Tidal Power is Not a New Concept
Not only is tidal power one of the oldest forms of energy used by people for centuries, it is reliable, predictable and non-polluting. As far back as 787 A.D., this type of energy was used along the coastlines of France, Great Britain and Spain.
The process was known as tide mills and the energy harnessed was used to turn waterwheels to mill grain. One example of a tide mill is still in use in New York and was in operated during the 20th century.
Tide mills use a storage pond that is filled by incoming tides (flood) twice a day and emptied by the outgoing tide (ebb) twice a day through a water wheel. Ocean tides are predictable and reliable and by turning a water wheel with the surge of water escaping from the storage pond, gears power the mechanical process to grind grain.
The tides are a part of our natural environment just like the sun and the wind. Today, tidal power can be used by building barriers across natural ponds (estuaries) where the tidal range is high. The range is the difference in water levels between the incoming and outgoing tides.
Another way to harness this type of energy is to capture the power of offshore tidal streams. This is done with undersea turbines that are driven by the tidal surge and currents. Undersea turbines are fairly new and several types of turbines are being developed.
Pros and Cons
Tidal power is reliable and predictable but is also expensive when used to produce power. The biggest downside to using this alternative energy source is the natural limitation imposed by the 12 ½ hr tidal cycle. The cycle allows scientists to estimate the total potential power available.
Tidal range is measure by the difference in waterline between the surge of an incoming tide and the waterline when the area is at the lowest point of an outgoing tide. Tidal range along a coastline may be less than 15 ft to as much as 40 ft. To use tidal power in an economically feasible way requires a tidal range of 15 ft or more. A tidal range less than 15 ft is not considered enough to power the turbines.
There is often a wide variance in the levels of tidal range along a coastline. Along the coast of the Pacific Northwest there are areas perfect for capturing this type of energy with undersea turbines.
The Pacific tides in that region have a dramatic range. Energy producing potential is high along the coasts of Washington state, British Columbia and north to Alaska. Maine also has a good potential for tidal power on the Atlantic coast but in that area machinery used for undersea production will have to contend with a hostile under water environment.
Today, there are only a few tidal generating stations in operation. One is on the coast of France and has been producing electricity reliably for 45 years (since 1966). This tidal plant was intended to be the first of many but the plan was abandoned when France moved into nuclear energy. Other tidal plants in Nova Scotia and Russia are operating as well.
Recent interest in alternative energy has been bolstered by the need to create more power and the knowledge that fossil fuels are limited in quantity. Today areas such as Cool Inlet in Alaska and along the White Sea in Russia are being evaluated for the tidal power potential for generating electricity.
Environmentally, tidal power is a responsible choice as there are no gasses to be emitted and no global warming associated. However, there are risks associated with changing the tidal flows. So far, environmental impact of reducing tidal flows with storage ponds has been negligible but in some areas that might not hold true.
The use of storage ponds can decrease the tides by a small amount. The environmental impact might have some negative results in slight changes of the coastline or could affect coastal wildlife and fish populations especially in areas of high tidal range.
Demand and Supply
We know the demand placed on an electrical grid by the population varies widely throughout the hours of a day. Though the tides are predictable and reliable the tidal schedule will not match the demands on a commercial power grid.
However, tidal power may be combined with other forms of natural energy such as solar and wind power to provides some of the electrical power to a populated area. This could result in a reduction of fossil fuel use and extend the number of years before our supply of fossil fuels is depleted.
For decades the potential for using tidal power took a backseat to building nuclear reactors and nuclear plants. Concerns over safety and the massive number of regulations and overlapping agencies that are now required for building a nuclear power plant have literally stopped the growth of nuclear power in the U.S. Plants currently in operation were built thirty years ago and are not currently being replaced with the addition of new nuclear reactors.
We know nuclear power is effective but the safety factor is questionable in the public's mind. Though few serious nuclear incidents have occurred, the recent core meltdown in Japan raised the subject of nuclear safety once again.
Previous smaller incidents have been explained with excuses about aging equipment or operator error and in the U.S. the terrible Chernobyl nuclear accident was often attributed to a poorly built and poorly maintained power plant.
The Japanese meltdown was a different story. These were plants built with the latest and safest technology and multiple backups systems for safety. One act of nature destroyed all of the safety elements man had designed and installed.
Capturing tidal power is expensive and there is not enough potential to provide a large source of electrical power to the planet. However, this type of energy is used in conjunction with other alternative power sources like thermal energy, solar power and wind farms would have the potential, at least, to replace part of the fossil fuels currently used in the country.
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