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Temporal variability in renewable energy presents a major challenge for electrical grid systems. Tides are considered predictable due to their regular periodicity; however, the persistence and quality of tidal-stream generated electricity is unknown. This paper is the first study that attempts to address this knowledge gap through direct measurements of rotor-shaft power and shore-side voltage from a 1 MW, rated at grid-connection, tidal turbine (Orkney Islands, UK). Tidal asymmetry in turbulence parameters, flow speed and power variability were observed. Variability in the power at 0.5 Hz, associated with the 10-min running mean, was low (standard deviation 10–12% of rated power), with lower variability associated with higher flow speed and reduced turbulence intensity. Variability of shore-side measured voltage was well within acceptable levels (∼0.3% at 0.5 Hz). Variability in turbine power had 2 = 85% and ∼14% error). Therefore, the predictability and quality of tidal-stream energy was high and may be undervalued in a future, high-penetration renewable energy, electricity grid.

Population dynamics of marine species that are sessile as adults are driven by oceanographic dispersal of larvae from spawning to nursery grounds. This is mediated by life‐history traits such as the timing and frequency of spawning, larval behaviour and duration, and settlement success. Here, we use 1725 single nucleotide polymorphisms (SNPs) to study the fine‐scale spatial genetic structure in the commercially important cockle species Cerastoderma edule and compare it to environmental variables and current‐mediated larval dispersal within a modelling framework. Hydrodynamic modelling employing the NEMO Atlantic Margin Model (AMM15) was used to simulate larval transport and estimate connectivity between populations during spawning months (April–September), factoring in larval duration and interannual variability of ocean currents. Results at neutral loci reveal the existence of three separate genetic clusters (mean F ST = 0.021) within a relatively fine spatial scale in the north‐west Atlantic. Environmental association analysis indicates that oceanographic currents and geographic proximity explain over 20% of the variance observed at neutral loci, while genetic variance (71%) at outlier loci was explained by sea surface temperature extremes. These results fill an important knowledge gap in the management of a commercially important and overexploited species, bringing us closer to understanding the role of larval dispersal in connecting populations at a fine geographic scale.

International audience; Reynolds-Averaged Navier Stokes (RANS) models have, in the past, primarily been implemented to assess the available tidal kinetic energy resource, neglecting the influence of turbines on tidal hydrodynamics. However, evaluating environmental impacts, as well as array layouts, requires integration of the turbine wakes with the ambient flow field (Goward Brown et al., 2017). The widely used method, commonly integrated in depth-averaged models, consists of integrating an additional bed friction term related to array scale turbine effects. Such approach permits to simulate the global effect of a tidal array. However, the flow interactions between turbines are neglected. A fully three-dimensional (3-D) approach is here developed to account for cumulative effects of individual interacting turbine wakes. The actuator disc sub-model, that represents the turbine as a non-rotating porous disc, is implemented and incorporated into the Regional Ocean Modelling System (ROMS), following the method initially developed by Roc et al. (2013). A nested grid technique is adopted to cascade processes from the regional scale to the high resolution local farm domain. This method was first implemented in the steady-state laboratory experiment of Myers and Bahaj (2010). Numerical predictions match measurements of velocity and turbulent intensity profiles along the disc wakes for minimum spatial resolutions of 1/5th the turbine diameter. This is also confirmed at ocean scale. The modelling methodology is finally applied to the tidal stream energy site of the Fromveur Strait (western Brittany), where an array of 20 m-diameter turbines is considered. The computation is conducted over an inner-nested array domain that is 700 m in length and 200 m in width, at a spatial resolution of 4 m, embedded in two nested regional grids with resolutions of 100 m (intermediate) and 500 m (outer). Different configurations varying in scale from one to 14 devices are investigated in terms of wake interactions and power output from individual turbines to the whole array.