System and method for floating structure and power cable

Abstract

A system comprising a renewable power floating structure (1) arranged in a body of water, and a power cable (4) extending from the floating structure (1) into the body of water and along the seabed (3). The power cable (4) extends from the floating structure (1) for a first portion (41) of its length, extends in a catenary shape to an imparting element (6) providing buoyancy to the power cable (4) and a second portion (42) of the power cable (4) extends from the imparting element (6) to a tethered point (7) of the power cable connected to the seabed (3) and a third portion (43) of the power cable (4) extends from the anchored point (7) to a touch down point (10) of the power cable (4) where the power cable (4) is laying on the seabed (3). That the second portion (42) is forming a curved configuration of concavity down turned towards the seabed (3) and the power cable continuing this curvature in the third portion (43) of the power cable (4) to the touch down point (10) of the power cable (4) when projected in a vertical plane comprising a first portion connection point (5) to the structure (1) and the anchored point (7) of the power cable (4).

Description

[0001] System and method for floating structure and power cable

[0002] Technical Field

[0003] The present invention relates to a system and method of providing a power cable laying configuration for a floating offshore structure. Especially for a floating offshore structure with a windmill or wind turbine arranged on the floating structure which experiences large positional offset while being anchored to the seabed.

[0004] Background

[0005] There is a need for developing ways of harvesting renewable energy, and a possible way is to provide wind farms positioned offshore. There is then also a need to move these windfarms to areas where they no longer are bottom fix structures, but rather floating structures that form the basis for each wind turbine in the wind farm. The wind mills of such a wind farm will each be arranged on a floating offshore structure which then will be anchored to the seabed. For offshore wind mills there is a need to provide inter array cables to transport the energy harvested from each wind mill and transport this energy to an offshore user or to an export line to shore.

[0006] Floating wind mills will due to the inherent influence of the wind that they are facing and harvesting the energy from, move and in shallow water depths up to around 150-200 meters the floating structure may experience floater offsets that are up to 50% of the water depth. Specifically for water depths less than 120 meter this will be a specific issue. Hence the inter array cable for exporting the generated electricity will need to accommodate for large dynamic behaviours. If the power cable is laid with a conventional S-shape configuration of the power cable from the floating structure to the seabed, which is similar to the reverse pliant wave or lazy wave for risers, umbilicals or pipelines, movement of the floating structure in the direction towards the touch down point of the power cable will result in the radius of the bottom part of the S, experiencing curvature issues with a smaller radius, exceeding the allowable minimum bend radius (MRB) of the product, hence reducing life span and possibly damage to the power cable.

[0007] The present invention seeks to reduce or alleviate the impact the positional offset the offshore structure has on the power cable life span. There are different laying principles for pipelines offshore, however these principles are developed and configured for pipelines where there is internal fluid transport within the pipeline, and pipelines will inherently act and experience fatigue differently than a power cable. It is desirable to provide an improved offshore renewable power floating system and method of providing such systems.

[0008] SUMMARY

[0009] It is an object of the present invention to provide a system comprising a floating structure and a power cable, a wind farm comprising such a system, and a method of installing a cable for a floating structure. This object can be achieved by the features as defined by the independent claims. Further enhancements are characterised by the dependent claims. The invention is defined by the claims.

[0010] In a first aspect of the invention, a system comprising a renewable power floating structure (e.g. a floating structure which supports a renewable power source or generator) arranged in a body of water is provided. The system comprises a power cable, extending from the floating structure into the body of water and along the seabed. The power cable comprises a first portion, a second portion and a third portion. The power cable (e.g. extending from the) floating structure for a first portion of its length, extends in a catenary shape to an imparting element providing buoyancy to the power cable. In other words, the first portion of the power cable extends from the floating structure to a buoyant imparting element, wherein the first portion forms a catenary shape. The second portion of the power cable extends from the (e.g. buoyant) imparting element to a point of the power cable connected (e.g. anchored) to the seabed. The third portion of the power cable extends from the anchored point to a touch down point) of the power cable where the power cable is laying on the seabed. The second portion forms a curved configuration of concavity down turned towards the seabed and the power cable continues this curvature in the third portion of the power cable to the touch down point of the power cable when projected in a vertical plane comprising a first portion connection point to the structure and the anchored point of the power cable. Optionally, the vertical plane is a plane perpendicular to the seabed that bisects the touch down point and the first portion connection point.

[0011] The renewable power source or generator could be a wind turbine, a wave harvesting solution or a tidal harvesting solution or a combination of these. All of these will experience dynamic influence of the energy form they are made to harvest which will impact the floating structure and give it a dynamic movement pattern. The present invention is thus specifically relevant for floating structures with a wind turbine arranged on the floating structure, as the floating structure will experience large dynamic movement or positional offset as the wind interact with the floating structure and the tower with the wind turbine. The movement of the structure is dependent of the shape and form of the structure and also on the mooring solution. However, wind turbines will be positioned in an area which has a main dominant wind and environmental influence direction or directions. The connection point of the power cable to the floating structure is based on the floater geometry and layout, there among also the mooring solution. The floating structure will have a “nominal” position which is the baseline position for the structure. However, it will be appreciated that the floating structure can move and positional offsets will be present dependent on geometry of the structure, the mooring solution, wind influence, other environmental influences as waves and water movements etc.. Furthermore, the connection of the power cable to the floating structure and the nominal point of the floating structure will depend on the structure geometry and the main dominant wind and environmental impact directions. The floating structures movement out of the nominal position, the positional offset, of the floater will be of different horizontal lengths around the floating structure nominal position, where the most extreme position would be in the main dominant wind direction.

[0012] The power cable thus extends from the floating structure into the body of water and along the seabed. This cable may thus be used to export energy harvested on the floating structure. This “inter array” power cable or power cable in general, can extend from the floating structure into the body of water and, for a first portion of its length, extend in a catenary shape to one or more imparting elements or buoyancy elements which provides buoyancy to the power cable attached thereto.

[0013] Optionally, the system comprises a plurality of (e.g. separate) buoyancy elements attached to or incorporated into the power cable. Optionally, the power cable further comprises a buoyant portion between the first portion and the second portion, where the buoyant portion is attached to the one or more buoyant elements.

[0014] The second portion of the power cable extends from the buoyancy element(s) to a tethered point, e.g. the point of the power cable that is connected (e.g. anchored) to the seabed (e.g. via a tether attached to an anchor). The third portion of the power cable extends from the tethered point to a position where the power cable engages with the seabed.

[0015] Optionally, the second portion of the power cable includes the buoyant element(s), which may be divided over a length of the second portion of the power cable, forming a part of the second portion or forming the whole of the second portion.

[0016] Optionally, the power cable may be connected (e.g. anchored) to the seabed by a clamp attached to the power cable at the tethered point. Optionally, the clamp is connected to a foundation structure or anchored to the seabed via a tether or similar. This can also be called a hold-down system. The tethered point of the power cable, anchored to the seabed, is limited in the distance it can move away from the seabed but can move towards to seabed. Put another way, the tethered point has a maximum distance from which is can vertically move away from the seabed. As the hold-down system is via a tether / sling, the Touchdown Point (TDP) of the power cable can change since the clamp can move up / down and also laterally in the water column. Because of this, the power cable at the TDP location could also move laterally on the seabed. Alternatively, the point anchored to the seabed may have limited to substantially no movement on the seabed (e.g. be a more fixed point where the power cable is fixed to a bottom structure and in this instance the TDP is more fixed).

[0017] As discussed herein, the second portion curves downwardly towards the seabed and the third portion has a curvature that is continuous with the curvature of the first portion without passing through an inflection point. Put another way, the power cable has a continuous curvature between the second portion and the third portion when the curvature of the power cable is projected onto a plane perpendicular to the seabed. For example, the plane perpendicular to the seabed may bisect the point (e.g. connection point) at which the power cable connects to the floating structure and the tethered point where the power cable is connected (e.g. anchored) to the seabed.

[0018] The second portion of the power cable thus may be considered to form a curved configuration of concavity down-turned towards the seabed when projected into a vertical plane comprising a first portion connection point to the structure and the anchored point of the power cable. The power cable may also thus be considered to continue this curvature direction into the third portion of the power cable, until a fourth portion, where the power cable extends along the seabed. The power cable may thus form a substantially U-shape from the buoyancy element(s) to the point where the power cable is resting on the seabed.

[0019] In other words, the second portion of the power cable may be considered to form a curve towards the seabed due to the buoyancy at both ends (closest to floater and furthest away from floater. The third portion of cable (connected to the second portion furthest from the floater) thus may be considered to incorporate a bend which continues in the same direction towards the seabed.

[0020] Optionally, the curvature of the third portion of the power cable extends from the second portion towards the seabed in a direction towards the floating structure.

[0021] Optionally, the power cable further comprises a fourth portion (44), wherein the fourth portion engages with, and extends along, the seabed from the touch down point (e.g. the point at which the third portion engages the seabed) in a direction towards the floating structure. In other words, the third portion is curved such that the power cable curved back on itself and extends back towards the direction of the floating structure (although vertically displaced therefrom).

[0022] Such a configuration of the power cable from the floating structure to where it is laying on the seabed is similar to what is called a pliant wave configuration developed for risers or pipelines. However, the settings are very different giving different behaviour of the element extending from the floating structure to the seabed and the element extending from the floating structure to the seabed is also different. A pipeline or riser is open in the middle or within, for transportation of fluids while a cable transmitting electrons don’t have that open void in the power cable for transportation of a fluid. That giving different behaviour both in relation to fatigue and buckling issues.

[0023] By having the power cable configured so that it from the point where it is anchored to the seabed extend backwards underneath of itself, or with other word extends in a direction backwards towards the floater until it is resting on the seabed, is especially beneficial for a cable for a floating wind installation. As the floating structure moves out from its nominal position in a direction towards the power cable anchoring point, due to environmental effects, the power cable experience “an opening” of the bend, resulting in larger curvatures between the anchoring point of the power cable and the location where the power cable rests on the seabed . The point of the power cable anchored to the seabed will move away from the point of the power cable where it is touching down on the seabed. This gives that the bend of the third portion of the power cable will open up, get a larger bending radius and this is beneficial for the power cable.

[0024] For the same given floater offset, a cable with an S-Shape / Lazy Wave / Reverse Pliant Wave Configuration would see the bend in the power cable between the clamp and the TDP “tightening” i.e. larger curvatures, the curvature radius becoming smaller, and as such could impact the service life / integrity of the product.

[0025] By having such a cable configuration one can allow larger positional offsets of the floating structure than for other configurations as for instance a lazy wave or reverse pliant wave cable. This meaning that the anchoring system of the floating structure can be dimensioned to allow larger movements while still keeping the life expectancy span of the power cable.

[0026] Optionally, the third portion of the power cable may extend from the second portion, initially at least for a part in a direction towards the floating structure. The power cable may be positioned such that it forms a U-shape of the second and third part of the power cable, where the II is laying on the side. The two legs of the II may be positioned directly above each other or they may be arranged so that they form a U-shape when projected in a horizontal plane.

[0027] Optionally, the third portion of the power cable may extend from the second portion towards the floating structure until its touch down point on the seabed where it engages with the seabed. Optionally, the fourth portion of the power cable extends along the seabed in a mainly straight line, e.g. continuing in the same direction as the third portion, e.g. towards the floating structure.

[0028] Alternatively, the fourth portion may comprise a bend such that the direction of the power cable along the seabed is altered. Preferably, the bend is in a plane parallel to the seabed such that the power cable substantially maintains contact with the seabed along the bend of the power cable. The fourth portion of the power cable may be considered to be a static cable as it rests on the seabed and is not moved by movement of the floating structure or by environmental impact, i.e. it is stable on the seabed. The touch down point of the power cable is not a fixed point and thus may be considered to be a part of the third portion. The touch down point will be dependent of the movement of the floating structure and the environmental impact.

[0029] Optionally, the power cable may be connected to the floating structure at a point of the floater facing away from the dominant prevailing wind direction and / or dominant prevailing current direction. Alternatively, it may be connected to the floating structure on the half of the structure facing away from the dominant prevailing wind direction, when the floating structure is provided in its nominal position.

[0030] Optionally, the floating structure may a three-legged floating structure. Alternatively the floating structure is a four legged structure in the shape of a star. The legs may be connected to each other by a deck arranged above sea level. The legs may be connected to each other by a structure arranged below sea level. The connection point of the power cable may be arranged between the legs of the structure or alternatively in connection with one of the legs of the structure. There are a number of different floater or floating structure designs whereby the product or cable entry point could be on the side of a column, between columns or on the back / side face. In the scenarios where the power cable configuration is aligned / closely aligned with the predominant environmental conditions, the way of connecting the power cable to the structure and laying it on the seabed as according to the invention, mitigates the product curvature issues seen due to the large floater positional offsets.

[0031] Optionally, a wind turbine may be arranged on the floating structure. There may be wave or tidal energy harvesting means on the floating structure.

[0032] Optionally, the system comprises: two or more renewable power floating structures arranged in a body of water, wherein each of the two renewable power floating structures support one or more wind turbines; and one or more power cables. Wherein each power cable comprises a first end connected to a first renewable power floating structure, and a second end connected to a different renewable power floating structure, such that each power cable provides an inter array cable between two wind turbines on two of the two or more renewable power floating structures.

[0033] In a second aspect of the invention there is provided a wind farm comprising a plurality of systems of the first aspect, wherein a first end of the power cable is connected to one floating structure and the second end of the same power cable is connected to another floating structure, forming inter array cables between the wind turbines arranged in a daisy chain configuration..

[0034] Optionally, a first end of the power cable is connected to one floating structure and the second end of the same cable is connected to another (e.g. different) floating structure. As such, a dynamic inter array cables (DIAC) is formed between the wind turbines arranged in a daisy chain configuration.

[0035] According to a third aspect of the invention there is also provided a method of installing a cable for a floating renewable energy installation, the method comprising wet parking a first end of the power cable which first end is connectable to the floating wind installation, further laying the power cable along the seabed with a clamp connecting it to the seabed in position and the rest of the power cable along the seabed, then pulling the first end up from the water, adding buoyancy elements and end protection to it, releasing it and pulling it into the floating structure for attachment to the floating structure.

[0036] Optionally, the method may comprise wet parking a first end of the power cable which first end is connectable to the floating wind installation, further laying the power cable along the seabed so it rests statically on the seabed, thereafter pulling the first end up from the water to a vessel, adding buoyancy elements and anchoring clamp elements to it, thereafter releasing it from the vessel and pulling it into the floating structure for attachment to the floating structure so that the power cable is forming a shape according to the invention as discussed above. Preferably, the floating structure should not be present in its nominal working position when initially wet parking the first end of the power cable. The wet parking of the first end and the power cable can be done in good time before the rest of the steps are performed. The process of wet parking the power cable end is fundamental for achieving a curvature of the power cable as according to the invention.

[0037] Optionally, when pulling the first end up from the water the vessel may also pull the power cable so that it is positioned above the rest of the power cable resting on the seabed.

[0038] Optionally, the initial wet parking of the power cable is done as a static cable. This meaning that there are not clamps or buoyancy elements attached to it, so that it acts as static cable laying on the seabed.

[0039] In a fourth aspect of the invention, a system is provided. The system comprising: a renewable power floating structure arranged in a body of water; and a power cable extending from the floating structure into the body of water and along the seabed, wherein the power cable comprises a first portion, a second portion and a third portion. Wherein the first potion extends from the floating structure to one or more buoyancy elements and adopts a catenary shape there between; wherein the second portion extends from the one or more buoyancy elements to a tethered point of the power cable, wherein the tethered point is connected to the seabed; and wherein the third portion of the power cable extends from the tethered point to a touch down point of the power cable, wherein the power cable engages with the seabed at the touch down point. Wherein the second portion curves downwardly towards the seabed with a curvature; and wherein the third portion has a curvature that is continuous with the curvature of the second portion such that there is no inflection point along the second portion or the third portion. It will be appreciated that embodiments and optional features relating to the first aspect (as described above) equally apply to the fourth aspect and are thus combinable therewith.

[0040] At least one of the above embodiments provides one or more solutions to the problems and disadvantages with the background art. Other technical advantages of the present disclosure will be readily apparent to one skilled in the art from the following description and claims. Various embodiments of the present application obtain only a subset of the advantages set forth. No one advantage is critical to the embodiments. Any claimed embodiment may be technically combined with any other claimed embodiment or embodiments.

[0041] Brief Description of the Drawings

[0042] Fig. 1a and 1b prior art showing pipeline riser laying configuration “pliant wave” and “reversed pliant wave”.

[0043] Fig. 2 showing a floating wind configuration for a cable in a nominal position.

[0044] Fig. 3a showing a near position of a cable configuration for a floating wind installation.

[0045] Fig. 3b showing a far position of a cable configuration for a floating wind installation.

[0046] Fig. 4 showing one possible wind wave configuration seen as a horizontal and vertical projection.

[0047] Fig. 5a-e steps in a laying procedure.

[0048] Detailed Description

[0049] In fig 1a and 1b there are shown two versions of a riser configurations between a floating structure and a wellhead for an oil gas well. A “pliant wave” configuration of the riser is to have the riser from the floating structure extending down and into the water forming a laying S with buoyancy elements in the one curvature, then the end of the S being tethered to the seabed with an anchor element taking the forced from the riser in the anchor instead of the wellhead. In the pliant wave configuration, the well is arranged below the floating unit, so the riser extend from the anchor and back on itself to a position below the floating structure as shown in the left part of fig. 1a. In the reversed pliant wave as shown in fig. 1b, the riser extends from the anchor and further away from the floating structure. These solutions are developed for riser configurations, for transportation of a fluid from or to a wellhead.

[0050] According to the invention there is provided a configuration for a power cable which is specifically relevant for offshore floating wind structures as they experience high positional offsets from a nominal position. A cable compared with a riser have different behaviour features both with regards to buckling, fatigue and stress.

[0051] In fig. 2 there is shown a cable configuration (lying in a plane perpendicular to the seabed), preferably for use in water depths around 70-150 meters. The floating structure 1 is arranged floating in the water with parts above the water surface 2.

[0052] From the floating structure 1 there is a cable 4 extending through the water column and to a position where it is laying on the seabed 3. The power cable extending into the water from a connection point 5 to the floater downwards and out into the water in a catenary shape to a buoyancy element 6. This part of the power cable forming the first portion 41 of the power cable 4. From the buoyancy element 6 the power cable 4 further extend downwards to a clamp 7 attached to the power cable 4. The part between the buoyancy element 6 and the clamp 7 being the second portion 42 of the power cable 4. The clamp 7 is anchored to the seabed 3 through a tether element 8 and an anchoring element 9. This fixing a maximum distance between the power cable 4 at the clamp 7 and the anchoring element 9 at the seabed, still allowing the power cable 4 with the clamp 7 to move relative the anchoring element 9. The power cable 4 then continues the curve from the anchoring point, the clamp 7 to a touch down point 10, where the power cable touch down and rests on the seabed. This part of the power cable is the third portion 43. The further extension of the power cable after the touch down point 10 when seen from the floating structure 1 the power cable 4 will rest on the seabed 3 and be a static cable not experiencing dynamic forces. This part of the power cable 4 is the fourth portion 44 of the power cable.

[0053] Depending on the position of the floating structure 1 from its nominal position the touch down point will wary somewhat. The forth portion 44 of the power cable starts from the point where the power cable is considered static laying on the seabed not experiences movement as such due to floating structure offset.

[0054] As can be seen from fig 2 the third portion 43 of the power cable 4 is extending in a direction towards the floating structure 1 , forming a laying U-shape of the power cable in a vertical projection. When seen in a horizontal projection it may form a line out from the floating structure to the clamp and then double back the same way towards the floating structure. There is also the possibility of it forming a II shape in the horizontal projection in a nominal position or when the floating structure moved to a side.

[0055] A nominal position of the floating structure 1 is to be understood to be the centre position of the floating structure 1 when it is not directly influence by wind or water, i.e. environmental loads. When the wind is blowing from the prevailing wind direction the floating structure 1 will be force out of the nominal position and in a direction of the anchoring element 9. This being the most frequent out of centre position, called the near position of the floating structure 1. The floating structure will also move in other directions dependent on wind influence, the opposite direction of the near position being what is called a far position.

[0056] Fig. 3 a-b show the floating structure 1 in respectively a near and far position, and show the influence the offset of the floating structure 1 have on the power cable 4 configuration. One can see that in both the near and far positions the power cable 4 keep the same configuration and the third portion 43 of the power cable will open up the curvature of the third portion of the power cable in the near position and close the curvature somewhat in the far position. In general a near position is also further away from a nominal position than the far position of the floating structure. This is beneficial for the power cable as the floating structure is more often in a near position than it is in a far position as the near position is based on the prevailing wind direction at the site of the wind turbine.

[0057] Fig 4a show the power cable 4 connected to a floating structure 1 in a perspective view, not to scale. Fig. 4b show a vertical projection in the vertical plane (as indicated with V in fig. 4a) and fig. 4c show a horizontal projection in the horizontal plane (as indicated with H in fig. 4a).

[0058] As can be seen, the power cable (4) of the present invention is not limited to being provided in a single plane (e.g. one single plane perpendicular to the seabed). As shown in Figure 4a and 4c, the fourth portion 44 can include a bend 45 which changes the direction of the power cable extending along the seabed. As such, the power cable can accommodate for large dynamic behaviours (e.g. from underwater currents and / or movement of the floating structure) without reduced function.

[0059] Fig. 5 a-e shows different steps in a cable laying process. Fig. 5a show the end of the power cable 4 with a bend restrictor 14 connected (e.g. being tied) to a clump weight 12 as it is to be wet parked on a pre-laid mattress 13, and fig 5b showing it laying on the mattress 13. Fig. 5c show both ends of the power cable 4 laying on mattresses 13, wet parked on the seabed 3. In fig. 5d a vessel 11 (not shown) have picked up the end of the power cable 4, attached the clamp 7, tether 8 and anchoring element 9 to form the anchoring of the power cable 4 and also added buoyancy elements 6 to the power cable so that part of the power cable floats in the body of water. The vessel 11 have in addition also moved the power cable 4 back on itself to form the basis for the wind wave cable configuration according to the invention. In fig. 5e a vessel 11 with a vessel hook up line 15 has connected to the end of the power cable 4, and in addition the floating structure 1 also have a floater hook up line 16 connected to the end of the power cable, being ready to be pulled in to the floating structure and connected to the equipment on the floating structure 1.

[0060] In the above the invention has been explained with non-limiting embodiments of the invention as defined in the attached claims.

[0061] A set of preferred embodiments is described below. Any of these embodiments, or parts of these embodiments, may be technically combined with any other embodiment or embodiments described herein.

[0062] In a first embodiment there is provided a system comprising: a renewable power floating structure arranged in a body of water, a power cable extending from the floating structure into the body of water and along the seabed, wherein the power cable comprises a first portion, a second portion and a third portion ; wherein the first potion extends from the floating structure to one or more buoyancy elements and adopts a catenary shape therebetween; wherein the second portion extends from the one or more buoyancy elements to a tethered point of the power cable, wherein the tethered point is connected to the seabed; wherein the third portion of the power cable extends from the tethered point to a touch down point of the power cable, wherein the power cable engages with the seabed at the touch down point; and characterized in that the second portion curves downwardly towards the seabed with a curvature; and wherein the third portion has a curvature that is continuous with the curvature of the second portion such that there is no inflection point along the second portion or the third portion. A second embodiment comprising the features of embodiment 1 , wherein the curvature of the third portion of the power cable extends from the second portion towards the seabed n a direction towards the floating structure.

[0063] A third embodiment comprising the features of embodiment 1 or embodiment 2, wherein the tethered point has a maximum distance from which is may move vertically from the seabed.

[0064] A fourth embodiment comprising the features of any one of embodiments 1 to 3, wherein the power cable further comprises a fourth portion, wherein the fourth portion engages with, and extends along, the seabed from the touch down point in a direction towards the floating structure.

[0065] A fifth embodiment comprising the features of any one of embodiments 1 to 4, wherein the fourth portion extends along the seabed in a substantially straight line.

[0066] A sixth embodiment comprising the features of embodiment 5, wherein the fourth portion comprises at least one bend such that the direction of the power cable extending along the seabed is altered.

[0067] A seventh embodiment comprising the features of any one of embodiments 1 to 6, wherein the power cable is connected to the floating structure at a point of the floating structure facing away from the dominant prevailing wind direction.

[0068] An eighth embodiment comprising the features of any one of embodiments 1 to 7, wherein the floating structure is a multi-legged floating structure.

[0069] A ninth embodiment comprising the features of any one of embodiments 1 to 8, wherein a wind turbine is arranged on the floating structure.

[0070] A tenth embodiment comprising the features of any one of embodiments 1 to 9, wherein the system comprises: two or more renewable power floating structures arranged in a body of water, wherein each of the two renewable power floating structures support one or more wind turbines; and one or more power cables; wherein each power cable comprises a first end connected to a first renewable power floating structure, and a second end connected to a different renewable power floating structure, such that each power cable provides an inter array cable between two wind turbines on two of the two or more renewable power floating structures.

[0071] In an eleventh embodiment, there is provided a wind farm comprising the features of embodiment 10, wherein the two or more renewable power floating structures are arranged in a daisy chain formation; and wherein the one or more power cables provide inter array cables between the wind turbines of the two or more renewable power floating structures.

[0072] In a twelfth embodiment a method of installing a cable for a floating renewable energy installation is provided, the method comprising wet parking a first end of the power cable, wherein the first end is connectable to a first renewable power floating structure, further laying the power cable along the seabed, connecting the power cable to the seabed with a clamp, then pulling the first end of the power cable up from the water, adding buoyancy elements and end protection to the power cable, and attaching the first end of the power cable to the floating structure.

[0073] The features of embodiments 1 to 12 may be combined in any suitable and / or desirable combination with any of the optional features and / or embodiments described above in relation to any one of the first, second, third or fourth aspects of the invention.

[0074] This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using the subsea template system and performing the methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.

[0075] List of reference numerals

[0076] 1 floating structure

[0077] 2 water surface

[0078] 3 seabed

[0079] 4 cable

[0080] 41 first portion

[0081] 42 second portion

[0082] 43 third portion

[0083] 44 forth portion

[0084] 45 bend

[0085] 5 connection point

[0086] 6 buoyancy element

[0087] 7 anchored point / clamp

[0088] 8 tether element

[0089] 9 anchoring element

[0090] 10 touch down point

[0091] 11 vessel

[0092] 12 clump weight

[0093] 13 mattress

[0094] 14 bend restrictor

[0095] 15 hook up line vessel

[0096] 16 hook up line floating structure

[0097] 17 wind turbine

Claims

Claims1. A system comprising: a renewable power floating structure (1) arranged in a body of water; and a power cable (4) extending from the floating structure (1) into the body of water and along the seabed (3), where the power cable (4) from the floating structure (1) for a first portion (41) of its length, extends in a catenary shape to an imparting element (6) providing buoyancy to the power cable (4) and a second portion (42) of the power cable (4) extends from the imparting element (6) to a tethered point (7) of the power cable connected to the seabed (3) and a third portion (43) of the power cable (4) extends from the anchored point (7) to a touch down point (10) of the power cable (4) where the power cable (4) is laying on the seabed (3); characterized in that the second portion (42) is forming a curved configuration of concavity down turned towards the seabed (3) and the power cable continuing this curvature in the third portion (43) of the power cable (4) to the touch down point (10) of the power cable (4) when projected in a vertical plane comprising a first portion connection point (5) to the structure (1) and the anchored point (7) of the power cable (4).

2. System according to claim 1 , wherein the third portion (43) of the power cable (4) extends from the second portion (42) towards the seabed (3) in a direction towards the floating structure (1).

3. System according claim 1 or claim 2, wherein the tethered point (7) has a maximum distance from which is may move vertically from the seabed.

4. System according to one of the previous claims, wherein the third portion (43) of the power cable (4) extends from the second portion (42) towards the floating structure (1) until its touch down point (10) on the seabed (3), where it continues in a fourth portion (44) of the power cable which rests laying on the seabed (3), extending along the seabed (3) in a mainly straight line or the fourth portion (44) is provided with at least one bend (45) on the seabed (3) altering the direction of the power cable (4) extending on the seabed (3).

5. System according to one of the previous claims, wherein the power cable (4) is connected to the floating structure (1) at a point of the floating structure (1) facing away from the dominant prevailing wind direction.

6. System according to one of the previous claims, wherein the floating structure (1) is a multi-legged floating structure.

7. System according to one of the previous claims, wherein a wind turbine is arranged on the floating structure (1).

8. System according to any one of the previous claims, wherein the system comprises: two or more renewable power floating structures arranged in a body of water, wherein each of the two renewable power floating structures support one or more wind turbines; and one or more power cables (4); wherein each power cable comprises a first end connected to a first renewable power floating structure, and a second end connected to a different renewable power floating structure, such that each power cable (4) provides an inter array cable between two wind turbines on two of the two or more renewable power floating structures.

9. A wind farm comprising a plurality of systems according to claim 7 or claim 8, wherein a first end of the power cable (4) is connected to one floating structure and the second end of the same cable is connected to another floating structure, forming inter array cables between the wind turbines arranged in a daisy chain configuration.

10. Method of installing a cable for a floating renewable energy installation; wet parking a first end of the power cable (4) which first end is connectable to the floating wind installation, further laying the power cable (4) along the seabed with a clamp connecting it to the seabed in position and the rest of the power cable along the seabed; then pulling the first end up from the water, adding buoyancy elements and end protection to it, releasing it and pulling it into the floating structure (1) forattachment to the floating structure (1) and attaching the first end of the power cable (4) to the floating structure (1) using the system according to claim 1.

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