Abstract:
A device and method to generate electricity via a wind turbine. The device includes a first stator ring or a portion thereof, a second rotor comprising a ring encircling a set of blades, and wherein a rotation of the second rotor ring with respect to the first stator ring or the portion thereof generates energy.

Description:
FIELD OF THE INVENTION 
       [0001]    This relates to the field of energy generation via wind turbines. In particular the generation of electricity via horizontal-axis wind turbines. 
       BACKGROUND 
       [0002]    Typically, wind turbines are configured to convert kinetic energy from the wind into mechanical energy. Typically, the mechanical energy is used to produce electrical energy for an electrical grid. In some examples, wind turbines rotate a set of large blades in response to a wind, the blades coupled to a central hub. Wind turbines may have at least one or a plurality of gearboxes coupled to these large blades and the central hub due to low angular velocity of the hub in response to the rotation of the blades. The gearbox typically functions such that even slow rotations of the large blades can be converted, via the gearbox, to higher rotations within a generator, the generator typically configured to sit within a space at the center of the wind turbine. 
         [0003]    Wind turbines are generally designed with the exploitation of local wind energy, e.g., a generating air flow, in mind Wind turbines typically include a support structure; often the location of the wind turbine or structural design necessitates a very tall structure, a rotor and blade unit, and the generator unit configured to convert the rotation of the blades into electrical energy. The generator is typically mounted in a nacelle, i.e., a relatively large housing, at the top of a support structure, behind the hub of the turbine rotor. 
         [0004]    Aerodynamic modeling is typically used to determine the optimum height, control and blade shape of the turbine. Blade design is an essential component in wind turbine design and economics. Wind turbines often include a large footprint, given the wingspan of their blades. Blade speeds are typically limited due to air density near the speed of sound. Typically, the slower a blade rotates the less energy it can produce. 
         [0005]    Wind turbines, by their nature, are very tall and slender structures often necessitating specific structural designs for the foundations that must both deal with vertical and horizontal loads. Support structure heights tend to be a multiple of the blade length; typically, blades have a length ⅔ the height of the support structure. Taller support structures or masts, as well as longer blades, not only create unsightly eyesores, visible from greater distances, but they increase transportation and installation costs, often rivaling the costs of some of the parts of the apparatus. 
       SUMMARY 
       [0006]    In some examples, a wind turbine is constructed with concentric rings that may not necessitate the typical support structure height. The center ring in the wind turbine may allow non turbulent wind to pass through to downstream wind turbines. 
         [0007]    Typically, a wind turbine apparatus includes an outer ring, or portion thereof coupled to a support structure, the support structure having a top, a movable inner ring configured to rotate within the outer ring, a center ring coupled to a set of blades, the set of blades configured to rotate within the inner ring in response to wind, and wherein the rotating of the movable inner ring within the outer ring generates electricity. 
         [0008]    In some examples, the outer ring may be coupled to the support structure, above the top of the support structure. 
         [0009]    In some examples, the outer ring may contain a set of coils configured to conduct electricity. 
         [0010]    In some examples, a movable inner ring may contain a set of magnets, e.g., electromagnets, the magnets configured to rotate past a set of coils in the outer ring. 
         [0011]    In some examples, the center ring may be configured to allow wind to pass through unimpeded. 
         [0012]    In some examples, the wind turbine may be configured to be placed in a body of water. 
         [0013]    In some examples, the blades of the wind turbine may be configured to rotate above the top of the support structure. 
         [0014]    In some examples, the outer ring may be configured to be static relative to the support structure. 
         [0015]    In some examples, the outer ring is configured to rotate relative to the support structure. 
         [0016]    Typically, a method for converting kinetic energy to electrical energy, according to an example includes, includes rotating a movable inner ring within a static outer ring, or portion thereof, rotating a set of blades, typically connected to a center ring, within the inner ring; and, allowing wind to pass through a void, typically a hollow portion of a center ring, and minimizing impediments to air flow. 
         [0017]    In some examples, electricity may be generated by passing at least one magnet in the inner ring past a set of coils in the outer ring. 
         [0018]    In some examples, the set of blades may rotate above a top of a support structure. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]    The subject matter regarded as the invention is particularly pointed out and distinctly claimed in the concluding portion of the specification. Embodiments of the invention, however, both as to organization and method of operation, together with objects, features, and advantages thereof, may best be understood by reference to the following detailed description when read with the accompanying drawings in which: 
           [0020]      FIG. 1A  is a schematic illustration of an example of a wind turbine apparatus according to an example; 
           [0021]      FIG. 1B  is a schematic illustration of an example of a wind turbine apparatus according to an example; 
           [0022]      FIG. 2  is a schematic illustration of a cross section of an example of a wind turbine and down stream wind turbines, according to an example; 
           [0023]      FIG. 3  is a schematic of the electrical generating portion of a wind turbine, according to an example; and, 
           [0024]      FIG. 4  is a flow chart of a method of generating electricity via a wind turbine, according to an example. 
       
    
    
       [0025]    It will be appreciated that for simplicity and clarity of illustration, elements shown in the figures have not necessarily been drawn to scale. For example, the dimensions of some of the elements may be exaggerated relative to other elements for clarity. Further, where considered appropriate, reference numerals may be repeated among the figures to indicate corresponding or analogous elements. 
       DETAILED DESCRIPTION 
       [0026]    In the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of the invention. However, it will be understood by those skilled in the art that the present invention may be practiced without these specific details. In other instances, well-known methods, procedures, and components have not been described in detail so as not to obscure the present invention. 
         [0027]      FIG. 1A  is a schematic illustration of an example of a wind turbine apparatus. Wind turbine  10  typically includes three concentric rings, an outer ring  20 , a movable inner ring  70 , and a center ring  30 . In some examples, there may be an alternative to a center ring. In some examples, there may be a non-hollow center structure. 
         [0028]    Outer ring  20  may be configured to act as a stator. In some examples, outer ring  20  may to be static, and may be coupled to a support structure  40 . In some examples, outer ring  20  may be movable. In some examples, outer ring  20  may be only a portion of a ring, as described below. 
         [0029]    Typically, outer ring may be coupled to support structure  40 . In some examples, outer ring  20  is coupled to the support structure above the top of support structure  40 . In some examples, outer ring  20  may be coupled to support structure  40  such that support structure  40  is configured to minimize the impedance of air flow to and away from a set of blades, the blades described below. 
         [0030]    In some examples, a generator may be configured to be connected to outer ring  20 . In some examples, outer ring may be a component of a generator  50 , as described below. 
         [0031]    Typically, outer ring  20  has a diameter of between 100-200 meters, e.g., 150 meters. In some examples, outer ring may have a larger or smaller diameter. 
         [0032]    In some examples, outer ring  20  may be connected to support structure  40  by one or a plurality of members. The members may be constructed from materials as are known in the art. 
         [0033]    Typically, the members may be one or a plurality of struts  120 , may be configured in a V formation to support the outer ring. In some examples, struts  120  may be configured in an alternative formation to support the outer ring. In some examples, outer ring  20  may be connected to support structure  40  by other methods known in the art. 
         [0034]    In some examples, outer ring  20  may be constructed of at least steel or composite materials. In some examples, other materials known in the art may be used. 
         [0035]    In some examples, inner ring  70  may be configured to act as a rotor in a generator. In some examples, inner ring  70  may be constructed of at least steel or composite materials. In some examples, other materials known in the art may be used. 
         [0036]    Typically, wind turbine  10  includes a set of blades, the set of blades including one or more blades  60 , are configured to be attached to center ring  30 . In some examples, there are between two and seven blades  60 , e.g., five blades, connected to center ring  30 . In some examples, there may be greater or fewer blades attached to center ring  30 . In some examples, blades  60  may be attached to a central point. In some examples, blades  60  may be attached to a central structure, as described below. In some examples, the central structure may have a void, as described below. 
         [0037]    In some examples, blades  60  may be attached to center ring via motors  65 , the motors configured to rotate blades  60 , such that they are better able to rotate inner ring  70  at a particular speed. In some examples, motor  65  rotate blades  60  in response to the direction and/or force of the wind. 
         [0038]    Blades  60  are typically shaped like wind turbine blades that are known in the art. Blades  60  are typically constructed from materials known in the art. In some examples, one or a plurality of blades  60  may change their pitch to accommodate different wind speeds and directions. In some examples, other aspects of blade  60  may change to accommodate environmental factors, or for other needs known in the art. 
         [0039]    Typically, center ring  30  may include drivers, e.g., motors  65 , as are known in the art, to control and/or maintain the change of the pitch of one or a plurality of blades  60 . 
         [0040]    Typically, blades  60  may have a length of between 40 and 100 meters, e.g., 70 meters. Other blade lengths that are longer or shorter may also be used as are known in the art. 
         [0041]    Typically, blade  60  may have a tip  80 . Tip  80  may have two or more sides. Typically, one side of tip  80  may face the wind. 
         [0042]    Typically, the speed of rotation of tip  80  is distinct (i.e., faster) than the speed of rotation at the other end of the blade  60 , the other end, closer to the center of wind turbine  10 . Typically, the relationship between the two may be measured by the tips speed ratio, as is known in the art. 
         [0043]    An outer ring unit  90  may be composed of two separate rings, an outer ring  20  and a movable inner ring  70 . Typically, inner ring  70  may be coupled to one or a plurality of blades  60 , and may be configured to rotate with blades  60 . 
         [0044]    Typically, outer ring  20  and inner ring  70  are close together. Typically, there may be a gap  140  between inner ring  70  and outer ring  20 . 
         [0045]    In some examples, gap  140  may be maintained via ball bearings between outer ring  20  and inner ring  70 . Typically, gap  140  may be maintained via a cushion of air, typically, a cushion of compressed air. In some examples, the compressed air for the cushion of compressed air may exit through holes in outer ring  20  to create the cushion of air between inner ring  70  and outer ring  20 . In some examples, compressed air may exit through holes in inner ring  70  to create the cushion of air. In some examples, other methods of maintaining gap  140 , as are known in the art, may also be employed. 
         [0046]    In some examples, blades  60  may be configured to rotate clockwise. In some examples, blades  60  may be configured to rotate counterclockwise. In some examples, blades  60  may be configured to rotate either clockwise or counterclockwise. In some examples, blade rotation may depend on the wind. 
         [0047]    In some examples, as one or a plurality of blades  60  rotate, a pressure gradient may form on either side of tips  80 , the pressure gradient typically the result of high pressure on a first side of one or a plurality of blades  60  and low pressure on a second side of one or a plurality of blades  60 . Configured to help minimize or limit the development of vortices at tips  80  and the potential resulting air turbulence resulting from the pressure gradient, blade  60  may be typically configured to be in close proximity to inner ring  70 , typically attached to inner ring  70 , the close proximity configured to prevent or limit movement of air down the pressure gradient and around tip  80 . 
         [0048]    Typically, center ring  30  has a diameter of between approximately 20% to 40%, e.g., 25% to 33%, of the diameter of outer ring  20 . Typically, center ring  30  may be configured to allow most wind to pass through uninhibited. 
         [0049]    In some examples, the wind may pass through center ring  30  wholly uninhibited, e.g., minimizing turbulent air or wakes to downstream wind turbines. In some examples, the passage of wind through center ring  30  may allow individual wind turbines, typically individual wind turbines on wind farms, as are known in the art, to be placed more closely together, as described below, 
         [0050]    Typically, appropriate spacing between turbines may be dependent on terrain and wind rose for a particular site. In some examples, the design of wind turbine  10 , and the minimization of wake due to center ring  30  allows other wind turbines to be spaced closer than current average spacing in the art. 
         [0051]    In some examples, the typical availability of turbulence and wake free air, resulting from air passing through center ring  30 , may generally reduce mechanical loads on wind turbine  10 , on downstream turbines, and on support structure  40  of wind turbine  10  and on other support structures of other wind turbines that may be situated in close proximity to wind turbine  10 . 
         [0052]    Typically, support structure  40  may provide clearance between blades  60  and the ground. In some examples, support structure may rotate in such a way as to rotate the rings toward the wind. 
         [0053]    The construction of wind turbine  10  may allow for a shorter support structure  40  than other support structures known in the art, and that may be typical in the art. In some examples, the support structure can be up to 33% shorter than support structures of similarly sized wind turbines that are known in the art. In some examples, support structure  40  may support the entirety, or most of the length of blade  60  above the top of support structure  40 . 
         [0054]    Support structure  40  may be configured to be placed on the ground or in a body of water. 
         [0055]    Typically, with the entirety, or in some examples, most of the length of one or a plurality of blades  60  sitting above a top of support structure, air may move freely to a large portion of one or a plurality of blades  60 , in some examples, air may move freely to the majority of one or a plurality of blades  60 . In some examples, air may move freely, i.e., with limited or no impediments, to all of one or a plurality of blades  60 . 
         [0056]    In some examples, air may move feely, and may not be substantially obstructed by support structure  40 . The movement of air without being substantially obstructed by support structure  40  may be configured to reduce vibrations that may result if a support structure were to be placed in-between an upstream wind and one or a plurality of blades  60 . In some examples, most upstream air used by wind turbine may move feely, and may not be obstructed by support structure  40 . 
         [0057]    In some examples, the placement of support structure  40  below a projected path of one or a plurality of blades  60  may be configured to reduce the development of a dynamic pressure gradient in the area where one or a plurality of blades  60  would otherwise cross in front of upstream air that may have encountered support structure  40  first. 
         [0058]    Typically, with wind turbine  10  configured to allow non-turbulent wind to reach most of one or a plurality of blades  60 , and in some examples, configured to allow non-turbulent wind to reach the entirety of one or a plurality of blades  60 , and with the reduction of vortices at tips  80  of blade  60 , a large portion of the surface area of one or a plurality of blades  60 , in some examples, most of the surface of one or a plurality of blades  60 , may be harnessed to convert kinetic energy to electricity or other forms of usable energy. In some examples, all of the surface of one or a plurality of blades  60  may be harnessed to convert kinetic energy to electricity or other forms of commercially usable energy. 
         [0059]    Typically, to harness kinetic energy and convert that energy to electrical energy, generator  50  may include outer ring  20  and inner ring  70 . Typically, outer ring  20  may serve as the housing for a stator and inner ring  70  may serve as housing for a rotor for electrical generator  50 . 
         [0060]    In some examples, energy is produced as a result of the inner ring  70  spinning around within outer ring  20 , or a portion thereof. Typically, inner ring  70 , coupled to tips  80 , typically may spin faster than center ring  30  coupled to an opposite end of blade  60  as described above, as is known in the art. 
         [0061]    With the relevant speed for producing energy typically at tips  80 , and typically not at center ring  30 , wind turbine  10  may be able to generate more electricity at low wind speeds than had wind turbine  10  generated energy via the rotations of center ring  30 , or in some examples, if wind turbine  10  had a hub attached to a gearbox at the confluence of one or a plurality of blades  60  at the center of wind turbine  10 . 
         [0062]    Typically, there is no gearbox when energy is generated as a result of the rotation of inner ring  70  coupled to tips  80 ; the current generating inner ring  70  may be typically rotating at or near the speed of tips  80 . 
         [0063]    The lack of a gearbox may minimize the amount of regular maintenance necessary to upkeep wind turbine  10 . In some examples, a reduction in regular maintenance and upkeep may allow wind turbine  10  to be placed in remote locations and may reduce other long term costs associated with wind turbines, as are known in the art. 
         [0064]    Typically, wind turbine  10  may produces a lesser amount of torque as the wind rotates one or a plurality of blades  60  when power is generated at tips  80 , than when power may be generated as a result of the rotation of center ring  30 , or in some examples, if wind turbine  10  had a hub attached to a gearbox at the confluence of one or a plurality of blades  60  at the center of the turbine. 
         [0065]    In some examples, when wind turbine produces less torque, there may be less stress on outer ring  20 . In some examples, there may be less stress on other components of wind turbine  10 . Typically, when there is less stress on outer ring  20 , wind turbine  10  may not need as much maintenance. In some examples, when there is less torque produced by spinning one or a plurality of blades  60 , there may be less stress on support structure  40 . 
         [0066]    In some examples, when wind turbine  10  lacks a gearbox, this may reduce the vertical load on support structure  40 . 
         [0067]    In some examples, wind turbine may have a braking system, as described below. 
         [0068]      FIG. 1B  is a schematic illustration of a wind turbine, according to an example. 
         [0069]    In some examples, outer ring  20  may be only a portion of a ring. In some examples, outer ring  20  may be a sleeve-like structure through which inner ring  70  rotates. In some examples, outer ring  20  may be a portion of a ring between 10-90 degrees of a circle, e.g., 45 degrees. 
         [0070]    Typically, when outer ring  20  is only a sleeve like structure it may be coupled to struts  120 . Struts  120  may be coupled to support structure  40 . Support structure  40  may house a control unit  150 . Typically, control unit  150  may be involved in orienting wind turbine  10 , blades,  60  and/or rings  20 ,  70  and  30  toward the wind and other functions of wind turbine  10  as known in the art. 
         [0071]    In some examples, a solenoid or coils  100 , described below, may be incorporated into the outer ring  20  sleeve structures. 
         [0072]    In some examples, a movable and/or slidable electrode  160 , e.g., an electrode that can act as a variator to change the parameters of the wind turbine&#39;s generation of energy, and in some applications, the effective length of the coil, may be positioned to move along the length of coil  100 , the coil having opposite ends. In some examples, there may be a second electrode  170 , either fixed or movable, at or near an opposite end of the coil  100 . Typically, the two electrodes allow energy to be collected and distributed out of wind turbine  10 . 
         [0073]    As described below, a moving electromagnet  110  in inner ring  70  may generate voltage, typically via inductance, as it passes past coil  100 . In some examples, slidable electrode  160  may move toward or away from second electrode  170 , the distance between the electrodes being related to the eventual and/or desired voltage generated by the wind turbine. Typically, as the electrodes are positioned further away from each other, a greater amount of torque, in some examples, the torque generated via the wind, may be necessary to move electromagnets  110  past coil  100 . 
         [0074]    In examples where there is less wind in the environment, the electrodes may be positioned closer to each other, requiring less torque to generate a voltage, the voltage being converted into a generated energy output, typically electricity, as described below. 
         [0075]    In some examples, wind turbine  10  may have an external power unit  165  for providing external or non-generated electricity to power components of wind turbine  10 . Typically, external power unit may connect to wind turbine  10  via electrodes  165 . In some examples electrodes  165  may be a positive terminal, +Vin, and a negative terminal, −Vin, coupled to wind turbine  10 , in some examples, coupled to outer ring  20  Powered components may include motors  65 , movable and/or slidable electrode  160 , and electromagnets  110 . Other components that may be powered by external electricity unit  165 , as are known in the known in the art, may also be connected to, and powered by, external electricity unit  165 . 
         [0076]    In some examples, wind turbine may have a braking system  180  similar to rim brakes on a bicycle. In some examples, the rim brakes may be similar to one or more of the following bicycle brake designs, including: rod-actuated brakes, caliper brakes, side-pull caliper brakes, center-pull caliper brakes, U-brakes, cantilever brakes, V-brakes, rollercam brakes, delta brakes, hydraulic rim brakes, and/or other brakes known in the art. Typically, the brakes are near the portion of the windmill where outer ring  20 , or a portion thereof, is near structure  40 . 
         [0077]      FIG. 2  is a schematic illustration of a cross section of a wind turbine, on a wind farm according to an example. 
         [0078]    Typically, wind turbine may be on a wind farm  5  where there may be one or a plurality of additional wind turbines, here depicted as wind turbines  12  and  14 . 
         [0079]    Wind turbines  10 ,  12 , and  14  are depicted on flat ground and at the same level and height for illustrative purposes only. 
         [0080]    Typically, center ring  30  may be configured, in some examples, to provide a clear and uninterrupted central air flow through wind turbine  10 , typically through a central void  35  in center ring  30 . In some examples, the central void may be independent of center ring  30  and may be surrounded by a holding structure  25 . In some examples, the holding structure for central void  35  is center ring  30 . This may facilitate a downstream arrangement of a plurality of wind turbines in relatively close formation because of the uninterrupted central air flow that quickly regains its kinetic energy. 
         [0081]    Typically, downstream wind turbines, e.g., wind turbines  12  and  14  may be placed closer together when wind turbine  10  has center ring  30 . 
         [0082]      FIG. 3  is a schematic illustration of a cross section of an energy generating portion of the wind turbine, according to an example. 
         [0083]    Typically, outer ring  20  may contain a set of coils or solenoids, the set of coils including one or a plurality of coils  100 . Coils  100  may be similar in function to field coils or field windings as are known in the art. In some examples, outer ring  20  may contain a set of coils  100  in a small portion of a circumference of outer ring  20 . In some examples, outer ring  20  may contain a set of coils in a portion of the circumference of outer ring  20  wherein the portion of the circumference is near support structure  40 . In some examples, outer ring  20  contains coils throughout a large portion of the ring. In some examples, outer ring  20  contains coils throughout the entirety ring. 
         [0084]    Typically, the size of the coils  100  in outer ring  20  may result in more or less torque resistance against moving inner ring  70 . In some examples, the orientation of one or plurality of blades  60  may also result in less torque resistance. In some examples, the effective length of coil  100  may be varied by variators and/or movable electrodes, as described above. 
         [0085]    In some examples, inner ring  70  may have one or a plurality of magnets, typically, electromagnets  110  within the structure of inner ring  70 . In some examples, said one or a plurality of electromagnets  110  may be configured to be coupled to an outer surface of inner ring  70 . In some examples, said one or a plurality of electromagnets  110  may be configured to be coupled to an inner surface of inner ring  70 . 
         [0086]    Typically, said one or pluralities of electromagnets are configured to be placed throughout the circumference of inner ring  70 . In some examples, electromagnets  110  are configured to be evenly placed throughout circumference of inner ring  70 . In some examples, one or plurality of electromagnets  110  are placed in only specific portions of inner ring  70 . 
         [0087]    Typically, electricity is generated by passing electromagnets in inner ring  70  past the set of coils  100  in outer ring  20 . As inner ring  70  spins in conjunction with one or a plurality of blades  60 , the coupled electromagnets will pass over the area of outer ring  20  where coils  100  are configured to be coupled. 
         [0088]    In some examples, electricity may be generated by passing set of coils  100  in inner ring  70  past electromagnets  110  in outer ring  20 . 
         [0089]    When said one or plurality of electromagnets  110  move past the set of coils, the resulting changes in the magnetic field may lead to the creation of electricity, as is known in the art. As the magnetic field around coil  100  changes, voltage may be induced within coil  100 , as is known in the art. 
         [0090]    As is known in the art, the voltage may drive electrical current. In some examples, the current may be alternating current. In some examples, the alternating current is sent out of wind turbine  10  through power lines for distribution. In some examples, the current is stepped down, as is known in the art, for greater efficiency in transmission of the electricity through a power grid. 
         [0091]    Typically, an output voltage from wind turbine  10  is a result not of the speed of one or a plurality of blades  60 , but rather the speed of the movement of electromagnets  110  past the coils  100 , their size, and the magnetic field intensity of the stator, i.e., typically electromagnets  110  in inner ring  70 . 
         [0092]    A faster-moving electromagnet  110  may induce a greater amount of voltage, as is known in the art. Typically, the speed of rotation may be limited. In some applications, rotation of one or a plurality of blades  60  within wind turbine  10  maybe configured to be slower than the speed of sound. 
         [0093]    In some examples, structural constraints in support structure  40  and/or other components of wind turbine  10  may limit the torque output of wind turbine  10 . In some examples, the design of wind turbine  10  may reduce torsional forces on support structure  40 . In some examples, this reduced torsional force may allow for alternatives in the construction of support structure  40 . 
         [0094]      FIG. 4  is a flow chart of a method for generating electricity via wind turbine  10 , according to an example. Typically, wind turbine  10  is operational and generating energy when the wind is blowing. The wind may be harnessed by wind turbine  10 , as depicted by block  199 . In some examples, the wind is harnessed by blades  60  to rotate inner ring  70  within outer ring  20 , or a portion thereof. In some examples, the wind is harnessed by central ring  30 , where central ring  30 , allows for the passage of the wind downstream to downstream wind turbines. 
         [0095]    In some examples, a set of one or a plurality of blades  60  connected to an inner ring  70  is rotated, as depicted by block  200 . Typically, a movable inner ring  70  is rotated within a static outer ring  20 , as depicted by block  210 . The rotation of inner ring  70  containing electromagnets  110  within outer ring  20  containing a conducting coil  100  typically results in the generation of energy which may be converted into electricity, as depicted by block  220 . In some examples, the rotation of inner ring  70  containing a conducting coil  100  within an outer ring  20  containing electromagnets  110  may typically result in the generation of electricity. When rotating inner ring  70  within outer ring  20 , wind turbine  10  is typically configured to allow wind to pass through central ring  30 , as depicted by block  230 . Typically, when wind is allowed to pass through central ring  30 , impediments to downstream air flow may be minimized. 
         [0096]    Features of various embodiments discussed herein may be used with other embodiments discussed herein. The foregoing description of the embodiments of the invention has been presented for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed. It should be appreciated by persons skilled in the art that many modifications, variations, substitutions, changes, and equivalents are possible in light of the above teaching. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the invention.