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.