Page 324 - Alternative Energy Systems in Building Design

298 OCEAN ENERGY TECHNOLOGIES

Turbidity Turbidity is the amount of silt and sediment in water, which in time
results in a smaller volume of water being exchanged between the basin and the sea.
Suspended particulates in the water also prevent light from the sun from penetrating
the water, which affects aquatic ecosystem conditions.

Salinity Salinity, or the dissolved salt content in a body of water, is the result of less
water exchange with the sea. The average salinity inside the basin decreases, which also
affects the ecosystem. Lagoons, when designed properly, can remedy this problem.

Sediment Movement In general, rivers flowing through estuaries provide a high
volume of sedimentation, which eventually is moved to the sea. The introduction of a
barrage into estuaries frequently results in sediment accumulation within the barrage,
which negatively affects the ecosystem and creates a significant maintenance and
drainage dilemma.
Pollutants Biodegradable pollutants, such as sewage, increase in concentration and
cause bacteria growth within the basin, which, in turn, results in negative human and
ecosystem health consequences.

Fish Pass In some instances, fish pass through these tidal power systems safely.
However, when the gates are closed, fish get sucked through turbine fins. Mitigation
measures, such as screens or fish-friendly turbine design, seldom prevent fish mortality.
Recent research in sonic guidance hopes to provide a solution to this ongoing problem.

ECONOMIC CONSIDERATIONS

Tidal power is both labor- and material-intensive and requires very high capital
expenditure. However, once implemented, these systems are relatively inexpensive to
run. Most tidal power projects do not produce returns on investment for decades; as
such, it is very difficult to attract investors. At present, worldwide projects have been
supported by governments that have the required financial resources to support such
undertakings.

TIDAL STREAMS
Tidal streams are fast-flowing volumes of water caused by the motion of the tide.
These usually occur in the shallow depths of seas, where a natural construct forces the
water to speed up. The technology involved is similar to wind energy, although there
are differences.
Water is 800 times denser than air and has a much slower flow rate. This means that
the turbine experiences much larger forces. This results in turbine designs that have
much smaller diameters. The turbines are used to either generate power on both ebbs
of the tide or to be able to withstand severe structural strain resulting from the currents.
The technology is still in its developmental stage but has the potential to be a reliable
and predictable renewable-energy source.