited?

Criteria

Strong currents

Reason Logical Sites

Power flux goes

with the cube of

velocity

Constrictions in

estuaries with good

tidal range

Large cross-

sectional area

Channel power

product of power

flux and area

Large-scale

constrictions

ElectricalInfrastructure

Need to put thepower to use

Close proximity toexisting electrical

infrastructure

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(more siting issues)

Criteria

Solid seabed

Reason Logical Sites

Needs to support

or hold turbine

foundation

Scoured gravel or rock

seabed

Port Facilities Maintenance and

installation costs

lower if site near

port

Close proximity to

majorport

Multiple Use Estuaries used for

shipping and

recreation

Minimize conflicts in

design stage (e.g. fully

submerged turbines)

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So lets look at a case study close

to home Tacoma Narrows

Port of Tacoma(base for installation

and maintenance)

Tacoma Narrows Bridge

Point Evans Possible

Turbine Site

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High velocity currents in a relatively wide channelresults in a strong resource

0

200

400

600

800

1000

1200

1400

0:00 12:00 0:00

Hour

ChannelPow

er(MW)

Channel Power- Single Day -

0

20

40

60

80

100

120

140

Jan Mar May Jul Sep Nov

Month

AverageChannelPower(MW)

nnual Average= 106 MW

0

200

400

600

800

1000

1200

1400

1-Feb 6-Feb 11-Feb

Date

ChannelPow

er(MW)

Channel Power- Tidal Cycle -

Channel Power- Monthly Average -

Extraction Limit (15% Annual Average) = 16 MW

High hourly

variability

(two ebb and

flood tides per

day)

High daily

variability

(14 day lunar

cycle) Low monthly

variabilitystable long-term

resource

The seabed is relatively deep at Point Evans plenty of

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The seabed is relatively deep at Point Evans - plenty ofspace to install large diameter turbines

Tacoma Narrows

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The seabed is composed of dense sand and clay andshould support either pile or gravity foundations

Seabed Surface Seabed Geology

Predominantly clay and sand

Soil layers have beenglacially consolidated and

are very dense

High voltage interconnection is possible on the west

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High voltage interconnection is possible on the westside of Tacoma Narrows

Pt. Evans channel

marker

Tacoma Power has a

right of way (ROW)running south along the

bluffs from the channel

marker. Turbine power

cable would come ashorethere.

Tacoma Power

ROW115kV cable

crossing towers

115kV transmission line

(Tacoma Power)

Turbine array power

would connect with

existing 115kV line nearcable crossing towers

Marine Current Turbines is the best fit for megawatt

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Marine Current Turbines is the best fit for megawatt-scale generation in Tacoma Narrows

GCK (Gorlov)

Lunar Energy

Marine Current Turbines

Open Hydro

SeaPower

SMD Hydrovision

UEK

Verdant

Design Device

A number of devices are

unsuitable (in the near

term) due to immature:

Maintenance

FoundationPower train

Of the remaining

devices, Marine Current

Turbines fit the site best

A surface piercing pilot plant could be tested followed

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A surface piercing pilot plant could be tested, followedby installation of a larger array of submerged turbines

SeaGenDual-rotor

Surface piercing

Ready for deployment in short-term

Pilot Plant

Next-generation design

Fully submergedCompatible with shipping traffic

Requires new support structure and lifting

mechanismSame power train and foundation as SeaGen

Requires further development prior to

deployment

Commercial Plant

Device selection is driven by a need to minimize impact

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Device selection is driven by a need to minimize impacton Tacoma Narrows

Category Issue Design Approach

Biological Activity Kelp wrapped around rotors

Bio-accumulation on rotor and

support structure

Marine mammals and fish

Rope cutters at base of hub

Use of glass-based anti-fouling paints to prevent

bio-accumulation without introducing toxins to

ecosystem

Low rotational speed (~12 RPM)

Shipping Traffic Array footprint overlaps with

conventional shipping lane

15m LAT (lowest astronomical tide) overhead

clearance for fully submerged turbines

Pilot at edge of shipping lane

Eddies and

Turbulence

Eddies and large-scale

turbulence degrade turbine

operation and shorten life

Eddies from bridge and points

Far enough north of bridge to avoid caisson wake

Far enough offshore to be out of Point Evans eddy

Far enough south for Point Defiance turbulence todissipate

Recreational Use Swimming, diving, fishing all

take place in Tacoma Narrows

May require exclusion zone around turbine

array (< 10% total surface area). Enforceable?

Sport fishing lines unlikely to effect rotors

Turbines need to be separated to prevent the wake from

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Turbines need to be separated to prevent the wake fromone from degrading the operation of another

8 m17 m

Seabed

18 m

9 m

15 m

(minimum)

Surface

10 m

46 m 46 m

Lateral Spacing

and Clearance

Downstream

Spacing

Channel Edge

Channel Edge 180 m180 m

Dual rotor turbine

(46m tip-to-tip)

A commercial scale array at Point Evans might look like

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A commercial scale array at Point Evans might look likethis...

Turbine

Electrical

Cabling

f lik thi

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perform like this

Equipment Installed 64 fully submerged next-

generation MCT arranged

in 5 rows - 18,600 tons of

equipment

0

5

10

15

20

25

30

1-Jan 20-Feb 11-Apr 31-May 20-Jul 8-Sep 28-Oct 17-Dec

Date

Daily

Average

Power

(MW)

Average Array Output = 13.7 MW

Enough renewable energy to power

more than 10,000 homes

7.4 km of subsea cablerated to 33 kV

1700 m of trenching and

400 m of directional

drilling

Average installation depth

of 56 m

and produce dependable electricity at a cost-

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and produce dependable electricity at a cost-competitive rate!

Utility GeneratorMunicipal

Generator

cents/kWh (RealNominal)

7.68.8 5.76.5

Locally available renewable energy:

Low speed wind - ~10 cents/kWh

Solar PV - ~50 cents/kWh

And unlike solar and wind, tidal energy is

predictable centuries in advance!

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http://www energy washington edu

In-stream tidal energy represents

an environmentally benign, low-cost, sustainable, predictable

source of energy in our own

backyard

Thank you

me tidal

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