Tidal energy, or tidal power, is a little known and little used energy source. Yet it is a very old energy source, dating back to the middle ages in Europe. Tidal energy is created by the relative motion of the Earth, Moon, Sun, and the gravitational interactions between them. Every coastal region has two high and two low tides in each approximate 24 hour period. A big advantage of tidal energy is its predictability. The size and time of tides can be predicted very efficiently.
Tidal energy is little used around the world. In order for electricity to be generated, differences between high and low tides must consistently reach 16 feet. There are few regions in the world where this occurs. There are currently no tidal energy facilities in the United States although there is potential in the Pacific Northwest and the Atlantic Northeast.
Harnessing Tidal Energy.
Barrage or Dam. There are only three barrage tidal plants in the world. Essentially, a barrage is built which forces tidal flows through turbines, creating electricity. When the water levels on both sides of the barrage are significantly different, gates are opened, allowing water to flow through and activate the turbines. The Rance Tidal Plant in France is a prime example of the barrage method of tidal energy.
Tidal Turbines. A relatively new technology, tidal turbines are very similar to wind turbines but underwater. They are positioned strategically at entrances to bays or rivers, among others, where currents are fast. Because seawater is much denser than air, a single tidal turbine can produce significantly more energy than a wind turbine of the same size.
Tidal energy is a renewable resource, but the classic, barrage method of harnessing tidal energy has some negative environmental impacts. Most notably, tidal power plants upset fish migrations and, by disrupting water flows, can upset entire estuarine ecosystems. Tidal turbines however, because they do not block water flow, may be a viable answer to these concerns.
How Tidal Compares to Solar.
Tidal turbines are a very efficient source of energy, and that is an advantage over solar to this point. However, there are only 40 locations in the world where tidal power is feasible. The sun shines everywhere. Nonetheless, they are both certainly part of the solution. While I support solar energy wholeheartedly, tidal power could be a great source for green energy. Especially for northern coastal regions where the sun is not as prevalent. I live in Oregon and I’ve personally witnessed the dramatic turn of tides (I’m talking about starfish clinging on at eye-level during low tide!)
image credit:Tidalstream Partners