Abstract:
Wind screens for reducing wind loading on one or more solar collectors are disclosed. The wind screens move with the solar collector as the collector tracks the sun in one or more dimensions. The wind screen pivotably connects to at least one solar panel of the collector. Another side of the wind screen may connect to the ground or to an adjacent collect, thus serving to divert wind over the collector. Wind screens may be made of various materials including rigid, flexible, or elastic materials and can change position, orientation, and/or effective length as the one or more collectors track the sun from East to West.

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
     This application claims the benefit of U.S. Provisional Patent Application Ser. No. 61/005,697 filed Dec. 7, 2007, entitled “LOW-PROFILE SINGLE-AXIS TRACKER WITH WIND MITIGATION,” which is hereby incorporated by reference herein for all purposes. 
    
    
     TECHNICAL FIELD 
     The invention generally pertains to solar collectors for generating power from the sun. In particular, the invention pertains to a technique for mitigating the effects of wind on a solar tracker or array of solar trackers. 
     BACKGROUND 
     Some solar collectors employ a tracking system that enables the collector to dynamically orient the collector and optimize the acquired energy. As the collector tracks the sun as it moves from East to West over the course of a day, the orientation of the collector may, at times, expose the collector to significant wind loading. As a result, the solar collector must be engineered with a more rigid structure and stronger supports which adds to the construction and/or installation cost of the collector. If the wind speed exceeds a threshold, the solar collector may even retreat to a stow mode in which suboptimal solar power or no power is acquired. There is therefore a need for a solar collector that is less sensitive to wind loading in order to reduce the cost of the solar collector and increase the time that the collector actively tracks the sun. 
     SUMMARY 
     The invention features one or more wind screens for shielding the solar collector from lateral winds. In some embodiments, the solar collector includes one or more solar panels that pivot about single axis in order to track the sun over the course of the day. The wind screen may comprise one or more screens that couple the outer edges of the panels to the ground so as to divert the wind over the collector. In some other embodiments, the solar collector includes an array of collectors in which solar units are arranged side-by-side. The wind screens then connect to adjacent solar collectors so as to provide a continuous surface across the array and inhibit wind from generating lift under any of the units. Of course, a combination of these ground-attached screens and cross-collector screens may be employed together in order to mitigate wind at the edges and interior of a solar collector array. 
     The wind screens in the present invention are configured to move with the one or more collector to which it is connected. In particular, the wind screens can change position, orientation, and/or dimensions as the one or more collectors track the sun from East to West. In some embodiments, for example, the wind screen is pivotably connected to a solar panel so that the screen may shift and elevate as the edge of the panel pitches upward. In other embodiments, the wind screen is a flexible fabric one or more rollers, thus allowing it to roll up or unwind as the gap between adjacent solar collectors changes. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention is illustrated by way of example and not limitation in the figures of the accompanying drawings, and in which: 
         FIG. 1  is a perspective view of the low-profile single-axis tracker, in accordance with the preferred embodiment of the present invention; 
         FIG. 2  is a side view of the low-profile single-axis tracker, in accordance with the preferred embodiment of the present invention; 
         FIGS. 3 and 4  are side views of the low-profile single-axis tracker in two tracking positions, in accordance with the preferred embodiment of the present invention; 
         FIG. 5  is a side view of the single-axis tracker with two-part screen, in accordance with a preferred embodiment of a present invention; 
         FIG. 6  is a side view of the single-axis tracker with sliding screen, in accordance with a preferred embodiment of the present invention; 
         FIGS. 7 and 8  are side views of the single-axis tracker with retractable screens, in accordance with a preferred embodiment of the present invention; 
         FIG. 9  is a side view of the single-axis tracker with tensioned screen, in accordance with a preferred embodiment of the present invention; 
         FIG. 10  is a side view of the single-axis tracker with a flexible, inelastic screen, in accordance with a preferred embodiment of the present invention; 
         FIG. 11  is a side view of another single-axis tracker with flexible, elastic screen, in accordance with a preferred embodiment of the present invention; 
         FIG. 12  is a side view of the single-axis tracker with elastic screen, in accordance with a preferred embodiment of the present invention; and 
         FIG. 13  is a side view of the single-axis tracker with deformable screen, in accordance with a preferred embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Illustrated in  FIGS. 1-4  is a low-profile solar collector that follows the sun with a single-axis mechanism. In addition to efficiently collecting light, the collector is configured to mitigate the effects of winds that exert dynamic loads on the collector and its mounting structure. To achieve this, the collector employs one or more wind screens that pivot to deflect wind over the top of the collector for the range of motion exhibited during tracking operations. 
     The low-profile solar collector  100  in the preferred embodiment comprises one or more photovoltaic (PV) solar panels  110 , reflectors, or lenses; a base  120  rotatably mounted to panels via a pivot  322  at the apex of an end mount  124 ; and a plurality of wind screens that are rotatably connected to the panels and base. The panels  110  are configured to rotate about a longitudinal axis that coincides with the center of the pivot  322 . During tracking operations, the panels  110  are configured to rotate through an angular range to maximize the energy collected from the sun. In particular, the panels  110  rotate from a first orientation shown in  FIG. 3  to the second orientation shown in  FIG. 4 . The angular displacement of the panels between  FIGS. 3 and 4  corresponds to approximately 25 degrees in the preferred embodiment, although this may be tailored to the application. As one skilled in the art will appreciate, the longitudinal axis is generally oriented in the North-South direction or East-West direction when the collector is installed. 
     The low-profile solar collector  100  in the preferred embodiment further includes one or more wind screens  130 ,  132  that divert lateral winds up and over the top of the panels  110 . Each of the screens  130 ,  132  has a proximal end pivotably connected to the panel  110  and a distal end pivotably connected to a tab  350  via a hinge  340 , for example. Each of the tabs  350  is held captive in a recessed slot that runs the length of the base  120 , thereby allowing the tabs to slide in the horizontal direction. As the panels  110  rotate, the distal ends of the wind screens  130 ,  132  slide one direction or the other to compensate for raising or lowering of the panel edges. At all times, the panels and screens cooperate to form a substantially continuous surface starting from the distal end of the upwind screen and ending at the distal end of the downwind screen. The combination of panels and screens also present a gradually sloping surface to the wind whether the wind approaches from the East or West, which can help to prevent a lifting force from being exerted on the solar collector  100 . With the distal ends of the screens located immediately adjacent to the mounting surface, wind is also inhibited from getting under the collector where it might generate a lifting force. The mounting surface on which the collector is installed may be the ground, a south-facing roof, a flat roof, or a carport, for example. 
     The one or more wind screens  130 ,  132  in the preferred embodiment are solid panels of sheet metal, e.g., aluminum, powder coated steel, or galvanized steel. In other embodiments, however, a wind screen may include a perforated sheet like a residential window screen or a solid sheet with louvers cut into it. A wind screen with perforations, orifices, apertures, or louvers, for example, may be configured to enable a moderate amount of air to pass under the panels to reduce the collector&#39;s aerodynamic drag and remove waste heat produced by the panels. The screen may also be made from a non-perforated material including metal sheets, corrugated steel, plastic sheets, or fiberglass sheets, for example. 
     In the preferred embodiment, the panels  110  and wind screens are driven by an actuator (not shown) configured to induce a torque on one or more panels. The actuator may include a linear actuator, motor and gear set, motor and lead screw, or combination thereof. The motor may include, for example, a stepper motor to incrementally turn the direction in the direction of the sun. The linear actuator may include, for example, an electric, hydraulic, or pneumatic drive that periodically or continuously turns the panels and rotates the wind screens by pushing and/or pulling the distal end of one or more wind screens where they engage the slotted tracked in the base  120 . 
     The actuator that aims the panel  110  is driven by a tracking control configured to maximize the collected power. The tracking controller may be closed-loop tracking system that determines the proper panel orientation based on a feedback signal from the panels themselves, or be an open-loop tracking system that orients the panels based on the time of day determined from an internal clock. In some other embodiments, the collector employs a self-power mechanism taught in copending provisional patent application No. 60/874,994 filed Dec. 15, 2006, which is hereby incorporated by reference herein. 
     In some embodiments, the wind screen is configured to connect two or more adjacent solar panels  110  or connect multiple panels associated with two or more adjacent solar collector  100 , thereby providing wind mitigation for an array of single-axis solar collectors. Illustrated in  FIG. 5 , for example, are two representative solar collectors that share a common wind screen that creates a continuous surface that inhibits wind from inducing lift in the collectors. The first collector includes first solar panel  502 , a base  504 , and pivot  506  enabling the panel to rotate relative to the base. Similarly, the second collector includes second solar panel  552 , a base  554 , and pivot  556  enabling the panel  552  to rotate relative to its base. The first solar panel  506  is connected to the second solar panel  552  using a multi-part wind screen comprising two or more portions  512 ,  562 . The first portion  512  of the wind screen  512  is rotatably coupled to the first panel using hinge  510 , for example, while the second portion  562  of the wind screen  562  is rotatably coupled to the second panel  552  with hinge  560 . The first and second portions  512 ,  562  are held in slidably relationship to one another using guides  514 ,  564 . 
     As the first and second panels track the sun, the distance between the first hinge  510  and second hinge  560  changes which then causes the effective length of the wind screen to change. In particular, the first and second portions slide in a co-linear manner in which the distance between portions is fixed. As one skilled in the art will appreciate, the first and second portions  512 ,  562  are sized and configured to substantially obstruct any gap that might permit wind from getting under the down-wind panel throughout the entire range of motion of the two panels  502 ,  552 . 
     Illustrated in  FIG. 6  is another embodiment of a cross-collector wind screen that provides an obstructing surface between adjacent solar panels. In the embodiment, the wind screen  610  includes a single rigid sheet that couples to the first collector by means of a first pin  612  held captive in a slotted channel  614  and couples to the second collector by means of a second pin  662  held captive in a slotted channel  664 . As the first and second panels track the sun, the ends of the wind screen  610  coinciding with pins  612 ,  662  slide within their respective channels so as to compensate for the change in distance between the solar panels. 
     Illustrated in  FIG. 7  is another embodiment of a cross-collector wind screen employed between adjacent solar panels. In this embodiment, the wind screen  712  includes a single flexible sheet that couples to the first collector by means of a first roller  710  and couples to the second collector by means of a second roller  760 . Each of the rollers  710 ,  760  includes a biasing spring (not shown) that induces a torque to encourage the rollers to retract. As the first and second panels track the sun and the distance between the adjacent ends of the panels is reduced, the rollers automatically retract and real in the slack so as to keep tension on the ends of the wind screen  712 . As the distance between the ends of the panels increases, the flexible sheet is forced to unwind from the rollers  710 ,  760 . Illustrated in  FIG. 8  is another embodiment of a cross-collector wind screen  812  with single flexible sheet. As in  FIG. 7 , the embodiment in  FIG. 8  employs rollers  810 ,  860  that couple to the first panel  502  and second panel  552 . Each of the rollers  810 ,  860  includes a biasing spring (not shown) that induces a torque to encourage the rollers to retract. As the first and second panels track the sun and the distance between the adjacent ends of the panels changes, the rollers retract or unwind to keep tension on the ends of the wind screen  712 . Unlike  FIG. 7 , the rollers  810 ,  860  are configured on the panels so that one roller turns in the clockwise direction while the other turns in the counter-clockwise direction, and vise versa. 
     Illustrated in  FIG. 9  is another embodiment of a cross-collector wind screen with a flexible but non-elastic sheet  912 . In this embodiment, the wind screen is fixedly attached to the first panel  502  at edge  910  and fixedly attached to the second panel  552  at edge  960 . The wind screen  912  is held taunt by adjusting the lateral position of a rod  914  positioned over the screen  912  and runs parallel to the axis associated with pivots  506 ,  556 . Although the screen  912  is free to move relative to the rod  914 , the rod is position such that the screen possesses little or no slack. As the panels  502 ,  552  rotate, the rod  914  can be moved either to the left or the right. One skilled in the art will appreciate, however, that the tension induced in the wind screen  912  should selected such that the effect on the tracking position of the associated panels in minimal. 
     Illustrated in  FIG. 10  is another embodiment of a cross-collector wind screen with a flexible but non-elastic sheet  1012 . In this embodiment, the wind screen is fixedly attached to the first panel  502  at edge  1010  and fixedly attached to the second panel  552  at edge  1060 . As the panels rotate and the distance between edges  1010 ,  1060  changes, the wind screen  1012  is permitted to drape between the collectors in an unrestricted manner. 
     Illustrated in  FIG. 11  is an embodiment of a cross-collector wind screen with a elastic sheet  1112 . In this embodiment, the first solar panel  502  includes a lever arm  1114  in fixed angular relationship with the panel. Similarly, the second solar panel  552  includes a second lever arm  1118  in fixed angular relationship with that panel. The sheet  1112  is then fixedly attached to the distal end of the first lever  1114  at point  1116 , and fixedly attached to the distal end of the second lever arm  1118  at point  1120 . As the panels  502 ,  552  rotate, the sheet  1112  shifts substantially laterally to create a continuous wind barrier between adjacent solar collectors. If and when the second solar panel  552  reaches an extreme angular position, a lower end  556  of the panel interferes with the sheet  1112 . The sheet responds  1112  by stretching to conform to the underside of the panel. In doing so, the wind screen provides an continuous wind barrier between the adjacent solar collectors. 
     In an alternate version of the embodiment shown in  FIG. 11 , one or more of the lever arms  1114 ,  1118  are configured to be flexible or pivotable with a spring bias. In turn, the screen material  1112  may be selected to be flexible but inelastic material. Thus, the wind screen generally moves in unison with the rotation of the solar panels  502 ,  552 . If and when a panel rotates to an angle sufficient to interfere with the screen  1112 , one or more of the lever arms  1114 ,  1118  flexes or rotates to compensate for the downward deflection of the wind screen. One will appreciate that the lever arms should be biased to maintain tension across the flexible sheet  1112  over the range of motion of the solar panels. 
     Illustrated in  FIG. 12  is another embodiment of a cross-collector wind screen with a flexible, elastic sheet  1212 . In this embodiment, the wind screen is fixedly attached to the first panel  502  at edge  1210  and fixedly attached to the second panel  552  at edge  1260 . As the panels rotate and the distance between edges  1010 ,  1060  changes, the sheet  1212  stretches or contracts to fill the distance between the two collectors. 
     Illustrated in  FIG. 13  is another embodiment of a cross-collector wind screen with a flexible, semi-rigid sheet  1312 . The wind screen is fixedly attached to the first panel  502  at edge  1310 A,  1310 B and fixedly attached to the second panel  552  at edge  1360 A,  1360 B. When the first and second panels are in the inclined positions (illustrated by white rectangles  502 A,  502 B), the sheet  1312  remains in a slightly bowed position  1312 A between panels. However, when the panels are rotated to inclined positions (illustrated by solid rectangles  552 ,  552 B), the sheet  1312  assumes a highly bowed or arced position  1312 B between the panels. Throughout all tracking angles, however, the wind screen provides a continue surface between adjacent solar panels. 
     Wind screens may made from a number of material including, but not limited to: perforated metal, louvers or blinds, netting, matting, metal sheets or steel more generally, fiberglass or other composite material, wire or chain mesh, reinforced or unreinforced metal foil, polymer films, glass or clear plastic, wood or other organic material, shade fabric, or flexible thin film configured to generate electricity from light incident on the screen. In wind screens in some embodiments also be transparent or possess a reflective surface or diffuse surface so as to redirect light incident on the screen to an adjacent solar collector. The light reflected from the wind screen may be redirected to the either the front side of the collector facing the sun or to the back side of the solar panel (opposite the sun) if the solar panel is a bi-facial panel configured to receive light from both sides. Bifacial photovoltaic panels are available from SANYO Solar (U.S.A.) L.L.C., Carson, Calif. 
     Although the description above contains many specifications, these should not be construed as limiting the scope of the invention but as merely providing illustrations of some of the presently preferred embodiments of this invention. 
     Therefore, the invention has been disclosed by way of example and not limitation, and reference should be made to the following claims to determine the scope of the present invention.