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EP-4323643-B1 - OFFSHORE WIND TURBINE WITH A FLOATING PLATFORM

EP4323643B1EP 4323643 B1EP4323643 B1EP 4323643B1EP-4323643-B1

Inventors

  • STIESDAL, HENRIK

Dates

Publication Date
20260506
Application Date
20220407

Claims (9)

  1. An offshore wind turbine system comprising a wind turbine (8) in combination with a floating platform (1), the platform (1) comprising a tower support (10) that carries a tower (2) of the wind turbine (8), the tower (2) carrying a wind rotor; wherein the platform (1) comprises three buoyancy modules (6) providing buoyancy to the platform (1) when in water, the three buoyancy modules (6) being arranged in a triangular configuration in corners (5A, 5B, 5C) of an isosceles triangle (9), optionally equilateral triangle, the triangle (9) having a base line (3) and two equally long sides (4A, 4B) extending from two base corners (5B, 5C) at ends of the baseline (3) and meeting at a top corner (5A) of the triangle (9), wherein the platform (1) comprises a frame of braces (12A, 12B, 13A, 13B, 15) rigidly connecting the buoyancy modules (6) with the tower support (10) in an approximate tetrahedral configuration, characterized in that the center axis of the tower (2) is located - on the baseline (3) or at a distance (X1, X2) from the baseline (3), the distance being in the range of 0-15% of the length L of the baseline (3); - equidistant to the base corners (5B, 5C) or deviating from such equidistant configuration by less than 10% of L.
  2. System according to claim 1, wherein the center axis (2A) of the tower 2 is located outside the triangle (9).
  3. System according to claim 1, wherein the center axis (2A) of the tower 2 is located inside the triangle (9).
  4. System according to any one of the preceding claims, wherein the platform (1) comprises a frame of braces (12A, 12B, 13A, 13B, 15) rigidly connecting the buoyancy modules (6) with the tower support (10), wherein the frame comprises a planar arrangement of braces (12A, 12B, 13A, 13B) of: - a first support brace (12A) connecting the tower support (10) with the buoyancy module (6) at the top corner (5A); - a further support brace (12B) to each of the buoyancy module (6) at the base corners (5B, 5C), connecting them rigidly to the tower support (10); - additional braces (13A) and (13B) extending from opposite sides of the first support brace (12A) towards the buoyancy modules (6) at the base corners (5B, 5C) and forming a triangular configuration with the further support brace (12B) or further support braces (12B), wherein the frame further comprises stabilizer braces (15) outside the plane of the planar arrangement (12A, 12B, 13A, 13B), the stabilizer braces (15) connecting the tower support (10) with the three buoyancy modules (6).
  5. System according to claim 4, wherein the first support brace (12A) and the further support brace (12B) or further support braces (12B) connect to the base of the tower support (10), and the stabilizer braces (15) to an upper part of the tower support (10)
  6. System according to any preceding claim, wherein the buoyancy modules (6) are dimensioned for reaching downwards into water to a depth of no more than 8 m for a wind turbine having a weight of 2,000,000 kg, when the platform (1) at the top corner (5A) is provided with a ballast having a weight that is in the range of 30-50% of the weight of the wind turbine.
  7. System according to any preceding claim, wherein the center axis (2A) is located at a distance (X1, X2) from the baseline (3), the distance being in the range of 0-10% of the length L of the baseline (3), and deviating from the equidistant configuration by less than 5% of L.
  8. System according to any one of the preceding claims, wherein the center axis of the tower (2) is located equidistant to the base corners (5B, 5C).
  9. System according to any one of the preceding claims, wherein the buoyancy module (6) comprises a plurality of buoyancy tanks.

Description

Field of the Invention The present invention relates to a floating platform for a wind turbine. In particular, it relates to a wind turbine and floating structure as disclosed in the preamble of the independent claim. Background of the invention Description of Prior Art For floating platforms for offshore wind turbines, triangular shapes are often preferred due to their high degree of stiffness relatively to size and, thus, also with respect of the necessary material, which is substantial for large wind turbines. Examples are given in WO 2017/157399, WO 2009/064737 A1 and US 2014/060411 A1. In triangular floating platforms, each corner of the triangle typically comprises one or more vertical buoyancy columns, and the wind turbine tower is typically positioned in the center of the triangle. However, for large wind turbine towers, this arrangement implies challenges for the assembly, since the assembly crane has to reach from the periphery of the platform to the center of the platform, which can be up to 35 m or more. In some configurations of triangular floating platforms, it has been preferred to position the wind turbine above one of the corners, since it can then be easily reached by the crane. A corner position has turned out not to be optimal, however, since the added weight of the turbine on one corner needs to be compensated by similar weight added to the two other corners. Installing a 2000-ton turbine on one corner thereby leads to a need to add 1000 tons of ballast at each of the two other corners. This significant addition of balancing ballast typically leads to an undesirable draft, which will often exceed 12 m. A draft not exceeding 8 m would be preferable, since this significantly expands the number of ports available for floating offshore wind installations. It is the objective of the invention to disclose a configuration of a triangular floating offshore wind platform that significantly reduces the crane reach required for turbine installation while at the same time maintaining a moderate draft. Summary/Description of the invention It is an objective of the invention to provide an improvement in the art. In particular, it is an objective to provide an improved configuration for floating offshore platforms. This objective and further advantages are achieved with a system and method as described below and in the claims. In short, the objective is achieved with an offshore wind turbine system comprising a wind turbine in combination with a floating platform. The platform comprises three buoyancy modules in corners of a triangular configuration. The tower is located off-centered near a baseline of the triangle midway or almost midway between two buoyancy modules that are located at the ends of the baseline. The term "buoyancy module" is used for an element that provides buoyancy and/or stability to the platform. For example, the buoyancy module is a buoyancy tank or comprises a plurality of buoyancy tanks fitted together. Optionally, a buoyancy module comprises or is a vertical or near-vertical cylinder, a group of two or more vertical or near-vertical cylinders, or other configuration of relevant vertical or near-vertical vessels that are located at the corners of the triangular configuration and can provide buoyancy and/or stability to the platform. As compared to the prior art, where the tower is supported in the center of a triangular configuration, the presented construction significantly reduces the outreach of the crane used to install the wind turbine on the platform. As compared to the prior art, where the tower is supported in a corner of a triangular configuration, the presented construction requires less ballasting to counterbalance the weight of the load of the wind turbine, as not one but two buoyancy modules are used to support the turbine. This reduces the operational depth when the turbine is installed. For example, installing an offshore wind turbine with a power rating of 15 MW would typically require a water depth in the order of 12 m for a corner location of the wind turbine, whereas this presented construction only requires a depth in the order of 8 m, seeing that two corner buoyancy modules, one at each end of the baseline, support the tower. It is pointed out that this typically implies that the third buoyancy module is provided with some ballast to balance the platform, for example a ballast on the order of one-third to two-thirds of the weight of the wind turbine. In more detail, the offshore platform comprises a tower support, for example tower support column, which carries the tower of the wind turbine, the tower carrying a wind rotor. The platform comprises three buoyancy modules. For example, each module comprises a group of buoyancy members, for example a group of two, three or more buoyancy members, such as buoyancy tanks. The buoyancy modules are lighter than water and provide buoyancy to the platform when in water. The three modules are arranged in a triangular c