Civil Engineering Reference
In-Depth Information
oceans are still in early stages of development. In some optimistic research reports
the potential for renewable energy generated from the ocean is estimated to be as
high as seven thousands E Joules per year (7,000 EJ/year) (Rogner et al.
2000
),
while others predict that it will only be about seven E Joules per year (7 EJ/year)
(Sims et al.
2007
). Predictions aside, the records show that at the end of year 2009,
the worldwide, installed capacity of the ocean generated power has been less than
300 MW (Lewis et al.
2011
).
Current major conceptual energy extraction technologies from the ocean are the
use of the ocean waves and currents, vertical (most of the current actual generated
power is by utilizing this method) and horizontal movement of the ocean water due
to what is known as tidal effects, ocean thermal conversion, and salinity gradient.
When the wind comes in contact with the ocean surface creates two different
movements on the body of the water. The body of water either is pulled up or pushed
forward with the wind. The action of water pulling up creates a potential energy in
water that if it is captured when the water comes back down can be useful for power
generation. Also the action of pushing water forward can cause utilization of this
kinetic energy in generation of power. All these kinetic and potential energies can
be utilized to generate power and electricity if the proper technology is
implemented.
Ocean tides are another energy source that is generated due to the combination
of the inertial, centrifugal, gravitational and rotational forces acting among the
Earth, the Moon, and the Sun. When the alignment of the Sun, Earth and Moon
changes from all being located on the same direction to a condition that direction of
lines that connect each two of them together are perpendicular to each other, the
changes in combined forces among them cause the tides height changes between the
maximum height and the minimum height extremes. This continuous up and down
movement, in conjunction with the confi guration of the ocean bed near the location
of the tides, generates another horizontal movement for the body of the ocean water.
These movements also can be the resources for generating power and electricity by
utilizing proper technologies.
Also due to low thermal conductivity of the sea water almost all of the thermal
energy received from sun and absorbed with the water stays in the upper layers of
the ocean water. Very small portion of this heat is transferred to the lower layers of
the ocean, and therefore this condition creates a differential temperature level
between the upper and lower layers of the ocean water. With proper technology this
temperature difference can be utilized for generating power and electricity as well.
Finally, salinity gradient (Osmotic power) which is the difference in concentra-
tion of salt in seawater and river (fresh) water can be also used for power and elec-
tricity generation. The potential methods for collecting this energy are reverse
electrodialysis and pressure retarded osmosis. Both methods are based on potential
of two fl uids with different level of concentration of salt to come to a balance of
concentration acting on two sides of a membrane. For a detail discussion on all
aspects of ocean energy see (Lewis et al.
2011
).
