Abstract
A refined assessment of tidal currents variability is a prerequisite for successful turbine deployment in the marine environment. However, the numerical evaluation of the tidal kinetic energy resource relies, most of the time, on integrated parameters, such as the averaged or maximum stream powers. Predictions from a high resolution three-dimensional model are exploited here to characterize the asymmetry and misalignment between the flood and ebb tidal currents in the “Raz de Sein”, a strait off western Brittany (France) with strong potential for array development. A series of parameters is considered to assess resource variability and refine the cartography of local potential tidal stream energy sites. The strait is characterized by strong tidal flow divergence with currents’ asymmetry liable to vary output power by 60% over a tidal cycle. Pronounced misalignments over 20 ∘ are furthermore identified in a great part of energetic locations, and this may account for a deficit of the monthly averaged extractable energy by more than 12%. As sea space is limited for turbines, it is finally suggested to aggregate flood and ebb-dominant stream powers on both parts of the strait to output energy with reduced asymmetry.
Highlights
The hydro-kinetic energy of tidal currents has the potential to contribute to a significant part of the exploitation of marine renewable resources in industrial countries, bringing a highly predictable power with reduced visual impacts for coastal users and communities [1]
As stream power output is related to the velocity cubed, tidal current asymmetry may strongly impact the extractable energy over a tidal cycle, by modifying the available kinetic energy between the flood and ebb phases
The evaluation of model predictions is performed against available in situ observations of current amplitude and direction acquired by the French navy SHOM (“Service Hydrographique et Océanographique de la Marine”) from June–July 1993 in the northwestern part of the “Raz de Sein”
Summary
The hydro-kinetic energy of tidal currents has the potential to contribute to a significant part of the exploitation of marine renewable resources in industrial countries, bringing a highly predictable power with reduced visual impacts for coastal users and communities [1]. As extensive in situ observations cannot reasonably encompass the tidal hydrodynamics conditions at the regional scale, the associated resource assessments rely, most of the time, on numerical modeling tools. Besides the uncertainty of these large-scale predictions [5,6,7], these resource assessments consider generally a restricted number of parameters, primarily the averaged and maximum amplitude of tidal current and associated stream power, setting aside further studies about the spatial and temporal variability of available kinetic energy. As stream power output is related to the velocity cubed, tidal current asymmetry may strongly impact the extractable energy over a tidal cycle, by modifying the available kinetic energy between the flood and ebb phases.
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