Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
1
A SYSTEM OF CLOSELY INTERCONNECTED
WAVE ENERGY COLLECTORS
COMPRISING OF
SELF-ORIENTING POWER TAKE-OFFS
FIELD OF THE INVENTION
The present invention generally relates to devices and methods for harnessing
energy from ocean waves, particularly suitable for large scale energy
production.
BACKGROUND OF THE INVENTIION
Waves from oceans have the potential to become a major source of sustainable
and renewable energy. Wave energy is far more concentrated and reliable, when
compared to solar or wind energy. Oceans cover about two-third of the planet,
and
wave energy can be harnessed practically anywhere on the ocean surface. It is
estimated that the total wave energy resources available can exceed the entire
global energy need. Large scale energy production from waves, together with
other
renewable energy sources could almost eliminate the need of fossil energy, and
save our planet from pollution and global warming. Global warming is a very
serious
issue which need to be addressed urgently.
Wave energy has proven quite difficult to harness, even after decades of
research and genuine interest. A reliable and cost effective method of
harnessing
wave energy remains to be found. To this day, while an impressive number of
concepts have been proposed, there is still no commercial scale energy
production
from waves, except some few ongoing experiments. The constantly changing
energy
flux carried in the waves leads to a great diversity of devices, as designers
continuously explore best possible methods to harness wave energy. The
different
environmental conditions offshore and near the shore, largely influence the
designs
of these wave devices, and how they operate. There are wave devices that
float,
those that sit on the ocean floor, and those installed on the shore. The large
diversity
of concepts may have actually slowed down the commercial development of wave
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energy, as winning concepts find it more difficult to immerge from the lots,
and go
through further refinements.
The harsh environment of the ocean greatly affects survivability and
reliability of
equipments. Violent storms are frequent, and the sea water is corrosive. Cost
of
installation in the open sea and construction of underwater infrastructure,
are much
higher compared to land based infrastructures. The ocean environment also
makes
access to installations particularly difficult for routine maintenance and
repairs.
Another difficulty lies in the fact that wave energy devices are mostly not
scalable to
be economically viable. The optimum size of a wave device depends on the size
and
1.0 frequency of the waves, and is usually much less than one megawatt. A wave
energy installation of reasonable power capacity would generally comprise of a
large
number of wave devices, spread over a wide area of the ocean. This
significantly
add to installation cost, as more underwater cables are required to
interconnect
these dispersed wave devices, and the need of as many mooring systems to
secure
these devices. The cost of construction, installation, and exploitation of
such wave
energy installations is the main reason which has prevented the development of
wave energy.
A basic approach to reduction of cost is the sharing of basic installations
among
as many wave energy devices, or power take-offs within an installation.
Several
power take-offs may be mounted on a single wave device, or several devices may
be installed very close to each other. This allows sharing of infrastructures
and
equipments more effectively. Close proximity of wave energy devices allow
significant reduction in the amount of interconnecting cables and various
monitoring
equipments. Group of connected wave devices have a higher capacity factor, as
the
combined power is smoother, which allow reduction in the installed capacity of
power
equipments being shared. Significant economy is also achieved during
installation,
commissioning and maintenance. In several prior arts, power take-offs are
often
mounted close together, in order to improve cost effectiveness.
The patent WO 00/17519 known as the Pelamis and the patent US 8,806,865,
are examples of wave energy concepts where several power take-offs are mounted
on single floating wave devices. However the modules comprising these wave
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devices are connectable only in single rows, and in limited in numbers. These
wave
devices are generally constructed as long as it is technically possible to
operate.
They are usually oriented in the direction of the waves, and they take up
large
amount of marine space to account for changes in wave direction. Some patents
s such
as, US 2011/0057448 Al and WO 2010/082033 A3 overcome this shortcoming
by disclosing concept of devices where larger numbers of modules are connected
in
several arrays, and which does not need to be oriented in the direction of the
waves.
However, all these wave devices remain extremely vulnerable to the condition
in the
ocean. While the power take-off of these devices may be disconnected for self-
preservation, the external articulating members and joints comprising these
wave
devices remain exposed to extreme mechanical forces resulting from the waves.
The
risk of water infiltration through defective seals at these articulating
members is also
a permanent concern. Patent WO 2014/026219 Al is also another wave device
comprising of several connected modules, but is most suitable for shallow
water.
Wave energy devices with completely enclosed hulls, are the most suitable in
order to harness the most intense offshore waves, and harmlessly endure the
worst
condition that prevail. The enclosed articulating or reciprocating elements of
the
power take-offs are less exposed to the direct force of the waves, and the
risk of
water infiltration is also greatly reduced. However, these wave devices can be
operated as standalone units within energy farms at some distance from
adjacent
devices, making it difficult to share most infrastructures. While heaving type
devices
would operate in all direction of waves, they are subjected to interference by
similar
devices in the proximity. Pitching type wave devices, as in patent US
2011/0089690
Al also need some operating distances, as they need to be oriented in the
direction
of the waves. In order to operate in waves from all direction, pitching-type
wave
devices, as in patent US 8,129,854 B2 have to rely on a plurality of power
take-offs,
aligned in several directions. The design is rendered complex, and the power
take-
offs are not fully utilised.
If wave energy is to become a reliable and popular energy source of the
planet, it
is most desirable that wave energy devices should be able to harness the
higher
concentration of energy contained in the offshore waves, and most cost
effectively.
Another desirable feature is that these wave devices may also be used in most
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diverse ocean environments. Hopefully, the abundant numbers of wave energy
devices concepts may be narrowed down to a fewer most suitable concepts, which
when mass produced on a larger scale would further lead to reduction in cost.
s OBJECTS OF THE INVENTION
The main object of the invention is to provide a method and system of
harnessing
energy from ocean waves, while reducing cost of construction, installation and
maintenance.
Another object of the invention is to provide for wave energy harnessing
devices
which can operate in diverse marine environments, with all critical components
sheltered within waterproof enclosures, well above the waterline for easy
access.
It is also another object of the invention to provide for wave harnessing
devices
which are particularly suitable for the use of conventional rotary electrical
machines
and electronic equipment similar to those used in wind energy conversion,
which are
largely available and with proven track record.
A further object of the invention is to provide for wave energy harnessing
devices
which can operate without causing harm to marine life, and is not disrupted by
debris
in the oceans.
Yet another object of the invention is to provide for versatile wave energy
harnessing devices which can be operated offshore in the deep seas, in shallow
lagoons, or even nearer to the shoreline.
SUMMARY OF THE INVENTION
In this present invention, several embodiments of wave energy systems and
related components are disclosed. Herein, wave energy harnessing devices are
generally referred as wave energy collectors. The most prominent features will
be
discussed briefly in this summary, without limiting the scope of the invention
as
expressed by the detail description, drawings and claims that follows.
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In accordance with embodiments of the invention, a system of interconnected
devices for harnessing energy from waves is disclosed, comprising of a
plurality of
wave energy devices which are electrically and mechanically coupled together,
forming a single large floating structure with a high combined power capacity.
The
use of underwater cables to interconnect the multitude of devices is
eliminated, while
underwater infrastructures and moorings are considerably reduced. The modular
concept of the invention makes possible the construction of wave devices and
installation of diverse power capacity, with relative ease. A large numbers of
these
wave devices may be assembled in a port facility and then tug to installation
site
ready for use. The power capacity of these installations may even be
significantly
upgraded if required at a later stage, as more wave devices may be coupled to
the
existing installations without the need of additional underwater
infrastructures. All
these features contribute to the reduction of cost during construction,
installation,
and maintenance. In comparison, current method to harnesses large amount of
power from a given installation is by the use of a plurality of interconnected
wave
devices within energy farms. Each device within such energy farm has to be
maintained at a safe reasonable distance from each other by independent
moorings,
and then interconnected by underwater power cables. High numbers of wave
devices are required. The power capacity of each wave device is usually
limited by
the characteristics of the waves, and scaling up of these devices is usually
not
possible.
In accordance with other embodiments of the invention, a wave energy device is
disclosed, comprising preferably of a single power take-off which would rotate
and
self-align instantly in the direction of the incoming waves, while the
external buoyant
body of the device would maintain a permanent orientation. Energy from the
waves
is extracted as the buoyant body of the device would pitch and roll from side
to side
in any direction. The buoyant body of the wave device may be mechanically
couple
by some suitable means to a multitude of other similar wave devices in any
numbers
of rows and columns, forming a system of interconnected devices as referred
earlier.
As a matter of fact, it is of highest importance that these devices harness
energy
efficiently from any direction of waves, as it is technically not always
practical to
constantly having to orient a high numbers of interconnected devices with the
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changing direction of the waves. Existing pitching-type wave devices are
mostly
designed to operate only in a given direction of waves, and hence cannot be
coupled
together. A pitching-type wave energy device designed to harness incoming wave
from all direction would generally, according to prior art, comprise of a
plurality of
power take-offs within the device, each aligned to handle waves in a
particular
direction most efficiently. The need of higher numbers of power take-offs only
add to
the complexity and cost of the installation. The use of less efficient and
less reliable
hydraulic systems is then mostly preferred due to cost consideration.
In accordance with yet another embodiment of the present invention, a large
standalone wave energy device is disclosed, comprising of a plurality of self
orienting
power take-offs mounted on a single floating structure. While comparable in
several
aspects with the system of interconnected wave devices introduce earlier, such
a
single device of high capacity allow for further economy of scale.
The features, functions, and advantages in various embodiments of the present
invention, can be achieved independently or may be combined in yet other
embodiments.
BRIEF DESCRIPTION OF THE DRAWINGS
The present invention is described with reference to the following drawings:
FIG. 1 is an isometric view of a group of wave energy collectors
interconnected in
an array configuration, floating in the ocean.
FIG. 2 is a top view of a group of wave energy collectors interconnected in a
different configuration, floating in the ocean.
FIG. 3 is a side view of a coupling means used to couple two adjacent the wave
energy collectors, as shown in FIG. 1 and FIG. 2.
FIG. 4 is a side view of a group of interconnected wave energy collectors,
pitching
in the waves.
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FIG. 5 is a side sectional view of a completely enclosed nacelle, showing the
main components of the Power Take-off.
FIG. 6 is a top sectional view of the nacelle shown in FIG. 5.
FIG. 7 is a side view of the nacelle in FIG. 5 in a pitched position during
s operation, shown with some internal details.
FIG. 8 is a side sectional view of another embodiment of a nacelle with some
externally mounted components.
FIG. 9 is the top view of another embodiment of a wave energy collector,
comprising of a nacelle shown in FIG. 8.
FIG. 10 is a side view of the wave energy collector shown in FIG. 9.
FIG. 11 is a top view of several wave energy collectors shown in FIG. 9
coupled
together, comprising of completely enclosed nacelles.
FIG. 12 is a side view of interconnected wave energy collectors shown in FIG.
9,
pitching in the waves.
FIG. 13 is a top view of another embodiment of a wave energy collector,
comprising of a plurality of enclosed nacelles as shown in FIG. 5.
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the invention are set forth in the detailed description that
follows
herein and the accompanying drawings. The drawings are not to scale and are
for
illustration only. The detailed description is subdivided into several sub-
sections for
clarity, discussing different aspects of the invention. Corresponding
components and
components having similar functions in the drawings are designated by the same
numerals, except in cases where specific parts are referred. Embodiments of
the
invention may have different structures and shapes, without departing from the
scope of the invention. Some used terms are also defined for the purpose of
clarity.
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The term "wave energy collector", herein refers to wave energy harnessing
devices. "WEC" or "WECs", is used as an abbreviation of the word "wave energy
collector". The terms "wave energy device" or "wave device" also generally
refer to
embodiments of the wave energy harnessing devices. Wave energy harnessing
devices are known by several other names in different literatures.
"Pontoon" herein refers to a floating body which may be completely closed or
open at the top similar to the hull of a floating vessel, purposely designed
to have
pronounced pitching and rolling movements when interacting with the waves. The
"pontoon" would be constructed in relation to the dimension of the wave, in
order to
lo pitch most efficiently.
"Buoy" refers to a floating body of smaller dimension relative to the ocean
waves,
which enable them to heave most efficiently in the waves. The "buoys" may be
of
any shape, generally completely enclosed to prevent ingress of water.
"Power Take-Off" abbreviated as "PTO", refers to a power extraction means
installed within a WEC for transforming the energy from waves into a useful
form of
energy. The "PTO" is operated by movement of the WEC relative to a fix
reference,
or by the relative movement of articulating members connected to the "WEC".
The
wave energy is transformed into useful energy, in the form of hydraulic,
pneumatic,
or electrical energy.
"Flexible coupling device" or "coupling device" in this detail description
refers to a
wide range of devices for the purpose of securing two separate bodies, while
allowing the connected bodies a certain amount of movements relative to each
other,
with none or little mechanical resistance. This includes any mechanical
coupling
devices which can perform this function, such as universal joints, but also
chains,
ropes, or connecting members having elastomeric properties. "Flexible coupling
devices" may comprise of a single or several devices assembled together.
"Power conduit" herein refers to connecting elements used for the transmission
of
energy in the formed of fluid or electricity. "Power conduits" would comprise
of hollow
pipes when energy is carried in fluids, such as air, water, or oil. The term
"cable bus"
is also a type of "power conduits" comprising of electrical cables for
transmission of
electrical energy.
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"Cable support" refers to various devices and structures which may provide
support for "cable bus" or "power conduit" laid across two adjacent WECs which
are
coupled together by "coupling device". This include support structures, cable
channel, cable trays, cable ladders, articulating cable carriers, conduits,
including
aerial cable supports.
General concept
Embodiments of the invention generally comprise of a plurality of independent
wave energy collectors (WECs) which are coupled together mechanically and
electrically, so as to form large connected floating structures. In FIG. 1, a
group of
WECs 20 is shown coupled together in an array configuration within an
installation.
In FIG. 2, another group of WECs 20 is shown coupled together in a different
configuration. The WECs 20 are usually of similar size and power capacity to
facilitate interconnection. The WECs 20 may be coupled together forming
installations of various shapes, to maximise the absorption of wave energy,
better
resist rough weather, or to fit certain installation site. For example, rows
of
interconnected WECs 20 may stretch along the shoreline over long distances,
facing
the incoming waves. By absorbing as much energy from the waves, the arrays of
WECs 20 may also act as a wave breakers preventing coastal erosion. In
offshore
installation, the WECs 20 may be bundled in some tight configurations to
better
resist rough weather.
The WECs 20 may be designed to various scales, in order to operate either in
large offshore waves or in relatively smaller waves near the shore.
Embodiments of
WECs 20 would generate between a few kilowatts to several hundreds of
kilowatts
(KW) of energy, depending on the dimension of the WECs 20 and the wave
characteristics, such as intensity and wavelength. A WEC 20 may be operated as
a
single standalone unit, but in general a single installation would comprise of
several
numbers of interconnected WECs 20, ranging from a few to several thousands in
numbers, with the aim to produce several megawatt or even gigawatt of
electrical
energy. Installation of such high capacity can be easily deployed as no
extensive
underwater infrastructures is required, except the laying of underwater power
transmission cable to the shore, and moorings to secure the installation in
the ocean.
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Large numbers of WECs 20 may be coupled together in port facilities, and then
tugged in the open sea to the installation site ready for operation. Power
capacity of
a given installation may even be substantially increased by coupling
additional
WECs 20, without the need of additional moorings or power transmission cable.
Embodiments of the invention, because of the ease of deployment and
installation,
can be use as temporary power installations in coastal areas following
disasters and
major power network failures.
As shown in FIG.1 and FIG. 2, each of the WECs 20 includes a pontoon 21 and a
nacelle 22 firmly secured at the center. The nacelle 22 is a waterproof
enclosure
3.0 which houses the Power Take-Off (PTO). In preferred embodiments of the
invention,
the PTOs generate electrical energy as the nacelles 22 pitch and roll about
the
horizontal plane together with the pontoons 21. The pontoon 21 of a given WEC
20
is coupled to the pontoons 21 of adjacent WECs 20 within an installation by
flexible
coupling devices 23. This allows each of the WECs 20 to move freely about the
joints of the coupling devices 23. A cable bus 24 of appropriate power
capacity
connects and combines all the power generated in the PTOs. Waterproof cable
entries are provided in the nacelles 22 for interconnection of the PTOs. The
cable
bus 24 is properly secured to the side of the pontoons 21, and to the cable
supports
where the cable bus 24 is laid across the coupling devices 23. The cable
supports
20 25 allow free movements of the interconnected WECs 20, while preventing
the cable
bus 24 from potential damages.
The combined power of the interconnected PTOs is usually transmitted by a
single underwater transmission cable 26 to the power grid on shore. But
certain large
embodiments of the invention may comprise of several underwater transmission
25 cables 26 for increased reliability. The underwater transmission cable
26 may also
connect the installation to other groups of wave energy devices, located at
some
distance within an energy farm. In other use of the invention, the power may
be
consumed by manufacturing and processing plants installed within the WECs 20,
or
on separate floating platforms. The energy harnessed may be used for undersea
mining in the proximity of the installation, or the production of fresh water.
A very
practical use of wave energy is the production of hydrogen from the seawater,
which
can then be transported by ships or pipelines. Embodiments of the invention
may
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also be mounted on watercrafts of appropriate designs, and the energy from the
waves used for propulsion of the watercrafts.
Main structures
The WEC 20 is designed in shape and size so as to interact with the waves, and
harnessed wave energy most effectively. The pontoon 21 may be constructed in
the
shape of a buoyant ring, as shown in FIG. 1 and FIG. 2. The buoyant edge of
the
pontoon 21 further from the center of the nacelle 22 provides better leverage
and
torque required to operate the PTO. The nacelle 22 is secured at the center of
the
pontoon 21 by a number of spars 27, or any alternative structural framework,
or
platform to ensure integrity of the construction. The spars 27 may be made
steel
frames members, such as hollow pipes or steel sections. Steel must be
galvanised,
painted, or coated by some other protective materiel to better resist
corrosion. Other
construction material, such as wood, fibreglass, or similar synthetic
materials may be
used for construction of the spar 27, provided they are of adequate size to
endure
the work load. A number of spars 27 are used distributed evenly about the
perimeter
of the pontoons 21 to ensure integrity of the construction. In FIG. 1, the
nacelle 22 is
shown secured to the pontoon 21 by four set of spars 27. In FIG. 2, the
nacelle 22 is
shown secured by eight set of spars 27. As an alternative to pontoon 21, a
plurality
of independents floating bodies may be disposed around the nacelle 22, each
secured directly to the nacelle 22, or by the use of a plurality of spars 27.
In other
embodiments of the invention, the nacelle 22 may be secure at the center of
the ring-
shaped pontoon 21 by a plurality of support cables or ropes under tension. The
cables are used as an alternative to rigid spar 27 in a construction similar
to wire
wheel, where the central hub is secured to the rim by cables under tension. In
some
other embodiments of the invention, the pontoon 21 may be constructed as a
circular
hull like platform. The nacelle 22 may then be mounted above at the center, or
inside
the hollow body of the hull.
The circular shape of the pontoon 21 allows efficient spatial distribution of
the
WECs 20 when they are coupled together. The interconnected pontoons 21 can
then
move about the coupling devices 23 with minimum interaction with each other.
The
symmetrical circular shape of the pontoon 21 also allows energy to be
harnessed
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from waves in all direction with same uniformity. The WEC 20 would generally
have
the center of gravity and the center of buoyancy vertically aligned, in order
to ensure
flotation stability and correct operation of the PTO. The WECs 20 which are
used as
standalone units may be designed with a lower center of gravity to enhance
flotation
stability in rough weather condition. Embodiments of the invention comprising
of
large numbers of interconnected WECs 20 are naturally stable in rough weather.
The pontoons 21 are robust construction so as to withstand extreme weather
condition. The design of the pontoons 21 may vary widely in different
embodiment of
the invention. The pontoons 21 may be made of metal or other synthetic
material
io such as fibreglass, and air-filled to ensure flotation. The pontoon 21
is built to
required dimension, so as to enable the WEC 20 to float and also provide the
forces
required to operate the PTO in the nacelle 22. The pontoon 21 may be entirely
constructed of some solid lightweight material of density lower than water.
Pontoons
21 with air filled cavities would generally comprise of several separate
airtight
is compartments to ensure integrity in case of damage. The pontoons 21 may
also be
made of soft inflatable material, such as rubber or equivalent synthetic
material, as a
cost effective alternative. Pontoons 21 made of soft material also effectively
cushion
the contacts between each other during operation. Additional internal or
external
reinforcement structures may be required to ensure stiffness and strength of
the
20 pontoons 21. Pontoons 21 may be constructed in other cost effective shapes,
depending on the manufacturing means and material of construction. As such,
the
pontoons 21 may be constructed as regular polygons with a number of sides,
instead
of being circular. The pontoon 21 may also comprise of a plurality of
independent
modular segments assembled and secured together in required numbers, in order
to
25 accommodate WECs of different dimension. As the pontoons 21 within an
installation of interconnected WECs 20 would be constantly rubbing and bumping
with each other, the sides of the pontoons 21 may need to be protected from
premature wear and damages. Marine fenders, bumpers, old tires, or pads may be
mounted around the perimeter of the pontoons 21 for additional protection
where
30 required. The parts of the WEC 20 exposed to seawater may need some
antifouling
treatment, but in general fouling do not seriously affect performance of the
WECs 20,
because of the absence of any external articulating members or joints.
Furthermore,
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it should be noted that the proliferation of marine life in the underside of
the WECs
20 may be rather beneficial to the marine ecosystem.
The coupling devices 23 are used only as a means to secure the pontoons 21
together, and take no part in the operation of the PT0s. The coupling devices
23
also allow each of the pontoons 21 to move freely with the waves, so that the
PTOs
mounted on each pontoon 21 can harness energy from the waves. So, the coupling
devices 23 are designed to provide as little mechanical resistance as
possible, to the
movement of the pontoons 21. The coupling devices 23 are also designed to
resist
extreme mechanical forces in all weather conditions. The sides of the pontoons
21
where the coupling devices 23 can be reliably mounted, are reinforced in order
to
endure the forces involve. The coupling devices 23 are positioned where
required on
the side of the pontoons 21, according to the layout of the interconnected
WECs 20
in a given installation. The coupling devices 23 can be constructed in a
variety of
ways. Coupling devices 23 may comprise of one, or a combination of several
standard off-the-shelves mechanical devices, such as universal coupling,
spring
coupling, elastomeric coupling, bellow coupling, knuckle coupling and others.
Coupling devices 23 may be custom-made. Coupling devices 23 may also comprise
of other components such as spring, ropes, chains, fabrics, used tires, and
any
flexible material. When large numbers of WECs 20 are coupled together, their
movement may become significantly damped as the pontoons 21 would pull and
push mutually on each other, hence reducing the overall energy extraction
efficiency.
This problem is attenuated by the use of coupling devices 23 which are able to
extent and contract in length substantially. These embodiments of coupling
device
23 may then also comprise of telescopic joints, springs, material of
elastomeric
properties, or made of articulating members, so as to allow the coupling
device 23 to
stretch and contract by the amount required. Each of the WECs 20 within such
large
installation, is then able to surge and sway sideways more freely within the
extra
space provided, hence reducing the mechanical forces the WECs 20 may exert
mutually on each other.
An example of a coupling device 23 is shown in FIG. 3, comprising of standard
marine equipment commonly use to secure floating structures and boats. The
same
type of coupling means is used in embodiment of the invention shown in FIG. 1
and
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FIG. 2, but any other alternative coupling means which meet the operation
requirements could have been used. As shown in FIG. 3, a marine fender 31 of
cylindrical shape is secured between the pontoons 21 of two adjacent WECs 20
by
mooring pendants 32. The mooring pendants 32 are maintained slack, which allow
the pontoons 21 to move relative to each other with negligible mechanical
resistance. The mooring pendants 32 may comprise of chains, or synthetic
ropes.
The mooring pendants 32 may also have some elastic properties to better endure
and absorb shocks. Mooring rings 33 are provided on the side of the pontoons
21
and the marine fender 31. The mooring springs 34 of appropriate load capacity
provide a graded restraining force, and manage the excess slack in the mooring
pendants 32. The mooring springs 34 are mounted on the sides of respective
pontoons 21 and the marine fender 31. Marine fenders 31 of suitable size and
diameter are selected according to the size of the pontoons 21, in a given
installation. The marine fenders 31 may float between the sides of the
pontoons 21,
or secured above the ocean surface or waterline 35 as shown in FIG. 3. Marine
fenders 31 are usually made of synthetic material, such as rubber which is
adequately deformable, pliable, and with good cushioning properties. The
marine
fenders 31 may be filled with air or foam. Marine fenders 31 of other shape
and
design may be used to improvise other form of coupling device 23. Alternative
mounting arrangements may be used to secure the marine fender 31 to the
pontoons 21.
FIG. 3 also shows an example of a cable support 25 which carry the cable bus
24
between two adjacent pontoons 21, in order to connect the PTOs in the
respective
nacelles 22. Cable supports 25 are placed along the path of the cable bus 24
where
require, and are firmly secured to the side of the pontoons 21. The cable
support 25
may comprise as shown, of an articulated cable carrier or tray. The members
comprising the cable support 25 articulate about a plurality of hinges 36,
hence the
cable support 25 opposes no resistance to the free movements of the pontoons
21.
The cable bus 24 is secured on the cable support 25 and the side of the
pontoons 21
by cable clamps 28 or any other appropriate means. The cable bus 24 would have
a
reasonable amount of excess length in order to allow bending around the
articulations of the cable support 25. The articulations of the cable support
25 must
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accommodate the most extreme movements between the pontoons 21 and the
marine fender 31, without causing damage to the cable bus 24.
The cable supports 25 may be constructed in a number of various other ways.
The cable supports 25 may comprise of flexible synthetic material which can
easily
twist, stretch and bend. The segment of the cable bus 24 across the flexible
coupling
device 23 may comprise of spiral power cable, so as to easily stretch and
contract.
The cable bus 24 may be secured by some aerial means across the pontoons 21.
In
some other embodiments of the installation, cable supports 25 may not be used.
The
cable bus 24 may be secured directly to coupling device 23 of appropriate
designs.
In other embodiments of the invention, the cable bus 24 may be allowed to hang
loose and free between the connected pontoons 21, or even trail in the sea
water. In
these cases, the cable bus 24 may be provided with additional protective
sheath for
protection against mechanical damage due to possible interaction with the WECs
20,
and protection against the seawater. In other embodiment of the invention, the
coupling devices 23 may include internal cableways for the cable bus 24.
Internal
cableways may be also provided within the pontoons 21, so that the cable bus
24
between the interconnected WECs 20 is completely internal and not visible from
the
outside. It is understood that power conduits other than electrical cables may
be
used to carry the harnessed energy from the interconnected WECs 20, in other
embodiments of the invention. Such power conduits may comprise of network of
pipes or hoses which carry fluids from the PT0s, and then transformed into
electricity by a centralised generator. These power conduits may be installed
in
similar manner as described for the cable bus 24.
Operation of interconnected WECs
FIG. 4 shows some interconnected WECs 20 pitching in the waves. The pontoons
21 are able to pitch from side to side because the opposite sides of the
pontoons 21
alternatively rest on the crest and the trough of the waves travelling across
the
lengths of the interconnected WECs 20. The pontoon 21 is made rigid, in order
not to
bend under the forces of the waves, so that the turning moment of the forces
is
efficiently transferred to the PTO in the nacelle 22. The diameter of the
pontoon 21 is
generally designed not to exceed half the wavelength of the waves, so that the
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pitching angle is a maximum, half a wavelength being the distance between an
adjacent crest and trough. At wavelength less than the diameter of the pontoon
21,
the pitching angle is reduced, and less wave energy is extracted. The diameter
of
the pontoons 21 can measure in the range of a few meters, in order to operate
both
s in waves of those magnitudes and in larger waves. In larger embodiments of
the
invention, the diameter of the pontoons 21 may measure in the range of 20-50
meters, in order to operate in offshore waves of those magnitudes. An
installation of
equivalent power capacity may comprise of a greater number of WECs 20 of
smaller
diameter, or a fewer number of WECs 20 of larger diameter. As the waves at a
given
installation site would normally vary between a maximum and minimum
wavelength,
the diameter of the pontoons 21 would be selected based on the most cost
effective
options, taking into consideration the construction and operation cost of the
installation and the total energy that may be harnessed during the life time
of that
installation.
As shown in FIG. 1 and FIG. 2, all the PTOs of the interconnected WECs 20 are
linked by a common cable bus 24. Together, they form a large power generating
system of capacity equivalent to the total numbers of interconnected WECs 20
within
a given installation. The cable bus 24 is preferably secured on the surface of
the
WECs 20 and the cable supports 25, as the cable bus 24 may then be easily
inspected during routine maintenance. The cable bus 24 should resist wear and
tear,
as they undergo a large numbers of bending cycles about the coupling devices
23,
during the lifetime of the installation. The pontoon 21 would generally carry
only a
single PTO, secured at the center within the nacelle 22. However several PTOs
of
small capacity may be secured about the center of pontoon 21, as a replacement
for
a single PTO of larger capacity. In other different embodiments of the
invention
where the wave energy is harnessed in a first stage by PTOs in the form of a
compressed fluid, then a network of flexible conduits may collect the
compressed
fluid from all the PTOs, and then converted into electricity by a common
generator.
The generator may be installed within one of the WECs 20, or alternatively on
a
separate floating structure, in an underwater station. In near shore
installation, the
compressed fluid may even be brought by under water pipes to drive generators
located on the shore.
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Because of the highly variable intensity of the waves, the PTOs would generate
electrical energy of highly fluctuating amplitude and frequency, without the
use of
appropriate power interface within the nacelle 22. The power interface system
ensures that the electrical supply from the PTO conforms within certain
constant
s electrical parameter before being connected to the cable bus 24. Power is
transferred from the PTOs to the cable bus 24 only at correct calibration of
these AC
or DC electrical parameters. The power interface system may comprise of
diverse
power electronic devices such as converters, inverters, rectifiers which are
widely
used in the wind power systems. The electrical power supply from the PTOs is
generally designed to be connected in parallel by the cable bus 24 in a radial
configuration, as shown in FIG. 1 and FIG. 2. The cable bus 24 may also be
laid
according to some other configuration for higher reliability. The ways the
PTOs are
designed may also influence how they may be electrically connected, in
parallel or in
series, by the cable bus 24.
The design of the power transmission systems from the interconnected WECs 20
to the main electrical grid on the land would mostly depend on the power
capacity of
the installation, and the distance from the shore. In small embodiments of the
invention as shown in FIG. 1 and FIG. 2, the use of a single underwater
transmission
cable 26 is most economical. However in larger embodiments of the invention,
the
power may be transmitted by several separate underwater transmission cables
26,
for increased reliability. The connections between the PTOs in the nacelles 22
are
then also usually organised in separate clusters and subgroups by several
segregated networks of cable bus 24, for still higher reliability. The power
for the
transmission cable 26 may be tap-off directly at the cable bus 24 and
transmitted to
shore in the form of direct or alternating current supply (also referred as DC
or AC
supply). When the power from the cable bus 24 is transmitted over long
distances,
the DC or AC supply voltage is preferably stepped up by power transformers and
appropriate equipment for higher voltage transmission, before connection to
the
transmission cable 26. The high voltage transmission equipment may be
installed
within one of the nacelles 22, on a separate floating platform, or in an
underwater
substation. The power transmission cable 26 may not always be under water. In
embodiments of the invention operating very near the shoreline, the power
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transmission cable 26 may be installed by some aerial means, or some alternate
method under specific installation layout conditions. Switchgears for
isolation and
disconnection of the installation are required for safe and reliable operation
of the
installation. The cable bus 24 and the transmission cable 26 must be protected
from
electrical overload. Faulty WECs 20 should be able to be selectively
disconnected,
in order to allow continued operation of the installation.
Deployment and mooring
Large embodiments of the WEC 20 are generally assembled in dry dock
facilities,
and then floated. Smaller embodiment of WECs 20 may be factory mounted. The
plurality of WECs 20 is then coupled to each other by means of the coupling
devices
23, according to pre-layout designs in the calm water of a port, most likely.
The cable
supports 25 are then fitted where required. The cable bus 24 is later
installed
between the nacelles 22 and all the PTOs are interconnected. At this stage,
the
installation may be pre-commissioned and tested before being tugged in the
open
sea. Upon reaching the site of installation, selected WECs 20 are immediately
secured to the mooring line 43 and the system connected to the underwater
transmission cable 26. Installations of the mooring systems on the seafloor 45
and
the underwater transmission cable 26 have been completed prior to the arrival
of the
WECs 20. The installation is then ready for final commissioning and
exploitation.
Embodiments of the invention comprising of very large numbers of WECs 20 may
be
partly assembled in several segments, and then tugged separately to the
operation
site, where the segments are then coupled together. An existing installation
may be
substantially upgraded at a later stage by coupling addition WECs 20, without
the
need of additional underwater infrastructures, provided the existing mooring
systems
and the underwater transmission cable 26 have some spare capacity for such
expansion. Similarly, installed capacity of an existing installation can be
easily
downgraded by removal of a number of WECs 20. Embodiments of the invention are
generally provided with means for personals to move safely and swiftly between
the
coupled WECs 20, which is of extreme importance during installation and
maintenance work. Protection means for personals would include, provision of
anchors, footholds, safety nets, protection rails, where required on the WECs
20.
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19
Accommodations for visiting or permanent technical personnel may be provided
within larger embodiments of the WECs 20.
Embodiments of the invention are maintained on the ocean surface 35 by a slack
mooring system. The slack mooring allows the WECs 20 to heave and pitch
without
restrain, and also prevent the installation from drifting due to wind and sea
currents.
The mooring system is designed to resist severe weather condition. As shown in
FIG. 1, only a few selected pontoons 21 are secured by mooring lines 43 to
concrete
blocks 44 on the seafloor 45. The mooring lines 43 may be directly anchored to
the
seafloor 45. The mooring lines 43 would comprise of chains, or synthetic
ropes.
lo Mooring buoys 46 are attached at the end of the mooring lines 43 in order
to
facilitate the mooring operation. The moorings lines 43 are spaced relative to
each
other, so as to prevent the installation from making a complete spin, hence
avoiding
potential damage to the underwater transmission cable 26 by twisting. The
length of
mooring lines 43 and the transmission cable 26 should account for seasonal
tides
variations and height of the waves. The slack in the mooring lines 43 and the
transmission cable 26 are prevented from resting on the seafloor 45 by the use
of
underwater buoys 47. Dragging of the mooring lines 43 and the transmission
cable
26 on the seafloor 45, may cause gradual damage to the fauna and the reefs.
The
use of underwater buoys 47 also reduces possible interference in the operation
of
the WECs 20, by the weight of the mooring lines 43 and the transmission cable
26.
Embodiments of the invention may also be secured to other structures, such as
the
masts of offshore wind farms and oil rigs. Installation very close to the
shoreline may
be secured to land based structures. A properly designed mooring system must
be
carried out by the recommendation and skills of those familiar in the art.
The power take-off (PTO)
The PTO is another important aspect of the embodiments of this invention for
efficiently harnessing the wave energy. The pontoons 21, as they interact with
the
waves are subjected to various kinds of motions about the flexible coupling
device
23. In different embodiments of the invention, PTOs mounted in the nacelles 22
may
exploit any of these motions, such as the heaving, the lateral surge motions,
or the
pitching and rolling motions of the pontoons 21. Energy is harnessed as the
pontoon
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20
21 moves in relation to a fix reference connected to the PTO, where the fix
reference
provides the resistive force to operate the mechanism inside the PTO. In some
embodiments of the invention, the fix reference may be provided by a tether
lines
secure to the seabed and to related components in the PTO. In other
embodiments
of the invention, the fix reference may be provided by the inertial of a
reaction mass,
where the reaction mass resists the motion of the pontoons 21. In yet other
embodiments of the invention, the fix reference may be provided by a member
with a
high drag coefficient in water, which resists the motion of the pontoons 21.
In
preferred embodiments of the invention, the pontoons 21 being coupled by the
flexible coupling devices 23 on several sided, would pitch and roll most
efficiently,
than any other motions induced by the waves. As such, in preferred embodiments
of
the invention, the PTOs are designed so as to utilize most particularly the
pitching
and rolling motion of the pontoons 21 about the horizontal plane.
A preferred embodiment of the PTO is shown in FIG. 5 to FIG. 7. The PTO
harnesses wave energy as the pontoon 21 pivots about the joints of the
coupling
devices 23, pitching and rolling about the horizontal plane. This arrangement
allows
the PTOs to harness energy from waves reaching the connected network of
pontoons 21, from any direction. As shown in FIG. 5, the components comprising
the
PTO are completely enclosed and protected within the body 49 of the nacelle
22.
The PTO comprises of a support frame 50 which is firmly secured to the lower
section of a support shaft 51. The support shaft 51 is mounted vertically at
the
symmetrical center of the nacelle 22 on roller bearings 53 and 54, which
together
with the support frame 50 form a rotatable base. A pair of opposing tapered
roller
bearings 53 and 54 mounted within a bearing housing 55, allow the rotatable
base to
endure a large amount of radial and axial forces, during operation of the PTO.
The
bearing housing 55 may be designed differently with different numbers of
bearings
and in different arrangements, to fulfill the same purpose. The rotatable base
allows
components of the PTO to rotate freely about the vertical axis of the support
shaft
51, and to align in any direction within the nacelle 22. As shown in FIG. 6,
the
bearing housing 55 is firmly secured at the symmetrical center of the nacelle
22 by a
support structure, which may comprise of several truss members 56. The side of
the
nacelle 22 may need to be reinforced about the circumference by appropriate
frame
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21
structures, such as a number of ring members 57 and lateral struts 58. The
spars 27
(not shown in FIG. 5 to FIG. 7) which secure the pontoon 21 to the external
side of
the nacelle 22, are preferably secured to the ring members 57 so as to reduce
mechanical stress to the body 49. In other embodiments of the nacelle 22, the
spars
27 may be directly to the sides of the bearing housing 55, rather than to the
sides of
the nacelle 22. It is understood that the support frame 50 with the ability to
rotate
about a vertical axis of the nacelle 22, may be constructed in a number of
different
ways, and which may not always require the need of a centrally mounted support
shaft 51 as shown in FIG. 5 to FIG. 7. In these alternative embodiments, the
support
lo frame 50 may be mounted on wheels which roll on a peripheral circular
rail secured
to the ring member 57 of the nacelle 22.
The fix reference, or reference mass for operation of the PTO is provided by a
heavy weight 59 inside the nacelle 22. The weight 59 is made from some low
cost
and dense material, such as concrete. Preferably, a pair of suspension rods 60
is
used to secure the weight 59 to either side of the pivot shaft 61, both
mounted on the
support frame 50. The suspension rods 60 also significantly off-set the center
of
gravity of the weight 59 acting on the pivot shaft 61. The pivot shaft 61 is
mounted on
roller bearings 62 and 63, which allow the weight 59 to hang vertically by the
force of
gravity, even as the nacelle 22 is pitched sideway as shown in FIG. 7. The
roller
bearings 62 and 63 are preferably tapered so as to bear significant amount of
radial
and axial forces during operation. Clearance is provided between the weight 59
and
the internal wall of the nacelle 22, to the extent of the maximum pitching
angle of the
nacelle 22. The need for clearance applies to the internal wall of the nacelle
22 all
around the support shaft 51, given that the pivot shaft 61 may be positioned
in any
direction within the nacelle 22 during operation. The body 49 of the nacelle
22 is
shaped so as allow operation of the PTO in normal conditions and at pitching
angle
most commonly experienced by the pontoon 21. Cushioning bumpers 64 are
provided on both sides of the weight 59, in order to prevent any hard contacts
with
the truss member 56 or the ceiling of the nacelle 22, which may occur in most
extreme conditions. The pivot shaft 61 is also symmetrically aligned with the
axis of
the support shaft 51, with a balanced lateral weigh distribution, to ensure
correct
operation of the PTO. In other embodiments of the PTO, the weight 59 together
with
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the suspension rod 60 may be mounted within the support frame 50, in order to
allow
even more extreme pitching angle of the pontoon 21. The gearbox 65 and the
generator 66 are then mounted on the external sides of the support frame 50.
In this
arrangement, the weigh 59 may be provided with sufficient headroom within the
support frame 50, so as to rotate completely about the pivot shaft 61, during
most
extreme pitching of the nacelle 22. Embodiments of WEC 20 with PTO designed
accordingly, may be most useful as standalone units in very rough sea
conditions,
where during operation the WECs 20 may capsize without disrupting operation.
Energy is harness in the PTO when the longitudinal axis of the pivot shaft 61
is
lo positioned perpendicularly to the travel direction of the ocean waves.
Reciprocal
movements take place between the suspension rod 60 and the support frame 50,
as
the nacelle 22 is pitched alternately from side to side. The lateral forces
acting on the
bearing 53 and 54 are then symmetrically balanced, and the pivot shaft 61
remains
perpendicular to the direction of the waves. When the direction of the waves
changes and is no longer perpendicular to the axis of the pivot shaft 61, the
pitching
movement of the nacelle 22 with the waves causes unbalanced lateral reaction
forces in the bearing 53 and 54. The support frame 50 would then rotate about
the
axis of the support shaft 51, until the pivot shaft 61 is repositioned
perpendicularly to
the direction of the waves. The lateral reaction forces acting on the bearings
53 and
54 are balanced and symmetrical again. The ability for components of the PTO
to
rotate and align with the wave, while the nacelle 22 maintains a permanent
orientation, is an important aspect of the invention. This feature makes it
possible for
WECs 20 to be couple together, as shown in FIG. 1 and FIG. 2 in large numbers.
As
the support frame 50 responds almost immediately to the change in wave
direction,
energy can be harnessed even in choppy irregular waves.
A diverse range of mechanical or hydraulic equipments may be used to convert
the slow movements of the articulating joints at the pivot shaft 61, into high
rotational
mechanical movement suitable to drive the generator 66. In some embodiments of
the nacelle 22, linear generators may be mounted on the support frame 50 and
directly coupled to the articulating joint about the pivot shaft 61 by mean of
suitable
linkage mechanisms. In the embodiment as shown in FIG. 5, the mechanical
transmission system comprising of a gearbox 65 is coupled to a rotary
generator 66
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by a drive shaft 67. Both the gearbox 65 and the generator 66 are firmly
secured to
the support frame 50. In this embodiment of the PTO, the pivot shaft 61 is
also used
to drive the input shaft of the gearbox 65 and is hence lock to the suspension
rods
60, in order to allow transmission of torque. The gearbox 65 may comprise of
several
stages of gear trains, including chain drive or belt drive. The pivot shaft 61
or the
drive shaft 67 generally includes a clutch mechanism, so that power
transmission to
the gearbox 65 or the generator 66 may be disconnected during severe weather
conditions. In these conditions the nacelle 22 would pitch freely in the waves
about
the pivot shaft 61, without causing damage to the mechanical transmission, or
io overload the generator 66. There is a great flexibility in the design of
the mechanical
transmission and the way it is connected to the driveshaft 67 of the generator
66. In
some other design, the generator 66 may even be secured on the weight 59, with
appropriate gears mechanism mounted on both the drive shaft 67 and the support
frame 50. An electrical cable 68 connects the generator 66 to the power
interface 69
in the equipment room 70, located above the platform or internal deck 71. The
support shaft 51 is made hollow or provided with grooves. This allows the
passage of
the cable 68, and any other cables for control and monitoring purposes,
between the
support frame 50 and the equipment room 70. A slip ring 72 mounted on the
support
shaft 51 is required for connection of the cable 68 to the terminals of the
power
interface 69. The slip ring 72 and the support frame 50 mounted together on
the
support shaft 51, rotate to a new position every time there is a change in the
direction of the waves. Brushless rotary transformers may be used as an
alternative
to conventional slip rings 72. However conventional slip rings 72 which have a
higher
current capacity remain a practical choice, as the device is not subjected to
intensive
use. Additional low power slip rings may be required to connect the cables of
any
control and monitoring equipment located on the support frame 50.
The equipment room 70 and space above the support frame 50 may
accommodate various monitoring and control equipments. Energy storing devices
such as batteries, capacitors, flywheels etc, may be installed within the
equipment
room 70, or any other location of the nacelles 22. Waterproof access traps or
doors
are provided to allow access inside the nacelle 22 for the purpose of
installing
equipment and maintenance. In larger embodiments of the invention, the nacelle
22
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24
or other part of the WEC 20 may include storage areas and living space for
maintenance crew. Weigh of equipments on the deck 71 also need to be evenly
distributed and laterally balanced to ensure flotation stability, and correct
operation of
the self-alignment mechanism of the PTO. Waterproof cable passages are
provided
in the equipment room 70 for all electrical cables, such as the cable bus 24,
the
transmission cable 26, and cables required or any other devices.
The power supply by the generator 66 is highly variable in intensity and
frequency. The power interface 69 transforms the supply from the generator 66
into
AC or DC power supply with constant parameters which are compatible for
electrical
connection to the cable bus 24. Only then, the power supply from the power
interface
69 can be transmitted into the power network formed by the cable bus 24.
Switchgear is provided to disconnect and isolate the power interface 69
automatically during faults or for maintenance purposes. The underwater
transmission cable 26 may be connected to the cable bus 24 at the output
terminals
of the power interfaces 69. For higher voltage transmission to shore, the
supply from
the cable bus 24 is stepped up before connection to the transmission cable 26.
The
equipment room 70 may accommodate the power transformer and convertor
necessary for stepping up the voltage of the cable bus 24. The power interface
69
can be designed in a number of ways, and would generally comprise of various
power electronic equipment such as frequency convertors, frequency invertors,
rectifiers, and boosters. The power interface 69 may also be constructed
almost
entirely of various interconnected electro-machines. The design of the power
interface 69 largely depends on the type of generator 66. The generator 66 can
be of
the permanent magnet type, or the most affordable and reliable induction type.
The
power interfaces 69 usually rectify the fluctuating supply from the generator
66,
before converting it into AC or DC supply, compatible for connection to the
cable bus
24. Electrical current is generated (as wave energy is harnessed in the PTO)
when
the stator and the rotor of the generator 66 rotates relative to each other,
under the
action of an external forces or torque. As the nacelle 22 is pitched from side
to side
by the action of the waves, the stator of the generator 66 rotates, forward
and
backward repeatedly, about the rotor. The induced current in the stator also
produces a torque on the rotor, which prevent the relative rotation between
the stator
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25
and rotor of the generator 66 from taking place. A rotor which is not
restrained
mechanically by an opposite restraining torque would rotate together with the
stator,
and no power would be generated by the stator windings of the generator 66.
The restraining torque acting on the rotor of the generator 66, is the result
of the
sideway displacement 73 of the weight 59 at the end of the suspension rods 60,
about the pivot shaft 61, as shown in FIG. 7. The sideway displacement 73 from
the
vertical axis 74 occurs in the direction of movement 75, as the nacelle 22 is
pitched
from side to side. The restraining torque is proportional to the amount of the
displacement 73 and the mass of the weight 59. The length of the suspension
rods
60 and the weight 59 are selected so that the sideway displacement 73 is a
minimum
for efficient extraction of energy by the PTO. A means to modulate the amount
of the
restraining torque would allow the WEC 20 to operate in very intense waves
without
having to shut down completely. The restraining torque can be modulated by the
use
of a suspension rod 60 of adjustable length, where the length is reduced
during
intense waves. Similarly the weight 59 may comprise of container fill with
seawater,
where the amount of liquid can vary, in order to modulate the amount of the
restraining torque. The restraining torque may also be modulated electrically
by the
power interface 69.
The dimension of the nacelle 22 as shown in FIG. 5 to FIG. 7 is mainly
determined by the size of the weight 59 and the length of the suspension rod
60. An
alternative embodiment of a nacelle 82 is shown in FIG. 8, which allow for
greater
flexibility in the design of the PTO. The support frame 50 together with the
gearbox
65 and the generator 66 are enclosed within a separate lower enclosure 83. The
lower enclosure 83 together with the support frame 50 is secured to the
support shaft
51. The pivot shaft 61 extends through openings outside the enclosure 83 to
secure
the pair of externally mounted suspension rods 60 and the weight 59. While the
upper enclosure 84 is secured to the pontoon 21 by a number of spars 27, the
lower
enclosure 83 is free to rotate and align in the direction of the waves. The
nacelle 82
allows a great deal of flexibility in the construction of WECs 20 of different
power
capacity. The nacelle 82 has the ability to accommodate a wide range of
weights 59,
together with suspension rods 60 of different length, in relation to the power
rating of
the generator 66. Similarly, the enclosures 83 and 84 may be constructed of
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26
standard sizes to accommodate components of PTO for a wide range of power
capacity. The weight 59 may be completely submerged below the water surface
35,
if constructed of material significantly denser than water. Watertight seals
85 are
provided on the support shaft 51 and the pivot shaft 61 to prevent water
infiltration
inside the different compartments of the nacelle 82. Other alternative means,
such
as rubber bellows, and barriers may be used to prevent water infiltration.
The preferred embodiments of the nacelles 22 and 82 as disclosed, harness
wave energy by means of a PTO comprising of single reciprocating mechanism
which rotate a generator 66, wherein the reciprocating mechanism is maintained
align in the direction of the incoming waves by an orientation mechanism. In
other
embodiments of the PTO, the reciprocating mechanism may comprise of a
different
orientation mechanism, such as a motor or actuator operated by a control
system
which detect the direction of the waves, and consequently rotate the
reciprocating
mechanism in the direction of the waves. In embodiments of the invention where
the
direction of the waves is mostly constant, the PTO may be aligned permanently
in a
given direction, without the need of an orientation mechanism. In yet other
embodiments of the invention, orientation mechanism is not required when the
PTO
comprises of a plurality of reciprocating mechanisms aligned permanently in
different
directions, and thus is able to harness incoming waves from all direction. In
such
alternative designs, the suspension rod 60 with the weight 59 at its lower end
may be
suspended to an articulating joint, secured at the symmetrical center directly
to the
truss members 56 within the nacelle 22. As the nacelle 22 would pitch in any
direction about the articulating joint, a plurality of compression cylinders
disposed
and secured around the perimeter of the nacelle 22 may be operated through
linkage
members connecting the suspension rod 60 to the pistons of the compression
cylinders. The compressed fluid from the cylinders may then be transformed at
some
stage into electrical power. The articulating joint may comprise of universal
joints
mounted on rotary supports, knuckle joints, or any equivalent means.
WEC comprising of heaving buoys
An embodiment of the invention is shown in FIG. 9 and FIG. 10, comprising of
only three set of independent buoys 87. The WEC 86 shown in FIG. 9 and FIG. 10
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27
comprises of nacelle 82. Other embodiment of the WEC 86 may comprise a nacelle
22. The buoys 87 are symmetrically disposed and firmly secured around the
nacelle
82 or 22, by independent set of spars 27. Alternative to spars 27, such as a
structural platform may also be used to secure the buoys 87 to the nacelle 22
or 82.
The pitching movement required to operate the PTO, is the result of the
heaving
movements of the buoys 87 interconnected by the spars 27. The spars 27 are
designed to withstand the load during normal working condition and extreme
weather. Additional support frames may be use to reinforce the spars 27. The
use of
buoys 87, which is more compact, is also more cost effective than fabrication
of large
floating body of elaborate shape. The use of three set of buoys 87 allows the
WEC
86 to harness incoming waves from all direction with a fair degree of
symmetry,
compared to a perfectly circular floating body in the like of pontoon 21.
The buoys 87 are watertight hollow structures and may be constructed in a
number of ways. The buoys 87 may be made of metal or some synthetic material
such as fibreglass. Internal or external reinforcement structures may need to
be
provided for the buoys 87 to withstand the water pressure and to provide
support for
the coupling devices 23. The buoys 87 may also be constructed of soft
inflatable
material, such as rubber or some other similar synthetic material. The buoys
87 are
generally constructed as spheres which are better able to resist water
pressure, or in
any other shape most suitable for fabrication. The buoy 87 may comprise of
several
modular elements assembled together, so that the size may be easily adapted to
different power rating of WEC 86, or to facilitate repair. Mooring rings 33 or
alternative suitable mooring points are provided on the buoys 87, so that the
WEC
86 can be couple to other similar WECs 86 or anchored to the seafloor 45.
Mooring
point may also be provided at the base of the spars 27 when the buoys 87 are
made
of material not suitable for such installation.
WECs 86 are coupled together in numbers, in order to form large power
generating systems. FIG. 11 shows a few interconnected WECs 86 floating on the
ocean surface 35, connected by an underwater transmission cable 26 to the
electrical grid on land. The WEC 86 may comprise of nacelle 22 or 82. The WEC
86
are coupled in a similar manner described earlier to couple WECs 20, which
allow
each of the WECs 86 to heave and pitch independently. The coupling device 23
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shown in FIG. 11 comprises of marine fenders 31, but may be constructed in
alternative ways, comprising of various coupling devices and other means.
Appropriate cable supports 25 are provided where required for crossing of the
cable
bus 24 between the WECs 86. Higher numbers of WECs 86 may be secured
together in a similar configuration as shown in FIG. 11, or in some other
configurations. The cable bus 24 is shown secured on the surface of the spars
27,
but may be installed within internal cable ducts provided within the WECs 86.
Appropriate numbers of mooring lines 43 and mooring buoys 46 are used to
secure
the installation to the seafloor 45. The PTOs within larger installations may
be
connected in separate clusters by several networks of cable bus 24, and with
several
underwater transmission cables 26 for increased reliability.
A side view of interconnected WECs 86 fitted with nacelle 82 pitching in the
waves is shown in FIG. 12. The maximum pitching angle of the WECs 86 occurs
when the distance between the buoys 87 is about half the wavelength of the
waves.
The WEC 86 may be easily optimised for the wave characteristics at a given
location
by selecting the most suitable length of the spars 27, or the size of the
buoys 87.
With many buoys 87 heaving in close proximity and also acting as generators of
waves, the interference pattern of these waves are difficult to predict in
real time.
During operation of large numbers of interconnected WECs 86, some of the buoys
87 may experience little or no heaving motion, being in areas of destructive
interferences. However the operation of the WECs 86 is not permanently
affected, as
all the buoys 87 of a particular WEC 86 do not remain together for extended
period
in an area of destructive interferences, or in a state of synchronised heaving
motion.
Actually, the dip in power output of a few WECs 86 would be compensated by
other
WECs 86 within the installation experiencing more intense pitching movements.
The
constant changing direction of the waves due to the interference has no
significant
consequences on the power harnessing ability of the WECs 86, as each of the
PTOs
independently and almost instantly reacts to the changing direction of the
waves.
Embodiment of a WEC comprising of a plurality of PTOs
Another embodiment of the invention shown in FIG. 13 is a single WEC 90
comprising of a plurality of PTOs mounted within nacelles 22. Other
embodiments of
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WEC 90 may comprise of nacelles 82, with respective PTOs. The WEC 90 shown in
FIG. 13 is equivalent to the layout of interconnected WECs 86 shown in FIG.
11.
Both have the same general layout configuration, and the same numbers of PTO
within nacelles 22. Other embodiments of WEC 90 may be constructed to
different
s scale, according to different layout configurations, or with different
numbers and type
of PTOs. In general, embodiments of WEC 90 comprises of a plurality of spars
27
connecting a plurality of flotation buoys ( buoys 87, 91, and 92), and a
plurality of
PTOs, all permanently assembled together as a single unit, in a manner so that
the
PTOs can experience independent pitching movements. In any embodiments of the
WEC 90, the PTOs need to be firmly secured to at least two separate spars 27,
each
spar 27 resting on two different buoys so that the heaving motion of the buoys
can
cause the PTO to pitch from side to side. In order to harness waves from all
direction
most effectively, the PTOs are supported by three set of spars 27
symmetrically
disposed, with each spar 27 resting on a separate buoy, as shown in FIG. 13. A
given buoy within the embodiment in FIG. 13 would then accommodate a single,
or
up to three spars 27, each spar 27 secured to a different PTO.
The size of the buoys within embodiments of WEC 90 varies, depending on the
forces acting on them, and which depend on the numbers of spars 27 mounted on
them. The size of buoy 87 is designed to support only a single spar 27. The
buoy 91
is larger in order to support two set of spars 27, and provides twice as much
upthrust
compared to buoy 87. The buoy 92 is made even larger as it support three set
of
spars 27 and provide thrice as much upthrust, compared to buoys 87. The
embodiment shown in FIG. 13 comprises of a single larger buoy 92, but other
larger
embodiments of WEC 90, with different layout of buoys, may comprise of a
plurality
of buoys 92. It should be noted that the buoy 87 is used only for illustration
purposes
to appreciate the comparison between embodiments of the invention as shown in
FIG. 11 and FIG. 13.
When two or more spars 27 are mounted on a single buoy, a flexible base
coupling 93 is used to secure each of the spars 27 to the buoys. The base
couplings
93 allow each of the connected spars 27 to move independently from each other,
as
each of the spars 27 is connected through respective nacelles 22 or 82 to
other
buoys, which are heaving at different phase and pace relative to each other.
This
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arrangement enable the PTOs mounted in their respective nacelles 22 or 82, to
pitch
independently from each other. The base couplings 93 may be constructed of
various standard couplings devices such as universal couplings, elastomeric
couplings, spring couplings, bellow joints, and other similar devices. The
base
s couplings 93 may comprise of custom made mechanical devices or
constructed of
some soft and flexible material, such as textiles, rubbers, etc.
In large embodiments of the device 90 comprising of a high numbers of buoys
(buoys 87, 91, and 92), the spar 27 may include telescopic joint or suitable
linkage
mechanisms, to allow the length of the spars 27 to stretch or contract freely
by some
amount. This reduces the damping forces on the heaving movements of the buoys,
caused by the buoys themselves pushing upon each other through the connecting
spars 27. Cable bus 24 running across the flexible base 93 are installed in
appropriate supports to prevent damage and premature wear. The WEC 90 may be
coupled to other similar WECs, according to method discussed earlier by the
use of
coupling devices 23, to form even larger installations.
The invention has been described with reference to certain preferred
embodiments thereof. The invention is not limited to these preferred
embodiments,
and many other variations are possible Embodiments of the invention are also
not
intended to be limited by the drawings herein, but may be carried with other
choice of
designs, and methods of construction. The invention may have embodiments
within
a form which does not provide all the features and benefits set forth, as some
of the
features may be used or practice separately from others. It should be
understood
various omission, substitution, and changes in design may be made without
departing from the spirit of the invention. The invention is also not limited
by
construction material. Embodiments of the invention may be constructed with
material most suitable to the particular size of the embodiments and the
condition of
operation. The scope of the invention is indicated by the appended claims
rather by
the foregoing descriptions.
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