Patent Publication Number: US-2009217851-A1

Title: Rotor sail and ship with a rotor sail

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a Section 371 of International Application No. PCT/DE2006/001821, filed Oct. 17, 2006, which was published in the German language on Apr. 26, 2007, under International Publication No. WO 2007/045220 A1 and the disclosure of which is incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     The invention relates to a rotor sail with a base, a rotary cylinder, which is mounted on the base in a manner permitting rotation about its longitudinal axis designed as the rotor axis, and whose enclosing outer surface serves as a wind-exposed surface in operation, and a drive for rotating the rotary cylinder. 
     A rotor sail of this kind is also known as a Flettner rotor, which rotates when driven by a drive. When the wind flows against the rotating rotor sail, a force transverse to the direction of flow of the wind is formed in accordance with the so-called Magnus effect as a result of surface friction between the rotor sail and the air flowing around it, as well as within the air adjacent to the rotor sail. The environmental pollution caused by the drive is, however, a disadvantage. 
     BRIEF SUMMARY OF THE INVENTION 
     The object of the invention is therefore to develop the rotor sail in such a way that it can be operated in a more environmentally friendly manner. 
     According to the invention, the object is achieved by providing a photovoltaic system with solar cells to generate electric energy for the drive, where the drive includes an electric motor, by locating the solar cells in the rotary cylinder, by facing the photoelectrically active layers of the solar cells toward the enclosing outer surface, and by designing the sleeve of the rotary cylinder as transparent, at least in the area covering the solar cells. The photovoltaic system thus serves to generate electric current, which can be used directly, via a corresponding control system, to operate the drive, such that the rotor sail, like a conventional wind sail, can be operated in the wind completely independently of additional systems, such as diesel generators or the like. Since a rotor sail of this kind is independent of an additional fuel supply, it can also be used in remote regions. Arranging the solar cells in the rotary cylinder also protects them at the same time. Moreover, this does not require any increase in size compared to a conventional rotor sail. The photovoltaic system can even be installed in existing rotor sails. For adaptation to the direct current generated by the solar cells, the electric motor can be designed as a DC motor. 
     Expediently, the end face of the rotary cylinder that is free in operation can also be of transparent design, at least in its radially outer areas. This can further increase the solar irradiation toward the solar cells. 
     As on the familiar rotor sail, the so-called Flettner rotor, the end faces of the rotary cylinder preferably project radially beyond the cylindrical sleeve of the rotary cylinder, as a result of which more favorable flow conditions can be achieved, particularly on the end areas of the surface of the cylindrical sleeve of the rotary cylinder adjacent to the end faces, when the wind flows against the rotor sail. 
     The solar cells are preferably located on the outer side of a core in the rotary cylinder. In this context, the core should provide a sturdy support for the solar cells. Furthermore, the longitudinal axis of the core should be identical with the rotor axis of the rotor sail. 
     The core should preferably have a round or polygonal cross-section. A highly symmetrical core is proposed here as the support for the solar cells, thus enabling the possible peripheral arrangement and orientation of the solar cells to be symmetrical and uniform, such that identical conditions for generating electric current via the solar cells can be created over the periphery. 
     In this context, the cross-section of the core is preferably of circular design. In this embodiment, the core can be designed as a cylinder whose sleeve is located parallel to the sleeve of the rotary cylinder, thus resulting in advantages regarding design and uniform generating conditions. 
     In one embodiment of the core, the core can be designed to taper prismatically or conically toward the top over its height in operating position. As a result, the solar cells can be arranged on the core at a more favorable angle to the incident solar radiation in operating position, thus making it possible to increase the efficiency of the photovoltaic system. 
     To this end, the core can be favorably designed as a truncated pyramid in the case of a prismatic taper, or as a truncated cone in the case of a conical taper. 
     In one embodiment of the core, the core can have a variable opening angle, formed between the center axis and the side face. In this way, the orientation of the solar cells located on the core can be optimized in accordance with a current mean solar altitude, or a mean solar altitude determined by the geographical location. 
     The core can preferably be mounted in non-rotating fashion relative to the base, meaning that the rotary cylinder rotates about a static core. The result of this is that the sun only ever illuminates one side of the core, meaning that only this side would need to be equipped with solar cells. To this end, a device can be provided that orients the core in accordance with the current direction of the incident solar radiation, in such a way that the surface of the solar cells is positioned as perpendicular as possible to the direction of the incident solar radiation. To this end, the core can also have a planar, flat body, whose dimensions, for preferred maximum exploitation of the available area in the rotary cylinder, can be designed to be slightly smaller than the height and inside diameter of the rotary cylinder. In the case of non-rotating mounting, it is necessary for the sleeve of the rotary cylinder to be of transparent design over its circumference at the level of the solar cells. 
     In another embodiment, the core can be mounted in a manner permitting rotation about its longitudinal axis. To this end, the core can be expediently connected to the rotary cylinder in non-rotating fashion. As a result, the solar cells located on the core are stationary in relation to the section of the sleeve of the rotary cylinder that covers them. The rotary cylinder and the core with the photocells thus form a common rotary body whose inert mass is increased compared to the rotary cylinder alone, meaning that uniform operation, i.e., more uniform rotation of the rotary cylinder, is possible in the case of fluctuating winds. To simplify the structural design of the rotor sail and for maximum exploitation of the space inside the rotary cylinder, the core and the rotary cylinder can have common end faces. 
     In another embodiment, the solar cells can be located directly on the enclosing inner surface of the rotary cylinder. As a result, the rotary cylinder can serve simultaneously as the support and a guard for the solar cells. This moreover greatly simplifies the structure of the rotor sail as a whole. 
     It is furthermore possible, in the case of particularly stable modules, such as those marketed by the Bayer company under the trademark MAKROLON, for the rotor sleeve to be constructed, at least in segments or in rings, from these stable modules or from the corresponding solar cells. 
     The solar cells can be designed as thin-film solar cells, for example. These thin-film solar cells are usually flexible and can thus easily be applied to a round core or the inner surface of the sleeve of the rotary cylinder. Depending on the respective application or the design of the solar sail, particularly of the core, different types of solar cell are open to consideration as optimum types. 
     Solar cells that are inflexible, due to being thicker, require application to a plane supporting surface, meaning that the embodiments of the core with prismatic side faces are open to consideration in this case. However, these inflexible solar cells usually demonstrate greater efficiency. The solar cells can be made, for example, using amorphous silicon, cadmium telluride (CdTe), copper-indium-diselenide (CuInSe 2 ; CIS), copper-indium-gallium, or the like as the active layers. However, since a relatively large sleeve surface of the core or inside surface of the sleeve of the rotary cylinder can be available on relatively large rotor sails, the solar cells can also have flexible, semiconductive organic polymers in the active layer, these currently being a low-cost alternative to inflexible solar cells, but demonstrating far lower efficiency. 
     With today&#39;s solar cells, the photovoltaic system can achieve an output of roughly 150 W/m 2 , which can be fed to a corresponding DC motor. Particularly in the embodiments in which the core is connected to the rotary cylinder in non-rotating fashion, the axis of rotation of the motor itself can be arranged in such a way that the motor drives the rotary cylinder and the core directly. 
     The electric drive is preferably located in the base, where the axis of rotation of the rotor sail can extend into the base. The drive is protected as a result. In addition, a storage device can be provided to store the energy generated by the photovoltaic system. It is possible to store surplus electric energy generated in calm weather or when the rotary cylinder is not in operation, for example. The storage device can expediently have storage batteries as storage media. The stored energy can serve to supply the drive, particularly at night or in the case of undersupply of the drive due to a greatly reduced level of incident light. This surplus electric energy can, however, also be used, e.g., in the case of a lull, to operate other units, e.g., on a ship to drive an electrically powered propeller or for a seawater desalination unit for supplying the ship with fresh water. 
     For use in the rotor sail, a customary control system for a photovoltaic system can have additional open-loop and/or closed-loop control elements that control the electric energy generatable and generated by the photovoltaic system, particularly its feeding into and tapping from the electric drive, as well as into and from the storage device. In this context, closed-loop control can ensure, for example, a constant rotational speed of the rotary cylinder or, by measuring the wind speed, regulate the rotational speed of the rotary cylinder in such a way that a roughly constant force perpendicular to the direction of the wind is generated by the Magnus effect. In this respect, a peripheral speed of the rotary cylinder corresponding to three to five times the wind speed is considered to be a favorable value. The drive can be designed in such a way that, during deceleration of the rotary cylinder, it acts as a generator, whose generated energy can be stored. 
     Less preferred because of the currently higher technical outlay, but nevertheless considered, is the use of a hybrid motor instead of, or in addition to, the electric motor, where the electric energy generated by the solar cells is used to hydrolyze water and store hydrogen. To this end, a storage facility for storing the generated hydrogen should also expediently be provided. As is generally known, the hydrogen can be burned in the hybrid motor in an environmentally friendly manner, producing water. 
     The rotor sail can preferably be installed in a vehicle, preferably a ship, in the known manner, where the ship has at least one rotor sail, according to one of the embodiments described above, which is arranged vertically on the ship in operating position and projects beyond the ship. The rotor sail can furthermore be installed in an airship, where, for better controllability of the airship, the rotor sail can also be installed on the airship with variable orientation of the axis of rotation of the rotary cylinder. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       The foregoing summary, as well as the following detailed description of the invention, will be better understood when read in conjunction with the appended drawings. For the purpose of illustrating the invention, there are shown in the drawings embodiments which are presently preferred. It should be understood, however, that the invention is not limited to the precise arrangements and instrumentalities shown. In the drawings: 
         FIG. 1  is a schematic, side view of a rotor sail according to a first embodiment of the invention; 
         FIG. 2  is a schematic, side view of a rotor sail according to a second embodiment of the invention; and 
         FIG. 3  is a schematic, side view of a rotor sail according to a third embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
       FIGS. 1 to 3  each show, in the form of a highly schematic and simplified diagram, a rotor sail  1  in three different embodiments. Rotor sail  1  has a base  2 , a rotary cylinder  3 , which is mounted on base  2  in a manner permitting rotation about its longitudinal axis designed as the rotor axis r, and whose enclosing outer surface  4  serves as a wind-exposed surface in operation, and a drive  5  having an electric motor  6  for rotating rotary cylinder  3 . Drive  5  and motor  6  are located in base  2 , where rotor axis r extends into drive  5 . 
     According to embodiments of the invention, a photovoltaic system  7  with solar cells  8  is provided to generate electric energy for drive  5 . Solar cells  8  are arranged in rotary cylinder  3  in such a way that their photoelectrically active layers face toward enclosing outer surface  4 . Provision is furthermore made for rotary cylinder  3  to be of transparent design in its sleeve  9  and in its end face  10  pointing away from base  2 . Moreover, end faces  10  in each case project radially beyond enclosing outer surface  4 , thus creating more favorable flow conditions when the wind flows in, as is generally known. In the embodiments of rotor sail  1  described here, solar cells  8  are located on the outer side of an elongated core  11  in rotary cylinder  3 , where the longitudinal axis of core  1  is identical to rotor axis r. 
     In the first and second embodiments of rotor sail  1 , shown in  FIGS. 1 and 2 , core  11  has a circular transverse cross-section, while the third embodiment, shown in  FIG. 3 , has a polygonal transverse cross-section. Structurally assigned to electric drive  5  is a storage device  13  having at least one storage battery  12  for storing the energy generated by photovoltaic system  7 , particularly the surplus electric energy generated, for example, when motor  6  is not in operation, e.g., while a ship equipped with the rotor sail is berthed. 
     In the two embodiments of rotor sail  1  shown in  FIGS. 1 and 2 , core  11  is connected to rotary cylinder  3  in non-rotating fashion and is thus driven together with rotary cylinder  3  by drive  5 . In this context, rotary cylinder  3  and core  11  have common end faces  10 . In the embodiment of rotor sail  1  shown in  FIG. 3 , on the other hand, core  11  is connected to base  2  in non-rotating fashion and thus designed as a stator relative to rotary cylinder  3 . In this context, core  11  is held in place via a supporting element  14 . 
     In all the embodiments of rotor sail  1  shown, vent holes  15  are provided in end faces  10  of rotary cylinder  3  to ventilate rotary cylinder  3 , particularly to extract air heated by sunlight in rotary cylinder  3 . 
     Core  11  in  FIGS. 2 and 3  is designed in upwardly tapering fashion over its height. In this context, core  11  in  FIG. 2  has the form of a truncated cone with a circular cross-section, while that in  FIG. 3  has the form of a truncated pyramid with prismatic side faces  16 . As a result, the orientation of solar cells  8 , applied to core  1 , relative to rotor axis r is inclined at an opening angle μ, formed between the longitudinal axis and sleeve-shaped side face  16  of core  11  having the form of a truncated cone, or the individual prismatic side faces  16  of core  11  having the form of a truncated pyramid. Given a customary vertical arrangement of rotor sail  1  in operating position, as also illustrated in  FIGS. 1 to 3 , solar cells  8  are thus more oriented toward the incident sunlight than those on core  11  shown in  FIG. 1 , thus increasing their efficiency. 
     Deviating from the second embodiment of rotor sail  1 , shown in  FIG. 2 , side faces  16  of core  11  in the third embodiment of rotor sail  1  are, on their side facing toward base  2 , mounted in a joint  17  permitting pivoting in a radial pivoting direction s about a pivoting axis perpendicular to rotor axis r. As a result, opening angle μ between the center axis and side face  16  can be varied, and thus the orientation of solar cells  8  arranged on core  11  toward the sunlight. Side faces  16  are divided into longitudinal sections  18  for structural execution. Via a radially acting pivoting device  19 , the upper end of the respective longitudinal segment  18  in installed position is pivoted radially outward in pivoting direction s, out of a home position shown in  FIG. 3  and into a pivoting position not shown here, in which the lateral edges of longitudinal segments  18  are separated from each other by an increasing distance over their height. 
     In the three embodiments of rotor sail  1  shown, rotor axis r is expediently designed as a hollow axle, through which electrical lines or conductors and the like (not shown) are routed to solar cells  8 , drive  5  and storage device  13 . 
     Further provided in all three embodiments is a control system  20 , located in base  2 , which controls the feeding of the electricity generated by solar cells  8  into drive  5  and into storage device  13  with storage battery  12 , as well as the tapping of electricity from storage battery  12 . 
     It will be appreciated by those skilled in the art that changes could be made to the embodiments described above without departing from the broad inventive concept thereof. It is understood, therefore, that this invention is not limited to the particular embodiments disclosed, but it is intended to cover modifications within the spirit and scope of the present invention as defined by the appended claims.