Transcript Ocean Energy - Essex County College Faculty Web Server

Ocean Energy
Prof. Park
UTI-111
Essex County College
Ocean Energy
• The world's ocean may eventually provide us
with energy to power our homes and
businesses. Right now, there are very few ocean
energy power plants and most are fairly small.
But how can we get energy from the ocean?
• There are three basic ways to tap the ocean for
its energy. We can use the ocean's waves, we
can use the ocean's high and low tides, or we
can use temperature differences in the water.
Let's take a look at each.
Wave Energy
• Kinetic energy (movement) exists in the moving waves of
the ocean. That energy can be used to power a turbine.
In this simple example, to the right, the wave rises into a
chamber. The rising water forces the air out of the
chamber. The moving air spins a turbine which can turn
a generator. When the wave goes down, air flows
through the turbine and back into the chamber through
doors that are normally closed.
• This is only one type of wave-energy system. Others
actually use the up and down motion of the wave to
power a piston that moves up and down inside a
cylinder. That piston can also turn a generator.
• Most wave-energy systems are very small. But, they can
be used to power a warning buoy or a small light house.
Wave Energy
Wave Farm
• The World’s First Wave Farm Goes Live in Portugal
by Bridgette Meinhold, 10/22/08
• The world’s first commercial wave farm went live at the
end of September in Agucadoura, located off the coast of
northern Portugal. Designed by Pelamis Wave Power,
the farm employs three Wave Energy Converters –
snakelike, semi-submerged devices that generate
electricity with hydraulic rams driven by waves. This first
phase of the new renewable energy farm is rated at 2.25
MW with 3 machines, and the the second phase will add
an additional 25 machines to bring the capacity to 21
MW – enough to power 15,000 homes!
Wave Farm
Tidal Energy
• Another form of ocean energy is called tidal
energy. When tides comes into the shore, they
can be trapped in reservoirs behind dams. Then
when the tide drops, the water behind the dam
can be let out just like in a regular hydroelectric
power plant.
• Tidal energy has been used since about the 11th
Century, when small dams were built along
ocean estuaries and small streams. the tidal
water behind these dams was used to turn water
wheels to mill grains.
Tidal Energy
• In order for tidal energy to work well, you need large
increases in tides. An increase of at least 16 feet
between low tide to high tide is needed. There are only a
few places where this tide change occurs around the
earth. Some power plants are already operating using
this idea. One plant in France makes enough energy
from tides (240 megawatts) to power 240,000 homes.
• This facility is called the La Rance Station in France. It
began making electricity in 1966. It produces about one
fifth of a regular nuclear or coal-fired power plant. It is
more than 10 times the power of the next largest tidal
station in the world, the 17 megawatt Canadian
Annapolis station.
Tidal Energy
La Rance Tidal Power Plant
Tidal Energy
• Tidal energy is the utilization of the sun and moon's
gravitational forces - as the tide is the result of their
influences.
• Tidal energy is a type of energy that produces electricity
and other forms of power through the use of water.
• Tidal energy is energy that could be obtained from the
changing sea levels. In other words, tidal energy is a
direct result of tide shifting from low to high.
• Tidal energy is one of the oldest forms of energy. Tide
mills, in use on the Spanish, French and British coasts,
date back to 787 A.D. Tide mills consisted of a storage
pond, filled by the incoming tide through a sluice and
emptied during the outgoing tide through a water wheel.
Tidal Energy
• The tide moves a huge amount of water twice each day
and although the tidal energy supply is reliable and
plentiful, converting it into useful electrical power is not
easy.
• There are two basic theories on how to convert tides into
power. The first involves converting the power of the
horizontal movement of the water into electricity. The
second involves producing energy from the rise and drop
of water levels.
Severn Barrage Tidal Power
• The Severn Barrage is a proposed tidal power station
to be built across the Bristol Channel (Severn Estuary).
The River Severn has a tidal range of 14 metres - the
second highest in the world - making it perfect for tidal
power generation.
• The 20 billion pound ($US30bn) Severn Barrage would
involve the construction of a 10 mile long barrage (dam)
between Lavernock Point south of Cardiff, Wales, and
Brean Down in Somerset, England. The barrage would
act as a bridge between England and Wales and will
have an operational lifetime of up to 200 years. It would
be the world's largest ever renewable energy project,
and the UK's largest engineering project since the
Channel Tunnel.
Severn Barrage Tidal Power
Tidal Energy
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•
Energy calculations
The energy available from a barrage is dependent on the volume of water.
The potential energy contained in a volume of water is:[49]
•
•
•
•
where:
h is the vertical tidal range,
A is the horizontal area of the barrage basin,
ρ is the density of water = 1025 kg per cubic meter (seawater varies
between 1021 and 1030 kg per cubic meter) and
g is the acceleration due to the Earth's gravity = 9.81 meters per second
squared.
The factor half is due to the fact, that as the basin flows empty through the
turbines, the hydraulic head over the dam reduces. The maximum head is
only available at the moment of low water, assuming the high water level is
still present in the basin.
•
•
Ocean Thermal Energy
Conversion (OTEC)
• The idea is not new. Using the temperature of water to
make energy actually dates back to 1881 when a French
Engineer by the name of Jacques D'Arsonval first
thought of OTEC. The final ocean energy idea uses
temperature differences in the ocean. If you ever went
swimming in the ocean and dove deep below the
surface, you would have noticed that the water gets
colder the deeper you go. It's warmer on the surface
because sunlight warms the water. But below the
surface, the ocean gets very cold. That's why scuba
divers wear wet suits when they dive down deep. Their
wet suits trapped their body heat to keep them warm.
Ocean Thermal Energy
Conversion (OTEC)
• Power plants can be built that use this difference
in temperature to make energy. A difference of at
least 38 degrees Fahrenheit is needed between
the warmer surface water and the colder deep
ocean water.
• Using this type of energy source is called Ocean
Thermal Energy Conversion or OTEC. It is being
demonstrated in Hawaii. More info on OTEC can
be found on the archive pages for the Natural
Energy Laboratory of Hawaii at:
www.hawaii.gov/dbedt/ert/otec-nelha/otec.html
Diagram of a closed cycle OTEC plant