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

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

Turbine Variants Horizontal Axis Ducted Vertical Axis Basics 006,09-17-07,UW.ppt

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 009,09-17-07,UW.ppt

Foundation Variants Monopile Gravity Base Tension Leg Chain Anchors Basics Foundation Variants Monopile Gravity Base Tension Leg Chain Anchors 007,09-17-07,UW.ppt

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 #2 008,09-17-07,UW.ppt

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 005,09-17-07,UW.ppt

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

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 010,09-17-07,UW.ppt

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 012,09-17-07,UW.ppt

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 011,09-17-07,UW.ppt

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 013,09-17-07,UW.ppt

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) 014,09-17-07,UW.ppt

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 015,09-17-07,UW.ppt

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 016,09-17-07,UW.ppt

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 017,09-17-07,UW.ppt

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

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 002,09-17-07,UW.ppt

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 004,09-17-07,UW.ppt

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 003,09-17-07,UW.ppt

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 001,09-17-07,UW.ppt