Implications of Tidal Phasing for Power Generation at a Tidal Energy Site

Spatial resource gradients have been observed at a number of proposed tidal energy sites. However, these gradients are typically quantified using the first or second moments (i.e., mean or standard deviation) of time series which obscures information about the co‐temporal amplitude and phase variation. These co‐temporal variations have a number of interesting implications for power production from arrays of tidal turbines. Here, co‐temporal time series data from several locations in northern Admiralty Inlet, Puget Sound, Washington (USA) are used to investigate phase variations in kinetic power density over length scales of less than 5 km. Results demonstrate that large phase variations in kinetic power density are routinely produced by phase variations in the harmonic and aharmonic currents. However, exploiting these phase variations in a way that reduces power generation intermittency requires that locations which are out of phase have similar mean kinetic power density and intermittency. Further investigation of local phasing at tidal energy sites of commercial interest is recommended. INTRODUCTION Resource characterization is an essential early‐stage activity in tidal energy project development. The information obtained feeds into structural load calculations, as well as estimates for power generation from individual turbines or small arrays. [1] present a set of resource metrics that describe characteristics of the mean (as opposed to turbulent) currents at potential turbine deployment locations within Admiralty Inlet, Puget Sound, WA (USA). These are statistical quantities either averages (first moment) or variances (second moment), which obscure information about co‐temporal amplitude and phase variations between locations. These variations can have a number of interesting implications for power production from arrays. For example, if the amplitude of the currents is similar at two locations, but the currents are out of phase, their aggregate power generation profile will be more continuous than for the individual locations. The potential to benefit from “tidal phasing” has been investigated at a national scale by Iyer et al. [2], but has not been investigated at smaller scales. Here, we investigate tidal phasing within a single site over length scales less than 5 km.