DE-ICING OF A WIND TURBINE BLADE

Abstract

A heating assembly for a wind turbine: generator, the assembly comprising: a heat reservoir mounted within a blade of the wind turbine generator; a heat source for supplying heat to the heat reservoir; a plurality of thermal conductors projecting front said heat reservoir to a surface of said blade.

Description

FIELD OF THE INVENTION

The invention relates to wind turbine generators (WTG's) used in the generation of electricity. In particular, the invention relates to means of removing ice from a rotor blade of a wind turbine generator.

BACKGROUND

Blade de-icing is critical in WTG because there is a 20% to 50% increase in the loss production factor. Ice accretion on wind turbine blades causes:

• • Change in aerodynamic shape resulting in significantly reduced power production
  • Increased root loads and reduced blade life
  • Unbalanced mass on the rotor plane
  • Danger of ice throw from the blades

In the case of melting ice, the principal characteristic is the surface-ice interface temperature which has to be above freezing. When melting occurs at the blade surface-ice interface, chunks of ice fall off as a result of wind and gravity forces.

The amount of heat and the time required to melt the ice depends on numerous factors. These include the thickness of the ice layer, the loss of heat from the external surfaces of the blade, the external ambient temperature, and most importantly, the efficiency of the method fro transferring the heat from the source to the frozen areas.

SUMMARY OF INVENTION

In a first aspect the invention provides a heating assembly for a wind turbine generator, the assembly comprising: a heat reservoir mounted within a blade of the wind turbine generator; a heat source for supplying heat to the heat reservoir; a plurality of thermal conductors projecting from said heat reservoir to a surface of said blade.

Accordingly, the delivery of heat through conduction from the reservoir to, or adjacent to, the surface of a rotor blade, then the elevation of temperature to the surface will consequently create a liquid/solid phase change allowing the ice to break up and fall from the blade.

In one embodiment the heat source may include an insulated duct for delivering hot air from a hot air source to the heat reservoir. Further, the heat reservoir may be substantially hollow or void into which the hot air is directed. Further, such a void may include an array of heat transfer fins within the void of the heat reservoir such that hot air delivered from the duct into the heat reservoir heats the heat transfer fins delivering heat to a thermal mass of said heat reservoir.

In one embodiment the heat reservoir may be mounted to a structural support, or spar, of the blade. Alternatively, the heat reservoir include a portion of said spar. For instance, the heat reservoir may have a portion for receiving heat such as a cavity for receiving hot air with a portion of the spar acting as a thermal mass for receiving heat such that conductors project from said thermal mass. In a further embodiment the heat conductors may project from the heat reservoir to a surface layer of the blade. In a further embodiment the surface layer may be a heat conductive material such as aluminum nitride or boron nitride. Still further, said conductive layer may be a single layer covering the blade. Alternatively, there may be to plurality of heat conductive layers located on said blade.

The thermal conductors, or conductive rods, may cover the final third of the blade span. Accordingly, the weight of the heating assembly may be reduced by concentrating the application of heat to the most critical region of the blade.

The thermal conductors may project from the heat reservoir and terminate at a point adjacent to the surface of the blade. A tip of the thermal conductors may be sandwiched in between the material of the leading edge, and so allow the heat to be conducted to the leading edge and spread uniformly along the length of the leading edge. In a still further embodiment, heat may be applied to the blade adjacent to both the leading edge and the trailing edge. Ice that is removed from the leading edge may migrate around the blade and re-freeze on the trailing edge. By providing heat to the trailing edge, this migrating ice may be prevented from re-freezing and so prevented from re-forming.

Alternatively, the thermal conductors may terminate so as to be flush with a surface of the blade. In a further alternative, the thermal conductors may terminate at, or adjacent to, a leading edge of the blade. In a still further embodiment, the thermal conductors may terminate at a thermal layer applied to the surface, or leading edge of the blade.

An advantage of the present invention may include, the speed at which the blade surface-ice interfacial layer reaches above freezing point is increased.

The present invention may operate when the blades are either stationary or when they are rotating.

The use of thermally conductive Aluminium or Boron Nitride may be advantageous as both materials have good dielectric properties (dielectric constant values are similar to that of E-glass, which is used in the construction of the blades). Such materials also have good thermal conductivity. The use of these materials will not result in additional susceptibility to lightning strikes on the blades.

BRIEF DESCRIPTION OF DRAWINGS

It will be convenient to further describe the present invention with respect to the accompanying drawings that illustrate possible arrangements of the invention. Other arrangements of the invention are possible and consequently, the particularity of the accompanying drawings is not to be understood as superseding the generality of the preceding description of the invention.

FIG. 1 is a cross-sectional view of a wind turbine generator blade having a heat assembly tab according to the embodiment of the present invention;

FIG. 2 is a detailed view of an end of a wind turbine generator blade showing a portion of the heating assembly according to a further embodiment of the present invention;

FIG. 3 is a cross-sectional view of a heat reservoir according to a further embodiment of the present invention.

FIG. 4 is an elevation view of a wind turbine generator for receiving a heat assembly according to the present invention.

DETAILED DESCRIPTION

FIG. 1 shows a cross-section of a rotor blade 10 for a wind turbine generator. The blade 10 has suffered an accretion of ice 35 on a leading edge. As a means of removing the ice and/or preventing its formation, a heating assembly 5 has been mounted within the blade 10 which provides heat to the leading edge 25 so as to melt the contact interface of the ice with the blade and so allowing the ice to fall off.

The heating assembly 5 comprises a heat reservoir 12 mounted within the blade 10. The blade may be mounted directly to the structural spar 30 of the blade. Alternatively, the heat reservoir may be formed as part of the spar itself.

The heat reservoir 12 receives heat from a heat source through a heat transfer conduit 15 which may be a conventional duct depending upon the delivery of heat. For instance, in the case of hot air being pumped to the heat reservoir 12, the duct 15 may be an insulated hot air duct.

Projecting from the heat reservoir 12 is a plurality of thermal conductors 20 projecting to the leading edge 25 or alternatively adjacent to the leading edge. Accordingly, the conductors may penetrate the blade so as to be flush with a surface of the blade or alternatively applying heat to the surface in order to achieve heating of the ice 35.

FIG. 2 shows one embodiment of the present invention whereby the conductor 45 projects to the leading edge 50 so as to be in contact with a thermal layer 40 placed, or applied, about the leading edge. The conductor transmits heat 47 from the heat reservoir (not shown) to the layer 40 so as to transfer heat around the leading edge so as to either remove ice or prevent its formation. Such a thermal layer/skin may be of a similar material to the conductor. For instance, both the conductor and skin may be of material such as aluminum nitride or boron nitride. These materials are effective thermal conductors, and avoid the use of metals within the blade which may represent a lightning hazard to the overall structure.

The layer 40 may be of the order of 150 to 200 microns subject to the material. Thus, the layer may be a spray-on layer which is consistent with such thickness.

It is not the intention to make the leading edge, or the thermal layer, a thermal mass for retaining heat, but merely to elevate the temperature of the leading edge sufficiently so as to remove or prevent ice build-up. The heat reservoir which is more easily insulated therefore provides a thermal mass to maintain the communication of heat to the leading edge. Accordingly, the heat reservoir may be of sufficient thermal mass to allow for intermittent transfer of heat from the heat source and so avoid the need for a continuous flow of heat. Alternatively, such a continuous flow of heat, such as a continuous flow of hot air, may be used in order to transfer sufficient heat to the leading edge.

FIG. 3 shows one possible arrangement of the heat reservoir 65. Here, a hollow container 70 having sufficiently thick walls to provide a thermal mass and defining a void/cavity therein. Within the cavity is an array of heat transfer fins 75 arranged to receive heat from a heat source. In this embodiment the heat source is hot air delivered to the heat reservoir 70 through an insulated hot air duct 80.

The heat reservoir 65 is mounted to a spar 85 acting as a structural element within a blade 60. The heat reservoir 65 is located within a 1st third of the blade 60 with the heat conductors (not shown for clarity) having as short a path as possible from the heat reservoir 65 to the leading edge of the blade.

FIG. 4 shows a wind turbine generator 90 into which the heat assembly may be mounted. A heat generator (not shown) may be mounted in the nacelle 94 or the tower 92 supporting the nacelle, subject to the form of the heat generator. This may include a heating coil through which hot air is passed, or a hot water interface heated by solar thermal energy. The particular form the heat generator does not limit the invention, and many such generators of heat may be used to provide sufficient heat to operate the heat assembly.

The blades 95 into which the heat assembly is mounted include a leading edge 100, about which the ice forms. The blade further includes a first third 105 which, by virtue of the distance from the nacelle will have the greatest influence on the torque of the blade, and the final third 107, allowing the most efficient application of heat to the blade.

Claims

1. A heating assembly for a wind turbine generator, the assembly comprising: a heat reservoir mounted within a blade of the wind turbine generator;a heat source for supplying heat to the heat reservoir;a plurality of thermal conductors projecting from said heat reservoir to a surface of said blade.

2. The heating assembly according to claim 1, wherein the terminal conductors project to a leading edge of said blade.

3. The heating assembly according to claim 1, wherein said thermal conductors are flush with a surface of said blade.

4. The heating assembly according to claim 1, further including a thermal layer applied to surface of blade adjacent to said thermal conductors to distribute heat transferred from said thermal conductors.

5. The heating assembly according to claim 4, wherein the thermal layer is applied to the leading edge of said blade.

6. The heating assembly according to claim 1, wherein the heat reservoir is mounted to a spar of said blade.

7. The heating assembly according to claim 1, wherein said material is aluminum nitride or boron nitride.

8. The heating assembly according to claim 1, wherein the heat source is a hot air source, said supply of heat provided through hot air ducts from said heat source to the heat reservoir.

9. The heating assembly according to claim 8, wherein the heat reservoir includes a void into which the hot air is directed, and a thermal mass arranged to receive heat from the hot air.

10. The heating assembly according to claim 9, wherein the void includes an array of heat transfer fins for receiving heat from the hot air.

11. A heating assembly for a wind turbine generator, the assembly comprising: a heat reservoir mounted within a blade of the wind turbine generator, wherein the heat reservoir is mounted to a spar of said blade;a heat source for supplying heat to the heat reservoir;a plurality of thermal conductors projecting from said heat reservoir to a surface of said blade, wherein the terminal conductors project to a leading edge of said blade.

12. The heating assembly according to claim 11, further including a thermal layer applied to surface of blade adjacent to said thermal conductors to distribute heat transferred from said thermal conductors.

13. The heating assembly according to claim 12, wherein the thermal layer is applied to the leading edge of said blade.