Tidal Power: Wave of the Future?

By: Cem Ozcan

Tidal power is using the tides to extract energy to convert into electricity. The tides are the result of the gravitational force between the Earth and Moon. On a daily basis this force pulls up tons of water, thus the tides. The tides are also brought back down, allowing for tidal power to be used twice daily, which would sum to about 10 hours. Tidal power is catching this water when it is at high tide and storing it in reservoir type structures until the time of low tide. During low tide, the water is released, allowing it to flow back out to sea through the turbines, and thus generating power. In order to create a tidal plant, we build a dam, called a barrage, at the bottom of a tidal basin. This includes a device called a sluice, which opens up allowing the tide to come in at high tide. This water rushes past a turbine that is attached to a generator, or in some cases the water pushes air through tunnels that then act like wind through a turbine. When it is time for the tide to go out at low tide, the function of the sluice reverses and the water flows back out through the turbines.

History

Utilizing the tides was first done in the 18th century to compete with windmills and another water technology--water wheels. Water mills were quite popular but became scarce once the steam engine gained its popularity. Tidal power plants have not traditionally been a popular way to convert energy into electricity.

Current Usage

Presently France is the only country that successfully uses the tides as a power source. In their country, tidal power accounts for just about 240 megawatts of power at the world's largest tidal plant--the La Rance. This facility was constructed in 1966, and is currently Europe's only tidal plant. This plant provides roughly enough energy to fuel 240,000 homes. Though the energy source is both reliable and plentiful, extracting usable power from it is not.

Future

The comparison between tidal energy now and wind energy 10 years ago has been made. Researchers are hopeful that developments to the technology can be made. One offshoot of tidal power that is currently being researched is the possibility of using the energy extracted from waves to produce hydrogen for fuel or fuel cells. There is hope that this would be used specifically in remote areas such as the Highlands and Islands of Scotland.
World wide only about 20 sites have been identified as having the potential to harness the power from the waves. This is due to the fact that between 12 and 18 feet difference (called 'head') between high and low tide is needed, and very few areas experience this range of heights. (In the United States one of the only usable sites is at Nantucket, though it is unlikely that they will begin construction due to the unpleasing appearance of the plants)
Another option yet to be completely explored would be to use offshore turbines
(Somewhat comparable to an underwater wind farm.) These would be quite a lot cheaper than building the large-scale bridges and wouldn't pose such risks to the environment. There are many more potential sites for this type of technology than the current tidal technologies. Some would speculate that these would pose risk to marine life, but it has been pointed out that they pose far less risk than the propellers on ships, as they are both stationary and rotate 10 times more slowly.

Advantages and Disadvantages:

Once constructed, it is a free source.
No greenhouse or other gas emissions.
Reliable.
Inexpensive to maintain.
Tides are very predictable.
Needs to be close to the coast.
Not a continual energy supply throughout the day.
Not aesthetically pleasing.

Tidal power has the potential to one-day account for one fiftieth of our total power consumption, so they could never solve our current energy dilemma. They could provide assistance, but never more than that--we could not totally rely on this technology. The greatest drawback is that we know little about the effect this has on marine life. There is always a potential threat to the natural ecosystems when we disrupt nature's processes, and the ocean is no exception. The reduced tidal flow that Tidal energy systems cause has environmental impacts on tidal basins because they decrease the flow of the tides and also silt buildup. There is speculation that if we use this technology to a great degree the tides will slow down, posing a great treats to the ecosystem.

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