WO2007068254A1

WO2007068254A1 - Warning lights in a wind turbine

Info

Publication number: WO2007068254A1
Application number: PCT/DK2006/000718
Authority: WO
Inventors: Peter Grabau
Original assignee: Lm Glasfiber A/S
Priority date: 2005-12-16
Filing date: 2006-12-15
Publication date: 2007-06-21
Also published as: DK200501778A

Abstract

The invention concerns a blade for a wind turbine which is characterised in comprising a passage for transmission of light from an area at the blade root (101) to an optical system near the blade tip (102) for light-marking the blade with warning lights. The passage is delimited by sides comprising a super- reflective material, where the light is transmitted via reflections on the super- reflective material. The passage may be a part of the blade interior or a tube manufactured in advance. The invention further relates to a method of light-marking a wind turbine by using such blade. The method of light-marking may be made dependent on e.g. the windspeed, the deformation of the blade or the presence of planes.

Description

WARNING LIGHTS IN A WIND TURBINE

The invention relates to a blade for a wind turbine, wherein the blade tip is marked with warning lights, a wind turbine featuring such blade, a method of manufacturing such blade and use of such blade for light-marking a wind turbine.

Background

The wind turbine industry develops and constructs increasingly larger wind turbines for energy recovery, and consequently it has become a requirement in some countries that the turbines are to be provided with warning lights. The warning lights should warn the air traffic about the whereabouts of the wind turbines in order to thereby minimise the risk of collision between an airplane and a wind turbine. Constructions in excess of a specific number of meters must be marked at the highest point of the structure, being - for wind turbines - the blade tips. Since the blades of the wind turbine rotate, it is moreover conceivable that the warning lights are to be regulated to the effect that they are lit only when the individual blade constitutes the highest point of the plant.

Moreover it may be a requirement that the warning light is lit only the minute an airplane is within a specific distance from the wind turbine, and that the light has a specific colour and is emitted in specific directions. In case of wind farms consisting of several wind turbines, it may be a requirement that the warning lights on all turbines flash synchronously. It is therefore necessary to regulate when the light is to be activated.

Today, various methods are known of arranging a light source in the blade tip and simultaneously regulating when the light source is to be activated. One method consists of arranging an electric bulb, a halogen spot, light emitting diodes or other electric light source in the blade tip and subsequently powering it, quite simply by conveying a wire out through the blade to the blade tip. The regulator mechanism deciding when the light in the individual blade is to be activated is typically provided in the nacelle of the wind turbine. However, a number of problems arise in connection with that solution. The electric light sources that are known today have a limited longevity and are therefore to be replaced when breaking. It is a comprehensive task due to the light sources being situated at the tips of the wind turbine's blades, and consequently it requires a crane or the like to replace the light source. Moreover the replacement requires that the wind turbine is stopped and hence the wind turbine does not produce energy during the replacement procedure. Another problem associated with the electric light sources in the wind turbine's blade tips is that the electric installation will act as light arresting and light grounding device with increased risk of the electric installations of the turbine being destroyed by strike of lightning.

Today it is known (DE20101375U1 , US2005/0079052, JP11182409, DE10348994) to arrange a light source at the root of the blade or in the hub of the turbine in order to subsequently convey the light from the root of the blade to the blade tip via an optical fibre. The optical fibres are either moulded integrally in the blade or deployed within the cavity of the blade. However, the optical fibres are fragile and kink easily or break. This is a problem, both in production and in operation. In the production the fragile optical fibres are to be handled with care, which makes the production process difficult and adds to the cost of it. In operation the optical fibres may kink when the blade of the wind turbine is exposed to flexing and twisting movements by the forces of the wind, and it will entail a cumbersome and expensive replacement of the optical fibres. If the optical fibre is moulded integrally in the blade, it is better protected against influences - but in turn it is impossible or very difficult to replace. It is a further drawback of the use of optical fibres that it is necessary to simultaneously construct a precise coupling of the light from the light source to the optical fibre due to the diameter of the optical fibre being small (often less than 1 mm) and moreover accepts only light that hits the opening of the optical fibre within a specific angle cone. This means that, in connection with the coupling, a precise optical system is to be devised. It makes high demands to correct alignment in order for it to work, and at the same time the system is very sensitive to shocks and vibrations that may cause the system to leave its correct setting. This is a major problem in a wind turbine due to the blades moving cyclically and being exposed to many shaking forces and vibrations that depend both on the position of the blade in the rotation and the force and speed of the wind. This results in a need for the optical system to be checked and adjusted frequently, which is cumbersome and expensive. The same problems also apply when the light is to be conducted/dig rated out of the optical fibre and out of the blade tip.

Moreover, the optical fibres are sensitive to kinks and twists which mean that the light loses intensity if optical fibres are kinked or twisted excessively. The blade of a wind turbine is deformed in use and therefore it cannot be avoided that the optical fibre is also deformed with an ensuing unacceptable loss of light intensity.

Finally, the optical fibres are designated for specific wavelengths, meaning that the optical fibre conducts light primarily within a specific wave-length bandwidth. It is a problem if white light is to be transmitted, which is precisely the case when high structures are to be marked in respect of the air traffic, the white light consisting of an infinitely wide spectre of wave lengths and the optical fibre consequently serving as a filter that allows only specific wavelengths/colours to pass. DE 676 166 describes a blade for a wind turbine, wherein, at the blade root, a light source is arranged for light-marking the blade. According to one embodiment, the light source illuminates the outside of the blade, whereby the light is dispersed into the surroundings to the effect that the blade becomes visible to eg airplanes. According to another embodiment, the light source illuminates the internal cavity of the blade, where the light is dispersed when it hits the inside of the blade. By providing windows/openings in the blade, a portion of the dispersed light will beam out of such openings to the effect that the blade is light-marked by such openings. This kind of light- marking of the blade requires that the blade is illuminated by a very powerful light source to ensure that enough light is dispersed to the surroundings to enable the wind turbine to be seen at long distances. This means that it takes large amounts of energy to illuminate the blade and it is therefore very cost- intensive to light-mark the blade in this manner. Moreover the light-marking will be a great nuisance to the environment surrounding the wind turbine due to the light being dispersed into many different directions. It is a further problem that the blade tip is light-marked very poorly, as the light must beam directly from the light source and out to the blade tip from where it can be dispersed to the surroundings. This is a problem in particular when the blade deforms eg due to powerful winds, the deformation of the blade preventing the light from beaming directly to the blade tip.

Object and description of the invention

It is the object of the invention to provide a blade with light-marking at the tip, whereby the above problems of conducting the light efficiently and with low loss of energy to the blade tip is solved or obviated; to provide an efficient method of light-marking a wind turbine; and to provide a method for the manufacture of such blade. This object is accomplished by a blade for a wind turbine, said blade comprising a blade root and a blade tip that is arranged opposite the blade root, wherein the blade comprises at least one passage for transmission of light from an area at the blade root to an optical system near the blade tip for light-marking the blade by means of warning lights, said passage being bounded by sides comprising a super-reflective material, wherein the light is transmitted via reflections on said super-reflective material. Hereby a light passage is constructed which may transport light from the blade root to the blade tip without the same loss of light intensity as occurs when optical fibres are used. In particular the problem associated with transport of white light is solved in that the loss of white light is very great when optical fibres are used. Moreover, the light passages can be constructed on a considerably larger scale compared to optical fibres and thereby it is made considerably easier to couple light into the light passage than it is to couple light into an optical fibre. This means that the coupling and decoupling of light into the light passage becomes much less sensitive to the shocks and vibrations suffered by the blade. The light passage may furthermore be constructed from materials that are easier to handle and less fragile than the optical fibres. This facilitates production and prolongs the longevity of the light passage. Finally the problem of installing electric light sources in the blade tip is obviated as the light passage enables arrangement of the light source at the blade root. Hereby it is avoided that the light source in the blade tip will act as light arresting and light grounding device since there is no wiring between the blade root and the blade tip. The optical system near the blade tip transmits the light from the passage and out of the blade. Hereby it is accomplished that the light-marking can easily be adjusted, set and controlled by control of the optical system to the effect that the light-marking is adapted to the relevant regulatory requirements and can be adjusted continuously if new requirements to the marking occur. Finally, the optical system is able to direct the light both towards an airplane and a ship, ie in different directions. According to one embodiment a portion of the internal sides of the passage is coated with a super-reflective foil. By "super-reflective foil" is to be understood a foil or material surface that reflects more than 80 percent of the light. Such super-reflective material may eg by a Vikuiti™ (Enhanced specular reflector) foil from 3M which, according to the manufacturer, reflects about or more than 98 percent of the light. The passage may also be painted with a super-reflective paint with corresponding optical properties. This simplifies the construction of the light passage as its inner fades must be coated with the foil or be applied like paint. Such foil or paint is easier to handle in the production compared to use of mirrors of glass, which are often very fragile, for the sides. Correspondingly the sides of the passages may, according to one embodiment, be coated with a super-reflective tape. This gives advantageous mounting of the super-reflective surface due to the fact that the super-reflective tape is easily applied onto the sides of the passage without use of glue or eg nails or staples.

According to a further embodiment, at least a portion of the passage is constituted by a part of the blade's interior, such as a part of the inner side of the blade shells and/or a part of the reinforcing beams of the blade. Hereby the advantageous aspect is obtained that a part of the blade as such constitutes the sides of the light passage, which will save materials for the construction of the light passage. Moreover the passage is hereby integrated as a part of the blade and will therefore be just as flexible as the remainder of the blade.

According to a further embodiment, at least a part of the passage is configured as a pre-manufactured tube arranged within the blade. Hereby the advantageous aspect is accomplished that the light passage can be produced independently of the blade and be mounted at a later stage. Additionally, swift mounting of the passage within the blade is ensured and simultaneously dust and glue residue is avoided within the passage. According to one embodiment the blade comprises an optical system near the blade root for transmission of light from a light source and into the passage. Hereby the advantage is obtained that the coupling between the light source and the light passage can be optimised, whereby the most light possible from the light source is coupled into the light passage. Moreover the coupling of light in the passage can be modified without necessarily having to change the entire passage. This may be the case eg if another type of light source is to be used.

The invention further relates to a wind turbine comprising at least one blade as described above. Hereby the advantageous aspect is accomplished that a large wind farm consisting of several wind turbines can be provided with the same kind of warning light.

Moreover the invention relates to a wind turbine according to one embodiment, which comprises a control system for controlling at least one light source, from which light is transmitted into the at least one passage. Hereby the advantageous aspect is accomplished that the light in the wind turbine can be activated as needed and controlled or regulated if it becomes necessary, eg when an airplane or ship is in the vicinity of the wind turbine.

The invention also relates to a wind turbine in an embodiment that comprises a control system for controlling at least one optical system. Hereby the advantageous aspect is accomplished that, at the blade root, the optical system can be adjusted automatically, eg by an optimisation, whereby the most light possible is coupled into the light passage. Likewise, at the blade tip, the optical system can automatically be adjusted to the effect that, at all times, the warning light, observes the regulatory requirements. This may be of use eg when the blade is deformed by the wind. Moreover, the invention also comprises a method of light-marking a blade in wind turbine, wherein the blade comprises a blade root and a blade tip arranged opposite the blade root, wherein light is transmitted from a light source near the blade root, through at least one passage by multiple reflections from a super-reflective material in the bounding sides of the passage to an optical system near the blade tip, whereby the blade can be marked with warning lights. Hereby a light passage is constructed to the effect that light can be transported from the blade root to the blade tip without the same loss of light intensity as is the case when optical fibres are used. The light passage makes it possible to transport white light from the blade root to the blade tip, which is advantageous relative to optical fibres, where there is a great loss of white light. The light passage can furthermore be constructed on a considerably larger scale compared to the optical fibres, and thereby it becomes much easier to couple light into the light passage than it is to couple light into an optical fibre. This means that the coupling and decoupling of light in the light passage become much less sensitive to the shocks and vibrations of the blade. Moreover, the light passage can be constructed of materials that are easier to handle and less fragile than optical fibres. This makes the production easier and prolongs the longevity of the light passage. Finally, the problem associated with installing electrical light sources in the blade tip is obviated, because the light passage makes it possible to arrange the light source at the blade root. Hereby it is avoided that the light source in the blade tip will act as light arresting and light grounding device, since no wiring is taken through the blade root and the blade tip.

Moreover, the invention comprises a method of light-marking a blade in wind turbines as described above in an embodiment comprising a use of the wind speed, blade deformation, blade position or the blade's number of revolutions for controlling the light-marking of the blade. Hereby it is accomplished that the light-marking can be regulated in accordance with various circumstances such that the marking functions optimally and observes the requirements to the marking. The wind speed or the blade deformation can be used eg for adjusting the beaming direction of the light in order to maintain correct beaming direction even when the blade is deformed. The position of the blade or its number of revolutions can be used to control in which blade the light-marking is to be lit. This ensures that only light-marking in the blade which eg constitutes the highest point of the wind turbine is activated.

Moreover the invention comprises a method of light-marking a blade in wind turbines in a further embodiment comprising use of the presence of objects, such as eg planes or ships within an area around the wind turbine, for controlling the light-marking of the blade. This means that the warning lights in a wind turbine are activated only when it is relevant - eg when there is a plane or a ship near the plant. The result is that the warning lights do not constitute a nuisance to the surroundings and that savings in the power consumed by the warning lights can be obtained.

Moreover, the invention relates to a method of manufacturing a blade for a wind turbine as described above, wherein at least a part of the inner sides of the blade is coated with a super-reflective material, such as a super-reflective foil, a super-reflective tape or is painted with a super-reflective paint. This means that, as described above, the light passage can be constructed interiorly of the blade and simultaneously use existing parts to the effect that there is no need to mount additional parts in the blade. Moreover the light passage will have the same flexibility as the blade due to the sides of the passage consisting of precisely the interior parts of the blade. The blade is manufactured by moulding the top face, bottom face and beams of the blade separately and subsequently gluing the parts to each other. The interior parts of the blade can easily be coated with the super-reflective material prior to or in connection with the two blade shells and beams being glued together. In particular, the use of a super-reflective tape will simplify the manufacturing process due to the tape automatically adhering to the faces to be coated. Moreover, the manufacturing method has the advantage that the super- reflective foil, tape or paint does not have to be treated as carefully as is the case when mirrors of glass are used. The same requirements to treatments of the materials also provide an advantage, compared to the embodiment in which optical fibres are used to convey the light from the blade root to the blade tip.

Finally, the invention relates to use of a blade for a wind turbine, wherein the blade and its advantages were described above.

BRIEF DESCRIPTION OF DRAWINGS

In the following, the invention is described with reference to the drawings, wherein

Figure 1 shows a blade for a wind turbine;

Figure 2 illustrates the principles behind the invention and shows a sectional view along a blade for a wind turbine;

Figure 3 illustrates the principles behind the invention and shows a sectional view of a blade for a wind turbine deformed by the wind.

Figure 4 illustrates an embodiment of the invention and shows a cross- sectional view of a blade for a wind turbine with reflective tape introduced between the beams;

Figure 5 illustrates an embodiment of the invention and is a cross-sectional view of a blade for a wind turbine with a light passage made of reflective tape; Figure 6 illustrates an embodiment of the invention and is a cross- sectional view of a blade for a wind turbine with a light passage made of reflective tape, wherein a part of the light passage consists of the interior beams of the blade;

Figure 7 illustrates an embodiment and is a cross-sectional view of a blade for a wind turbine with a light passage made of reflective tape, wherein a part of the light passage consists of the interior beams of the blade and the shell of the blade.

Figure 8 illustrates how light can be coupled into a light passage;

Figure 9 illustrates how the light can be decoupled from the light passage in the blade tip;

Figure 10 illustrates how the warning light in the blade tip is activated, when a plane is within a specific area around the blade;

Figure 11 illustrates how the warning light on the various wind turbines in a large wind farm can be activated synchronously;

Figure 12 illustrates a block diagram showing how the regulation of the warning light can be implemented.

DESCRIPTION OF EMBODIMENTS

Figure 1 shows a blade for a wind turbine. The blade root (101) is coupled to the hub sitting on the main shaft of the turbine and hence on the nacelle. The blade tip (102) is provided with warning lights (103). The warning light is arranged at the blade tip and is to warn planes and ships to the effect that a collision between the wind turbine and planes or ships is avoided. Today, the warning light is either mounted as a light source at the blade tip, following which a wire is pulled to the blade root, or by optical fibres being drawn from the blade root to the blade tip, whereby the light source can be arranged near the blade root and the light be transported to the blade tip in the optical fibres. The warning light need not necessarily be arranged precisely in the blade tip; rather it should be mounted in an area around the tip as such.

Figure 2 illustrates the principle behind the invention and shows a section along the blade, seen from the fore edge. Within the blade, a light passage (201 ) is arranged which was constructed by coating a tube with a super- reflective foil. This foil can be eg a Vikuiti™ (Enhanced specular reflector) from 3M configured as a tape. The light from the light source (202) is coupled into light passage (201 ) at the blade root (101 ) and is subsequently propagated through the light passage by being reflected on the sides of the passage. The figures shows how two light beams (203, 204) are reflected on the sides of the light passage and hence propagate to the blade tip (102). At the blade tip (102) an optical system is provided which directs the light out of the light passage in the desired directions. The light source need not necessarily be arranged as shown in the figure and may therefore very well be arranged elsewhere in the wind turbine; however, advantageously as much light as possible is coupled into the light passage. This can be ensured by constructing an optical system directing the light from the light source and into the light passage.

Figure 3 shows the same cross-section as Figure 2, but the figure shows exaggerated deformation of the blade by the forces of the wind. The figure shows how the two light beams (203, 204) will be reflected onto the sides of the light passage and hence will propagate to the blade tip (102). In the blade tip (102) an optical system is provided that directs to the light out of the light passage into the desired directions. Despite the deformation of the blade, the light (203, 204) will still propagate through the light passage due to the reflection of the sides of the passage taking place on super-reflective material and not via internal reflection, which is the principle behind optical fibres. The internal reflection in optical fibres is sensitive to the angle of incidence of the light, which will result in loss of light intensity if the optical fibre is deformed. As it is, a portion of the light will be lost in the internal reflection when the angle of incidence of the light exceeds a specific angle. This is not the case with a super-reflective material, where the reflection is approximately independent of the angle of incidence of the light. Nor is this light passage sensitive to the same degree as the optical fibres to the wave length of the light and therefore it is possible to transport broad-spectred white light through the passage and coloured light within specific wave lengths. It is therefore possible to use the light passage for different light sources depending on the requirements made to the colour composition of the light- marking.

Figure 4 illustrates an embodiment and shows a cross-sectional view of the blade transversally of the blade. Between the top (401) and bottom (402) sides of the blade, two beams (403, 404) are arranged that stabilise the construction. Here, the cavity (405) between the two beams is bounded by a super-reflective material mounted on the beams (403 and 404) and the inner side of the blade shells. Any cavity inside the blade can be delimited by means of super-reflective material mounted on the sides of the cavity in order to thereby construct a light passage. The shown blade is merely exemplary, blades being available that have fewer or more than two beams and hence also more cavities. The super-reflective material may be a foil, tape or paint which is easily mounted during manufacture of the blade. The blade is manufactured to moulding the top face, bottom face and beams of the blade separately to subsequently join the parts by gluing. Prior to the sides being joined by gluing, the cavity within the blade is easily provided with a super- reflective foil or painted with super-reflective paint. If a super-reflective tape is used, the internal cavities in the blade are easily coated, as all it takes is to roll on the tape. Moreover, tape is a simple product which does not crack and is able to resist deformations of the blade.

Figure 5 shows the same cross-sectional view as figure 4, but illustrates another embodiment wherein, in the cavity (405) between the two beams, a cylindrical tube is provided, the interior of which is coated with super- reflective material as described in the context of Figure 4. The tube can be manufactured in advance, and therefore it can quickly and readily be mounted in one of the cavities of the blade when the blade parts are joined by gluing. Moreover, the tube can be made of a flexible material so as to follow the deformations of the blade. Finally the tube need not necessarily be cylindrical; rather it may also be configured as a rectangular tube.

Figures 6 and 7 show the same cross-section as Figure 4, but they illustrate other embodiments where the light passage is constructed as a combination of new sides along with the beams and/or the interior sides of the blade shells. In Figure 6, the light passage is constituted of a part of the beams in combination with new sides. In Figure 7, the sides of the light passage are constituted both of a part of the beams, a part of the inner side of the blade shells and new sides. The advantage of these embodiments are that material savings can be obtained in respect of the sides of the light passage which may considerably reduce the production costs and blade weight. Finally the light passage can be arranged where convenient eg relative to the position of the light source or to how the light is directed out of the blade.

Figure 8 shows an embodiment of how the light can be coupled into the light passage (201 ) at the blade root. Here a light source (202) is arranged in the focal point of a light-reflecting dish (801) serving as a reflector. Herby all light beams from the light source will be coupled approximately in parallel into the light passage which means that the light is reflected fewer times on the sides of the light passage. If the light beams (802) hit the sides of the passage, eg due to the light passage curving because of the deformation of the blade, they will be reflected within the passage and hence propagate to the end of the light passage. A regulator device may be introduced, whereby it is possible to change the colour of the light. This can be accomplished by mounting a mechanism with different light sources and which can automatically position the different light sources in the focal point.

Figure 9 shows an embodiment of how the light can be directed out of the light passage (201 ) and conducted out of the blade at the blade tip. At the end of the light passage, a conical mirror (901 ) is arranged that reflects the light beams (902) out of the light passage. Dispersing lenses (903) are provided that are designed to disperse the light into the desired directions. The design of the optical system depends on the regulatory requirements in the relevant country to the warning system. Moreover, a regulation can be installed in the optical system which is controlled eg by the deformation of the blade or the speed of the wind, whereby it is ensured that the light is dispersed correctly even when the blade deforms. This regulation can be a micromotor or some other type of actuator that displaces mirrors or lenses in the system. One example of such displacement is shown by the dotted lines in the Figure (904).

Figure 10 shows how the warning system in the blade tip (1001) is activated when an airplane (1002) is within a specific area around (1003) the wind turbine (1004). Hereby the warning lights can be turned off for as long as there are no planes around, whereby it is avoided that the warning lights are a nuisance to the surroundings and, simultaneously, power savings are obtained. The sensor which is to record whether there is a plane around can be configured as an intelligent radar which may record, eg via radio waves, whether a plane is within the area of the wind turbine. The planes can also be provided with a radio transmitter telling the sensor that they approach the wind turbine. The sensor is coupled to a control system which is able to activate and regulate the warning light in the blade. A corresponding system may also be implemented for ships if the wind turbine is located at sea.

Figure 11 shows how the warning light in the various wind turbines of a larger wind farm can be activated to flash synchronously. This will make it easier for pilots to see a wind farm consisting of several wind turbines due to the lights flashing synchronously, and consequently the pilot is not confused by different warning lights that flash at random. There may be requirements that the lights flash at specific time intervals or are constantly lit. Moreover, there may be requirements as to the colour of the light. Finally, the warning lights may be required to flash with infrared light which is invisible to the human eye, but visible to the pilots when they use infrared goggles (Night vision goggles) that makes the infrared light visible. This is advantageous in that the warning lights of the wind turbine will not be a nuisance to the surroundings, their being invisible, but they can still be used as warning lights for planes where the pilots use infrared goggles. The same applies to ships.

Figure 12 shows a block diagram of how the regulation of the warning'light in wind farms consisting of several wind turbines can be implemented via a central control unit (1201 ). The control unit receives a signal from a sensor (1202) which is able to record whether there is a plane or ship within the wind turbine area. The sensor is arranged in connection with the wind turbine - e.g. on one of the wind turbines or a separate arrangement. The physical position of the sensor is of no consequence, the object of it being that the area around the turbine is monitored, and that it is connected to the control system. The sensor can be based on an intelligent radar technology, where the sensor itself is able to record the objects, but is also capable of receiving signals that are emitted from planes and ships in order to thereby provide reliable recording. Based on that signal, the control unit determines whether the warning lights on the wind turbine are to be activated. If the control unit determines that the warning lights are to be activated, signals are transmitted to the individual wind turbines, where a local control system (1211 , 1221 , 1231 ) is provided. Each local control system receives a signal from a blade sensor (1212, 1222, 1232) detecting which blade is at the top in the turbine in question. Based on the signal from the blade sensor, the local control system activates the warning light (1A, 1 B, 1C, 2A, 2B, 2C, 3A, 3B, 3C) of the blade that is at the top of each wind turbine. Thus the warning lights in turbine 1 (1A, 1 B, 1 C) be activated in turn in pace with a new blade tip being the uppermost point of the turbine. The same applies to the warning lights in turbine 2 (2A, 2B, 2C) and turbine 3 (3A, 3B₁ 3C).

The shown embodiments are merely examples of how the invention can be configured and thus constitute no limitation as to how the invention can be executed. A person skilled in the art of the invention will encounter no problems finding alternative embodiments. Moreover the invention is not limited to contain only one passage with light-reflecting sides, it being in some cases advantageous to provide several different passages in a blade. For instance in case the blade is to feature different kinds of light-markings. The invention can also be configured with a number of different light sources, which in turn may be advantageous if it is a requirement that the blade must have different kinds of light-markings. Finally, the light passage can also be constructed with several outputs where a portion of the light is directed out of the passage, whereas another portion continues until the end of the passage. This can be accomplished be inserting a semi-permeable mirror centrally in the tunnel. The mirror will allow a portion of the light to leave the passage, while another portion will continue inside the tunnel. It may be advantageous, if the blade is also to be provided with markings centrally on the blade, or if the turbine is to run with different light intensities in response to visibility.

It will be under stood that the invention as disclosed in the present specification and figures can be modified or changed while continuing to be comprised by the protective scope of the following claims.

Claims

C l a i m s

1. A blade for a wind turbine, said blade comprising a blade root and a blade tip arranged opposite the blade root, characterised in that the blade comprises at least one passage for transmission of light from an area at the blade root to an optical system near the blade tip for light-marking the blade with warning light, said passage being bounded by sides comprising a super- reflective material, where the light is transmitted via reflections on said super- reflective material.

2. A blade for a wind turbine according to claim 1 , characterised in that at least a portion of the inner sides of the passage is coated with a super- reflective foil, paint or tape.

3. A blade for a wind turbine according to one or more of claims 1-2 claims, characterised in that at least a part of the passage is constituted by at least a portion of the blade interior.

4. A blade for a wind turbine according to one or more of claims 1-3, characterised in that at least a portion of the passage is configured as a pre-manufactured tube and arranged within the blade.

5. A blade for a wind turbine according to one or more of claims 1-4, characterised in further comprising at least one optical system near the blade root for transmission of light from at least one light source and into the passage.

6. A wind turbine comprising at least one blade described by one or more of claims 1-5.

7. A wind turbine according to claim 6, characterised in that the wind turbine comprises a control system for controlling at least one light source, from which light is transmitted into at least one passage.

8. A wind turbine according to one or more of claims 6-7, characterised in that the wind turbine comprises a control system for controlling at least one optical system.

9. A method of light-marking a blade for a wind turbine, wherein the blade comprises a blade root and a blade tip arranged opposite the blade root, characterised in that light is transmitted from at least one light source near the blade root through at least one passage by multiple reflections from a super-reflective material in the bounding sides of the passage to an optical system near the blade tip, whereby the blade can be marked with warning lights.

10. A method of light-marking a blade for a wind turbine according to claim 9, characterised in further comprising use of the wind speed for controlling the light-marking of the blade.

11. A method of light-marking a blade for a wind turbine according to one or more of claims 9-10, characterised in further comprising the use of the deformation of the blade for controlling the light-marking of the blade.

12. A method of light-marking a blade for a wind turbine according to one or more of claims 9-11 , characterised in further comprising the use of the position of the blade for controlling the light-marking of the blade.

13. A method of light-marking a blade for a wind turbine according to one or more of claims 9-12, characterised in further comprising use of the number of revolutions of the blade for controlling the light-marking of the blade.

14. A method of light-marking a blade for a wind turbine according to one or more of claims 9-13, characterised in further comprising the use of the presence of objects, such as eg planes or ships, within an area around the wind turbine for controlling the light marking of the blade.

15. A method of manufacturing a blade for a wind turbine, characterised in comprising coating of at least a part of the inner sides of the blade with a super-reflective material, such as a super-reflective foil, paint or tape.

16. Use of a blade for a wind turbine described by one or more of claims 1 -5.