Riding the Tide: Hydropower: Eco20/20

Riding the Tide

Amazing as it sounds; the sun is twenty seven billion times larger than the moon. Due to the locations of the sun and moon, however, the sun has only approximately one fourth of the gravitational pull of the moon. The gravitational pull of these two celestial beings, along with the movement of the earth on its axis and in orbit, help to create one of the most fascinating renewable energy resources: tidal energy.

Tidal energy is basically the same as hydroelectric power. Dams are used for barrage tidal energy to electricity conversion. When the water level on the two sides of the dam is significantly different, the barrage is opened so that the water rushes through the dam, pushing the turbine propellers, creating electricity. There are, at this time, only three known barrages in the world.

The underwater wind turbine, or tidal turbine, is another type of hydropower electricity generating plant that uses the tidal current. In some cases, the turbines are a mere six feet from the surface of the water. Tests are being done with these new power plants to determine the danger to marine life and to verify that the propellers will not be weighed down by barnacles. The propellers are currently thought to be safe, until proven otherwise, due to the slow spinning motion of the turbine as well as the fact that the propellers have blunt edges. Tidal turbines can move slower than wind turbines because of the difference in density between water and air. These tidal turbine propellers actually move at approximately one tenth the speed of ship propellers. The slow-moving turbines may prove to be a problem, however, if barnacles begin attaching to the propellers, weighing them down. At this time, most tidal turbines produce an average of thirty-five kilowatts.

As with many renewable resources, research is being moved towards following the acts of nature when capturing or creating energy. For the tidal turbines, the research is focusing on the flippers of the humpback whales. This species of whale has tubercles on their flippers, which cause slight circular currents when they swim. These circular currents decrease drag, which in turn increases the velocity of the water displaced by the fin. Not only have propellers with tubercles proven to produce more energy, they also require less force to begin the spinning movement of the propellers.

Another type of tidal turbine being researched is the kite tidal turbine. Tidal turbines are expected to lose more energy than they create when used in high velocity tidal streams. Also, the more work the turbines do, the more likely it is that damage can be done to the propellers. By using two propellers moving in opposite directions, it is hoped that the reactive torque will be decreased. Reactive torque is the force of the water used against the turbine. Currently the tidal waves cause the turbine to move up and down along with the waves, and that disrupts the energy pattern, but research is ongoing to improve the efficiency of the kite tidal turbines.