The quest to turn the motion of the world's waterways into a significant source of energy may still be in its nascent stage, but several tidal power projects are making headway. Whether they operate in lakes, rivers or the oceans, projects attempting to harness the tides share the same mission: to improve the technology and offer an economical alternative to fossil fuels.
Renewable hydrokinetic power comes from a number of different sources, including the up-and-down motion of waves and the smooth flow of the tides caused by the sun and moon's gravitational forces on Earth's bodies of water. Tidal power is seen as a promising source of energy because of its predictability and from the potential to draw it from ocean currents and estuary channels that connect rivers with the sea.
There are only a handful of tidal energy projects in place around the world, and none is producing commercially available electricity at this time. Most of these projects use some sort of turbine to capture the tide's kinetic motion. In general, as the turbines slowly spin, they turn the gears in an attached gearbox to create electricity. Cables connected to those gearboxes carry that electricity ashore.
Although it is unclear just how much electrical energy that the tides have the potential to generate, the Electric Power Research Institute (EPRI) has studied several tidal power project sites. In 2008 EPRI estimated those sites together have the potential for generating as much as 115 terawatt-hours of electricity annually, although the practical potential for energy generation from those sites is about 14 terawatt-hours per year. (Total electricity consumption in the U.S. is about 4,000 terawatt-hours per annum, according to EPRI.) Much of that energy would come from Alaska, thanks to high power density and large-size sites in southeast Alaska, Cook Inlet and the Aleutian Islands. Other locations studied were in Maine, San Francisco and Washington State's Puget Sound. Although New York City and the Chesapeake Bay were not studied for the 2008 report, EPRI concluded these sites could also make use of tidal hydrokinetic energy resources.
Read more from Larry Greenmeier in Scientific American
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