Environmental Engineering Reference
In-Depth Information
Tidal Power
In contrast to the lack of commercial development of wave power, a
commercial tidal power plant that generates 240 megawatts of electricity
has been operating since 1966 in the estuary of the Rance River in
northwestern France. The plant produces 0.01 percent of France's elec-
tric power at 70 percent of the cost per kilowatt-hour of the country's
nuclear power installations.
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The design of the tidal station has been
superseded by newer technologies that have a lesser environmental
impact on aquatic life.
Electricity can be generated by water fl owing in and out of a bay.
As there are two high and two low tides each day, electrical genera-
tion from tidal power plants is characterized by periods of maximum
generation every 12 hours, with no electricity generation at the six-
hour mark in between. Alternatively, the turbines can be used as
pumps to pump extra water behind the linear barrage during periods
of low electricity demand. The water can then be released when demand
on the system is greatest, thus allowing the tidal plant to function
with some of the characteristics of a pumped storage hydroelectric
facility.
Selection of location is critical for the tidal turbine. In order to
produce commercial amounts of electricity a difference between high and
low tides of at least 16 feet is required. Tidal systems need to be located
in areas with fast currents where natural fl ows are concentrated between
obstructions, such as the entrances to bays and rivers, around rocky
points, headlands, or between islands or other land masses. Three pos-
sible sites have been suggested in the United States: Cook Inlet in Alaska,
the Golden Gate in San Francisco Bay, and the East River in New York
City. As of mid-2009, fi ve tidal units of a planned 300 have been suc-
cessfully placed in the East River. When the project is completed, it will
generate 10 megawatts of electricity, barely commercial but enough to
power 10,000 homes.
Ocean Currents
More futuristic is the possibility of obtaining energy from fast-moving
ocean currents such as the Gulf Stream. The amount of water moving
past Miami is more than fi fty times the total of all the rivers in the world,
and the surface velocity sometimes exceeds 8 feet per second.
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The total
power of the kinetic energy of the Gulf Stream near Florida is equivalent
to approximately 65 gigawatts. How much of this energy can be cap-
tured economically is unknown.
