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Ocean
Energy
By
Paul Morris
Kyle Pucci
David Yang
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CONTEXT
Abstract……………………………………………………………………………………………………………… 3
How It Works……………………………………………………………………………………………………….4
Instillation…………………………………………………………………………………………………………...6
Maintenance………………………………………………………………………………………………………..8
References…………………………………………………………………………………………………………10
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Abstract
What if instead we work with the planet by harnessing its already existing
energy? This is the vision our team has in producing clean power that is both
sustainable and reliable. Ocean currents are continuous and directed movements of
seawater, created by the reactions between waves, temperatures and salinity
differences in the water. There are three important steps one must take before
understanding the true extent of this technology; how it works, how to install it, and
how to maintain it. Our team believes by implementing underwater turbines at such
locations in these currents, we can harvest energy cleaner and more effectively. The
potential of this technology seems almost limitless if one takes into account the
sheer amount of ocean currents located around the planet.
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How underwater turbine works
Under water turbine are basically windmills installed onto an ocean floor or
riverbed. The turbine captures the energy stored in ocean tides, which are created
by the gravitational attraction between the sun, earth and moon. The earth surface
that faces the moon experiences a slightly stronger gravitational pull, while the side
opposite of the earth experiences a slightly weaker pull. This results in a slight bulge
in the ocean on the side farthest and nearest from the moon at the given period. The
sun impacts tides on earth in a similar way. Although the sun is much more massive
compare to the moon, the moon is also much closer to earth than the sun, and so the
tide-generating power of the moon is much stronger than that of the sun. The tides
of the ocean rise and fall along the coast generate the currents. Far off the shore, the
tidal current is continuous, and the direction changes through all points, describing
a complete loop during the course of a single tidal period.
Underwater turbine is similar to windmill turbine except underwater turbines
harness natural currents to generate electricity, while wind turbines harness
natural winds to generate electricity. The concept of the underwater turbine is to
have three large airplanes like metal propellers placed underwater to the position
where the tide currents will cause it to rotate. The current produced by the tides
spins the blades of the turbine, which the arms of the fan are connected to a shaft,
and the rotation of the rotor shaft in the shaft house by way of bearings and gears to
another shaft that turns a magnetic coil generator to generate electricity; this is
essentially the same way a wind turbine works. Then the produced electricity is
carried by the cables to the shore and plugged into an electrical grid that the
electricity can be distributed.
Figure 1. Underwater turbine component
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Just like the windmill turbine, underwater turbines are typically arranged in rows,
usually close to the shore in waters ranging from 20 to 30 meters in depth. The best
settings are place where current speed is between 3.6 and 4.9 knots (6.7 to 9
kilometers per hour).
Comparing underwater turbine to windmill turbine, underwater turbine can
generate much more power. Water is 832 times denser than air, which means an 8knot tidal current has more energy than a 380kph wind. Water is able to produce
much more power than wind turbine. In order for wind turbine to generate the
same power, wind turbine blades would need to be much larger than water turbine
blades; the wind turbine would have to spins in much faster speed, and have to take
over much more land than water turbine. The greatest difference is that underwater
turbines are designed to work with water current flow from either the front or the
rear. This allows them to take advantage of the back and forth motion of tidal wave
systems. Also, underwater turbine is more reliable than their counterpart wind
turbine, the currents patterns of the ocean are much more predictable than wind
currents. The movement of the tide out to sea and flowing in from the sea can be
very predictable; a given tidal area can be expressed in the amount of kilowatthours of electricity it can produce per underwater turbine. While the amount of
wind current that passes over any given area of land cannot be predictable.
Therefore the power production can be estimated and projected during different
times of the day, resulting in consistent annual production trends.
The impact of underwater turbine have on marine ecosystems are really minor.
However, some might think that the rapidly spinning blade of the turbine could
easily slice small marine animals into chums. Unlike the windmill turbine where
they can kill birds in flight by sucking them into their blades, underwater turbine
pushes fish out of the way. Also underwater turbine do not require to have fast
spinning propeller in order to generate the same amount of energy; since water is
much more denser than wind. The underwater turbines spin really slowly; around
one set turns at 10 to 20 rotations per minute. A turbine that moves a couple of feet
per second will not pose much of threat to marine life.
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Installation of Oceanic Turbines
In today's world there is a huge demand for new alternative energy sources.
Energy sources that require fossil fuels are becoming more and more obsolete,
because of the soaring prices of gas. Fossil fuels are not only harmful to your wallet,
but also the environment. “Against the backdrop of climate change and energy
security, the European Union have set a target to obtain 20% of their energy
generation from renewable sources by 2020”(Siemens, n.d.).
To solve this growing concern, oceanic turbines can provide a constant and reliable
source of energy. Currents drive the turbines 24/7 and can potentially provide more
energy to the grid compared to any other alternative energy source. For this reason
installation of these oceanic turbines is an important process to utilizing this
developing alternative energy. The key factors in determining an area of installation
are contingent on making the installation geographically responsible, geographically
ideal for energy production, and safe for the underwater ecosystem.
The first step in determining a spot for installation is the finding the source of
energy. Turbines depend on the constant flux of moving water in order to be
powered. Finding a reliable current no more than 1 km away is preferred. The
importance of installing turbines close to the shore line is to reduce overhead costs
and so it can be easily accessed. Since most near shore currents are not that strong,
the location has to be well researched. Channels, constrictions between islands, and
large headlands are considered ideal spots for finding strong and fast flows (23m/s). During the this phase it's important to get a lease agreement and make sure
the spot is free of any shipping or navigation hotspots. Since the turbines operate at
a maximum depth of 25 m, it is vital for the safety of the equipment and ships to
have no contact with the turbine. In addition to safety, the safety of the ecosystem in
which the turbine resides is of high importance. It’s important to find a site that is
away from sensitive environmental sites, such as key migratory areas and food
sanctuaries for marine life. The turbines are not a natural phenomena in the ocean
so as little impact of the ecosystem is necessary. Currents are used by marine life to
promote travel and food opportunities. Not disrupting this cycle allows for no
impact on the marine life.
Once a suitable spot has been well researched and analyzed, installation of
the turbine is ready to commence. Installation is organized in an array for
maximum energy production of the turbines. “Installation makes up 18% of lifetime
costs for a wave array” (SI Ocean, 2013, p. 15), so making installation inexpensive is
the key to making more turbines. To get the turbine to its location it is important to
note the turbine must be buoyant. The purpose for making the turbine buoyant, is so
the turbine can be towed to the spot to minimize the fee it takes to lug a massive
turbine. The floating aspect of the turbine makes it far superior than turbines that
are bottom mounted. Bottom mounted turbines are harder to access and require
more money to instal. Having the floating turbine allows for easy maintenance and
quicker installation. If there are ever any changes needed to where the installation
took place, the turbine can resurface without any additional mechanism to help it
rise.
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In addition, according to Seagen Tidal Power, “Another key element in
minimising the installation costs is maximising the weather window during which
installation is possible” ( SI Ocean, 2013, pg.16)Installation is the most consuming
aspect of the job, so picking a fair weather day will help minimize installation costs
and time. Making sure the seas are calm makes for an ideal situation, this increases
the chances of a successful installation that will last many years. Installing large
diameter monopiles is the first step to mounting the turbine. The monopiles must be
drilled deep into the ground using a drill-drive technique. By using this technique
whatever ground conditions are found shouldn’t be a problem. Once the drilling is
completed and monopile is in place, a casing is set around the drilling site and
monopile. Following, grout is injected in, this fills the empty space. After the grout is
put into place, the final step is waiting for the grout to cure, so that there is sufficient
strength for the turbine and the parts to be assembled. This process of drilling and
casing is then continued to many other spots around the turbine, so that more
turbines can be added to harness all the energy the current can provide. The same
precautions are taken into account when installing the other turbines. The
placement is set into an array of turbines, the tactical formation of the array insures
maximum energy harnessing and proper spacing between turbines. Once the array
of turbines are installed, electrical cables from the turbines are then connected to
the grid.
All in all, there is much research and planning that goes into the installation
of an oceanic turbines. The turbine requires proper placement in a location where
there is no environmental impact, ideal for energy harvesting, legal, and avoids
conflicts with sea users. These energy saving turbines are very useful in creating an
alternative energy supply that provides consistent and reliable energy to the grid,
which can not be said about any other alternative energy provider. The harvesting
of energy of the currents is very useful, so the importance of proper installation will
ensure the long term efficiency and lifespan of the turbine and base components.
The base components need to be securely installed so the heavy turbine will not fail.
Ultimately, the installation of the turbines is only the beginning process of the
brilliant benefits the these turbines have to offer.
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Maintenance Of Ocean Turbines
As we have read, there are many similarities between the windmill turbine
and the ocean current turbine, yet where they differ heavily is in the way of
maintenance. Windmill turbines have consistently less force applied to them at any
time in comparison to Ocean turbines. This is because, unlike wind, water within
these currents constantly moving at a steady speed. This alone wears out turbine
blades at a faster rate, due to their higher work output. In addition, we must factor
in the environments in which they are placed. Since the ocean currents that
produce the most energy are farther out to sea, these machines must be built to
handle extreme underwater conditions. Water temperature, speed, and weather
heavily influence the function of the machines, making constant maintenance a must
to preserve their integrity.
Figure 1. Ocean Turbines
Unlike Windmill turbines, the fact that these are located from 25 to 50
meters below the water add another dimension of difficulty in manually repairing
such things as marine growth or turbine wear and tear. Scuba-drivers must be on
hand in the staffing department, with such skills as underwater welding and
electronic operations in order to effectively handle the required tasks.
Each separate machine has a total lifetime expectancy, which can be
calculated by taking the respective parts and their composition and running it
through field-tests which simulate the harsh environment they will be sent to. Some
components, typically the non-moving pieces of machinery have a much higher
lifetime expectancy due to the fact they are built from more rugged materials and do
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not need to be in motion. The generator, shaft, cables and support columns are such
pieces. Yet the problem lies with the elements that must move in order for the
whole to operate. The turbine blades, gearbox, and axle are all such portions that
must be carefully monitored for signs of stress. All of these factors must be taken
into account when overviewing the maintenance of one of these massive pieces of
machinery. With water being eight hundred times denser than air, a twelve milesper-hour current passing through a turbine could generate the same amount of
energy as a sustained wind of one hundred ten miles-per-hour doing as so. That is a
lot of pressure to handle.
Another important aspect that must be taken into account is the lines
connection to the shore, as well as the ability to restrict ocean travel within the
turbine farms compound. However high the marine environments risk is to these
turbines, human risk is also a factor one needs to take into consideration. The areas
where these machines operate must display clear warnings to passing nautical
navigators in order to reduce risk of accidental impact with shallow cables or
turbines. If an accident would occur, the clean up and appropriate repair would cost
exceedingly more than any incident on land, for specialists in ocean repair and
containment would be required.
However complicated this maintenance seems, we as a team believe the
benefits of a cleaner source of energy stemming from a renewable location such as
these super powerful ocean currents are worth it. The power harvest from such
currents yields much more power than wind, and are more abundant and
predictable.
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References:
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commercialization” Oceans03’, v 4, 2003, p 2278-2283
Garret C and Cummings P (2004) “ Generating Power from Tidal
Currents” ASCE Journal of waterway, port, coastal and ocean
engineering May/June 2004
Hammons TJ.(1993) “Tidal Power” Proceedings of the IEEE,
1993;89(3):419–33.
Marine Current Turbines. (n.d.). Retrieved June 17, 2015, from
http://www.marineturbines.com/Tidal-Energy
REUK.co.uk - The Renewable Energy Website. (2014, September 24). Retrieved June
17, 2015, from http://www.reuk.co.uk/Introduction-to-Tidal-Power.htm
Currents and Tides - MarineBio.org. MarineBio Conservation Society. Web.
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Sleight, K. (2013, March 2). How Do Underwater Turbines Work? | Ecopedia.
Retrieved June 17, 2015, from http://www.ecopedia.com/energy/how-dounderwater-turbines-work/
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http://www.alternative-energy-news.info/seagen-tidal-power-installation/
Siemens.Retrieved from www.marineturbines.com/Tidal-Energy
Siemens. (n.d.). Tidal energy. Retrieved from
www.marineturbines.com/Tidal-Energy
SI Ocean. (2013). Ocean Energy: Cost of Energy and Cost Reduction Opportunities.
Retrieved from
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f