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Tidal In-Stream Energy Overview. Brian Polagye Research Assistant University of Washington Department of Mechanical Engineering. September 11, 2006. Agenda. Resource and Performance TISEC Devices Siting Arrays in Puget Sound UW Research.

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slide1

Tidal In-Stream Energy Overview

Brian Polagye

Research Assistant

University of Washington

Department of Mechanical Engineering

September 11, 2006

slide2

Agenda

  • Resource and Performance
  • TISEC Devices
  • Siting Arrays in Puget Sound
  • UW Research
tidal power is different than other forms of renewable energy
Tidal power is different than other forms of renewable energy

Tidal Power

- Comparison to Wind -

Resource and Performance

Wind

Tidal

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

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
  • Mature technology
  • Developing technology

Maturity

017,09-07-06,SNOPUD.ppt

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

Resource and Performance

Tidal Power

- Utilizing the Resource -

Barrage

In-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

016,09-07-06,SNOPUD.ppt

slide5
At a very basic level, tidal currents are generated by the rise and fall of the tides – water runs downhill

Resource and Performance

Tidal Currents

Side View

Top View

Ocean

Ocean

Water level increasing

Flood tide

Tidal Basin

Slack water

Tidal Basin

Ebb tide

Water level decreasing

Seabed

  • 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

015,09-07-06,SNOPUD.ppt

tidal currents vary primarily on a fourteen day lunar cycle

Spring Tides (strongest)

Neap Tides (weakest)

Tidal currents vary primarily on a fourteen day lunar cycle

Resource and Performance

Tidal Cycle

014,09-07-06,SNOPUD.ppt

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

Device Performance

- Resource Utilization -

Resource and Performance

Device Performance

Representative Day

Rated Speed

Cut-in Speed

018,09-07-06,SNOPUD.ppt

slide8
Power generation varies day-to-day, but is consistent on a monthly basis and shows no seasonal dependency

Device Performance

- Variable Predictability -

Resource and Performance

Daily Average

Monthly Average

019,09-07-06,SNOPUD.ppt

slide9

Agenda

  • Resource and Performance
  • TISEC Devices
  • Siting Arrays in Puget Sound
  • UW Research
all turbines have a number of common components but many variants
All turbines have a number of common components, but many variants

TISEC Devices

Turbine Overview

Gearbox

  • Increase rotational speed of shaft from turbine
  • 80-95% efficient

Generator and Power Conditioning

Powertrain or Drivetrain

  • Generate electricity
  • Condition electricity for grid interconnection
  • Turns at high RPM
  • 95-98% efficient

Rotor

  • Extracts power from flow
  • Turns at low RPM
  • Efficiency varies with flow velocity (45% max)

Foundation

  • Secure turbine to seabed
  • Resist drag on support structure and thrust on rotor

009,09-07-06,SNOPUD.ppt

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

TISEC Devices

Rotor Variants

Horizontal Axis

Vertical Axis

Gearbox and Generator

Gearbox and Generator

013,09-07-06,SNOPUD.ppt

ducted turbines have been proposed to augment power production
Ducted turbines have been proposed to augment power production

TISEC Devices

Power Augmentation

  • 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?

012,09-07-06,SNOPUD.ppt

foundation selection is usually driven by site water depth
Foundation selection is usually driven by site water depth

TISEC Devices

Foundation Types

Monopile

Gravity Base

Heavy foundation of concrete and low cost aggregate placed on seabed

Hollow steel pile driven or drilled into seabed

Pros:

  • Deep water installation feasible

Pros:

  • Small footprint
  • Established technology used in offshore wind

Cons:

  • Large footprint
  • Scour problems for some types of seabed
  • Decommissioning problems

Cons:

  • High cost in deep water
  • Installation expensive for some types of seabed

(10-40m)

Chain Anchors

Chains anchored to seabed and turbine

Tension Leg

Submerged platform held in place by anchored cables under high tension

Pros:

  • Small footprint
  • Deep water installation feasible

Pros:

  • Small footprint
  • Deep water installation feasible

Cons:

  • Problematic in practice
  • Device must have high natural buoyancy

Cons:

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

010,09-07-06,SNOPUD.ppt

slide14

TISEC Devices

Maintenance Options

Divers

Divers service turbine

  • Marine intervention extremely costly and must be minimized if TISEC devices can hope to compete economically
  • All device developers pursuing low-maintenance philosophies

Pros:

  • Divers widely available

Cons:

  • Difficult to work underwater
  • Very high intervention cost
  • In deep water, dive time measured in minutes per day

Device Retrieval

Crane barge mobilized to retrieval entire turbine

Integrated Lift

Lifting mechanism integrated directly into turbine support structure

Pros:

  • Maintenance without specialty craft
  • Deep water feasible

Pros:

  • Less costly than divers
  • Deep water feasible

Cons:

  • Cost of lifting mechanism
  • Support structure may be surface piercing (aesthetic and shipping concerns)

Cons:

  • High cost to mobilize heavy-lift crane barge

011,09-07-06,SNOPUD.ppt

marine current turbines is furthest along in the development process
Marine Current Turbines is furthest along in the development process

TISEC Devices

Marine Current Turbines (MCT)

Horizontal axis (2 bladed)

Planetary gearbox

Induction generator

Rated from 1.2 – 2.5 MW

Power train

Monopile drilled or driven into seabed

Two turbines per pile

Foundation

Lifting mechanism pulls turbine out of water for servicing

Maintenance

3 years of testing prototype in UK

1.5 MW demonstration planned for installation in 2006/2007

Conceptual fully submerged units

Development

Large Scale

(18 m diameter)

002,09-07-06,SNOPUD.ppt

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

TISEC Devices

Verdant

Horizontal axis (3 bladed)

Planetary gearbox

Induction generator

Rated at 34 kW

Power train

Foundation

Monopile drilled or driven into seabed

Retrieval of power train by crane barge

Divers employed during installation

Maintenance

Small Scale

(5 m diameter)

Development

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

First permitted test project in US

002,09-07-06,SNOPUD.ppt

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

TISEC Devices

Lunar Energy

Horizontal axis (ducted)

Hydraulic gearbox

Induction generator

Rated at 2 MW

Power train

Foundation

Gravity foundation using concrete and aggregate

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

Maintenance

Large Scale

(21 m diameter inlet)

Tank testing

Nearing end of design for first large scale unit

Development

001,09-07-06,SNOPUD.ppt

slide18

Agenda

  • Resource and Performance
  • TISEC Devices
  • Siting Arrays in Puget Sound
  • UW Research
environmental issues are probably the biggest unknown for siting arrays of tidal in stream turbines
Environmental issues are probably the biggest unknown for siting arrays of tidal in-stream turbines

Case Study

Siting

Environmental Issues

- Marine Life Considerations -

Environmental Issue

Answers (so far)

Key Questions

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)
  • Unknown. Considerable cost and effort being expended by developers to prove technology is benign. No Altamont Passes.
  • Will the rotor injure or harass fish and marine mammals?

Indirect impacts

  • Will anti-fouling paints used on turbines and supports degrade environment?
  • Developers are testing inert, glass-based anti-fouling paints to minimize this impact.
  • Will oils and lubricants leak from the turbine?
  • Not in large quantities, but developers are working to minimize any leakage.
  • 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.

007,09-07-06,SNOPUD.ppt

slide20

Case Study

Siting

Environmental Issues

Environmental Issue

Answers (so far)

Key Questions

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
  • 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

008,09-07-06,SNOPUD.ppt

slide21

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.

Case Study

Siting

Array Siting Issues

- General -

Issue

Status

Key Questions

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

Port Facilities

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

005,09-07-06,SNOPUD.ppt

and the list goes on
And the list goes on…

Siting

Case Study

Array Siting Issues

- General -

Issue

Status

Key Questions

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

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

006,09-07-06,SNOPUD.ppt

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

Puget Sound Resource Study

- Overview -

Siting

Spieden Channel

Power Density

(kW/m2)

Resource

(MW)

Depth

(m)

Guemes Channel

Site

  • Tacoma Narrows

1.7

106

40

  • Admiralty Inlet
    • Point Wilson
    • Marrowstone
    • Bush Point

San Juan Channel

0.6

0.6

0.4

167

195

132

60

71

75

Deception Pass

  • Deception Pass
    • Deception Pass
    • Yokeko Point

5.5

0.4

26

3

30

16

Admiralty Inlet

  • Guemes Channel

1.5

35

14

  • Bainbridge Island
    • Agate Passage
    • Rich Passage

1.5

0.9

3

9

6

15

Agate Passage

  • San Juan Islands
    • San Juan Channel
    • Spieden Channel

0.6

0.6

45

56

63

69

Rich Passage

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

020,09-07-06,SNOPUD.ppt

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

San Juan Channel

- Overview -

Siting

Preliminary Array Layout

Preliminary Turbine Layout

0.8 km

(0.5 mi)

Turbine + Lateral Spacing

San Juan Channel Ref.

0.6 kW/m2

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

024,09-07-06,SNOPUD.ppt

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

Spieden Channel

- Overview -

Siting

Preliminary Array Layout

Preliminary Turbine Layout

1 km (0.6 mi)

Limestone Point Ref.

Preliminary Array Performance

Turbine + Lateral Spacing

0.6 kW/m2

  • 8 MW average electric power
  • 26 MW rated electric power
  • 62,700 MWh annual generation
  • 168 turbines (20 m diameter)
  • Average installation depth ~83m

025,09-07-06,SNOPUD.ppt

slide26

Agenda

  • Resource and Performance
  • TISEC Devices
  • Siting Arrays in Puget Sound
  • UW Research
question 1 how much tidal energy can be environmentally extracted
Question 1: How much tidal energy can be environmentally extracted?

Extraction Limits

- Balancing Resource Against Environmental Impact -

Case Study

UW Research

  • 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

Admiralty Head

?

Point Wilson

?

Marrowstone Point

Indian Island

Bush Point

?

003,09-07-06,SNOPUD.ppt

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

Array Packing

- Most Economic Use of Resource -

Case Study

UW Research

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

Low Power Density

Lopez Island

High Power Density

San Juan Island

Low Power Density

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

004,09-07-06,SNOPUD.ppt