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Archive for the ‘Tidal’ Category

Global Wave Power

Physics 30 Alternative Energy  Assignment

                                                                                                                                                                                                                                                  Eric K

As the world continues to grow and find new technology, we find ourselves trying to replace fossil fuels with new and improved energy sources.  As we are running out of fossil fuels, researchers are trying to find new energy sources that are clean and renewable to use, and researching whether or not the energy source will be effective in everyday use.  One of the researched sources is wave power, the largest power source on Earth.  Wave power is the transport of energy by the waves in oceans, lakes, rivers, etc, and the capture of that energy to do work, such as generate electricity.  Global wave power is estimated to be 1 terawatt as revealed by previous studies.  Wave-power generation is not a widely employed commercial technology, but there has been attempts to use it since at least 1890.  The major competitor of wave power is offshore wind power.  Please keep in mind that wave power is distinct from the diurnal flux of tidal power and the steady gyre of ocean currents.

Waves are generated by wind passing over the surface of the body of water.  eric1As long as the waves propagate slower than the speed of the wind just above the waves, there is an energy transfer from the wind to the waves.  Both air pressure differences between the upwind and the lee side of a wave crest, as well as friction on the water surface by the wind, making the water go into the shear stress causes the growth of the waves.  Wave height can be determined by wind speed, the duration of time the wind has been blowing, the distance over which the wind excites the waves (fetch), and by the depth and topography of the seafloor, which can focus or disperse the energy of the waves.  A given wind speed has a matching practical limit over which time or distance will not produce larger waves.  When this limit is reached, the sea is said to be “fully developed”  What this means is that larger waves are more powerful, but wave power is not only determined by size, but by speed, wavelength, and water density.  The waves propagate on the ocean surface and the wave energy is also transported horizontally with the group velocity.  The average transport rate of the wave energy through a vertical plane of unit width, parallel to a wave crest, is called the wave energy flux or wave power, which must not be confused with the actual power generated by a wave power device.

Wave power is proportional to the wave period and to the square of the wave height.  eric2When the significant wave height is given in metres, and the wave period in seconds, the result is the wave power in kilowatts (kW) per meter of wavefront length.  In very deep water where the water depth is larger than half the wavelength, the wave energy flux is:

P = (ρg/64π) (Hm0)2 T ≈ (0.5 kW/m3•s) (Hm0)2 T

Where P is the wave energy flux per unit of wave-crest length, Hm0 is the significant wave height, T is the wave period, ρ is the water density, and ɡ is the acceleration of gravity.  For example, with a wave height of 3 meters and a wave period of 8 seconds, there are 36 kilowatts of power potential per meter of wave crest.  According to linear wave theory, in a sea state, the average energy density per unit area of gravity waves on the water surface is proportional to the wave height squared.

E = 1/16 (ρg (Hm0)2 )

Where E is the average wave energy density per unit horizontal area (J/m2), the sum of kinetic and potential energy density per unit horizontal area.  As the waves propagate, their energy is transported.  The energy transport velocity is the group velocity.  As a result, the wave energy flux, through a vertical plane of unit width perpendicular to the wave propagation direction, is equal to:   P = E C

where Cg is the group velocity (m/s).  Due to the dispersion relation for water waves under the action of gravity, the group velocity depends on the wavelength or equivalently on the wave period.  The dispersion relation is also a function of the water depth resulting in the group velocity behaving differently in the limits of deep, intermediate, and shallow depths of water.

There is also a conceptual study focused on using Oscillating Water Columns, eric3which is considered as the most efficient way utilize wave power.  There are 2 variations: onshore and offshore.  Oscillating water columns use a large volume of moving water as a piston in a cylinder.  Air is forced out of the column as a wave rises and fresh air is drawn in as the wave falls.  This movement of air turns a weir turbine at the top of the column.  Deep water wave power resources are enormous.  They lie between 1 terawatt and 10 terawatts, but it is not practical to capture all of this.  The useful worldwide resource has been estimated to be greater than 2 terawatts.  Locations with the most potential for wave power include the western seaboard of Europe, the northern coast of the UK, and the pacific coastlines of North and South America, Southern Africa, Australia, and New Zealand.  The north and south temperate zones have the best sites for capturing wave power.  The prevailing westerlies in these zones blow strongest in the winter.  Countries that are surrounded by seafronts could tap into an alternative source of power generation which could be generated by the waves during the different seasons of the year.  The findings of this study could be adapted to evaluate the capability to generate electricity on shore from lakes and rivers with undulated waves.  Researchers have begun this conceptual study with the derivation of mathematical equations for each component in the electrical generation system after taking into consideration the sea wave as the input to facilitate the workability of the entire system.  The researchers verified the validity of the developed and derived mathematical equations for each stage of the research.  They did this to establish and confirm its workability.  Electrical and mechanical relationships were derived to relate the workability of each component in the system for the purpose of electricity generation.  Numerous experiments were conducted to optimize the results in this study which would eventually lead to the generation of electricity.  The results obtained from the experiments indicated that the proposed model appears practical and could be implemented.

Pros:

– Wave Power

– Low Maintenance

– No greenhouse gases released

– Renewable energy source obtained by the wind via the Sun’s heating of our atmosphere

– Capable of high efficiency in ideal conditions (60% – 80%)

– Low upfront construction costs

– Minimal environmental impact when properly placed

– Oscillating Water Column

– Moving parts are housed outside for a greater lifetime of the material

– Can be built near shore for easy access to the power grid and for maintenance

Cons:

– Wave Power

– Efficiency drops significantly in rough weather due to safety mechanisms

– Limited locations where waves are strong enough to produce electricity without                         damaging equipment

– Power is only produced near oceans making transmission to inland customers difficult

– Winds can be unpredictable and far from reliable.  Can’t produce electricity at all times

– Improperly placed wave power plants can damage the marine ecosystem

– Initial building cost

– Could be considered an eyesore

References:

– Replacing Fossil Fuels: Utilizing Sea Waves to Generate Electricity                http://www.sciencedaily.com/releases/2012/12/121203080814.htm

Retrieved on January 4, 2013

– Oscillating Water Column (OWC)

http://owcwaveenergy.weebly.com

Retrieved on January 6, 2013

– Wave Power

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

Retrieved on January 3, 2013

– Advantages and Disadvantages of Wave Power

http://renewableenergyindex.com/hydro/advantages-disadvantages-wave-power

Retrieved on January 6, 2013

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Tidal Energy

Tidal Energy

By Troy S, Wesley C, Tanner M, Nosh M.

As the world begins to develop and create new technology there is a constant demand to find new and improved energy sources. Society is making strides to lean away from the use of fossil fuels to clean and renewable energy sources. One of these energy sources being used and tested is Tidal Energy as it is renewable, predictable and environmentally friendly. In the simplest of terms, Tidal Energy converts Tidal flow into electricity. Tidal Energy is a reliable source due to the predictable cycle of tides which has the flow of sea water transfer from the middle of the ocean to the shores and vice versa. The Tidal Energy used through the variations of sea levels caused by the gravitational effects of the moon along with the rotation of the Earth.

As of now there have been three different types of tidal plants produced, tidal fences, barrage plants, and turbines. Each is intended to harness the energy possessed from the change in water levels and the flow of water.

There are three main parts to barrage tidal plants, the most common type of tidal plant. The barrage, which acts like a damn, holds back water to be released later. Sluice gates allow the water through the turbine. The turbine spins due to water flowing through it, which also rotates an electricity producing generator. The generator converts kinetic energy into electric energy, while water is stored in the barrage, building up potential energy for when the tide is falling. The generator works by the movement of a solenoid, mechanically by tides, inside of a magnetic field, which induces a current in the solenoid. Tidal turbines functions similarly to the barrage tidal plant, but it is placed in the ocean, which provides a constant tide and kinetic energy source. The greater the momentum, mass and velocity, of the water equals a greater kinetic energy produced. The animation on this link clarifies the mechanics of the barrage tidal plant,

http://www.odec.ca/projects/2006/wong6j2/tidalAnimation.html

With any relatively new idea that has the potential to replace previously established methods there are pros and cons that arise once the new idea is compared to previous traditional methods. Tidal energy allows for the production of energy by using the predictable environmental changes as opposed to the harmful fumes emitted from burning of fossil fuels.

Pros

  • This type of energy does not emit emissions or create waste
  • Is easy to predict and track
  • Involves an abundant and inexpensive fuel source that is renewable
  • It contributes over 6% of the energy demand in the world

Cons

  • The apparatus necessary for harvesting and storing the energy are initially expensive
  • Limit amount of locations that meet mandatory requirements
  • Can cause some environment damage by disturbing wildlife habitat

Overall the energy created from the earths pull on earth’s oceans can create enough energy to benefit society in ways that can influence the environment and its inhabitants positively. Although the space necessary for the setup of an effective tidal fences, plants and turbines is hard to come by it allows for a clean emission free production of energy. Tidal energy is an effective alternative to previous energy producing processes.


BIBLIOGRAPHY
Tidalenergy. (n.d.). Retrieved May 20, 2012, from http://www.odec.ca/projects/2006/wong6j2/

tidal.html

N/A, unknown. (2010, May 24). Tidal Power Benefits and Drawbacks [Online forum message]. Retrieved

from Green Environment: http://egreenitems.com/renewable-energy/tidal-energy-pros-and-cons.html

Tidal energy. (n.d.). Retrieved May 20, 2012, from http://www.darvill.clara.net/altenerg/images/

tidalreefevans.jpg

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The Power of Waves

The constant development of current methods for powering our homes every day is not something that is new to us. In the short of amount of time from when the discovery of electricity was made, we have made an incredible advance on the knowledge of electromagnetism and stat electricity. A particular unique development for the production of electricity that has risen is the not so developed wave generator. This is a form of hydropower but instead of capturing the immense power of falling or flowing water, this method captures the slightly smaller power in a wave.

A wave generator is simply a small-scale hydroelectric dam, without the environmental consequence of having to flood a large area just to harbour the necessary effect of a dam. They are usually used in powering buoy and such. In the case of a wave generator, a wave rises into a chamber of the generator, as the water rises air is pushed out of the chamber and in turn forces a turbine to spin. In order to find out how much electricity can be produced in the turbine, we must first figure out the amount of kinetic energy the wave possesses. From this we may then proceed to transfer this kinetic energy into usable electrical energy. The energy of the wave drives the rotation or oscillation of a magnet in close proximity of a coiled wire. As the coiled wire comes into contact of the magnets magnetic field a current is induced. This current is your raw from of electricity which is then transfered to homes in the area as either AC (alternating current) or DC (direct current). DC being the type that comes out of our wall sockets to power our appliances and many gadgets.

Alex R.

References:

Retrieved on June 7th 2011

Information retrieved from:

  1. http://www.windpowerengineering.com/policy/the-physics-and-economics-of-wind-turbines/
  2. http://www.altenergymag.com/news_detail.php?pr_id=2654
  3. http://www.eia.gov/energyexplained/index.cfm?page=electricity_use
  4. http://en.wikipedia.org/wiki/Tidal_power

Pictures retrieved from:

  1. Image #1: http://www.inhabitat.com/wp-content/uploads/pelamis.jpg
  2. Image#2: http://www.school-for-champions.com/science/images/electromagnetism-coiled_wire.gif

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Kanchana M, Harley C, John C.

While most environmentalists place emphasis on the solar and wind turbine systems to generate electricity, another plentiful source of energy is often disregarded. The immense kinetic energy of waves in shallower waters possess can be converted into electrical energy by the means of several different methods. These methods are not only clean and nearly maintenance free, they have very little impact on the environment. Unlike hydro-electric dams which build up potential energy by storing water at higher elevations and then harnessing their kinetic energy as it flows down, wave-motion generators harness the already available kinetic energy of the waves.There are a multitude of different methods harnessing the kinetic energy of waves. They range from a turbine like generator that uses the motion of the air as it is disturbed by the waves, a jet engine turbine design that uses the force of the water to drive turbines, to an underwater station that uses an arm that extends up to the surface which is moved by the motion of the waves.

Click the image for a full size preview
However, the most common and most widely used method of generation is by using a floating platform that rides on top of oncoming waves. This pontoon is comprised of multiple smaller sets of pontoons each of which are connected to the adjacent one by a set of hinges. Inside each pontoon is a motor and a generator. As each pontoon is lifted and dropped back down by the motion, which in turn is transferred to pistons attached to the hinges and powers the turbine.The turbine then rotates the armature of  the motor which produces an electric current which is sent to the power grid.
Click the picture for a full size image

Video demonstration of pontoon-type wave power generation

Major advantages of wave power is that it is a renewable energy source, since waves are generated by gravitational force from the moon and partial influence from wind. So long as there is a body of water it will generate energy indefinitely. It also creates very little pollution, and has the potential to displace 1-2 billion tonnes of carbon dioxide emissions every year. Noise pollution is the type of major pollution that this technology would output, however as the waves are generally loud themselves, this is not a concern.

Obvious disadvantages of wave power is that it is very area dependant, similar to wind turbines. Other disadvantages also include inconsistent energy production, as strong tides only occur when the moon is closest to the earth, and when there are strong winds. When the ocean is calm so to is the power generator. Not to mention the enormous feat that would have to take place in order to install the generators along the coastline.

“Energy Resources: Wave Power”, Darvill.clara.net, May 18, 2011
Retrieved on June 6th, 2011 from:
http://www.darvill.clara.net/altenerg/wave.htm

“Ocean Wave Power” United States Department of Energy. n.d.
Retrieved on June 6, 2011 from:
http://www.energysavers.gov/renewable_energy/ocean/index.cfm/mytopic=50009

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