Patent Publication Number: US-2007120004-A1

Title: Aerial wind power generation system and method

Description:
This application is a divisional of Ser. No. 11/307,890 filed Feb. 27, 2006, which is a continuation-in-part of Ser. No. 11/164,512 filed Nov. 28, 2005. 
    
    
     TECHNICAL FIELD  
      The present invention relates to power generation and more particularly to systems and methods that convert wind energy acting on aerial wind driven elements to rotary or electrical power.  
     BACKGROUND ART  
      As fossil fuels become depleted and more expensive, the need for cost competitive methods and apparatus for harnessing renewable energy sources increases. The wind was long used for powering sailing ships and windmills, but the advent of steam engines or turbines, internal combustion engines, and gas turbines provided cheaper, more convenient energy sources. Less expensive and more efficient apparatus and methods for utilizing wind power would now be beneficial.  
      Windmills (or wind turbines) are currently being used to generate electricity and to drive pumps, however the cost to generate electricity with a windmill is still more expensive than the cost of electricity generated from fossil fuels. Windmills have a high capital cost relative to power generated. Wind speed, in general, is higher and more consistent with increasing altitude. There is potential to generate significant power with airborne or aerial apparatus at altitudes above the heights reasonably reachable by ground-based windmills.  
      The challenge with wind power generation is to convert the linear power of the wind to rotary motion to drive an electrical generator or a pump. One known approach to aerial wind power generation is a tethered, aerial windmill. Such aerial windmills can be supported by lighter than air aircraft, such as a blimp, or by lift from airfoil wing structures. These aerial windmills are relatively heavy and require long, heavy electrical cables to transmit the generated power to ground level.  
      A second known approach to aerial wind power generation is a wind powered element, such as a kite, blimp or airfoil, that is connected to a tow line. The tow line wraps around a reel on the shaft of a ground level power generation device. As the wind powered element is pulled by the wind, the distance from the wind powered element to the shaft increases and the tow line rotates the reel and shaft to generate power. The angle of attack or the shape of the wind powered element is changeable so that the wind powered element can be reeled back towards the ground level power generation device with little power use.  
      A third known approach to aerial wind power generation is an endless chain of spaced kites linked to the shaft of a ground level power generation device. The kites follow an ascending path and a descending path. The kites are adjustable to provide higher lift while on the ascending path.  
     DISCLOSURE OF THE INVENTION  
      An aerial power generation system includes a guide line that extends skywards at a selected angle. The guide line is connected at the upper end to a support body. A wind powered driven element is slidably mounted on the guide line. The driven element uses a sail-like design with curvature about a horizontal axis so as to maximize the lift and drag wind forces, or the driven element includes a rotatable hub with a plurality of airfoil blades. The driven element is connected by a tow line to a reel on a shaft of a means for generating power. Means are provided for changing the driven element from high force configurations to low force configurations.  
      Another aerial power generation system includes a plurality of wind powered driven elements connected by tow lines to spaced attachment points on a revolving apparatus that drives a means for generating power. A means for changing the driven elements between high force configurations and low force configurations changes each driven element to high force configurations when the respective attachment point is moving downwind and to low force configurations when the respective attachment point is moving upwind to cause rotation of the revolving apparatus. The driven elements are flown in a pattern at a high speed perpendicular to the tow line, when in the high force configurations, to increase the power generated.  
      Another aerial power generation system includes an airfoil driven element and a means for adjusting the elevation and azimuth angles of the driven element connected through a swivel to a tow line that is connected to a means for generating power. A method of aerial power generation includes flying the driven element at high speed perpendicular to the tow line in a selected pattern, such as a circle. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      Details of this invention are described in connection with the accompanying drawings that bear similar reference numerals in which:  
       FIG. 1  is a perspective view of an aerial wind power generation system embodying features of the present invention.  
       FIG. 2  is a front elevation view of a driven element of the system of  FIG. 1 .  
       FIG. 3  is a side elevation view of a driven element of the system of  FIG. 1 , in a high force configuration.  
       FIG. 4  is a side elevation view of a driven element of the system of  FIG. 1 , in a low force configuration.  
       FIG. 5  is a side elevation view of a driven element of the system of  FIG. 1 , with an alternative control line arrangement.  
       FIG. 6  is a top plan view of a means for generating power of the system of  FIG. 1 .  
       FIG. 7  is a sectional view taken along line  7 - 7  of  FIG. 6 .  
       FIG. 8  is a perspective view of another aerial wind power generation system embodying features of the present invention, with two guide lines.  
       FIG. 9  is a perspective view of a support body of  FIG. 8 .  
       FIG. 10  is a perspective view of another support body for the system of  FIG. 8 .  
       FIG. 11  is a side elevation view of another support body for the system of  FIG. 8 .  
       FIG. 12  is a perspective view of a driven element for the system of  FIG. 8 .  
       FIG. 13  is a top schematic view of another aerial wind power generation system embodying features of the present invention.  
       FIG. 14  is a top plan view of a revolving apparatus of the system of  FIG. 13 .  
       FIG. 15  is a partial side elevation view of the revolving apparatus of the system of  FIG. 14 .  
       FIG. 16  is a perspective view of a driven element of the system of  FIG. 13 .  
       FIG. 17  is a top plan view of another revolving apparatus of the system of  FIG. 13 .  
       FIG. 18  is a top plan view of another revolving apparatus of the system of  FIG. 13 .  
       FIG. 19  is a perspective view of a driven element for the revolving apparatus of  FIG. 18 .  
       FIG. 20  is a perspective view of the driven element of  FIG. 19  with a modified line configuration.  
       FIG. 21  is a perspective view of another driven element for the revolving apparatus of  FIG. 18 .  
       FIG. 22  is a top view of a variation of the driven element of  FIG. 21 .  
       FIG. 23  is a top view of another variation of the driven element of  FIG. 21 .  
       FIG. 24  is a perspective view of the driven element of  FIG. 21  with a modified line configuration.  
       FIG. 25  is front view of another driven element for the revolving apparatus of  FIG. 18 .  
       FIG. 26  is a side view of the driven element of  FIG. 25 .  
       FIG. 27  is a top plan view of another revolving apparatus of the system of  FIG. 13 .  
       FIG. 28  is a side elevation view of another revolving apparatus of the system of  FIG. 13 .  
       FIG. 29  is a perspective view of another aerial wind power generation system embodying features of the present invention.  
       FIG. 30  is a perspective view of another aerial wind power generation system embodying features of the present invention.  
       FIG. 31  is a front elevation view of a support body for the system of  FIG. 30 .  
       FIG. 32  is a side elevation view of the support body of  FIG. 31 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
      Referring now to  FIG. 1 , an aerial wind power generation system  11  embodying features of the present invention includes a first guide line  14 , a first support body  15 , a driven element  16 , a first tow line  17 , a second tow line  18  and a means for generating power  19 . The first guide line  14  has a first end  21  that is tethered at the ground or to a structure, and the first guide line  14  extends skywardly at a selected elevation angle to a spaced second end  22  that is attached to the first support body  15 . The first support body  15  is an aircraft that is lifted by the wind, such as a kite as shown, or a lighter than air aircraft, such as a blimp or a balloon. Preferably the lift of the first support body  15  can be varied to maintain the elevation angle of the first guide line  14 .  
      The driven element  16  is slidably attached or mounted on the first guide line  14 . The driven element  16  is a kite, sail, airfoil or other element that generates both drag and lift from the wind. The first and second tow lines  17  and  18  each connect at one end to the driven element  16 . The first tow line  17 , and generally the second tow line  18 , connect to the means for generating power  19  to rotate the means for generating power  19  to generate power. The means for generating power  19  is generally positioned near the first end  21  of the first guide line  14 , and can be an electrical generator, a rotary pump, a compressor or other rotary power generation equipment.  
       FIGS. 2, 3  and  4  show a driven element  16  including an upper spar  25 , a spaced, substantially parallel lower spar  26 , and a generally rectangular, flexible fabric sail portion  27  extending between the upper and lower spars  25  and  26 . The sail portion  27  includes a plurality of spaced, flexible, longitudinal spars or battens  28  transverse to the upper and lower spars  25  and  26 . The battens  28  are shaped to curve the sail portion  27  into an airfoil shape with greater curvature near the upper spar  25  than near the lower spar  26  to provide increased lift force when needed. The battens  28  can be shaped to provide such curvature by tapering the upper ends  31  relative to the lower ends  32  to make the upper ends  31  more flexible, as in some sailboat or iceboat sails. Airfoils  29  can be provided if needed to enhance the stability and minimize drag when the driven element  16  is moving upwind. An airfoil  29  is shown attached to each end of the lower spar  26  and projects laterally therefrom to further control the shape of the driven element  16 . The rotation angle of the airfoils  29  about a horizontal axis can be remotely controlled. The pair of airfoils  29  could also be used along the bottom edge of the sail and would thus be similar to conventional aircraft ailerons.  
      A pulley block  34  having three pulleys  35  in a triangular arrangement is slidably mounted onto the first guide line  14 , with two pulleys  35  above and one pulley  35  below the first guide line  14 . A plurality of support lines  37  attach to the pulley block  34 , and diverge outwardly and downwardly therefrom to attach in a spaced arrangement along the upper spar  25  of the driven element  16 . The first tow line  17  attaches to the upper spar  25  and the second tow line  18  attaches to the lower spar  26 . Although a single driven element  16  is shown, a train or string of driven elements  16  can be used.  
       FIG. 3  shows the driven element  16  in a high force configuration. The wind acting on the driven element  16  is represented by an apparent wind vector  41 . The apparent wind vector  41  is equal to the true wind vector  42  minus the driven element velocity vector  43 . The first and second tow lines  17  and  18  are tensioned to bow the sail portion  27  into an airfoil shape and to position the sail portion  27  such that the leading edge  39  of the sail portion  27  points into the apparent wind vector  41 .  FIG. 4  shows the driven element  16  in a low force configuration. The second tow line  18  is lengthened relative to the first tow line  17 , allowing the sail portion  27  to flatten and point into the apparent wind vector  41 . The second tow line  18  acts as a control line.  
      In  FIG. 1  the second tow line  18  extends to the means for generating power  19 , and in combination with the means for generating power  19  forms a means for changing  45  the driven element  16  between high force and low force configurations.  FIG. 5  shows an alternative means for changing  45  the driven element  16  between high force and low force configurations, with the second tow line  18  extending from the lower spar  26  of the driven element  16  to a remote control winch  47  that is mounted on the first tow line  17  and spaced from the upper spar  25  of the driven element  16 . The winch  47  can include, by way of example and not as a limitation, a wind or solar powered electrical generator, batteries and a communications device for remote control. The winch  47  lengthens and shortens the second tow line  18 . The winch  47  can be used in applications where the weight of the winch  47  is less than the weight of a second tow line  18  extending from the driven element  16  to the means for generating power  19 .  
      Referring to  FIGS. 6 and 7 , the means for generating power  19  includes an electrical motor/generator  50  with a shaft  51  extending from one end, and spaced first and second reels  52  and  53  on the shaft  51 . Preferably the means for generating power  19  is mounted on a rotating platform  55  that rotates about a pivot  56  to maintain the orientation of the power generation system  11  relative to the direction of the wind. The motor/generator  50  is rigidly mounted on the platform  55  with the shaft  51  being supported by spaced support bearings  58  that are also mounted on the platform  55 . Three support bearings  58  are shown, with two support bearings  58  on the outer sides of the first and second reels  52  and  53 , and one support bearing  58  between the first and second reels  52  and  53 .  
      The first tow line  17  wraps around the first reel  52  and the second tow line  18  wraps around the second reel  53 . The first reel  52  is rigidly attached to the shaft  51  and the second reel  53  is rotatably mounted on the shaft  51 . The second reel  53  has cylindrical drum  60  mounted on the shaft  51  by bearings, and spaced first and second flanges  61  and  62  at opposite ends of the drum  60 . A toothed gear  64  is rigidly attached to the shaft  51  and spaced from the second flange  62 . Two control motors  66  are mounted on the outside of the second flange  62  on opposite sides of the shaft  51 . A worm gear  67  is connected to and driven by each control motor  66 , with the worm gears  67  being parallel and meshing to opposite sides of the toothed gear  64 . Two motors are used to provide good mass balance of the reel assembly and thus allow for higher rotation rates. Slipring assemblies  69  on the end of shaft  51  opposite the motor/generator  50  and inside the drum  60  provide power to the control motors  66 . Driving the control motors  66  rotates the second reel  53  relative to the first reel  52 , lengthening or shortening the second tow line  18  relative to the first tow line  17 , thereby providing a means for changing  45  the driven element  16  between high force and low force configurations. Therefore, the second reel  53 , toothed gear  64 , worm gears  67  and control motors  66  form a means for shortening and lengthening the second tow line  18  relative to the first tow line  17 . Alternatively, the means for generating power  19  could include two independent, vertically stacked motor/generators to provide a means for changing  45  the driven element  16  between high force and low force configurations.  
      The first guide line  14  provides stability to the driven element  16 , allowing the use of driven elements  16  with higher power and less stability than the driven elements  16  that could be used without the first guide line  14 . The first guide line  14  also guides the driven element  16  along a path having a selected elevation angle, so that the power of the driven element  16  can be further optimized.  
       FIG. 8  shows an aerial wind power generation system  11  embodying features of the present invention including a first guide line  14 , a second guide line  71 , a first support body  15 , a second support body  72 , a driven element  16 , a first tow line  17 , a second tow line  18  and a means for generating power  19 . The first guide line  14  has a first end  21  that is tethered at the ground or to a structure, and the first guide line  14  extends skywardly at a selected elevation angle to a spaced second end  22  that is attached to the first support body  15 . The second guide line  71  has a first end  74  that is tethered at the ground or to a structure, and the second guide line  71  extends skywardly, spaced from and generally parallel to the first guide line  14 , at a selected elevation angle to a spaced second end  75  that is attached to the second support body  72 . The first and second support bodies  15  and  72  are each an aircraft that is lifted by the wind, such as a kite as shown, or a lighter than air aircraft, such as a blimp or a balloon. Preferably the lift and angle of attack of the first and second support bodies  15  and  72  can be varied to maintain an optimum elevation angle of the first and second guide lines  14  and  71 .  
      Referring to  FIG. 9 , the first support body  15  includes a kite  77  and a bridle  78 . The kite  77  is generally a modified sled kite and has a substantially rectangular framework  80  with a top spar  81 , a spaced bottom spar  82 , and two spaced, parallel side spars  83  that extend from the top spar  81  to the bottom spar  82 . A sail portion  84  covers the framework  80  and has equal triangular wings  85  extending laterally beyond the side spars  83 . The outward corners  86  of the wings  85  are located significantly nearer to the top spar  81  than to the bottom spar  82 . A pair of spaced, triangular holes  87  are located in the sail portion  84  near the bottom spar  82  to add stability to the kite  77 .  
      A winch  88  is mounted in each lower corner of the framework  80 . Wires  91  extend from each winch  88  to a control module  90 , suspending the control module  90  below the bottom  82 , intermediate the winches  88 , and connecting the control module  90  to the two winches  88 . The suspended control module  90  acts as a tail for the kite  77 , increasing the stability of the kite  77 . The control module  90  can include, by way of example, and not as a limitation, a two way radio link to the ground, a rechargeable battery, a wind or solar battery charging device, measurement devices and aircraft warning lighting. The measurement devices can include wind speed, light, altitude, GPS, three dimensional acceleration, temperature, humidity, and orientation sensing and measurement.  
      The bridle  78  includes two each upper bridle lines  93 , lower bridle lines  94  and common bridle lines  95 . One end of each upper bridle line  93  connects to an outward corner  86  of a wing  85  of the sail portion  84 . One end of each lower bridle line  94  connects to a winch  88 . The other ends of the upper and lower bridle lines  93  and  94  on each side of the kite  77  connect together and to one end of a common bridle line  95 . The other ends of the common bridle lines  95  connect together and to the second end  22  of the first guide line  14 . The lower bridle lines  94  in combination with the winches  88  can vary the angle of attack of the kite  77  relative to the wind, thereby forming a means for varying lift  96  (or drag) of the kite  77 . Differential control of the lower bridle line lengths will allow for azimuth angle control with respect to the wind direction. Although first support body  15  is shown, second support body  72  will be substantially identical. Although a single kite  77  is shown, a train of kites  77  can be used to form the first or second support body  15  or  72 .  
       FIG. 10  shows the kite  77  with a modified bridle  97  for providing support to both the first and second guide lines  14  and  71 . One end of each upper bridle line  93  connects to an outward corner  86  of a wing  85  of the sail portion  84 . One end of each lower bridle line  94  connects to an end of the bottom spar  82  of the framework  80  of the kite  77 . A tube  98 , sized to extend between the first and second guide lines  14  and  71 , has the control module  90  incorporated into the middle and the winches  88  incorporated into opposite ends. The other ends of the upper bridle lines  93  connect to opposite ends of the tube  98 . The other ends of each of the lower bridle lines  94  connects to a winch  88 . The second end  22  of the first guide line  14  connects to one end of the tube  98  and the second end  75  of the second guide line  71  connects to the opposite end of the tube  98 . The winches  88  shorten or lengthen the lower bridle lines  94  to vary the angle of attack of the kite  77  relative to the wind.  
      As shown in  FIG. 11 , the first support body  15  can be a blimp  99  with a transverse support bar  100 . The second end  22  of the first guide line  14  connects to one end of the support bar  100  and the second end  75  of the second guide line  71  connects to the opposite end of the support bar  100 . The use of the blimp  99  eliminates the need to bring the aerial portions of the power generation system  111  to the ground during low wind conditions and may allow for larger scale systems with higher power generation.  
       FIG. 12  shows the driven element  16  with pulley blocks  34  at opposite ends of the upper spar  25  to slidably mount the driven element  16  on the spaced first and second guide lines  14  and  71 . A plurality of bridle lines  101  attach at one end in a spaced arrangement to the upper spar  25  and converge to attach to the first tow line  17 . A plurality of bridle lines  101  attach at one end in a spaced arrangement to the lower spar  26  and converge to attach to the second tow line  18 . The first and second tow lines  17  and  18  are shown extending beyond the driven element  16  and may attach to additional driven elements  16  that are above and downwind from the shown driven element  16 .  
      Referring to  FIG. 13 , an aerial wind power generation system  103  embodying features of the present invention includes a plurality of aerial wind powered driven elements  104 , a tow line  105  for each of the driven elements  104 , a means for changing  106  each of the driven elements  104  individually between high force and low force configurations, a revolving apparatus  107 , and a means for generating power  108 . The revolving apparatus  107  has a center  110  and, for each driven element  104 , a tow line attachment point  111 . The revolving apparatus  107  is represented by circle  112  and the tow line attachment points  111  are evenly spaced around the periphery of the revolving apparatus  107 . One end of each tow line  105  connects to a driven element  104  and the other end of each tow line  105  connects to a tow line attachment point  111 . The means for generating power  108  is linked to and driven by the revolving apparatus  107 . The means for generating power  108  can be directly connected or can be linked by gears, belts, driveshafts or other means, and might be located near the center  110  and driven by a rotating shaft below the revolving apparatus  107 .  
       FIGS. 14 and 15  show a revolving apparatus  107  with four cross bars  113  projecting horizontally from the center  110 , and spaced ninety degrees from each other. At the end of each cross bar  113 , opposite the center  110 , an upright member  114  projects upwardly and transversely. An upper rotating collar  115  rotates around the upper end of each upright member  114  and a lower rotating collar  116  rotates around the lower end of each upright member  114 . The upper rotating collar  115  provides the tow line attachment point  111 . The lower rotating collar  116  provides a control line attachment point  118  for one end of a control line  119 . The opposite end of the control line  119  connects to the driven element  104 .  
      As shown in  FIG. 16 , a driven element  104  includes an upper spar  133 , a lower spar  134  spaced from the upper spar  133 , and a rectangular sail portion  135  extending between the upper and lower spars  133  and  134 . A plurality of upper bridle lines  136  connect in a spaced arrangement to the upper spar  133  and converge to connect to the tow line  105 . A plurality of lower bridle lines  137  connect in a spaced arrangement to the lower spar  134  and converge to connect to the control line  119 . Three sled kites  138  are connected to the driven element  104  by support lines  139 , to increase stability and support, with a kite  138  connecting to each end of the upper spar  133  and one kite  138  connecting to the middle of the lower spar  134 . The angle of attack of the driven element  104  relative to the wind changes as the tow line  105  and control line  119  are pulled in or let out relative to each other, changing the driven element between high force and low force configurations. A similar change in the angle of attack of the kites  138 , as described above, might also be used in synchronization with the changes in the driven element  104 . The driven element  104  can also be an inline train of sled kites  138 . The sled kites  138  can be radio controlled or controlled by multiple lines to the ground.  
      Referring to  FIG. 14 , when a cross bar  113  is moving directly downwind, the respective upright member  114  projects downwind. At this position the end of the cross bar  113  has the longest distance, relative to other points of rotation of the revolving apparatus  107 , to the attachment of the tow line  105  to the upper bridle lines  136 . The lengths of the tow line  105  and control line  119  are tailored so that the driven element  104  is in the highest force configuration when the end of the cross bar  113  is moving directly down wind. The cross bar  113  moving directly upwind has the shortest distance, relative to other points of rotation of the revolving apparatus  107 , from the end of the cross bar  113  to the attachment of the tow line  105  to the upper bridle lines  136  and this is the position of the lowest force configuration. The upright member  114  and control line  119  provide the means for changing  106 . The driven elements  104  are pulled downwind by the wind in high force configurations and upwind by the revolving apparatus  107  in low force configurations, causing the revolving apparatus  107  to revolve and to drive the means for generating power  108 .  
      The means for changing  106  can be a remote control system as described above or other mechanical means for lengthening and shortening the tow line  105  and control line  119  relative to each other. The means for generating power  108  can be an electrical generator, a liquid pump, a compressor or other power transfer device. The power generation system  103  can be scaled from smaller to larger sizes. For smaller sizes of the power generation system  103 , the cross bars  113  of the revolving apparatus  107  can be self supporting. Larger versions of the power generation system  103  could have the revolving apparatus  107  as large as a revolving agricultural irrigation system. The cross bars  113  of a large revolving apparatus  107  can be supported by wheels  124  and linked by cables  125 . The wheels  124  can carry and drive a generator  126 .  
       FIG. 17  shows an aerial wind power generation system  103  with another revolving apparatus  128  having an endless, closed track  129  with a plurality of spaced, linked cars  130  on the track. The track  129  can be a railroad type track and the cars  130  can be similar to railroad cars. The track  129  does not have to have a circular shape and can be shaped to optimize power generation. Generally, the means for generating power  108  is carried on the cars  130  and connected to wheels  131  to generate power. The tow line  105  attaches forwardly on the car  130  and the control line  119  attaches rearwardly on the car  130 , to change the driven element between high force and low force configurations as the cars  130  travel around the track. The aerial wind power generation system  103  could alternatively have a revolving apparatus with a plurality of towers with bullwheels similar to ski chairlifts and aerial trams. A cable could pass around the bullwheels in a generally circular path with tow lines  105  and control lines  119  attaching to the cable.  
       FIG. 18  shows an aerial wind power generation system  103  with another revolving apparatus  141  having a center  142  with a pair of cross bars  143  projecting horizontally in opposite directions from the center  142 . A tow line attachment point  144  is provided at the end of each cross bar  143 , opposite the center  142 . A tow line  105  connects a driven element  145  to each tow line attachment point  144 . Referring to  FIG. 19 , the driven element  145  shown is a modified sled kite and has a substantially rectangular framework  147  with a top spar  148 , a spaced bottom spar  149 , and two spaced, parallel side spars  150  that extend from the top spar  148  to the bottom spar  149 . A sail portion  151  covers the framework  147  and has equal triangular wings  152  extending laterally beyond the side spars  150 . The outward corners  153  of the wings  152  are located significantly nearer to the top spar  148  than to the bottom spar  149 .  
      A bridle  155  for the driven element  145  includes two upper bridle lines  156  and two lower bridle lines  157 . The upper bridle lines  156  connect at one end to corners  153 , and the lower bridle lines  157  connect at one end to opposite ends of the bottom spar  149 . A generally spherical control module  158  incorporates four winches  159  with the opposite ends of the upper and lower bridle lines  156  and  157  each connecting to a separate winch  159 . The control module  158  connects to the upper end of a tow line  105 . The control module  158  is remotely controlled and can change the length of each of the upper and lower bridle lines  156  and  157  independently. The control module  158  and the upper and lower bridle lines  156  and  157  provide a means for changing  106  the driven element  145  between high force and low force configurations, and a means for adjusting  160  the azimuth angle of the driven element  145 .  
      Alternatively, the two lower bridle lines  157  can connect to the tow line  105 , and two upper control lines can be provided. The upper control lines each connect from a corner  153  of a wind  152  of the sail portion  151  to the end of the cross bar  143  that is opposite the center  142 . The two upper lines are independently controlled so that the elevation and azimuth angles can be independently adjusted. The arrangement, with the lower bridle lines  157  connected to the tow line  105  and the two independently controlled upper control lines, provides another structure for the means for changing  106  the driven element  145  between high force and low force configurations, and another structure for the means for adjusting  160  azimuth angle of the driven element  145 .  
       FIG. 20  shows an alternative configuration for driven element  145  with the two lower bridle lines  157  connecting to the tow line  105 . Two spaced upper control lines  164  replace the two upper bridle lines  156 , each connecting from a corner  153  of a wing  152  of the sail portion  151  to the end of the cross bar  143  that is opposite the center  142 . The two upper control lines  164  are independently controlled so that the elevation and azimuth angles can be independently adjusted. This arrangement, with the lower bridle lines  157  connected to the tow line  105  and the two independently controlled upper control lines  164 , provides another structure for the means for changing  106  the driven element  145  between high force and low force configurations, and another structure for the means for adjusting  160  the azimuth angle of the driven element  145 .  
      Referring again to  FIG. 18 , the direction of the wind is shown by wind vector  162 . By varying the azimuth angle of the driven elements  145 , the driven elements  145  can fly at an angle relative to the wind vector  162 . Each driven element  145  is changed to a high force configuration for a selected portion of the rotation of the respective tow line attachment point  144 , where the selected portion is an arc of more than 180 degrees. The azimuth angle of the driven elements  145  is adjusted through this selected portion so that the driven elements  145 , through the tow lines  105 , each generate torque on the cross bars  143  throughout the selected portion. By generating torque for more than 180 degrees, the driven elements  145  generate more power than would be generated without a means for adjusting  160  the azimuth angle of the driven element  145 .  
       FIG. 21  shows another driven element  165  having a leading edge  166  and a trailing edge  167 . The driven element  165  includes an upper spar  168  at the leading edge  166 , a lower spar  169  at the trailing edge  167 , spaced from the upper spar  168 , and a rectangular sail portion  170  extending between the upper and lower spars  168  and  169 . The sail portion  170  includes a plurality of spaced, flexible, longitudinal spars or battens  171  transverse to the upper and lower spars  168  and  169 . The battens  171  are shaped to curve the sail portion  170  into an airfoil shape with greater curvature near the upper spar  168  than near the lower spar  169  to provide increased lift force when needed. A plurality of first upper bridle lines  172  connect in a spaced arrangement to one half of the upper spar  168  and a plurality of second upper bridle lines  173  connect in a spaced arrangement to the other half of the upper spar  168 . A plurality of lower bridle lines  174  connect in a spaced arrangement to the lower spar  169 .  
      The first upper bridle lines  172  converge to connect to a first upper control line  175  and the second upper bridle lines  173  converge to connect to a second upper control line  176 . The lower bridle lines  174  converge to connect to the tow line  105 . The first and second upper control lines  175  and  176 , and the tow line  105  connect to the end of the cross bar  143  that is opposite the center  142 . The first and second upper control lines  175  and  176  are independently controlled so that the elevation and azimuth angles can be independently adjusted. This arrangement, with the lower bridle lines  174  connected to the tow line  105  and the independently controlled first and second upper control lines  175  and  176 , provides another structure for the means for changing  106  the driven element  165  between high force and low force configurations, and another structure for the means for adjusting  160  the azimuth angle of the driven element  165 .  
       FIG. 22  shows a variation of the driven element  165  where the first and second upper bridle lines  172  and  173  are replaced by an extension  180  of the sail portion  170 , that forms the leading edge  166 . The extension  180  extends from the upper spar  168  and has a trapezoidal shape with two spaced side edges  182  that slope inwardly from opposite ends of the upper spar  168  to a top edge  183  that is spaced from and parallel with the upper spar  168 . The battens  171  extend into the extension  180  to the top edge  183 . The first and second upper control lines  175  and  176  attach near opposite ends of the top edge  183 .  
       FIG. 23  shows another variation of the driven element  165  where the first and second upper bridle lines  172  and  173  are replaced by a pair of triangular extensions  185  of the sail portion  170  that extend from the upper spar  168  and form the leading edge  166 . The extensions  185  each have a pair of side edges  186  that slope inwardly from the upper spar  168  to converge at a corner  187 . A batten  171  extends into each extension  185  to or near to the corner  187 . The first and second upper control lines  175  and  176  each attach to a corner  187 .  
       FIG. 24  shows another variation of the driven element  165  where the lower bridle lines  174  converge to connect to a lower control line  189 . The first and second upper control lines  175  and  176 , and the lower control line  189  all connect to a control module  190 . The control module  190  connects to the tow line  105  through a swivel  191 . The control module  190  includes winches or other means, connected to the first and second upper control lines  175  and  176 , for controlling the first and second upper control lines  175  and  176  independently of each other. The swivel  191  allows the driven element  165  to rotate without twisting the tow line  105 .  
      The control module  190  includes instrumentation such as listed above and a power supply such as a battery for powering the winches and the instrumentation. The control module  190  includes a wireless link for remote control and can also include sensors that measure the tension on the first and second upper control lines  175  and  176  and the lower control line  189 . Ground instrumentation, including cameras can also be used to sense the precise position and orientation of the driven element  165 . The swivel  191  can incorporate or include a small electrical generator  192 , that is turned by rotation of the driven element  165  relative to the tow line  105 , to provide power to the power supply. A stabilizer  193 , in the form of a weight, as shown, or a fin, is suspended from the tow line  105  below the swivel  191 , as a means for preventing the tow line from twisting when the driven element  165  rotates. Alternatively, two independently controlled lines can connect to the trailing edge  167  with at least one other line connecting to the leading edge  166 .  
       FIGS. 25 and 26  show another driven element  195  that generally resembles a rigid wing aircraft. The driven element  195  has a small diameter, elongated fuselage  196  and a pair of laterally extending, rigid, airfoil shaped wings  197  on opposite sides of an intermediate portion of the fuselage  196 . A spaced pair of control surfaces  198  extend upwardly and laterally outwardly from the tail  204  of fuselage  196 . Alternatively, a conventional elevator and rudder configuration can be used at the tail  204  of the driven element  195 . A plurality of laterally spaced bridle lines  199  attach to the underside of the wings  197  and fuselage  196 .  
      A control line  200  extends from the nose  201  of the fuselage  196 . A winch inside the fuselage  196  reels the control line  200  in and out. The interior of the fuselage also contains instrumentation such as set forth above. The bridle lines  199  and the control line  200  converge to connect to a swivel  202  that connects to the tow line  105 . An attachment point  203  on the fuselage  196  above the wings  197  facilitates stacking of the driven elements  195 . The control surfaces  198  and control line  200  provide means for adjusting the azimuth and elevation angles of the driven element  195 . The control line  200  is a means for changing the driven element  195  between high force and low force configurations, and is reeled in until the fuselage  196  is substantially parallel to the tow line  105 , to change the driven element  195  to a low force configuration.  
       FIG. 27  shows an aerial wind power generation system  103  with another revolving apparatus  205  having a center  206  with three equally spaced bars  207  projecting horizontally from the center  206 . The revolving apparatus  205  is mounted to rotate about the center  206 . A turntable  209  is rotatably mounted about a vertical axis at the end  210  of each bar  207 . A pair of winches  211  mount on each turntable  209 . The first and second upper control lines  175  and  176  each connect to a winch  211 . The tow line  105  attaches at the tow line attachment point  212  on the turntable  209  downwind of the winches  211 . A means for generating power  213  is linked to and driven by the revolving apparatus  205 .  
      Winches  211  independently control the lengths of the first and second upper control lines  175  and  176 , and thereby form a means for independently adjusting the elevation and azimuth angles of the driven element  165 . Through adjustment of the elevation and azimuth angles, the direction of the lift of the driven element  165  is adjusted. If the lift perpendicular to the tow line  105  is greater than the drag perpendicular to the tow line  105 , the driven element  165  will accelerate perpendicular to the tow line  105 . The driven element  165  can be flown at a selected speed perpendicular to the tow line  105 , and can be flown in a selected pattern, by constant adjustment of the lengths of the control lines.  
      The lift of the driven element  165  is proportional to the square of the velocity of the apparent wind flowing perpendicular to the upper spar  168 . The velocity of the apparent wind flowing perpendicular to the upper spar  168  will generally increase as the velocity of the driven element  106  perpendicular to the tow line  105  increases. By adjusting the elevation and azimuth angles of the driven element  165  the driven element  165  can be flown in a circle at high speed. The forces are balanced with inwardly directed force providing centripetal acceleration, forwardly directed force balancing with the drag, and the force parallel to the tow line  105  providing the force that pulls on the revolving apparatus  205 .  
      To prevent tangling, when the first and second upper control lines  175  and  176 , and the tow line  105 , all attach to the turntable  209 , the driven element  165  is flown in a pattern of two connected circles, as shown, flying clockwise through one circle and counter-clockwise through the other circle. By flying the driven element  165  through the pattern at high speed, the total lift and the lift parallel to the tow line  105  are increased, increasing the power generated by the aerial wind power generation system  103 .  
      Referring to  FIG. 28 , another variation of the aerial wind power generation system  103  has an elongated, substantially vertical tower  217 , a nacelle  218  rotatably mounted about a vertical axis on top of the tower  217 , a revolving apparatus  219 , and a means for generating power  220 . The revolving apparatus  219  has a shaft  221  that is rotatably mounted on and extends horizontally though the nacelle  218 . A beam  222  is rigidly mounted on the shaft  221  on each side of the nacelle  218 , each beam  222  extending in both directions perpendicular to the shaft  221  to ends  223 . The two beams  222  are mounted on the shaft  221  at right angles to each other. A tow line attachment point  224  is provided at each end  223  of each beam  222 . Tow lines  105  connect from the tow line attachment points  224  to the driven elements  145 . The means for generating power  220  is mounted in the nacelle  218  and driven by rotation of the shaft  221 . The azimuth angles of the driven elements  145  are adjusted such that the driven elements  145  fly slightly off to the sides, to prevent tangling of the tow lines  105 .  
       FIG. 29  shows another power generation system  227  having a tow line  228  connected to a means for generating power  229  at one end and to a driven element  230  by a swivel  231  at the opposite end. The driven element  230  includes means for changing the driven element  230  between high force and low force configurations, and means for adjusting the azimuth and elevation angle of the driven element  230 . The driven element  230  can be similar to the driven element  165  as shown in  FIG. 24 , driven element  195  as shown in  FIGS. 25-26 , or other driven element with means for adjusting the elevation and azimuth angles.  
      The means for generating power  229  includes a generator  233  connected to a capstan  234 . A winch  235  is provided behind the capstan  234  for reeling the tow line  228 . The tow line  228  is wrapped around the capstan  234  and turns the capstan  234  to turn the generator  233 . The arrangement with a separate capstan  234  and winch  235  prevents excess tension on the wraps of tow line  228  on the winch. The driven element  230  is flown at a high velocity perpendicular to the tow line  228  in a generally circular pattern while the tow line  228  pulls out from the means for generating power  229 , forming a corkscrew flight path. When the tow line  228  extends to a predetermined distance, the driven element  230  is changed to a low force configuration and reeled back towards the means for generating power  229 . By flying the driven element  230  through the pattern at high speed, the total lift and the lift parallel to the tow line  228  are increased, increasing the power generated by the aerial wind power generation system  227 .  
      Referring to  FIG. 30 , another power generation system  238  includes a support body  239 , a guide line  240 , a driven element  241 , a tow line  242 , and a means for generating power  243 . The guide line  240  is tethered at one end at the ground or to a structure, and extends skywardly at a selected elevation angle with the other end being attached to the support body  239 . The tow line  242  is connected to and drives the means for generating power  243 .  
      The driven element  241  has a sleeve  245 , a hub  246 , a plurality of airfoil blades  247 , and a pitch control mechanism  248 . The sleeve  245  is slidably mounted on the guide line  240  and connected to one end of the tow line  242 . The hub  246  is rotatably mounted on the sleeve  245 . The blades  247  preferably have a twisted shape as in propeller or wind turbine rotor blades. The blades  247  are circumferentially spaced on the hub  246  and extend radially therefrom in a plane perpendicular to the guide line  240 . The pitch control mechanism  248  links to the blades  247 , providing a means for adjusting the pitch of the blades  247  and a means for changing the driven element  241  between high force and low force configurations.  
      The pitch control mechanism  248  can be controlled by a remote control module  249  mounted on the sleeve  245 , as shown, and/or by other sensors such as an altimeter or GPS. The blades  247  are adjusted to spin in response to the wind to change the driven element  241  to a high or low force configuration. As the speed of the blades  247  increases, the direction of the lift from the blades  247  rotates towards the direction of the tow line  242 , increasing the force in the direction of the tow line  242 . The blades  247  are adjusted such that the lift and drag are minimized while the driven element  241  is in the low force configuration.  
      Referring to  FIGS. 31 and 32 , the support body  239  is shaped generally like a double sled kite, having a longitudinal middle spar  251  between two spaced, longitudinal side spars  252 , and a sail portion  253  connecting the middle and side spars  251  and  252 . A triangular wing  254  extends downwardly from each of the middle spar  251  and side spars  252  to a corner  255 . The corners  255  are closer to the front than the back of the support body  239 . A bridle line  256  connects to each corner  255 . The three bridle lines  256  converge and connect to the guide line  240 .  
      A control module  257  mounts on the middle spar  251 , forward of the centerline of the support body  239 . The control module  257  includes two winches  258 . Each winch  258  has a control line  259  that connects to a side spar  252 . The control lines  259  can pull the side spars  252  inwardly to change the shape of the support body  239 . Pulling inwards with one control line  259  causes the support body  239  to fly to one side. Pulling inwards or reeling out both control lines  259  changes the lift and drag of the support body  239 . The instrumentation in the control module  257  can provide automatic correction and/or the instrumentation can be remotely controlled. The instrumentation in the control module  257  can provide self-stabilization of the support body  239  in response to wind fluctuation.  
      Other configurations can be used for the support body  239  and the first and second support bodies  15  and  72 , described above. By way of example and not as a limitation, the designs of the driven elements that include azimuth and elevation angle adjustment can be used as support bodies, including the driven element  145 , shown in  FIGS. 19 and 20 , the driven element  165 , shown in  FIGS. 21-24  and the driven element  195 , shown in  FIGS. 25 and 26 . Similarly, a support body such as the support body  239 , as shown in  FIGS. 31 and 32 , that can be changed between high force and low force configurations, is also suitable for use as a driven element. Although the driven elements and support bodies are each generally shown and described herein as a single element, the driven elements and support bodies can each be implemented in trains of two or more units.  
      Although the present invention has been described with a certain degree of particularity, it is understood that the present disclosure has been made by way of example and that changes in details of structure may be made without departing from the spirit thereof.