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)