Types of Tides

There are actually many types of tides. That is what makes tidal energy so interesting. There is a sinusoidal fluctuation of the energy of waves.

The strength of tides is determined by the relationship between where the moon is relative to the Earth.

On Atlantic Coast, semi-diurnal tides occur. These consist of two high and two low tides daily with little variation. On the other side, diurnal tides consist of one high and one low tide. Mixed tides are the same as semi-diurnal tides but have greater disparity between high and low tides.

An incoming tide is a flood tide and an outgoing tide is a ebb tide. The period in between is the slack tide. We also have riptides, which are strong, subsurface currents that conflict with another current. These usually occur at areas of violent underwater activity. They are usually underwater currents and cannot be seen on the surface. On the other hand, tiderips can be seen on the surface and look like choppy water.

Pictures of types of tides:
RIPTIDE

TIDERIP

Sources:
http://oceanmotion.org/html/background/tides-types.htm

http://www.oregon.gov/DSL/SSNERR/docs/EFS/EFS02typetides.pdf

http://en.wikipedia.org/wiki/Rip_tide

Tidal Ecosystems-

After talking a bit about the effects on the environment caused by tidal power plants, I felt obligated to write a bit about the organisms that inhabit tides.

Above is a simple layout of what a tidal ecosystem looks like. There are various advantages to living in a tidal ecosystem. There is an abundance of nutrients and oxygen. Food sources are readily available and there are various places to inhabit in a tide that provide great protection and homes for aquatic creatures. There are some challenges that organisms living in tides have to deal with. They must be able to deal with decreased moisture and increased water temperature. Also, salinity constantly changes in tidal zones and organisms need to tolerate a wide range of salinity levels. Animals also have to compete for limited living space as tidal ecosystems are not extremely large areas.

One must also note that at various times, the inter tidal is exposed to the air. Many organisms have adapted to living both underwater and on land. The tidal ecology is extremely diverse and is filled with various species including crabs, urchins, shrimps, sea anemones, starfish, clams, krill, and various bivalve organisms like clams and oysters. These organisms have adapted to all the above listed challenges and help to create a sustainable food web in a dynamic ecosystem with large fluctuations.

As the organisms in tidal ecosystems are already dealing with many challenges, it can be said that tide power plants will cause increased strain on these animals and their already "stressful" lives. Therefore, we must really consider if tidal power plants are a viable solution to aid our energy concerns.

Sources:

http://en.wikipedia.org/wiki/Intertidal_ecology

http://seaworld.org/animal-info/ecosystem-infobooks/tide-pools/intertidal-ecology/

http://www.enchantedlearning.com/subjects/ocean/Intertidal.shtml

Possible Solutions to Negative Tidal Power Impacts on Marine Life

The negative impacts brought upon by the usage of tidal waves do have possible solutions!

Many studies have been conducted on the movement of marine life near tidal generators, and whether or not a high number of collisions would occur between the animal and blade. For instance, a study was conducted on a tidal stream generator in the East River in New York. 24 different motion detectors were placed underwater to determine the movement of marine life around the tidal generators. The results were promising, indicating that almost no fish used the portion of the river where blades existed. Those that did use that particular portion tended to avoid areas of imminent danger. This study seemed to indicate that the generators were placed in a smart area, away from heavy marine animal population; the fish that did swim around the area also knew how to avoid potential hazards.

Problems presented by the production of the tidal generators also have potential solutions. Experts suggested using sound insulators to keep in the sound, as well as using devices to cancel acoustics that do get emitted. Another possible mitigation technique would be to avoid sensitive areas at all, and turn off production during peak marine life movement seasons. Similar techniques were suggested to mitigate the electro-magnetic fields produced. Devices can be implemented to contain the leakage of electro-magnetic fields, as well as to limit the amount of field emitted in the first place. By using non-toxic chemicals and coatings in and on the tidal power generator, the chemical problem can be easily solved.

It is clear that there are options available to mitigate potential problems presented by tidal power generator. Some of these have been well researched, while there are still other studies that are under way to determine even better ways to control these environmental impacts.

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Sources:

http://www.hydroworld.com/articles/hr/print/volume-30/issue-3/articles/ocean-tidal-stream-power-identifying-how-marine-and-hydrokinetic-devices-affect-aquatic-environments.html

http://www.renewableenergyworld.com/rea/blog/post/2011/03/understanding-the-effects-of-oceantidalstream-power

http://www.king5.com/story/tech/science/environment/2014/08/05/13351802/

http://www.energybc.ca/profiles/tidal.html

Environmental Impact of Tidal Power

Power generated from tides, in the form of tidal stream generators and tidal barrages, are both sustainable and efficient forms of energy production. However, they do not come without risks and impacts, especially on the marine animals that live in the surrounding environment.

The greatest concern with the tidal stream generator is the collision risk that it poses to surrounding organisms and animals. Because stream generators use blades to harness the energy of the tides, animals (such as fish) are susceptible to being struck by these fast moving blades. The risk of blade strike is exacerbated by the high speeds of the water, which draws the animals into, or very close to the blades.

Stream generators also produce a heavy amount of noise and electro-magnetic fields, both of which can be highly disruptive to animals living in the water. The noise in itself can seriously injure or kills animals that are nearby. The electro-magnetic fields are especially harmful to animals that rely on echolocation. Mammals such as dolphins and whales rely on echolocation to communicate and navigate in the ocean. Because the electro-magnetic fields are underwater, the acoustic output generated by the tidal stream generators are even greater than they would be on land. 

Additionally, the construction and operation of the tidal stream generators also encompass the use of certain chemicals and fluids. An accidental leakage of these fluids would be extremely harmful to the surrounding marine animals, and could possibly have an effect much like an oil spill. The chemical coatings on the outsides of the equipment could also erode over time, resulting in damage to the ecosystem as well.

Despite all its positive selling points, tidal power generators also come with many possible harmful impacts to the surrounding marine animals. These problems could be mitigated or completely solved in the future, but for now there still remain unanswered questions as to the true impact of tidal power generators.

Sources:

http://www.hydroworld.com/articles/hr/print/volume-30/issue-3/articles/ocean-tidal-stream-power-identifying-how-marine-and-hydrokinetic-devices-affect-aquatic-environments.html

http://www.renewableenergyworld.com/rea/blog/post/2011/03/understanding-the-effects-of-oceantidalstream-power

http://www.king5.com/story/tech/science/environment/2014/08/05/13351802/

http://www.energybc.ca/profiles/tidal.html 

So What's the Big Deal?

There are mainly two types of method to harvest energy from tide. The first on is tidal stream generator. The second kind is tidal barrage.  There are another two kinds of proposed methods including dynamic tidal power and tidal lagoon. Because these are pure mechanical device with no heat transformation and reduced energy transformation process, efficiencies are higher than traditional power plant. Tidal power is more predictable than wind and solar power. Even though tide power plant cannot generate electricity all the time. It can capture tide energy for roughly 10 hours per day. Problems associate with tide power are that most of tide power plant will be built at remote area. Electricity being generated needs to be transported through long distance in order to reach populated area. Time integral that tide power plants generate power is not peak electricity usage hour. Electricity energy needs to be stored in some other form which is a challenge for current technology (Siegel, 2012).

Pros of tidal power (Siegel, 2012):

·        Renewable

·        Emission-free

·        Reliable (power plant can last over 100 years)

·        High efficiency

·        Predictable output

·        Could potentially provide a storm surge barrier.

Cons of tidal power:

·        Expensive to build.

·        Location specific (only able to build at place with high tide difference)

·        Technology challenge for storing energy that being produced

·        Change tide height for surrounding area and disrupt regular tidal cycle

·        Environmental impact on surrounding area

·        Slow down costal ocean current which may lead to dirt, waste build up

Tidal stream generator utilizes kinetic energy of moving water to power turbines. Tidal turbines are freestanding machines that spin with water pass through. It is similar to winder powered turbines, but tide power hydroelectric plants are more predictable. Some turbines can be installed on current existing infrastructures such as bridge.  Many types of tidal stream generators are available for use. Most popular one is axial turbines. Its shape is close to traditional windmills. Cross-flow turbines have the advantage that able to be installed either vertically or horizontally (“Tides”). Flow augmented turbines theoretically produce more energy than traditional windmill turbines. These generators are normally deployed where ocean current is strong therefore higher amount of electricity can be produced.

Second type of popular method is tidal barrage. It is like a dam which captures energy from current flow by. Normally tidal barrages are being built near mouth of river or bay. When sea level rises, water rushes into the river or bay. When tide is gone, a potential difference created. Water with high potential is released back into ocean. Water body flows huge turbines to create electrical power though large generator.

Dynamic tidal power is a proposed method that may able to produce electricity. It utilizes the potential energy with kinetic energy. A long T shape dam into the ocean will create phase difference for wave at shallow water. The significant water level difference may able to be utilized and converted into electricity (Evans, 2007).

Tidal lagoon proposes to construct a circular wall that will hold large body of water. It will let in water when high tide comes and use water’s high potential energy difference to produce electricity.  

 

Citation:

Hulsbergen, K., R. Steijn, G. Van Banning, and G. Klopman. Dynamic Tidal Power – A New Approach to Exploit Tides. 2008. Print.

Evans, Robert. "Fueling Our Future: An Introduction to Sustainable Energy." New York: Cambridge University Press (2007). Print.

"Tidal." Welcome to Tethys. U.S. Department of Energy. Web. 1 Dec. 2014. <http://tethys.pnnl.gov/technology-type/tidal>.

Siegel, RP. "Tidal Power: Pros and Cons." Triple Pundit RSS. 1 June 2012. Web. 1 Dec. 2014. <http://www.triplepundit.com/2012/06/tidal-power-pros-cons/>

Energy of the Sea

Newton's law of universal gravitation states that any two bodies in the universe attract each other with a force that is proportional with their masses and inversely proportional to the square of the distance between them. (Wikipedia Newton’s law of universal gravitation)

Every point mass attracts every single other point mass by a force pointing along the line intersecting both points. The force is proportional to the product of the the two masses and inversely proportional to the square of the distance between them. (Wikipedia Newton’s law of universal gravitation)

·        F is the force between the masses, measured in newtons (N)

·        G is the gravitational constant, equals to .6.74 * 10^-11 (N*m² * kg^-2)

·        m₁ is the first mass, in kilograms (kg)

·        m₂ is the second mass, in kilograms (kg)

·        r is the distance between the centers of the masses, in meters (m)

Gravitational attraction is inversely proportional to the square of the distance between two masses.

The tide generating force is inversely proportional to the cube of the distance between each point on Earth and the center of the tide-generating body (Sun or Moon).

Tide-generating forces are small averaging about one-millionth the magnitude of Earth’s gravity. However, their maximum value at points on Earth’s surface at “latitude” of 45 degrees relative to the “equator” between the zenith and nadir.

Using tide power as source of energy:

There have been people in the history use ocean tides as a source of power. In the 12^th century, water wheels driven by the tides were used to power gristmills and sawmills. During the 17^th and 18^th centuries much of Boston’s flour was produced at a tidal mill.

Tide power is considered to be a clean, renewable source of energy with vast potential of generating electricity. Tides are more predictable than wind and solar energy. Like other kinds of renewable energy, it suffers from high cost and limited availability of sites. Even though the initial cost of building the plant is relativity higher than traditional thermal power plant, but the operating cost would less because it does not use fossil fuels or radioactive substances to generate electricity. (From our text book, pg 296)