Tidal InStream Energy: Understanding Environmental Effects

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Tidal In-Stream Energy Understanding
Environmental Effects
Brian Polagye Research Assistant University of
Washington Department of Mechanical Engineering
September 17, 2007
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Agenda

• Basics of Turbine Operation
• Limits on Array Size
• Research on Extraction Impacts

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Basics
Turbine Variants
Horizontal Axis
Ducted
Vertical Axis
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Basics
Drive Train
Conventional
Generator

• 200 RPM
• Induction or synchronous

Electricity
Rotor
Gearbox

• 10 RPM

• Increase rotational speed of shaft from turbine

Maximum speed of rotor limited by cavitation
Smaller rotors can turn faster
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Basics
Foundation Variants
Monopile
Gravity Base
Tension Leg
Chain Anchors
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Basics
Power Take-off
Pilot Scale
Commercial Scale
115kV transmission line
Substation
115kV transmission line
Substation
New 115 kV transmission line
12kV distribution line
New substation
Cable landfall
Cable landfall
Horizontal directional drilling (multiple cables)
Horizontal directional drilling lt 500m
12 kV cable
Trenched
Trenched 30-35 kV
Turbine
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Basics
The Perfect Site
Does Not Exist
Top View
Cross-Section View
5 km
30-40m
20 km
Regular, constant cross-section
Very long, and wide
Uniform, high kinetic power density
1-2 kW/m2 OK
2-4 kW/m2 Great
gt4 kW/m2 Outstanding
No existing uses, biologically dead, and near a
major electrical load
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Agenda

• Basics of Turbine Operation
• Limits on Array Size
• Research on Extraction Impacts

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Array Size
Limit 1 Fundamental Fluid Limit
Beyond a certain point, installing more turbines
produces less power
Increasing number of turbines
Turning Point installing additional turbines
will produce less power
Turning point is site-specific
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Array Size
Limit 2 Real Estate
Regions of high power density are finite
Available power drops off rapidly outside
constrictions
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Array Size
Limit 2 Real Estate
Minimum separation required between each row of
turbines
Ideal
Too Close
Inefficient
Turbine
Free stream
Downstream turbines operate in wake
Turbines not making best use of resource
Low velocity wake
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Array Size
Limit 3 Electrical Infrastructure
Electric grids have limited capacity

• If grid is far from potential in-stream site,
  probably uneconomic to interconnect
• If grid is nearby, capacity depends largely on
  line voltage
• Distribution lines (12 kV) limited to a few MW
  peak
• Transmission lines (115 kV) limited to around 100
  MW peak

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Array Size
Limit 4 Social and Environmental Concerns
No sites identified to date are biological and
social deserts

• Estuary-scale fluid impacts
• Tidal range
• Pollutant flushing
• Oxygen saturation
• Local Impacts
• Scour
• Sediment transport
• Coolants and lubricants
• Noise
• Strike or harassment of fish and marine mammals
• Endangered or protected species
• Electromagnetic radiation

• Recreation
• Sport fishing
• Scuba diving
• Recreational boating
• Commerce
• Shipping
• Commercial fishing
• Tribes
• Accustomed fishing
• Military
• Navy traffic (surface and submerged)

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Array Size
Example 1 Spieden Channel
Weak electrical grid at northwest corner of San
Juan Island

• Sufficient space to install gt 150 turbines with
  rated electrical output of 26 MW (8 MW average)
• Nearest interconnection point only 15 kV
• Accommodate at most 5 MW of peak power
• New 69 kV cable would have to be trenched
  overland 5 miles at very high cost

Spieden Island
Spieden Channel
San Juan Island Island
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Array Size
Example 2 Agate Pass
Very limited space to install turbines

• High power density under bridge
• 115 kV transmission lines
• Power density drops off rapidly to the north
• Overhead and seabed clearance requirements
  (optimistically) leave a 2m thick layer for
  turbine deployment

Kitsap Peninsula
Agate Pass
200m
Bainbridge Island
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Array Size
Example 3 Admiralty Inlet
Environmental and social issues dominate

• Large region of high power density
• 115 kV transmission lines on Whidbey Island and
  in Port Townsend
• Many stakeholders
• Environmental concerns at an estuary level

Whidbey Island
3 km
Admiralty Inlet
4 km
Port Townsend
Marrowstone Island
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Agenda

• Basics of Turbine Operation
• Limits on Array Size
• Research on Extraction Impacts

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So far, lots of questions have been raised, some
harder to answer than others
Research
Questions and Answers (so far)
Are turbines likely to stress fish and marine
mammals?
How will turbines affect salmon recovery?
Example Question
Will turbines make sushi?
How will fluid flows change around arrays?
Method of Answer
Experiments and Modeling
Analysis
Pilot Tests
?
State of the Art
Cavitation limits maximum tip speed of rotor
Local speed increase around turbines, overall
reduction in flow rate
Locale-specific results only, no regional scale
work
?
Effort and cost required to answer questions
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Research
Activities at University of Washington

• Inter-disciplinary effort involving
• Oceanography Dr. Mitsuhiro Kawase, and Dr.
  Dimitri Leonov
• Mechanical Engineering Dr. Phil Malte, Dr. Jim
  Riley, Kristen Thyng
• General research on fluidic effects of extraction
  on idealized systems
• Working with Snohomish PUD on site assessment
• Coordination of current velocity measurements in
  Admiralty Inlet and Deception Pass
• Numerical modeling of currents in Deception Pass
• Going forward
• Numerical modeling of currents in Admiralty Inlet
• Numerical modeling of turbines in the flow

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Research
Estuary-scale Extraction Effects - State of the
Art -

• All theory no physical experiments or
  real-world tests
• Best near-term approach is numerical modeling
• No attempts yet to put results of modeling in an
  ecosystem context
• Extraction will have effects (not always
  measurable!)
• What level of impact is tolerable? Can an estuary
  withstand a 10 reduction in the tidal range? Is
  1 tolerable?
• General agreement that a pilot turbine in a tidal
  stream is not likely to alter estuary-scale
  circulation
• Bigger picture, longer-term question

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Research
Effects of Kinetic Power Extraction on Estuaries
Key Questions
First-order Answers

• Multiple effects, including
• Flow volume reduction
• Range reduction
• Kinetic power reduction

• What are the effects of kinetic power extraction
  from time-varying systems?

• What factors most strongly influence these
  effects?

• Multiple factors, including
• Magnitude of extraction
• Estuary geometry
• Tidal regime

Work submitted for publication, Brian Polagye et
al, PhD Candidate, University of Washington
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