Energy potential of a tidal fence deployed near a coastal headland

Abstract

Enhanced tidal streams close to coastal headlands appear to present ideal locations for the deployment of tidal energy devices. In this paper, the power potential of tidal streams near an idealized coastal headland with a sloping seabed is investigated using a near-field approximation to represent a tidal fence, i.e. a row of tidal devices, in a two-dimensional depthaveraged numerical model. Simulations indicate that the power extracted by the tidal fence is limited because the flow will bypass the fence, predominantly on the ocean side, as the thrust applied by the devices increases. For the dynamic conditions, fence placements and headland aspect ratios considered, the maximum power extracted at the fence is not related in any obvious way to the local undisturbed kinetic flux or the natural rate of energy dissipation due to bed friction (although both of these have been used in the past to predict the amount of power that may be extracted). The available power (equal to the extracted power net of vertical mixing losses in the immediate wake of devices) is optimized for devices with large area and small centre-to-centre spacing within the fence. The influence of energy extraction on the natural flow field is assessed relative to changes in the M2 component of elevation and velocity, and residual bed shear stress and tidal dispersion.

A Comparison of Numerical Modelling Techniques for Tidal Stream Turbine Analysis

“…The scenario tested in this paper was based on [49] and the BEM-CFD case more fully described in [25]. The domain was 770 m wide for both cases with the headland extending by 230 m. The offshore boundary was set to full slip condition in both cases.…”

Resource assessment for future generations of tidal-stream energy arrays

“…Further, the undisturbed kinetic energy flux of 1st generation sites is~4 TJ, which equates to an average of 1 GW throughout the year using the measured power curve of the Seagen-S 600 kW twin drive train tidal turbine (Fig. 4) e assuming a density of two devices per 270 m 2 Although our estimate does not include device feedbacks between energy extraction and the resource [32], and device density/array configuration is currently unknown, it appears that 1st generation tidal-stream energy sites within the entire Irish Sea could meet~25% of the 2025 Welsh Government's marine renewable target of 4 GW [19].…”

“…3c; however, we chose not to use the traditional power density calculation (e.g., kWm À2 ) to quantify the Irish Sea resource because estimates cannot be spatially aggregated to represent the resource over a region [33]. Moreover, no device feedbacks to the kinetic energy flux were included [5,32] because of uncertainties within array configurations, power extraction, rated velocities, and device cut-in speeds e which are beyond the scope of this study. Rather, our third approach to quantifying the potential Irish Sea tidal-stream energy resource was to calculate the practical power available (at each model grid cell) applying the measured power curve of the twin-rotor Seagen device (Fig.…”

“…To quantify the undisturbed tidal-stream energy resource that is theoretically hydrodynamically suitable for development (i.e., irrespective of other factors such as distance to grid connection) and excluding inter-device and inter-array interactions [32], we use three methods in this paper. Firstly, to quantify the sea space available, the maximum potential area available for development is calculated.…”

Aspects of tidal stream turbine modelling in the natural environment using a coupled BEM–CFD model

“…Ref. [10] abstract this further into what is effectively an actuator fence and consider the interactions between the fence and a headland. Also of interest are actuator line approaches, where a rotating line of energy sinks represents each of the rotor blades at a sub grid scale.…”