TIDAL ENERGY

  Origin: tides are caused by the gravitational pull of the moon and sun, and the rotation of the earth. Near the shore, water levels can vary up to 40 feet. The tidal cycle is perfectly predictable so it helps to its exploitation.

Extraction: the simplest generation system for tidal plants involves a dam, known as a barrage, across an inlet. Sluice gates on the barrage allow the tidal basin to fill on the incoming high tides and to empty through the turbine system on the outgoing tide, also known as the ebb tide. There are two-way systems that generate electricity on both the incoming and outgoing tides.

  Utilities: the tidal energy generates electricity. But there is an important condition. Because water is about 800 times denser than air, tidal turbines will have to be much sturdier than wind turbines. They will be heavier and more expensive to build but will be able to capture more energy.

Producer regions: there are currently two commercial sized barrages in operations. One is located in La Rance, France; the other is in Annapolis Royal, Nova Scotia, Canada. France, England, Canada, and Russia have much more potential.