Constraints on extractable power from energetic tidal straits. (September 2015)

• Record Type: Journal Article
• Authors: Evans, P.; Mason-Jones, A.; Wilson, C.; Wooldridge, C.; O'Doherty, T.; O'Doherty, D.
• Is Part Of: Renewable energy. Volume 81(2015)
• Page Start: 707
• Page End: 722
• Publication Date: 2015-09
• Subjects: ADCP -- Hydrodynamics -- Marine resources -- Alternative energy -- Site assessment -- Tidal stream turbines; Renewable energy sources -- Periodicals; Power resources -- Periodicals; Énergies renouvelables -- Périodiques; Ressources énergétiques -- Périodiques; 333.794
• DOI: 10.1016/j.renene.2015.03.085
• Languages: English
• ISSNs: 0960-1481

Abstract

Abstract: National efforts to reduce energy dependency on fossil fuels have prompted examination of macrotidal nearshore sites around the United Kingdom (UK) for potential tidal stream resource development. A number of prospective tidal energy sites have been identified, but the local hydrodynamics of these sites are often poorly understood. Tidal energy developers rely on detailed characterisation of tidal energy sites prior to device installation and field trials. Although first-order appraisals may make macrotidal tidal straits appear attractive for development, detailed, site-specific hydrodynamic and bathymetric surveys are important for determining site suitability for tidal stream turbine (TST) installation. Understanding the ways in which coastal features affect tidal velocities at potential TST development sites will improve identification and analysis of physical constraints on tidal energy development. This paper presents and examines tidal velocity data measured in Ramsey Sound (Pembrokeshire, Wales, UK), an energetic macrotidal strait, which will soon host Wales' first TST demonstration project. While maximum tidal velocities in the strait during peak spring flood exceed 3 m s −1, the northern portion of Ramsey Sound exhibits a marked flood-dominated tidal asymmetry. Furthermore, local bathymetric features affect flow fields that are spatially heterogeneous in three dimensions, patterns that depth-averaged velocity data (measured and modelled) tend to mask. Depth-averaging can therefore have a significant effect on power estimations. Analysis of physical and hydrodynamic characteristics in Ramsey Sound, including tidal velocities across the swept area of the pilot TST, variations in the stream flow with depth, estimated power output, water depth and bed slope, suggests that the spatial and temporal variability in the flow field may render much of Ramsey Sound unsuitable for tidal power extraction. Although the resource potential depends on velocity and bathymetric conditions that are fundamentally local, many prospective tidal energy sites are subject to similar physical and hydrodynamic constraints. Results of this study can help inform site selection in these complicated, highly dynamic macrotidal environments. In order to fully characterise the structure of the tidal currents, these data should be supplemented with 3-D modelling, particularly in areas subject to a highly irregular bathymetry and complicated tidal regime. Highlights: Vessel-mounted ADCP surveys of tidal currents are conducted within an energetic tidal channel. The effect of depth-averaging on velocities in fast-flowing tidal straits is discussed. The marked tidal asymmetry of the flood/ebb tidal regime and high spatial variability across the Sound is examined. The available power within the system is calculated. Suitable tidal stream turbine locations within the northern portion of the Sound are postulated.