Abstract:
A linear wind powered electric generator (LWPEG), which is particularly adapted for installation at geographical sites subject to lower wind intensities. More specifically, there are provided design concepts for an LWPEG, possessing reasonable economic parameters for utilization at the lower-intensity wind sites. Moreover, the linear wind powered electric generator is based on a track based wind power generator, incorporating aerodynamic designs, which are adapted to reduce mechanical complexities presently encountered in this technology, while being cost-effective both in construction and in connection with the operation thereof.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a novel linear wind powered electric generator (LWPEG), which is particularly adapted for installation at geographical sites subject to lower wind intensities. More specifically, the invention is directed to the provision of a track based design concept for an LWPEG, possessing reasonable economic parameters for utilization at the lower-intensity wind sites. Moreover, the linear wind powered electric generator is based on a track based wind power generator, incorporating aerodynamic designs, which are adapted to reduce mechanical complexities presently encountered in this technology, while being cost-effective both in construction and in connection with the operation thereof. 
     The concept of windmills has been proposed over a considerable period of time for harnessing the power of the wind, in the form of wind turbines generating electrical energy. Wind power provides a plentiful, renewable, geographically widely distributed, clean source of energy, while concurrently ameliorating the danger of generating deleterious by-products and greenhouse gas emissions, by replacing fossil fuel-derived electricity. 
     Wind energy, which is similar to solar energy in representing a clean form of renewable energy, can be exploited for generating viable electrical power and is becoming more and more economically and environmentally relevant. In this technology, there are currently known many diverse essentially conventional axis-based windmill or turbine designs operating with horizontal (wind) axes, and others functioning with vertical (cross) axes. 
     Measured on a worldwide scale, the geographically available wind energy resources are immense, and are potentially capable of satisfying all current energy needs of mankind several times over. However, unfortunately, wind energy is not available universally in equal wind intensities. Based upon so-called energy density, wind intensities are classified into seven general classes, with the 7 th  class being identified as being the strongest and the 1 st  class as being the weakest. Thus, wind density in a country, for example, such as India, is very poor compared with that available, for instance, in North America and Northern Europe, wherein all current wind turbine designs are rated for a Class 6 wind density, which was defined as a reference wind regime by the United States of America in the mid-1980s. In this connection, the annual energy available for the Class 6 wind density is about 5200 kWh/year/m 2 , and reduces for a Class 2 wind density to about 1200 kWh/year/m 2  at a height of 50 m above ground level. 
     Generally, large expanses in area have been identified as Class 2 wind sites, i.e., possessing a wind power density of 1200 kWh/year/m 2  at 50 m above ground levels. Thus, for example, official data for India alone indicates that nearly 89% of installable wind power capacity here is at the low Class 2 wind density. Horizontal axis wind turbine (HAWT) technology, as presently employed, is deemed inappropriate for Class 2 wind density sites. Consequently, in order for low wind energy having to significantly contribute within the next or future decades, installations imbued with good operating economics under Class 2 wind density conditions are required. Such installations must afford a substantially higher annual energy extraction under prevailing annual wind velocity distributions when compared to HAWTs, such as the linear wind powered electric generator (LWPEG) contemplated by the present invention. 
     Pursuant to the current state of the art, over 95% of current wind turbine designs are three-bladed or two-propeller-type horizontal axis wind turbines (HAWT) whereas vertical axis wind turbines (VAWT) are normally considered for stand-alone units possessing low power ratings, whereby also a few multi-bladed HAWT and split-drum type VAWTs are employed for water pumping purposes. Over 25 years ago, as mentioned, the United States Department of Energy and NASA defined Class 6 wind density as the reference wind regime for the United States, which is geographically close to the average wind resource of the United States. Currently, all major wind turbine manufacturers base their designs on Class 6 wind densities, which are slated to operate under Class 6 to Class 7 wind ranges. Special efforts have been made somewhat more recently to develop the so-called ‘Low Speed Wind Technology’, as referred to in Class 4 wind density whereby, in fact, winds of Class 3 and above are considered as an energy resource. Consequently, at this time, there are no competitive technological solutions available for Class 2 wind resources, with major wind turbine manufacturers, who developed their designs for Class 6 wind resources, making an attempt to market the designs for low-wind sites by either increasing the wind turbine hub height and rotor diameter at a higher cost, or by de-rating the design, again at a higher cost for energy. 
     Most of the presently installed wind turbine power, for example, in countries like India, is in HAWT designs and occupies Class 3 to Class 5 wind sites. However, it is noted that only about 10% of the wind energy potential is available in these wind intensity classes, with the remainder being in Class 2.The total wind energy potential in Class 3 to 5 winds adds up to about 5000 MW. Thus, if wind energy is to contribute substantially to power generation within the next decades, then it becomes necessary to be able to develop power generating designs with reasonable economic parameters for Class 2 wind sites. 
     2. The Prior Art 
     Although numerous windmills in the form of power-generating wind turbines are currently known, and are widely installed and operated at numerous sites in different countries and locales, these are primarily prevalent of the designs which are required for high-density wind applications, i.e., significantly higher than for Class 2 wind sites. 
     Thus, among publications of interest there may be considered the disclosures of U.S. Pat. No. 4,218,183, U.S. Pat. No. 7,360,995; U.S. Patent Publication No. 2004/164562; U.S. Pat. No. 4,302,684; U.S. Patent Publication No. 2004/080166; U.S. Pat. No. 6,672,522 B2; U.S. Pat. No. 5,758,911; U.S. Pat. No. 4,114,046 and U.S. Pat. No. 5,730,643. 
     There are represented two primary types of wind turbines, i.e., the widely employed horizontal axis wind turbine (HAWT) designs, and the somewhat less used vertical axis wind turbine (VAWT) design, whereby the horizontal axis wind turbine (HAWT) technology is clearly deemed to be inappropriate for Class 2 wind sites. Thus, installations with good operating economics under low-velocity winds, and which provide substantially higher annual energy extraction levels under local prevailing annual wind velocity distributions, when compared with presently available HAWTs and other designs must be developed. 
     In the above referenced prior art publications, there are disclosures which are concerned with vertical and horizontal axis wind power generating systems, as well as track-based, pulley-guided wind power generating systems with different complex combination of mechanical components, such as sails or the like, or which utilize earlier technologies that do not translate well into modern economies of scale. Further, the existing design concepts of wind power generating systems are only adapted for operation with higher-density classes of winds, and as such, are not readily capable of being utilized successfully, especially on commercial scales, for the low density Class 2 wind sites. 
     SUMMARY OF THE INVENTION 
     Accordingly, the present invention provides for an alternative and novel concept termed as “Linear Wind Powered Electric Generator”, hereinafter designated as ‘LWPEG’, and which is based on a linear windmill, or turbine and linear electric generator design of unique configuration. Summarizing the foregoing, it can be ascertained that there is a need to explore new concepts, designs and technologies, which will operate efficiently at the low Class 2 wind speeds, (50 m AGL, wind speed: 5.6-6.4 m/s; wind power density: 200-300 W/m 2 ; Installable Power in India: 43106 MW, which is 8 times higher than all higher speed Classes 3, 4 and 5 combined). Heretofore, the major windmill technology developers have exclusively concentrated on designs for about Classes 5, 6 and 7 wind densities for economic reasons, whereby such wind conditions are not available in all countries, for example, such as India, among others. Thus, it is important to be able to provide installations satisfying this need. Hereby, previous concepts ordinarily use one axis, horizontal or vertical, around which ‘lift’ type blade elements rotate at the same angular speed, whereby the linear blade element speed varies essentially from zero at the center axis of rotation to a maximum value at the outermost radial blade location, the so-called blade tip speed in the conventional HAWT. The blade design is normally optimized to facilitate obtaining the best aerodynamic and structural performance, but the fact remains that blade elements very close to the center axis of rotation are aerodynamically ineffective, whereas those close to or at the blade tip produce considerable levels of noise due to high speeds and vortex shedding. The larger the unit power for a given wind class, the larger is the diameter, the taller is the tower, and more complex are the therewith associated structural problems. The designs with one axis of rotation are, however, very compact in configuration, especially the HAWT with just two or three blades. 
     Basically, all the aerodynamic disadvantage of lengthy blades rotating around a single center axis can be mitigated if a blade of constant or variable cross section is moved across the wind in a straight line, and by using the component of the lift force to move the blade and to thereby extract energy. However, for a continuous operation, the blade element must return back to its starting point, consequently, there is a need in the technology to develop a highly efficient, simple, cost-effectively competitive linear wind power-generating installation that is more specifically adapted for ultra-low Class 2 wind density sites, wherein the invention provides a significant advance in the field of wind power energy, designed to be predicated on a simple linear track-based arrangement. 
     A primary objective of the invention resides in developing a new and unique track-based aerodynamic wind turbine design for wind power generation, which is intended to compensate for the mechanical complexities of existing wind power electric generators. 
     Another objective of the present invention is to develop a highly efficient, cost effective track based linear wind power generator installation, which is particularly efficient for Class 2 low wind density sites. 
     According to the present invention a novel linear windmill or turbine configuration consists of a suitable number of blades or wings, of selectively suitable chord, airfoil section, span, planform shape, internal load bearing structure, and tip wing plates. The blades are adapted to move along an essentially continuous orbit of various shapes like oval or trapezoidal, but are not limited thereto. The blades or wings may be mounted on pylons, which arrange the former on a closed-loop track or on a conveyor, whereas wing-setting structures retain the blades or wings in predetermined orientations. In various embodiments, corner guide pulleys may hold the conveyor in pre-tension and mounted on a conveyor frame. Torque converter units (at least one), which are integral with the corner guide pulleys, may be adapted to mount devices, such as electric generators, air compressors or water pumps. A windmill base frame is connected with the structural frames, and may comprise a turntable that is free to be rotated around a vertical axis on a base foundation by using the torque provided by both a rudder weathercock vane and arm, or by means of external power. 
     Pursuant to an aspect of the present invention, the blades may be guided within rail guide tracks with conventional wheel-bearings or very recently available ‘Straight-Curved Guide’ system, while a wing-setting gear maintains the wings in predetermined orientations. Distributed linear permanent magnet and electric generating elements are mounted on the blades and/or are located within the rail guide tracks, whereby at least two essentially parallel-extending rail guide tracks form an integral guide-track-frame. A windmill base frame, such as a turntable, which is free to rotate the rail guide tracks and blades around a vertical axis on the base foundation, such as by using the torque provided by both a rudder weathercock vane and arm, or through external power. According to an embodiment of the present invention, the wing setting gear comprises endless guide tracks within which guide rollers mounting the blades or wings move smoothly. 
     According to a preferred embodiment of the present invention, the wing-setting-gear may comprise a self-contained active or passive blade or wing pitch-setting controller and actuator for an outboard wing span turning or outboard wing leading edge extender/retractor system. 
     The blades or wings, when mounted on pylons with end wheel bearings may be connected to each other only mechanically or electrically, or mechanically and electrically, so as to maintain their relative fixed positions, while the conveyor frame or the guide track frame are located in either vertical or horizontal orientations, but preferably in a vertical orientation. 
     Finally, pursuant to various embodiments of the present invention, electrical power or energy may be extracted at least at one support pulley by a rotary generator, or through a distributed permanent magnet linear generator, of either moving iron or moving magnet type, extending along the rail guide tracks. 
     According to the present invention, the blades or wings, while operating as lift elements, move in a substantially straight path across the freely-streaming wind, resulting in a significantly improved aerodynamic performance, and hence, in an enhanced degree of energy extraction from the wind in comparison with the prior art. The blades or wings must move several times (typically 3 to 6 times) faster than the speed of the wind to achieve the best aerodynamic performance, inasmuch as the rotating parts of the installations are subjected to inertial loads while turning around corners along the paths of travel. According to the present invention, such an operation is feasible in a practical mode at the very low or ultra-low wind speeds of Class 2. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates, generally diagrammatically, a perspective view of a first embodiment of the linear wind-powered electric generator of the invention; 
         FIG. 2  illustrates a detailed representation of the wing mount and integral linear electric generator arrangement of  FIG. 1 ; 
         FIG. 3  illustrates an enlarged perspective sectional detail of a portion of the guide rail structure and elements of linear electric generator of  FIG. 1 ; 
         FIG. 4  illustrates, diagrammatically, another embodiment of the invention; 
         FIG. 5  illustrates, diagrammatically, another embodiment with a modified guide rail frame arrangement but oriented in a horizontal plane rather than vertical, according to the present invention; 
         FIG. 6  illustrates, diagrammatically, on an enlarged scale, a sectional view of the guide rail frame of  FIG. 5 ; 
         FIG. 7  illustrates, diagrammatically, another embodiment of the invention; 
         FIG. 8  illustrates a schematic view of a track path for the blades pursuant to the invention; 
         FIG. 9  illustrates another track path for the blades; 
         FIG. 10  illustrates another track path for the blades; 
         FIG. 11  illustrates another track path for the blades; 
         FIG. 12  illustrates another track path for the blades with support system; 
         FIG. 13  illustrates another track path for the blades with a modified support system; 
         FIGS. 14 and 15  illustrate, respectively, plan and side views of a modified embodiment of path for blades in horizontal plane; 
         FIGS. 16 and 17  illustrate, respectively, side and front views of blade track path with  FIG. 18  being a variant of the embodiment of  FIG. 17 ; 
         FIGS. 19 and 20  illustrate, respectively, side and front views of a modified embodiment of the invention; and 
         FIGS. 21(   a ) through  21 ( c ) illustrate, respectively, side, front and bottom plan views of another embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Basically, in general terms, the novel linear wind powered electric generator (LWPEG) according to the present invention is aerodynamically optimally designed for very low and ultra-low wind velocities, such as Class 2 wind intensity sites. The linear wind powered electric generators (LWPEG) as illustrated in the various embodiments of the present invention each comprise a suitable number of blades or wings of predetermined chord, airfoil section, span, planform shape, internal load bearing structure and tip wing-plate dimensions, and are made to travel along preferably non-circular orbits of various configurations, such as oval or trapezoidal, but are not limited to thereto. In that connection, the blades or wings functioning as lift elements move in a substantially straight path across a free streaming wind, resulting in a wind turbine effect with a significantly improved aerodynamic performance, and hence, an increased energy extraction from the wind. As the wings or blades must move several times (typically 3 to 6 times) faster than the wind speed in order to achieve best aerodynamic performance, the rotating or traveling elements are subjected to inertial loads while turning around the corners or orbital directions, whereby such an operation is in practice feasible at very low or ultra-low wind speeds at Class 2 wind densities or intensities. 
     Referring to  FIG. 1  of the drawings, represented is a diagrammatic illustration of a preferred embodiment of the ‘LWPEG’  10 , comprising a ground-supported frame  14  with freedom of yaw structure  12 , which is mounted on a base support frame  16 , and which hold a pair of spaced, parallel extending curved guide rail tracks  36  attached to each other by cross supports  22 . A plurality of wing-like blades  24  each include a central wing section  26  and have (radially) outer wing end plates  28 , which are mounted with the support of wing pylons  30  on straight sections  32  of the guide rail tracks  20 , while including a linear power generator assembly (as illustrated in drawing  FIGS. 2 and 3 ). Hereby, the wing-like blades  24  are caused to slide linearly along the guide rail track sections  32  to the maximum extent in order to utilize the maximum kinetic energy, resulting in a substantially high electromagnetic energy extraction, as elucidated hereinbelow. 
     As shown, the pair of guide rail tracks  20  include both the straight guide rail track sections  32  and curved guide rail track sections  36 , forming closed loops. The guide track support frame  12  may be provided in either a preferably vertical, or in horizontal orientation, as may be required for specific operations or geographic applications. 
       FIG. 2  is a detailed view of a part of the ‘LWPEG’  10 , as illustrated in  FIG. 1 , such as a segment of the tracks  20 . The linear generator assembly, as shown in  FIG. 3 , for electromagnetic power generation consists of a stator core  38 , stator coils  40 , rotor element  42 , and wheel bearings  44 . The wing-like blades  24  have wing side plates  46 , and are mounted on the guide tracks  20 , with the support of the pylons  30 , which are covered with a wing pylon cover  48 . 
       FIG. 3  is an enlarged and more detailed sectional view of the ‘LWPEG’, as shown in  FIG. 2 , comprising a segment of the guide rail track  20 , including a wheel assembly  50  for the blades  20 . The wheel assembly  50  includes two wheels  52 ,  54  fitted to roll within the guide rails  20 , and having end wheel bearings  56 , which are connected to each other through an axle  58 . Two such axles are connected to each other either mechanically, electrically, or jointly mechanically and electrically, so as to maintain their relative fixed positions. A permanent magnet  60  is interposed between groups of stator coils  40 . The linear generator rotor is connected to the wing pylons through the rotor core  42  and forms an air gap with the stator iron core  38 . In order to effectuate power generation, relative motion is implemented between the stator and rotor elements responsive to the linear movement of blades  24  along guide rail track sections  32 . 
     Referring to  FIG. 4 , there is provided a diagrammatic illustration of another LWPEG Embodiment  70 . Provided in this case, are a pair of parallel relatively widely spaced tracks  72 . A ground support structure  74  has a turntable  76  arranged thereon. A horizontal base frame  78  mounts a support frame  80  with vertical frames  82 . Yaw control vanes  84  are supported from the vertical frames  82 . The tracks  72  comprise conveyors  88 , which include blades  90  extending therebetween. Corner pulleys  92  have the conveyors  88  entrained thereover, and with the pulleys importing the electromagnetic energy generators producing energy as the wind-dependent linear motions of the conveyors responsive to the displacement thereof by the wind impacted blades which are connected between the conveyors. This assembly shows the inventive arrangement being mounted on the turntable  76  for rotation of the installation about a vertical axis depending upon wind direction for optimum deployment thereof. 
       FIG. 5  is a diagrammatic illustration of a ‘LWPEG’  91  having a wing central support section  93 , which is mounted on a rail guide track frame  95  that is oriented in the horizontal plane, and which is further supported by a ground frame  96  with freedom to yaw, and vertical support frames  99 , suitable blades  101  may be mounted on the wing central support section  93 , which is adapted to house the electromagnetic generator device, as previously described in  FIG. 3 . 
       FIG. 6  is a diagrammatic illustration of the ‘LWPEG’, as illustrated in  FIG. 5 , in a view of the guide rail track cross-section, comprising wheel bearings  102 , which is interconnected by a transverse support axle  104 , and is guided on the rails of the guide rail track frame  94 . The linear generator assembly consists of a generator stator iron  106 , a permanent magnet  110 , generator stator coils  110   108  and a generator rotor iron core  112 . 
     Referring to the embodiment of  FIG. 7 , there is represented an LWPEG arrangement  120  possessing two widely spaced apart, parallel extending track loops  122  and  123 , which define a generally oval travel path for blades  126  (of which only one is shown). The blades  126 , a plurality of which are spaced apart, have their opposite ends provided with suitable linear generators  128  so as to be able to slide along the tracks  122 ,  124  and produce electromagnetic energy for conversion into usable electric power. 
     The track loops  122 ,  124  are shown as being generally upright and have support framework  130 ,  132  for maintaining them supported on a platform  136 . The platform  136  may be a turntable which can be supported on a ground frame (not shown). 
     As disclosed in drawing  FIG. 8 through 21(   c ), there are represented various configurations for LWPEG installations. 
       FIG. 8  illustrates a schematic representation of an oval track  140  for blades, shown on a vertical plane.  FIG. 9  discloses an essentially inverted teardrop shaped track  142  with large upper radius  144  and smaller bottom radius  146 . This shape may enable a varying blade speed for maximum power extraction and almost constant blade loading, and possibly facilitate an automatic operating start. 
       FIG. 10  shows an oval track  146  in a vertical plane but forwardly inclined for possible automatic start and negotiating high wind speeds. This also applies to  FIG. 11  wherein the track  148  is inclined backward for essentially similar operating conditions. 
       FIG. 12  illustrates an oval track  150  oriented in the vertical plane having blades  152  moving within the oval track, and including an external support framework  154 . To the contrary, in  FIG. 13 , the blades  156  more externally of the oval track  158 , and the support framework  160  extends from the interior outwardly. 
       FIGS. 14 and 15  disclose an oval track  162  arranged in a horizontal plane, with blades  164  moving from inside or outside the track; and including a support framework  166  extending from either outside, inside or both sides of the track  162 , as may be warranted by particular sites. 
       FIGS. 16 and 17  represent side and front views of oval tracks  168  oriented in a vertical plane with two side support frames  170 ,  172  (somewhat similar to that of  FIG. 7 ); and with blades or vanes  174  connected for linear movement between the tracks  168 .  FIG. 18  is similar to  FIG. 17 , but includes further blades  176  extending on either side of track planes of the tracks  168  in a cantilevered configuration. 
       FIGS. 19 and 20  illustrate side and front views of an oval track system, wherein three spaced tracks,  180 ,  181 ,  182  are supported in a framework  184  providing for blades or vanes  188  moving within two blade spans, each supported at opposite ends and moving within the tracks in a parallel arrangement. 
       FIGS. 21(   a ) through  21 ( c ) disclose two oval track systems  190  combining those of  FIGS. 8 and 9  in a vertical plane, with changeover tracks in the top circular section; blades or vanes  192  with adjustable spans and supported on both ends and moving from outside the oval tracks. The blades are mechanically linked by means of preferably adjustable links. At a wind speed below a so-called ‘cut in’ condition, the blades are brought on the teardrop-shaped oval track  200  into self-starting motion, and after the wind speed becomes greater than a value, the blades or vanes are guided to the symmetrical oval track  202  for maximum energy extraction. The blades are made from adjustable spans, when two outriggers  204  are moved over the central support span  206 . 
     In another embodiment (not shown) the support wheels can be slidably fitted and the outrigger portion of the blades can be folded upward to ensure transition from inner to outer tracks and vice versa. 
     While it is apparent that the invention herein disclosed is well calculated to fulfill the objects stated above, it will be appreciated that numerous modifications and embodiments may be devised by those skilled in the art, and it is intended that the appended claims cover all such modifications and embodiments as fall within the true spirit and scope of the present invention.