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8/2/2019 Seminar Times

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BY


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Introduction

Federal Agency for Science and Innovation, 2010 Moscow, Russia

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The main overview is

mainly related tostudy of ocean and its

wave, the ways to

harness energy and the

technologies


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The ocean is the world's largest solar collector andcan provide huge amount of energy (kinetic andthermal) which is absolutely clean (zero CO2emission), sustainable, strategic, and predictable.

Changes in salinity, thermal gradients, tidal sealevel change and currents, or ocean waves can beused to generate electricity.

The number of ocean energy technology conceptshas increased to +100 known devices.

Available global Ocean Energy resource is in thesame order of magnitude of the present electricity

production worldwide (even more!).

Why Ocean?


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Basic technique for producing electricity from ocean

When this wind skims over the sea, an interaction is caused in which

energy is exchanged between the wind and the sea surface.

At first, little ripples arise on the surface. Then, the wind that skims

along these ripples causes higher air pressure at the front of the wave

than at the back. As a result the ripples change into small waves.

As this process continues, the waves become higher and the distance

between the tops (wave length) becomes longer.

Wind is caused by differences in temperature due to the solar heating

of the earth's atmosphere.


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Table compiled from International Energy Agency, Policy Report, 20065


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Ocean energy mainly consists of the following 3 types

1] Tidal power:-due to high and low tides over a day.

2] Ocean current:-they are due to temperature gradient in the different part of sea.3] Surface waves;-These are the waves due to wind over the surface of a sea.

Tidal energyThis technology has been in use since the 11th Century.

When tides come 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.

There are two different means to harness tidal energy:

first is to exploit the cyclic rise and fall of the sea level using barrages

second is to harness local tidal currents, analogous to wind power also called marine

current turbine.


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Barrage

An artificial dam to increase the depth of water for use in irrigation or

navigation, or in this case, generating electricity.

Flood

The rise of the tide toward land (rising tide)

Ebb

The return of the tide to the sea (falling tide)

TIDAL BARRAGE METHODS

Two types of barrages:

SINGLE BASIN BARRAGE

DOUBLE BASIN SYSTEMS


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SINGLE BASIN BARRAGEDOUBLE BASIN SYSTEMS


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Marine current turbines work, in principle, much like submerged windmills, but

driven by flowing water rather than air.

The main difference is that marine current turbines of a given power rating are

smaller, (because water is 800 times denser than air) and they can be packed closer together

(because tidal streams are normally bi-directional whereas wind tends to be multi-directional).

750 kW1.5 MW

1520 m diameter rotors

3 m monopile

1020 RPM

Deployed in multi-unit farms

or arrays Like a wind farm, but

Water 800x denser than air

Smaller rotors

More closely spaced AXIAL TURBINES


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VERTICAL AXIS CROSS-FLOW TURBINES


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Advantages & Disadvantages of Tidal

Turbines Low Visual Impact

Mainly, if not totally

submerged.

Low Noise Pollution

Sound levels transmitted are

very low

High Predictability

Tides predicted years in

advance, unlike wind

High Power Density

Much smaller turbines than

wind turbines for the same

power

High maintenance costs

High power distribution costs

Somewhat limited upside

capacity

Intermittent power generation


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WAVE ENERGYTypes of wave energy

technologies

Oscillating water

column

Pelamis

Wave dragon

Archimedes wave

swing

Mccabe wave

pump

Power buoy

Aqua bouy


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The Oscillating Water Column generates electricity in a two step process. As a wave enters the

column, it forces the air in the column up the closed column past a turbine, and increases the

pressure within the column. As the wave retreats, the air is drawn back past the turbine due to thereduced air pressure on the ocean side of turbine.

Oscillating Water Column


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The energy is produced when a wave runs on the length of the systems. Joints,

connected to pump oil and to a hydraulic generator (smoothing systems), allow

movement between each section and produce electricity as the wave moves by.

THE PELAMIS

Main features about the Pelamis:

Overall length = 390x220Diameter = 14000 m3

Overall power rating = 0.75MW

Nominal wave power = 55kW/m

Annual power production =2.7GW

Water depth = >50m


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THE WAVE DRAGON

The wave dragon is a system that temporarily stores water in a reservoir before falling into a

turbine

The waves reach the reservoir by way of a ramp. After going through an alternator, the water is

released to the source. This means of generation can be comparable to a dam with three steps:

absorption, storage and power take off.

Main features about the largest WaveDragon:

Width and length = 390x220m

Reservoir = 14,000 m3

Rated power/unit = 11MW Annual

power production/unit =35GWh

Water depth = >30m


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THE ARCHIMEDES WAVE SWING (AWS)

The working procedure is based on the principle of the float (Archimedes). The only moving part

is an air-filled floater. Waves create an up and down movement due to applied pressure on the

floater which is located in a lower fixed cylinder. A linear generator based in the cylinder, this

movement is converted into electricity and then transmitted to the shore

Each unit is currently rated at 1.2 Megawatts, equal to the

electrical demand of approximately 500 households energy.


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MCCABE WAVE PUMP

The McCabe Wave Pump has three pontoons linearly hinged together and pointed parallel to the

wave direction.

The center pontoon is attached to a submerged damper plate, which causes it to remain still

relative to fore and aft pontoons. Hydraulic pumps attached between the center and end pontoons are activated as the waves

force the end pontoons up and down.

The pressurized hydraulic fluid can be used to drive a motor generator (rated at 250500 kW)


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THE AQUA BUOY

The vertical movement of the buoy drives a broad,

neutrally buoyant disk acting as a water piston

contained in a long tube beneath the buoy. The waterpiston motion in turn elongates and relaxes a hose

containing seawater, and the change in hose volume

acts as a pump to pressurize the seawater


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High capital costs for initialconstruction

High maintenance costs Wave energy is an intermittent

resource

Requires favorable waveclimate.

Investment of powertransmission cables to shore

Degradation of scenic oceanfront views

Interference with other uses of

coastal and offshore areas navigation, fishing, and

recreation if not properlysited

Reduced wave heights may

affect beach processes in the

Onshore wave energy systems

can be incorporated into harbor

walls and coastal protection

Reduce/share system costs

Providing dual use

Create calm sea space behind

wave energy systems

Development of mariculture

Other commercial and

recreational uses;

Long-term operational life time

of plant

Non-polluting and inexhaustible

supply of energy

Wave Power Advantages & Disadvantages


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OTEC Description Oceanic Thermal Energy Conversion OTEC utilizes the oceans 20C natural

thermal gradient between the warmsurface water and the cold deep seawater to drive a Rankine Cycle

OTEC utilizes the worlds largest solarradiation collector - the ocean. Theocean contains enough energy powerall of the worlds electrical needs.


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1. Power input to pumpsto start process

4. Expanding vapor drivethe turbine, and electricity is

created by a generator

5. Heat extraction from

cold-water sink tocondense the working

fluid in the condenser.

Cycle begins

againReturn to step 2

3. Heat addition from the hot-water source used to evaporate

the working fluid within the heat

exchanger (Evaporator)

2. Fluid pump pressurizes and pushesworking fluid to evaporator


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Open-cycle OTEC


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Hybrid systems

Hybrid systems combine thefeatures of both the closed-cycleand open-cycle systems.

In a hybrid system, warmseawater enters a vacuum

chamber where it is flash-evaporated into steam, similar tothe open-cycle evaporationprocess.

The steam vaporizes a low-

boiling-point fluid (in a closed-cycle loop) that drives a turbineto produces electricity.

APPLICATIONS FOR OTEC


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a.OTEC systems can produce fresh water as well as electricity.

This is a significant advantage for an island, such as the Virgin

Islands for example, where fresh water is limited.b.There is enough solar energy received and stored in the

warm tropical ocean surface layer to provide most, if not all, of

present human energy needs.

DISADVANTAGESi.OTEC plants must be located where a difference of about 40

degrees Fahrenheit occurs year round. Ocean depths must be

available fairly close to shore-based facilities for economic

operation.

ii.Construction of OTEC plants and laying pipes in coastalwaters may cause localized damage to reefs and near-shore

marine ecosystems.

OTEC ADVANTAGES

Ocean Thermal Energy Conversion


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Ocean Thermal Energy Conversion(OTEC)

Theworld'so

nlyOpenCycleOTECfacilityat

KeaholePointontheKonac

oastofHawaii

(UnitedS

tatesDepartmen

tofEnergy

)

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CONCLUSION

Each system has its own advantages and disadvantages. Several common points to

these three main technologies stand out.

The positive aspects of using ocean energy are:

Reduction in dependence on fossil fuels.

Source of energy is free, renewable and clean.

Clean electricity is produced with no production of greenhouse gas or pollution

(liquid or solid).Energy produced is free once the initial costs are recovered.

These technologies are renewable sources of energy.

The negative aspects of using ocean energy are:

1)At present, electricity produced would cost more than electricity generated from

fossil fuels at their current costs.

2)It leads to the displacement of wild life habitats.

3)Technologies are not fully developed.

4)Problems exist with the transport of electricity to onshore loads.

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