OCEAN ENERGY

RENEWABLE ENERGY SOURCE

Ocean Energy

Potential Energy }
Kinetic Energy Mechanical Energy

Electrical Energy
Forms of Ocean Energy
Wave Energy
Tidal Energy Energy
Current
Temperature
Desalina
tion
Salinity
Biomass

WAVE ENERGY

Energy from ocean = 2 x electricity production as on

now
Wave power is more than tidal power
Wave exists everywhere
Only few stations with potential tides
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 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)
Wave energy
Potential Energy: (PE) WAVE=1/16pgH2
Kinetic Energy: ( KE)WAVE = 1/16pgH2
Total Energy: (E) WAVE = 1/8pgH2

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
• Up to 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
 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.

Wave energy devices

Using one of the following principles:
• Focussing of wave energy
• Pressure difference due to free surface oscillation
• Relative buoyancy
CLASSIFICATION OF THESE DEVICES
• Terminators: devices aligned parallel to the wave
front and perpendicular to the wave direction.
• Attenuators: lies in the principle wave direction and
attenuates the wave as it passes by.
• Point Absorbers: These devices diffract waves and
capture energy from a width greater their own
dimensions.
Terminators:
the oscillating water column

Attenuators : e.g. the Pelamis

Point Absorbers
A 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 system 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 run up waves into a reservoir.

Cockerel Raft
• Consists of joined sections the movement of 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 the Black Sea.
Cockerel wave raft

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 cause
movement in a part of the device as it move up and down in
the wave.

As engineers we have to produce optimized designs for:

• The wave energy collector
• Installation
• The power conversion system
• The moorings
• The power transmission system
• Generation controls
• Access and maintenance
• Recovery and decommissioning

OWC
• Oscillating water column is a device used for
extracting energy from waves.
• Energy conversion:
Principles of Energy Conversion Chain
TARGETS:
-Demonstration plant.
Design, Installation & Evaluation.
-Semi Commercial Prototype II.
Design, Installation & Evaluation.
-Commercial module.
Design Conditions

Specifications of the Wave Energy Plant

TIDAL POWER PLANTS

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 head
Water can be stored in an estuary during high tide
Release during low tide, through turbines
Tidal Barrage

• Sea level drop during outgoing tide

• Gates containing turbine opened at sufficient head
• Water flows out through gate driving turbine

Power generated
Tidal Power Generation

Advantages of Tidal Barrages

High predictability
Tides predicted years in advance, unlike wind
Similar to low-head dams
Known technology
Protection against floods
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.
 Not expensive to maintain.

Disadvantages of Tidal barrages

High capital costs
Few attractive tidal power sites worldwide
Intermittent power generation
Silt accumulation behind barrage
Accumulation of pollutants in mud
Changes to estuary ecosystem
Barrage style only produces energy for about 10 hours out of the day
Barrage style has environmental affects
Such as fish and plant migration
Silt deposits
Local tides change- affects still under study
Available Power
• Energy α (Tidal range)2
• Turbine Power

where Cd = discharge coeff.

A = CS area
ρ = density
g = acceleration due to gravity

Tidal Streams
• Fast flowing volumes of water caused by motion of
tide
• Natural constriction forces water to speed up
• Occur in shallow sea

How Energy Produced?

• 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 = 1/2ρAv3Cp
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

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 MW tidal power has been envisaged.
Introduction to OTEC
 Principle OTEC
 Types
 Efficiency
 Uses of Ocean Thermal Energy
 Advantages

Ocean Thermal Energy Conversion

Concept of OTEC
• 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 temperaturedifference existing between warm surface
sea water of 27 - 29" C and the cold deep sea water of around 5 to 7" C,
which is available at a depth of 800 to-l000 m.
TYPES
 Closed Cycle
 Open Cycle
 Hybrid Cycle
.

USES
 Energy
 Fresh Water - Desalination
 Food
 Cooling
Chilled Soil Agriculture
Coastline of 7000 km INDIA
Estimated overall potential – 180000 MW
• 2.56 million sq.km EEZ
IDENTIFIED SITES
 Kavaratti
 Kulasekarapattinam
 Andaman & Nicobar Islands
OTEC Plant – Kulasekarapattinam

FRESH WATER (Kavaratti)

• Hybrid OTEC plant
 •10 MW pl nt 2 24 million liters of plant – 2.24
million liters of fresh water everyday
 Kavaratti island – Lakshwadeep – 1 lakh litre of
fresh water per day 39.80 paise per liter
 Model for Chennai under research

1 MW floating OTEC plant

 Site identified (about 40km off Tiruchendur)
• Temperature gradient of 21º C average
• SST varying from 26º – 29º C
 Closed cycle with ammonia as working fluid
 Power module on floating barge – not susceptible with storms
 Cold water pipe 1000m length

MAJOR SYSTEMS AND COMPONENTS

POWER MODULE
 Turbo-Generator
 Plate Heat exchangers
 Sea Water Pumps
FLOATING PLATFORM
 Barge
 Cold and Warm Water Box
SEA WATER SYSTEMS
 Cold Water Pipe
 Flexible Hose
Specifications
• Gross Power Output : 1 MW
• Warm water temperature : 29°C
• Cold water temperature : 7°C
• Depth of cold water intake point : 1000m

Platform
• Off-shore or Shore-based?
Required temperature difference occurs only after 40
km from coast. So, shorebased plant not feasible
Cycle
• The low pressure generator needed in Open Cycle are
huge in size and are not suited for low rating plants of
the order of
MW
• So, Closed Rankine Cycle is being employed

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°
Model Tests
• 1kW model prepared
• Tests performed for various conditions of sea water velocity
and temperature
• Vibration found under allowable limits.

ADVANTAGES OF OTEC SYSTEMS

• Power-continuous, renewable & pollution free.
• 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% of net potential in next 4 decades
 100 MW plants for competing with
conventional sources

Estimated Potential and Status of

Ocean Energy in India