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

l 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. 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 1 MW 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 (>1 MW) 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. 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 1 1 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. 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. 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 1 1 , 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 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 crossbeam.