A wind turbine blade

Abstract

A wind turbine blade having an outer surface and a lightning protection system comprising an electrically conductive part adjacent the outer surface of the blade; wherein the outer surface of the blade has a first colour and a second colour, the second colour being darker than the first colour; and the second colour is located within a footprint of the electrically conductive part and does not extend substantially outside of the footprint of the electrically conductive part.

Description

[0001] A Wind Turbine Blade

[0002] The present invention relates to a wind turbine blade. In particular, the present invention addresses the issue of bird collisions by providing a wind turbine blade with a colour scheme designed to enhance visibility to birds, thereby reducing the risk of collisions.

[0003] It is known that painting wind turbine blades black can reduce the risk of collision between birds and the wind turbine blades. It is an aim of the present invention to provide a colour design that can be applied to wind turbine blades.

[0004] According to the present invention there is provided a wind turbine blade having an outer surface and a lightning protection system comprising an electrically conductive part adjacent the outer surface of the blade; wherein the outer surface of the blade has a first colour and a second colour, the second colour being darker than the first colour; and the second colour is located within a footprint of the electrically conductive part and does not extend substantially outside of the footprint of the electrically conductive part.

[0005] The electrically conductive part comprises a layer of electrically conductive material adjacent the outer surface of the blade, such as a metal layer. The electrically conductive part may be in the form of a surface protection layer which intercepts lightning strikes so that components with an interior of the blade are protected. The lightning protection system may further include discrete lightning receptors and conductors that are electrically connected from the blade, through a nacelle and tower, to ground.

[0006] The blade is provided with at least two colours, a first light colour and a second dark colour. The provision of the light and dark colours on a blade reduces “motion smear”, making a rotating blade more visible to birds, enhancing the visibility of the rotating blade to birds and thereby decreasing the likelihood of bird strikes.

[0007] The second colour is darker than the first colour under daylight conditions. This may provide a contrast ratio sufficient to enhance visibility to birds.

[0008] To provide a dark colour, such as a black colour, pigments which provide the colour may comprise electrically conductive material, such as carbon based pigments. In a lightning event, streamers extend from the blade and form when the electric field around the blade becomes strong enough to ionize the air. Streamers typically extend from a tip of the blade and other sharp edges, creating a path for the lightning to follow. However, conductive material on the blade, such as the second colour, can also enhance the electric field around the blade. This increased electric field can lead to the formation of streamers resulting in a lightning strike on the second colour.

[0009] The second colour may comprise electrically conductive pigments, such as carbon based pigments.

[0010] Locating the second colour within the footprint of the electrically conductive part, which is part of the lightning protection system of the blade, helps to prevent lightning strikes to parts of the blade that are not directly protected by the lightning protection system. As the second colour is within the footprint of the electrically conductive part, and does not extend substantially outside of the footprint of the electrically conductive part, any lightning strikes on the second colour will be directly transferred to the electrically conductive part which is part of the lightning protection system and directed to ground.

[0011] This design not only enhances bird safety but also ensures that the wind turbine blade remains protected from lightning damage, offering a dual benefit of improved environmental compatibility and operational safety.

[0012] The arrangement of the second colour substantially exclusively within the footprint of the electrically conductive part achieves a dual technical effect: (i) enhancing visibility to birds to reduce collisions, and (ii) preventing lightning strikes on unprotected areas of the blade

[0013] The footprint of the electrically conductive part may be seen as the area of the electrically conductive part, projected onto the outer surface of the blade. In other words, when looking at the blade in plan view, the footprint is defined within a perimeter of the electrically conductive part.

[0014] The expression “does not extend substantially outside of the footprint of the electrically conductive part” means that the second colour does not significantly extend outside of the footprint of the electrically conductive part. For example, if the second colour has a given surface area, at least 95% of the given area of the second colour will be within the footprint of the electrically conductive part. This accounts for manufacturing tolerances when applying the second colour to the blade. The second colour is located within a footprint of the electrically conductive part and does not extend substantially outside of the footprint of the electrically conductive part such that at least 95% of an area of the second colour lies within the footprint of the electrically conductive part.

[0015] The outer surface of the blade may have the second colour over substantially the entire footprint of the electrically conductive part. This advantageously maximises the area of the second colour on the wind turbine blade helping to prevent bird strikes.

[0016] The outer surface of the blade may have the second colour over a partial part of the footprint of the electrically conductive part. This still provides the advantage of reducing motion smear while further helping to prevent lightning strikes to parts of the blade that are not directly protected by the lightning protection system. For example, the second colour may be provided towards a tip end of the blade or a root end of the blade.

[0017] Preferably, the electrically conductive part is a metallic foil, such as a metal mesh or expanded metal foil. The electrically conductive part has a thickness of less than 1mm. The electrically conductive part is provided as a thin layer of conductive material that can carry high current in the event of a lightning strike, without significantly increasing the mass of the blade.

[0018] Preferably, the electrically conductive part extends along a majority of a span of the blade from a root end to the tip end of the blade. This advantageously increases the lightning protection of the blade and also provides a bigger area for the second colour and thus helps to prevent bird strikes.

[0019] The electrically conductive part may be formed as a stripe extending in a spanwise direction of the blade, and the electrically conductive part is spaced, in a chordwise direction from a leading edge and a trailing edge of the blade. Advantageously, this provides a suitable area for the lightning protection system while at the same time, providing a suitable area for the second colour to prevent bird strikes.

[0020] The term spanwise is used to refer to a direction from a root end of a wind turbine blade to a tip end of the blade, or vice versa. The term chordwise is used to refer to a direction from the leading edge to the trailing edge, or vice versa.

[0021] The stripe may not need to have a rectangular shape, for example, it could have a trapezoidal shape. In further examples, chordwise stripes of the second colour may be provided within the footprint of the electrically conductive part. In examples, the second colour may not be continuous, but may be provided as a pattern.

[0022] The blade comprises a windward side and a leeward side, and preferably the electrically conductive part is provided at the windward side and at the leeward side. In other words, both sides of the blade may be provided with the second colour to prevent bird strikes.

[0023] Preferably the first colour is a white colour or an off-white colour. An off-white colour is a colour that differs slightly from white, e.g. a white colour with a shade of grey.

[0024] Preferably the second colour is a black colour or an off-black colour. An off-black colour is a colour that differs slightly from black, e.g. dark grey.

[0025] The first colour may have an albedo of 0.75 or greater. The second colour may have an albedo of 0.08 or less.

[0026] A contrast ratio between the first colour and the second colour may be at least 3:1 .

[0027] A tip side of the electrically conductive part may be connected to a lightning receptor at a tip end of the blade, and a root side of the electrically conductive part may be connected to electrical ground.

[0028] The second colour being darker than the first colour; and the second colour being located within a footprint of the electrically conductive part and does not extend substantially outside of the footprint of the electrically conductive part is configured, in use, to reduce collisions between birds and the wind turbine blade while ensuring lightning strikes are discharged through the lightning protection system.

[0029] According to a further aspect of the present invention, there is provided a horizontal axis wind turbine comprising a plurality of wind turbine blades, wherein at least one of the wind turbine blades comprises the wind turbine blade as set out above.

[0030] A single blade of the plurality of blades may comprise the wind turbine blade as set out above.

[0031] The other blades of the plurality of blades may not comprise the second colour. This advantageously helps to reduce motion smear. An example of the present invention will now be set out with reference to the accompanying Figures in which:

[0032] Figure 1 is a view of a wind turbine;

[0033] Figure 2 is a schematic perspective view of a wind turbine blade;

[0034] Figure 3 is a plan view of a wind turbine blade;

[0035] Figure 4 is a plan view of a windward side and a leeward side of a wind turbine blade.

[0036] Figure 1 shows a wind turbine 10 including a tower 12 mounted on a foundation and a nacelle 14 disposed at the apex of the tower 12. The wind turbine 10 depicted here is an onshore wind turbine such that the foundation is embedded in the ground, but the wind turbine 10 may be an offshore installation in which case the foundation would be provided by a suitable marine platform.

[0037] A rotor 16 is operatively coupled to a generator, potentially via a gearbox housed inside the nacelle 14. The rotor 16 includes a central hub 18 and a plurality of wind turbine blades 20, which project outwardly from the central hub 18. It will be noted that the wind turbine 10 is the common type of horizontal axis wind turbine (HAWT) such that the rotor 16 is mounted at the nacelle 12 to rotate about a substantially horizontal axis defined at the centre at the hub 18. While the example shown in Figure 1 has three blades, it will be realised by the skilled person that other numbers of blades are possible.

[0038] When wind blows against the wind turbine 10, the blades 20 generate a lift force which causes the rotor 16 to rotate, which in turn causes the generator within the nacelle 14 to generate electrical energy.

[0039] Figure 2 shows an example of one of the wind turbine blades 20 for use in such a wind turbine. The blade 20 has a root end 21 proximal to the hub 18 and a tip end 22 distal from the hub 18. The blade 20 includes a leading edge 23 and a trailing edge 24 that extend between the root end 21 and tip end 22. The blade 20 includes a leeward side 25 and a windward side 26. A thickness dimension of the blade extends between the leeward side 25 and the windward side 26.

[0040] The blade 20 has a cross section that is substantially circular near the root end 21 , as the blade portion near the root must have sufficient structural strength to support the blade portion outboard of that section and to transfer loads into the hub 18. The blade 20 may transition from a circular profile to an aerofoil profile moving from the root end 21 of the blade towards a "shoulder" 28 of the blade, which is the widest part of the blade 20 where the blade 20 has its maximum chord. The blade 20 has an aerofoil profile of progressively decreasing thickness in an outboard portion of the blade, which extends from the shoulder 28 to the tip end 22.

[0041] The wind turbine blade 20 may include an outer blade shell defining a hollow interior space with a shear web extending internally between upper and lower parts of the blade shell.

[0042] As shown schematically in Figure 3, the blade 20 may include one or more lightning receptors 36 and one or more lightning down conductor cables 38 which form part of a lightning protection system for the wind turbine blade. The lightning receptors attract the lightning strike and the down conductor cables 38, which run through the hollow interior of the blade, conduct the energy of the lightning strike down the blade 20 via the nacelle 14 and tower 12 to a ground potential. In addition, the lightning protection system includes an electrically conductive part 40 in the form of a surface protection layer adjacent the outer surface of the blade. The electrically conductive part 40 is electrically connected at each end to the down conductor cables 38. The surface protection layer may be a metallic foil, such as a metal mesh or expanded metal foil.

[0043] The surface protection layer 40 serves to shield material in the blade from a lightning strike, and may act as either a lightning receptor, a down conductor, or both. The down conductor may extend substantially the full length of the blade. In some examples, the down conductor cable 38 may connect to the surface protection layer 40 adjacent the tip end 22 of the blade and adjacent the root end 21 of the blade, with no down conductor cable 38 along the length of the blade covered with the surface protection layer 40. The surface protection layer 40 may extend in sections along the length of the blade with down conductor cable sections between the surface protection layer sections. Down conductor cable 38 may alternatively extend under the surface protection layer 40 (inside the blade) so that the down conductor cable 38 and surface protection layer 40 are electrically connected in parallel.

[0044] At the root end 21 of the blade 20, the down conductor cable 38 may be electrically connected via an armature arrangement to a charge transfer route via the nacelle 14 or hub 18 and tower 12 to a ground potential. Such a lightning protection system therefore allows lightning to be channelled from the blade to a ground potential safely, thereby minimising the risk of damage to the wind turbine 10. The down conductor cable 38 and surface protection layer 40 may be connected by one of more connectors or receptors. The connectors may comprise an electrically conductive pin 61 that extends through the surface protection layer 40 and connects to the down conductor cable 38. Figure 3 shows five electrically conductive pins 61 connecting the down conductor cable 38 and the surface protection layer 40, although it will be understood that any number of electrically conductive pin 61 may be used, including one.

[0045] The electrically conductive part 40 may be formed of any suitably electrically conductive metal, for example aluminium, copper, stainless steel, brass, or bronze. The electrically conductive part 40 may be any suitably thin sheet-like conducting material. The sheet material for forming the electrically conductive part 40 may have a thickness of less than 1 mm, optionally between 0.2 mm and 0.6 mm, and optionally between 0.25 mm and 0.5 mm or between 0.2mm and 0.3mm.

[0046] The electrically conductive part 40 faces an outer surface of the blade 20. The electrically conductive part 40 is essentially at the outer surface of the blade 20, but may be covered by a layer of glass fibre fabric and gel coat, for example.

[0047] The electrically conductive part 40 has a footprint on the outer surface of the blade. The footprint is defined by the edges of the electrically conductive part 40, that is a perimeter 45 of the electrically conductive part 40.

[0048] Figure 3 shows a leeward side 25 of the blade 20. The windward side 26 may comprise substantially the same arrangement as the leeward side.

[0049] Figure 4 is a plan view of the leeward side 25 and the windward side 26 of the blade. Within the footprint of the electrically conductive part 40, the blade has been painted a black colour. Outside of the footprint of the electrically conductive part 40, the blade is a white colour.

[0050] The blade may also comprise other paint colours, not shown. For example the blade may comprise red aviation stripes at the tip end.

[0051] It has been found that the provision of a blade that is partially painted black can reduce the possibility of a bird striking the blade. At the same time, because the black paint is within the footprint of the electrically conductive part, the lightning protection system of the wind turbine blade is not degraded.

Claims

Claims1. A wind turbine blade having an outer surface and a lightning protection system comprising an electrically conductive part adjacent the outer surface of the blade; wherein the outer surface of the blade has a first colour and a second colour, the second colour being darker than the first colour; and the second colour is located within a footprint of the electrically conductive part and does not extend substantially outside of the footprint of the electrically conductive part.

2. A wind turbine blade according to claim 1 , wherein the outer surface of the blade has the second colour over substantially the entire footprint of the electrically conductive part.

3. A wind turbine blade according to claim 1 or claim 2, wherein the electrically conductive part is a metallic foil, such as a metal mesh or expanded metal foil.

4. A wind turbine blade according to any one of the preceding claims, wherein the electrically conductive part has a thickness of less than 1mm.

5. A wind turbine blade according to any one of the preceding claims, wherein the electrically conductive part extends along a majority of a span of the blade from a root end to the tip end of the blade.

6. A wind turbine blade according to any one of the preceding claims, wherein the electrically conductive part is formed as a stripe extending in a spanwise direction of the blade, and the electrically conductive part is spaced, in a chordwise direction from a leading edge and a trailing edge of the blade.

7. A wind turbine blade according to any one of the preceding claims, wherein the blade comprises a windward side and a leeward side, and the electrically conductive part is provided at the windward side and at the leeward side.

8. A wind turbine blade according to any one of the preceding claims, wherein the first colour is a white colour or an off-white colour.

9. A wind turbine blade according to any one of the preceding claims, wherein the second colour is a black colour or an off-black colour.

10. A wind turbine blade according to any one of the preceding claims, wherein the second colour comprises electrically conductive pigments, such as carbon based pigments.

11. A wind turbine blade according to any one of the preceding claims, wherein the second colour being darker than the first colour; and the second colour being located within a footprint of the electrically conductive part and does not extend substantially outside of the footprint of the electrically conductive part is configured, in use, to reduce collisions between birds and the wind turbine blade while ensuring lightning strikes are discharged through the lightning protection system.

12. A wind turbine blade according to any one of the preceding claims, wherein a tip side of the electrically conductive part is connected to a lightning receptor at a tip end of the blade, and a root side of the electrically conductive part is connected to electrical ground.

13. A horizontal axis wind turbine comprising a plurality of wind turbine blades, wherein at least one of the wind turbine blades comprises the wind turbine blade according to any one of the preceding claims.

14. A horizontal axis wind turbine according to claim 13, wherein a single blade of the plurality of blades comprises the wind turbine blade according to any one of claims 1 to 12.

15. A horizontal axis wind turbine according to claim 14, wherein the other blades of the plurality of blades do not comprise the second colour.

Images