OCEAN ENERGY - 123seminarsonly.com€¦ · Forms of Ocean Energy Wave Energy Tidal Energy Energy ... • Waves are the most dynamic feature of the ocean ... electro generators.

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OCEAN ENERGY

RENEWABLE ENERGY SOURCE

Ocean EnergyOcean EnergyPotential EnergyPotential EnergyKinetic EnergyKinetic Energy

Mechanical EnergyMechanical Energy

Electrical EnergyElectrical Energy

Forms of Ocean EnergyForms of Ocean EnergyWave EnergyWave EnergyTidal Energy EnergyTidal Energy EnergyCurrentCurrentTemperatureTemperature

DesalinationDesalination

gygy

TemperatureTemperatureSalinitySalinity

BiomassBiomass

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Energy from ocean = 2 x electricity production Energy from ocean = 2 x electricity production as on nowas on now

W i th tid lW i th tid lWave power is more than tidal powerWave power is more than tidal powerWave exists everywhereWave exists everywhereOnly few stations with potential tidesOnly few stations with potential tides

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Wave Energy

• Waves are the most dynamic feature of the ocean

• Carry energy in the form of potential energy which is characterized by height and wave length which definecharacterized by height and wave length which define energy parameters

• Energy extracted from the Ocean waves is called Wave Energy in the form of,– Potential Energy (pressure fluctuations below free

surface)Kinetic Energy (energy from free surface)– Kinetic Energy (energy from free surface)

Wave energy

Potential Energy:2

16

1)( gHPE wave

Kinetic Energy:

Total Energy:

16

2

16

1)( gHKE wave

gy2

8

1)( gHE wave

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WAVE POWER• Wave power refers to the capture of (ocean) wave energy to do

useful work including electricity generation, desalination, and filling a reservoir with water

• Wave Power is renewable energy and is a form of solar energy transferred to water by the wind

• Upto 2 terawatts (1 terawatt = 1 trillion watts)

• Initial solar power level of 100 W/m2 is concentrated to an average wave power level of 70 kW per meter of crest length

• This rises to 170 kW per meter of crest length during winter and to more than 1MW per meter during storms.

Variability of waves

Strength of waves vary significantly with time

The direction of waves vary The direction of waves vary

Now, from this highly variable source one needs a constant flow of electricity!

For shoreline devices, the water level changes with the tide level.

Apart from this power transmission too is a major

One of the design constraint

challenge.

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Wave energy devices

Using one of the following principles:Using one of the following principles:

Focussing of wave energyFocussing of wave energy

Pressure difference due to Pressure difference due to free surface oscillationfree surface oscillation

Relative buoyancyRelative buoyancy

CLASSIFICATION OF THESE DEVICES

• Terminators : devices aligned parallel to the wave front and perpendicular to thethe wave front and perpendicular to the wave direction.

• Attenuators : lies in the principle wave direction and attenuates the wave as it passes by.P i t Ab b Th d i diff t• Point Absorbers: These devices diffract waves and capture energy from a width greater the their own dimensions.

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Terminators:the oscillating water column

Attenuators : e.g. the Pelamis

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Point AbsorbersA point absorber is a floating structure with components that move relative to each other due to wave action (e.g., a floating buoy inside a fixed cylinder). The relative motion is used to drive electromechanical or hydraulic energy converters.

Functional Categorization

• Dynamic Systems: one element of the t i t d i t it ti b thsystem is tuned into excitation by the

waves. e.g. Salter’s Duck, Cockerel raft and devices with oscillating water column.

• Passive Systems : site specific

e g TAPCHAN which uses a ramp to rune.g. TAPCHAN which uses a ramp to run up waves into a reservoir.

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Cockerel Raft

• Consists of joined sections the movement f hi h i t itt d t ithof which is transmitted to pumps with

electro generators.

• A 3-section raft 100m long, 50 m wide and 10m high can produce about 2000kW of electricity. This has been tested in theelectricity. This has been tested in the Black Sea.

Cockerel wave raft

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Principle of a TAPCHAN

Wave energy devices …• Devices which channel waves into tapered

chambers, or an oscillating water column, whose bottom end is submerged in water.

• Fixed or semi-fixed offshore devices which make use of the pressure differential in the water that occurs at a submerged point as the wave passes over that point.

• Offshore devices which utilize their buoyancy to• Offshore devices which utilize their buoyancy to cause movement in a part of the device as it moves up and down in the wave.

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As engineers we have to produce optimized designs for:

The wave energy collector• The wave energy collector

• Installation

• The power conversion system

• The moorings

• The power transmission system

• Generation controlsGeneration controls

• Access and maintenance

• Recovery and decommissioning

OWC• Oscillating water column is a device used for

extracting energy from waves.

• Energy conversion:

KE of waves

Pneumatic energy of airConverted into high velocity, bi-directional air flow.

Mechanical shaft power

Electrical Energy through Generator

The turbine generates unidirectional pulsating torque.

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Principles of Energy Conversion Chain

Type of Energy

C i

Structure/Device Efficiency

Conversion

Wave to Pneumatic

Oscillating Water Column

Frequency and load dependent

Pneumatic to Mechanical

Impulse Turbine Non-linear, load dependentMechanical dependent

Mechanical to Electrical

Slip-ring Induction generator

Linear system

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OWC at Vizhinjam, KeralaOWC at Vizhinjam, Kerala

TARGETS:

-Demonstration plant.

Design, Installation & Evaluation.

-Semi Commercial Prototype II.

Design, Installation & Evaluation.

-Commercial module.

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Design Conditions

Storm OperationalSi ifi W h i h ( ) 8 2 4 2Significant Wave height (m) 8.25 4.25

Wave period (secs) 12.7 7.3

Wind speed (m/s) 45.8 23.15

Surface current speed (m/s) 2.0 1.0

Specifications of the Wave Energy Plant

OWC caisson - 23.2m x 17m x 15.3m dimensiondimension

Turbine - Impulse turbine coupled to configuration Induction generator

Axis - Horizontal

Power at rated speed - 55kW speed

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Wave power resource around the worldWave power resource around the world

TIDAL POWER PLANTS

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Tidal Barrages• Barrage built across estuary

• Gates open during incoming high tides

• Gates closed when tides stop coming in

• Barrage store water to create hydrostatic• Barrage store water to create hydrostatic head

Water can be stored in an estuary during high tide

Release during low tide, through turbines

Tidal Barrage

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• Sea level drop during outgoing tide

• Gates containing turbine opened at sufficient head

• Water flows out through gate drivingWater flows out through gate driving turbine

Power generated

Tidal Power GenerationTidal Power Generation

Fig. 14.29 Environmental Geology, 6th ed, Montgomery, 2003

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Advantages of Tidal Barrages

High predictabilityTides predicted years in advance, unlike wind

Similar to low-head damsKnown technology

Protection against floods

B fi f i (b id )Benefits for transportation (bridge)

Some environmental benefits

Advantages of tidal energy

Once you've built it, tidal power is free

It produces no greenhouse gases or other waste.

It needs no fuel.

It produces electricity reliably.

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Not expensive to maintain.

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Disadvantages of Tidal barrages

High capital costsFew attractive tidal power sites worldwideFew attractive tidal power sites worldwideIntermittent power generationSilt accumulation behind barrageAccumulation of pollutants in mud

Changes to estuary ecosystemBarrage style only produces energy for about 10

h f h dhours out of the dayBarrage style has environmental affectsSuch as fish and plant migrationSilt depositsLocal tides change- affects still under study

Available Power• Energy α (Tidal range)2

• Turbine Powerwhere Cd = discharge coeff.A = CS areaρ = densityρ = densityg = acceleration due to

gravity

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Potential Tidal Sites

Only about 20 sites in the world have been identified as possible tidal stations

Tidal Streams

• Fast flowing volumes of water caused by ti f tidmotion of tide

• Natural constriction forces water to speed up

• Occur in shallow sea

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How Energy Produced?

• Fast moving water rotate blades of turbine• Fast moving water rotate blades of turbine generating electricity.

• Almost similar to wind currents

• But water 800 times denser than air so force experienced by turbines more

Power Obtained• Power = 1ρAv3Cp

2

Where ρ = Density of water

A = Area of rotor blades

v = Velocity of marine currents

Cp = Power coefficient

• Min. marine current velocity for effective power generation = 2.0-2.5 m/s

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TIDAL POWER-INDIAN EXPERIENCE

•NO TIDAL POWER PLANTS CONSTRUCTED AS YET IN INDIA. •FEASIBILITY STUDY – GULF OF KUTCHCH, GUJARAT. •PRE-FEASIBILITY STUDY – GULF OF KHAMBHAT, GUJARAT This is multipurpose project for the development of the Gulf of Khambhat. The average tidal range is about 7 M and area of the tidal basin is about 500 Sq. Km. with this basin size and the average tidal range a scheme for generation of 5000 MWaverage tidal range, a scheme for generation of 5000 MW tidal power has been envisaged.

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Introduction to OTEC Principle

OTEC

Principle Types Efficiency

Uses of Ocean Thermal EnergyUses of Ocean Thermal Energy

Advantages

Concept of OTEC

O th l i

Ocean Thermal Energy Conversion

• Ocean thermal energy conversion, or OTEC, is a way to generate electricity using the temperature difference of seawater at different depths. Utilizes Ocean temperature Gradient

• OTEC utilizes the temperature-difference existing between warm surface sea water of 27 - 29" Cand the cold deep sea water of around 5 to 7" C, which is available at a depth of 800 to-l000 m. OTEC facility at Keahole Point on

the Kona coast of Hawaii. US

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Vertical Profile of Temperature

TYPES

Closed Cycley

Open Cycle

Hybrid Cycle

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CLOSED CYCLE

OPEN CYCLE

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HYBRID CYCLE

CLASSIFICATION BASED ON SITE

LOCATION

Land Based Plant

Shelf Based Plant

Floating Plant

Submerged Plant

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OTEC generation on land:

OTEC generation on floating platform

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USES

Energygy

Fresh Water - Desalination

Food

Cooling

Chilled Soil Agriculture

Coastline of 7000 km

INDIA

Estimated overall potential – 180000

MW

2 56 million sq km EEZ2.56 million sq.km EEZ

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OTEC resource within EEZ of India

IDENTIFIED SITES

Kavaratti

Kulasekarapattinam

Andaman & Nicobar Islands Andaman & Nicobar Islands

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OTEC Plant - Kulasekarapattinam

Alternative No.

Cold water intake Temp.

¢J

Depth of Cold water Intake

(m)

Distance from

shore to plant (m)

Project Cost

(million Rs)

(1985 Rates)

Unit Cost

(Rs/kWh)

Rates)

I 8.7 765 2200 309 3.69

II 10.0 620 1500 287 3.12

Hybrid OTEC plant10 MW pl nt 2 24 milli n lit s f

FRESH WATER (Kavaratti)

10 MW plant – 2.24 million liters of fresh water everyday Kavaratti island – Lakshwadeep - 1 lakh litre of fresh water per day 39 80 lakh litre of fresh water per day 39.80 paise per liter Model for Chennai under research

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Pilot OTEC Plant in Tuticorin

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1 MW floating OTEC plant

Site identified (about 40km off Tiruchendur)

• Temperature gradient of 21º C averageTemperature gradient of 21 C average

• SST varying from 26º – 29º C

Closed cycle with ammonia as working fluid

Power module on floating barge – not susceptible ith twith storms

Cold water pipe 1000m length

MAJOR SYSTEMS AND COMPONENTS

POWER MODULE Turbo Generator Turbo-Generator Plate Heat exchangers Sea Water Pumps

FLOATING PLATFORM Barge Cold and Warm Water Box Cold and Warm Water Box

SEA WATER SYSTEMS Cold Water Pipe Flexible Hose

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Specifications

• Gross Power Output : 1 MW

• Warm water temperature : 29°C

• Cold water temperature : 7°C

• Depth of cold water intake point : 1000m

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Platform

• Off-shore or Shore-based?

Required temperature difference occurs only after 40 km from coast. So, shore-based plant not feasiblebased plant not feasible

Cycle

• The low pressure generator needed in O C l h i i d tOpen Cycle are huge in size and are not suited for low rating plants of the order of MW

• So, Closed Rankine Cycle is being employedemployed

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Heat Exchangers

• Titanium being used

• Having an additional layer of Stainless Steel on ammonia side was found to increase the heat transfer by 30-40%

Barge

• Monohull barge

• 685m X 16m X 4m

• A huge cold water sump of dimensions 4.5m X 4.5m X 14m and is retractable

• Sump locked on deck to reduce pitch, roll

• Pitch and Roll < 2.5°

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Model Tests

• 1kW model prepared

T t f d f• Tests performed for various conditions of sea water velocity and temperature

• Vibration found under allowable limitsallowable limits

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ADVANTAGES OF OTEC SYSTEMS

• Power-continuous, renewable & pollution freefree.

• Cold deep sea water-rich in nutrients-utilized for aqua-culture.

• Open cycle : fresh water as by product.

• Closed cycle : desalination-fresh water.

• OTEC-Alternative power-remote islands.

• Floating OTEC-offshore mining.

OTEC FUTURE FOR INDIA

14% f t t ti l i t 4 14% of net potential in next 4

decades

100 MW plants for competing 100 MW plants for competing

with conventional sources

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Estimated Potential and Status of Ocean Energy in India

Potential Status Unit Cost

US$/kWhMW kW

US$/kWh

(Rs./kWh)

OTEC 1,80,000 Nil0.189

(8.12)

0 167TIDAL 8,000 Nil

0.167

(7.17)

WAVE 40,000 500.174

(7.50)