The output from conventional fossil-fueled generating stations can be reduced when the tidal plant begins generation, and it can be brought back into the system during the few hours that a tidal plant must remain idle. Large, modern power systems can readily absorb the intermittent output of a tidal plant. Using new technology, turbines can be built to generate electricity in both directions, and also to operate as pumps in both directions. These cycles take place about twice a day (two flood tides and two ebb tides during each lunar day). When the tide begins to turn and the sea level rises, the sluiceways are opened once more, so that the tidal basin can be filled for the next cycle of electrical generation. When this difference becomes large enough, flow is allowed through the tidal generators until the difference in levels becomes too low to drive the turbines. The sluiceways, artificial channels with gates, close at high tide and the ebbing sea level causes a differential head between the basin level and the sea. One of the most practical ways to harness tidal energy is still the old tide mill concept: closing off an estuary or tidal basin from the sea with a structure composed of a powerhouse, a sluiceway and a solid embankment section. With the world’s highest tides occurring in the Bay of Fundy, there is additional opportunity for large-scale tidal energy projects in Canada. North America’s only tidal energy plant is located at Annapolis Royal, Nova Scotia. While the potential of tidal hydroelectricity has long been recognized, compared to river dams, tidal power projects are expensive because massive structures must be built in difficult saltwater environments. Tidal energy is a largely untapped, renewable energy source based largely on lunar gravitation.
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