12
2 CHAPTER 2
OCEAN WAVE ENERGY
2.1
INTRODUCTION
There is a sign of increased concern over importance of utilising
sustainable renewable energy sources all over the world. Though the
negligible compared to other conventional energy generation systems, the
scenario could be very different in a few years from now. In the mission of
climate change initiatives and sustainable energy development, the evolution
of renewable energy industry is emerging. The present contribution of ocean
energies in the context of energy generation in India is at its early stage of
development. Though the technology of generating electricity from sea is new
to the entire world, India is not even close to initiating the activities of
exploiting ocean renewable energy sources. Inability of the ocean energy
technologies to compete with wind energy conversion technology in overall
cost leads to the unattractive interest from investors. Until recently, little
concern had been focussed on exploiting ocean based renewable energy
sources. Since 2002, there has been a healthy sign of activities in this
direction. A number of investments have been made by many countries to
prove that ocean energy sources could be as attractive as sources such as solar
and wind. The world has seen already a number of technologies progressed to
the point of commercial installation.
13
The term ocean energy is used to describe various renewable
energies derived from the sea, including ocean wave energy, tidal energy,
ocean current energy (sometimes called marine hydrokinetic energy), offshore
wind energy, and ocean thermal and salinity gradient energy. The increased
technological development, emergence of new sciences, increased pressure on
reducing global warming and wealth of on-going R&D leaves no consensus
over one technology emerging as best technology to capture any of the ocean
energy more efficiently and cheaply.
A variety of new ocean power technologies initiated funded and
supported by governments to address the global pressure on clean and
sustainable energy development. Progresses in the area of ocean energy
technologies are slow and least attractive when compared to other land and
fossil fuel based energy conversion technologies due to their cheaper prize
and high accessibility.
2.2
OCEAN ENERGY TECHNOLOGIES
The Oceans contain vast amounts of energy. As discussed earlier,
two different forms of ocean energy offer possible energy resources: thermal
energy and the mechanical energy. In the proceeding section, various
technologies available to harvest each of the ocean renewable energy sources
are discussed in brief.
14
2.2.1
Tidal Energy
Tidal energy concerns the natural rise and sink of ocean surface
elevation, which are influenced mainly by the interaction of the gravitational
fields of the Earth, moon and sun (Figure 2.1). The ocean water level gets
peak twice daily, filling and emptying natural reservoirs along the shoreline.
The flow of water in and out of these natural reservoirs can be used to turn
turbines to produce electricity (Figure 2.2).
Figure 2.1 Tidal Bugle (Clerici et al 2004)
Conversion of tidal stream or marine current is one method of
exploiting the tidal energy. This method uses the fast water currents, which
are created by the tides and magnified by topographical features such as
peninsulas, bays and channels or by the shape of the seabed when water is
forced through narrow channels.
15
Figure 2.2 SeaGen (Courtesy of Marine Current Turbines Limited)
Another method of harnessing ocean tides is similar to
conventional hydroelectric power plants (Figure 2.3). The concept is called as
tidal range technology. Openings and turbines are installed along a barrage or
sea and storage becomes adequate, the openings are activated and water is
allowed to flow across through the turbines. Rotation of turbine due to the
flow of water is then connected with an electricity generating unit and
electrical energy is produced. Energy can be generated by water flowing both
into and out of the reservoir. As there are two high and two low tides each
day, the energy can be generated in every six hours.
In India, the Gulf of Cambay and the Gulf of Kutch in Gujarat on
the west coast were found to be the suitable sites with a tidal variation of 11m
and 8m with average tidal range of 6.77m and 5.23m respectively. An average
tidal variation of 2.97m was measured in the Sundarbans of Ganges delta. The
identified economic power potential is of the order of 8000 MW with about
16
7000 MW in the Gulf of Cambay, about 1200 MW in the Gulf of Kutch in the
State of Gujarat and about 100 MW in the Gangetic Delta in the Sundarbans
region in the State of West Bengal.
Indian government has sanctioned a project for setting up a 3.75
MW demonstration tidal power plant at Durgaduani Creek in Sunderbans,
West Bengal to the West Bengal Renewable Energy Development Agency
(WBREDA), Kolkata.
Figure 2.3 Tidal Barrage (Courtesy Of Encyclopaedia Britannica)
2.2.2
Ocean Currents
Ocean currents are mainly driven by tidal stream, blowing wind
and solar heating of the waters close to the equator, the variation in water
density and salinity may also lead to flow of sea water under the surface. The
17
constant flow and direction of ocean currents gives them an advantage of high
convertibility and reduced investment, in contrast to the tidal currents where
the varying gravitational pulls of the sun and moon result in variable current
intensity and direction. Ocean currents in the Gulf Stream, Florida Straits
Current, and California Current are some of the best examples (Figure 2.4).
Ocean currents are mainly concentrated at the surface, although a significant
current continues through the deeper sea.
Figure 2.4
Major Ocean Currents (Courtesy of National Oceanic and
Atmospheric Administration)
A similar principal to the wind turbines can be used to extract
energy from ocean currents by placing a submerged turbine. The turbine
rotates due to the hydrodynamic lift and drag generated by flowing current at
the vicinity of rotor blades. Coupling an electricity generating unit would
produce electrical energy from the rotation of current turbines. As the density
of water is roughly 700 times denser than air, the energy generated through
current turbines is significantly higher than wind turbines even when the
18
current is much slower than wind. Presently there is no identified source of
ocean current in the region of seas around India.
2.2.3
Ocean Thermal Energy Conversion
Ocean Thermal Energy Conversion (OTEC) is an indirect
conversion of solar energy in to electric power. The OTEC exploits the
thermal gradient between surface water of ocean and the deeper water to
produce electrical energy. The average variation in water temperature found
between surface of ocean and water in 1000 m depth are around 20 0C. The
colder.
Figure 2.5 OTEC Layout - (Bedard et al 2008)
The Rankine cycle is used as method of effectively harnessing the
available thermal gradient (Figure 2.5). Surface water treated like heat source
and deeper water works like refrigerators. A working fluid with low boiling
19
temperature can be vaporized using the warm water at the surface, the
vaporization leads to increased pressure. The expanding high pressure vapour
with can be made to flow through a turbine and make it rotate. Once the work
is done by expanded vapour, deeper cold water is pumped and the vapour is
made condensed back to its liquid phase. The cycle is repeated continuously
and the turbine is made to power the electricity generating unit. The
weather). This makes the OTEC possible of producing electricity everyday
and the whole day with nearly the same energy output.
Three types of OTEC systems can be used to generate electricity:
1.
Closed-cycle plants circulate a working fluid in a closed
system, heating it with warm seawater, flashing it to vapour,
routing the vapour through a turbine, and then condensing it
with cold seawater (Figure 2.6).
2.
Open-cycle plants flash the warm seawater to steam and route
the steam through a turbine (Figure 2.7).
3.
Hybrid plants flash the warm seawater to steam and use that
steam to vaporize a working fluid in a closed system.
Despite the advantage of availability and density, the OTEC has a
very low Carnot Efficiency, near 7.5% (Bedard et al 2008). The present
technology holds a maximum efficiency of 2-3% because of energy consumed
by pumping and thermal losses. The present low efficient technology prevents
the OTEC from becoming a suitable alternative to the present energy demand.
National Institute of Ocean Technology (NIOT), Chennai, is in the
process of commissioning a 1 MW OTEC plant off Tuticorin (2010 Survey of
Energy Resources, 2010). The plant is designed to generate electricity using
20
the Rankine cycle with ammonia as the working fluid. The OTEC plant was
mounted on a barge and it is named as Sagar Shakthi (Pursuit and Promotion
of Science: The Indian Experience., 2001). A 1,000m long, 1m diameter
HDPE pipe which will bring cold seawater of 7º C to the plant barge is
already assembled and deployed at the OTEC site, approximately 60 km south
east of Tuticorin harbour, and upended on reaching the site. It will be
integrated with OTEC plant barge, when it reaches the OTEC site.
Figure 2.6 Closed Cycle OTEC (Clerici et al 2004)
21
Figure 2.7 Open cycle OTEC (Clerici et al 2004)
2.2.4
Ocean Wave Energy
Winds are caused by differential heating of earth by sun and it
generates water waves as it passes over ocean surface. In the wave generation
process, wind transforms some of its energy to the waves and the wave starts
moving in the wind direction. Conversion of energy available in the waves is
more efficient than direct collection of energy from the wind, due to the fact
that waves are a more concentrated form of solar energy than wind. It has
been estimated that the theoretical wave energy potential is in the order of 1 to
But there are many factors affecting wave energy conversion
becoming a reality. Waves are not as consistent as tides and therefore there is
a specific problem regarding the match of supply and demand. This is one of
the main reasons why wave power has so far been restricted to small scale
schemes; no large scale commercial plant is in action. The detailed discussion
on various wave energy converters and its characteristics are made in chapter
3
22
2.3
OCEAN WAVE MECHANICS
2.3.1
Origin of Ocean Wind Waves
The energy in travelling waves is indirect form of concentrated
solar energy. The energy comes from the sun through the winds as they blow
over the ocean surface due to the differential heating of the earth. Transfer of
energy takes place during the formation of waves from wind to the water
ripples. The exact energy transfer mechanism is quiet complex and studied for
long by researchers.
To make the understanding simple the process can be briefed as
follows:
The wind waves are generated due to the wind blowing over the sea
surface (Figure 2.8). They develop with time and space under the repetitive
action of the wind and become huge waves called ocean surface waves.
Variation in shear stresses and pressure fluctuations are created by turbulent
air flowing on the sea surface.
Figure 2.8
Generation of Wind Waves (Courtesy Thomson Higher
Education 2007)
23
Further wave intensifies and development happens when these
oscillations and fluctuations are in phase with the waves. Wind exerted force
on the upward face of the wave directly affects the generated wave height;
this causes further growth of waves. At each of the above steps leads to
transfer of energy from wind to waves (Figure 2.9). The amount of energy
transferred and hence the size of the resulting waves is a function of the wind
speed, the length of time it blows and the distance over which it blows called
the fetch. As the wave continues to grow the surface facing the wind becomes
higher and steeper and the wave building process becomes much more
efficient. However the wave steepness is limited and no longer the waves can
grow beyond a steepness value. Steepness is the ratio of the height of the
wave (distance between a crest and the following trough) to its length
(distance between a crest and the following one) is approximately 1:7 in deep
water. At the upwind end of the fetch the waves are small but with distance
they develop i.e. their period and height increase and eventually they reach
maximum dimensions possible for the wind that is raising them. In the
process, the waves start getting its regular shape and the phenomenon is
called as swell. The wave is said to be fully developed when the water
particles excited by the wind follow a circular trajectories (Figure 2.10) with
highest diameter at the ocean surface and diminishing exponentially with
depth.
2.3.2
Description of Waves
Ocean waves travel with different speed, amplitude and direction
due to its highly random nature. The waves with different magnitudes
superimpose on other waves and travel in ocean. Figure 2.11 shows
superposition of monochromatic propagating waves of different amplitude,
frequency and directions to represent a real ocean wave. Hence, a detailed
description seems impossible and it becomes necessary to make some
simplifications, which makes it possible to describe the wave pattern.
24
Figure 2.9
Transfer of Energy from Wind to Water Waves (Courtesy
The Open University)
Figure 2.10 Water Particle Motion in a Wave (Courtesy Thomson
Higher Education 2007)
25
Figure 2.11 Illustration of Superposition of Waves (Beatty 2009)
Waves are classified into one of the following two classes
depending on their directional spreading:
Long-crested waves: 2 dimensional waves with short crest and
travelling perpendicular to the coast.
Short-crested waves: 3-dimensional waves with short crest and
travelling in different directions.
The properties of deep water waves are summarised as follows
(Twidell and Weir 2006):
26
The real ocean waves are sets of unbroken sine waves of
irregular amplitude, period and direction.
The motion of any particle in a wave is circular. Any particle
in a wave has no net progression, whereas the surface form
of the wave shows a visible progression.
An ocean wave is rising and falling water level that is
transmitted along the ocean surface.
Ocean waves transmit energy away from an initial
disturbance without the physical transport of water.
Particles on the surface always on the surface during the
wave progression.
The magnitude of circular motion of water particle decrease
exponentially with depth.
The amplitude A of the surface wave is depends on the wind
velocity c or period T of the wave, however the maximum
amplitude of waves rarely exceed one-tenth of the wave
length.
A wave breaking happens when the slope of the surface is
about 1 in 7, and the energy is dissipated in the form of heat.
The patterns of rising and falling water of ocean surface are
complex and ever changing. However, these patterns can be
described by superposition of ideal waves.
No two waves are similar in its height and they move across
the surface at different velocities and in different directions.
Though real ocean waves can never be uniform in practice,
most of the ocean structures are investigated in regular
waves due to the fact that all random waves are
superposition of regular waves.
27
Figure 2.12 Wave Nomenclature
Following are the terms used to define the parts of a typical wave
(Figure 2.12)
Crest: The highest point of a wave
Trough: The lowest point of a wave.
Wave height H : Vertical distance from trough to crest.
Wave amplitude a : Vertical distance of wave crest from
mean sea level
Wave length L : Horizontal distance between adjacent
crests.
Wave period T : The time in seconds for a wave crest to
travel a distance equal to one wave length.
Wave steepness s :
the wave period
Wave number k :
.
28
Wave celerity c : The ratio of wave length and wave
period
.
Water depth h
It becomes important to understand that there is a direct
relationship between wave period and wavelength but wave height is
independent of either.
The wave are called as deep water waves when
, the
waves no longer influenced by presence of sea floor. These waves are
relatively much slower and steady when compared to significant variations it
show at the coast line. The wave bottom surface interactions leads to
significant changes in the characteristics of deep water waves. Focusing,
defocusing and sheltering of waves are some of the results of this sea floor
interaction. In shallow water region, waves loose considerable amounts of its
energy in the form of heat and sediment transportation due to bottom friction
and reduced depth. As waves approach the shore (i.e. h
longer considered to be deep water waves and, as such, they can be modified
in various ways:
Shoaling: This is a phenomena occurs to the wave when it
reaches proximity to the shore line (Figure 2.13). During this
approach, the wave group velocity decreases and thus the wave
height increases. When the water depth decreases further, the
wave steepness increases to a limit and the wave becomes
unstable and breaks. The net energy and power density of waves
increases in shallow water due to shoaling.
29
Figure 2.13 Shoaling Process (Courtesy the COMET Program)
Friction and Wave Breaking: The raise in wave height and
steepness produced by shoaling are compensated by wave breaking
(Figure 2.15). As waves become steeper the top layer of wave
moves with constant velocity and the bottom layer slow down due
to the friction developed by closing sea floor in the shallow water.
Beyond a limit, the top layers of waves break and create a turbulent
water motion thereby losing both height and energy.
Refraction: As the waves travel into shallow waters closer to the
shore, the wave fronts are bent to become more oriented to the
bottom contour coast line (Figure 2.14). This phenomenon is of
great importance to the wave energy devices whose capture
efficiency is wave directionality dependent.
Diffraction and Reflection: The above phenomenon is similar to the
refraction of light. There are other behaviour of the waves similar
to the light such as diffraction (waves yielding around and barriers)
and reflection. The variation in seabed topography and shoreline
30
geometry is the primary reason for this entire phenomenon. These
behaviours lead to "hot spots" where the waves are focussed and its
energy is concentrated than surrounding.
Figure 2.14 Refraction Process (Courtesy the COMET Program)
Figure 2.15 Impact of Sea Bed Topography on Waves (Courtesy
Thomson Higher Education 2007)
31
2.3.3
Ocean Wave Climate
Enough computer and mathematical modelling tools are available
at present to estimate long term wave climate of any part of any coast given
enough data and analysis. The meteorological study of wave climate is a
complex task involving many variables. Wave energy is strongly variable in
time and space, involving a lot of uncertainty; energy levels in the waves can
be estimated and predicted as accurately as weather can be. An important
factor to determine is the directional climate of long fetch swell that contains
most of the energy.
Figure 1.4 shows the average estimated wave power density
(kW/m) at various locations around the world. The areas of the world which
are subjected to regular wind fluxes are those with the largest wave energy
resource. South westerly winds are common in the Atlantic Ocean, and
frequently pass through extensive distances, transferring energy into the water
to form the huge waves which arrive off the European coastline.
There are a number of places around the world with high incident
wave power levels, particularly suitable for wave energy exploitation. These
are generally extreme latitudes (between 40°- 60° latitude in the North and
South) and the west coast of continents including the western seaboards of
South and North America, Northern Europe and Australia. These areas
blessed with annual mean wave power per unit width of wave crest of 50 100 kW/m. In tropical regions annual mean power levels of 10 - 20 kW/m are
more typical.
In India the research and development activity for exploring wave
energy started in 1982. Primary estimates indicate that the annual wave
energy potential along the Indian coast is between 5 MW to 15 MW per
meter. Hence theoretical potential for a coast line of nearly 6000 Km works
32
out to 60000 MW approximately. However, the realistic and economical
potential is likely to be considerably less and 47 kW/m is available off
Bombay during Southwest monsoon period. Based on the wave statistics for
the southern tip of India, a mean monthly wave power of 4 - 25 kW/m is
estimated. The average wave potential along the Indian coast is around 5-10
kW/m.
India has a coastline of approximately 6500 km.
Even 10%
utilization would mean are source of 3750 7500 MW.
2.4
ENERGY FROM WAVES
Ocean waves are as mentioned above essential movement of
energy. Waves consist of two kinds of energy:
The individual water molecules are moving steadily and rather
slowly in circular way, and this energy (kinetic energy) can be utilized in
different kinds of wave energy converters, either directly via some kind of
propeller or indirectly by Oscillating Water Columns wave energy converters.
In its circular movement the individual water molecules are
elevated above the Stillwater line and thus represent a potential energy.
2.4.1
Wave Body Interaction
It becomes important to understand the various modes of motion a
floating body experience due to wave action. The modes of motion are also
called as degrees of motion of a body. For a floating elongated body
(Figure 2.16), the modes of motion are named as shown in the Table 2.1.
For an axisymmetric body or vertically oriented body, the modes 1 and 2
(and 4 and 5) are interchangeable and unclear. However, the ambiguity is
eliminated when there is an incident wave where the propagation direction
defines the x direction. For a two dimensional case, the axis y is eliminated
33
and hence an axisymmetric body experiences only three modes of motion
namely, surge, heave and pitch.
Figure 2.16 Six Modes of Motion of an Elongated Floating Object
(Falnes 2004)
Table 2.1 Various modes of motion of a floating body
Mode Number
1
2
3
4
5
6
2.4.2
Mode Name
Surge
Sway
Heave
Roll
Pitch
Yaw
Wave Energy Absorption by Oscillating Bodies
The energy absorption by an object interacting with waves is
directly related to the capability of radiating waves and creating destructive
interference with the incident waves. An object oscillating in water body will
create waves. A small body and big body may produce equally large waves,
provided the oscillation of small body is very large than the big body. This
phenomenon is utilised for the purpose of harnessing ocean waves. If a small
34
body is arranged such that it oscillates with larger amplitude than incident
wave, the device can be as efficient as devices with larger oscillating bodies.
In general a good wave absorber should be a good wave maker. To absorb
wave energy, the device should displace water in an oscillatory manner in
correct phase(interval). To absorb energy from waves the energy should be
removed from it. Hence, the passing wave must be cancelled or reduced in its
energy level. Such a cancellation or reduction of wave can occur only if the
device generates waves which oppose (are in counter-phase with) the passing
wave. In other sense, the generated wave should destructively interface with
passing wave. The paradoxical but true statement that "Destroy a wave means
to create a wave". The Figure 2.17 Interaction of Oscillating Body and Wave
(Falnes 2004) illustrates the possibility of 100% energy absorption by small
oscillating floating bodies infinitely long (perpendicular to the figure), evenly
interspaced a small gap (smaller than incident wave length). It is possible to
extract 100% of energy available at waves with an elongated body, of cross
section as illustrated in figure, and aligned perpendicular to the representative
image, provided the body oscillates in two linear modes (horizontal and
vertical) in an optimum manner.
Figure 2.17 Interaction of Oscillating Body and Wave (Falnes 2004)
35
In the above figure, the profile a represents an undisturbed incident
wave. The curve b represents the generated wave by the oscillation of evenly
spaced infinitely long array of small floating bodies in heave (up and down).
This shows that only 50% of energy can be absorbed by any floating body
when it oscillates only in heave. The curve c represents the anti-symmetric
wave generation by oscillation of array of small floating bodies. This case
shows the possibility of more than 50% of energy absorption by radiating
anti-symmetric wave. The superposition (addition) of all the above curves is
represented by curve d, which shows a complete absorption of the incident
wave energy. However, it is possible to absorb almost all the incident wave
energy in one mode of motion by a sufficiently non-symmetric body.
Another illustrative example is shown in Figure 2.18, where a
heaving point absorber has to radiate circular waves which destructively
interface with incident regular wave to harness energy available. A point
absorber is essentially a small device with horizontal dimension much less
than incident wave length. It was shown by (Falnes 2004) that the maximum
energy absorbed by a heaving axisymmetric body equals the wave transported
by the incident wave front of width equal to the w
The author named this width as absorption width of a device.
Figure 2.18 Radiated Waves by Small Heaving Body in Incident Wave
Field (Falnes 2004)
36
It becomes imperative that an optimum oscillation is necessary for
an oscillating body to increase its energy capture efficiency. For incident
wave sinusoidal characteristics there is an optimum amplitude and period for
oscillation. This can be emphasised by the curves b and c of figure, where the
radiated waves have to be exactly half of the amplitude of incident wave. This
action requires the oscillating body to be having a precise value of horizontal
and vertical displacement. In order to have optimum phase conditions for the
two modes of oscillation, the radiated waves towards right have to have the
same phase with each other. The same phase here refers to the matching of
wave trough and wave crest. This also means that the symmetric and
antisymmetric radiated waves destructively interface with each other towards
the left. In addition to all these requirements, the phase of two oscillations
should match with phase of incident wave, because the crest of both the
radiated waves (b and c) must coincide with the trough of the incident wave
(curve a). To be efficient any WEC should have the buoy oscillating in more
than one mode of motion and work in resonance with the incident wave. The
motion of oscillating body naturally becomes in phase with incident wave
during the resonance condition.
2.5
SIGNIFICANCE OF OCEAN WAVE ENERGY
the unexploited vast energy resource, there are a number of technical
challenges that need to be addressed before. The following are the common
advantages and challenges faced by a wave energy conversion technology to
be commercially viable alternative.
37
2.5.1
Advantages
The most important advantage of ocean wave energy is that it is
renewable energy source with completely free energy where no fuel is needed
and there is no problem with greenhouse gas emissions or other pollutions
like conventional energy conversion technologies.
As the waves are caused by winds it has the predictability in
advance. This gives the wave energy devices an advantage of preparing for
operational shutdown.
Any energy conversion technology is assessed by its utility factor,
which is the ratio between rated power and average energy production. The
utility factor is significantly low for any renewable energy conversion
technology due to the natural fluctuation of the source. The wave energy is
one of a few renewable energy sources with largest utility factor.
Due to the reason that the wave energy device is located off the
shore and away from main land, these devices get low negative interaction
with surrounding. The low visual impact from the shore gives the wave
energy devices an advantage of having easy public acceptant.
Ocean wave energy is top in the list of renewable energy sources
with highest availability. It was reported that the waves are available for 90%
of the time.
Wave energy conversion technology is having a scope for high
economic competitiveness when compared to other renewable energy
technologies as it is not still matured and a best technology has not yet
arrived.
38
The running cost for a wave energy device is much lower after its
initial construction due to the freely available abundant wave energy resource.
The only cost involve in the energy generation will be for general
maintenance.
2.5.2
Challenges
challenges that need to be addressed to obtain commercial competitiveness of
wave power devices in the global energy market.
Conversion of slow moving, random and highly intensive waves to
fuel an electricity generating unit which requires a high speed uniform
mechanical rotation needs a lot of engineering. Generated electricity will be
accepted by any utility network only if the supplied power is with
predetermined quality level. Wave energy level varies wave to wave due to
variation in their height and period. Though the average wave climate can be
predicted in advance, predictability of individual wave parameters are highly
technology demanding and which is being researched all over the world.
The wave energy devices are required to be orienting itself to the
incoming wave as the waves in the deep waters are highly variable in
direction, amplitude and phase. As installing a stable platform is quiet
expensive, the off shore devices are mostly a floating type devices where
directional control is complicated.
The disparity between most occurring waves and extreme waves
are so huge, that the device faces a tremendous economic challenge. To have
high efficiency, the device needs to be designed for average wave climate.
However, the device also has to withstand during the extreme wave
conditions that occur rarely. Not only does this problem pose engineering
difficulty, but it also requires high capital and running expenses.
39
The highly corrosive nature of the ocean environment pose a
serious challenge to the life cycle of any ocean based devices. The marine
growth is an another threat to the ocean surface based man made devices
where the growth can be up to 10cm thick in less than a year. Access to off
shore structures require boats and helicopters which is an uneconomic method
of transportation. The installation and maintenance of off shore device require
divers and skilled personal which leads to.
Significant variation is annual average wave energy potential
between different parts of the world motivates only a very few countries to be
interested in exploiting waves. Even a matured technology can be
economically competitive to a few countries which possess high average
wave energy density.
Apart from the cost of fabrication, installation and maintenance of a
wave energy conversion device, the energy transportation cost significantly
contributes in overall cost of the device. The energy transportation concerns
on deployment of underwater cables and energy losses during the
transmission.
The lack of experience in world wave energy research community
in designing off shore device will result in over-sizing of equipment and
increased investment cost.
There have been a tremendous amount of research publications
made based on the hydrodynamic, mathematical and computer modelling of
various wave energy devices to improve the performance. However, a
detailed overall development and study is required to arrive a technology
which can be made suitable for any wave climate and hence the wave energy
conversion can be attractive to the entire world.