Page 304 - Fundamentals of Ocean Renewable Energy Generating Electricity From The Sea

Other Aspects of Ocean Renewable Energy Chapter | 10 289

FIG. 10.10 Increase of drag coefficient due to wave-current interaction, assuming a 1 m/s tidal
current. U w is the near-bed wave orbital velocity; γ represents the ratio of the drag coefficient in the
presence and absence of waves.

friction can significantly affect the tidal energy resource over long-time pe-
riods. At some sites, up to 20% reduction in tidal energy resources has been
reported [26,30].

10.2.2 Accounting for Ocean Energy Devices in Numerical
Models
Up until now, we have only considered undisturbed wave and tidal energy
resources. However, the act of harvesting energy from these resources will
disturb the underlying hydrodynamics (e.g. [31]). By contrast, only at very large
levels of energy extraction would there be significant feedback between wind
energy conversion and the wind resource [32], hence wind energy feedbacks
are not considered here. In this section, we consider the implications of (and
methods for) extracting wave and tidal energy within numerical models.

Tidal Models
Tidal energy extraction can influence both near- and far-field hydrodynamics.
Locally, energy extraction can lead to the generation of wakes and changes
in eddy patterns, and far-field effects can lead to tidal flow diversion from
the project site, and changes in tidal phasing [31]. When assessing the tidal
energy resource, it is therefore necessary to consider the impact of various