Implications of Tidal Phasing for Power Generation at a Tidal Energy Site Brian Polagye and Jim Thomson Northwest National Marine Renewable Energy Center University of Washington Current: Resource Characterization April 11, 2013

Spatial Variability in Mean Currents  Meaningful variations in flow characteristics on spatial scales as small as 100 m  Important implications for resource assessment and power estimates 1.8±0.04 kW/m 2 Admiralty Head 1.4±0.06 kW/m 2 0.6±0.02 kW/m 2 Polagye, B. and Thomson, J., 2013, “Tidal energy resource characterization: methodology and field study in Admiralty Inlet, Puget Sound, US,” Proc. IMechE Part A, J. Power and Energy, doi: /

Phase Variations Iyer, A. S., S. J. Couch, G. P. Harrison, and A. R. Wallace. "Variability and phasing of tidal current energy around the United Kingdom." Renewable Energy 51 (2013):  If currents are out of phase between locations, this be theoretically exploited to reduce the intermittency of power generated  Investigated on a national scale in the UK  What about phase variations on a local scale (< 10 km)?

Tidal Phase in Puget Sound Large phase changes across Admiralty Inlet and Tacoma Narrows Large power dissipation across these sills High velocity through narrow channels

Current Measurements Current Velocity Doppler profiler NNMREC Sea Spider Sites A & B Site F Sites D & E

Near-Headland Sites (A & B) AB 5-minute average to filter most turbulence

Near-Headland Sites (D & E) DE

Headland and Center Channel (A & F) AF

Harmonic Analysis of Currents Amplitude (m/s) Period (h) Phase ( o ) Horizontal Velocity (m/s) DatesM2K1 A (m/s)g ( o )A (m/s)g ( o ) 5/11- 8/9/ ± ± ± ± 1.2 7/5- 8/9/ ± ± ± ± 0.5 2/13- 5/9/ ± ± ± ± 1.8 Analysis in U_TIDE (T_TIDE enhancement)  Ordinary Least Squares solver (OLS)  Constituent signal to noise ratio = 3  Rayleigh criteria = 1 Results for Site A

Near-Headland Sites (D & E) DE SiteM2 A (m/s)g ( o ) D 1.73 ± ± 0.4 E 1.81 ± ± 0.3

Headland and Center Channel (A & F) SiteM2 A (m/s)g ( o ) A 1.57 ± ± 0.6 F 1.45 ± ± 0.5 AF

Turbine-Adjusted Power Density U cut-in = 0.7 m/s U rated = 2.0 m/s

Array Phasing: Headland – Center Channel

Array Phasing Potential Thyng, K.M., 2012, “Numerical simulation of Admiralty Inlet, WA, with tidal hydrokinetic turbine siting application,” PhD dissertation, University of Washington, Seattle, Washington (USA)

Conclusions  Large power density phase variations can occur over relatively short distances (< 10 km)  Exploiting these differences may be able to reduce the intermittency of power output from arrays at the same nominal “site”  To realize these benefits in practice, out of phase locations need to have similar power density and intermittency

Acknowledgements This material is based upon work supported by the Department of Energy under Award Number DE-FG36- 08GO Many thanks to Joe Talbert and Alex DeKlerk for maintaining the Sea Spider platforms over several years of deployments and to Captain Andy Reay-Ellers for helping us put them in the right place.