Page 318 - Alternative Energy Systems in Building Design

292 OCEAN ENERGY TECHNOLOGIES

GEARBOX
GENERATOR

TURBINE

Figure 9.4 Diagram of a
FLOWING WATER
tubular turbine.

Current Tidal Generation Technologies

The world’s largest tidal power barrage station was constructed on the Rance estuary
in France nearly 40 years ago. The project generates 240 MW of power. Annapolis
Royal Barrage, located in Nova Scotia, Canada, was constructed in 1984. It produces
18 MW of power.

TIDAL FENCES
Tidal fences are composed of individual vertical-axis turbines that are mounted within
the fence structure, known as the caisson. They can be thought of as giant styles com-
pletely blocking a channel and forcing water through them. Currently, there are two
developing technologies for harvesting the oceans’ energy, one from tidal barrages and
the other from tidal streams.

TIDAL BARRAGE
A barrage, or dam, is built across an estuary or bay that has adequate tidal range, which
is usually in excess of 5 m. The purpose of the barrage is to let water flow through it
into the basin as the tide comes in. The barrage has gates that allow the water to pass
through. The gates are closed when the tide stops coming in, trapping the water within
the basin or estuary and creating a hydrostatic head. As the tide recedes, the barrage
gates are opened, and the hydrostatic head causes the water to come through these
gates, driving the turbines and generating power. Power can be generated in both direc-
tions through the turbine, although this usually affects efficiency and the economics of