WO2010028653A2

WO2010028653A2 - Low power heating

Info

Publication number: WO2010028653A2
Application number: PCT/DK2009/050235
Authority: WO
Inventors: Yoshiki Haraguchi; Chee Kang Lim; Erwin Merijn Wouterson; Srikanth Narasimalu
Original assignee: Vestas Wind Systems A/S
Priority date: 2008-09-11
Filing date: 2009-09-11
Publication date: 2010-03-18
Also published as: WO2010028653A3

Abstract

The invention relates to de-icing of a wind turbine plant comprising a rotor with at least one rotor blade. The at least one rotor blade comprises at least one area with electrical conductive nano particles forming an electrical conductive area on the rotor blade. The invention also relates to a method for manufacturing a rotor blade for a wind turbine plant and the rotor blade as such and use of nano particles for rotor blades.

Description

LOW POWER HEATING

Technical field The technical field of the present inventive concept is heating of a rotor blade in a wind turbine plant comprising a rotor with at least one rotor blade. More precisely the invention relates to a wind turbine plant, a method for manufacturing a rotor blade in a wind turbine plant and the rotor blade as such and use of nano particles for rotor blades.

Background of the invention

When using wind turbine plants in areas where the temperature may fall below O⁰C (the freezing point), e.g. northern or arctic areas, ice accretion on the rotor blades of the rotor may frequently appear. Besides significantly reducing the efficiency of the wind turbine plant and, consequently, the power output, ice formation on the rotor blades may also lead to damages on the rotor and the wind turbine plant. This is of course not desirable, and several solutions to avoid ice formation on the rotor blades have been proposed. One solution is to use hot air and let it run through the leading edge of the blade. However when the blade is large, which is normally the case in modern wind turbine plants, the hot air solution is not efficient as the temperature of the air will be reduced with the distance.

Another solution is to heat up the blades using electric heating, e.g. by applying an electric wiring system or a metallic foil to the rotor blade, and connect the wiring system or metallic foil with an electric source. Examples of such electric heating systems are disclosed in e.g. WO 95/15670 and WO 00/79128 Al

Moreover, WO 2006/085054 discloses ice protection of aerodynamic surfaces. The ice protection is obtained by electro-thermal heater mats manufactured by printing onto a substrate with a thermo-setting ink loaded with electrically conductive particles. The system offers significant manufacturing cost advantages in comparison with other systems.

The known electrical heating systems have, however, a rather large consumption of power when in use. This consumption of power significantly reduces the outcome of the wind turbine plant in periods where ice accretion appears. Consequently, there exist a need for de-icing systems with low power consumption and with high efficiency.

An object of the present invention is to provide a de-icing system for rotor blades in a wind turbine plant, which de-icing system is very economical in use.

Another object is to provide an electric heating system for rotor blades, that is easy to adapt to all types of blades. The system should also be easy to incorporate in the manufacturing process.

Summary of the invention

Thus, the invention provides a wind turbine plant comprising a rotor with at least one rotor blade, wherein the at least one rotor blade comprises at least one area with electrical conductive nano particles with sizes in the range 0,1 nm to 250 nm forming an electrical conductive area on the rotor blade. The electrical conductive area comprising the electrical conductive nano particles has surprisingly appeared to require less electric power than expected to function as a heating element for de-icing. A non-binding theory is that nano particles which are known to have extreme small sizes cause a synergetic effect that provides for the excellent electrical properties in respect of electric heating, electric resistance, and power consumption. Trials have shown that the power consumption may be reduced with 50-75% in comparison with known systems. In the context of this invention the term area has to be interpreted broadly, and is meant to comprise layers in the structure of the rotorblade, but the area may also comprise the entire rotorblade or the entire internal or external surfaces of the entire rotorblade. The latter is to be understood as a layer with a certain thickness is applied on the internal or external surface of the rotorblade.

Although the electrical conductive nano particles have sizes in the range 0.1 nm to 250 nm the particles may have sizes in the alternative range 1 nm to 250 nm. Moreover, the electrical conductive nano particles preferably have sizes in the range 0.1 nm to 150 nm, more preferably in the range 0.1 nm to 100 nm, and even more preferably in the range 0.5 nm to 100 nm. With the preferred ranges of particles a highly effective conductive area may be obtained. To function as a heating element the area (or areas) with electrical conductive nano particles is connected to an electrical source, preferable by electrodes and wires, which are well-known and easy means to establish electrical connection. The wiring and electrode system will be able to let an electric current pass through the area with electrical conductive nano particles, and the electrical resistance of the nano particles will cause the area to be heated.

The electric wiring system may be arranged in the internal part of the rotor blade and optionally connected with a control system that controls when heating is required to avoid ice accretion. The control system may be based on a computer and temperature sensors.

For the purpose of providing the best de-icing properties, the area with electrical conductive nano particles is preferably located on the external surface or near the external surface of the rotor blade because the ice accretion normally appears on the external surface of the rotor blade. Of course the area with electrical conductive nano particles may be placed in the internal part of the rotor blade, however, such an embodiment will require more power supply to the area(s) with electrical conductive nano particles to be able to function as a de-icing device, as more material of the rotor blade has to be heated.

The electrical conductive nano particles must be in electrical contact to form a conductive path in the conductive area. When the conductive nano particles are in electrical contact they may be fixed in relation to each other. The fixation may be obtained by use of glue or similar, but preferably the electrical conductive particles are embedded in a matrix of a resin. Preferably the resin is selected from epoxy and polyester resins or mixtures thereof, which resins are both flexible and durable. The content of the nano particles in the resin should be larger than the percolation threshold to form the conductive path in the matrix.

Although the electrical conductive particles may be placed on any suitable substrate, e.g. from a polymer or ceramic material, it is preferred that the electrical conductive nano particles are located on a substrate having insulating properties at least in a layer adjacent the area of said electrical conductive particles. The insulating material is preferably insulating in respect of both heat and electrical conductivity. In particular the insulating material should be thermal insulating, so that the major part of the heat caused by an electric current passing through the area with electric conductive particles is directed in a direction along the surface extension of the insulating material and towards the external surface of the rotor blade where the ice accretion normally appears. In principal it is possible to apply all electrical conductive nano particles like indium tin oxide (ITO), antimony-doped tin oxide or borides, however, due to industrial accessibility and cost, the electrical conductive nano particles are preferably selected from carbon nano tubes, carbon nano fibers, copper nano particles and silver nano particles.

The rotor may have one, two, three, four or more rotor blades. However, in an embodiment of the wind turbine plant according to the invention, the rotor comprises three rotor blades and each rotor blade comprises at least one area with conductive nano particles. This embodiment provides for a rotor with excellent balance and oscillation properties, having the possibility for effective de-icing.

In a further embodiment of the wind turbine plant according to the invention, the one or more rotor blades each comprises several areas with conductive nano particles. The areas may be connected in series to an electrical source. However, the areas may also be connected individually to an electrical source. In this manner it is possible to compensate for different levels of ice accredation on the rotor blade and furthermore minimize the power consumption for de-icing. Moreover, to obtain areas with different heating properties it is also possible to apply areas with different contents of conductive nano particles or one or more area(s) containing different conductive nano particles.

In an alternative embodiment, the at least one area with conductive nano particles is located at the leading edge of the rotor blade. The embodiment is advantageous as ice accredation normally appears on the leading edge the rotor blade and a cost effective rotor blade with de-icing means is obtainable.

In a further embodiment the present invention relates to a method for manufacturing a rotor blade with de-icing properties for a rotor in a wind turbine plant, said method comprises the steps of: providing a rotor blade or a part of a rotor blade; applying at least one layer of a mixture comprising electrical conductive nano particles having sizes in the range of 0.1 nm to 250 nm and at least one resin onto the rotor blade or a part of a rotor blade to form at least one area with conductive nano particles onto the rotor blade. The electrical conductive nano particles may also have sizes in the range 1 nm to 250 nm. To obtain the best possibly properties of the conductive layer, the electrical conductive nano particles preferably have sizes in the range 0.1 nm to 150 nm, more preferably in the range 0.1 nm to 100 nm, and even more preferably in the range 0.5 nm to 100 nm.

The method according to the invention may be applied during or after manufacture of the rotor blade. If the method is applied during manufacture it will applied to a part of a rotor blade, i.e. the non-final rotor blade. If the method is applied after manufacture of the rotor blade it is applied on the final rotor blade as a post treatment to provide the rotor blade with de-icing properties.

The method may comprise the further step of applying one or more layers of non-conductive resins onto the rotor blade or a part a rotor blade before the step of applying the mixture comprising electrical conductive nano particles and at least one resin.

The optionally one or more areas applied before the at least one layer with the mixture comprising electrical conductive nano particles and at least one resin may comprise a layer that is thermally insulating. In this manner the area comprising conductive nano particles is placed on an insulating layer and the heat provided by the area comprising the conductive nano particles, when this area is exposed to an electric current, can be directed in a direction away from the insulating layer and i.e. be directed towards the external surface of the rotor blade.

The method may further comprise the step of applying one or more layers of non-conductive resins onto the rotor blade or a part of a rotor blade after the step of applying the mixture comprising electrical conductive nano particles and at least one resin. The optionally one or more further layers of non-conductive material applied after the mixture comprising electrical conductive nano particles and at least one resin may constitute protective layers.

The method may comprise the step of connecting the area with conductive nano particles to electrodes and electric wirings for the purpose of exposing the area to an electric current.

The amount of the conductive nano particles in the mixture comprising electrical conductive nano particles and at least one resin is larger than the percolation threshold to form a conductive path in the at least one resin when applied to the rotor blade. When the amount of conductive nano particles is larger than the percolation threshold it is ensured that there is electrical contact between the conductive nano particles in the mixture. In an embodiment of the method the layer of the mixture comprising electrical conductive nano particles and at least one resin is applied to be substantially parallel with the external surface of the rotor blade. In this embodiment the conductive area follows the external surface of the rotor blade and thereby is able to provide an effective heat source to the surface. The invention also relates to a rotor blade for a rotor in a wind turbine plant, wherein the rotor blade comprises at least one area with electrical conductive nano particles having sizes in the range from 0.1 nm to 250 nm alternatively with sizes in the range 1 nm to 250 nm, and preferably in the range 0.1 nm to 150 nm, more preferably in the range 0.1 nm to 100 nm, and even more preferably in the range 0.5 nm to 100 nm forming an electrical conductive area on the rotor blade. Such a rotor blade provides excellent de- icing properties and improves the overall performance of the wind turbine plant in which it is installed. The specific features of the rotor blade have previously been discussed in terms of a wind turbine plant, whereby reference is made to the sections above.

In a further aspect the invention also relates to use of electric conductive nano particles having a size in the range of 0.1 nm to 250 nm alternatively with sizes in the range 1 nm to 250 nm, and preferably in the range 0.1 nm to 150 nm, more preferably in the range 0.1 nm to 100 nm, and even more preferably in the range 0.5 nm to 100 nm to form an electrical conductive area or layer on at least a part of a rotor blade for a rotor in a wind turbine plant and in one embodiment the the conductive nano particles form an electrical pathway within a resin. The formed layer may then be heated by an electric current and function as a de-iceing device with excellent properties in respect of power consumption.

In one embodiment the conductive nano particles are applied to the rotor blade in a layer of resin during manufacture of the rotor blade. In this embodiment it is easy to control the position of the conductive areas and connect them with electrodes and wiring.

In an alternative embodiment the conductive nano particles are applied to the rotor blade in a layer of resin subsequent to the manufacture of the rotor blade. This embodiment facilitates the application of the conductive area as the layer of resin may be applied to the external surface of the rotor blade by spraying or by a brush. The conductive area may be further coated with a protective layer. This embodiment provides an easy and cost-effective way of producing rotor blades with de-icing properties as standard rotor blades may form the basis.

Brief description of the drawings The above, as well as additional objects, features and advantages of the present invention, will be better understood through the following illustrative and non-limiting detailed description of preferred embodiments of the present invention, with reference to the appended drawings, where the same reference numerals will be used for similar elements, wherein: Figure 1 illustrates a wind turbine plant according to the invention.

Figure 2 illustrates a rotor blade with areas with conductive nano particles.

Figure 3 illustrates a cross section of a rotor blade with areas with conductive nano particles. Figure 4 illustrates a cross section of a rotor blade with ice on the surface.

Detailed description of preferred embodiments

Nano particles as used in view of the present invention are structures with sizes in the range 0.1-250 nm. Thus, the structures are too large to be described by simple atom models and too small to be described by classical theories like thermodynamic, electromagnetism and Newtonian physics. Consequently, the behavior of nano particles are unpredictable in view of classical science. Although the structures are referred to as nano particles, they may have any shape, e.g. spherical, tubular or fiber shape.

The applied area comprising conductive nano particles has an extension in two dimensions forming a layer. However, the area in this context also have an extension in a third dimension, i.e. the area has a certain thickness. According to the invention the area may form an uniform layer all over the rotor blade or more separated areas may be formed.

The surfaces of the rotor blade is referred to as the internal or the external surface. If it is stated that the area comprising conductive nano particles is placed on the external surface of rotor blade, the conductive area may still be coated with e.g. a protective coating, although the coating in principle forms the external surface. The percolation threshold is the lower limit of the volumetric concentration of randomly distributed conductive particles within a medium which will result in bulk conductivity.

Fig. 1 shows a wind turbine plant 1 of the commonly used type having a rotor 2 with three rotor blades 3. The rotor 2 is mounted in a housing 4 on the tower 5. The wind turbine plant 1 may be located on land or offshore. Each rotor blade 3 is equipped with areas with conductive nano particles according to the invention as shown in more details in Fig. 2.

Fig. 2 shows a rotor blade 3 having areas 6 with conductive nano particles forming the conductive areas. The areas 6 are formed on the surface 7 of the blade 3. Moreover the areas with conductive nano particles are mainly located at the leading edge 8 of the rotor blade where ice accretion tends to appear. To heat the areas 6 it is necessary to pass a current through the areas 6 with the conductive nano particles. For this purpose electrodes 9 are located at each end of the areas 6 . The wiring for the electrodes (not shown) is hidden within the rotor blade.

In Fig. 3 a cross section of the rotor blade 3 with areas with conductive nano particles 6 integrated in the surface 7 is shown. The thickness of the areas with conductive nano particles 6 are exaggerated for the purpose of illustration. In the embodiment the area is placed in an recess in the external surface of the rotor blade, however, the area may also be placed on the external surface of the rotor blade.

Fig. 4 shows a more detailed cross section in part of rotor blade 3. The area with conductive nano particles 6 is placed an a layer of insulating material 10 located on the resin material 11 of the rotor blade. The layer forming the area with conductive nano particles 6 is further coated with a protective coating 12, which is heat-conductive so that heat generated in the area with conductive nano particles 6 can pass through the coating 12 and melt the ice 13 on the surface 7 of the rotor blade 3. The layer of insulating material 10 significant reduces the heat that is lead to the resin material 11 and where the heat will have no function. In this way the major part of the generated heat in the area 6 will be led to the surface 7 of the rotor blade 3 and contribute to melt the ice 13.

The power consumption for a typical rotor blade having a surface area of 195 m² is for the start up or initial melting of ice approximately 11 kilowatt and for running condition approximately 6 kilowatt. Thus, the power consumption is significant lower for a heated rotor blade according to the invention in comparison with traditional heated rotor blades.

As it appears from the above illustrative figures 1-3, the areas 6 with conductive nano particles are integrated in the rotor blades. Although the embodiments of the figures 1-3 show selected areas with conductive nano particles, it may also be envisaged that the entire surface of the rotor blade may be an conductive area with conductive nano particles. The areas with conductive nano particles can be introduced into the rotor blade structure in various ways, and different embodiments are disclosed below. During manufacture of the rotor blade, the conductive nano particles can be mixed into the resin or mixture of resins to form a conductive composite. Subsequent to curing the resin, the wires and electrodes can be applied and connected and one or more layers of glass fibers can be placed on top of the conductive composite as in normal rotor blade manufacturing. This embodiment will allow for heating of the entire blade surface. However, a large amount of conductive nano particles is needed.

The amount of conductive nano particles needed can be reduced by using two different types of resin - one resin without the conductive nano particles and one resin with the conductive nano particles. The resin with the conductive nano particles can then be located at the positions where heating will be required. Such positions can form isolated areas along by way of example the leading edge of the blade.

After the resin without conductive nano particles has been applied and cured, cured strips of the resin with conductive nano particles can be placed at the desired positions. These strips come with wires and electrodes. After the strips have been placed, one or more layers of glass fibers may be placed on the top as in normal manufacturing. This embodiment is favorable as lesser amounts of the conductive nano particles are required, which will also keep the cost low and also reduce the changes in the current structure to a minimum. In addition, a lesser area of the rotor blade will be heated thereby reducing the power consumption of the rotor blade.

If the rotor blades alternatively are manufactured as wood/carbon blades, the conductive nano particles may be mixed into the infusion resin (for the wood/carbon blades) to form a conductive mixture and infuse the mixture throughout the blade as normally done in the manufacture of wood/carbon blades. In this embodiment the conductive nano particles may not only increase the electric conductivity but also increase the structural properties of the formed composite. Moreover, in this embodiment the entire rotor blade can then be heated.

In a further embodiment the conductive nano particles may be mixed into a resin and sprayed or applied by brush onto the external surface of the blade to form conductive areas, which are subsequently connected to electrodes and electric wiring. This embodiment is advantageously as the amount of conductive nano particles required can be reduced as the conductive material may be applied in very thin layers. Moreover, the conductive areas may be applied on desired locations. The conductive areas may be more vulnerable to wear, unless they are coated with a protective coating.

The invention has mainly been described above with reference to a few embodiments. However, as is readily appreciated by a person skilled in the art, other embodiments than the ones disclosed above are equally possible within the scope of the invention, as defined by the appended patent claims.

Claims

1. A wind turbine plant comprising a rotor with at least one rotor blade, wherein the at least one rotor blade comprises at least one area with electrical conductive nano particles with sizes ranging from 0.1 nm to 250 nm forming an electrical conductive area on the rotor blade.

2. A wind turbine plant according to claim 1 , wherein the electrical conductive nano particles have sizes in the range 1 nm to 250 nm.

3. A wind turbine plant according to claim 1 , wherein the electrical conductive nano particles have sizes in the range 0.1 nm to 150 nm, preferably in the range 0.1 nm to 100 nm, more preferably in the range 0.5 nm to 100 nm.

4. A wind turbine plant according to anyone of the claims 1-3, wherein the at least one area with electrical conductive nano particles is located on the external surface of the rotor blade.

5. A wind turbine plant according to the anyone of the claims 1 -4, wherein the electrical conductive nano particles are embedded in a resin.

6. A wind turbine plant according to claim 5, wherein the resin is an epoxy resin.

7. A wind turbine plant according to claim 5, wherein the resin is a polyester resin.

8. A wind turbine plant according to anyone of the preceding claims, wherein the conductive nano particles are located on a thermal insulating resin.

9. A wind turbine plant according to anyone of the preceding claims, wherein the electrical conductive nano particles are selected from carbon nano tubes.

10. A wind turbine plant according to anyone of the preceding claims, wherein the electrical conductive nano particles are selected from carbon nano fibers.

1 1 . A wind turbine plant according to anyone of the preceding claims, wherein the rotor comprises three rotor blades and each rotor blade comprises at least one area with conductive nano particles.

12. A wind turbine plant according to anyone of the preceding claims, wherein the rotor blade comprises at least two areas with conductive nano particles.

13. A wind turbine plant according to anyone of the preceding claims, wherein the at least one area with conductive nano particles is located at the leading edge of the rotor blade.

14. A method for manufacturing a rotor blade with de-icing properties for a rotor in a wind turbine plant, said method comprises the steps of: providing a rotor blade or a part of a rotor blade; and applying at least one layer of a mixture comprising electrical conductive nano particles with sizes in the range of 0.1 nm to 250 nm and at least one resin onto the rotor blade or a part of a rotor blade to form at least one area comprising conductive nano particles on the rotor blade.

15. A method according to claim 14, wherein the electrical conductive nano particles have sizes in the range 1 nm to 250 nm.

16. A method according to claim 14, wherein the electrical conductive nano particles have sizes in the range 0.1 nm to 150 nm, preferably in the range 0.1 nm to 100 nm, more preferably in the range 0.5 nm to 100 nm.

17. A method according to anyone of the claims 14-16, comprising the further step of connecting the at least one area comprising conductive nano particles to electrodes and electrical wirings.

18. A method of according to anyone of the claims 14-17, comprising the further step of applying one or more layers of non-conductive resins onto the rotor blade or a part a rotor blade before the step of applying the mixture comprising electrical conductive nano particles and at least one resin.

19. A method according to anyone of the claims 14 to 18, comprising the further step of applying one or more layers of non-conductive resins onto the rotor blade or a part of a rotor blade after the step of applying the mixture comprising electrical conductive nano particles and at least one resin.

20. A method according to anyone of the claims 14 to 19, wherein the amount of the conductive nano particles in the mixture comprising electrical conductive nano particles and at least one resin is larger than the percolation threshold to form a conductive path in the at least one resin when applied to the rotor blade.

21. A method according to anyone of the claims 14 to 20 wherein the layer of the mixture comprising electrical conductive nano particles and at least one resin is applied to be substantially parallel with the external surface of the rotor blade.

22. A rotor blade for a rotor in a wind turbine plant, wherein the rotor blade comprises at least one area comprising electrical conductive nano particles with sizes in the range of 0.1 nm to 250 nm, said area forming an electrical conductive area on the rotor blade.

23. A rotor blade according to claim 22, wherein the electrical conductive nano particles have sizes in the range 1 nm to 250 nm.

24. A rotor blade according to claim 22, wherein the electrical conductive nano particles have sizes in the range 0.1 nm to 150 nm, preferably in the range 0.1 nm to 100 nm, more preferably in the range 0.5 nm to 100 nm.

25. Use of electric conductive nano particles having a size in the range 0.1 nm to 100 nm to form an electrical conductive area or layer on at least a part of a rotor blade for a rotor in a wind turbine plant.

26. Use according to claim 25, wherein the electrical conductive nano particles have sizes in the range 1 nm to 250 nm.

27. Use according to claim 25, wherein the electrical conductive nano particles have sizes in the range 0.1 nm to 150 nm, preferably in the range

0.1 nm to 100 nm, more preferably in the range 0.5 nm to 100 nm.

28. Use according to anyone of the claims 25 to 27, wherein the conductive nano particles form an electrical pathway within a resin.

29. Use according to anyone of the claims 25 to 28 wherein the conductive nano particles are applied to the rotor blade in a layer of resin during manufacture of the rotor blade.

30. Use according to anyone of the claims 25 to 28 wherein the conductive nano particles are applied to the rotor blade a in layer of resin subsequent the manufacture of the rotor blade.

31. Use according to claim 30, wherein the layer of resin is applied to the external surface of the rotor blade by spraying or by a brush.