Abstract:
The present invention relates to a method for transporting a blade for a wind turbine, comprising the steps of lowering said wind turbine blade into water, whereby it floats, and transporting said blade in the water. The invention further relates to a wind turbine blade with its holes sealed, making the blade transportable by floating, and a blade comprising a keel, propeller and a rudder.

Description:
CROSS REFERENCE TO PRIOR APPLICATIONS 
     This is a U.S. National Phase application under 35 U.S.C. §371 of International Patent Application No. PCT/DK2008/000390, filed Nov. 3, 2008, and claims the priority of European Patent Application No. 07388086.6, filed Nov. 27, 2007 both of which are incorporated by reference herein. The International Application published in English on Jun. 4, 2009 as WO 2009/068031 under PCT Article 21(2). 
     FIELD OF THE INVENTION 
     The present invention relates to transportation of blades for wind turbines. 
     The transportation of blades for wind turbines has become more difficult due to, among others, the continuous increase of the blade length, and thereby also increased weight. Transportation along roads is therefore characterized by very long vehicles, typically escorted by service cars and often directed to drive at night in order not to disturb the daily traffic. The dimensions (road width, space in tunnels and on bridges, etc.) of the road is, however, not compatible with the increasing dimensions of the wind turbine blades. As a consequence, some blades are manufactured in several parts that can be assembled later, which is an economically costly solution and technologically undesirable. The latter due to the rendez vous of high loads in the assembly points of such blades. 
     Due to the geographically widespread use of wind turbines, there are often long distances between the place of manufacture and the location where the wind turbines are installed. Seaborne transportation of wind turbine blades constitutes a widely used transportation means in bringing finished blades to their final destination or part of the way thereto. This seaborne carriage is, however, encumbered with a number of problems and high associated costs. The problems arise as a combination of the twists that ships make at sea and due to the geometrical characteristics of the blades. Hence, the blades can have a length of up to 60 meters or even longer, and are typically both slightly curved and twisted along a longitudinal axis. With such a span of length, the twists of the ship can seriously damage the blades, resulting in costly repair work. In order to compensate for the ships&#39; twists and reduce the damages to the blades, special fixtures are used. These fixtures are customized and thereby unique for every blade type, for which reason every new type of blade requires new and different fixtures. Furthermore, the curvature of the blades makes them difficult to stack in a cost efficient manner. Typically, the fixtures are welded onto the deck of the ship and designed in a way enabling a stacking of the blades in three to four layers. Due to the customization of the fixtures and the elaborate procedures encumbered therewith, seaborne carriage of wind turbine blades is associated with high costs. 
     However, with a world wide growing market for wind turbines installed both onshore and offshore, there is a huge demand for transportation of wind turbine blades. 
     OBJECT AND SUMMARY OF THE INVENTION 
     The objective of the present invention is to propose methods for transporting wind turbine blades. Furthermore, it is an object of this invention to eliminate or at least diminish the above mentioned problems by providing a low-cost, simple, and highly efficient way of transporting wind turbine blades. 
     According to one aspect the present invention relates to a method for transporting a blade for a wind turbine, comprising the steps of lowering said wind turbine blade into water, whereby it floats, and transporting said blade in the water. The proposed method is advantageous by providing a simple, inexpensive and fast way of transporting wind turbine blades, as the blades are simply lowered in water without, in the simplest case, any further arrangements. The blades can be transported alone or in groups. Furthermore, the transportation of the blades can constitute just a part of the way from the manufacturing site to the installation site, whereas wind turbine blades for both onshore and offshore installations can be transported in this way. Blades for offshore wind turbines can also be transported directly to the installation location, even if this is in areas with a low water level. By having the blades transported directly to each offshore wind turbine, several steps in the process of erecting these wind turbines can be eliminated. For example the crane lifting the blades when mounting these can be positioned in proximity of the erected tower and nacelle. Each time a blade has been mounted, the next blade can simply be moved into the lifting-range of the crane. Therefore the crane does not have to move back and forth between the ship carrying the blades and the location of the offshore wind turbine. 
     The blades for an offshore wind turbine can also be mounted by the use of a lifting device placed in the hub, wired to the blade root. By means of the wires the blade is simply hoisted to the hub bearing and fastened thereto. Thus there is no need for cranes. Offshore wind turbines are most often placed in water depths of 10-15 m. Therefore, during this hoisting movement of an offshore blade, the tip of the blade will eventually hit the seabed. In order to avoid this potentially damaging impact, the outermost part of the blade can be supported by a rubber boat or other supporting means. In the case of an onshore wind turbine, the blade can be hoisted in a similar way and the blade tip supported by a truck, trailer or other means. 
     Another advantage is that there are no limitations on the length or weight of the wind turbine blades. Moreover, this kind of transportation does not disturb road users and requires no special and expensive fixtures as with the present seaborne carriage. In continuation of this, many of the elaborate working procedures can also be eliminated. The invention is further advantageous providing transportation where the blade is free to flex and deform without the risk of damage. From the range of advantages listed above it is clear that this method for transporting wind turbine blades in water is inexpensive and thereby a low cost alternative compared to the possibilities known in the state of the art. 
     In an embodiment said method comprises sealing at least one opening in said wind turbine blade such as a opening in the root end of the wind turbine or drain holes along the wind turbine blade in a watertight way, such that said wind turbine blade can be transported floating in water and where said at least one opening can be at least partly restored after transportation. 
     In an embodiment said method comprises towing at least one wind turbine blade by a vessel, such as a towboat. This is advantageous as one or a plurality of blades can be transported over long distances. 
     In an embodiment said method comprises transporting a plurality of wind turbine blades in water in single file behind a vessel. This particular way of transporting is advantageous in narrow or low waters such as a rivers and canals. 
     In a further embodiment said method comprises transporting a plurality of wind turbine blades in water side-by-side behind a vessel. 
     In an embodiment said method comprises fastening at least one stabilizing unit to said blade. This is advantageous when the blades are transported through e.g. troubled water. 
     In an embodiment said method comprises fastening at least one propelling means to said blade. Hereby a very flexible transportation of a blade is obtained providing great maneuverability. 
     In an embodiment said method comprises fastening at least one towing means to said blade. 
     In an embodiment said method comprises fastening at least one protecting unit, such as a fender, to said blade. This is particular advantageous as it prevents damages caused by blades hitting each other, by other ships, by floating material, etc. 
     In a further embodiment the present invention relates to a wind turbine blade for a wind turbine, wherein at least one opening in said wind turbine blade such as a opening in the root end of the wind turbine blade or drain holes along the wind turbine blade has been sealed in a watertight way, such that said wind turbine blade can be transported floating in water and where said at least one opening is at least partly restored after transportation. Hereby it is obtained that the inside of the blade, possibly containing sensitive equipment, is protected. 
     In an embodiment said wind turbine blade comprises at least one keel detachably fastened to said wind turbine blade. This is advantageous as it stabilizes the blade in the water. 
     In an embodiment said wind turbine blade comprises at least one stabilizer unit detachably fastened to said wind turbine blade. This is also advantageous as it stabilizes the blade in the water. 
     In yet a further embodiment said wind turbine blade comprises at least one detachable propelling means. Hereby a very flexible transportation of a blade is obtained, providing great maneuverability. 
     In an embodiment said wind turbine blade comprises at least one rudder detachably fastened to said wind turbine blade such that said wind power can be navigated. This also serves to improve the maneuverability of the blades. 
     In an embodiment said wind turbine blade comprises at least one fitting detachably fastened to said wind turbine blade for connecting at least one other wind turbine blade to said wind turbine blade such that the connected wind turbine blades can be transported jointly in water. This is advantageous as a plurality of blades can be transported over very long distances. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the following, preferred embodiments of the invention will be described referring to the figures, where 
         FIG. 1  illustrates a wind turbine blade floating in water. 
         FIG. 2  illustrates a towboat towing a number of floating wind turbine blades arranged in a single file manner. 
         FIG. 3  illustrates a towboat towing a number of floating wind turbine blades arranged side-by-side. 
         FIG. 4  illustrates the tower and nacelle of an offshore wind turbine with a floating wind turbine blade at its side. 
         FIG. 5  illustrates a wind turbine blade adapted to be transported in water, wherein a propelling module has been fastened to the root, and side propeller and rudder fastened the blade tip. 
         FIG. 6  illustrates a wind turbine blade with openings at the root end, drain holes and lightening conductor. 
         FIG. 7  illustrates a floating wind turbine blade mounted with a stabilizing unit. 
         FIG. 8  illustrates a wind turbine blade adapted to be transported in water, on which a keel has been mounted. 
         FIG. 9  illustrates a wind turbine blade arranged inside a sealed bag floating in water. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
       FIG. 1  illustrates a wind turbine blade  100  floating in water. Modern blades are most often hollow, which means that they can float. Thus, modern blades are made of glass and/or carbon fibers and different core materials such as balsa tree, foamed materials, of which all materials are resistant to water. The net upward buoyancy force on the wind turbine blade is equal to the magnitude of the weight of fluid displaced by the wind turbine blade. This force enables the wind turbine blade to float. 
       FIG. 2  illustrates a towboat  210  towing a number of floating wind turbine blades  100  arranged in a single file manner. Each wind turbine blade  100  is mounted with one or more fittings  214  used for connecting the wind turbine blades  100  together with a blade connection  216 . The fitting  214  can e.g. be a belt or a clamp which is fastened to the blade  100  and can comprise e.g. one or more fastening means (not shown) such as rings for securing the blade connection  216 , hawsers and towlines  212 , etc. The fitting  214  can also be fixed in permanent fastening members (not shown) in the blade  100  or fastened directly in the blade  100  using e.g. screws (not shown), where after the holes from the screws could be closed. The blade connection  216  connects each of the wind turbine blades  100  to each other in e.g. the fittings  214  or in the blade root (not shown). The blade connection  216  can e.g. be a simple towline of hawser, in which the case the fittings  214  can be omitted and replaced by tying the blade connection  216  directly to the blade  100 . The blade connection  214  can also be rigid such that a constant distance between each of the connected wind turbine blades  100  is kept. The blade connection  214  can have the shape of a bar or an arc, and be made of metal, glass fibre, rigid rope, etc. A constant distance between the wind turbine blades  100  is advantageous in order to ensure that the wind turbine blades  100  do not damage each other during the transportation Furthermore a rigid blade connection  214  ensures that the wind turbine blades  100  cannot move in a way not intended. The wind turbine blade  100  closest to the towboat  210  is connected thereto by the towline  212 . This connection may also be rigid to ensure a safety distance between the towboat  210  and the wind turbine blade  100 , and to obtain a sufficient maneuverability of both towboat  210  and the connected wind turbine blades  100 . The wind turbine blades  100  can also be transported in reverse order, such that the blade tip would be in front. Regardless of how and with what means the wind turbine blades  100  are transported, the blades ability to float is exploited. 
       FIG. 3  illustrates a towboat  210  towing a number of floating wind turbine blades  100  arranged side-by-side. Each wind turbine blade  100  is mounted with a fitting (not indicated) used for connecting the wind turbine blades  100  together with one or more blade connections  320 . Each end of the blade connection  320  is connected to the fittings (not indicated) of neighboring wind turbine blades  100 . Again the blade connection  216  can e.g. be a simple towline of hawser, in which case the fittings (not indicated) can be omitted and replaced by tying the blade connection  320  directly to the blade  100 . To avoid that the blades  100  damage each other fenders (not shown) can be arranged between the blades  100 . The blade connection  320  can also be rigid such that a constant distance between each of the connected wind turbine blades  100  is kept. Again, the constant distance between the wind turbine blades  100  is advantageous in order to ensure that the wind turbine blades  100  do not damage each other during the transportation. Furthermore the blade connection  320  ensures that the wind turbine blades  100  cannot move in ways not intended. The wind turbine blades  100  are rigidly connected to the towboat via the towline  212 , fastened to the root sealing (not indicated) of the wind turbine blades  100 . This towline  212  can likewise also rigid ensure a safety distance between the towboat  210  and the wind turbine blade  100 , and to obtain a sufficient maneuverability of both towboat  210  and the connected wind turbine blades  100 . For improving the maneuverability of the towboat  210  and the connected wind turbine blades  100 , additional towlines  212  between the two could be added. The towline  212  can also be flexible like an ordinary towline or a hawser, and may be directly tied to the blade  100 . The blade connections  320  can also be fastened to permanent fastening members (not shown) in the blade  100 . 
       FIG. 4  illustrates the tower  440  and nacelle  442  of an offshore wind turbine with a floating wind turbine blade  100  at its side. The wind turbine blade  100  may be lifted in e.g. the fittings  214 , such that the blade root can be fastened to one of the wind turbine blade bearings  446  in the wind turbine nacelle  442 . The fittings  214  are similar to the ones described above (see description of  FIG. 2 ). The wind turbine blade  100  can be lifted by for example an offshore crane (not shown) located in the proximity of the wind turbine or by a helicopter. As the wind turbine blades are floating in the water and can be easily moved around the offshore crane can maintain its position during the whole installation of the wind turbine blades  100 . 
       FIG. 5  illustrates a wind turbine blade  100  adapted to be transported in water, wherein a propelling module  550  has been fastened to the root of the wind turbine blade  100 , and side propeller  560  and rudder  570  fastened to the tip end of the blade  100 . The propelling module  550  can be fastened to the blade root, and comprises a propeller  552 , whereby the wind turbine blade  100  can be moved through the water. The propeller  552  can optionally be pivoted around an axis (not shown) perpendicular to the rotational axis of the propeller  552 , whereby the floating wind turbine blade  100  can be moved in a desired direction. The propelling module  550  may be controlled remotely or be manned by a trained operator. The maneuverability of the wind turbine blade  100  can be further increased by mounting the blade  100  with a side propeller module  560  and/or a rudder module  570 . The side propeller module  560  may comprise a fitting  564  used for mounting the side propeller module  560  on the wind turbine blade  100  and propeller  562 . The propeller  562  can be pivoted around an axis (not shown) perpendicular to the rotational axis of the propeller  562 . Hereby the wind turbine blade  100  can be maneuvered in a desired position, especially in narrow water as in harbors or at the installation location of an offshore wind turbine. The rudder module can  570  comprise a rudder  572  and a rudder fitting for mounting the rudder module  570  around the wind turbine blade  100 . The rudder module increases the maneuverability of the wind turbine blade  100  in water, and can therefore the purposefully used in narrow water such as in harbors or at the installation location of an offshore wind turbine, and at open sea where a continuous adjustment of the rudder can compensate for current and weather conditions. Both the side propeller module  560  and the rudder module  570  can be detached after use, and need not be attached near the tip as shown in the figure, but can be arranged anywhere along the blade. The side propeller module  560  and the rudder module  570  do not necessarily have to be mounted on a wind turbine blade  500  fastened to a propelling module, but can be applied to a wind turbine blade towed by e.g. a towboat. Neither do is the side propeller module  560  and the rudder module  570  have to be mounted in combination, but can be used a single module as well. A wind turbine blade can also be mounted with a plurality of side propeller modules  560  and rudder modules  570 . In another embodiment the propelling module  550 , side propeller module  560 , and the rudder module  570  can also be fixed directly in the blade  100  with e.g. screws (not shown). When the modules are no longer needed, the holes from screws can be closed. In a further embodiment the modules  550 ,  560 ,  570  could also be fixed to the blade  100  using permanent fastening members (not shown) in the blade  100 . 
       FIG. 6  illustrates a wind turbine blade  100  comprising the openings at the root end  680 , drain holes  682 , and lightening conductor  684 . Prior to transporting the blade  100  these openings  680 ,  682  and the lightening conductor  684  can optionally be sealed or covered in a way that they openings and the lightening conductor can be at least partly restored. Thus the blade  100  could be arranged in a bag (not shown), or at least partly be wrapped with e.g. tape or another elastic and/or adhesive material (not shown). The openings  680 ,  682  and the lightening conductor  684  could also be padded with a material that could be optionally removed in order to restore these. Regardless of whether the seals or covers are applied, the blade  100  maintains its buoyancy. The drain holes  682  and the lightening conductor  684  can also be drilled and mounted, respectively, after the blade  100  has been transported to its end station, that is the installation location of the wind turbine (not shown). Depending on which direction the blade  100  is transported, the root opening  680  could be sealed using a plane plate or a have a shape suited for hydrodynamic conditions. Thus the root sealing could for example be shaped as a stem bulb. In another embodiment the blade  100  could at least partly be filled with water (not shown) in order to stabilize it when floating. In this way the inside of the blade would have a function resembling ballast water tanks in e.g. ships and vessels. To protect the inside of the blade this embodiment could also be realized by arranging a bag (not shown) inside the blade  100  and then at least partly fill this bag with water. 
       FIG. 7  illustrates a floating wind turbine blade  100  mounted with a stabilizing unit  790 . The stabilizing unit  790  is fastened to the blade  100  with a blade connection  320  similar to the ones described in  FIG. 3 . One end of the blade connection  320  is fastened to the fittings  214 , which again are fastened to the blade  100 . The other end of the blade connection  320  is fastened directly the stabilizing unit  790 . The stabilizing unit  790  can be any element having buoyancy, such as a glass fibre structure. Furthermore the stabilizing unit  790  advantageously has a hydrodynamic shape suited for transportation is water. The stabilizing unit  790  stabilizes the transportation of the blade  100 , and, among others, prevents the blade  100  from twisting in the water. The keel  830  could also be fastened directly in the blade  100 , using e.g. screws (not shown). When the keel  830  is no longer needed the holes from the screws are closed. 
       FIG. 8  illustrates a wind turbine blade  100  adapted to be transported in water, on which blade a detachable keel  830  has been mounted. The keel  830  has been mounted to the blade  100  by fittings  214  fastened to the blade  100 . The purpose of the keel  830  is to stabilize the transportation of the blade  100  in water, by among others preventing it from twisting in the water. The keel  830  can be removed prior to its installation, as the aerodynamic shape of the blades  100  is important for the efficiency of the wind turbine. 
       FIG. 9  illustrates a wind turbine blade  100  arranged inside a sealed bag  999  floating in water. The bag  999  is inflatable and comprises a keel  997  and compartments  998 , where the keel  997  stabilizes the bag and the compartments  998  provide additional buoyancy. Both the keel  997  and compartments  998  can be optionally inflated. Instead of inflating the bag  999 , a partly vacuum can also be established in the bag  999 . 
     It should further be noted that the above-mentioned embodiments illustrate rather than limit the invention, and that those skilled in the art will be able to design many alternative embodiments without departing from the scope of the appended claims. In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. The word ‘comprising’ does not exclude the presence of other elements or steps than those listed in a claim. 
     REFERENCES 
     
         
           100 , wind power blade 
           210  towboat 
           212 , towboat connection 
           214 , fitting 
           216  blade connection 
           320  blade connection 
           440  wind turbine tower 
           442  wind turbine nacelle 
           444  wind turbine hub 
           446  wind turbine blade bearing 
           550  propelling module 
           552  propeller 
           560  side propeller module 
           562  propeller 
           564  side propeller fitting 
           570  rudder module 
           572  rudder 
           574  rudder module propeller 
           680  root opening 
           682  drain holes 
           684  lightening conductor 
           790  stabilizing unit 
           830  keel 
           997  keel 
           998  compartment 
           999  sealed bag