Page 323 - Alternative Energy Systems in Building Design

CURRENT TIDAL GENERATION TECHNOLOGIES 297

The concept involves a wave chamber that is constructed on the shore. The waves
cause the air in the chamber to rise and decompress, resulting in a rush of air that
drives a Wells’ turbine that generates power. Therefore, the turbine has to be capable
of turning regardless of the direction of airflow.
This device is currently generating 5 MW of power. This is an example of how the
technology can be used to meet small-scale local needs. Wavegen has said that at
present, the answer lies not in huge operating plants but rather in small ones such as
these, which can concentrate on meeting local or regional needs.
The device, which is rated at 5005 kW according to the following calculations,
provides power to 400 households.

Maximum power generated per annum = 500 × 8760 (hours in a year)
= 4,380,000 kWh

Assuming a capacity factor of 40 percent,

Annual electricity generated = 4,380,000 × 0.40 = 1,752,000 kWh

Assuming a 4377-kWh power demand for each home every year,

Number of homes receiving power = 1,752,000/4377 = 400

Pumping The turbines in a barrage also can be used to pump extra water into the
basin at periods of low demand. This usually coincides with cheap electricity prices,
generally at night, when demand is low. Establishments that provide tidal power gen-
erally buy inexpensive electrical energy from the grid during periods of low demand,
such as night hours, to pump water in the basins and then generate power at times of
high demand, when prices are high. This practice is commonly used by hydroelectric
power providers and is known as storage.

TIDAL POWER SYSTEM OUTPUT
The tidal power schemes just described are not considered a constant source of energy
because within a 24-hour period, power production is limited to a maximum of
6–12 hours. Since tidal cycles are based on the revolution of the moon, and electricity
demand is based on the revolution of the sun, the energy-production cycle is not long
enough to satisfy the power-demand cycle. As a result, grid connection becomes
somewhat incompatible.

ENVIRONMENTAL CONSIDERATIONS

Impact on aquatic habitat The construction of barrage systems in estuaries has
a considerable negative impact on the aquatic life within the basin, such as shellfish.
With proper ecologic design consideration, lagoons, however, could be used for fish
or lobster farming, which could benefit local economies.