Wind turbine blade with de-icing system

Abstract

The present disclosure relates to a wind turbine blade comprising: a leading edge heating element extending along at least a portion of a leading edge of the wind turbine blade, the leading edge heating element configured for de-icing a corresponding portion of an outer surface of the leading edge; a first plurality of heating strips, each of the first plurality of heating strips extending in a substantially spanwise direction of the wind turbine blade, the first plurality of heating strips forming part of a first shell portion of the wind turbine blade wherein the first shell portion is a pressure side shell portion or a suction side shell portion, the first plurality of heating strips are spaced apart from each other in a chordwise direction and from the leading edge heating strip, each heating strip comprising a carbon fiber yarn and / or tow material.

Description

Technical Field

[0001] The present invention relates to de-icing of wind turbine blades. Background Art

[0002] When wind turbines operate in cold weather climates, ice can accumulate on wind turbine blades and negatively impact turbine performance by disrupting airflow across the blades. Ice can also cause noise as air flows across the blades. Furthermore, ice can become dangerous when it breaks off the blade surface. Therefore, in such climates, wind turbine blades are often equipped with systems that slow ice formation (anti-icing) or melt away ice (de-icing).

[0003] Hot air electric heating systems operate on the principle of supplying heated air to the interior of a wind turbine blade, which in turn increases the surface temperature of the blade, thereby reducing ice formation or removing ice that has already formed on the blade.

[0004] It is also known to utilize electrical heating systems and mechanical electrothermal systems embedded in the blades. However, when conductive material is included in the blades, especially near the outer surface, the risk of lightning striking such material rather than the dedicated arrester increases. This problem is further exacerbated when the conductive material is located near the tip of the blade, as this area of the blade is already at a higher risk of receiving a lightning strike.

[0005] Since wind turbine blades are often made of fiber reinforced composite materials, it would be advantageous to provide an improved de-icing system for fiber reinforced composite wind turbine blades. Summary of the Invention

[0006] A first aspect of the present invention provides a wind turbine blade having a suction side shell portion and a pressure side shell portion, each shell portion extending between a leading edge of the wind turbine blade and a trailing edge of the wind turbine blade, the wind turbine blade extending along a longitudinal axis from a root end of the wind turbine blade to a tip end of the wind turbine blade, the wind turbine blade comprising:

[0007] a leading edge heating element extending along at least a portion of a leading edge of a wind turbine blade, the leading edge heating element being configured for de-icing a corresponding portion of an outer surface of the leading edge,

[0008] a first plurality of heating strips, each heating strip of the first plurality of heating strips extending in a substantially spanwise direction of the wind turbine blade, the first plurality of heating strips forming part of a first shell portion of the wind turbine blade, wherein the first shell portion is a pressure side shell portion or a suction side shell portion, the first plurality of heating strips being spaced apart from each other and from the leading edge heating strips in a chordwise direction, each heating strip having a first end and a second end, the first end being closer to the tip end than the second end, each heating strip comprising a carbon fiber yarn and / or tow material, and

[0009] - a power supply configured to provide power to each heating bar of the first plurality of heating bars so as to generate heating in said each heating bar, said heating being generated by the carbon fiber yarn and / or tow material.

[0010] This type of wind turbine blade allows for de-icing of the first shell section downstream of the leading edge. Ice can adhere to the blade there and negatively impact its aerodynamic performance, leading to reduced power generation efficiency and noise. The use of carbon fiber yarns and / or tows has the following benefits in addition to providing heating for de-icing the blade: the heating strips also provide mechanical strength, especially if embedded in resin. In this case, the heating mat is actually a fiber-reinforced composite material.

[0011] In a preferred embodiment, the first plurality of heating strips are not exposed at the outer surface of the wind turbine blade. That is, the first plurality of heating strips are embedded inside the first shell portion or are positioned so that the heating strips are exposed to the inner side of the wind turbine blade. As a result, they are protected from environmental influences. In some embodiments, one or more heating strips of the first plurality of heating strips are embedded in the first shell portion, while other heating strips of the first plurality of heating strips are exposed to the inner side of the wind turbine blade. To provide the heating strips exposed to the inner side of the wind turbine blade, the heating strips can, for example, be glued to a portion of a fiber layer or other layer facing the inner side of the wind turbine blade. Embedded heating strips are typically embedded during the layup of the wind turbine blade material, where they are placed between other layers.

[0012] In some embodiments, one or more of the first plurality of heating strips comprises one or more carbon fiber yarns / tows extending from a first end to a second end of the heating strip. This allows the individual yarns / tows to all transmit electricity along the heating element.

[0013] The heating strips may be slightly curved in the spanwise direction, for example to follow the curvature of the trailing edge of the blade. Although within the scope of the invention, such embodiments are more difficult to manufacture because the heating strips are more complex to manufacture and must also be adapted to the shape of the material surrounding the heating strips in the blade.

[0014] In some embodiments, one or more of the yarns / tows used to generate the heating extend from the first end to the second end of the corresponding heating strip in a non-linear manner. In some embodiments, the yarns / tows used to generate the heating extend from the first end to the second end of the corresponding heating strip in a wavy manner, such as in a substantially sinusoidal manner.

[0015] In some embodiments, one or more of the heating strips used to generate heating are made of unidirectional carbon fiber. In some embodiments, one or more of the heating strips used to generate heating include biaxial carbon fiber material.

[0016] An advantage of using a yarn / tow that extends from a first end to a second end is that the resistance is more consistent from one heating strip to another, reducing the need to determine the resistance of the heating strip in order to determine how much heat a given applied voltage will result. Biaxial carbon fiber materials include overlapping, but non-continuous, fibers, and the resistance depends on the degree of contact between the fibers in the biaxial material. Therefore, the resistance can vary significantly from mat to mat, and calibration may be required to determine how much heat the heating strip will generate for a given voltage applied across it.

[0017] The advantage of using yarns / tows arranged in a wavy manner (such as a sinusoidal manner) is that the heating strip is less rigid. Therefore, such heating strips can be used without adding too much rigidity to the blade.

[0018] In some embodiments, the length of each heating strip is at most 80% of the length of the blade from the root end to the tip end, such as at most 50% of the length of the blade, such as at most 33% of the length of the blade, such as at most 25% of the length of the blade. This may depend on the shape of the blade, but the inventors have found that the heating strips do not necessarily need to extend along the entire length of the blade. In some embodiments, at least one heating strip (such as all heating strips) in the first plurality of heating strips still extends along substantially the entire length of the blade.

[0019] In some embodiments, the heating strips extend from the tip to a position corresponding to the length of each strip. This addresses the problem of higher airflow cooling at the tip due to higher wind speeds. It is important to note that heating strips that are shorter than the blade length will not extend all the way to the root end.

[0020] In some embodiments, the heating generated by at least one of the first plurality of heating strips can be controlled independently of the heating generated by another of the first plurality of heating strips. In some embodiments, the heating can be controlled individually for all of the heating strips. This allows for more localized heating, particularly in areas where ice spots have formed. In some embodiments, the heating of one of the heating strips is controlled based on measurements of physical properties near the strip. For example, in some embodiments, a vision system, such as a camera, is used to monitor the surface of the blade. If an ice spot is identified in a particular portion of the blade, the heating strip(s) below the ice spot can be activated to remove the ice spot. If the ice spot is located above, for example, two of ten heating strips, only those two heating strips need to be activated. This saves electrical energy and reduces unwanted expansion and contraction in the blade during temperature cycling.

[0021] In some embodiments, the total chord-wise extent of the first plurality of heating strips at a first location along the longitudinal axis of the blade is at least 30% of the chord length at the first location, such as at least 50% of the chord length at the first location, or at least 80% of the chord length at the first location. That is, when viewing the blade from the top in a direction normal to the chord line, at the first location, the ratio between the area of heating strips and the area without heating strips is at least 30%, such as at least 50%, or at least 80%. Due to the gradual change in chord length along the longitudinal axis of the blade, this ratio typically varies slightly in the span-wise direction. Furthermore, leading edge heating elements already cover a portion of the chord, thus affecting the required ratio. Preferably, the ratio is tailored for a given blade to ensure that the heating strips are able to de-ice the blade surface (in the area with heating strips) under substantially all foreseeable conditions. If the heating strips are spaced too far apart, some areas between the heating strips may not be de-iced. At the same time, the blade may have areas whose shape substantially prevents ice from adhering to the extent necessary for de-icing. In such cases, the ratio may be lower.

[0022] In some embodiments, a first end of each heating bar in the first plurality of heating bars abuts a corresponding first metal mesh, and a second end of each heating bar abuts a corresponding second metal mesh, whereby the corresponding first metal mesh and the corresponding second metal mesh are electrically connected to each other via the heating bar, wherein the first metal mesh and the second metal mesh are connected to a power source to allow heating to be generated in the heating bar. The mesh can be made of, for example, copper or a copper alloy, aluminum or an aluminum alloy, or other metal or metal alloy.

[0023] To allow for individual control of the power supplied to different heating strips, each heating strip is provided with a corresponding first and second metal mesh. In other embodiments, two or more heating strips share the same first metal mesh (at the first end of the heating strip) or second metal mesh (at the second end of the heating strip). Power can be individually controlled by connecting or disconnecting the heating strips from the power supply via a switch device at the other end of the heating strip. For example, the first ends of the heating strips may share the same first metal mesh. If a switch device is provided for each heating strip to allow the second end of each heating strip to be connected to or disconnected from the power supply, heating can be generated in a specific heating strip by turning on its corresponding switch device. Heating strips that share the same metal mesh at either the first or second end are essentially connected in parallel. In some embodiments, all heating strips in the first plurality of heating strips are electrically connected to each other via the shared metal mesh at either the first or second end. If the ends of the heating strips (at the first or second end, or both) terminate at different locations, it may be necessary to provide a larger metal mesh or a custom metal mesh, the latter embodiment reducing weight. Alternatively, if separate metal meshes are provided for the different heating strips, other types of conductors, such as wires, may be used instead to electrically connect the separate metal meshes, thereby coupling the separate meshes in parallel.

[0024] Above, the first and second metal meshes are essentially contacts for electrically coupling the heating strip to a power source, to allow a voltage to be applied across the heating strip.The contacts may be provided in other ways, ie not as metal meshes.

[0025] In some embodiments, a metal mesh, such as a copper mesh, is positioned between the heating strip and the outer surface of the first shell portion. The metal mesh reduces the risk of flashover and the risk of lightning striking the heating strip instead of the dedicated lightning arrester in the blade. The heating strip and the metal mesh are electrically separated by an insulating layer, such as a polyethylene terephthalate (PET) film. In some embodiments, the insulating layer is sandwiched between fiber layers, such as fiberglass layers.

[0026] In some embodiments, the first plurality of heating strips includes a first heating strip and a second heating strip, wherein the first heating strip is closer to the leading edge than the second heating strip, and wherein the first heating strip is longer than the second heating strip. Chord length varies along a typical blade, and therefore, it may be necessary to terminate the strips earlier than the strips closer to the leading edge. This has been shown to allow for complete de-icing in the region where the heating strips terminate, even when leaving a region slightly further from the heating strips. Another option is to taper the heating strips where needed, but this requires additional steps (and therefore additional time) and, as mentioned, has not been shown to be necessary.

[0027] In some embodiments, starting from the leading edge toward the trailing edge, each heating strip in the first plurality is at most as long as or shorter than the previous heating strip in the first plurality. That is, the lengths of the heating strips are at most equal to one another or become shorter in the direction from the leading edge to the trailing edge. Due to the motion of the blade and the local airflow velocity, this configuration can still de-ice the blade (in the area containing the heating strips). Depending on the shape of the specific blade, this configuration may require slight adjustments.

[0028] In some embodiments, the number of strips in the first plurality of strips is in the range of 2 to 50, such as in the range of 5 to 50, such as in the range of 10 to 50, such as in the range of 10 to 30, such as in the range of 10 to 20. This number of heating strips is suitable for most blade curvatures. The width of the heating strips (not necessarily all heating strips are the same) combined with the number of heating strips preferably leads to an embodiment as described above, wherein in the first position, the ratio between the area of heating strips and the area without heating strips is at least 30%, such as at least 50%, such as at least 80%.

[0029] In some embodiments, both the suction side shell portion and the pressure side shell portion comprise a plurality of heating strips. In other words, the second blade portion of the blade, i.e. the shell portion opposite the first shell portion (which is the suction side shell portion or the pressure side shell portion), comprises:

[0030] a second plurality of heating strips, each of the second plurality of heating strips extending in a substantially spanwise direction of the wind turbine blade, the second plurality of heating strips forming part of a second shell portion of the wind turbine blade, the second plurality of heating strips being spaced apart from each other and from the leading edge heating strips in a chordwise direction, each heating strip having a first end and a second end, the first end being closer to the tip end than the second end, each heating strip comprising carbon fiber yarn and / or tow material, each of the second plurality of heating strips being connected to a power source configured to provide power to each of the second plurality of heating strips so as to generate heating in said each heating strip, said heating being generated by the carbon fiber yarn and / or tow material in the respective heating strip.

[0031] Since the two sides do not have the same shape, the heating strips on one side can and typically will have different parameters than the other side. That is, the number of heating strips and / or the ratio between the heating strip area and the area without heating strips and / or the width of the heating strips can be different on one side than on the other.

[0032] A second aspect provides a method for manufacturing a wind turbine blade according to the first aspect of the present invention. The method comprises:

[0033] - laying down material for forming the first shell portion in a first mould, including laying down fibre material, a leading edge heating element and a first plurality of heating strips,

[0034] - embedding the paving material in resin, such as by resin infusion,

[0035] -Connect the first and second ends of each heating strip to a power source.

[0036] In some embodiments, the switch is configured to allow the heating of one of the heating strips to be adjusted independently of the other heating strips.

[0037] The considerations described with respect to the first aspect apply equally to the second aspect.

[0038] A third aspect provides a method for de-icing a wind turbine blade according to the first aspect of the invention. The method comprises:

[0039] - providing power to each of the heating bars in the first plurality of heating bars to generate heat in the heating bar.

[0040] In some embodiments, the power provided to a first heating strip in the first plurality of heating strips can be controlled independently of the power provided to a second heating strip in the first plurality of heating strips. This allows heating to be generated only when necessary, thereby saving electrical energy and reducing fatigue due to expansion and contraction in the blade caused by temperature changes caused by heating.

[0041] In some embodiments, heating in each heating strip can be controlled independently of heating in all other heating strips in the first plurality of heating strips.

[0042] In some embodiments, heating of each of the heating strips is controlled based on images of the blade surface obtained from a vision system. Heating is controlled in such a way that if de-icing is determined to be necessary near a particular heating strip based on images from the vision system, heating is provided to that particular heating strip. This results in a particularly efficient de-icing process, as heating is provided only where and when needed. When the vision system detects that the amount of ice near a particular heating strip has decreased below a threshold or has been completely eliminated, heating in that particular heating strip can be reduced or completely turned off.

[0043] A fourth aspect provides a heating bar comprising a plurality of carbon fiber yarns and / or tows extending from a first end to a second end of the heating bar. Such a heating bar can be used in the above aspects. An advantage of having yarns and / or tows extending from the first end to the second end of the heating bar is that the electrical performance of the heating bar is more consistent from one manufactured heating bar to another, compared to, for example, a heating bar using biaxial fiber material instead.

[0044] In some embodiments, the carbon fiber yarns and / or tows extend from a first end to a second end of the heating strip in a wavy manner, such as in a substantially sinusoidal manner. This results in the heating strip being more ductile and less stiff.

[0045] In some embodiments, a contact is provided at either end of the heating strip, for example in the form of an adjoining metal mesh (such as a copper mesh). This solution provides a low resistance connection between the metal mesh and the heating strip. The area of the metal mesh is advantageously 2 cm 2 Up to 500cm 2 within a range such as 5 cm 2 Up to 250cm 2 within a range such as 5 cm 2 Up to 100cm 2 within a range such as 10 cm 2 Up to 100cm 2 within a range such as 25 cm 2 Up to 75cm 2 This may depend on the width of the heating strip. For example, a 100 mm wide heating strip can be adjacent to a 10 cm x 10 cm metal mesh. The metal mesh width is advantageously the same as the width of the heating strip, but this is not required. These values result in a good connection between the metal mesh and the heating strip while keeping the weight and cost of the metal mesh (such as copper mesh) low.

[0046] In some embodiments, the metal mesh is substantially as wide as the heating strip, and the length of the metal mesh is in the range of 0.5 cm to 100 cm, such as in the range of 1 cm to 50 cm, such as in the range of 5 cm to 50 cm. These numbers result in a good connection between the metal mesh and the heating strip while keeping the weight and cost of the metal mesh (such as copper mesh) low. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] The present invention will be explained in detail below with reference to the embodiments shown in the drawings.

[0048] Figure 1 is a schematic diagram illustrating an exemplary wind turbine.

[0049] Figure 2 is a schematic diagram illustrating an exemplary wind turbine blade.

[0050] Figure 3 A wind turbine blade with ice spots is shown in perspective.

[0051] Figures 4a to 4f A wind turbine blade with ice spots is shown in a top view, and a wind turbine blade according to the invention and a de-icing process according to the invention are shown.

[0052] Figures 5 to 7 Different schedules for generating heat in the heating strip are schematically shown.

[0053] Figure 8A cross section of a wind turbine blade according to the invention is shown.

[0054] Figure 9a Shown Figure 4a 、 Figure 8 and Figure 9c Detail of the cross section AA indicated in .

[0055] Figure 9b Shown Figure 9c Detail of the cross section BB indicated in .

[0056] Figure 9c A heating strip is shown with an adjoining metal mesh at each end of the strip.

[0057] Figures 10 to 11 Different types of heating strips are shown. DETAILED DESCRIPTION

[0058] Embodiments of the present invention will now be described in more detail with reference to the accompanying drawings. Like reference numerals generally refer to like elements throughout. The drawings illustrate selected ways of implementing various aspects of the present invention and should not be construed as limiting. Unless otherwise indicated, the drawings are not necessarily drawn to scale. The relative sizes of various elements and their shapes may have been selected to make various elements or details clearly distinguishable.

[0059] Figure 1 A conventional modern upwind wind turbine 2 according to the so-called "Danish concept" is shown, having a tower 4, a nacelle 6, and a rotor with a substantially horizontal rotor axis. The rotor comprises a hub 8 and three blades 10 extending radially from the hub 8, each blade having a blade root 16 closest to the hub and a blade tip 14 with a tip end 15 furthest from the hub 8. The present invention is not limited to this type of wind turbine.

[0060] Figure 2 A schematic diagram of an exemplary wind turbine blade 10 is shown. Wind turbine blade 10 has the shape of a conventional wind turbine blade with a root end 17 and a tip end 15, and includes a root region 30 closest to the hub, a profile or airfoil region 34, and a transition region 32 between root region 30 and airfoil region 34. Blade 10 includes a leading edge 18 that faces in the direction of rotation of blade 10 when the blade is mounted on the hub, and a trailing edge 20 that faces in the opposite direction of leading edge 18.

[0061] The airfoil region 34 (also referred to as the profile region) preferably has an ideal shape for rotation relative to the hub, while the root region 30 has a substantially circular or elliptical cross-section due to structural considerations, which, for example, makes it easier and safer to mount the blade 10 to the hub. The diameter of the root region 30 can be constant along the entire root region 30. The transition region 32 present in the wind turbine blade 10 of this example has a transition profile that gradually changes from the circular shape of the root region 30 to the airfoil profile of the airfoil region 34. The chord length of the transition region 32 typically increases in an outward direction from the hub. The airfoil region 34 has an airfoil profile with a chord extending between the leading edge 18 and the trailing edge 20 of the blade 10.

[0062] The different sections of the blade generally do not have a common plane, since the blade may be twisted and / or bent (i.e. pre-bent) in the direction from the root region to the tip, which is the most common case, for example to more or less compensate the local speed of the blade depending on the distance from the hub.

[0063] The wind turbine blade 10 includes a blade shell, which may, for example, include two blade shell parts, a first blade shell part 24 and a second blade shell part 26, e.g., made at least partially of fiber-reinforced polymer. The first blade shell part 24 may, for example, be part of a pressure-side or upwind blade part. The second blade shell part 26 may, for example, be part of a suction-side or downwind blade part. The first blade shell part 24 and the second blade shell part 26 are typically joined together, such as glued together, along a join line or glue joint 28 extending along the trailing edge 20 and the leading edge 18 of the blade 10. Typically, the root ends of the blade shell parts 24, 26 have a semicircular or semi-elliptical outer cross-sectional shape, which forms a root region, such as a circular or oval root region, when the first shell part and the second shell part are joined.

[0064] Figure 3 A wind turbine blade 10 is shown with precipitation in various states on blade 10. Blade 10 has a de-icing element 19 extending along a portion of blade 10 for de-icing a corresponding portion of leading edge 18 of blade 10. Ice spots 328-329 have formed on leading edge 18 of the blade. Ice spots 331-337 have also formed on the visible side of the blade, in this case, pressure side 36. Such ice spots affect the aerodynamic properties of the blade, reducing its efficiency and potentially causing noise. Figure 3 Also shown is melted ice 323 that is produced when the leading edge heating element 19 is active and melts ice, such as ice spots 328. Ice patches 321 behind the leading edge illustrate ice that is being removed from the blade, such as due to heating on the leading edge or simply due to airflow across the blade 10. Similarly, Figure 3 The removed ice is shown in the form of liquid water 322 .

[0065] A problem has been found, that melt water (such as Figure 3 Meltwater 323 (shown in FIG. 1 ) refreezes on the blade downstream of the leading edge 18 of the blade. For example, ice spot 337 may be the result of such meltwater refreezing on the blade. One or more of ice spots 331-336 may be formed by the same mechanism (or by another mechanism). For example, ice spot 332 may form during the melting of ice spot 329 on the leading edge 18 of the blade. Although the size of ice spot 329 is reduced due to the heating of the leading edge heating element 19, water has partially refreezed on the blade in the form of ice spots 332-333. Similarly, ice spots 331 and 334-336 may be the result of ice melted due to de-icing of the leading edge 18 freezing on the blade 10 downstream of ice spot 329.

[0066] Figure 4a The blade 10 is shown as seen in a top view towards the pressure side 36 of the blade 10 . Figure 4a The top view shows Figure 3 The ice spots 328-329, 331-337, the removed ice 321 and the melted ice 322-323 are shown in FIG. Figure 4a A plurality of heating strips 401-405 are shown arranged in the pressure side shell portion 36 in accordance with an embodiment of the present invention. The heating strips comprise carbon fiber yarns and / or tows and are connected to a power source via conductors (the conductors and power source are not shown). Each of the heating strips in this example is connected to a power source at either end of the heating strip (i.e. at the left and right ends of the heating strips in the figure). By applying a voltage across each of the strips 401-405, heat is generated which heats up the surface of the blade 10, which in turn melts the ice on the surface of the blade 10. Note that the heating strips are not visible in practice as they are positioned below the outer surface of the wind turbine blade so as not to be exposed to the environment. In this example, as Figure 8 and Figures 9a-9c As shown in FIG, heating strips are embedded in a wind turbine blade. By embedding the heating strips, heating can be provided closer to the outer surface (where ice forms). If the heating strips were located on the inner surface of the shell portion (exposed to the inside of the wind turbine blade), more heating would be required to increase the temperature at the outer surface because it is further away from the outer surface of the shell portion.

[0067] In this example, the longest of the heating strips (i.e., heating strips 401 and 402) is approximately 50% of the length of the blade from root to tip (not visible in the figure). The total extent of the heating strips at the location indicated by section AA is approximately 52%. This can also be considered the degree of coverage. Specifically, heating strips 401-405 cover 52% of the chord length at location AA.

[0068] The heating strips 401-405 extend substantially parallel and are spaced apart from each other in the chordwise direction. Different ice spots 331-337 are located above different heating strips, and in some cases, the ice spots also extend to the surface portions between the strips, such as ice spots 331, 333, and 335.

[0069] In this example, not all heating strips terminate at the same longitudinal position. This is due to the blade narrowing towards the blade's tip. Thus, in this example, the rearmost heating strip 405 terminates further from the tip than the other heating strips. The two heating strips 401 and 402 extend the furthest towards the tip (and, in this example, are of equal length).

[0070] Figures 4b to 4f The deicing process according to an embodiment of the present invention is shown. Figure 4b As shown in FIG, the heating strips 401 closest to the leading edge 18 of the blade 10 are heated by applying a voltage across the strips, ie between the ends of the strips 401. The generation of heat is schematically shown by the cross-hatching of the strips 401.

[0071] Due to the relatively low electrical conductivity of carbon fibers, the carbon fiber yarns and / or tows in heating strip 401 heat up, causing the surface temperature of the pressure-side portion near heating strip 401 to rise. In this example, this melts ice spot 335, ultimately removing it. It is also possible that heating simply removes ice spot 335. This depends on the shape and size of ice spot 335.

[0072] In this example, ice spots 329 on the leading edge have been removed from the leading edge 18 by heating the leading edge 18 using the leading edge heating element 19 .

[0073] The power supplied to strip 401 can be controlled separately from the other heating strips 402-405. In some embodiments, all heating strips are connected in parallel to the power supply and thus provide heating at the same time, or they are all turned off. In this example, as described below with reference to Figures 4c-4f As further described, all strips are individually controllable.

[0074] For illustration purposes, Figure 4b Further shown is ice 421 that has been removed, for example due to heating of ice spot 329 by leading edge heating element 19 or due to heating of ice spot 335 by heating strip 401 .

[0075] Due to the heating in the heating strip 401, the ice on the surface of the blade 10 is now reduced. Therefore, the noise and / or vibration caused by the ice spots 335 are eliminated. The heating time of the heating strip 401 can be selected depending on parameters such as the ambient temperature and the amount of ice on the blade 10.

[0076] In the next step, heating strip 402 is activated and heating strip 401 is deactivated. Figure 4c As shown in FIG. The heating of the heating strip 402 causes the ice spot 332 and a portion of the ice spot 337 to melt. Figure 4c As shown in FIG, a portion of ice spot 337 is sufficiently far from heating strip 402 that it has not melted. Due to the heating by heating strip 401 and the heating by heating strip 402, blade 10 has even less ice on the pressure side surface. As a result, noise and vibration that could otherwise be generated due to ice spots 332, 335, and the now-melted portion of ice spot 337 are eliminated. The elimination of vibration also results in reduced mechanical wear of components and improved blade efficiency.

[0077] As the next step in this embodiment, Figure 4d As shown in FIG, heating strip 403 is activated and heating strip 402 is deactivated. This causes the remaining portion of ice spot 337 to melt. In addition, a portion of ice spot 331 and a portion of ice spot 333 melt. The unmelted portions are too far from heating strip 403 for the heat generated by heating strip 403 to melt the entirety of ice spots 331 and 333.

[0078] Nevertheless, another portion of the blade 10 is now free of ice which would otherwise cause mechanical wear, noise generation and efficiency losses.

[0079] Next, if Figure 4e As shown in FIG, heating strip 404 is activated and heating strip 403 is deactivated. Ice spots 336 and 334, which were partially melted in the previous step, and the remaining ice spots 331 and 333 have now been removed from blade 10. Furthermore, due to the heating of the leading edge by leading edge heating element 19, another portion of ice spot 328 on leading edge 18 of blade 10 has been removed. However, according to the problem addressed by the present invention, a new ice spot 451 has formed from the water from the partially melted ice spot 328. Thus, even though all other ice spots have been removed by the continuous heating of multiple heating strips 401-405, new ice spot 451 has now appeared on the surface of blade 10.

[0080] Through the above-described de-icing cycle, the blade 10 has been partially de-iced.

[0081] As a final step, Figure 4f As shown in , the last heating strip 405 is activated and the previous heating strip 404 is deactivated. In this example, there is no ice in the heating area of the heating strip 405, and therefore the heating in the heating strip 405 will not remove any ice.

[0082] The newly formed ice spot 451 and any other ice spots formed can be eliminated by repeating the above steps. Depending on the level of ambient temperature, humidity and precipitation, this cycle can be repeated at a higher frequency.

[0083] Figure 5 The heating power provided by the five heating strips 401-405 is shown schematically and in arbitrary units as a function of time, corresponding to the above description of the heating power provided by the five heating strips 401-405. Figures 4a-4f The example described above corresponds to Figure 4b , a certain amount of power is provided to heating strip 401 for a certain amount of time. Then, the power in heating strip 401 is turned off, and power is provided to heating strip 402 as shown by power graph P2, then power is provided in heating strip 403 as shown by power graph P3, then power is provided in heating strip 404 as shown by power graph P4, and finally power is provided in heating strip 405 as shown by power graph P5.

[0084] The advantage of this approach is that ice that has melted (e.g. melted while heating strip 401 was active but refreezed back onto the blade, such as near heating strip 404) will be removed during a subsequent heating step, in this case when heating strip 404 is activated.

[0085] Figure 6 Another arrangement for providing power to heating strips 401-405 is shown. In this example, power is provided to all strips simultaneously. This arrangement has the advantage that the surface of the blade 10 is heated across the entire chord length, and therefore, ice removed above heating strip 401, for example, cannot reattach to the blade because the blade is also heated downstream of the leading edge 18.

[0086] Figure 7 A more advanced power scheduling is shown. In this example, the power P in the different heating strips 401-405 is i In some embodiments, de-icing is determined by visual inspection, such as by automated visual inspection of the shell portion 36 using a vision system such as a camera. Figure 7 In the example shown in FIG, a visual inspection determined that a significant amount of ice had formed above heating strip 401. Therefore, heating was applied for a certain amount of time. In this example, the heating time was relatively long because it was determined that a significant amount of ice had formed above heating strip 401, and despite the application of heating, a significant amount of ice remained attached to the heating strip.

[0087] The heating time can be carried out while monitoring the blade 10, and when it is determined through monitoring that the ice above the heating strip 401 has been eliminated, the heating can be stopped. Figure 7 The heating in the heating strip 402 shown in FIG is performed for a certain amount of time, reflecting that it has been determined that a certain amount of ice exists above the heating strip 402. When it is determined that the ice above the heating strip 402 has been removed, the heating in the heating strip 402 ends.

[0088] The heating strip 403 was not powered at all during the time period shown because no ice was located above the heating strip 403 as determined by the vision system.

[0089] Since the vision system identifies two ice spots forming in succession, the heating strip 404 is heated twice in rapid succession. Both ice pieces are removed quickly, and therefore the heating in the heating strip 404 is also terminated quickly.

[0090] Finally, if Figure 7 , heating strip 405 overlaps the heating in heating strip 404. The ice removed by the heating in heating strips 404 and 405 may be, for example, re-frozen water resulting from de-icing performed by heating strips 401 and 402 as described above, or from de-icing the leading edge by leading edge heating element 19.

[0091] Figure 7 The advantage of the scheme shown in FIG is that power is provided only where and when it is needed. If there is no ice accumulation on blade 10, there is no reason to expend energy heating these heating strips 401-405. Similarly, if ice accumulates only near heating strip 403, there is no reason to expend energy heating heating strips 401-402 and 404-405. Selective heating saves electrical energy and reduces fatigue caused by expansion and contraction due to temperature changes caused by heating and subsequent cooling.

[0092] As another example, from Figure 4a Initially, visual inspection reveals that ice spots have formed over heating bars 401-404, but not over heating bar 405. Therefore, heating is turned on in heating bars 401-404. This eliminates ice spots 331-337. When the ice is removed from over a heating bar, such as heating bar 402, the heating is turned off. Ice spot 331 is thicker and may take longer to remove or melt. Therefore, heating bar 403, over which ice spot 331 is located, must remain on for a longer period of time. Therefore, after the heating in heating bar 402 is turned off, the heating in heating bar 403 is eventually turned off as well. On the other hand, the vision system determines that no ice is located over heating bar 405, and therefore no heating is provided in heating bar 405, which is consistent with the above. Figure 4f In contrast to what is shown in Figure 4f In the case of a heating strip, heating is provided regardless of whether there is ice above the strip. This saves energy and reduces fatigue.

[0093] Figure 4e As shown in and about Figure 4e The described ice spot 451 may not form in the case of power scheduling based on visual inspection, for example because the vision system would detect the ice spot 451 earlier and provide heating in the heating strips 401 and 402 in response to eliminate the ice spot.

[0094] In general, the heating in the heating strips may be operated on a schedule that may depend on the ambient temperature, or may be operated based on a vision system or other system that can detect the presence of ice above the heating strips. It is also possible to simply power all the heating strips at the same time and turn them off at the same time.

[0095] In some embodiments, the system does not run continuously. The higher the ambient temperature, the less ice will form on the blades. Consequently, ice accumulation downstream of the blades will progress more slowly, and de-icing will be less necessary. After a certain amount of time (in some embodiments, depending on the ambient temperature), the heating schedule is allowed to run to remove the accumulated ice. At lower temperatures, ice accumulates at a faster rate. Therefore, the de-icing process is performed more frequently than at higher temperatures.

[0096] When using a vision system to detect ice, the de-icing process may be postponed until the vision system determines that the ice speck has grown above an acceptable size. That is, even if there is an ice speck on the shell portion, de-icing will not be performed. Once the ice speck grows to a threshold size, heating will be provided in the corresponding heating strip to remove the ice speck. This saves power compared to continuously removing even small ice specks. Figure 4a For example, when ice spot 331 reaches a threshold size, the vision-based system is activated and heating is applied to remove it. Similarly, by providing heating in heating strips 401, 403, and 404, relatively large ice spots 333 and 335 can be removed before they exceed the threshold size (ice spot 333 spans both heating strips 403 and 404). Another advantage of this schedule is that smaller ice spots 332, 334, 336, and a portion of ice spot 337 are also removed and, therefore, do not grow larger.

[0097] Figure 8 Shown Figure 4a Cross section AA is indicated on the middle blade 10 . Figure 8 Five heating strips 401-405 are shown arranged as part of the pressure side shell portion 36, also shown in FIG. Figures 4a-4f As shown in . Figure 8 Also shown is a leading edge heating element 19 that provides de-icing for the leading edge 18 of the blade 10. As described above, when power is supplied to the heating strips 401-405, the generated heat is transferred to the outer surface of the pressure side shell portion, causing ice located on the outer surface to melt or be removed from the outer surface. According to the present invention, the heating strips 401-405 are spaced apart. Preferably, this spacing ensures that the heat transferred from the heating strips 401-405 to areas not immediately above one of the heating strips 401-405 is sufficient to melt ice or at least remove ice from the surface of the blade 10.

[0098] Figure 8A second plurality of heating strips is shown, consisting of four heating strips 801-804, arranged as part of the suction side shell portion 38 for de-icing the surface of the suction side shell portion 38. They operate similarly to the heating strips 401-405 described above as part of the pressure side shell portion 36. Similar to the heating strips 401-405 in the pressure side shell portion 36, the heating provided by each of the heating strips 801-804 can be individually controllable to achieve the advantages described above with respect to the heating strips 401-405, including avoiding unnecessary heating that causes a loss of wind turbine efficiency, and reducing expansion and contraction caused by temperature fluctuations due to heating and subsequent cooling of the shell portion 38.

[0099] Figure 8 It is also shown that the heating strips can have different widths and be spaced apart by different amounts. Figure 8 Also instructed Figures 9a-9b Details described in more detail in 810.

[0100] Figure 9a Schematically shown in more detail Figure 8 Indicated in section 810. With Figure 9a The corresponding cross section AA is Figure 4a and Figure 9c As indicated in FIG, the latter figure only shows the carbon fiber material and the metal mesh used to connect the carbon fiber material to the power supply. Portion 810 includes an inner skin 911 forming a portion of the inner surface of shell portion 36, and an outer skin 914 forming a portion of the outer surface of shell portion 36. The shell portion further includes a metal mesh 913, such as a copper mesh, arranged between the heating strip 401 and the outer surface of shell portion 36. This metal mesh 913 reduces the risk of lightning currents propagating through the heating strip 401, which could be detrimental to the strip and seriously damage the blade 10. An electrically insulating layer 912 (such as a PET film) electrically isolates the heating strip 401 from the copper mesh 913. In some embodiments, the insulating film may be sandwiched between fiber layers (such as glass fiber layers). Portion 810 further includes a metal mesh 915, such as a copper mesh, overlapping the heating strip 401. Thus, the heating strip 401 and the metal mesh 915 are electrically connected. The metal mesh 915 serves as a contact portion connecting the first end of the heating strip 401 to the power supply. Figure 9c , a heating strip 401 is shown with a metal mesh 915. To illustrate that the metal mesh 915 abuts the heating strip 401 in a direction from the inner surface to the outer surface of the shell portion, the metal mesh 915 is shown as not extending all the way to the first end of the heating strip 401. However, in some embodiments, the metal mesh begins at the very end of the heating strip. Figure 9c Also shown is a second metal mesh 916 similarly arranged at a second end of the heating strip 401. By applying a voltage across the metal meshes 915 and 916, heating is generated in the heating strip. Figure 9bShown with Figure 9c The cross section corresponding to the designation BB in FIG. In this region, no metal mesh abuts the carbon fiber material. Thus, metal meshes 915 and 916 are electrically separated by the carbon fiber material in heating strip 401 to allow heating in heating strip 401. Figure 9b Further shown are an inner skin 911, an insulating film 912, a metal mesh 913 and an outer skin 914 (while Figure 9c For illustration purposes only carbon fiber material 401 and metal meshes 915 and 916 are shown).

[0101] Figure 10 An exemplary heating strip 1000 for use in the present invention is shown for de-icing the blade shell portion of a blade, particularly downstream of the leading edge of the blade in the chordwise direction. For example, the heating strip 1000 may be used with any of the heating strips 401-405. In this example, the heating strip 1000 comprises a glass fiber material, such as a glass fiber mat 1002, having a plurality of carbon fiber yarns and / or tows 1001 sewn thereon. The carbon fiber yarns and / or tows extend between opposite ends of the heating strip 1000. In this example, contact portions 1011 and 1012 are provided at opposite ends of the heating strip 1000. As described above with respect to Figures 4a-4f As described above, by applying a voltage V(t) across contact portions 1011 and 1012, the carbon material generates heat, which is used to de-ice the surface of blade 10. A heating strip 1000 having carbon fiber yarns / tows arranged in a wavy pattern (such as a sinusoidal pattern) has the advantage that the stiffness ratio of heating strip 1000 is lower than that of a unidirectional fiber mat. Therefore, heating mat 1000 can be used without adding excessive stiffness to blade 10.

[0102] Figure 11 Another exemplary heating strip 1100 is shown. Heating strip 110 includes biaxial fiber material 1101. As described above, similar to heating strip 1000, contacts 1111 and 1112 are configured to allow application of voltage V(t) whereby the carbon material generates heat to de-ice the surface of blade 10.

[0103] Another option is to use unidirectional fiber mats as heating strips, but a disadvantage of unidirectional mats is that they are too stiff and therefore their use as heating strips is not preferred in the context of the present invention.

[0104] Reference Mark List

[0105] 2 Wind turbines

[0106] 4 Tower

[0107] 6 Cabin

[0108] 8 hub

[0109] 10 blades

[0110] 14 Leaf tips

[0111] 15 distal end

[0112] 16. Blade root

[0113] 17 root end

[0114] 18 Leading Edge

[0115] 19 Leading edge heating element

[0116] 20 trailing edge

[0117] 24 First blade shell part (pressure side)

[0118] 26 Second blade shell part (suction side)

[0119] 28 bonding lines / glue joints

[0120] 30 Root Zone

[0121] 32 Transition Zone

[0122] 34 Airfoil area

[0123] 36 Blade pressure side shell

[0124] 38 Suction side shell of the blade

[0125] 40 Blade shoulder

[0126] 321 removed ice

[0127] 322 water removed

[0128] 323 Melting Ice

[0129] 328-329 Ice Spots

[0130] 331-337 Ice Spots

[0131] 401-405 Heating strips in the pressure side shell section

[0132] 421 removed ice

[0133] 801-804 Heating strips in the suction side shell

[0134] 810 shell details

[0135] 911 shell inner skin

[0136] 912 Electrical insulating film

[0137] 913 Metal Mesh

[0138] 914 Shell outer skin

[0139] 915 heating strip contact part

[0140] 916 heating strip contact part

[0141] 1000 Heating Strips

[0142] 1001 carbon fiber yarn / tow

[0143] 1002 Fiberglass Mat

[0144] 1011 Heating strip contact part

[0145] 1012 heating strip contact part

[0146] 1100 Heating Strip

[0147] 1101 Biaxial fiber material

[0148] 1111 Heating strip contact part

[0149] 1112 heating strip contact part

[0150] L longitudinal axis of the blade

[0151] P i Power supplied to generate heating in heating strip i

[0152] V, V(t) are the voltages applied to generate heating in the heating strip

Claims

1. A wind turbine blade (10) having a suction side shell portion (38) and a pressure side shell portion (36), each shell portion extending between a leading edge (18) of the wind turbine blade and a trailing edge (20) of the wind turbine blade, the wind turbine blade extending along a longitudinal axis (L) from a root end (30) of the wind turbine blade to a tip end (15) of the wind turbine blade, the wind turbine blade comprising: - a leading edge heating element (19) extending along at least a portion of the leading edge of the wind turbine blade, the leading edge heating element being configured for de-icing a corresponding portion of the outer surface of the leading edge, a first plurality of heating strips (401-405, 801-804), each of the first plurality of heating strips extending in a substantially spanwise direction of the wind turbine blade, the first plurality of heating strips forming part of a first shell portion of the wind turbine blade, the first plurality of heating strips being embedded inside the first shell portion or positioned such that they are exposed to the inside of the wind turbine blade, wherein the first shell portion is the pressure side shell portion or the suction side shell portion, the first plurality of heating strips being spaced apart from each other and from the leading edge heating strips in a chordwise direction, each heating strip having a first end and a second end, the first end being closer to the tip end than the second end, each heating strip comprising carbon fiber yarn and / or tow material (1001, 1101), and - a power supply configured to provide power to each of said first plurality of heating strips so as to generate heating in said each strip, said heating being generated by said carbon fiber yarn and / or tow material.

2. The wind turbine blade of claim 1 , wherein one or more of the first plurality of heating strips comprises one or more carbon fiber yarns and / or tows (1001 , 1101 ) extending from a first end to a second end of the heating strip.

3. A wind turbine blade according to claim 1 or claim 2, wherein one or more of the carbon fiber yarns and / or tows, such as all of the carbon fiber yarns and / or tows, extend from the first end to the second end (1001) of the respective heating strip in a wavy manner, such as in a substantially sinusoidal manner.

4. A wind turbine blade according to any one of the preceding claims, wherein one or more of said first plurality of heating strips comprises a unidirectional carbon fiber material or a biaxial fiber material (1101) for generating said heating.

5. A wind turbine blade according to any one of the preceding claims, wherein the length of each heating strip is at most 80% of the length of the blade from the root end to the tip end.

6. A wind turbine blade according to any one of the preceding claims, wherein the heating generated by at least one heating strip of the first plurality of heating strips is controllable independently of the heating generated by another heating strip of the first plurality of heating strips.

7. A wind turbine blade according to any one of the preceding claims, wherein the total extent of the first plurality of heating strips in the chordwise direction at a first position along the longitudinal axis of the blade is at least 50% of the chord length at the first position.

8. A wind turbine blade according to any one of the preceding claims, wherein a first end of each heating strip of the first plurality of heating strips abuts a respective first metal mesh (915), and a second end of each heating strip abuts a respective second metal mesh (916), whereby the respective first metal mesh and the respective second metal mesh are electrically connected to each other via the heating strip, and wherein the respective first metal mesh and the respective second metal mesh are connected to the power supply to allow heating to be generated in the heating strip by providing power to the heating strip.

9. A wind turbine blade according to any of the preceding claims, further comprising a metal mesh, such as a copper mesh, arranged between the heating strip and the outer surface of the first shell part.

10. The wind turbine blade of any one of the preceding claims, wherein the first plurality of heating strips comprises a first heating strip and a second heating strip, wherein the first heating strip is closer to the leading edge than the second heating strip, and wherein the first heating strip is longer than the second heating strip.

11. The wind turbine blade of any one of the preceding claims, wherein in a direction from the leading edge to the trailing edge, the length of each of the first plurality of heating strips is at most as long or shorter than a preceding heating strip of the first plurality of heating strips.

12. A wind turbine blade according to any one of the preceding claims, wherein both the suction side shell portion and the pressure side portion comprise a plurality of heating strips according to claim 1.

13. A method of manufacturing a wind turbine blade according to any one of claims 1 to 12, comprising: - laying down material for forming the first shell portion in a first mould, including laying down fibre material, the leading edge heating element and the first plurality of heating strips, - embedding the paving material in resin, such as by resin infusion, and - connecting each of said heating strips to a power source to allow heating to be provided to each of said heating strips by applying a voltage across each heating strip.

14. A method for de-icing a wind turbine blade according to any one of claims 1 to 12, the method comprising: - providing power to each of the heating bars of the first plurality of heating bars to generate heat in the heating bar.

15. The method of claim 14 , wherein the heat generated in each of the heating strips is controlled based on an image of the blade surface obtained from a vision system, wherein heating is provided in a particular heating strip if de-icing is determined to be required in the vicinity of the heating strip based on the image from the vision system, and wherein heating in the heating strip is reduced or turned off when the level of ice in the vicinity of the heating strip decreases below a threshold, such as when ice is completely removed in the vicinity of the heating strip.

Images