David Yang
Jun 16, 2015
ENGL 202C
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
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.
References
David Yang
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.
Accessed 2:07 AM 6/17/2015. http://marinebio.org/oceans/currents-tides/
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/