1 l aboratory for e nergy and e nvironmental c ombustion tidal in-stream energy overview brian...

1LABORATORY FOR ENERGY AND ENVIRONMENTAL COMBUSTION http://www.energy.washington.edu

Tidal In-Stream Energy Overview

Brian PolagyeResearch Assistant

University of WashingtonDepartment of Mechanical Engineering

September 11, 2006


Agenda

• Resource and Performance

• TISEC Devices

• Siting Arrays in Puget Sound

• UW Research


Tidal power is different than other forms of renewable energy

017,09-07-06,SNOPUD.ppt

Tidal Power- Comparison to Wind -

WindWind

Resource • Driven by uneven heating of earth’s surface by sun

• Occurs throughout the world

• Driven by gravitational pull of moon and sun

• Highly localized - requiring specific tidal range and bathymetry

TidalTidal

Availability • Intermittent• Long-term predictions as good

as a weather forecast

• Intermittent• Predictable centuries in advance

Proximity to Loads

• Often distant from load centers • Often close to load centers

Resource and PerformanceResource and Performance

Maturity • Mature technology • Developing technology


There are two very different approaches to harnessing the energy of the tides

Resource and PerformanceResource and PerformanceTidal Power

- Utilizing the Resource -

016,09-07-06,SNOPUD.ppt

BarrageBarrage In-stream TidalIn-stream Tidal

• Dam constructed across estuary― High cost ($ Bn)― Long construction period (decade)

• Power produced by closing dam at high tide and allowing water to run through turbines once ocean has returned to low tide

― Completely alters estuary circulation― Power produced in twice-daily surge― All attendant problems of hydro-

electric dams

• Low-cost power production at very large scale

• Turbines installed in estuary at constrictions in groups called arrays

― Moderate unit cost ($ MM)― Short unit construction time (weeks)

• Power produced directly from tidal currents

― More continuous (but still intermittent) power production

― Smart choice of turbines and layout of arrays should avoid significant environment impact

• Moderate-cost power production at varying scales


At a very basic level, tidal currents are generated by the rise and fall of the tides – water runs downhill

Resource and PerformanceResource and PerformanceTidal Currents

015,09-07-06,SNOPUD.ppt

Seabed

Tidal Basin

Flood tide

Ocean

• Slack water― Constant water height― No velocity

• Flood Tide― Water level higher outside

estuary than in main basin― Water flows into estuary

• Ebb Tide― Water level higher in basin

than ocean― Water flows out of basin

Ebb tide

Slack water

Tidal Basin

Ocean

Water level decreasing

Water level increasing

Side ViewSide View Top ViewTop View


Tidal currents vary primarily on a fourteen day lunar cycle

Resource and PerformanceResource and PerformanceTidal Cycle

014,09-07-06,SNOPUD.ppt

-4

-3

-2

-1

0

1

2

3

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

Date

Cu

rren

t V

eloc

ity

(m/s

)

Neap Tides (weakest)

Spring Tides (strongest)


Flow power has a cubic dependence on velocity – small velocity changes have a large effect on power

018,09-07-06,SNOPUD.ppt

Device Performance- Resource Utilization -


0

200

400

600

800

1000

1200

1400

0.0 1.0 2.0 3.0 4.0 5.0

Current Velocity (m/s)

Pow

er (

kW

)

Fluid Power

Electric Power

0

1000

2000

3000

4000

5000

6000

7000

8000

9000

0:00 4:48 9:36 14:24 19:12 0:00

Time

Pow

er (

kW

)

Fluid Power

Electric Power

Device PerformanceDevice Performance Representative DayRepresentative Day

Rated Speed

Cut-in Speed

Area Velocity Density 2

1 3 xxx


Power generation varies day-to-day, but is consistent on a monthly basis and shows no seasonal dependency

019,09-07-06,SNOPUD.ppt

Device Performance- Variable Predictability -


0

50

100

150

200

250

300

350

400

450

500

1/1 2/20 4/11 5/31 7/20 9/8 10/28 12/17

Date

Ave

rage

Pow

er (

kW

)

Daily AverageDaily Average

0

50

100

150

200

250

Jan

Feb

Mar

Apr

May Ju

n

Jul

Aug

Sep Oct

Nov

Dec

Month

Ave

rage

Pow

er (

kW

)

Monthly AverageMonthly Average


Agenda


• TISEC Devices


• UW Research


All turbines have a number of common components, but many variants

TISEC DevicesTISEC DevicesTurbine Overview

009,09-07-06,SNOPUD.ppt

Rotor• Extracts power from flow• Turns at low RPM• Efficiency varies with flow

velocity (45% max)

Gearbox• Increase rotational speed of shaft

from turbine• 80-95% efficient

Foundation• Secure turbine to seabed• Resist drag on support structure

and thrust on rotor

Generator and Power Conditioning

• Generate electricity• Condition electricity for

grid interconnection• Turns at high RPM• 95-98% efficient

Powertrain or Drivetrain


Two basic types of rotors have been developed – horizontal axis and vertical axis

TISEC DevicesTISEC DevicesRotor Variants

013,09-07-06,SNOPUD.ppt

Horizontal AxisHorizontal Axis Vertical AxisVertical Axis

Gearbox and Generator

Gearbox and Generator


Ducted turbines have been proposed to augment power production

TISEC DevicesTISEC DevicesPower Augmentation

012,09-07-06,SNOPUD.ppt

• Enclosing turbine in diffuser duct boosts power

• A number of questions remain unanswered regarding this approach

• Is it economically justified?―Ducts were never justified for wind turbines―Different set of circumstances for tidal

turbines

• Is there an increased hazard to marine mammals and fish?

―Can a large fish or mammal become trapped in the duct?


Foundation selection is usually driven by site water depth

TISEC DevicesTISEC DevicesFoundation Types

010,09-07-06,SNOPUD.ppt

Monopile

• Small footprint• Established technology used

in offshore wind

Gravity Base

Chain Anchors Tension Leg

Hollow steel pile driven or drilled into seabed

Pros:

• High cost in deep water• Installation expensive for

some types of seabed

Cons:

Heavy foundation of concrete and low cost aggregate placed on seabed

• Deep water installation feasible

Pros:

• Large footprint• Scour problems for some

types of seabed• Decommissioning problems

Cons:

• Small footprint• Deep water installation

feasible

Chains anchored to seabed and turbine

Pros:

• Problematic in practice• Device must have high

natural buoyancy

Cons:

Submerged platform held in place by anchored cables under high tension

• Small footprint• Deep water installation

feasible

Pros:

• Immature technology now being considered for offshore wind in deep water

Cons:

(10-40m)


TISEC DevicesTISEC DevicesMaintenance Options

011,09-07-06,SNOPUD.ppt

• Marine intervention extremely costly and must be minimized if TISEC devices can hope to compete economically

• All device developers pursuing low-maintenance philosophies

Divers

Device Retrieval Integrated Lift

Divers service turbine

• Divers widely availablePros:

• Difficult to work underwater• Very high intervention cost• In deep water, dive time

measured in minutes per day

Cons:

• Less costly than divers• Deep water feasible

Crane barge mobilized to retrieval entire turbine

Pros:

• High cost to mobilize heavy-lift crane barge

Cons:

Lifting mechanism integrated directly into turbine support structure

• Maintenance without specialty craft

• Deep water feasible

Pros:

• Cost of lifting mechanism• Support structure may be

surface piercing (aesthetic and shipping concerns)

Cons:


Marine Current Turbines is furthest along in the development process

TISEC DevicesTISEC DevicesMarine Current Turbines (MCT)

002,09-07-06,SNOPUD.ppt

Power trainPower train

FoundationFoundation

MaintenanceMaintenance

DevelopmentDevelopmentLarge Scale

(18 m diameter)Large Scale

(18 m diameter)

Horizontal axis (2 bladed)Planetary gearboxInduction generatorRated from 1.2 – 2.5 MW

Monopile drilled or driven into seabedTwo turbines per pile

Lifting mechanism pulls turbine out of water for servicing

3 years of testing prototype in UK1.5 MW demonstration planned for

installation in 2006/2007Conceptual fully submerged units


Verdant is positioned to install the first array of TISEC devices in the world

TISEC DevicesTISEC DevicesVerdant

002,09-07-06,SNOPUD.ppt




DevelopmentDevelopment

Monopile drilled or driven into seabed

Retrieval of power train by crane bargeDivers employed during installation

Small Scale (5 m diameter)Small Scale (5 m diameter)

Horizontal axis (3 bladed)Planetary gearboxInduction generatorRated at 34 kW

Installing 6 turbines off Roosevelt Island, NY City (Starting mid-Sept)

First permitted test project in US


Lunar Energy has adopted a different philosophy with an emphasis on a “bulletproof” design

TISEC DevicesTISEC DevicesLunar Energy

001,09-07-06,SNOPUD.ppt




DevelopmentDevelopment

Large Scale (21 m diameter inlet)

Large Scale (21 m diameter inlet)

Horizontal axis (ducted)Hydraulic gearboxInduction generatorRated at 2 MW

Gravity foundation using concrete and aggregate

Heavy-lift crane barge recovers “cassette” with all moving parts

Tank testingNearing end of design for first large

scale unit


Agenda


• TISEC Devices


• UW Research


Environmental issues are probably the biggest unknown for siting arrays of tidal in-stream turbines

007,09-07-06,SNOPUD.ppt

Case StudyCase StudySitingSiting

Environmental Issue

Environmental Issue Key QuestionsKey Questions Answers (so far)Answers (so far)

Direct “impact” of turbine on marine life

• Will a turbine make sushi in addition to electricity?

• No. Maximum tip velocity limited by cavitation. (~10 RPM for large turbines)

Indirect impacts • Developers are testing inert, glass-based anti-fouling paints to minimize this impact.

• Will anti-fouling paints used on turbines and supports degrade environment?

Environmental Issues- Marine Life Considerations -

• Will the rotor injure or harass fish and marine mammals?

• Unknown. Considerable cost and effort being expended by developers to prove technology is benign. No Altamont Passes.

• How much of the seafloor will be disturbed during installation?

• Depends on type of foundation and construction techniques. Choices will be driven by site depth and local concerns.

• Not in large quantities, but developers are working to minimize any leakage.

• Will oils and lubricants leak from the turbine?

20LABORATORY FOR ENERGY AND ENVIRONMENTAL COMBUSTION http://www.energy.washington.edu 008,09-07-06,SNOPUD.ppt

Case StudyCase StudySitingSitingEnvironmental Issues

Effect of energy extraction on the environment

• What is the effect of energy extraction?

• Altered circulation in estuary• Effects complicated and counter-

intuitive― Velocity increases downstream of

an array and water depth decreases― Overall flow rates are reduced

Environmental Issue

Environmental Issue Key QuestionsKey Questions Answers (so far)Answers (so far)

• How much energy can be extracted without substantially altering circulation?

• Rough estimates. 15% of the kinetic energy in a channel used as placeholder in resource studies.

― Overly conservative in some cases, overly optimistic in others.

― Question needs to be addressed on a case-by-case basis


In addition to environment, a number of factors need to be considered when siting turbine arrays. Most have not yet been addressed for sites in Puget Sound.

005,09-07-06,SNOPUD.ppt

Case StudyCase StudyArray Siting Issues- General -

SitingSiting

IssueIssue Key QuestionsKey Questions StatusStatus

Resource Size and Quality

• How large is the extractable resource?

• How many turbines in an array?

• Preliminary estimates using NOAA single-point current predictions

• Next Step: Current measurements

Electrical Infrastructure

• Will new transmission lines need to be built?

• What local loads exist?

• Not yet determined – requires consultation with local utilities

Bathymetry and Seabed Geology

• What foundation types are suitable for water depth?

• What foundations can seabed support?

• Not yet determined – requires geologic survey

Port Facilities • Are there local marine contractors capable of performing installation and maintenance of an array?

• Not an issue in Puget Sound for most types of construction


And the list goes on…

006,09-07-06,SNOPUD.ppt

Case StudyCase StudySitingSiting

IssueIssue Key QuestionsKey Questions StatusStatus

Shipping Traffic

• What is the maximum draft of shipping traffic in channel?

• Not yet determined – requires consultations with marine exchange and Coast Guard

Large-scale Turbulence

• Not yet determined – requires consultations with oceanographic experts

Multiple Use • How is the site currently used?• Does the site overlap with

major recreation or fishing areas?

• Not yet determined – requires consultations with regional stakeholders

Economics • Will turbines produce cost-effective power?

• Tacoma Narrows study predicted a cost of energy of ~10 cents/kWh

• Next step: Feasibility study

• Are there local geographic features that would give rise to large-scale eddies?

Array Siting Issues- General -


There are a number of prospective tidal energy sites in Puget Sound

020,09-07-06,SNOPUD.ppt

Puget Sound Resource Study- Overview - SitingSiting

Spieden Channel

San Juan Channel Deception

Pass

Admiralty Inlet

Agate Passage

Rich Passage

Guemes Channel Site Power Density

(kW/m2)Resource

(MW)Depth

(m)

• Tacoma Narrows

• Admiralty Inlet―Point Wilson―Marrowstone―Bush Point

• Deception Pass―Deception Pass―Yokeko Point

• Guemes Channel

• Bainbridge Island―Agate Passage―Rich Passage

• San Juan Islands―San Juan Channel―Spieden Channel

1.7

5.50.4

1.5

1.50.9

0.60.60.4

0.60.6

106

263

35

39

167195132

4556

40

3016

14

615

607175

6369

Tacoma Narrows estimated COE ~10 cents/kWh. Other sites?


San Juan Channel represents a substantial resource, but the channel is quite deep

024,09-07-06,SNOPUD.ppt

San Juan Channel- Overview - SitingSiting

Preliminary Array LayoutPreliminary Array Layout

Preliminary Array Performance

Preliminary Array Performance• 116 turbines (20 m diameter)

• Average installation depth ~95m • 5 MW average electric power• 16 MW rated electric power• 39,900 MWh annual generation

0.6 kW/m2

Turbine + Lateral Spacing


Preliminary Turbine Layout


0.8 km (0.5 mi)

San Juan Channel Ref.

San Juan Channel Ref.


Spieden Channel also represents a substantial resource, but is again a deep water channel

025,09-07-06,SNOPUD.ppt

Spieden Channel- Overview - SitingSiting

Preliminary Array LayoutPreliminary Array Layout



• 168 turbines (20 m diameter)• Average installation depth ~83m

• 8 MW average electric power• 26 MW rated electric power• 62,700 MWh annual generation

0.6 kW/m2

Limestone Point Ref.

Limestone Point Ref.





1 km (0.6 mi)


Agenda


• TISEC Devices


• UW Research


Question 1: How much tidal energy can be environmentally extracted?

003,09-07-06,SNOPUD.ppt

Case StudyCase StudyExtraction Limits

- Balancing Resource Against Environmental Impact -UW ResearchUW Research

Admiralty Head

Point Wilson

Bush Point

Marrowstone Point

Indian Island

• How much kinetic energy can be extracted by an array?

― Current estimates are 15% of kinetic energy in a channel (little physical reasoning)

― Probably much more site specific and closely related to frictional losses in channel

• Does the construction of one array preclude

the construction of others?― Can 20+ MW arrays be built at Pt. Wilson,

Marrowstone and Bush Point?― Can an array be built at Admiralty Inlet if

one already operating in Tacoma Narrows?

• Building an understanding with 1-D models― Very interesting preliminary results― Will be expanding to 2-D and 3-D cases

?

?

?


Question 2: How tightly can turbines in an array be packed?

004,09-07-06,SNOPUD.ppt

Case StudyCase StudyArray Packing

- Most Economic Use of Resource -UW ResearchUW Research

• Regions of high power flux may be relatively short and narrow

San Juan Island

Lopez Island

Low Power Density

High Power

Density

Low Power Density

• How close is too close?― Since flow is bi-directional, wind

turbine spacing rules are probably too conservative

― Downstream turbines must be beyond wake of upstream turbines

― Wakes degrade performance and accelerate metal fatigue

• Approaching with a combination of analytical and computational tools

― Little or no physical data available (since no arrays operating)

― Plan to leverage results of CFD modeling to suggest “engineering rules” for array layouts

• Economic reasons to site as many turbines in high power density regions as possible

1 l aboratory for e nergy and e nvironmental c ombustion tidal in-stream energy overview brian...

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