Environmental Engineering Reference
In-Depth Information
range of ocean energy technologies gained a new lease of life (JRC 2011 ; Lewis et al.
2011 ) .
King Canute's Lesson
King Canute famously demonstrated that the oceans do not respond to human command. 29
However, human ingenuity has managed, if not to tame, then at least to harness the great
power of the oceans. Several different methods have been developed. In summary, these
are the following:
• Wave power: The rhythmic motion of the ocean surface is transformed into
electricity.
• Tides and currents: Water flow, driven by tides or ocean currents, passes through a
barrage containing water turbines.
• Ocean thermal energy conversion (OTEC): The difference in temperature between
the surface and the depth of the oceans is exploited either for heating or to operate
a turbine.
• Salinity gradients: at the mouth of rivers, where freshwater mixes with saltwater,
differences in salinity can be harnessed to produce electricity (Lewis et al. 2011 ) .
Wave Power
As the wind blows over the ocean, some of the wind's energy is transferred to the water,
forming waves. The rise andfall ofwaves isaformofkinetic energythat may beharnessed
similarly to the piston in an internal combustion engine. This linear movement (up and
down) can be converted into a circular movement of a shaft, which is, in turn, connected to
a generator (see Figure 4.58 ) (Lewis et al. 2011 ) . But this is not the only way. More than
fifty different models of wave energy plant, either floating or anchored to the sea bed, are
currently under development.
Figure 4.58. Two types of wave energy converters. In the model on the left, waves
entering and exiting a chamber causes the air in the chamber to rise and fall, which, in
turn, drives a turbine. The second device comprises five tube sections linked by flexible
joints. The movement of these joints caused by waves is converted into electricity via
hydraulic systems housed inside each joint. Power is transmitted to shore using subsea
cables. Source: Lewis et al. ( 2011 ) (modified) and www.pelamiswave.com .
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