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

2. Agenda
Basics of Turbine Operation
Limits on Array Size
Research on Extraction Impacts

3. Turbine Variants Horizontal Axis Ducted Vertical Axis Basics
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4. Drive Train “Conventional” Direct Drive
Basics
Drive Train
“Conventional”
Direct Drive
Generator
~10 RPM
Permanent magnet
Electricity
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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5. Foundation Variants Monopile Gravity Base Tension Leg Chain Anchors
Basics
Foundation Variants
Monopile
Gravity Base
Tension Leg
Chain Anchors
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6. Power Take-off Pilot Scale Commercial Scale 115kV transmission line
Basics
Power Take-off
Pilot Scale
Commercial Scale
115kV transmission line
Substation
115kV transmission line
Substation
12kV distribution line
New 115 kV transmission line
New substation
Cable landfall
Cable landfall
Horizontal directional drilling
< 500m
Horizontal directional drilling
(multiple cables)
Cluster #3
12 kV cable
Trenched
Trenched
30-35 kV
Turbine
Cluster #1
8 Turbines
Cluster #2
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7. Regular, constant cross-section
Basics
The Perfect Site
Does Not Exist
Cross-Section View
Top 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
>4 kW/m2 Outstanding
No existing uses, biologically dead, and near a major electrical load
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8. Agenda
Basics of Turbine Operation
Limits on Array Size
Research on Extraction Impacts

9. Limit #1: Fundamental Fluid Limit
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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10. Regions of high power density are finite
Array Size
Limit #2: Real Estate
Regions of high power density are finite
Available power drops off rapidly outside constrictions
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11. Minimum separation required between each row of turbines
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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12. Limit #3: Electrical Infrastructure
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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13. Limit #4: Social and Environmental Concerns
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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14. Example #1: Spieden Channel
Array Size
Example #1: Spieden Channel
Weak electrical grid at northwest corner of San Juan Island
Sufficient space to install > 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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15. Very limited space to install turbines
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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16. Example #3: Admiralty Inlet Environmental and social issues dominate
Array Size
Example #3: Admiralty Inlet
Environmental and social issues dominate
Whidbey Island
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
3 km
Admiralty Inlet
4 km
Port Townsend
Marrowstone Island
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17. Agenda
Basics of Turbine Operation
Limits on Array Size
Research on Extraction Impacts

18. Experiments and Modeling Effort and cost required to answer questions
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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19. Activities at University of Washington
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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20. Estuary-scale Extraction Effects
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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21. Effects of Kinetic Power Extraction on Estuaries
Research
Effects of Kinetic Power Extraction on Estuaries
Key Questions
First-order Answers
What are the effects of kinetic power extraction from time-varying systems?
Multiple effects, including:
Flow volume reduction
Range reduction
Kinetic power reduction
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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