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Far-field Effects of Tidal Energy Extraction in Puget Sound. ME 523: Energy and Environment Seminar. February 11, 2008. Brian Polagye PhD Candidate University of Washington Department of Mechanical Engineering. 031,02-11-09,TID. Tidal Energy in Puget Sound Modeling Extraction Effects

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slide1

Far-field Effects of Tidal Energy Extraction

in Puget Sound

ME 523: Energy and Environment Seminar

February 11, 2008

Brian Polagye

PhD Candidate

University of Washington

Department of Mechanical Engineering

031,02-11-09,TID

slide2

Tidal Energy in Puget Sound

  • Modeling Extraction Effects
  • Model Application to Puget Sound
slide3

Spieden Channel

Guemes Channel

San Juan Channel

Deception Pass

Project pending

Race Rocks

Demonstration turbine

Admiralty Inlet

Pilot project

Marrowstone Island

Demonstration array

Agate Passage

Preliminary permit returned

Rich Passage

Preliminary permit returned

Tacoma Narrows

No activity

Tidal Energy Projects in Puget Sound

001,02-11-09,TID

slide4

Tidal Energy Devices

  • (clockwise from left)
  • Verdant Power
  • Clean Current
  • Marine Current Turbines
  • Open Hydro

002,02-11-09,TID

slide5

Admiralty Inlet Pilot Project

Site Survey Area

003,02-11-09,TID

slide6

Site Characteristics

  • Resource intensity
  • Seabed geology
  • Electrical interconnection
  • Existing uses
  • Environmental concerns
  • Long-term potential

How do we measure this?

004,02-11-09,TID

slide7

Tidal Energy in Puget Sound

  • Modeling Extraction Effects
  • Model Application to Puget Sound
slide8

Problem Definition and Approach

  • Determine what effects extraction has on the natural environment, including changes to the resource.
  • Approach with numerical model that:
    • Captures basic physics of power extraction on the natural system.
    • Is sufficiently flexible to study a range of site types, tidal regimes, and turbine dynamics.
    • Performs these studies at low computational cost.
    • Focuses on far-field, barotropic effects.
  • Possible with a 1D, 2D, or 3D numerical models.

031,02-11-09,TID

slide9

Governing Equations

  • Tidal streams characterized by energetic, bidirectional flow

h

Q

  • 1D shallow water equations appropriate to problem:

027,02-11-09,TID

slide10

Numerical Solution

  • Many algorithms available to solve shallow water equations. For example, explicit algorithms include:
    • Lax
    • Leap Frog
    • MacCormack predictor-corrector
  • MacCormack algorithm (2nd order in time and space):

(compact notation)

(predictor)

(corrector)

(update)

027,02-11-09,TID

slide11

Boundary Conditions

  • Three required properties:
    • Radiative: allow outgoing wave to pass without reflection
    • Active: admit incoming waves (e.g. tides)
    • Stable: maintain mean sea level over long simulation times
  • Obvious solution is to prescribe tidal elevation at boundary:
  • This is a clamped boundary and does not radiate outgoing waves. A better option is a Flather boundary (e.g. Blayo and Debreu 2005).

029,02-11-09,TID

slide12

Channel Junctions

Serial (1:1)

Branching (1:2)

Merging (2:1)

2

1

3

1

2

1

3

2

  • 2 unknowns (velocity u and depth h) for each channel
  • Model by compatibility condition (e.g. for serial):

(1)

(3)

(2)

(4)

024,02-11-09,TID

slide13

Turbine Model

  • Requirements (from 1D momentum theory):
    • Reflect drop in pressure over plane of extraction.
    • Reflect total dissipated power (power extracted + wake losses).
  • Assume:
    • Turbines are infinitesimally small in comparison to water depth.
    • Turbines are distributed uniformly on channel cross-section.
  • Wake region is infinitesimally short and dissipation may be modeled as a discontinuous decrease in power.
  • Implement similarly to a channel junction,

(flood tide).

019,02-11-09,TID

slide14

Steady State Extraction

Δh = 0.5 m

H = 50 m

L = 5000 m

Water Depth

Velocity (no rows)

Velocity (two rows)

026,02-11-09,TID

slide15

Basic Channel Network

Inlet

Basin

Constriction

  • Three channel segments
  • Kinetic power extraction by one or more rows of turbines in constrictions
  • Single constituent tidal forcing:
  • Analytical theory formulated for this configuration

025,02-11-09,TID

slide16

1. Response is a continuous function of power dissipated

2. Diminishing marginal benefit

3. Kinetic resource has limits

Response to Extraction

005,02-11-09,TID

slide17

Response to Extraction

Basin

Narrows

Inlet

006,02-11-09,TID

slide18

Maximum Flow

(m3/s)

Seawater Density

(1024 kg/m3)

Tidal Amplitude

(m)

0.19 ≤ γ ≤ 0.26

Theoretical Response

Gravity constant

(9.81 m/s2)

Source: Blanchfield et al. (2008)

  • Theory developed by Garrett and Cummins (2005)
  • Extended to ocean-basin system by Blanchfield et al. (2008)
  • Further extended by Karsten et al. (2008) during Bay of Fundy modeling

007,02-11-09,TID

slide19

Comparison with Theory

Some disagreement between model and theory…

…but theory neglects important dynamics.

  • Comparison also in-line with site-specific 2D modeling results by Karsten et al. (2008) for Bay of Fundy

008,02-11-09,TID

slide20

Conclusions from Basic Networks

  • Extraction of kinetic power alters:
    • Tidal range
    • Currents, transport, and kinetic power density
  • These changes have environmental, social, and economic consequences.
  • Changes are generally site-specific, and depend on:
    • Level of power extraction (small extraction, small impact)
    • Geometry of segments
    • Type of network (basic, branching, etc.)
    • Tidal regime
    • Device dynamics

009,02-11-09,TID

slide21

Tidal Energy in Puget Sound

  • Modeling Extraction Effects
  • Model Application to Puget Sound
slide22

Modeling Extraction in Puget Sound

  • Concerns that tidal energy extraction could exacerbate existing stresses (hypoxia)
  • Modeling goals:
    • In-stream power potential for Puget Sound
    • Optimal siting of arrays
  • Assumptions:
    • Flow dominantly 1D
    • Neglect salinity effects
    • Neglect small-scale features

010,02-11-09,TID

slide23

Primary Semiduirnal Calibration

Phase Lag

(Model – Observations)

Amplitude

(Model/Observations)

011,02-11-09,TID

slide24

Amplitude Calibration

012,02-11-09,TID

slide25

Effect of Extraction on Transport

Extraction from

Admiralty Inlet

1

2

Extraction from

Tacoma Narrows

4

6

Extraction from

Both Sites

8

A

B

C

D

014,02-11-09,TID

slide26

Development Trade-Offs

Resource Intensity

More energetic resource in Tacoma Narrows

Resource Size

Larger potential resource in Admiralty Inlet

Extraction in Tacoma Narrows has no significant effect on Hood Canal

Impact on Hood Canal

For same level of power generation, extraction in Admiralty Inlet has less effect on South Sound

Impact on South Sound

016,02-11-09,TID

slide27

Effects of Pilot Project

Change in M2 Transport (%)

Change in M2 Tidal Range (mm)

3 MW rated electrical capacity

Power extraction from Admiralty Inlet

Currently in permitting phase

Immeasurable effects

017,02-11-09,TID

slide28

Effects of Commercial Project

Change in M2 Transport (%)

Change in M2 Tidal Range (mm)

135 MW rated electrical capacity

Power extraction from Admiralty Inlet

Subject of feasibility study

Measurable effects

Significant effects?

018,02-11-09,TID

slide29

Conclusions for Puget Sound

  • Tidal energy extraction can measurably change the tidal regime of Puget Sound.
  • Tidal energy extraction has the potential to provide significant quantities of predictable renewable energy to the region.
  • Insufficient information exists to perform a cost-benefit analysis. We can calculate the theoretical resource, but do not know what is recoverable.
  • Key next step is to determine the ecosystem implications for changes to the tidal regime.

023,02-11-09,TID

slide30

Questions?

This research is supported by

Snohomish Public Utility District and

the Electric Power Research Institute (EPRI)

020,02-11-09,TID