Detailed observations and modelling highlight the importance of micro-siting of tidal-stream arrays: A case study off northwest Wales, UK

We investigate variability of the tidal-stream energy resource over a licenced demonstration site at high spatial and temporal resolutions. The site, off northwest Wales, UK, is regarded as one of the most attractive in the UK in terms of extractable energy, and requires a broad understanding of the entire resource to be managed appropriately for device testing at different scales and for different specifications. A rigorous field campaign has been conducted between 2013 and 2015 (http://www.seacams.ac.uk), consisting of comprehensive (and repeated in places) multibeam echo sounder (MBES) bathymetric surveys, geophysical surveys, seven ADCP deployments, a Waverider wave buoy active deployment (http://cefasmapping.defra.gov.uk/Map), and various sediment sampling surveys. In addition, a coupled tide-wave-sediment model (Telemac Modelling System) has been applied to simulate the high-resolution spatial distribution of tidal currents, wave-tide interactions, and sediment transport in the region.

We find that topography, bathymetry, morphology, and wave-tide interactions result in markedly different flow and turbulence fields over the ~40 km² site, leading to significant spatial and temporal variance in power generation. Some areas are ebb-dominant, while others flood-dominant. The vertical velocity profile varies in accordance with bed friction and this may impact upon device performance. Furthermore, arrays can be optimised to minimise scour. Our results suggest that careful consideration should be given to micro-siting of devices; in our case, potential annual energy yield varies by 180% based on depth-averaged velocities of the undisturbed resource.