Page 315 - Alternative Energy Systems in Building Design

TIDAL POWER GENERATION 289

extracted are kinetic energy, which results from currents arising between ebbing and
surging tides, and potential energy, which results from the height or head differential
between high and low tides.
Power generation from the kinetic energy of tidal currents has proven to be more
pragmatic and much more feasible today than the building of ocean-based dams or
barrages. At present, many coastal sites worldwide are being evaluated for their suit-
ability for harvesting tidal current energy.
The technology for extracting tidal potential energy involves the construction of
barrages and tidal lagoons. The barrage technology traps water at a certain level inside
a basin, thus making use of created water differential heights that result when water
level outside the basin or lagoon changes relative to the level inside. The differential
head static energy is converted into dynamic energy when sluice gates open and a flow
is used to drive turbines. Tidal power is considered a renewable resource because the
tidal phenomenon is caused by the orbital mechanics of the solar system, which is
inexhaustible for the foreseeable future.
The efficiency of tidal power generation largely depends on the amplitude of the
tidal swell, which can rise up to 33 ft. These swells then are manifested as tidal waves,
which are funneled into rivers, fjords, and estuaries. Amplitudes of up to 56 ft have
been observed in the Bay of Fundy, Canada. Superimposition of tidal waves gives rise
to tidal resonance, which amplifies tidal waves.
The energy potential contained in a volume of water is determined by the formula
E = xmg, where x is the height of the tide, m is the mass of water, and g is the accel-
eration of gravitational energy.
Tidal energy generators are installed in locations where high-amplitude tides occur.
Some of the most significant worldwide installation locations include Russia, the
United States, Canada, Australia, Korea, and the United Kingdom, as discussed below.
Smaller-scale tidal power plants are also in operation in Norway.

BARRAGES

Tidal barrages, as mentioned earlier, are used to trap water in basins by means of
mechanical doors referred to as sluice gates. The basic elements of a barrage are caissons,
embankments, sluice gates, turbines, and ship locks. Sluices, turbines, and ship locks are
housed in the caisson, a large concrete-block compartment. Embankments are used to
seal the basins where they are not sealed by caissons. Sluice-gate construction resembles
a flap gate that is raised vertically.

INSTALLED CAPACITY
The total rated capacity of turbines is specially optimized to meet the performance
requirements of each barrage construction. In small-capacity installations, where a
barrage is capable of producing only small amounts of energy, the turbines will operate
at low power-production capacity over a long period of time.