Floating type offshore windmill system and method for building, disassembling, and maintaining the same

Abstract

To provide a floating type offshore windmill system including a structure which is helpful for achieving replacement of large components of a floating type offshore windmill.SOLUTION: A floating type offshore windmill system has a floating type offshore windmill, a main floating body, and a mooring body. The floating type offshore windmill includes: blades configured to receive wind; a hub to which the blades are fixed; a nacelle which stores a power generator for converting rotational energy of the hub into electric power; a tower supporting the nacelle; and a sub floating body supporting the tower. The main floating body is moored at a sea bottom by the mooring body and has a sub floating body insertion space which is fitted in the sub floating body. The sub floating body inserted into the sub floating body insertion space is connected to the main floating body in a manner that enables disconnection at the connection part with the main floating body.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a floating offshore wind turbine system having a separable floating structure, and to methods for constructing, dismantling and maintaining the same. [Background technology]

[0002] In recent years, wind power generation has been widely adopted worldwide as a measure to combat global warming. The locations of wind power generation facilities are expanding from land to offshore, and offshore installation locations are also expanding from shallow waters for bottom-fixed offshore wind turbines to deep waters for floating offshore wind turbines. However, because self-elevating vessels (jack-up vessels, JUVs) cannot be used in deep waters, it has been difficult to replace large parts during maintenance of floating offshore wind turbines, as these require large cranes on JUVs.

[0003] Therefore, the wind power generation facility in Patent Document 1 is described in the abstract as "a wind power generation facility having a tower that is installed on land or offshore and serves as a support for the generator, a nacelle that is installed on the tower and has the generator built in, and a rotor that is installed at one end of the nacelle and consists of a hub and blades that receives wind and converts it into rotational energy, wherein the wind power generation facility is characterized in that a winch is installed within the nacelle for transporting replacement parts for the generator between the land or offshore and the nacelle." This allows large parts inside the nacelle to be replaced using the winch inside the nacelle. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-110927 Summary of the Invention [Problem to be solved by the invention]

[0005] However, the winch in Patent Document 1 is only for replacing parts inside the nacelle, and is not capable of replacing large parts outside the nacelle, such as blades.

[0006] Therefore, an object of the present invention is to provide a floating offshore wind turbine system having a structure that is useful for realizing replacement of large components of the floating offshore wind turbine. [Means for solving the problem]

[0007] In order to solve the above problems, the floating offshore wind turbine system of the present invention is a floating offshore wind turbine system having a floating offshore wind turbine, a main floating body, and a mooring body, wherein the floating offshore wind turbine has blades that receive the wind, a hub to which the blades are fixed, a nacelle that houses a generator that converts the rotational energy of the hub into electricity, a tower that supports the nacelle, and a sub-floor that supports the tower, and the main floating body is moored to the seabed by the mooring body and has a sub-floor insertion space that fits into the sub-floor, and the sub-floor inserted into the sub-floor insertion space is connected to the main floating body at a connection part that allows it to be disconnected. [Effects of the Invention]

[0008] According to the floating offshore wind turbine system of the present invention, it becomes possible to realize replacement of large components of the floating offshore wind turbine. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a bird's-eye view showing an embodiment (barge type) of a floating offshore wind turbine system. [Figure 2] FIG. 1 is a side view of a floating offshore wind turbine system according to an embodiment. [Figure 3] 1 is a flowchart showing a method for constructing a floating offshore wind turbine system according to one embodiment. [Figure 4] A conceptual diagram showing the state of the main floating body or the sub-floating body at each step in Figure 3. [Figure 5A] A diagram showing how to pull out a non-self-supporting floating offshore wind turbine. [Figure 5B] A diagram showing how a free-standing floating offshore wind turbine is pulled out. [Figure 6] 1 is a flowchart showing a method for replacing a wind turbine in a floating offshore wind turbine system according to an embodiment. [Figure 7] A bird's-eye view of a tension leg platform floating offshore wind turbine system. [Figure 8] A bird's-eye view of a semi-submersible floating offshore wind turbine system. [Figure 9] Bird's-eye view of a spar-type floating offshore wind turbine system. [Figure 10] 10 is a flowchart showing a method for constructing a floating offshore system according to a modified example. [Figure 11] 10 is a flowchart showing a turbine replacement method for a floating offshore wind turbine system according to a modified example. [Figure 12] 10 is a flowchart showing a method for constructing a floating offshore system according to a modified example. [Figure 13] 13 is a conceptual diagram showing the state of the main floating body or the sub-floating body at each step in FIG. 12. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, an embodiment of the floating offshore wind turbine system of the present invention will be described with reference to the drawings.

[0011] Figure 1 is a bird's-eye view of a floating offshore wind turbine system 100 according to one embodiment of the present invention. The floating offshore wind turbine system 100 illustrated here is an offshore power generation system that is installed in a deep sea area at a depth of about 50 to 100 meters, converts the energy of offshore wind W into electricity, and transmits it to an onshore grid, and comprises a floating offshore wind turbine 1, a main float 2, a mooring body 3, an offshore cable 4, and a submarine cable 5. Each of these will be explained in detail below.

[0012] The floating offshore wind turbine 1 comprises blades 11 that receive offshore wind W, a hub 12 to which the blades 11 are fixed, a nacelle 13 that houses a generator that converts the rotational energy of the hub 12 into electricity, a tower 14 that supports the nacelle 13, and a sub-floating body 15 that is a base that supports the tower 14. Note that although the number of blades 11 in Figure 1 is three, the number of blades is not limited to this example.

[0013] The main float 2 is a float shaped to fit with the sub-float 15 of the floating offshore wind turbine 1, and is moored to the seabed by moorings 3 such as chains while floating on the sea surface SL. Note that Fig. 1 shows an example in which the main float 2 and the sub-float 15 are connected at a connecting part J to form a barge-type float. The method of connection at the connecting part J will be described later.

[0014] The marine cable 4 is an electric wire that relays the power generated by the generator in the nacelle 13, and the submarine cable 5 is an electric wire that transmits the generated power via the marine cable 4 to the land system.

[0015] FIG. 2 is a side view of the floating offshore wind turbine system 100 of FIG. 1 , showing the direction of the overturning moment M acting on the floating offshore wind turbine 1 when subjected to wind W. As shown here, when wind W blows from left to right in the figure, an overturning moment M is generated in the floating offshore wind turbine 1 in a clockwise direction in the figure. This overturning moment M generates a large shear force at the connection J between the sub-floor 15 and the main float 2 of the floating offshore wind turbine 1. To resist this shear force, the connection J is firmly connected in the vertical direction by bolts or welding. Therefore, the entire barge-type floater, which connects the sub-floor 15 and the main floater 2, is also affected by the overturning moment M. However, because the main floater 2 is moored to the seabed via the mooring structures 3, the barge-type floater as a whole can maintain an approximately horizontal posture (specifically, with a tilt of about 5°).

[0016] <Construction method for floating offshore wind turbine systems> Next, a construction method for the floating offshore wind turbine system 100 of this embodiment will be described using the flowchart in Fig. 3 and the conceptual diagram in Fig. 4. Note that in Fig. 4, configurations other than the main floating body 2 and the sub-floating body 15 are omitted from the illustration.

[0017] First, in step S1 of Figure 3, a construction company or the like installs the main float 2 in a desired sea area. Specifically, after towing the main float 2 to the desired sea area using a transport ship 6, a mooring body 3 is attached to the main float 2, and the main float 2 is moored to the seabed. Figure 4(a) is a conceptual diagram of the main float 2 after the work of step S1 is completed, viewed from the bottom left in Figure 1, or from the left in Figure 2. As shown here, a sub-float insertion space 21 is formed in the center of the main float 2 as a space intended for insertion of the sub-float 15. In addition, a notch 22 is formed in the upper part of the wall surface that contacts the sub-float insertion space 21. A space is formed inside the main float 2 for injecting ballast water, but at the time of step S1, no ballast water has been injected, or only enough ballast water has been injected to maintain the stability of the float, and since it is possible to inject more ballast water, the buoyancy of the main float 2 is large and the waterline (sea surface SL) of the main float 2 is at a relatively low position compared to the height of the main float 2.

[0018] Next, in step S2, the construction company or the like injects ballast water into the main float 2. This reduces the buoyancy of the main float 2. Figure 4(b) is a conceptual diagram of the main float 2 upon completion of the work in step S2. As shown here, the main float 2 sinks due to the weakening of its buoyancy, and the waterline (sea surface SL) of the main float 2 becomes higher relative to the height of the main float 2.

[0019] In step S3, the construction company or the like places the sub-float 15 of the floating offshore wind turbine 1 in a predetermined position in the sub-float insertion space 21 of the main float 2. Specifically, the construction company or the like uses the transport ship 6 to tow the floating offshore wind turbine 1 close to the main float 2, and then guides the sub-float 15 of the floating offshore wind turbine 1 to the back of the sub-float insertion space 21 of the main float 2. Figure 4(c) is a conceptual diagram of the main float 2 and the sub-float 15 after the work of step S3 is completed. As shown here, a protrusion 15a is formed on the upper part of the sub-float 15, which is shaped to fit into the cutout portion 22 of the main float 2. At this point, since the main float 2 is lowered more than it should be, there is a sufficient space between the underside of the protrusion 15a of the sub-float 15 and the upper surface of the cutout portion 22 of the main float 2, and there is no interference between the two. Therefore, construction workers or the like can smoothly insert the sub-floating body 15 into the sub-floating body insertion space 21 of the main floating body 2.

[0020] In step S4, the construction company or the like discharges ballast water from the main floating body 2. This causes the main floating body 2 to regain its original buoyancy. When the main floating body 2 regains its original buoyancy, the main floating body 2 rises relative to the sea surface SL. As a result, the cutout portion 22 of the main floating body 2 pushes up the protruding portion 15a of the sub-floor 15.

[0021] In step S5, the construction company or the like firmly connects the connection part J between the sub-float 15 of the floating offshore wind turbine 1 and the main float 2 using a releasable connection method such as bolts or welding. Figure 4(d) is a conceptual diagram of the main float 2 and the sub-float 15 upon completion of the work in step S5. By connecting the sub-float 15 and the main float 2 using the above procedure, it is possible to construct a floating offshore wind turbine system 100 of the type exemplified in Figures 1 and 2.

[0022] <Dismantling method for floating offshore wind turbine systems> Figures 3 and 4 explain the construction work of the floating offshore wind turbine system 100, but if a floating offshore wind turbine 1 has a broken large component such as a blade 11 and needs to be repaired in a port or other location, the floating offshore wind turbine system 100 can be dismantled using the following procedure.

[0023] That is, first, the bolts and welds are removed from the connection part J between the main float 2 and the sub-float 15 to release the connection between them, then ballast water is poured into the main float 2 to sink it, and then the sub-float 15 is pulled out of the sub-float insertion space 21 using a transport ship 6, thereby separating the floating offshore wind turbine 1 from the main float 2. The floating offshore wind turbine 1 pulled out from the main float 2 is then towed by the transport ship 6 to a port or land facility, where maintenance work such as repair and replacement of large parts is carried out using large cranes installed in the port or land facility. This has the special effect of allowing large parts that are difficult to maintain offshore to be transported to a port or land facility for maintenance.

[0024] Here, a method for extracting a faulty floating offshore wind turbine 1 from the main floater 2 will be explained using the side views of Figures 5A and 5B. Figure 5A shows a method for extracting a floating offshore wind turbine 1 that cannot stand on its own due to a large overturning moment M. In this example, a transport ship 6 is directly connected to the front of the floating offshore wind turbine 1, integrating the transport ship 6 and the floating offshore wind turbine 1. This allows the floating offshore wind turbine 1, which would overturn if it were to stand on its own, to be towed to the desired location in a stable state. On the other hand, Figure 5B shows a method for extracting a self-supporting floating offshore wind turbine 1. In this example, the floating offshore wind turbine 1 will not overturn even without the support of the transport ship 6, so the floating offshore wind turbine 1 can be towed while connected to the transport ship 6 via a towing chain 61.

[0025] <Method for replacing a wind turbine in a floating offshore wind turbine system> Next, we will explain a wind turbine replacement method that can be achieved by combining the construction and dismantling methods described above. The main float 2, which has few moving parts, has a longer lifespan than the floating offshore wind turbine 1, which has many moving parts. In addition, mooring the main float 2 to the seabed is a complicated task that requires a lot of man-hours. For these reasons, if the previous main float 2 can be reused when updating the floating offshore wind turbine system 100, the man-hours required for system updating can be significantly reduced.

[0026] Hereinafter, a method for replacing an old small floating offshore wind turbine 1A incorporated in a floating offshore wind turbine system 100 with a new large floating offshore wind turbine 1B will be described using the flowchart in FIG.

[0027] First, in step S11, the construction company or the like removes bolts and welds from the connection part J between the sub-float 15 and the main float 2 of the old floating offshore wind turbine 1A, and releases the connection between them.

[0028] Next, in step S12, the construction company or the like injects ballast water into the main floating body 2. This reduces the buoyancy of the main floating body 2. Therefore, the sub-floating body 15 and the main floating body 2 of the old floating offshore wind turbine 1A are in the relative relationship as shown in Figure 4(c).

[0029] In step S13, the construction company or the like pulls out the sub-floating body 15 of the old floating offshore wind turbine 1A from the sub-floating body insertion space 21 of the main floating body 2, as shown in FIG. 5A or 5B.

[0030] In step S14, the construction company or the like places the sub-float 15 of the new floating offshore wind turbine 1B at a predetermined position in the sub-float insertion space 21 of the main float 2. This corresponds to the work of step S3 in FIG.

[0031] In step S15, the construction company or the like discharges ballast water from the main floating body 2. This corresponds to the work of step S4 in FIG.

[0032] In step S16, the construction company etc. firmly connects the sub-floating body 15 of the new floating offshore wind turbine 1B to the connecting portion J of the main floating body 2 by bolts or welding. This corresponds to the work of step S5 in Figure 3.

[0033] According to the above procedure, the floating offshore wind turbine 1 of the floating offshore wind turbine system 100 can be updated from an old one to a new one without repeating the cumbersome task of mooring the main floating body 2 in a deep sea area.

[0034] <Modification> In the above, an example has been shown in which a barge-type float is formed by connecting the main float 2 and the sub-float 15, but other types of floats may be formed depending on the situation. For example, as shown in the bird's-eye view of Figure 7, a tension leg platform (TLP) type float may be formed, using tension moorings 31 instead of moorings 3, as shown in the bird's-eye view of Figure 8, a semi-submersible type float may be formed, or as shown in the bird's-eye view of Figure 9, a spar-type float may be formed.

[0035] Furthermore, although the above describes an example in which a space for injecting ballast water is formed inside the main float 2, a space for injecting ballast water may also be formed inside the sub-float 15. In this case, when constructing or dismantling the floating offshore wind turbine system 100, ballast water may be discharged from the sub-float 15 instead of injecting ballast water into the main float 2. This makes it possible to lower the relative height of the main float 2 with respect to the sub-float 15, just as in the case in which ballast water is injected into the main float 2. Similarly, instead of discharging ballast water from the main float 2, ballast water may be injected into the sub-float 15. This makes it possible to increase the relative height of the main float 2 with respect to the sub-float 15, just as in the case in which ballast water is discharged from the main float 2.

[0036] Furthermore, spaces for injecting ballast water may be formed inside both the main floating body 2 and the sub-floating body 15. In this case, ballast water may be discharged from the sub-floating body 15 at the same time as ballast water is injected into the main floating body 2, thereby lowering the relative height of the main floating body 2 with respect to the sub-floating body 15. Similarly, ballast water may be discharged from the main floating body 2 at the same time as ballast water is discharged from the main floating body 2, thereby raising the relative height of the main floating body 2 with respect to the sub-floating body 15.

[0037] That is, the floating offshore wind turbine system 100 may be constructed as shown in the flowchart of Figure 10. Step S21 is similar to step S1 in Figure 3, and a detailed description thereof will be omitted. In step S22, the construction company or the like adjusts the amount of ballast water inside the main float 2 and / or the sub-float 15, and adjusts the height of the main float 2 and / or the sub-float 15 relative to the sea surface to a height that allows the sub-float 15 to be placed in the sub-float insertion space 21. Also, step S22 may be performed before step S21. That is, before proceeding to step S23, the height of the sub-float 15 may be adjusted to a height that allows it to be placed in a predetermined position in the sub-float insertion space 21 of the main float 2. Step S23 is similar to step S3 in Figure 3, and a detailed description thereof will be omitted.

[0038] In step S24, the construction company etc. adjusts the amount of ballast water inside the main float 2 and / or the sub-float 15, and adjusts the height of the main float 2 and / or the sub-float 15 relative to the sea surface to a height that allows the sub-float 15 to be connected to the main float 2. Step S25 is similar to step S5 in Figure 3, and a detailed explanation will be omitted.

[0039] By connecting the sub-floating body 15 and the main floating body 2 in the above-described manner, the floating offshore wind turbine system 100 shown in Figs. 1 and 2 can be constructed.

[0040] The same can be said for the dismantling method of a floating offshore wind turbine system. That is, first, the bolts and welds are removed from the connection part J between the main float 2 and the sub-float 15 to release the connection between them, then the amount of ballast water inside the main float 2 and / or the sub-float 15 is adjusted to adjust the height of the main float 2 and / or the sub-float 15 relative to the sea surface to a height that allows the sub-float 15 to be pulled out from the sub-float insertion space 21, and then the sub-float 15 is pulled out from the sub-float insertion space 21 using a transport ship 6, thereby separating the floating offshore wind turbine 1 from the main float 2. Then, the floating offshore wind turbine 1 pulled out from the main float 2 is towed by the transport ship 6 to a port or an onshore facility, where maintenance work such as repair and replacement of large parts is carried out using large cranes installed in the port or onshore facility.

[0041] The same can be said about a method for replacing a wind turbine in a floating offshore wind turbine system. Below, a method for replacing an old small floating offshore wind turbine 1A incorporated in a floating offshore wind turbine system 100 with a new large floating offshore wind turbine 1B will be explained using the flowchart in Figure 11.

[0042] Step S31 is similar to step S11 in FIG. 6, and a detailed description thereof will be omitted.

[0043] Next, in step S32, the construction company etc. adjusts the amount of ballast water inside the main float 2 and / or the sub-float 15, and adjusts the height of the main float 2 and / or the sub-float 15 relative to the sea surface to a height that allows the sub-float 15 to be pulled out from the sub-float insertion space 22. As a result, the sub-float 15 and the main float 2 of the old floating offshore wind turbine 1A are in the relative relationship shown in Figure 4(c).

[0044] Steps S33 and S34 are similar to steps S13 and S14 in FIG. 6, and detailed description thereof will be omitted.

[0045] In step S35, the construction company etc. adjusts the amount of ballast water inside the main float 2 and / or the sub-float 15, and adjusts the height of the main float 2 and / or the sub-float 15 relative to the sea surface to a height that allows the sub-float 15 to be connected to the main float 2. This corresponds to the work of step S24 in Figure 10.

[0046] Step S36 is similar to step S16 in FIG. 6, and a detailed description thereof will be omitted.

[0047] According to the above procedure, the floating offshore wind turbine 1 of the floating offshore wind turbine system 100 can be updated from an old one to a new one without repeating the cumbersome task of mooring the main floating body 2 in a deep sea area.

[0048] In addition, the above example shows a case where a cutout 22 is formed in the upper part of the wall surface of the main float 2 that contacts the sub-float insertion space 21, and a protrusion 15a shaped to fit into the cutout 22 of the main float 2 is formed in the upper part of the sub-float 15. On the other hand, a protrusion 23 may be formed in the upper part of the wall surface of the main float 2 that contacts the sub-float insertion space 21, and a cutout 15b shaped to fit into the protrusion 23 of the main float 2 may be formed in the upper part of the sub-float 15. In the following, the sub-float 15 has a space inside for injecting ballast water.

[0049] Using the flowchart in Figure 12 and the conceptual diagram in Figure 13, we will explain the construction method of the floating offshore wind turbine system 100 of this modified example, in which a protrusion 23 is provided on the main float 2 and a cutout 15b is provided on the sub-float 15. Note that in Figure 13, configurations other than the main float 2 and the sub-float 15 are not shown.

[0050] Step S41 in Fig. 12 is similar to step S1 in Fig. 3, and detailed description thereof will be omitted. Fig. 13(a) is a conceptual diagram of the main floating body 2 after completion of the work of step S41, as viewed from the bottom left in Fig. 1, or as viewed from the left in Fig. 2. As shown here, a protrusion 23 is formed on the upper part of the wall surface that contacts the sub-floating body insertion space 21.

[0051] Next, in step S42, the construction company or the like discharges ballast water from the main float 2, or injects ballast water into the sub-float 15, or both. Step S42 may also be performed before step S41. That is, before proceeding to step S43, the height of the sub-float 15 may be adjusted to a height that allows it to be placed in a predetermined position in the sub-float insertion space 21 of the main float 2.

[0052] Here, because the main float 2 is moored to the seabed by the mooring bodies 3, there is little freedom to discharge ballast water from the stable moored state and raise its height relative to the sea surface. For this reason, in step S42, it is more desirable not to discharge ballast water from the main float 2, or to discharge it only to the extent that does not place excessive load on the mooring bodies, and to inject ballast water into the sub-float 15 and adjust the relative heights of the main float 2 and the sub-float 15.

[0053] In other words, in this modified example, adjustment of the relative height between the main float 2 and the sub-float 15 depends heavily on the ballast adjustment function of the sub-float 15. On the other hand, in the embodiment described in Figures 3 and 4, the main float 2 is lowered from a stable state in which it is moored to the seabed, so the above-mentioned restriction on the degree of freedom is small. In other words, by providing a cutout portion 2a in the main float 2 as in the embodiment described in Figures 3 and 4, it becomes possible to adjust the relative height from a stable state by injecting ballast water into the main float 2, and the ballast water adjustment function of the sub-float 15 can be reduced. This makes it possible to reduce the cost of the floating offshore wind turbine system 100.

[0054] In step S43, the construction company or the like places the sub-float 15 of the floating offshore wind turbine 1 at a predetermined position in the sub-float insertion space 21 of the main float 2. FIG. 13(b) is a conceptual diagram of the main float 2 and the sub-float 15 upon completion of the work in step S43. As shown here, the main float 2 has been adjusted to a relatively higher position with respect to the sub-float 15 in step S42. Also, as shown here, a notch 15b is formed in the upper part of the sub-float 15, shaped to fit with the protruding portion 23 of the main float 2. At this point, the main float 2 is more elevated than it should be, or the sub-float 15 is more submerged than it should be, so there is sufficient space between the underside of the protruding portion 23 of the main float 2 and the upper surface of the notch 15b of the sub-float 15, and there is no interference between them. Therefore, the construction company or the like can smoothly insert the sub-float 15 into the sub-float insertion space 21 of the main float 2.

[0055] In step S44, the construction company or the like injects ballast water into the main floating body 2, or discharges ballast water from the sub-floating body 15, or both. This causes the main floating body 2 to sink and the sub-floating body 15 to float. As a result, the cutout portion 15b of the sub-floating body 15 pushes up the protruding portion 23 of the main floating body 2.

[0056] Step S45 is similar to step S5 in Figure 3, and therefore a detailed description will be omitted. Figure 13(c) is a conceptual diagram of the main floating body 2 and the sub-floating body 15 upon completion of the work in step S45. By connecting the sub-floating body 15 and the main floating body 2 according to the above procedure, it is possible to construct the floating offshore wind turbine system 100 of the form exemplified in Figures 1 and 2.

[0057] <Effects of this Example> As described above, in the present invention, the floats of a floating offshore wind turbine system are composed of a main float that is moored to the seabed and a sub-float to which the wind turbine is fixed, and by connecting the main float and the sub-float in a detachable manner, even after the floating offshore wind turbine system has been installed offshore, it is possible to tow the wind turbine and the sub-float into a harbor or the like by disconnecting them. This makes it possible to replace large parts of the wind turbine using a large crane installed in the harbor or the like. [Explanation of symbols]

[0058] 100 Floating Offshore Wind Turbine System 1, 1A, 1B: Floating offshore wind turbines 11: Blade 12: Hub 13: Nacelle 14: Tower 15: Sub-float 15a:Protrusion 15b: Notch 2: Main float 21: Sub-floating body insertion space 22: Notch 23:Protrusion 2A Tension leg platform type main float 2B Semi-submersible main float 2C Spar-type main float 3: Mooring body 31: Tension mooring body 4: Maritime cable 5: Submarine cable 6: Transport ship 61: Towing chain

Claims

1. A floating offshore wind turbine system having a floating offshore wind turbine, a main floating body, and a mooring body, The floating offshore wind turbine comprises blades that catch wind, a hub to which the blades are fixed, a nacelle that houses a generator that converts rotational energy of the hub into electricity, a tower that supports the nacelle, and a sub-floating body that supports the tower, The main float is moored to the seabed by the mooring body and has a sub-float insertion space into which the sub-float is fitted, A floating offshore wind turbine system characterized in that the sub-floating body inserted into the sub-floating body insertion space is connected to the main floating body at a connection part in a manner that allows for disconnection.

2. The floating offshore wind turbine system according to claim 1, A floating offshore wind turbine system characterized in that a submarine cable that transmits the electricity generated by the generator to an onshore system is connected to the main float.

3. The floating offshore wind turbine system according to claim 1, A floating offshore wind turbine system characterized in that at the connecting portion, the protrusion of the sub-floor and the cutout portion of the main float overlap vertically, and the two are connected in the vertical direction by bolts or welding.

4. The floating offshore wind turbine system according to claim 1, A floating offshore wind turbine system, characterized in that the floating offshore wind turbine, which has been detached from the main floating body, can be towed by a transport ship.

5. The floating offshore wind turbine system according to claim 1, A floating offshore wind turbine system characterized in that by connecting the main float and the sub float, one of a barge-type float, a tension leg platform-type float, a semi-submersible float, and a spar-type float is formed.

6. 2. A method for constructing a floating offshore wind turbine system according to claim 1, comprising: mooring the main floating body to the seabed; Step A: adjusting the height of the main float and / or the sub float relative to the sea surface so that the sub float can be placed in the sub float insertion space; Placing the sub-floating body in the sub-floating body insertion space; Step B: adjusting the height of the main float and / or the sub float relative to the sea surface to a height that allows the sub float to be connected to the main float; connecting the main floating body and the sub-floating body; A construction method comprising:

7. 7. A method for constructing a floating offshore wind turbine system according to claim 6, comprising: The main float has a notch at the top of the wall surface that contacts the sub-floor insertion space, The sub-floating body has a protrusion shaped to fit into the cutout portion, Step A is a step of injecting ballast water into the main floating body and / or discharging ballast water from the sub-floating body, A construction method characterized in that step B is a step of discharging ballast water from the main floating body and / or injecting ballast water into the sub-floating body.

8. 7. A method for constructing a floating offshore wind turbine system according to claim 6, comprising: The main float has a protrusion on an upper part of a wall surface that contacts the sub-floor insertion space, The sub-floating body has a notch portion shaped to fit into the protrusion, Step A is a step of discharging ballast water from the main floating body and / or injecting ballast water into the sub-floating body, A construction method characterized in that step B is a step of injecting ballast water into the main floating body and / or discharging ballast water from the sub-floating body.

9. A method for dismantling a floating offshore wind turbine system according to claim 1, comprising: a step of releasing the connection between the main floating body and the sub-floating body; Step C: adjusting the height of the main float and / or the sub float relative to the sea surface to a height that allows the sub float to be pulled out from the sub float insertion space; Pulling out the sub-floating body from the sub-floating body insertion space; A dismantling method comprising:

10. A method for dismantling a floating offshore wind turbine system according to claim 9, comprising: The main float has a notch at the top of the wall surface that contacts the sub-floor insertion space, The sub-floating body has a protrusion shaped to fit into the cutout portion, A dismantling method characterized in that step C is a step of injecting ballast water into the main floating body and / or discharging ballast water from the sub-floating body.

11. A method for dismantling a floating offshore wind turbine system according to claim 9, comprising: The main float has a protrusion on an upper part of a wall surface that contacts the sub-floor insertion space, The sub-floating body has a notch portion shaped to fit into the protrusion, A dismantling method characterized in that step C is a step of discharging ballast water from the main floating body and / or injecting ballast water into the sub-floating body.

12. A maintenance method, comprising towing the floating offshore wind turbine, which has been pulled out from the main floating body by the dismantling method according to any one of claims 9 to 11, into a harbor for maintenance.

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