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The sea has long been seen as a source of energy. In the Middle Ages (1200-1500
AD) farmers used to trap sea water in mill ponds and use it to power water
mills as the tide dropped.
The gravitational pull of the moon causes water to flow in from the ocean
twice a day on the flood tides, and outward during ebb tides. Additional
monthly and annual lunar cycles vary the strength of these currents. This
energy follows the predictable relationship of the lunar orbit that is
known many years in advance.
Over the past forty years, there has been constant interest in harnessing
tidal power. Initially, this interest focused on estuaries, where large
volumes of water pass through narrow channels generating high current velocities.
Engineers felt that blocking estuaries with a barrage and forcing water
through turbines would be an effective way to generate electricity. This
was proved by construction of a tidal barrage at St. Malo in France in the
mid 1960s. La Rance tidal power plant still provides 90% of Brittany's,
and a major refurbishment program (due for completion in 2007) means it
will continue in operation well into the new millennium.
Despite the success of La Rance, no other major tidal barrages have been
built since, due in some part to environmental concerns. Barrages present
a barrier to navigation by boats and fish alike; reduced tidal range (difference
between high and low water levels) can destroy much of the inter-tidal
habitat used by wading birds; and sediment trapped behind the barrage
could also reduce the volume of the estuary over time. By the early 1990s,
interest in estuarine-derived tidal power had largely ceased, and scientists
and engineers began to look at the potential of tidally-generated coastal
currents instead.
As tides ebb and flow, currents are often generated in coastal waters,
in areas outside of bays and estuaries. In many places the shape of the
seabed forces water to flow through narrow channels, or around headland.
Because sea water has a much higher density than air, currents of 5-8
knots generate as much energy as winds of much higher velocity. In addition,
tidally-generated coastal currents are predictable. The tide comes in
and out every twelve hours, resulting in currents which reach peak velocity
four times every day. Two rival technologies -- tidal fences and tidal
turbines -- are now being developed to catch the energy of these currents.
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The World electrical energy market is at $800-billion-a-year and
rising. It has been estimated that there are 2 billion people who
still lack electricity today, and the world demand in developing countries
is doubling every eight years. In order to meet that demand, renewable
energy sources must be developed, while limiting production of green
house gases.
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Seabine Turbine is designed to have a significant impact
upon the Energy market estimated to be worth $800-billion-a-year and rising.
It has been estimated that " there are 2 billion people who still
lack electricity today, and the world demand in developing countries is
doubling every eight years" (World Watch Institute, May 1997). In
order to meet that demand, while limiting production of green house gases,
renewable energy sources must be developed.
Coastal currents are strongest at the margins of the world's
larger oceans. A review of likely tidal power sites in the late 1980s
estimated the energy resource was in excess of 330,000 MW. South East
Asia is one area where it is likely such currents could be exploited for
energy. In particular, the Chinese and Japanese coasts, and the large
number of straits between the islands of the Philippines and Thailand
are suitable for development of power generation from coastal currents.
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