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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




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


                             • Basics of Turbine Operation

                             • Limits on Array Size

                             • Research on Extraction Impacts




LABORATORY FOR ENERGY AND ENVIRONMENTAL COMBUSTION     http://www.energy.washington.edu   2
                                                                                              Basics

                                     Turbine Variants
                       Horizontal Axis
                                                                          Ducted




                         Vertical Axis




LABORATORY FOR ENERGY AND ENVIRONMENTAL COMBUSTION   http://www.energy.washington.edu   006,09-17-07,UW.ppt   3
                                                                                                            Basics

                                           Drive Train
                “Conventional”                                                Direct Drive

                                  Generator
                                    • ~200 RPM                                         Generator
                                    • Induction or                                      • ~10 RPM
                                      synchronous                                       • Permanent magnet


                                                     Electricity                            Electricity


Rotor
 • ~10 RPM         Gearbox
                    • Increase rotational speed of
                      shaft from turbine

                    Maximum speed of rotor limited by cavitation
                          Smaller rotors can turn faster
LABORATORY FOR ENERGY AND ENVIRONMENTAL COMBUSTION                 http://www.energy.washington.edu   009,09-17-07,UW.ppt   4
                                                                                              Basics

                                   Foundation Variants
                  Monopile                                      Gravity Base




                                                                Tension Leg
               Chain Anchors




LABORATORY FOR ENERGY AND ENVIRONMENTAL COMBUSTION   http://www.energy.washington.edu   007,09-17-07,UW.ppt   5
                                                                                                      Basics

                                          Power Take-off
                     Pilot Scale                                Commercial Scale
           115kV             Substation                   115kV                Substation
      transmission line                              transmission line
                             12kV distribution                                    New 115 kV
                                   line                                        transmission line
                                                      New substation
                                                       Cable landfall
                             Cable landfall
          Horizontal                                     Horizontal                           Cluster #3
      directional drilling     12 kV cable           directional drilling
            < 500m                                    (multiple cables)

               Trenched                                   Trenched
                             Turbine                      30-35 kV

                                                                                          Cluster #1
                                                                                          8 Turbines
                                                                    Cluster #2

LABORATORY FOR ENERGY AND ENVIRONMENTAL COMBUSTION         http://www.energy.washington.edu     008,09-17-07,UW.ppt   6
                                                                                                Basics

                                      The Perfect Site Does Not Exist
          Cross-Section View                               Top View


                                     30-40m                                                       5 km


                                                                20 km

             Regular, constant                       Very long, and wide
               cross-section

         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
LABORATORY FOR ENERGY AND ENVIRONMENTAL COMBUSTION     http://www.energy.washington.edu   005,09-17-07,UW.ppt   7
                                              Agenda


                             • Basics of Turbine Operation

                             • Limits on Array Size

                             • Research on Extraction Impacts




LABORATORY FOR ENERGY AND ENVIRONMENTAL COMBUSTION     http://www.energy.washington.edu   8
                                                                                                                   Array Size

                                     Limit #1: Fundamental Fluid Limit
         Beyond a certain point, installing more turbines produces less power

                                     1.8E+05
                                                             Increasing number of turbines
                                     1.6E+05
                                     1.4E+05
                  Flow Rate (m3/s)




                                     1.2E+05
                                     1.0E+05                                                     Turning Point:
                                     8.0E+04                                                     installing additional
                                     6.0E+04                                                     turbines will
                                     4.0E+04                                                     produce less power
                                     2.0E+04
                                     0.0E+00
                                               0    50      100   150    200       250     300     350
                                                         Kinetic Power Extracted (MW)

                                                   Turning point is site-specific
LABORATORY FOR ENERGY AND ENVIRONMENTAL COMBUSTION                             http://www.energy.washington.edu   010,09-17-07,UW.ppt   9
                                                                                               Array Size

                                  Limit #2: Real Estate

                        Regions of high power density are finite


                                                                          Available power drops
                                                                          off rapidly outside
                                                                          constrictions




                                                     0   0.2    0.4      0.6     0.8      1
                                                         Relative Power Density

LABORATORY FOR ENERGY AND ENVIRONMENTAL COMBUSTION         http://www.energy.washington.edu   012,09-17-07,UW.ppt   10
                                                                                               Array Size

                                  Limit #2: Real Estate

           Minimum separation required between each row of turbines

             Ideal                             Too Close                            Inefficient




                              Turbine




                            Free stream

                                           Downstream turbines               Turbines not making best
             Low velocity wake               operate in wake                      use of resource

LABORATORY FOR ENERGY AND ENVIRONMENTAL COMBUSTION         http://www.energy.washington.edu   011,09-17-07,UW.ppt   11
                                                                                            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



LABORATORY FOR ENERGY AND ENVIRONMENTAL COMBUSTION      http://www.energy.washington.edu   013,09-17-07,UW.ppt   12
                                                                                                  Array Size

                Limit #4: Social and Environmental Concerns
             No sites identified to date are biological and social deserts
  1.   Estuary-scale fluid impacts            3.     Recreation
       •    Tidal range                              •   Sport fishing
       •    Pollutant flushing                       •   Scuba diving
       •    Oxygen saturation                        •   Recreational boating

  2.   Local Impacts                          4.     Commerce
       •    Scour                                    •   Shipping
       •    Sediment transport                       •   Commercial fishing
       •    Coolants and lubricants
       •    Noise                             5.     Tribes
       •    Strike or harassment of fish             •   Accustomed fishing
            and marine mammals
       •    Endangered or protected           6.     Military
            species                                  •   Navy traffic (surface and submerged)
       •    Electromagnetic radiation
LABORATORY FOR ENERGY AND ENVIRONMENTAL COMBUSTION            http://www.energy.washington.edu   014,09-17-07,UW.ppt   13
                                                                                           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
             Spieden Island                            average)

                                                     • Nearest interconnection point
                                                       only 15 kV
                      Spieden Channel                    ― Accommodate at most 5 MW
                                                           of peak power

                           San Juan Island Island    • New 69 kV cable would have
                                                       to be trenched overland ~5
                                                       miles at very high cost

LABORATORY FOR ENERGY AND ENVIRONMENTAL COMBUSTION     http://www.energy.washington.edu   015,09-17-07,UW.ppt   14
                                                                                            Array Size

                                Example #2: Agate Pass

                          Very limited space to install turbines

                                                     • High power density under
                                                       bridge
     Kitsap Peninsula
                                                     • 115 kV transmission lines

                                                     • Power density drops off rapidly
                                                       to the north

                      ~200m                          • Overhead and seabed clearance
                                                       requirements (optimistically)
                        Bainbridge Island
                                                       leave a 2m thick layer for
                                                       turbine deployment

LABORATORY FOR ENERGY AND ENVIRONMENTAL COMBUSTION      http://www.energy.washington.edu   016,09-17-07,UW.ppt   15
                                                                                           Array Size

                             Example #3: Admiralty Inlet

                      Environmental and social issues dominate

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


LABORATORY FOR ENERGY AND ENVIRONMENTAL COMBUSTION     http://www.energy.washington.edu   017,09-17-07,UW.ppt   16
                                              Agenda


                             • Basics of Turbine Operation

                             • Limits on Array Size

                             • Research on Extraction Impacts




LABORATORY FOR ENERGY AND ENVIRONMENTAL COMBUSTION     http://www.energy.washington.edu   17
So far, lots of questions have been raised, some harder to answer than others


                                                                                                     Research

                                    Questions and Answers
                                                (so far)
                    Will             How will fluid        Are turbines            How will
   Example          turbines         flows change          likely to stress        turbines affect
   Question         make sushi?      around arrays?        fish and marine         salmon recovery?
                                                           mammals?


  Method of                          Experiments
                    Analysis                                 Pilot Tests                   ?
   Answer                            and Modeling


                   Cavitation        Local speed           Locale-specific         ?
                   limits            increase around       results only, no
    State of       maximum tip       turbines, overall
    the Art                                                regional scale
                   speed of rotor    reduction in          work
                                     flow rate


                             Effort and cost required to answer questions

LABORATORY FOR ENERGY AND ENVIRONMENTAL COMBUSTION             http://www.energy.washington.edu   002,09-17-07,UW.ppt   18
                                                                                             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



LABORATORY FOR ENERGY AND ENVIRONMENTAL COMBUSTION     http://www.energy.washington.edu   004,09-17-07,UW.ppt   19
                                                                                               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



LABORATORY FOR ENERGY AND ENVIRONMENTAL COMBUSTION       http://www.energy.washington.edu   003,09-17-07,UW.ppt   20
                                                                                                            Research

              Effects of Kinetic Power Extraction on Estuaries

               Key Questions                                            First-order Answers

  1.   What are the effects of kinetic                      1.    Multiple effects, including:
       power extraction from time-varying                         •       Flow volume reduction
       systems?
                                                                  •       Range reduction
                                                                  •       Kinetic power reduction

  2.   What factors most strongly                           2.    Multiple factors, including:
       influence these effects?                                   •       Magnitude of extraction
                                                                  •       Estuary geometry
                                                                  •       Tidal regime

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

LABORATORY FOR ENERGY AND ENVIRONMENTAL COMBUSTION                    http://www.energy.washington.edu   001,09-17-07,UW.ppt   21

				
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