New approach to tidal stream energy analysis at sites in the English Channel

Tidal stream power generation offers the prospect of predictable, low-CO2<br/>power at a number of locations around the UK and the world. Previous<br/>assessments of tidal energy resources have taken the form of desk studies<br/>based on simplified navigational data. Where numerical model data has been<br/>used it has been at too low a resolution to capture high velocity tidal flows<br/>constrained by coastal topography. Analytical solutions for maximum energy<br/>extraction in simple tidal channels have been produced, but they have not<br/>been extended to more complex open-boundary cases such as flow around<br/>headlands and islands. There is therefore a role for site-specific numerical<br/>modelling, which when validated, offers the twin advantages of a<br/>high-resolution picture of the resource and allowing simulation of momentum<br/>extraction within the model to take place.<br/><br/>In order to parameterize the sub-grid-scale momentum extraction in such<br/>models, a new analytical model of the velocity reduction in a large array of<br/>tidal turbines has been derived. The model extends previous models of large<br/>wind turbine arrays and uses analogies with flow through submerged<br/>vegetation. It provides an equivalent added drag coefficient suitable for use in<br/>a 2-D coastal numerical model.<br/><br/>A numerical model of the flows in the region of the Portland Bill headland<br/>has been produced, forced by tidal elevations at the free boundary. A site<br/>selection exercise was carried out for the Portland Bill location and an area of<br/>around 12 km2 was identified as having a high potential for development<br/>using mean cubed speed found through tidal analysis of model results<br/>without energy extraction.<br/><br/>A large tidal stream generator array has also been simulated within the<br/>Portland Bill model—linked to the new model for momentum extraction—and<br/>was found to have a significant effect on the tidal parameters in the locality.<br/>This was the first time that a large tidal array has been simulated in a realistic<br/>coastal domain of large extent, with a parameterization that takes into account<br/>the interaction of the turbines with the rough-wall flow in the natural state.<br/>Results predict that there is a region downstream of the array extending<br/>approximately 5–10 km around the simulated tidal stream turbine array in<br/>which the tidal stream ellipse major axis is reduced by at least 5%. In the area<br/>of momentum extraction the principal semi-diurnal tidal stream ellipse major<br/>axis length was reduced by 10–15%.

Name dc:type.qualificationname

Ph.D.

Level dc:type.qualificationlevel

doctoral

Grantor dc:publisher.institution

University of Southampton

Year dc:date.issued

2009

Author dc:creator

• Blunden, L.S.

Advisor dc:contributor.advisor

• Bahaj, AbuBakr