Page 152 - Fundamentals of Ocean Renewable Energy Generating Electricity From The Sea

142 Fundamentals of Ocean Renewable Energy

FIG. 6.1 North Atlantic gyre and the Gulf Stream. (Image kindly provided by Kevin Haas
and reproduced from K. Haas, X. Yang, V. Neary, B. Gunawan, Ocean current energy resource
assessment for the Gulf stream system: the Florida Current, in: Marine Renewable Energy, Springer,
New York, NY, 2017, pp. 217–236, with permission from Springer.)
and because ocean currents are relatively stable and predictable, they represent
a useful form of marine-based electricity generation that could be considered in
any future energy mix in countries that border a suitable ocean current resource.
Ocean gyres are driven by trade winds (easterlies) in combination with
westerlies (Fig. 6.1). Friction between these relatively persistent winds and the
surface of the ocean drives a mass flow of water, leading to basin-scale gyre
systems (e.g. the North Atlantic Gyre in Fig. 6.1). The eastward rotation of the
Earth offsets the centre of the gyre systems to the west of the ocean basin, and so
there is a western intensification of the associated currents. In contrast to eastern
boundary currents, which are relatively broad, shallow, and slow-moving, these
western boundary currents are therefore narrower, deeper, and faster. The five
main western boundary currents are
● The Gulf Stream
● Kuroshio Current
● Brazil Current
● Agulhas Current
● East Australia current
It is primarily these five western boundary currents that have been identified
as possible candidates for exploiting the ocean current resource. For example,
the Gulf Stream (in the North Atlantic) and its counterpart in the North Pacific
(the Kuroshio Current) are around 100 km wide, and in some places have surface
velocities in excess of 2 m/s (e.g. [2]).