Note: Descriptions are shown in the official language in which they were submitted.
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APPARATUS AND METHOD
This invention relates to an energy converting array.
Harnessing power from tidal energy is a well-proven method of energy
extraction from
the marine environment. However, there are major challenges with achieving a
Levelized Cost of Energy (LCOE) to enable justifiable commercial development
of tidal
energy. The key challenges have been:
= high costs and complexity of tidal turbines,
= high costs and complexity of sea bed foundations,
= high levels of fatigue in the sea bed foundations leading to reduced
lifespan
and higher complexity/cost,
= high installation costs owing to the need for construction vessels
capable of
lifting large loads,
= Poor availability of suitable installation vessels in certain
geographical areas,
= complex and high logistic costs associated with transporting and handling
heavy turbines and associated balance of plant equipment,
= very high operation and maintenance costs owing to the need to mobilise
the
heavy-lift construction vessels,
= large expenditure on mobilisation/demobilisation costs for offshore
marine
spreads,
= very limited windows of availability to site for construction activity.
Many of the best tidal sites in the World do not have availability of Offshore
Construction Vessels (OCV's) thus leading to very high costs of mobilising
such
vessels over long distances.
Floating Platforms are widely regarded as a potential solution. However, this
can
increase cost and risk due to the high mooring loads, mooring fatigue, mooring
elasticity/ yawing (fish-tailing), high costs and statutory requirements for
the floating
plant, expensive anchoring solutions and complex dynamic cable hook-up between
the seabed and the floating device, cable fatigue, heavy weather/survivability
issues,
collisions with vessels/debris, etc. Furthermore, there are limited sites
where such
floating solutions can be used and represent a major hazard to marine
navigation. The
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moorings and associated equipment also take up a lot of seabed space and as
such
the packing density is relatively low leading to lower energy recovery from a
given
area.
Subsea installation techniques of tidal turbines have become in recent times
very
efficient and well proven, there is no reason to deviate from using seabed
mounted
turbines.
In addition, the track record of using subsea connectors and hook-up
methodologies
have been well-understood and performed successfully using wet mate
connectors.
According to a first aspect of the present invention, there is provided
apparatus
comprising an energy converting array including a support structure and a
plurality of
tidal energy converter modules mounted to the support structure, each module
including at least one energy converter device, the arrangement being such
that the
plurality of tidal energy converter modules are mounted to the support
structure in a
staggered arrangement, each module separated both horizontally and vertically
from
adjacent modules, the arrangement being such that there are respective
unhindered
substantially vertical lifting corridors for each module and respective
unhindered
substantially horizontal flow corridors for each module.
According to a second aspect of the present invention, there is provided a
method of
installation of an energy converting array comprising installing on a seabed
location a
support structure, lowering, sequentially, a plurality of tidal energy
converter modules,
each module including at least one energy converter device and mounting the
plurality
of tidal energy converter modules to the support structure in a staggered
arrangement,
each module separated both horizontally and vertically from adjacent modules,
the
arrangement being such that there are respective unhindered substantially
vertical
lifting corridors for each module and respective unhindered substantially
horizontal
flow corridors for each module.
Owing to these aspects, a foundation structure can be provided where
individual
submerged energy converter modules can be easily accessed for recovery and the
foundation/ support structure can remain in situ.
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Preferably, the energy converter devices are turbines and whose blades are
rotated
about an axis by movement of fluctuating tides.
By taking advantage of the reduced cost and reduced weight of relatively
smaller tidal
turbines available in recent years and integrating/clustering a plurality of
these turbines
into a single energy converter module on a cross beam structure and further
integrating the hook-up and power management system of the modules, it is
possible
to extract the same amount of energy at a lower capital expenditure and at a
considerably reduced weight. For example, a small turbine of 50-200KW capacity
and
weighing around 1-10 tonnes, means that 1MW of generating capacity can be
achieved with a total of 5-20 turbines at a turbine weight as low as 20
tonnes. These
loads are easily handled by standard low cost workboats, supply vessels and
barges.
Conventional larger turbines (>1MW) of this capacity are generally in the
range of 130-
200 tonnes. This has major advantages in terms of the installation, logistics,
operation
and maintenance, allowing for moving from larger heavy-lift installation and
recovery
vessels to smaller work boats, supply boats and barges without need for
offshore
construction vessels. This approach has major advantages in being able to
adapt
locally sourced work vessels and barges in areas where there are few offshore
type
construction vessels.
Additionally, relatively smaller turbines have been demonstrated to deliver
not only a
considerably higher power-generation: weight ratio but also a considerably
higher
power-generation: manufacture cost ratio.
Additional advantages are that fatigue of the support structure (foundation
fatigue);
wake losses; installation, operation and maintenance costs are all much
reduced.
Additionally the requirements for ballasting of the support structure required
to mitigate
sliding and overturning are significantly reduced with associated cost
savings.
The downside of a multi-turbine approach is increase balance of plant costs
around
integration of the multiple units into a common grid and integration into a
foundation
structure.
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The object of this invention is to address these issues through:
= development of a multi-turbine foundation structure at a reduced cost,
= lower balance of costs by integrating several turbines as a single unit,
= spread fatigue load into the base structure in a more balanced manner and
to
increase fatigue life of the turbine support structure,
= develop of a robust operation and maintenance strategy using workboat
sized
vessels, barges or supply boats that can be locally sourced worldwide,
= use tried and tested subsea operation hook-up methodologies,
= use a purpose-built Launch and Recovery System (LARS) on a dual skid
arrangement that can be easily transported Worldwide and integrated easily on
any flat deck work vessel, supply vessel or barge with no need for crane
vessels.
= use lightweight/ low cost handling and transport equipment.
.. In order that the present invention can be clearly and completely
disclosed, reference
will now be made, by way of example only, to the accompanying drawings, in
which:-
Figure 1 is a perspective view of an energy converting array,
Figure 2 is a side view of the array of Figure 1,
Figure 3 is a rear view of the array of Figure 1,
Figures 4 to 9 show perspective views of stages of installation of the energy
converting
array
Figure 10 is a perspective view showing in more detail parts of the array of
Figure 1 in
a detached configuration, and
.. Figure 11 is a view similar to Figure 4 with the parts of the array in a
mounted
configuration.
Referring to Figures 1 to 3, an energy converting array 2 comprises a support
structure
or foundation 4 and a plurality of tidal energy converter modules 6 mounted to
the
support structure 4, each module 6 including a plurality of energy converting
devices
in the form of turbines 8 mounted on a cross-beam structure 10, which in the
example
shown is a wing-like cross-beam structure.
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Referring to Figures 4 to 9, during installation, each module 6 is lowered
from a surface
vessel or barge 14 onto the support structure 4 which has previously been
anchored
to a seabed SB location. The modules 6 are arranged to be mounted to the
support
structure 4 in a staggered pattern to separate adjacent or neighbouring
modules 6
both horizontally and vertically, to allow for unhindered access for
installation and
recovery and for unhindered flow of water through the turbines at different
levels
thereby optimising the energy extraction from the volumetric flow of water
through the
space occupied by the array 2. Referring back to Figure 2, arrows 7 indicate
unhindered substantially vertical lifting corridors for each module 6 to allow
for
unhindered access for installation and recovery and arrows 7' indicate
unhindered
substantially horizontal flow corridors for each module 6 to allow for
unhindered flow
of water through the turbines at different levels thereby optimising the
energy
extraction from the volumetric flow of water.
Referring specifically to Figures 4 and 5, each module 6 is preferably lowered
into the
water by way of a twin-davit system 12 mounted on the front-end or back-end
region
of the vessel or barge 14 and incorporating a carrying beam 16, substantially
the same
width as the cross-beam structure 10. The cross-beam structure 10 is
releasably
mounted to the carrying beam 16. The carrying beam 16 attached to the module 6
is
attached to lift wires 18 via a launch and recovery system frame (LARS frame).
The
twin-davit system 12 comprises the launch and recovery system and a sea-
fastening
arrangement for secure sea transport of the modules 6 and is designed so as to
be
capable of being fitted to the vessel 14, thus removing the need for any
cranes or other
large-scale lifting equipment. The lift wires 18 originate from first winch
drums 20. In
addition, two stabilising cables 22 are advantageously attached from amidships
of the
vessel 14 to the end regions of the carrying beam 16 to allow full control of
the lift at
all stages. The stabilising cables originate from second winch drums 24. The
stabilising cables 22 allow for launching of the module 6 in non-optimal,
adverse
weather conditions as the pendulum effect caused by high wind forces can be
reduced
owing to reduced working heights (as compared to cranes) and two points of
attachment with the two stabilising cables 22. As a result, the path the load
(the module
6) takes is much more controlled through the splash zone, through a column of
water
and during locating of the module 6 onto the support structure 4. In good
weather
conditions, use of the stabilising cables 22 may not be needed.
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Figure 6 shows the module 6 attached to the carrying beam 16 and part way
through
the water column to mate with the support structure 4. Figure 7 shows arrival
of the
module 6 at the support structure 4 at the desired mating position. The module
6 is
located or stabbed onto the support structure 4 by way of a stabbing
arrangement
discussed in more detail hereinbelow. Figure 8 shows the carrying beam 16
disengaged from the module 6 now connected to the support structure 4 and
being
raised back to the vessel 14 through the water column by the twin-davit system
12 for
being releasably connected to a further module 6 for installation or, as
shown,
.. completion of the installation task. The carrying beam 16 is released from
the module
6 by a hydraulic ram releasing a pin which secures the lifting cables through
a pad-
eye arrangement. The stabilising cables 22 remain attached to the module 6
throughout the operation.
Figure 9 shows a completed installation of the array and ready for use once
all the
electrical connections have been made.
Referring to Figures 10 and 11, each module 6 is located or stabbed onto the
support
structure 4 via an arrangement of stabbing guides 24 on the cross-beam 10,
increasing
the tolerance (in the version shown this tolerance being given by a frusto-
conically
shaped channel) for reception of a corresponding mating element 26 on end
regions
of mounting struts of the support structure 4. Intelligent arrangements such
as subsea
cameras, acoustic positioning systems, sonar based reference systems mounted
on
the lifting arrangements mean that expensive work-class Remote Operated
Vehicles
(ROVs) are not required. The module 6 may be mounted to the support structure
4 via
a remote locking pin arrangement actuated from the LARS frame. Additionally, a
wet
mate connector arrangement for the electrical hooking-up of the module 6 is
also
actuated from the LARS frame.
When one or more modules 6 require maintenance and/or repair, the vessel 14
can
return to the site and by way of the twin-davit system 12 with its LARS frame
can lower
the carrying beam 16 to engage with the desired module 6 on the support
structure 4.
Owing to the staggered arrangement of the modules 6 on the support structure 4
there
is no part of the array 2 that hinders removal of the module 6 through the
water column
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back to the vessel 14. The same applies to the re-connection of the module 6
after the
required maintenance and/or repair has taken place.
The modules 6 may be designed to create some downforce onto the support
structure
4 while simultaneously augmenting the flow around the turbines 8 by nature of
fairing
of the wing-like cross-beam 10. The support structure 4 may be in the form of
a tripod,
a duo-pod, or a quadro-pod structure and may be fixed into the seabed by
drilling into
the seabed or rest on top of the seabed by way of a gravity base/modular
gravity base.
The bracings of the support structure 4 may further include fairings so as to
augment
.. flow of water into the turbines 8. The turbines themselves may be suspended
from the
cross beam 10 (as shown), fixed above the cross-beam or be integrated into the
cross-
beam.
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