Heating wind turbine blades

Abstract

A first aspect of the invention provides a wind turbine blade having a blade shell defining a suction side, a pressure side, a leading edge and a trailing edge of the blade. The blade further comprises a blade heating system comprising one or more heating elements configured to heat the blade in first and second heating zones, wherein the first heating zone is closer to the leading edge than the second heating zone, and the heating system is configured to generate a heat flux in the first and second heating zones such that the heat flux generated in the first heating zone is lower than the heat flux generated in the second heating zone.

Description

Technical Field

[0001] The invention relates to a wind turbine blade and a method of heating a wind turbine blade. Background Art

[0002] Ice can form on wind turbine blades in conditions of low temperatures or when there is a lot of moisture in the air. This ice buildup can reduce the aerodynamics of the wind turbine blades, which can reduce the efficiency and performance of the wind turbine.

[0003] Electrothermal heating (ETH) elements can be used for either or both of anti-icing (preventing ice accumulation) or de-icing (removing ice accumulation) of blades. An example is shown in WO2017 / 190748, where two or more ETH panels are overlapped to provide a predetermined heat flux.

[0004] Conventionally, such ETH elements are only provided at the leading edge of the blade.A problem with conventional ETH elements is that when water droplets flow over the trailing edge of the ETH element, they freeze to form ice ridges. Summary of the invention

[0005] A first aspect of the invention provides a wind turbine blade having a blade shell defining a suction side, a pressure side, a leading edge and a trailing edge of the blade. The blade further comprises a blade heating system, the blade heating system comprising one or more heating elements configured to heat the blade in first and second heating zones, wherein the first heating zone is closer to the leading edge than the second heating zone, and the heating system is configured to generate a heat flux in the first and second heating zones such that the heat flux generated in the first heating zone is lower than the heat flux generated in the second heating zone, so that the heat flux generated in the second heating zone is sufficient to cause evaporation of water.

[0006] It has been realised that the heat flux required to evaporate water droplets decreases behind the leading edge of the blade. Therefore, positioning the second (higher heat flux) heating zone further from the leading edge than the first (lower heat flux) heating zone means that less heat flux is required to induce a significant degree of evaporation and inhibit the formation of ice ridges.

[0007] The first heating region may be configured for one or both of anti-icing (preventing ice accumulation) or de-icing (removing ice accumulation) of the blade.

[0008] The heating system may be configured to generate a heat flux in the first and second heating zones simultaneously such that the heat flux generated in the first heating zone is lower than the heat flux generated in the second heating zone.

[0009] The heating system may be configured to generate heat fluxes in the first and second heating zones during a heating period such that on average during the heating period the heat flux generated in the first heating zone is lower than the heat flux generated in the second heating zone.

[0010] The first heating zone may extend a greater chordwise distance than the second heating zone. This provides an efficient arrangement for a given amount of available power and can maximize the area heated (via the relatively large first heating zone) while utilizing the smaller second heating zone to prevent or at least inhibit the formation of ice ridges behind the first heating zone.

[0011] The first and second heating zones may be in an overlapping spanwise position. This ensures that water flowing across the blade flows from the first heating zone into the second heating zone.

[0012] The first and second heating zones may have the same (or substantially the same) span size, or they may have different span sizes.

[0013] The second heating zone may have a leading edge at a chordwise position of more than 5% chord, more than 10% chord, more than 15% chord, or more than 20% chord. Positioning the second heating zone at such a relatively high chordwise position may reduce power consumption because the power required to evaporate water tends to decrease as the chordwise position increases.

[0014] The one or more heating elements may include first and second heating elements configured to heat the blade in first and second heating zones, respectively.

[0015] The first heating element may comprise a panel of electrically conductive resistive material and the second heating element may comprise a thin strip or wire of electrically conductive resistive material.

[0016] The second electrothermal heating element may have a lower sheet resistance (in ohms squared) than the first electrothermal heating element.

[0017] The second electrothermal heating element may have a lower resistance (in ohms) than the resistance of the first heating element.

[0018] The one or more heating elements may be electrothermal heating elements.

[0019] The one or more heating elements may comprise an electrically conductive resistive material, for example a veil of fibres (such as carbon fibres) or a metal mesh.

[0020] The heating system can be configured to generate an average heat flux in the second heating zone that is at least twice the average heat flux generated in the first heating zone. In other words, the heating system can be configured to generate a first average heat flux in the first heating zone and a second average heat flux in the second heating zone, and the second average heat flux can be at least twice the first heat flux.

[0021] The second heating zone may be closer to the trailing edge than the first heating zone.

[0022] The entirety of the second heating zone may be closer to the trailing edge than the first heating zone is relative to the trailing edge.

[0023] The first and second heating zones may be adjacent. That is, there may be no gap between the first and second heating zones.

[0024] Another aspect of the invention provides a wind turbine comprising a wind turbine blade according to the first aspect of the invention.

[0025] Another aspect of the present invention provides a method of heating a wind turbine blade, the wind turbine blade having a blade shell defining a suction side, a pressure side, a leading edge and a trailing edge of the blade, the method comprising: heating the blade in first and second heating zones, wherein the first heating zone is closer to the leading edge than the second heating zone, and the first heating zone is heated at a lower heat flux than the second heating zone.

[0026] The second heating zone may be heated to a higher temperature than the first heating zone.

[0027] The method may include heating the blade simultaneously in first and second heating zones such that the first heating zone is heated at a lower heat flux than the second heating zone.

[0028] The method may comprise heating the blade in first and second heating zones during a heating period such that, on average during the heating period, the first heating zone is heated at a lower heat flux than the second heating zone.

[0029] Typically, the second heating zone is heated with a heat flux sufficient to evaporate water flowing through the second heating zone. Water may flow across the first heating zone into the second heating zone, where it evaporates. Water flowing across the first heating zone may not evaporate substantially. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Embodiments of the present invention will now be described with reference to the accompanying drawings, in which:

[0031] Figure 1 A wind turbine is shown;

[0032] Figure 2 A wind turbine blade with multiple heating elements is shown;

[0033] Figure 3 The driving mode of one of the heating units is shown;

[0034] Figure 4 is a comparative example showing a portion of a blade with a blade heating system; and

[0035] Figure 5 A section of a blade is shown with a blade heating system according to one embodiment of the invention. DETAILED DESCRIPTION

[0036] Figure 1 A wind turbine 1 is shown in a schematic perspective view. The wind turbine 1 comprises a tower 2, a nacelle 3 at the apex of the tower, and a rotor 4 operatively coupled to a generator housed inside the nacelle 3. In addition to the generator, the nacelle also houses various components required for converting wind energy into electrical energy, as well as various components required for operating, controlling and optimizing the performance of the wind turbine 1. The rotor 4 of the wind turbine comprises a central hub 5 and a plurality of blades 6 extending outwardly from the central hub 5. In the illustrated embodiment, the rotor 4 comprises three blades 6, but the number may be different, for example, the rotor 4 may have two or four blades 6. In addition, the wind turbine 1 comprises a control system. The control system may be placed inside the nacelle 3 or distributed at several locations inside the wind turbine 1 and connected for communication.

[0037] The wind turbine 1 may be included in a collection of other wind turbines belonging to a wind power plant, also called a wind farm or wind farm, which is connected to a power grid as a power plant via transmission lines. The power grid generally consists of a network of power stations, transmission circuits and substations coupled by a network of transmission lines that transmit electricity to loads in the form of end users and other customers of the power utility.

[0038] Each blade 6 has a blade heating system 10, which includes twelve heating units, six of which are in Figure 2 Each heating unit includes two heating elements.

[0039] like Figure 5 As best shown in FIG. 1 , each blade 6 has a blade shell defining a suction side 30, a pressure side 32, a leading edge 26 and a trailing edge 28 of the blade. Six heating units are arranged on the suction side 30, Figure 2 The other six heating units are on the pressure side 32, Figure 2 Hidden in.

[0040] like Figure 2As shown, the chord-wise dimension of the heating unit may decrease near the blade tip. For example, the heating unit closest to the blade tip may have the smallest chord-wise dimension, while the heating unit farthest from the blade tip (closest to the blade root) may have the largest chord-wise dimension.

[0041] The heating elements are identical (except for their chord-wise dimensions) so only one exemplary heating unit is numbered and described below.

[0042] The exemplary heating unit includes first and second electrothermal heating elements 12, 14 configured to heat the blade in first (anti-icing) and second (evaporative) heating zones, respectively. The first heating element 12 (and its associated heating zone) is closer to the leading edge 26 of the blade than the second heating element 14 (and its associated heating zone). The first and second heating elements 12, 14 are configured to generate heat fluxes in their respective first and second heating zones such that the heat flux generated in the first heating zone is lower than the heat flux generated in the second heating zone.

[0043] Each of the first and second heating elements 12, 14 may include a respective sheet 16, 18 of electrically conductive, resistive material, such as a yarn of fibers, or in particular, a yarn of carbon fibers.

[0044] Figure 3 An example of how two heating elements 12, 14 are driven is shown. Each heating element has an electrode 22 at one end and an electrode 24 at the other end. A power supply 20 drives the heating elements in parallel by applying an AC or DC voltage between the electrodes 22, 24. This causes current to flow through the sheets 16, 18, and the resistance in the carbon yarn material causes heat to be generated by resistive heating, Joule heating, or Ohmic heating.

[0045] The heat flux output by each heating element is V 2 / (R s *L 2 ), where V is the voltage between electrodes 22, 24, R s is the sheet resistance of the carbon yarn (in ohms squared), and L is the length between the electrodes 22, 24. Thus, the sheet resistance R of the carbon yarn sheet 18 of the second heating element 14 can be selected s The carbon yarn sheet 16 of the first heating element 12 has a lower sheet resistance (eg, the yarn material may be thicker, or it may have a higher carbon fiber density), so its heat flux is higher, typically two times higher or more.

[0046] Reference now Figure 4, a comparative blade heating system 100 is shown to demonstrate the problem of ice ridge accumulation. The heating system 100 includes a single anti-icing heating element 102 configured to heat a single heating zone 104 at the leading edge. When water droplets strike the heating zone 104, the heat from the heating element 102 ensures that most of the water droplets remain in a liquid state rather than freezing. The water droplets flow back over the trailing edge of the heating zone 104, where they freeze to form an ice ridge 106. This ice ridge 106 has a significant impact on the aerodynamic performance of the blade, and its presence has a negative impact on the efficiency and performance of the wind turbine. Such ice ridges can accumulate on both the suction side and the pressure side of the blade.

[0047] Figure 5 The operation of one of the exemplary heating units 12, 14 is shown. A water droplet hits the leading edge and the heat flux generated by the first heating element 12 ensures that the majority of it stays in the liquid phase and does not freeze.

[0048] The first heating element 12 is located at or near the leading edge 26 of the blade 6, where most water droplets impact the blade 6. In this example, the leading edge of the first heating element 12 (and its associated first heating zone) may be at the leading edge 26 of the blade (which is typically manufactured as two half shells).

[0049] The water droplets travel chord-wise across the first heating zone toward the trailing edge 28 and remain liquid due to the heating action of the first heating element 12. The water droplets then flow from the first heating zone into the second heating zone above the second heating element 14 where they experience higher temperatures and higher heat flux, which causes them to evaporate.

[0050] There may be little gap between the heating elements 12, 14 so that the first and second heating zones are adjacent, e.g. Figure 5 As shown, or there may be a small gap between the heating elements 12, 14, such as Figure 3 It is schematically shown in FIG.

[0051] The heat flux required to evaporate the water droplets is greatest at the leading edge 26 and decreases along the chord length. Therefore, positioning the second (evaporation) heating element 14 behind the first (anti-icing) heating element 12 (rather than vice versa) means that less heat flux is required to induce a significant degree of evaporation and inhibit the formation of ice ridges.

[0052] The leading edge of the second heating element 14 (and its associated second heating zone) may have a chordwise position, for example, in the 20%-30% chordwise range. The heat flux required to evaporate water at this chordwise position is less than that required at the leading edge.

[0053] The chord-wise dimension of the first heating element 12 may be greater than the chord-wise dimension of the second heating element 14. In other words, Figure 5A dimension C1 of the first heating element 12 projected onto the blade chord line 34 as shown in FIG. 3 may be greater than a dimension C2 of the second heating element 14 projected onto the blade chord line 34 .

[0054] The second heating element 14 only requires a relatively small chordal dimension, since the water droplets evaporate relatively quickly provided the heat flux is sufficient. Thus, the sheet 18 of the second heating element 13 may be a narrow strip or wire, whereas the sheet 16 of the first heating element 12 may be a relatively wide panel.

[0055] like Figure 2 As shown, the first and second heating elements 12, 14 may have the same span size. The first and second heating elements 12, 14 may also have the same or overlapping span positions, which means that a water droplet that crosses the surface of the blade in the chord direction starting from the leading edge 26 may flow across the first heating element 12 and then reach the second heating element 14. Figure 3 As shown, the first heating element 12 may be larger in area than the second heating element 14 .

[0056] In the above example, the heating elements 12, 14 are powered by the power source 20 at the same time. In another example, instead of driving the elements 12, 14 at the same time, the first heating element 12 is powered for a few seconds, and then the second heating element 14 is powered for a few seconds, and this cycle is repeated over a heating period (which may be hours or days, for example). Thus, the elements 12, 14 are hot at the same time, but are not necessarily powered at the same time.

[0057] In both examples, on average during the heating period, the heat flux (in watts per square meter) generated in the first heating zone by the first heating element 12 is lower than the heat flux generated in the second heating zone by the second heating element 14. The temperature of the second heating zone may also be higher on average than the temperature of the first heating zone.

[0058] In the above example, the heat flux generated by the first and second heating elements 12, 14 can remain substantially constant across the first and second heating zones, respectively. If the heat flux varies across the first and second heating zones, the average (and / or maximum) heat flux generated by the first heating element 12 across the first heating zone can be lower than the average (and / or maximum) heat flux generated by the second heating element 14 across the second heating zone.

[0059] The average heat flux generated by the second heating element 14 in the second heating zone is preferably at least twice the average heat flux generated by the first heating element 12 in the first heating zone.

[0060] As described above, the first and second heating elements 12, 14 are configured to heat the respective first and second heating zones so that the heat flux is different. This heat flux difference between the heating elements can be achieved by using carbon yarn materials with different sheet resistances as described above, but other methods are also possible.

[0061] In an alternative embodiment, the second heating zone may be heated by a pair of overlapping heating elements, as described in WO2017 / 190748, while the first heating zone is heated by only a single heating element.

[0062] In another alternative, the heating elements may be identical, but with the second heating element driven by a higher voltage.

[0063] In another alternative, the heating element 14 may be a heating wire or a heating mesh or an arrangement of heating wires.

[0064] As described above, the first and second heating zones may be heated by respective independent heating elements 12, 14. In other examples, a single heating element may heat both heating zones. For example, a single heating element may have carbon yarn regions with different sheet resistances that produce different heat fluxes.

[0065] In this example, each side of the blade has six heating units, each with a pair of heating elements 12, 14. Other arrangements are possible. For example, there may be only a single evaporative heating element, which replaces the six evaporative heating elements 14 and runs along the blade for the same span length.

[0066] The pressure side 32 of the blade may have Figure 2 The heating elements shown on the suction side 30 are identical heating elements (ie, with both the anti-icing heating element 12 and the evaporative heating element 14 ).

[0067] Alternatively, the pressure side of the blade may have only an anti-icing heating element 12 (i.e., it may not have an evaporative heating element 14). Or vice versa, that is, the pressure side 32 of the blade may have both an anti-icing heating element 12 and an evaporative heating element 14, while the suction side of the blade may have only an anti-icing heating element 12 (i.e., it may not have an evaporative heating element 14).

[0068] Although the invention has been described above with reference to one or more preferred embodiments, it will be appreciated that various changes or modifications may be made without departing from the scope of the invention as defined in the appended claims.

Claims

1. A wind turbine blade having a blade shell defining a suction side, a pressure side, a leading edge and a trailing edge of the blade, the blade further comprising a blade heating system, the blade heating system comprising one or more heating elements configured to heat the blade in first and second heating zones, wherein: The first heating zone is closer to the leading edge than the second heating zone, and the heating system is configured to generate heat flux in the first and second heating zones so that the heat flux generated in the first heating zone is lower than the heat flux generated in the second heating zone, wherein the heat flux generated in the second heating zone is sufficient to evaporate water.

2. The wind turbine blade according to claim 1, wherein: The heating system is configured to generate heat fluxes in the first and second heating zones during a heating period such that on average during the heating period, the heat flux generated in the first heating zone is lower than the heat flux generated in the second heating zone.

3. A wind turbine blade according to claim 1 or 2, wherein: The first heating zone extends over a greater chordwise distance than the second heating zone.

4. The wind turbine blade according to claim 1 or 2, wherein: The first and second heating zones are in overlapping spanwise locations.

5. The wind turbine blade according to claim 1 or 2, wherein: The second heating zone has a leading edge at a chordwise location exceeding 10% of the chord length.

6. The wind turbine blade according to claim 1 or 2, wherein: The one or more heating elements include first and second heating elements configured to heat the blade at first and second heating zones, respectively.

7. The wind turbine blade according to claim 1 or 2, wherein: The one or more heating elements are electrothermal heating elements.

8. The wind turbine blade according to claim 1 or 2, wherein: The heating system is configured to generate an average heat flux in the second heating zone that is at least twice the average heat flux generated in the first heating zone.

9. The wind turbine blade according to claim 1 or 2, wherein: The second heating zone is closer to the trailing edge than the first heating zone.

10. A wind turbine comprising a wind turbine blade according to any one of the preceding claims.

11. A method of heating a wind turbine blade, the wind turbine blade having a blade shell defining a suction side, a pressure side, a leading edge and a trailing edge of the blade, the method comprising: The blade is heated in first and second heating zones, wherein the first heating zone is closer to the leading edge than the second heating zone and the first heating zone is heated at a lower heat flux than the second heating zone, so that the heat flux generated in the second heating zone is sufficient to evaporate water.

12. A method according to claim 11, comprising heating the blade in first and second heating zones during a heating period such that on average during the heating period the first heating zone is heated at a lower heat flux than the second heating zone.

13. The method according to claim 11 or 12, wherein: Water flows across the first heating zone into the second heating zone where it is evaporated.

Images