Offshore wind farm with a plurality of floating single-point mooring wind turbines

Description

[0001] The invention relates to an offshore wind farm comprising a plurality of floating single-point mooring wind turbines. In particular, the invention relates to an offshore wind farm comprising a plurality of floating single-point mooring wind turbines arranged within tiled sub-areas and a collection station connected to the floating single-point mooring wind turbines, which is connected to a power grid via a transmission line.

[0002] The design of wind farms is known in particular from WO 2012 / 048743 A1, CN 110 654 510 A, DE 10 2015 121 371 A1 and US 2013 / 152839 A1.

[0003] In particular, WO 2012 / 048743 discloses an offshore wind farm with wind turbines arranged in a star shape around a central station at equal distances and individually connected.

[0004] The wind turbines of an offshore wind farm with firmly anchored wind turbines are usually anchored by means of a Fig. 1 shown ring cabling according to a ring topology ( Fig. 1a ) or as radial cabling according to a line topology ( Fig. 1b ) connected to the power grid.

[0005] At the Fig. 1a In the ring cabling shown, several wind turbines 10 of an offshore wind farm 100 are interconnected to form a ring line 30, the two ends of which are connected to a collecting station 20, designed, for example, as a transformer platform, which is connected to a power grid by means of a central transmission line (not shown). With this cabling, the entire power of all wind turbines 10 arranged in the ring is transmitted via the cable 30. To transmit the sum of the electrical currents of the individual turbines, the use of a very thick cable is necessary, and the installation of the cable is very complex due to its weight and rigidity. A further disadvantage of the ring topology is that three medium-voltage switchgear units are required for each individual turbine in order to be able to continue operating the remaining turbines in the ring in the event of a defect or maintenance of one of the turbines.These switchgear systems require space and are complex to manufacture and install, and are also susceptible to failure.

[0006] Another possibility - as in Fig. 1b As shown, the wind turbines 10 of the offshore wind farm are to be connected in series according to the line topology and then routed to the collection station 20 via a cable 30. Compared to ring cabling, this arrangement has the disadvantage that if a line between the turbines fails, the turbines 10 located behind the failure, as seen from the collection station 20, can no longer be operated and must be switched off. At the same time, this arrangement requires multiple switchgears for each individual wind turbine, resulting in a high installation effort.

[0007] Although the total cable length required for the line topology is shorter than for the ring topology, the use of a very powerful, thick cable and the number of switchgears required result in high material and labor costs for connecting the offshore wind turbines.

[0008] In particular, the use of a heavy submarine cable is a hindrance when installing floating single-point mooring wind turbines. Due to its inherent weight and rigidity, it impairs the floating properties, particularly the self-alignment, of these floating offshore wind turbines. In contrast to ground-based offshore turbines, the significant vertical and horizontal movement of the floating foundation of such wind turbines, as well as wind and wave loads, causes significant mechanical stress on the cables. The resulting movements place high demands on the durability of the cables, which consequently pose a weak point for continuous operation.

[0009] The object of the invention is therefore in particular to create an electrical connection of floating single-point mooring wind turbines to a collection station, which can be achieved with low material and labor expenditure, with the least possible impact on the floating properties of the wind turbines and with the greatest possible freedom of movement of the floating wind turbine and at the same time with a given long-term durability of the cables.

[0010] This object is achieved according to the invention by an offshore wind farm having the features of claim 1. The subclaims represent advantageous embodiments of the invention.

[0011] The basic idea of ​​the invention is to connect at least a subset of a plurality of floating single-point mooring wind turbines forming an offshore wind farm to a collection station using star cabling. Each cable leading from a wind turbine to the collection station transmits only the power of a single turbine and not the power of several turbines combined into a single strand, so that the cables used can be designed to be correspondingly thinner and more flexible. Furthermore, the sum of the lengths of the star-shaped connections between each floating single-point mooring wind turbine and the collection station is less than the length of an imaginary line connecting the collection station and the floating single-point mooring wind turbines. This measure can result in further material savings.

[0012] According to the invention, an offshore wind farm is proposed with a plurality of floating single-point mooring wind turbines arranged within parquet-arranged partial areas and with a collection station connected to the floating single-point mooring wind turbines, which is connected to a power grid by means of a transmission line, wherein at least a subset of the plurality of floating single-point mooring wind turbines is each connected directly to the collection station by means of its own submarine cable, forming a star-shaped power grid, wherein the sum of the lengths of the direct connections between the floating single-point mooring wind turbines and the collection station is less than the length of an imaginary line connecting the collection station and the floating single-point mooring wind turbines.

[0013] The design of the offshore wind farm according to the invention with a star-shaped topology therefore requires a shorter cable length overall than would be necessary for the design of a ring or line topology in which the collection station and the floating single-point mooring wind turbines are linearly connected to each other.

[0014] According to a preferred embodiment, the electrical voltage level of the current carried in the submarine cables leading to the collection station is identical to the electrical voltage level of the current carried in the transmission line connected to the transfer station. It is particularly preferred that the electrical voltage of the current carried in the submarine cables leading to the collection station is identical to the electrical voltage of the current carried in the transmission line connected to the transfer station. Most preferably, the voltage in both the submarine cables and the transmission line is 66 kV.

[0015] The direct connection of a floating single-point mooring wind turbine to the consolidating station is designed in such a way that the submarine cable used is as short and as thin as possible. In particular, the consolidating station also accommodates the switchgear of the wind turbines connected to the consolidating station, without the single-point mooring wind turbines themselves having switchgear, thus enabling a simple, cost-effective, and compact installation. With this interconnection, only a single switchgear is required per single-point mooring wind turbine, rather than three switchgears as in the case of ring cabling. A sub-area represents the (imaginary) polygonal area in a plan view of the offshore wind farm that is assigned to each floating single-point mooring wind turbine, including its anchoring.The parquet-arranged partial areas can be designed as a triangle, rectangle or hexagon, whereby the corner points of the partial area - as already known from DE 10 2015 121 371 B4 - represent in particular the positions of the foundations with the help of which the floating single-point mooring wind turbines are fixed to the waterbed.

[0016] Alternatively, these can be imaginary partial areas whose geometry is specifically defined by a predetermined distance between the wind turbines. This predetermined distance can, for example, be a multiple of the rotor diameter of the wind turbines installed in the offshore wind farm.

[0017] The collection station is not located outside a field containing the floating wind turbines, but rather in particular at the center of a perimeter encompassing at least a subset of the floating single-point mooring wind turbines. Specifically, the collection station connected to the floating single-point mooring wind turbines is particularly preferably located at the center of gravity of the tiling of the floating single-point mooring wind turbines connected to the collection station. These preferred arrangements each enable an advantageous embodiment of the invention, which can be implemented in a particularly material-saving manner with regard to cabling.

[0018] A particularly advantageous design with regard to the manufacture, installation, and maintenance of the offshore wind farm is also achieved when the collection station is designed as a floating structure. In this case, the collection station can be manufactured onshore, tested for functionality, and towed to the installation site, while still allowing for easy replacement. The floating collection station can be designed as a tension-leg platform (TLP) and, most preferably, connected to a foundation that secures a floating single-point mooring wind turbine to the ground. This further reduces the material and installation costs of the offshore wind farm.

[0019] Furthermore, it is preferably provided that a further subset of the plurality of floating single-point mooring wind turbines is each directly connected to a further collection station via its own submarine cable, forming a further star-shaped power grid. In other words, the offshore wind farm can be divided into individual groups (clusters), with each cluster consisting of a collection station and the floating single-point mooring wind turbines connected to it.

[0020] It has proven particularly advantageous if the subset or further subset of the plurality of floating single-point mooring wind turbines preferably comprises six floating single-point mooring wind turbines. This is particularly advantageous with regard to installation and material costs when tiling with hexagonal sub-areas.

[0021] Finally, the collection station is preferably connected to a land-based power grid via a central transmission line or to another larger collection or substation platform as part of a power grid. In particular, floating single-point mooring wind turbines are designed to generate electrical power at high voltage levels, e.g., 66 kV, which are connected together in the collection station using an electrical busbar. The collection station is connected to the land-based power grid via the central transmission line without further conversion to a higher AC or DC voltage level.

[0022] The invention will be explained in more detail below with reference to a particularly preferred embodiment shown in the accompanying drawings. They show: Fig. 2 shows a preferred embodiment of an offshore wind farm with floating single-point mooring wind turbines, which are each connected directly to a collecting station of the offshore wind farm by means of a separate submarine cable, forming a star-shaped power grid; Fig. 3 shows a particularly preferred embodiment of an offshore wind farm with floating single-point mooring wind turbines arranged within tiled partial areas; Fig. 4 shows a side view of a particularly preferred collecting station; Fig. 5 shows a perspective view of the Fig. 4 shown collection station; and Fig. 6 a detailed view of the upper area of ​​the previously shown collection station.

[0023] Fig. 2 shows a schematic plan view of a preferred embodiment of floating single-point mooring wind turbines grouped within an offshore wind farm, which are each connected by its own submarine cable directly to a collection station 20 of the offshore wind farm assigned to the group, forming a star-shaped power grid.

[0024] In particular, Fig. 2 a configuration of an offshore wind farm 100 comprising a plurality of floating single-point mooring wind turbines 10, each with a collection station 20, and a plurality of submarine cables 30 connecting each floating single-point mooring wind turbine 10 directly to the collection station 20, so that a star-shaped connection network is created.

[0025] The floating single-point mooring wind turbines 10 are arranged within predetermined sub-areas 40, which are arranged in a tiled pattern and represent the entire area of ​​the offshore wind farm. The sub-areas 40 are Fig. 2 formed as a hexagon. The tiling is either based on the foundation elements anchoring the respective floating single-point mooring wind turbine 10 or, alternatively, on another factor, in particular a multiple of the rotor diameter of the floating single-point mooring wind turbine 10 arranged in the offshore wind farm.

[0026] Collection station 20 is in Fig. 2 in the center of a dashed circle encompassing the floating single-point mooring wind turbines 10. The collection station 20 of the Fig. 2 shown offshore wind farm 100 is arranged in the center of gravity of the tiling of the floating single-point mooring wind turbines 10 connected to the collection station 20.

[0027] According to the invention, the sum of the lengths of the direct connections between the floating single-point mooring wind turbines 10 and the collection station 20 is less than the length of an imaginary line connecting the collection station 20 and the floating single-point mooring wind turbines 10, which would be required to form a ring or line topology.

[0028] The Fig. 2 The configuration shown has the shortest total length of the required connections between the floating single-point mooring wind turbines 10 and the collection station 20, with the total length being 5.19 times the distance between the individual turbines and the average cable length being 0.86 times the distance between the turbines. With a ring cabling system, the average cable length between the turbines would be at least 1.4 times the distance between the turbines, thus requiring a significantly thicker and therefore more expensive cable.

[0029] The collection station 20 is - as Fig. 4 bis Fig. 6 show - preferably floating, in particular designed as a tension leg platform (TLP) and furthermore connected to a foundation that fastens a neighboring floating single-point mooring wind turbine 10 to the ground, so that the material and installation costs of the offshore wind farm 100 are reduced compared to conventional offshore wind farms.

[0030] The one in Fig. 2 The exemplary embodiment shown is of particular importance, since the grouping of six floating single-point mooring wind turbines 10, which are arranged within parquetted partial areas 40 each formed as a hexagon, is suitable for the formation of larger offshore wind farms, in which - as Fig. 3 shows - further subsets of the floating single-point mooring wind turbines 10 forming the offshore wind farm 100 are each directly connected to a further collecting station 20 by means of their own submarine cable 30, forming further star-shaped power grids.

[0031] The average cable length of the groups, each consisting of six plants, is only 86% of the distance between the plants. To isolate the plants from the grid, only one switchgear per plant is required at the collection point 20 – in contrast to a ring cabling system, which requires three switchgears per plant. This means that even if one plant is shut down, all other plants remain unaffected and can continue to produce energy.

[0032] The hexagonal design of the sub-areas 40 has the advantage that a design with six mooring lines, each at an angle of 60°, can be used to anchor the floating single-point mooring wind turbines 10, which is advantageous in terms of tensile force distribution. With a clever arrangement of groups of six, the submarine cables 30 leading from the turbines 10 are each routed to a collection station 20, where the six switchgear for the six turbines is housed and the connection is established on an electrical busbar for connection to the transmission line.

[0033] If the 10 turbines are connected at a voltage level of 66 kV, this results in a transmission capacity of 6 x 15 MW = 90+ MW for six turbines in the future power class of >15 MW. This can be transmitted to land via a single transmission line, eliminating the need for an additional offshore substation in the wind farm.

[0034] Fig. 3 shows in particular an offshore wind farm 100 with a total of 102 floating single-point mooring wind turbines 10 with a total output of >1,500 MW. The single-point mooring wind turbines 10 are each divided into 18 groups of 6 turbines 10. The total output is transmitted to land in particular via 18 individual lines at a 66 kV level. Compared to a ring cabling system with 306 switchgears, only 102 switchgears are required in the design shown here. At a current unit price of approximately €100,000, this represents a cost difference of €20 million. The cable length of the farm cabling is reduced to 88 turbine spacings (approximately 110 km cable length) in this preferred embodiment, whereby a ring cabling system would require at least 144 turbine spacings (approximately 180 km cable length). Taking into account the installation and cable costs, this represents a difference of approximately €40 million.However, it should be noted that the cables used to connect individual turbines to the collection station are significantly thinner and more cost-effective. This example clearly demonstrates the reduction in material and installation costs for such offshore wind farms.

[0035] Fig. 4 , Fig. 5 and Fig. 6 show various views of a particularly preferred collection station, which protects six connected systems via medium-voltage switchgear, combines the power of the wind turbines via an electrical busbar and is connected to the onshore power grid at the same voltage level via a transmission cable.

[0036] In particular, the aforementioned figures show a collection platform 20 to which six submarine cables 30 from six wind turbines are interconnected. An anchoring element 120 is provided in the seabed 110, which may, for example, be a driven pile or a suction cup. This element provides a solid anchor between the bottom 110 and the collection platform 20 and, if necessary, also for additionally connecting the wind turbines 10 using mooring lines or chains 130. Several connecting elements 140, for example made of synthetic lines or wire ropes, are provided on this anchoring element 120. A buoyancy body 150 is attached to the upper end of these connecting elements 140, which, through its own displacement, generates enough buoyancy to keep the entire collection platform 20 floating upright in the water, without vertical movements and only minimal horizontal and rotational movements.Through a clever arrangement of the connecting elements 140, movements can be minimized, even in strong waves. A plurality of supports 180 are attached to the floating body 150, which extend vertically upward through the water surface 170. At their upper ends, a platform 190 is attached, which supports the switchgear 210 for each individual wind turbine 10. The length of the supports 180 is advantageously selected such that a largest anticipated wave neither exposes the top of the buoyancy body 150 nor strikes the platform 190 on its underside. By adjusting the length of the connecting elements 140, the floating height of the floating platform 20 can then be adjusted such that the top of the floating body 150 and the underside of the platform 190 are approximately evenly spaced from the mean water level of the water surface 170.Protective tubes 160 are attached to the support structure 180, which accommodate and protect the submarine cables 30 to the individual wind turbines 10.

[0037] Additionally, for maintenance purposes, access to platform 190 is provided by a boat landing 220. On platform 190, preferably in a circle, as many switchgears 210 are arranged as there are wind turbines 10 to be connected to a collecting platform 20 via the submarine cables 30. The entire platform 190, including the switchgears 210, is protected from the elements by a cladding (not shown). Dehumidifiers and heaters may be provided if necessary.

[0038] The switchgear 210 is brought together on an electrical busbar 230 and connected to a grid feed-in point on land or an offshore collection station via the transmission line 220. No electrical energy is converted on this collection platform 20; instead, the energy from the individual wind turbines 10 is combined at the same voltage level and discharged via the collection cable 220. Fiber optic cables, which are used, for example, to control the switchgear 210, are also routed via this transmission line 220.

Claims

1. Offshore wind farm (100) with a plurality of floating single-point mooring wind turbines (10) arranged within parquetised sub-areas (40) and a collection station (20) connected to the floating single-point mooring wind turbines (10), which is connected to a power grid by means of a transmission line (220) characterized in that at least a subset of the floating single-point-mooring wind turbines (10) is connected directly to the collecting station (20), forming a star-shaped power grid, in each case with its own submarine cable (30), the sum of the length of the direct connections between the floating single-point-mooring wind turbines (10) and the collection station (20) being less than the length of an imaginary line connecting the collection station (20) and the floating single-point-mooring wind turbines (10) to one another.

2. Offshore wind farm (100) according to claim 1, characterised in that the electrical voltage level of the current carried in the submarine cables (30) leading to the collection station (20) is identical to the electrical voltage level of the current carried in the transmission line (220) connected to the transfer station.

3. Offshore wind farm (100) according to one of the preceding claims, characterised in that the electrical voltage of the current carried in the submarine cables (30) leading to the collection station (20) is identical to the electrical voltage of the current carried in the transmission line (220) connected to the transfer station.

4. Offshore wind farm (100) according to one of the preceding claims, characterised in that the collection station (20) is arranged in the centre of a circumference comprising at least the subset of the floating single-point-mooring wind turbines (10).

5. Offshore wind farm (100) according to one of the preceding claims, characterised in that the collection station (20) is arranged in the median point of the parquetry of the floating single-point mooring wind turbines (10) connected to the collection station (20).

6. Offshore wind farm (100) according to one of the preceding claims, characterised in that the collecting station (20) is designed to float.

7. Offshore wind farm (100) according to claim 6, characterised in that the collection station (20) is designed as a tension leg platform (TLP).

8. Offshore wind farm (100) according to one of claims 6 and 7, characterised in that the collection station (20) is connected to a foundation fixing a floating single-point-mooring wind turbine (10) to the ground.

9. Offshore wind farm (100) according to one of the preceding claims, characterised in that a further subset of the floating single-point mooring wind turbines (10) is connected directly to a further collection station (20), forming a further star-shaped power grid, each with its own submarine cable (30).

10. Offshore wind farm (100) according to one of the preceding claims, characterised in that the subset or the further subset comprises six floating single-point mooring wind turbines (10).

11. Offshore wind farm (100) according to one of the preceding claims, characterised in that the power grid connected to the collection station (20) is an onshore power grid.

12. Offshore wind farm (100) according to one of the preceding claims, characterised in that the partial areas of the parquetry are designed as a triangle, rectangle or hexagon.