This summer, the first commercial electrical generator to draw power from the ocean tide began supplying Northern Ireland with energy. Installed in an inlet near Belfast, the generator works much like a wind turbine, with massive blades turned by the tide’s current. The angle at which the blades meet the current can be changed: rotating the blade face 180º lets the turbine catch the tide in both directions, while smaller rotations lessen the force exerted on the turbine, preventing damage.
Cost: 30 to 40 cents per kilowatt-hour; a planned installation with seven turbines will lower that cost to about 20 cents per kilowatt-hour
Companies: Marine Current Turbines