Farfield Effects of Tidal Energy Extraction in Puget

Far-field Effects of Tidal Energy Extraction in Puget Sound ME 523: Energy and Environment Seminar February 11, 2008 Brian Polagye Ph. D Candidate University of Washington Department of Mechanical Engineering Northwest National Marine Renewable Energy Center 1 031, 02 -11 -09, TID

• Tidal Energy in Puget Sound • Modeling Extraction Effects • Model Application to Puget Sound Northwest National Marine Renewable Energy Center 2

Tidal Energy Projects in Puget Sound Spieden Channel San Juan Channel Race Rocks Demonstration turbine Marrowstone Island Guemes Channel Deception Pass Project pending Admiralty Inlet Pilot project Demonstration array Agate Passage Preliminary permit returned Rich Passage Preliminary permit returned Tacoma Narrows No activity Northwest National Marine Renewable Energy Center 3 001, 02 -11 -09, TID

Tidal Energy Devices (clockwise from left) • • Verdant Power Clean Current Marine Current Turbines Open Hydro Northwest National Marine Renewable Energy Center 4 002, 02 -11 -09, TID

Admiralty Inlet Pilot Project Site Survey Area Northwest National Marine Renewable Energy Center 5 003, 02 -11 -09, TID

Site Characteristics ■ Resource intensity ■ Seabed geology ■ Electrical interconnection ■ Existing uses ■ Environmental concerns ■ Long-term potential How do we measure this? Northwest National Marine Renewable Energy Center 6 004, 02 -11 -09, TID

• Tidal Energy in Puget Sound • Modeling Extraction Effects • Model Application to Puget Sound Northwest National Marine Renewable Energy Center 7

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 1 D, 2 D, or 3 D numerical models. Northwest National Marine Renewable Energy Center 8 031, 02 -11 -09, TID

Governing Equations ■ Tidal streams characterized by energetic, bidirectional flow Q h ■ 1 D shallow water equations appropriate to problem: Northwest National Marine Renewable Energy Center 9 027, 02 -11 -09, TID

Numerical Solution ■ Many algorithms available to solve shallow water equations. For example, explicit algorithms include: — Lax — Leap Frog — Mac. Cormack predictor-corrector ■ Mac. Cormack algorithm (2 nd order in time and space): (compact notation) (predictor) (update) (corrector) Northwest National Marine Renewable Energy Center 10 027, 02 -11 -09, TID

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). Northwest National Marine Renewable Energy Center 11 029, 02 -11 -09, TID

Channel Junctions Serial (1: 1) 1 2 Branching (1: 2) 1 Merging (2: 1) 2 1 3 2 3 ■ 2 unknowns (velocity u and depth h) for each channel ■ Model by compatibility condition (e. g. for serial): (1) (3) (2) (4) Northwest National Marine Renewable Energy Center 12 024, 02 -11 -09, TID

Turbine Model ■ Requirements (from 1 D momentum theory): 1. Reflect drop in pressure over plane of extraction. 2. Reflect total dissipated power (power extracted + wake losses). ■ Assume: 1. Turbines are infinitesimally small in comparison to water depth. 2. 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). Northwest National Marine Renewable Energy Center 13 019, 02 -11 -09, TID

Steady State Extraction Δh = 0. 5 m H = 50 m L = 5000 m Water Depth Velocity (no rows) Velocity (two rows) Northwest National Marine Renewable Energy Center 14 026, 02 -11 -09, TID

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 Northwest National Marine Renewable Energy Center 15 025, 02 -11 -09, TID

Response to Extraction 1. Response is a continuous function of power dissipated 2. Diminishing marginal benefit 3. Kinetic resource has limits Northwest National Marine Renewable Energy Center 16 005, 02 -11 -09, TID

Response to Extraction Basin Narrows Inlet Northwest National Marine Renewable Energy Center 17 006, 02 -11 -09, TID

Theoretical Response Maximum Flow (m 3/s) Gravity constant (9. 81 m/s 2) 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 Seawater Density (1024 kg/m 3) Tidal Amplitude (m) 0. 19 ≤ γ ≤ 0. 26 Northwest National Marine Renewable Energy Center 18 007, 02 -11 -09, TID

Comparison with Theory Some disagreement between model and theory… …but theory neglects important dynamics. ■ Comparison also in-line with site-specific 2 D modeling results by Karsten et al. (2008) for Bay of Fundy Northwest National Marine Renewable Energy Center 19 008, 02 -11 -09, TID

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 Northwest National Marine Renewable Energy Center 20 009, 02 -11 -09, TID

• Tidal Energy in Puget Sound • Modeling Extraction Effects • Model Application to Puget Sound Northwest National Marine Renewable Energy Center 21

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 1 D — Neglect salinity effects — Neglect small-scale features Northwest National Marine Renewable Energy Center 22 010, 02 -11 -09, TID

Primary Semiduirnal Calibration Amplitude Phase Lag (Model/Observations) (Model – Observations) Northwest National Marine Renewable Energy Center 23 011, 02 -11 -09, TID

Amplitude Calibration Northwest National Marine Renewable Energy Center 24 012, 02 -11 -09, TID

Effect of Extraction on Transport Extraction from Admiralty Inlet 1 2 Extraction from Tacoma Narrows 4 6 8 Extraction from Both Sites A B C D Northwest National Marine Renewable Energy Center 25 014, 02 -11 -09, TID

Development Trade-Offs Resource Intensity More energetic resource in Tacoma Narrows Resource Size Larger potential resource in Admiralty Inlet Impact on Hood Canal Extraction in Tacoma Narrows has no significant effect on Hood Canal Impact on South Sound For same level of power generation, extraction in Admiralty Inlet has less effect on South Sound Northwest National Marine Renewable Energy Center 26 016, 02 -11 -09, TID

Effects of Pilot Project Change in M 2 Tidal Range (mm) Change in M 2 Transport (%) 3 MW rated electrical capacity Power extraction from Admiralty Inlet Currently in permitting phase Immeasurable effects Northwest National Marine Renewable Energy Center 27 017, 02 -11 -09, TID

Effects of Commercial Project Change in M 2 Tidal Range (mm) Change in M 2 Transport (%) 135 MW rated electrical capacity Power extraction from Admiralty Inlet Subject of feasibility study Measurable effects Significant effects? Northwest National Marine Renewable Energy Center 28 018, 02 -11 -09, TID

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 costbenefit analysis. We can calculate theoretical resource, but do not know what is recoverable. ■ Key next step is to determine the ecosystem implications for changes to the tidal regime. Northwest National Marine Renewable Energy Center 29 023, 02 -11 -09, TID

Questions? This research is supported by Snohomish Public Utility District and the Electric Power Research Institute (EPRI) Northwest National Marine Renewable Energy Center 30 020, 02 -11 -09, TID