Post on 10-Feb-2016
transcript
OCEAN ENERGY CONVERSION
TYPE OF OCEAN ENERGY
• Ocean surface water movementWave power
• Deep (bulk) water movementTidal power
• Using thermal gradient of ocean temperatureOcean thermal
energy
• Using osmotic pressure difference between fresh water and salt water
Ocean salinitationenergy
TIDES ENERGY
Tides occur due to the movement of water in the sea,
caused by the gravitational attraction of the moon and
the sun acting upon the oceans of the rotating earth.
As tides come in and out (flow and ebb), water near the coast is
raised and lowered and the potential energy of this tidal can be
exploited.
It is also possible to harness the kinetic energy of the moving
water in the tidal stream itself to drive turbines.
HOW DO TIDES WORK? https://www.youtube.com/watch?v=5ohDG7RqQ9I
WAVE ENERGY
Waves are formed by winds blowing over the water
surface, which makes the water particles to adopt circular
motions.
This motion carries kinetic energy, the amount of which is
determined by the speed and duration of the wind, the length of sea
it blows over, the water depth, sea bed conditions and also
interactions with the tides.
The extractable form of wave energy is the potential energy of the
water column during wave oscillation.
WAVE VERSUS TIDAL ENERGY
Waves occur only in the
volume of water close to the
water surface, and is caused
mainly by winds blowing over
the water surface
In waves, water does not
undergo a net movement itself,
but acts as a carrier for
energy, oscillating or
moving in some direction
In the case of tides, the entire
water body moves, from the
surface to the seabed;
The tide energy is due to a net
movement of water, and is
caused by the gravitational
attraction of the moon and the
sun acting upon the oceans of
the rotating Earth
TIDAL ENERGY
The relative motions of the sun and moon in relation to earth rotation
cause the surface of the oceans to be raised and lowered periodically,
according to a number of interacting cycles, which include:
a half day cycle, due to the rotation of the earth within the gravitational field
of the moon
a 14.25-day cycle, resulting from the gravitational field of the moon combined
with that of the sun to give alternating spring (maximum) and neap
(minimum) tides
other further complex gravitational interactions occurring over 19 years and
1600 years cycles.
As a result of the above event, two high tides occur simultaneously,
one on the side of the earth facing the moon and the other on the
opposite side.
INFLUENCE OF MOON AND
SUN ON TIDAL ARRANGEMENT
The period between spring ad neap
tides is approximately 14.25 days,
i.e., half the 29.5 day lunar cycle
TYPICAL TIDAL PATTERNS
TECHNOLOGIES FOR
EXPLOITING TIDAL ENERGY
To capture and store and then release the water
Use of barrages
Flow of water
Marine current
TECHNOLOGIES FOR EXPLOITING TIDAL
ENERGY: USE OF BARRAGES
Barrages are used to create
artificial impoundments that
can be used to control the
natural tidal flow (in shallow
water embankment are used).
Complete closure of estuaries
would be achieved by emplacing
a series of prefabricated sections,
made from concrete or steel
which could be floated and then
sunk into position.
TECHNOLOGIES FOR
EXPLOITING TIDAL ENERGY: USE
OF BARRAGES
Tidal barrages comprises
of :
sluice/dams to capture
the water,
gates and
turbine generators –
similar to hydraulic
turbines
TECHNOLOGIES FOR
EXPLOITING TIDAL ENERGY: USE
OF BARRAGES
Tidal power generation station on the Rance
River in Saint-Servan, France.
TECHNOLOGIES FOR EXPLOITING TIDAL
ENERGY: MARINE CURRENT
The global tidal/marine current
energy resource is mostly driven
by the tides and to a lesser
extent by thermal gradient and
density effects
They are more predictable
especially when caused by tides.
These use windmill-like
underwater turbines.
TECHNOLOGIES FOR EXPLOITING TIDAL
ENERGY: MARINE CURRENT
The tides cause water to flow
inwards twice each day (flood
tide) and seawards twice each
day (ebb tide) with a period of
approximately 12 hours and 24
minutes (a semidiurnal tide), or
once both inwards and
seawards in approximately 24
hours and 48 minutes (a
diurnal tide).
Ocean current are driven
by numerous forces or
mechanisms including:
Winds
Salinity gradient
Thermal gradients
The rotation of the Earth, and
Mainly by tides
TECHNOLOGIES FOR EXPLOITING TIDAL
ENERGY: MARINE CURRENT
Marine current turbines are, in principle, much like
submerged windmills.
They are installed in the sea at places with high
tidal current velocities, to take out energy from
the huge volumes of flowing water.
The basic requirements for cost-effective power
generation from tidal streams using Marine
current turbines (MCT's) technology are:
mean spring peak velocity of about 2.5m/s.
a depth of water of 20 to 30m.
TECHNOLOGIES FOR
EXPLOITING TIDAL ENERGY:
MARINE CURRENT
Water turbines work on the
same principle as wind
turbines by using the kinetic
energy of moving fluid and
transferring it into useful
rotational and then electrical
energy.
The velocities of the currents
are lower than those of the
wind, however owing to the
higher density of water (835
times that of air) water
turbines are smaller than
their wind counterparts
for the same installed
capacity.
TECHNOLOGIES FOR EXPLOITING TIDAL
ENERGY: MARINE CURRENT
Horizontal axis Vertical axis
ADVANTAGES OF MARINE CURRENT
With increased conflicts over land use, water turbines offer a solution
that will not occupy land and has minimal or zero visual impact;
The greatest resource is in close proximity to coastlines and many areas
with high population densities;
The technology is potentially modular and avoids the need for large civil
engineering works, which are required for offshore wind turbines.
Power density reaching 10 kW/m2, about one order magnitude of the
wind.
ADVANTAGES OF MARINE CURRENT
The global marine current energy resource is very large, the resource
has better energy density compared to wind site, so the diameter of
water turbines can be less than that of a wind turbine for the same
energy output;
The water velocities and therefore power outputs are completely
predictable, once accurate site measurements have been taken;
Water turbines will not need to be designed for extreme atmospheric
fluctuations as required with wind turbines, meaning that the design can
be better cost-optimised;
WAVE POWER
WAVE ENERGY
Wave power is determined by
wave height, wave speed, wave
length, and water density.
Wave size is determined by wind
speed, water depth and
topography of the seafloor
(which can focus or disperse the
energy of the waves).
Wave motion is highest at the
surface and diminishes
exponentially with depth.
WAVE ENERGY
Wave power technologies are based on a range of device
including:
Oscillating or Assisted Water Columns (OWC),
Heaving buoys and pontoons (the Hosepump)
Pelamis Wave Energy Converter
Other types include overtopping, flaps and tapered channels (the
Pendulor), etc.
OSCILLATING WATER COLUMN (OWC)
This comprises a partly submerged structure (‘collector’) which is open to the sea below the water surface so that it contains a column of water.
Air is trapped above the surface of the water column.
As waves enter and exit the collector, the water column moves up and down and acts like a piston on the air, pushing it back and forth.
The air is channeled towards a turbine and forces it to turn.
The turbine is coupled to a generator to produce electricity
HEAVING BUOY DEVICE (THE HOSE PUMP)
When wave lift the device, water in
the pipes is accelerated upward as it
cannot escape through the check
valve.
As the wave recedes, the pipe
accelerates downward against the
movement of the internal water
creating a hydraulic pressure.
The water can be allowed to escape
through the top or bottom to drive
a turbine, and simultaneously more
water enters through the check
valve.
THE PELAMIS WAVE ENERGY CONVERTER
The pelamis (named after a sea-snake), by Ocean Power Delivery Ltd in
Scotland.
It consists of a series of semi-submerged cylindrical segments connected by
hinged joints.
THE PELAMIS WAVE ENERGY
CONVERTERhttps://www.youtube.com/watch?v=F0mzrbfzUpM
THE WAVE DRAGON
The Wave Dragon - is a floating tap channel but using a pair of curved
reflectors to gather waves to overtop a ramped trough-like where water
is released though a low-head turbine.
THE WAVE DRAGON
Power generation on the Wave Dragon is based on the potential
energy in the water that has overtopped the ramp and is
temporarily stored in the reservoir.