Tidal Turbines’ Layout in a Stream with Asymmetry and Misalignment

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.

Annual and seasonal variabilities in the performances of wave energy converters

“…2-a) [29,30], and (ii) tidal currents of more than 3.5 m s −1 in mean spring conditions ( Fig. 2-b) [34,35,36]. This area experiences thus strong interactions between waves and tidal currents [37,38].…”

Effects of the Current Direction on the Energy Production of a Tidal Farm: The Case of Raz Blanchard (France)

“…Similar to other tidal straits [7,8,10,17], the flow in the Raz Blanchard is characterized by an asymmetry of the tidal current amplitude as well as a directional spreading around a predominant direction. Depending on the current direction (ebb or flood), the turbines of lines 1 and 3 are alternately in the free stream or located downstream the array.…”

“…However, previous studies were essentially performed with regional models where the turbines' thrust was spatially averaged over the area occupied by the tidal farm. This (spatially averaged) turbine representation implies that the interactions between the turbines' wakes are negated [5][6][7][8][9][10][11]. Such regional approach has been used at sites located in West Brittany such as the Sein Race [7] and the Fromveur strait [8], at Scottish sites such as the Orkney archipelago [9], at the Ramsey Sound strait [10], and at the Normand site of the Raz Blanchard [1].Recent works [11][12][13][14] deal with the implementation of methods developed (based on numerical results or experimental mapping) to optimize the identification of suitable sites for energy extraction.…”

“…Both papers confirm that Raz Blanchard has the stronger potential for the exploitation of the tidal kinetic energy resources of the region. In such sites, a marked tidal current asymmetry and misalignment was observed [7,8,11,15]. At the turbine scale, several studies were carried out to investigate the effect of the angle of attack on the turbine's performance [10,[16][17][18].…”

A Review of Software Tools to Study the Energetic Potential of Tidal Currents

“…There are several examples applying this code to simulate the tidal energy extraction by turbines, but they do not take into account their effect in the flow hydrodynamics. For instance, Cornett et al [96] analyzed the tidal current resources in the Bay of Fundy, and Gillou and Chapalain [97] studied the optimum location and alignment of tidal turbines in the "Raz de Sein", a strait off western Brittany in France. Table 2 shows the main characteristics of the 3D codes.…”