Abstract:
The present patent application concerns an apparatus for cleaning an outer surface of a rotor blade of a wind turbine, the apparatus comprising a first frame and a cleaning device, the cleaning device being adapted to conform to the outer surface and connected to the first frame, wherein the apparatus is adapted to be slidably positioned on the outer surface of the rotor blade, to slide along, and to be pressed onto the outer surface. Further, it concerns an apparatus for cleaning a leading edge of a rotor blade of a wind turbine, the apparatus comprising a first frame and a cleaning device, the cleaning device being adapted to conform to the leading edge and being connected to the first frame, wherein the apparatus is adapted to be slidably positioned on the leading edge of the rotor blade, to slide along and to be pressed onto the leading edge during standstill of a wind rotor comprising the rotor blade. Finally, it concerns a rotor blade of a wind turbine comprising an apparatus for cleaning a leading edge of the rotor blade, wherein the apparatus is mounted on said rotor blade, the apparatus comprising a first frame and a cleaning device, the cleaning device being adapted to conform to the leading edge and being attached to the first frame, wherein the apparatus is adapted to be slidably positioned on the leading edge of the rotor blade, to slide along and to be pressed onto the leading edge during rotation of a wind rotor comprising the rotor blade.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The present disclosure relates to an apparatus for cleaning a leading edge of a rotor blade of a wind turbine. Further it relates to a rotor blade of a wind turbine comprising an apparatus for cleaning a leading edge of the rotor blade 
         [0002]    Modem wind turbines operate rotor blades at tip speeds of up to 80 m/s (i.e. more than 150 mph or more than 250 km/h). During operation, dirt accumulates on a blade surface mainly at and close to a leading edge of the rotor blade. The accumulation of dirt on the blade surface results in increased surface roughness which changes the aerodynamical characteristics of the blade. On one hand, a maximum lift of the rotor blades decreases which leads to lower performance of the wind turbine. For example, the maximum power level for stall controlled turbines may, drop as much as 45%. Hence. power production is decreased. 
         [0003]    Further, an angle of attack at maximum lift decreases due to dirt accumulation on the blade surface, which results in a larger probability of stalling the blade. The angle of attack is the angle between an airfoil chord and a free-stream velocity of the airflow. For a pitch controlled turbine, blade stall not only decreases energy capture but also leads to an unnormal operation condition that potentially endangers the turbine safety at the moment of flow re-attachment. 
         [0004]    Additionally, flying bugs that collide with the rotor blade may cause blade fouling. The bug bloom is affected by several parameters such as temperature, humidity and also wind speed. Typically, bugs can only fly up to wind turbine rotor height during low wind speeds (e.g. less than 10 m/s). 
       BRIEF DESCRIPTION OF THE INVENTION 
       [0005]    In view of the above, an apparatus for cleaning an outer surface of a rotor blade of a wind turbine is provided, wherein the apparatus includes a first frame and a cleaning device, the cleaning device being adapted to conform to the outer surface and being connected to the first frame, wherein the apparatus is adapted to be slidably positioned on the outer surface of the rotor blade, to slide along, and to be pressed onto the outer surface. 
         [0006]    According to a further aspect, an apparatus for cleaning a leading edge of a rotor blade of a wind turbine is provided, the apparatus comprising a first frame and a cleaning device, the cleaning device being adapted to conform to the leading edge and being connected to the first frame, wherein the apparatus is adapted to be slidably positioned on the leading edge of the rotor blade, to slide along, and to be pressed onto the leading edge during standstill of a wind rotor comprising the rotor blade. 
         [0007]    According to another aspect a rotor blade of a wind turbine is provided comprising an apparatus for cleaning a leading edge of the rotor blade, wherein the apparatus is mounted on said rotor blade, the apparatus comprising a first frame and a cleaning device, the cleaning device being adapted to conform to the leading edge and being attached to the first frame, wherein the apparatus is adapted to be slidably positioned on the leading edge of the rotor blade, to slide along and to be pressed onto the leading edge during rotation of a Wind rotor comprising the rotor blade. 
         [0008]    Further aspects, advantages and features are apparent from the dependent claims, the description and the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    A full and enabling disclosure, including the best mode thereof, to one of ordinary, skill in the art, is set forth more particularly in the remainder of the specification, including reference to the accompanying figures wherein: 
           [0010]      FIG. 1  shows a schematical drawing of a wind turbine. 
           [0011]      FIG. 2  shows a schematical drawing of a cleaning apparatus on a wind turbine blade; 
           [0012]      FIG. 3  shows a schematical top view of the cleaning apparatus on the wind turbine blade of  FIG. 2 . 
           [0013]      FIG. 4  shows a schematical side view of a profiled blade with the cleaning apparatus of  FIG. 3 . 
           [0014]      FIG. 5  shows a schematical front view of a cleaning apparatus according another embodiment. 
           [0015]      FIG. 6  shows a schematical side view of a cleaning apparatus according to the embodiment of  FIG. 5 . 
           [0016]      FIG. 7  shows a schematical drawing of a cleaning apparatus on a rotor blade. 
           [0017]      FIG. 8  shows a cross-sectional view of a wind turbine blade with a cleaning apparatus according to a further embodiment. 
           [0018]      FIG. 9  shows a schematical drawing of a manual application of a cleaning apparatus according another embodiment; and 
           [0019]      FIG. 10  shows a schematical process flow diagram of an embodiment of a method. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0020]    Reference will now be made in detail to the various embodiments, one or more examples of which are illustrated in the figures. Each example is provided by way of explanation and is not meant as a limitation. For example, features illustrated or described as part of one embodiment can be used on or in conjunction with other embodiments to yield yet a further embodiment. It is intended that the present disclosure includes such modifications and variations. 
         [0021]      FIG. 1  shows a wind turbine  100 . The wind turbine  100  includes a tower  110  on which a nacelle  120  is mounted. The nacelle  120  is rotatable about a vertical axis of the tower. Within the nacelle  120  a generator (not shown) for transforming rotational energy into electrical energy is placed. The generator is connected to a hub  130  that is rotatable about a horizontal axis. Three rotor blades  140  are connected to the hub  130 . The rotor blades  140  and the hub  130  together form a vind rotor of the wind turbine  100 . The wind turbine  100  operates as follows. In a typical situation, the nacelle  120  is rotated about the vertical axis such that the horizontal axis of the hub  130  is substantially parallel to a wind direction. The wind exerts a torque on the wind rotor due to an aerodynamical profile of the rotor blades  140 . Accordingly, the wind rotor is rotating about its horizontal axis, thus driving the generator. The generator transforms the mechanical rotation into electric current. Hence, the kinetic energy of the wind is transformed into electric energy. 
         [0022]    During the operation of the wind turbine  100 , e.g. during warn seasons, bugs may accumulate on a leading edge of the blade  140  of the wind turbine  100 . Typically, the dirt accumulation occurs mainly in an outer portion of the rotor blade  140 . The outer portion may be an outer third of the rotor blade  140 . “Outer” and “inner” portions of a blade or “proximal” and “distal” are defined in this patent application with respect to the hub  130  in case the rotor blade is mounted on the hub, in particular with respect to the horizontal rotation axis of the hub  130 . The accumulation of dirt mainly in an outer portion is due to an absolute speed of the outer portion of the rotor blade  140  that is much higher in the absolute speed at the inner portion of the rotor blade  140  near the hub  130 . 
         [0023]      FIG. 2  shows in a perspective view a portion of a rotor blade  140  with its leading edge  145  and a cleaning apparatus  200 .  FIG. 3  shows a respective top view of the portion of the rotor blade  140  with the cleaning apparatus  200 .  FIG. 4  is a respective side view of the rotor blade of the section A-A of  FIG. 3 . Further in  FIG. 4  the view of  FIG. 2  is depicted schematically as B-B. The hub  130 , not shown in  FIG. 2 , or the inner portion of the rotor blade  140  is arranged on the right of the depicted portion of the rotor blade  140 . Therefore, the outer portion of the rotor blade  140  is arranged on the left of the depicted portion. The wind rotor of the wind turbine is rotating in direction R. The cleaning apparatus  200  is arranged on the leading edge  145  of the rotor blade  140 . The cleaning apparatus includes two bow-shaped frames  210 ,  220  conforming around the leading edge  145 , namely a driving frame  210  and a tension frame  220 . The driving frame  210  and the tension frame  220  have respective leading ends  212 ,  222  and two rear ends  214 ,  224  and  216 ,  226 , respectively. Rear end and leading end of the cleaning device is defined according to their orientation with respect to the leading edge  145  of the rotor blade  140 . A first rear end  214 ,  224  of the frames  210 ,  220  is arranged on the leeward side (suction side) of the rotor blade  140  during operation of the wind turbine  100  and a second rear end  216 ,  226  of the frames  210 ,  220  is arranged on the windward side (pressure side) of the rotor blade  140  during operation of the wind turbine  100 . The driving frame  210  and the tension frame  220  are connected with each other by hinges  230 ,  232  at their rear ends  214 ,  224 ,  216 ,  226  on the windward side and on the leeward side of the rotor blade  140 , respectively. In one embodiment, the spring is realized as a torsion spring adapted to push the driving frame  210  and the tension frame  220  away from each other. In other words, the hinges  230 ,  232  and springs are the same elements. [n a further embodiment, a separate spring is associated to the hinges  230 ,  232  to push the driving frame  210  and the tension frame  220  away from each other. In another embodiment, only the rear ends on one side of the rotor blade  140 , either the %vindward side or the leeward side of the rotor blade  140 , are connected by a spring to push the driving frame  210  away from the tension frame  220 . The driving frame  210  and the tension frame  220  may enclose an angle of about 60 degree to 120 degrees, in particular 80 to 100 degrees, in a typical embodiment of about 90 degrees. 
         [0024]    As shown in  FIG. 2  and  FIG. 3 , two cleaning wires  240 ,  242  are connected to the driving frame  210  on the windward side and on the leeward side, respectively. They may be connected to the driving frame  210  approximately in the middle between the leading end  212  and the rear ends  214 ,  216 . In another embodiment, the cleaning wires  240 ,  242  may be connected close to the rear ends  214 ,  216  of the driving frame. In further embodiments, also one, three or more cleaning wires may be used. The cleaning wires  240 ,  242  span about the leading edge  145  of the rotor blade  140 , in the case of a plurality of cleaning shires in a typical embodiment in spaced apart relationship on the leading edge  145  of the rotor blade  140 . For example, cleaning wires maybe nylon shires, but may also include other suitable materials, e.g. perlon wires, steel spires etc. In a typical embodiment, the cleaning wires  240 ,  242  are redirected, e.g. by a pulley  244 ,  246  or a pin, from the driving frame  210  to the tension frame  220 , where ends of the cleaning wires are fixed. Thus, in the deployed configuration the cleaning wires  240 ,  242  are tensioned, in particular due to the spring forces of the spring, e.g. the torsion spring, pushing the driving frame  210  and the tension frame  220  away from each other. In a further embodiment, both ends of the cleaning wires  240 ,  242  are redirected from the driving frame  210  to the tension frame  220 . It should be understood by those skilled in the art that a cleaning device according to the embodiments described herein arc very lightweight. Furthermore, due to their low profile the cleaning devices affect the aerodynamical properties of the blades only slightly or even not at all. 
         [0025]    The cleaning apparatus  200  may be passively or actively moved from a proximal portion to a distal portion of the rotor blade  140  along the leading edge  145  in a longitudinal direction M and back from the distal portion to the proximal portion of the rotor blade  140 . 
         [0026]    In an embodiment, the cleaning apparatus  200  is moved passively from the proximal portion to the distal portion by the wind. This embodiment is shown in  FIGS. 2 ,  3  and  4 . The proximal end of the rotor blade is arranged in the  FIG. 3  right to the cleaning apparatus  200  and the distal end on the left of the cleaning apparatus  200 .  FIG. 4  shows a side view of the cleaning apparatus  200  in the longitudinal direction M, i.e. from the proximal end to the distal end of the rotor blade  140 . The driving frame  210  has a substantially flat surface forming a driving blade for driving the cleaning device in the longitudinal direction M. Therefore, the surface of the driving frame  210  is adapted and/or disposed such that an air flow, in particular due to the rotation of the wind rotor that is substantially opposite to the rotating direction R, exerts a force in the longitudinal direction M on the driving frame and thus on the cleaning apparatus  200 . 
         [0027]    In case the tension frame  220  has also a flat surface perpendicular to a surface of the rotor blade  140 , such that a force is created in opposite direction to the longitudinal direction M, i.e. in a proximal direction, the surfaces of the tension frame  200  and the driving frame  210  are adapted such that an air flow impinging on the surfaces creates a resulting force in the longitudinal direction M. For example, the surface of the driving frame  210  may be greater than the surface of the tension frame. The flat surface of the tension frame  220  may further tension the cleaning wires  240 ,  242 . 
         [0028]    Typically, the air flow presses the cleaning device on the leading edge  145  of the rotor blade  140  due to the surface of the tension frame  220  and/or the surface of the driving frame  210 . 
         [0029]    In a further embodiment of a passively moved cleaning apparatus  200   a , the cleaning apparatus  200   a  may include an additional driving blade  213   a  that is mounted at the leading end  212   a  of the driving frame  210   a .  FIGS. 5 and 6  show such a cleaning apparatus in a front view ( FIG. 5 ) and in a side view in direction from the distal end to the proximal end of the rotor blade  140  (Section C-C of  FIG. 5 ). The driving blade  213   a  may have a surface normal that is oblique to the leading edge  145  of the rotor blade  140 . Therefore, the surface of the driving blade  213   a  is adapted such that an air flow, in particular the wind to the leeward side of the rotor blade  140  during stand still of the wind rotor, exerts a force in the longitudinal direction M on the driving blade  213   a  and thus on the cleaning apparatus  200   a.    
         [0030]    In the case of the cleaning apparatus  200 ,  200   a  shown in  FIGS. 2 ,  3 ,  4  and  5 , a driving blade of the cleaning apparatus  200 ,  200   a  is arranged such that the cleaning apparatus  200 ,  200   a  is driven in the longitudinal direction M. The air flow may depend on the rotational speed of the wind rotor. Therefore the optimal configuration of the driving blade may depend on the wind speed and the rotational speed of the wind turbine. 
         [0031]    Thus, only driven by the wind or by the air flow, the cleaning apparatus  200  will move along the leading edge  145  of the rotor blade  140  in the longitudinal direction M, and the cleaning wires  240 ,  240   a ,  242  will peel off dirt accumulated on the leading edge  145 . 
         [0032]    When the cleaning apparatus  200 ,  200   a  according to  FIGS. 2 to 6  has reached a final position, for example near the blade tip of rotor blade  140 , it may be retracted. This may be enabled by a retraction wire  250  that is connected at an attachment point  215 ,  215   a  to the driving frame  210 ,  210   a , typically close to the leading end  212 ,  212   a . In a further embodiment, the retraction wire  250  is connected on the leeward side of the rotor blade  140  close to the leading end  212 ,  212   a  at an attachment point to the driving frane  21 . 0 . For guiding the retraction wire  250 , the tension frame  220 ,  220   a  includes a guiding aperture  228 ,  228   a.    
         [0033]    The cleaning apparatus  200 ,  200   a  shown in  FIGS. 2 to 6  is in a deployed configuration. In a folded configuration, the driving frame  210 ,  210   a  and the tension frame  220 ,  220   a  arc arranged substantially in parallel. In the folded configuration, the cleaning wires  240 ,  242 ,  240   a  are not tightened around the leading edge of the rotor blade. In a typical embodiment, the guiding aperture  228 ,  228   a  and the attachment point  215 ,  215   a  cover each other in the folded configuration. When the cleaning apparatus  200  is retracted, the cleaning apparatus may be first brought from the deployed configuration to the folded configuration by pulling on the retraction wire. Then, the air stream acting in the driving blade  210 ,  210   a  may push the cleaning apparatus from the outer portion to the inner portion of the rotor blade  140 . In a further embodiment, the cleaning apparatus  200 ,  200   a  is retracted in the deployed configuration. It depends on the elastic force of the spring at the hinge  230 ,  230   a ,  232 ,  232   a  whether the cleaning apparatus  200 ,  200   a  is retracted in the deployed configuration or in the folded configuration. 
         [0034]      FIG. 7  depicts the rotor blade  140  with the cleaning apparatus  200 ,  200   a . The rotor blade  140  has a blade tip  147  and a leading edge  145 . The cleaning apparatus  200 ,  200   a  is first deployed in a starting position at the inner or proximal portion of the rotor blade  140  and then moved along the leading edge  145  of the rotor blade  140  to an end position near the blade tip  147 . As already described above, when the cleaning device is retracted by the retraction wire  250  the cleaning apparatus  200 ,  200   a  may be first brought from the deployed configuration into the folded configuration, so that the air flow does not further drive the cleaning device into the longitudinal direction M. The folded cleaning device may be, in a tropical embodiment, brought back into a shelter  149 . For example, the shelter may define the starting position. In the shelter  149 , the cleaning apparatus  200 ,  200   a  is typically kept in the folded configuration and not exposed to the air flow. In case the cleaning apparatus  200 ,  200   a  is retracted in the deployed configuration, it may be drawn against a stopper in the shelter  149 , so that the cleaning apparatus  200 ,  200   a  is brought from the deployed configuration to the folded configuration in the shelter  149 . 
         [0035]    In one embodiment, a motor for manipulating the retraction wire  250  may, be also located in the shelter  149 . The shelter may be located in an inner portion, in particular in the inner third, of the rotor blade  140 , so that the deteriorating aerodynamical effects of the shelter  149  are minimized. Thus, during normal operation of the wind turbine  100 , the cleaning device will be parked in the shelter  149  on the leading edge  145  of the rotor blade  140 , in particular at an inner location of the profiled section of the blade. The frames  210 ,  210   a ,  220 ,  220   a  of the cleaning apparatus  200 ,  200   a  are folded in parallel and pulled tight against the inner contour or stopper of the shelter, where the device will be held safely an without exposure to the air flow. The parallel folding also enables also a slender design of the shelter, which minimizes additional drag. Thus for cleaning of the leading edge  145  of the rotor blade  140 , the cleaning apparatus  200  is released from the shelter by loosening the retrieval or retraction wire  250 . In a typical embodiment, the spring at the hinges  230 ,  230   a ,  232 ,  232   a  will unfold the cleaning device in its deployed configuration and expose the driving blade  215   a  or the distal or driving frame  210  to the air flow. As the driving frame  210  of the cleaning apparatus  200 ,  200   a  is aerodynamically shaped, the air pressure during turbine operation keeps the cleaning apparatus  200  attached to the leading edge  145  of the rotor blade  140 , and drives the cleaning apparatus  200 ,  200   a  distally towards the blade tip  147 . As already described here above, the device %%ill be pulled out along the leading edge  145  all the way to the blade tip  147  and unspool the retraction wire  250 . Shortly before the blade tip  147 , the cleaning apparatus  200  will be stopped by the retraction wire  250  and then winched back in to the resting or starting position in the shelter  149 . The entire cleaning process will only take a few minutes, during which it might be necessary to change the operational parameters of the turbine in order to optimize the air flow around the rotor blade  140  for optimum cleaning results. 
         [0036]    In the following, a further embodiment is described with respect to  FIG. 8 .  FIG. 8  shows a section view of a rotor blade  140  from the backward direction. The same reference numbers refer to the same objects as in the previous drawings. A cleaning apparatus  200   b  of  FIG. 8  attached to the rotor blade  140  has substantially the same configuration as the cleaning apparatus  200  or  200   a  shown in  FIG. 2  or  FIG. 5 . The cleaning apparatus  200   b  includes a driving frame  210   b  and a tension frame  220   b  that are connected at their respective rear ends with hinges  230   b ,  232   b . Inside the blade  140 , on the inner side of the leading edge, a retaining device  260   b  is positioned approximately at the same distance to the hub  130  as the leading end of the driving frame  210   b . The retaining device  260   b  is attracting the driving frame  210   b  by magnetic forces or the like to the leading edge  145  of the rotor blade  140 . Therefore, the cleaning apparatus  200   b  may not able to fall of the rotor blade in any situation. In a further embodiment a second retaining device might be positioned to attract the tension frame  220   b  to the leading edge of the blade and to assure that cleaning wires are tensioned. The tensioning of the cleaning wires may be regulated by the distance between the retaining device  260   b  and the second retaining device. In a typical embodiment, the retaining device is guided by a rail  262   b  disposed on the inner side of the leading edge of the blade  140 . Therefore, the inner component of the cleaning device may be movable within the leading edge  145  of the rotor blade  140 . 
         [0037]    As in the embodiments described with respect to  FIG. 2  to  FIG. 6 , the cleaning apparatus  200   b  is pushed by an air flow or by a centrifugal force in case of rotation of the wind rotor in direction of the blade tip  147 . The retaining device  260   b  follows the driving frame  210   b  due to the magnetic attraction forces in the longitudinal direction. When the cleaning apparatus  200   b  has reached a final position near the blade tip  147 , the cleaning apparatus  200   b  has to be retracted to a starting position. This may be done in the same manner as described with respect to  FIG. 7 . In a further embodiment, the retaining device  260   b  is connected to a retraction wire  264   b  that is used to retract the retaining device to its starting position. As the retaining device attracts the driving frame  210   b  to the leading edge, and the leading end of the driving frame  210   b  follows the retaining device  260   b , also the driving frame  210   b  is retracted to its starting position. The cleaning apparatus  200   b  may be altered in the folded configuration, when the cleaning apparatus  200   b  is retracted to its starting position. If a guiding rail is used, larger cleaning forces than in the embodiment shown in  FIG. 2  are possible, so that the cleaning apparatus  200   b  is also suitable for cleaning if icing occurs. 
         [0038]    In a further embodiment, the driving frame  210   b  is not primarily driven by an air flow in direction of the blade tip  147 . In this embodiment the cleaning apparatus  200   b  is actively driven from the proximal portion of the rotor blade to the distal portion of the rotor blade. Inside the blade  140 , the retaining device  260   b  is connected to a driving wire  266   b,  that may pull the retaining device  260   b  in the longitudinal direction M. A winch for pulling the driving wire  266   b  may be located in the blade tip  147 , or if a driving wire pulley  268   b  is located in the blade tip  147  it may be disposed in the inner portion, in particular in the inner third, of the blade  140 . In an embodiment the winch for the driving wire  266   b  may disposed close to the winch for the retraction wire  264   b . Thus, with a driving mechanism that is located inside the blade, which is therefore not disturbing the aerodynamical properties of the blade  140 , the cleaning apparatus  200   b  can be driven along the leading edge of the blade  140  independently of the operation of the wind turbine  100 , i.e. if the wind rotor is rotating or not. 
         [0039]    In the embodiments shown in  FIG. 8 , the cleaning apparatus  200   b  is guided from the inside of the blade  140 . A carriage or retaining device is traveling along the leading edge on the inside, with the outside cleaning apparatus  200   b  only by magnetic forces. The magnets would pull the carriage or retaining device and the cleaning apparatus towards each other and thus hold both in place and assure sufficient stress on the cleaning wires. As the retrieval or retraction wire may be located on the inside of the blade, wind forces on the retrieval wire are avoided and tangling is prevented. 
         [0040]    In a further embodiment shown in  FIG. 9 , a cleaning apparatus  200   c  is provided. In this embodiment the cleaning apparatus  200   c  is also passively moved in the longitudinal direction M. The cleaning apparatus  200   c  has substantially the same parts as the embodiment of the cleaning apparatus  200  shown in  FIG. 2 , namely a driving frame  210   c  and a tension frame  220   c . Before the cleaning is performed, the rotor blade  140  to clean is rotated approximately into a 7 o&#39;clock position as shown in  FIG. 9 . Further, the rotor blade  140  may be pitched into a 0° position. Now the wind turbine  100  is in a park-position. The cleaning apparatus  200   c  is lowered, for example by a person on the nacelle or a winch located in the rotor blade  140  or a shelter  149  as shown in the embodiment of  FIG. 7 . The driving frame  210   c  may include weights, e.g. plumb weights, to support the driving of the cleaning apparatus  200   c  with gravity forces. When the cleaning apparatus  200   c  reaches the final position, for example near the rotor blade tip  147 , the cleaning apparatus  200   c  is pulled back with a retraction wire  250   c . This may be performed b, a winch or by a person as shown in  FIG. 9 . If additional pressure is needed, a pressing afire or rope  280   c  connected to the cleaning apparatus, either to the driving frame  210   c  or the tension frame  220   c , or both to the driving frame  210   c  and the tension frame  220   c . If the pressing wire  280   c  is drawn approximately perpendicular to the leading edge  145  of the rotor blade  140 , an additional pressure of the cleaning wires on the leading edge  145  is build up, so that also persistent dirt may be removed from the leading edge  145 . The pressing wire  280   c  may be pulled by a person on the ground. 
         [0041]    In a further embodiment, the cleaning apparatus  200   c  of  FIG. 9  may also be used during rotation of the wind rotor of the wind turbine. In this embodiment, the cleaning apparatus  200   c  is also passively moved in the longitudinal direction. The retraction wire  250   c  is connected to a winch in the rotor blade or a shelter like in the  FIG. 7 . The retraction wire  250   c  may be connected to the driving frame  210   c  or to the tension frame  220   c . If the retraction wire  250   c  is connected to the tension frame  220   c , the driving frame and the tension frame are pushed apart as described with respect of  FIG. 2  width a spring until a stop limits the further movement. The force of the spring has to be selected such that the cleaning apparatus is not folded during the cleaning process, when it moves in the longitudinal direction M. Further, the leading end of the driving frame  210   c  may include a weight as already described. Further, the tension frame  220   c  and the driving frame  210   c  may be formed such that during operation the apparatus  200   c  is pressed onto the leading edge by an air stream during the rotation of the wind rotor. This may in a further embodiment also or additionally be achieved by a retaining device located inside the rotor blade  140  as described with respect to  FIG. 8 . Therefore, during rotation of the wind rotor, the cleaning apparatus  200   c , in particular the driving frame  210   c  is pulled into the longitudinal direction M by centrifugal forces. The retraction wire  250   c  holds the cleaning apparatus, and the cleaning apparatus  200   c  is slowly slacked off by the winch in direction of the blade tip  147 , whereas the winch is connected to a proximal end of the retraction wire  250   c . If the cleaning apparatus reaches an outermost position near the blade tip  147  it is retracted back in particular into a shelter, by the wink. During the rotation the relative -wind or air stream imparting on the tension frame  220   c  and the driving frame  210   c  assures that the cleaning apparatus does not fell off the blade during a downward movement of the rotor blade  140 . 
         [0042]    The different embodiments of the present patent application may be combined like a kit of parts. Thus, the embodiment driven only by wind forces may be combined by the embodiment using gravitational or centrifugal forces. Or the embodiment using gravitational or centrifugal forces may be combined with an actively moving embodiment. The detailed design of the cleaning apparatus, in particular also a surface of the driving frame and the tension frame, may depend on the rotational speed of the wind rotor of the wind turbine and the wind conditions expected. Further it may depend if the cleaning may be performed during standstill of the wind rotor. In addition, the configuration of the cleaning device is such that already existing wind turbines may be retrofitted with such a device. Furthermore, it will be understood by those skilled in the art that the cleaning device may be provided in various shapes other than the ones shown in the accompanying drawings. 
         [0043]    The present patent application discloses a mechanical apparatus, which is able to clean off the prominent dirt and thus significantly lower surface roughness at the leading edge. The cleaning device may, be activated directly after detection of a bug bloom or other dirt accumulation on the leading edge. The cleaning process will only take a few minutes. The impairment of turbine performance due to drag increase is minimal, if a shelter is located on the inboard half of the blade. 
         [0044]      FIG. 10  shows a schematical process flow of an embodiment of the method according to the patent application. The method shown in  FIG. 10  may only be activated if certain environmental conditions apply. For example if, in summer time, the probability of a bug bloom is verys high or if the temperatures are below 2 degrees Celsius so that a risk of ice attachment on the leading edge of a wind turbine exists. If the method according to  FIG. 10  is activated, a controller permanently monitors the efficiency which might be,. e.g., the produced electrical power to wind force ratio (see step  1010 ). Also other methods for detecting a dirt accumulation on the rotor blade might be used. If the efficiency of the Wind turbine has dropped below a predetermined value that depends on the actual weather and wind conditions, the controller determines that a cleaning of the rotor blade due to dirt accumulation is needed (see step  1020 ). A self cleaning mechanism is activated in step  1030  to perform a cleaning operation of the leading edges of the rotor blades. This may be performed *with a cleaning device according to one of the embodiments described here above. Further, the cleaning may be performed during operation of the Wind turbine, i.e. the wind rotor of the wind turbine is rotating. Thus, no valuable time and energy is lost, as the wind turbine has not to be stopped and started again after the cleaning operation in the last case. Therefore, the overall efficiency of the rewind turbine may be raised. If the cleaning of the rotor blade is finished (see step  1050 ), the controller starts monitoring the efficiency again. 
         [0045]    The present patent application may further concern a method for automatically cleaning the rotor blades of a wind turbine comprising the steps: determining an actual performance of the wind turbine; comparing the determined performance With a reference value; activating a self-cleaning mechanism. 
         [0046]    Further, the cleaning may be only activated, if the wind rotor is rotating at least at a specific rotational speed and or of the rotor blades have a specific pitch angle. 
         [0047]    This written description uses examples to disclose an invention, including the best mode, and also to enable any person skilled in the art to practice this invention. While the invention has been described in terms of various specific embodiments, those skilled in the art will recognize that the invention can be practiced with modification within the spirit and scope of the claims. Especially, mutually non-exclusive features of the embodiments described above may be combined with each other. The patentable scope is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims of the; have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.