Environmental Engineering Reference
In-Depth Information
are driven by wind and solar heating of waters near the equator, though some ocean currents result
from density and salinity variations of water. These currents are relatively constant and flow in
one direction only, in contrast to tidal currents closer to shore. Some examples of ocean currents
are the Gulf Stream, Florida Straits Current, and California Current (USDOI 2006a).
While ocean currents move slowly relative to typical wind speeds, they carry a great deal of
energy because of the density of water. Ocean currents thus contain an enormous amount of energy
that may be captured and converted to a usable form. It has been estimated that taking just one-
thousandth of the available energy from the Gulf Stream would supply Florida with 35 percent
of its electrical needs (USDOI 2006a).
Technology for utilization of large-scale ocean current energy is at a very early stage of de-
velopment. There are no commercial grid-connected turbines currently operating in the United
States, and only a small number of prototypes and demonstration units have been tested (USDOI
2006a). According to the U.S. Minerals Management Service, under the most likely commercial
development scenario, energy would be extracted from ocean currents by using submerged water
turbines similar to wind turbines. These turbines would have rotor blades, a generator for con-
verting rotational energy into electricity, and a means of transporting electrical current to shore
for incorporation into an electrical grid. There would need to be a way to anchor turbines in a
stationary position, such as posts or cables anchored to the sea floor. In large open areas with fast
currents, it might be possible to install water turbines in groups or clusters to make up an ocean
current “farm,” with a predicted density of up to 37 turbines per square kilometer. Space would
be needed between the water turbines to eliminate wake-interaction effects and allow access by
maintenance vessels (USDOI 2006a).
Environmental Costs of Utilizing Ocean Energy Technologies
The ocean energy technology “fuel cycle” involves acquisition of materials, manufacture and
installation of generating and transmission equipment, operation of this equipment, and disposal
or recycling of waste materials from manufacturing processes and decommissioning, as illus-
trated in
Figure 11.2.
Manufacturing involves industrial-scale piping and sheet metal fabrication
of generators, with installation of turbine and electrical components, depending on the specific
technology utilized. Utility-scale ocean energy environmental costs include disturbance of the
marine environment, visual impacts, hazardous materials disposal, and potential impacts on water
and other resources, depending on the technology employed.
Tidal power plants that dam estuaries can impede migration of marine life, and silt builds up
behind dams, altering marine ecosystems. Tidal fences may also disturb migration of sea life
(USDOI 2011a). Tidal barrages alter marine ecosystems by changing the flow of saltwater into
and out of estuaries (Armaroli and Balzani 2011, 244). Newly developed tidal turbines like the
TidGen™ Power System of the Ocean Renewable Power Company may ultimately prove to be
the least environmentally damaging of the tidal power technologies because they do not block mi-
gratory paths, facilitate buildup of silt, or induce ecosystem change (ORPC 2011a; Sharp 2010).
Potential environmental costs of wave energy development include adverse impacts on marine
habitat (depending on the nature of associated submerged surfaces, above-water platforms, and
changes in the seafloor); toxic releases from leaks or accidental spills of hydraulic fluids; visual
and noise impacts above and below the water surface; and conflict with other ocean users, such
as commercial shipping, recreational boating (USDOI 2011b; Nelson 2008; Previsic 2004), and
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